Information PaperA Case Study of Using Metal Scaffold System for Demountable Grandstand: The Opening Ceremony of Hong Kong 2009 East Asian Games STRUCTURAL ENGINEERING BRANCH ARCHITECTURAL SERVICES DEPARTMENT December 2011 Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. :1/- File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Table of Contents 1. 2. 3. 4. 5. 6. 7. 8. Introduction ................................................................................................... 1 Structural Behaviour and Components ......................................................... 4 Design Loading ............................................................................................. 23 Dynamic Effects ............................................................................................28 Foundation .................................................................................................... 30 Construction Supervision .............................................................................. 30 Case Study .................................................................................................... 31 References ..................................................................................................... 52 Annex A Sample Checking Certificate Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. :1/- File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 1 1.1 Introduction A grandstand is a structure which provides seating for spectators at entertainment or sporting events. Grandstands are typically classified into three distinct types: permanent, demountable and retractable. Structural Engineering Branch (SEB) has promulgated a set of guidelines in September 2011 - SEB Guidelines SEBGL OTH5: Guidelines on the Design for Floor Vibration Due to Human Actions Part III: Vibration Effect to Grandstands, Sensitive Equipment and Facilities (available: http://asdiis/sebiis/2k/resource_centre/) – providing guidance the effect of human induced vibration on permanent grandstands. This paper will focus on the analysis, design and construction of demountable grandstands by sharing the experience on the demountable grandstands erected for the Opening Ceremony of Hong Kong 2009 East Asian Games held on 5 December 2009. Demountable stands (Photo 1(a)) are lightweight temporary structures whose trussed appearances are reminiscent of scaffolding systems. These stands are typically erected for a single specific event (e.g. parade, sports, and show) and therefore left in place for a short duration to house the large number of spectators. However, in some events (e.g. in the Opening Ceremony of Hong Kong 2009 East Asian Games), such demountable grandstands may have occupancies of up to thousands of people. Demountable grandstands were widely used in the Sydney 2000 and Beijing 2008 Olympics Games, and in the recent Auckland 2011 Ruby World Cup to increase the seating capacity of the competition venues. Photo 1(b) shows a large-scale example of demountable grandstands used in the softball centre of the Sydney 2000 Olympics Games, where 7,000 additional seats were provided by such demountable grandstands, and Photo 1(c) shows the scaffold system of another large-scale example of demountable grandstands used in Eden Park Stadium of the Auckland 2011 Ruby World Cup, where 10,000 additional seats were provided by such demountable grandstands. 1.2 Photo 1(a) Typical Demountable Grandstand (Bellinzona, Switzerland) Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 1 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Photo 1(b) Demountable Grandstand in Softball Centre at the Sydney 2000 Olympics Games (Source: www.austseat.com.au/) 1.3 Photo 1(c) Scaffold System of the Demountable Grandstand in Eden Park Stadium at the Auckland 2011 Ruby World Club (Source: www.zimbio.com/pictures/-sUagbFggBA/) PH Unlike permanent structures, demountable grandstands are usually designed to be repeatedly assembled and disassembled with the use of lightweight components such as slender steel tubes. The supporting structure and the member connections for such grandstands are also designed to make the assembly easily, rapidly and usually with the use of various types of proprietary scaffold system. Usually, Page 2 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- demountable stands are proprietary products designed, supplied in modular units and installed by specialist contractor employed by the event organizers. Moreover, to ease installation, the supporting scaffold structures consist of slender tubular members with short spans between supports, rather than having larger steel sections with longer spans in permanent grandstands. Ellis and Ji (2000) further note that because of the short spans and slender tubular scaffolds, sway and front-to-back vibration in horizontal direction are often the most important modes for demountable grandstands for human-induced dynamic crowd loads, while vertical modes are usually not a significant problem. 1.4 Because of the limited time for installation and the incentive to save cost, the structure of such demountable grandstand will just be able to achieve the minimum factor of safety. A number of accidents involving the collapse of such demountable grandstands have occurred overseas resulting in a number of casualties. Typical causes of these collapses are: overloading, lack of bracing, failure in support, problems with connections, and synchronized movements of audience (de Brito and Pimentel 2009). Two serious incidents of collapse of demountable stands occurred in the UK during 1993 and 1994. The UK Department of the Environment therefore appointed the Institution of Structural Engineers, who in collaboration with the Steel Construction Institute, published a guide for clients, contractors, engineers and suppliers of demountable structures. This guide has then been updated with latest technological and regulatory changes, and its latest version is published as Temporary Demountable Structures: Guidance on Procurement, Design and Use (IStructE 2007). The performance of demountable grandstand is the subject of this paper. First, structural forms and structural components of common types of grandstand are presented and discussed. Next, the design loading (including the dynamic loads) for the analysis and design of such structures will be detailed. Finally, the analysis, design, erection, and inspection process for the demountable grandstands erected for the Opening Ceremony of Hong Kong 2009 East Asian Games grandstands is presented and discussed. 1.5 Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 3 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 2. 2.1 Structural Behaviour and Components Demountable grandstands can be assembled in a variety of shapes and sizes depending on the client requirement, nature of the event, weather, type of spectator and terrain. These structures (Photo 2(a) and Photo 2(b)) typically have seats or benches arranged in tiered rows with access to the seats from aisles that run perpendicular to the rows of seating (Figure 1). These structures will usually be dismantled once the event is completed. Most common demountable grandstands are one that has a scaffold structure with bracing to provide lateral stability to which a modular floor and seating system is fixed at the top. Photo 2(a) Demountable Grandstand (Front Elevation) (Source: www.layher.com) Photo 2(b) Demountable Grandstand in Australia (Rear Elevation) (Source: http://www.austseat.com.au/) Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 4 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Figure 1 Typical Demountable Grandstand (Plan) (Source: Crick and Grondin 2008) 2.2 The structural behaviour of these structures is complex due to the presence of countless components connected by clamps or simply inserted into each other. The structural system is such that spans are reduced due to a significant number of vertical supports, and flexural stiffness in a vertical direction would benefit from that. On the other hand, along the line of seats (or sometimes called “sway”) direction, stiffness is mainly due to bracing, whereas perpendicular to the line of seats (or sometimes called “front to back”) direction, apart from bracing, there is also the presence of frames to support the seats then contributing to stiffen the structure in this direction. It is thus expected that the flexibility of the structure in each direction varies significantly, with implications on its static as well as dynamic behaviour. Components of Grandstand 2.3 2.3.1 Demountable grandstands are structures generally made of steel and consist of members, connectors, and planks erected on site. The structural system is a modular three-dimensional frame, in which height and length of the structure are adjusted during design to accommodate a specified number of users. Such 3-D frame consists of proprietary scaffolds (instead of conventional structural steel sections as the supporting structure for demountable grandstands due to the relatively faster speed of assemble and lower material and erection costs of scaffold. Structurally, these scaffolds serves as “support scaffold” (instead of as “access scaffold”), and are required to carry heavy imposed load similar to falsework used in concreting. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 5 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 However, those scaffolds used in falsework for concreting are sometimes manufactured as planar moment-resisting frames (or called the “door-type” scaffold Figure 2(a)). For the proprietary scaffold used in demountable grandstands (Figure 2(b)), the joints are usually assumed to be pinned-connection, and its stability must rely on the brace members. Figure 2(c) shows the structural components of a typical scaffold used for demountable grandstands. Most proprietary demountable grandstands have similar components in their structures, and the various common types of connector and bracing members in the scaffold will be discussed in the following paragraphs. Figure 2(a) Frame or Door-Type Scaffold Figure 2(b) Proprietary Scaffold Demountable Grandstand Figure 2(c) Structural Components of Typical Scaffold (Source: Rasmussen and Chandrangsu 2009) 2.3.2 Tubes To ease erection, all proprietary scaffolds are supplied as a modular system with tubes and connectors. Structural steel tubes are used to make up of the three elements of a modular unit: standard (the vertical element), ledger (the horizontal element), and brace (the diagonal element). The standards are connected to create a lift via connection tubes in sleeve joints (Photo 3), and are connected to the ledgers Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 6 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 via connectors (Figure 4). Figure 3 shows an example on the size of the connection tubes, sizes and dimensions of the pins for connecting the connection tube and standards as extracted from a supplier’s catalogue. Table 1 shows typical sizes of these three elements in a modular unit (Crick and Grondin 2008). Crick and Grondin (2008) note that the steel tubes are generally of Canadian Standard Grade 40.21 300W with minimum yield strength of 44ksi (300MPa). However, this paper has reservation on the applicability of such general statement, especially to those tubes used in Hong Kong. Hence, project officer should check the country of origin of the proprietary scaffold and refer to the catalogues for scaffold to determine the yield strength of the steel tubes. Pin Hole Photo 3 Connection tube between upper and lower standards Connection Tube Pin Hole Details of Connection Tube Figure 3 Connection Tube between Upper and Lower Standards (Source: http://www.scaffoldgold.com) Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 7 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Table 1 Typical Sizes of Tubes of a Modular Unit for Scaffold Elements Length Diameter (mm) Thickness (mm) Standard 0.5m, 1.0m, 1.5m, 2m or 3.2 49 3m Ledger US: 2.13m or 3.05m 3.2 49 Europe 2.25m or 1.35m Brace Length to suit standard 2.3 45 and ledger 2.3.3 Connector There are several systems of connector that can connect the tubes together. In this paragraph, three common systems, namely couplers, wedge-based connectors and spigot (Figure 4), will be described. Right-angle Swivel (a) Coupler/Clamp (b) Wedge-based connector (c) Spigot Figure 4 Common systems of connector (Source: De Brito and Pimentel 2009, and Labour Department 2001) 2.3.1.1 Coupler/Clamp Standards are connected to ledgers via right angle couplers (Photo 4(a)), and braces are connected to the scaffold via swivel couplers (Photo 4(b)) to form tube and couple (or tube and clamp) scaffold. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 8 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Photo 4(a) Right-Angle Couplers/Clamps (Source: www.tubeandclampscaffold.info) Photo 4(b) Swivel Couplers/Clamps (Source: www.aptsuspensions.co.uk) Tube and clamp scaffold is commonly used in construction. The ledgers and thus walking-decks can be placed at any height along the standard, and standards can be spaced at any distance apart up to the maximum distance allowed by engineering constraints. Tube and clamp scaffold is also the simplest and versatile system; but is among the most labour-intensive of all scaffolding applications, and is therefore generally used only when high capacity, unlimited adaptability and versatility are required. 2.3.1.2 Wedge-based connector Kwikform (or KwikStage) scaffold (Photo 5(a)) and allround scaffold are using wedge-based connector. A distinct feature for such connection system is that the wedge pin can provide some moment carrying capacity, and hence, unlike the other systems, braces are sometimes not provided for such scaffold system in light loading (e.g. access scaffold). Further discussion on the effectiveness of such connection in carrying moment will be given in Section 2.5. Kwikform scaffold has metal loops attached to the standard at fixed intervals. The ledger has a hooked head that fits into the loop and a wedge pin to tighten the connection (Photo 5(b)). A hammer blow is used to drive the wedge pin between the ledger head and the loop creating a secure connection. The wedge fixing of the ledgers gives a simple and fast means of erecting access scaffolding without loose parts, its rigid 4-way fixing giving a positive location without movement, and wedge fitting on the standard giving guaranteed vertical alignment. To install braces, steel tubes (Photo 5(c), 5(d) and 5(e)) with pivoted wedge devices at each end fitting onto the standards. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 9 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 (a) (b) (d) (e) Photo 5 Kwikform System (Source: www.scaffoldingcn.com and www.rmdkwikform.com) (c) Allround scaffold (Photo 6(a)) has a rosette (i.e. circular plate with slots) attached at fixed intervals along the length of the standard. The ledger has a ledger head at each end that has a horizontal slot that mate with a wedge pin drops down into the slot on the rosette. The rosettes have 8 slots that allow up to eight members at one connection. To make a connection, the wedge head is slid over the perforated rosette. A harmer blow is then used to force the wedge pin into the slot securing the ledger to standard. Typical connection procedure of the system is shown in Photo 6(b). Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 10 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Photo 6(a) Allround System (Source: www.layher.com) Photo 6(b) Connection Procedure of the Allround Scaffold (Source: www.layher.com) 2.3.1.3 Spigot Cuplock (or cuplok) scaffold (Photo 7(a)) uses spigot to connect ledger and standard together. Spigot is a cuplike element fixed to the standard at set intervals along its length. It allows four members to be connected at one place. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 11 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Photo 7(a) Cuplock Scaffold (Source: www.scaffoldgold.com and www.indiamart.com) To make a connection, the ledger end is placed into the bottom cup and the top cup is screwed down on to the top of the ledger end locking it into place. A hammer blow is used on the top cup to tighten the connection. Thus the top and bottom of the ledger head is secured against the standard. Typical connection procedure of the system is shown in Photo 7(b). Holes are intentionally left in the upper and lower standards so that pins can be inserted so that the standard is of the correct plumb and to transmit tensile force along the standard. Photo 7(b) Connection Procedure of Cuplock Scaffold (Source: www.scaffoldingasia.com) Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 12 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Photo 7(c) Special Braces for Cuplock Scaffold (Source: www.scaffoldgold.com and http://scaffoldsales.com) A distinct feature for such connection system (like wedge-based connector) is that it can provide some moment carrying capacity, and hence braces are sometimes not provided for such scaffold system (especially as access scaffold). Again, further discussion on the effectiveness of such connection will be given in Section 2.5. To install braces, steel tubes (Photo 7(c)) with couplers at each end for fitting onto the standards. 2.3.1.4 For demountable temporary grandstands, modular system scaffold such as the cuplock, Kwikform and allround scaffolds are used most frequently. Scaffold in the form of tube and clamp scaffold are considered too slow in construction and labour intensive. 2.4 Bracing 2.4.1 One of the main reasons for the collapse of demountable grandstands is an insufficient number of bracing members provided (Bolton 1992; Ji and Ellis 1997). Demountable grandstands must therefore be provided with sufficient bracing members to resist horizontal loads and wind loads. It is essential that diagonal bracing be installed at all times. Free-standing individual support towers, and the start and end bays must have diagonal bracing installed. Moreover, the bracing elements also have effects on the permissible loadings on the standards. The following figure shows 5 arrangements of bracing element in a scaffold system, namely (0) every bay, (A) every 2nd bay, (B) every 3rd bay, (C) every 4th bay, and (D) every 5th bay, in the descending order in their permissible loadings: Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 13 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 (Source: www.layher.com) 2.4.2 Theoretical study Extensive study of the effect of the bracing on such lightweight scaffold system has been carried out by Ji and Ellis (1997). The governing principles in providing bracing are: 1) the load shall take the shortest path to the supports (the “direct force path principle”); and 2) the internal forces shall be uniformly distributed (the “uniform force distribution principle”). Based on these two principles, they listed out the following five criteria for arranging bracings in an efficient way in order to achieve a larger lateral stiffness: (a) (b) (c) (d) (e) Bracing members in different storeys should be provided from the top to the support of the structure. Bracing members in different storeys should be directly linked where possible. Bracing members should be linked in a straight line where possible. Bracing members at the top adjacent bays should be directly linked where possible. If extra bracing members are required, they should be used following the above four criteria. 2.4.3 Table 2 shows six examples of typical bracing arrangement with descriptions on which criteria as listed above can be fulfilled. Those systems fulfilling all the above criteria would perform a higher static stiffness when subjected to horizontal loading. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 14 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Table 2 Typical Bracing Arrangement for Scaffold Type Bracing Arrangement Descriptions Satisfy criteria (a) Traditional bracing form Load transfer from top through all members Satisfy criteria (a) and (b) Shorter load path than type 1, higher static stiffness Satisfy criteria (a), (b) and (c) More straightforward force path Higher stiffness than type 1 & 2 Satisfy criteria (a), (b), (c) and (d) Highest stiffness amongst the first 4 types More bracing members used, but not fully follows the criteria Lower stiffness than type 4 Satisfy all 5 criteria More uniform inner force distribution The highest stiffness among all the above types 1 2 - 3 - 4 5 - 6 (Source: Ji and Ellis 1997) 2.4.3 Among the six types of bracing arrangement, Type 6, which consists of a pair of straight cross-bracing from the top to bottom, is the most effective bracing system. Type 6 in Table 2 only shows the ideal arrangement for a scaffold of two storeys height. Figure 5(a) shows how to modify Type 6 arrangement for scaffold with more than two storeys. Such bracing system can satisfy the first three criteria, and has small number of bracing members. Ji (2003) carried out tests on three models (frames A, B and C) of bracing system (Figure 5(b)(i)), which were made up of aluminium members same cross-section of 25 mm by 3 mm with an overall dimension of 1.025 m×1.025m. The frames were fixed at their supports and a hydraulic jack was used to apply a horizontal force at the top right-hand joint of the frame. At a load of 1.07kN, the horizontal displacement were respectively 3.0mm for frame A, 0.73mm for frame B and 2.2mm for frame C (Figure 5(b)(ii)). They Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 15 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 therefore verified that Type 6 arrangement, which satisfies all five criteria, is the stiffest. Figure 5(a) Type 6 Bracing for Multi-Storey Scaffold Figure 5(b)(i) Models of Bracing Systems (frames A, B and C being placed from the left to right) (Source: Ji 2003) Figure 5(b)(ii) Deflection Curves of Frames A, B and C (Source: Ji 2003) Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 16 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 2.4.4 Similar remarks have been made earlier in Grant (1975). Grant (1975) notes that Type 6 bracing arrangement can result in the vertical loads in the standards to resist the couple created by the horizontal loads to vary proportionately with their distance from the centre line (Figure 5(c)), whilst Type 1 or 2 bracing arrangement will create large vertical forces in the two legs adjacent to the standards in the bracing bay (Figure 5(d)). Grant (1975) further notes that Type 6 bracing arrangement can effectively redistribute a concentrated vertical load onto the other standards (Figure 5(e)). Figure 5(c) Induced vertical loads on standards using Type 6 bracing (Source: Grant 1975) Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 17 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Figure 5(d) Induced vertical loads on standards using Type 2 bracing (Source: Grant 1975) Figure 5(e) Redistribution of concentrated vertical load using Type 6 bracing (Source: Grant 1975) Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 18 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 2.4.5 Type 6 bracing arrangement, however, has the following disadvantages: a) there is no the bracing to the scaffold until its installation is completed, and hence cannot provide the required stability during erection and dismantle works; b) the erection of such bracing is much more difficult than the other types, as it is difficult to align the bracing straight, especially with in the jungle of scaffolds underneath the seating deck, and Bolton (1997) also raised concerns on the potential instability of the scaffold system during dismantle when such bracing has been removed; c) under the effect of lateral force, the bracing will induce a large tensile force onto the edge scaffold, which may not be of adequate strength, and anchor or kentledge may be required at the foundation level to counteract the tensile force; and d) such bracing may be required to tie to the scaffold at intermittent levels (Figure 5) by swivel couplers, producing a moment on the thin tubes of the scaffold. Grant (1975) further comments that in the case that it is not possible to tie the bracing member to a standard at a node, a ledger is preferred to a standard for such coupling, as the former is not already heavily loaded; Hence, in reality, such bracing system will not be adopted by most specialist contractors, although theoretically such bracing system provides the highest stiffness. Instead, the common arrangement of bracing system adopted is Type I (Photo 1(c) and Photo 8). Photo 8 Typical Bracing System (Source: http://www.austseat.com.au) 2.4.6 However, even though Type 1 bracing system is usually adopted as bracing system in such modular scaffold, this paper still recommends that global Type 6 crossbracing should be provided around the scaffold system in addition to Type 1 so as to increase the overall stiffness of the scaffold, especially when the demountable grandstand is tall. The number of Type 1 bracing may also be reduced. A suggested arrangement is shown in Figure 6. With such global bracing, there is the potential for eight braces to interest at one connection, exceeding the maximum of Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 19 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 4 braces even for allround scaffold system. Hence, it is necessary to attach the braces to the standard or ledger using swivel couplers. Figure 6 Preferred Bracing Arrangement at End Bays 2.5 Moment Carrying Capacity of Joint 2.5.1 It is generally assumed in the analysis and design that the joints in these scaffolds are modelled to be pinned connection (i.e. with no moment carrying capacity). In reality, they have some degree of fixity, especially the cuplike element in cuplock scaffold and wedge-based connector in Figure 7(a). The cuplock connections behave as semi-rigid joints, and show looseness with small rotational stiffness at the beginning of loading. Once the joints lock into place under applied load, the joints become stiffer (Godley and Beale 1997). Wedge-type joints are generally more flexible and closer to pinned connections. They also often display substantial looseness at small rotations (Godley and Beale 2001). As to spigot joints in the cuplock system, the spigot can create out-of-straightness of the standards, and the possibility of the joint to open up due to the gap between the standard and the spigot can produce complexity in modelling (Enright et al 2000). Figure 7(b) shows typical moment–rotation curves for cuplock and wedge-type joints. It should further be noted that the relationship for all types of joint is not generally the same for positive and negative rotations (Godley and Beale 2001), and that the curves do not show linear relationship. 2.5.2 Although there is moment carrying capacity of the connections (and indeed, the catalogues of many proprietary scaffold systems also provide their recommended moment carrying capacity), project officer should note that the uncertainty and limitations of such connections in carrying moment as discussed in the above paragraph. This paper still maintains that in the design of demountable grandstand, the joints should be modelled as pinned connection, and bracing members are required to provide lateral stability for the scaffold. The moment carrying capacity of the connections only serves as additional safety margin, especially during the Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 20 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 erection and dismantle processes, where the bracing members have not yet been installed or has been dismantled. (i) Wedge-based connector (ii) Cuplock connector Figure 7(a) Moment carrying capacity in wedge-based and cuplock connector (Source: Godley and Beale 1997, 2001) Figure 7(b) Typical moment against rotation graph of joint in proprietary scaffold (Source: Chandrangsu and Rasmussen 2006) 2.6 Elastic Critical Load Factor λcr 2.6.1 Eurocode 3 defines the elastic critical load factor λcr as the value of the load factor by which the loads are to be multiplied to check of buildings for “sway mode” failures. λcr is therefore an important parameter to classify the scaffold frame into non-sway, sway or ultra-sway sensitive frame. For both sway and ultra-sway sensitive frames, the load-carrying capacity of the steel tubes in the scaffold system decreases with the height of the scaffold, as the effective length of tubes increases Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 21 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 due to the P-- effects. The Code of Practice for the Structural Use of Steel 2005 (the “HK Steel Code”) issued by Buildings Department (as modified by SEI 08/2009: Design Code for Structural Steel) classifies frame using λcr as follows: a) when λcr 10, the frame is non-sway and the P-- effects can be ignored; b) when 5≤ λcr<10, the frame is sway and the P--δ effects can be included by checking the members by either the moment amplification or effective length methods; and c) when λcr<5, the frame is ultra-sensitive sway frame, and second order analysis should be used in the analysis and design to include the P-- effects. 2.6.2 Clause 6.3.2.2 of the HK Steel Code provides two methods to calculate λcr, namely, the deflection method or the eigenvalue analysis. If eigenvalue analysis is used to calculate λcr, project officer should first study the form of the buckling mode of the frame to see if it is a sway buckling mode (Figure 8(a)) or a local column buckling mode (Figure 8(b)). King (2005) commented that when using eigenvalue analysis in finding the first sway-mode, “it is important to study the form of each buckling mode to see if it is a frame mode or a local column mode. In frames where sway stability is ensured by discrete bays of bracing (often referred to as “braced frames”), it is common to find that the eigenvalues of the column buckling modes are lower than the eigenvalue of the first sway mode of the frame. Local column modes may also appear in unbraced frames at columns hinged at both ends or at columns that are much more slender than the average slenderness of columns in the same storey.” Similarly, Rathbone (2002) noted that “where the columns are axial load predicated, many of the lower buckling modes will be [local] column buckling modes. It is the [sway] buckling mode of the whole structure that is important” to include second-order effects. 2.6.3 Therefore, both the deflection method and eigenvalue analysis are applicable to calculate λcr for the frame with sway buckling mode; but if it is a local column buckling mode, then the lowest eigenvalue found by the eigenvalue analysis does not represent the first sway buckling mode λcr. Instead, the eigenvalue analysis finds the eigenvalue for the column buckling mode. In such case, project officer should take care in using the eigenvalue analysis and not just use the lowest eigenvalue which may be local column buckling mode (Figure 8(b)) and it is not the original intent to use it to define sway sensitivity. Should eigenvalue analysis be adopted, project officer should therefore scan the output to see which eigenvalue is the first sway buckling mode. Alternatively, in such case the deflection method can be used to calculate λcr for the first sway buckling mode. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 22 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 3 3.1 Figure 8(a) Sway Buckling Mode Figure 8(b) Local Column Buckling Mode Design Loading Demountable grandstand should be designed to form a robust and stable threedimensional structural arrangement, which will support the design loadings for the required period with an adequate margin of safety. The loading appropriate for the design of demountable grandstand comprises dead, imposed, wind and notional horizontal loads and may require consideration of dynamic loads from crowd. Dead Load Dead load shall include the self-weight of all fixed elements that form part of the demountable structure. 3.2 3.3 Imposed Load The minimum imposed load on demountable grandstands is controversial. BS 6399: Part 1 (BSI 1996) originally recommended it to be 5.0kPa, which is the same as that specified in the Code of Practice for Dead and Imposed Loads 2011 (the “HK Loading Code”) issued by Buildings Department. However, BS 6399: Part 1 has removed the specified minimum imposed load for grandstands in its amendment in 2002. At the same time, for assembly areas with fixed seating, both BS 6399: Part 1 and the HK Loading Code specify a minimum imposed load of 4.0kPa. Hence, project officer is advised to exercise judgment on choosing the minimum imposed load to be adopted in individual case. 3.4 Wind Load 3.4.1 Design Wind Pressure The design wind pressure acting on such temporary structures to be adopted in the analysis and design is a controversial issue. The Code of Practice on Wind Effects in Hong Kong 2004 (the “HK Wind Code”) issued by Buildings Department are applicable for permanent building structures. It gives the extreme 3-second gust wind velocity (and hence the wind pressure) for a return period of 50 years. However, for demountable grandstand, it is generally intended to be used for a short duration, and will then dismantled. The HK Wind Code states that the basic wind pressure may be modified by a factor of 0.7 for temporary building with design life less than one year. However, Buildings Department, when reviewing the design wind pressure for hoarding in 1999, recognised that the factor of 0.7 is conservative, as the original intent was that a temporary structure may last for more than one year though its design life is one year. Buildings Department therefore issued APP-21 (Demolition Works - Measures for Public Safety) and APP-23 (Hoardings, Covered Walkways and Gantries (including Temporary Access for Construction Traffic) - Building (Planning) Regulations Part IX) allowed the design wind pressure to be modified by a factor of 0.37 in hoarding design, as it Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 23 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 was noted that such hoarding would usually last for not more than three years, with a probability of exceedance of 63.6%. Moreover, another factor to be considered in choosing the design wind pressure is the seasonal effect. The design 3-second gust at gradient height of 500m in the HK Wind Code is specified to be 78.7m/s (i.e. a design wind pressure of 3.72kPa), and the highest recorded 3-second gust in Hong Kong was 65.0m/s (i.e. a design wind pressure of 2.54kPa) in 1999 due to Typhoon York at Waglan Island at a height of 90m above the mean sea level. BS 6399: Part 2 (BSI 1997) allows partial factors to be used by taking account of seasonal variations in wind speeds and if necessary by altering a probability factor to accept a greater than usual degree of risk that the design wind speed may be exceeded. During summer, it is unlikely that when typhoon signal no. 8 or above is hoisted, en event will not be cancelled or all the workers will still be required to work on the grandstand. A common situation is that when a typhoon signal no. 3 is hoisted, workers are still required to carry out erection or dismantle work and an event will still be held with the seats occupied. For a typhoon signal no. 3 is hoisted, the maximum hourly mean wind speed is only 62km/h, which corresponds to a 3second gust of 23.94m/s. During autumn or winter, easterly monsoon wind prevails in Hong Kong. The highest recorded monsoon 3-second gust at Hong Kong Observatory was only 29.9m/s (i.e. a design wind pressure of 0.54kPa), which occurred in 1934 at 61m above the mean sea level, and this recorded value is already the maximum 3-second gust measured in autumn or winter in Hong Kong over the past 70 years. As a compromise, this paper therefore considers that a design 3-second gust wind velocity of 23.94m/s (i.e. a design wind pressure of 0.41kPa) to be adopted for the design at a height of 0m-10m for temporary grandstand that is likely to experience typhoon during its service life, which provides a conservative estimate of the wind pressure when the grandstand is occupied or when the grandstand is being erected or dismantled. Project officer should exercise judgment in deciding the appropriate design wind pressure to suit the particular case. 3.4.2 Force Coefficient The HK Wind Code gives the force coefficient with different solidity ratios for open frame structures. The choice of solidity ratio for such open multiple frame structures is again controversial, especially whether the upstream frame can shield the frames behind (Figure 9). As any upstream obstruction to a permanent structure may be demolished during the design life of the permanent structure, the HK Wind Code states that no allowance shall be made for the general or specific shielding of other structures or natural features. BS 6399: Part 2 (BSI 1997) also states that an estimate of the total wind load can be obtained by summing up the loads on each individual frame; but admits that such summation may be very conservative, especially when the frames are dense and shielded as for demountable grandstands of this paper. Choi (1984) noted that the amount of shielding depends Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 24 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 on the solidity ratio of the upstream frame and the spacing between frames, and recommended to reduce the wind force on the downstream frames by a shielding factor. BRE Special Digest SD5 (Blackmore 2004) also recommends similar procedures to calculate the shielding factor to be included in calculating the total wind load for open frame structures. Figure 10 gives the total force coefficient Cf as a function of the solidity ratio of the upstream frame, the spacing S, the width of the structure in the direction of the frame, and the number of frames. Figure 9 Shielding Effect in Open Frame Structures Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 25 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Cf (a) B/S = 2 Cf (b) B/S = 5 Cf (c) B/S = 10 Figure 10 Shielding Effect on Force Coefficient Cf for Open Frame Structures 3.4.3 Dickie (1983) mentioned two aspects to be considered in the design of demountable grandstands to wind loads: possibility of structural damage at high wind speeds when the grandstand is empty, and increase in load actions at low wind speeds with spectators present on the structure. IStructE (2007) recommends three load cases to be included in the analysis and design: Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 26 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 1) 2) 3) a high load factor of 1.4 for the wind loading when the grandstand is empty combined with a load factor of 1.0 for dead load to check foundations; equal load factors of 1.2 for wind, dead, live, and nominal horizontal loads to check foundations; and equal load factors of 1.0 for all four aforementioned loads to check deflections. 3.5 Dynamic Load 3.5.1 For the design of any structure subject to dynamic loads the avoidance of resonance effects is important. Demountable grandstands are relatively flexible structures which will respond dynamically to spectator movements. In an investigation of the dynamic response of 40 empty demountable grandstands carried out by Littler (1996), only one grandstand was reported to have a vertical natural frequency below 9 Hz. On the other hand, the natural frequencies of the grandstands in the sway direction were much lower, in a range from 1.8 to 6.0 Hz, the majority being between 3.0 and 5.0 Hz. With regard to the front-to-back direction, in most cases the natural frequencies were higher than those in the sway direction, ranging from 2.1 to over 10 Hz. 3.5.2 Littler (1996) also carried out tests in some grandstands in use. In one of the tested grandstands, a reduction from 2.7 to 1.7 Hz was observed in the sway direction due to the presence of a passive audience. Horizontal natural frequencies above 4 Hz for empty temporary grandstands were therefore cited as a recommendation to avoid the range of maximum dancing frequencies. This would probably include an allowance to take into account the effect of human-structure interaction for structures in use. Horizontal natural frequencies above 4 Hz for the empty structure were also mentioned in BS 6399: Part 1 (BSI 1996) as a design strategy to avoid significant resonance effects. 3.5.3 The significance of the natural frequencies to the design is related to the possibility of potential resonance of the structure due to excitation produced by the spectators, e.g. in pop concerts or sports events. In the cases in which the fundamental natural frequencies of the structure are such that potential resonance can occur and there is a potential for synchronized and periodic movements, a full dynamic analysis is recommended instead of applying nominal horizontal loads. For grandstands which may be subject to synchronised and periodic crowd movements, the easiest approach would be to estimate the vertical and horizontal natural frequencies and to ensure avoidance of significant resonance effects. Ji and Ellis (1997) recommend a vertical frequency greater than 8.4 Hz and the horizontal frequencies greater than 4.0 Hz for an empty structure to avoid resonance effects. If it is not possible to avoid the resonance effect in this way, design of the grandstand will require a detailed analysis to assess the effects of dynamic loads arising from the anticipated resonance effects. Where resonance is unlikely, the use of a nominal horizontal load approach as per the recommendations of IStructE (2007) can be used. This approach will be discussed in the Section 4. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 27 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 4 4.1 Notional Horizontal Load Approach IStructE (2007) introduces the concept of using notional horizontal loads to account for, spectator action, and geometrical imperfections of frames (e.g. the lack of alignment of vertical members). The notional horizontal loads are taken as a percentage of the imposed vertical load. The notional horizontal loads should be applied in combination with the wind loads. IStructE (2007) recommends a simplified approach to include the following notional horizontal load (Table 3) to design the grandstand for the effect induced by different categories of spectator action. Table 3 Notional Horizontal Load for Different Categories of Spectator Action Notional Category Spectator activity horizontal load Nominal potential for spectator movement, which excludes synchronized and periodic crowd 1 movement. Examples include: lectures/exhibitions, 6% display/shows, athletic events, golf tournaments and agricultural shows. Potential for spectator movement more vigorous than Category 1. Category 2 excludes synchronized 2 7.5% and periodic crowd movement in major musical concerts, and rugby or football matches. Stands with a potential for synchronized and periodic crowd movement and having vertical and horizontal fundamental frequencies which avoid 3 10% resonance effects. An example is at pop concerts where strong musical beats are expected. Notes: For notional horizontal loads, the partial factor should be 1.5 for the load combination case with factored values of vertical dead and imposed loads. (Source: IStructE 2007) 4.2 Besides the recommendations in IStructE (2007), the HK Loading Code has recently introduced a requirement on horizontal imposed loads acting on the grandstands due to crowd movement. Clause 3.8.2 of the HK Loading Code states that grandstands, stadiums, assembly platforms, reviewing stands and similar, shall be designed to withstand minimum horizontal imposed loads due to crowd movement as follows: (a) for platforms with seats, the following separate load cases (not applied simultaneously), applied at floor level at each row of seats: (i) 0.35 kN/m of seating along the line of seats; or (ii) 0.15 kN/m of seating perpendicular to the line of the seats. for platforms without seats, 0.25 kPa of plan area applied in any direction. (b) Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 28 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 4.3 Usually, there will be about 4 rows of seats per 3m width of the structure, and the notional horizontal loads can therefore be expressed as an equivalent percentage of the imposed load as follows: (i) along the line of seats = 4×0.35/3 = 0.47 kPa = 9.3% of the imposed load (5 kPa); (ii) perpendicular to the line of seats = 4×0.15/3 = 0.2 kPa = 4.0% of the imposed load (5 kPa). Therefore, the HK Loading Code has specified a smaller notional horizontal load (i.e. 4%) perpendicular to the line of seats than that specified in IStructE (2007) (i.e. 6%) for nominal potential of spectator movement, but a larger notional horizontal load (9.3%) along the line of seats. It should be further noted that for grandstands without seats, the notional horizontal load is 0.25kPa in any direction, which is smaller than that along the line of seats for grandstands with seats. However, where there are no seats, the audiences are expected to erect a larger horizontal force on the grandstand due to the larger possibility of crowd movement. Moreover, in the HK Loading Code, the notional horizontal load is set without due consideration of the different responses of the audiences for difference types of events, e.g. lectures, football matches or pop concerts. Therefore, project officer is advised to refer to IStructE (2007), which is more reasonable, and exercise judgment in choosing the notional horizontal load to suit the particular case, especially the probability of synchronized crowd movement. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 29 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 5. 5.1 Foundation Demountable structures are generally lightweight and loaded for relatively short periods. Hence, the bearing pressures and settlement of the ground are not usually a problem, unless the structure will be in use for a long period, in which case a full engineering assessment of the ground should be made. The use of permanent foundations (e.g. pad footings) will be unlikely. Temporary pad steel bases will have to provide the reactions to the applied loadings. In addition to the dead and imposed load, there may be uplift forces and lateral loads on the foundation due to its lightweight. It is therefore necessary to check the methods of transferring such loads to the ground, usually using ground anchors by anchor bolts at the support points (Photo 9). Occasionally, ground anchors cannot be used because of the nature of the ground. For example, it may not be permissible to puncture asphalt or concrete finishes. The structure should then be designed to accept kentledge of sufficient weight to resist the factored uplift forces. 5.2 Photo 9 Use of Ground Anchor at the Support of the Standard 6. 6.1 Construction Supervision Usually, demountable stands are proprietary products designed, supplied and installed by specialist contractor employed by the event organizers. The event organizers may seek technical assistance from our Department to provide technical advice on the design which has been prepared and submitted by the Registered Structural Engineer employed by the specialist contractor. However, project officer should note that since these structures are often quickly erected immediately before an event, there may only be a short period of time available for the Registered Structural Engineer employed by the specialist contractor to check the design prior to submission and to inspect the workmanship prior to use. Another critical stage for a demountable grandstand is during construction and dismantle works, where bracing members have not yet been provided or are being removed respectively. In such stage, stability is only provided by the moment carrying capacity of the connections. Project officer should ensure that sufficient bracing members are still provided to ensure their stability. 6.2 Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 30 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 7. 7.1 Case Study – East Asian Games 2009 Background 7.1.1 Held once every four years, the East Asian Games is one of the major events in the Asian international sports arena. In 2009, Hong Kong hosted the 5th East Asian Games (EAG). It was the first time for Hong Kong to host such a large-scale multi-sport international event, and was an important milestone in holding international sports event for Hong Kong. An opening ceremony was held on 5 December 2009 at the open space outside the Hong Kong Cultural Centre Piazza facing the Victoria Harbour. In order to achieve the environmental-friendly and economical objectives of the event, four temporary demountable grandstands of different sizes were constructed to provide over 1,500 seats for the guests and audiences for the opening ceremony. Photo 10 shows the front and side elevations of the largest grandstand. The structural system including the design and analysis of the largest demountable grandstand will be discussed in the following paragraphs. Photo 10 Largest Demountable Grandstand at EAG Opening Ceremony 7.1.2 As such demountable grandstands were proprietary products, the procurement arrangement was that all demountable grandstands were design-and-build items designed, erected and dismantled by a specialist contractor employed by the organizer. The specialist contractor was required to engage a Registered Structural Engineer (RSE) to prepare the drawings and structural calculation for the grandstands. The RSE was also required to provide site supervision and to check that the member sizes, spacing, arrangement of bracings, support details of the structure had been constructed in accordance with the design drawings and made necessary arrangement to solve the site problems, e.g. discrepancies between the site conditions and the design drawings. Upon the completion of the erection of the grandstands, the RSE was required to certify their safety by issuing a checking certificate. Our Department was requested to provide technical support to the organizer on the structural stability of the design, erection and dismantle works. The specialist contractor was given about one-week time to erect the grandstands, though the design had been submitted to our Department for comment. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 31 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 7.2 Structural Layout and Member Capacities 7.2.1 The largest grandstand was of size 28×31m on plan with maximum height of about 10m above the ground level. It provided 1,572 seats for the audiences of the opening ceremony. The grandstand was assembled by use of portable tiered system for the seating and proprietary Layher scaffold for the supporting structure. The Layher scaffold was an allround scaffold system. The standards and ledgers of the scaffold were circular hollow section of size 49×3.2mm and the bracings of the scaffold were circular hollow section of size 45×2.3mm. The catalogue of the supplier contains the safe working load (Table 4 and Figure 11) on them, which depending the bracing arrangement, their lengths and their bay width. Table 4 Safe Working Load for Layher Scaffold (Model: Layher Variant II) Member Type Member Size Safe Working Load (kN) Remark The member capacity provided in the supplier’s catalogue is the safe working load for compression. Standard 49×3.2mm 37.2 (Compression)* Ledger 49×3.2mm 15.1 (= 22.7/1.5) Member capacity based on the condition that: - length of standard = 2m - one diagonal brace per 3 bays of standard (i.e. B diagonal brace) The loading provided in the supplier’s catalogue is the ultimate capacity. The safe working loads are obtained by dividing the ultimate capacity by 1.5. Bracing Notes: * Safe working loads of ledger and bracing are lower than that of the 5.6 45×2.3mm standard as they are controlled by (= 8.4/1.5) the connection joint capacity with the standard Tensile capacity of standard is controlled by the connection capacity of the pins ( = 3/8” approx.) between the upper and lower standards and the connection tube (see Figure 3). It should be noted that the safe working load is controlled by the connection joint capacity between the members and the computer program is difficult to model the connection joint capacity. Therefore, the safe working load in supplier’s catalogue instead of that obtained from the computer program will be used in the design. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 32 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 (a) For Standard (b) For Ledger and Bracing Figure 11 Members Capacity for Model Layher Variant II (Source: http://www.layher.com.au) 7.2.2 The standards were spaced at about 1.5m along the line of seats and about 3m perpendicular to the line of the seats. The ledgers were spaced at about 2m in the vertical direction. Type I bracings (as defined in Table 2 of section 2.4) were added to provide the lateral stability of the structure. Figure 12 shows the structural arrangement of the members of the demountable grandstand. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 33 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Standard Bracing members to provide lateral stability Ledger Figure 12 Typical Section of the Largest Demountable Grandstand at 2009 East Asian Games Opening Ceremony 7.2.2 The standards of the demountable grandstand were either rested on the surface of the existing structure or ground through pad steel bases in order to provide the reactions to the applied loads. Photo 11 shows the typical details of the bases of the standard on the supporting ground. Photo 11 Typical Base of the Standard 7.3 Structural Analysis and Design by the Specialist Contractor 7.3.1 The RSE employed software SPACE GASS (version 10.50b) in the analysis of the forces in the scaffold, where the connections between ledger and standard and the connections between bracing and standard were assumed to pin joints, and due to symmetry, two 2-D models for respectively along and perpendicular to the line of seats directions were adopted. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 34 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 7.3.2 In the design submission, the dead load was assumed to be 1 kPa. For the imposed load, there would altogether 1,572 seats in the largest grandstand of plan size 28m×31m, and the average weight of an audience was 75kgf. Hence, the actual imposed load on this grandstand would be 1.35kPa. The RSE had therefore taken the design imposed load as 4 kPa in accordance with the BS 6399: Part 1 (BSI 1997) and Building (Construction) Regulations Table 1 for the usage of assembly area with fixed seating. Two separate notional horizontal loads (NHL1 and NHL2) had been considered in the analysis. NHL1 was taken as 1 kPa in accordance with Table 2.2 of the HK Steel Code, while NHL2 was taken as 6% of the imposed load in accordance with the recommendations in IStructE (2007). Notional horizontal load, NHL1 = 1 kPa Notional horizontal load, NHL2 = 6% LL 7.3.3 Wind loads was taken to be the equivalent wind pressure at tropical cyclone warning signal no.3 and was calculated as 0.41 kPa. However, the wind loads were assumed to be not to control the design and ignored in the analysis, as the RSE noted that the notional horizontal force (NHL) due to the dynamic loads would exceed the wind loads. In addition, the RSE had imposed a restriction that the occupancy shall be vacant and structures shall be fenced off or dismantled when typhoon signal of No. 3 or above is hoisted. Therefore, the design case of wind loads acting together with the notional horizontal force was not required. Altogether three loading cases have been considered, including DL+LL, DL+LL+NHL1 and DL+LL+NHL2 for each of the two 2-D models along and perpendicular to the line of seats. 7.3.4 The design had been carried out by checking the working load against the safe working load of each member type as provided in the catalogue of the Layher system (Table 4). The member forces of the steel members were obtained by using the first order analysis method in the HK Steel Code. The summary of the maximum member force against the load bearing capacity for each member type is shown in Table 5. The location of the critical member of standard (i.e. the member with the highest utilization ratio) is shown in Figure 13. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 35 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Table 5 Summary of Maximum Member Forces Member Type Standard Ledger Bracing Double Bracing Maximum Axial Force (kN) 33.44 7.87 5.52 7.08 Safe Working Load (kN) 37.20 15.10 5.60 11.20 Utilization Ratio 0.90 0.52 0.99 0.63 Standard (Maximum axial force = 33.44 kN, section utilization = 0.90) Figure 13 Critical Members in the 2-D Model (showing the tallest frame along the line of seats direction) 7.3.5 With the adopted model, the maximum utilization factor was 0.986 at one of the bracing members. No dynamic analysis was carried out, and notational horizontal force approach was adopted to cater for the dynamic effect. To cater for the uncertainty and to guard against any lateral movement, altogether 6 pairs of Type 6 global bracing members (as defined in Table 2 of section 2.4) (Figure 14) were added at the request of our Department to increase the stiffness of the grandstands to lateral loads. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 36 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 (a) Perpendicular to the Line of Seats Direction (b) Along the Line of Seats Direction Figure 14 Added Global Bracing Members 7.4 Construction Supervision 7.4.1 Due to the tight schedule for erection, some of the connections were not completed according to the approved drawings, and some bracing members were missing or were not connected to the nodes between the standard and the ledger (Photo 12(a) and (b)), and the global bracing members were not provided (Photo 12(c)). Fortunately, such discrepancies were detected during inspection, and additional labour and materials were deployed to rectify the deficiencies. The rectification and final inspection were completed in time such that the checking certificate (at Annex A) to be issued prior to the opening ceremony. Photo 12(d) shows the grandstand with all works substantially completed. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 37 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Photo 12(a) Misalignment of the Bracing Member with the Nodes Photo 12(b) Misalignment of the Bracing Member with the Nodes Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 38 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Photo 12(c) Grandstand with global bracing members not yet installed and with many defects to be rectified (taken on 2.12.2009) Photo 12(d) Grandstand Substantially Completed (taken on 4.12.2009) 7.5 Lessons Learnt 7.5.1 The opening ceremony was successfully held on 5 December 2009 evening, and the grandstands served their function to provide temporary seating for over 1,500 audiences. The scaffold system could carry the design imposed load, and no significant vibration was noted by the audiences. Despite these facts, this paper would summarise the experience in providing technical support to their design, erection and construction supervision in the following paragraphs. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 39 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 7.5.2 Analysis 7.5.2.1 In the submission from of the specialist contractor, the connections between ledger and standard and the connections between bracing and standard were assumed to be pinned joints for simplicity. The elastic critical load factor λcr had not been checked, and the analysis and design was carried out using 1st order analysis with no due consideration of the 2nd order (P-) effect. Moreover, 2-D models were used, and hence the out-of-plane buckling mode was not included in the analysis. Yet, with our subsequent re-calculations (which are discussed in the following) the design by the RSE is generally in order. 7.5.2.2 Instead of the 2-D model used by the RSE, we have carried out a 3-D analysis of the same temporary grandstand by using the same design loading. When compared with the analysis results of the 3-D model with the 2-D model, it is found that the location of the critical member of standard (i.e. the standard with the highest utilization ratio) will be shifted to another member due to the redistribution of loadings between the members in the 3-D model. However, the value of the maximum compression force obtained from the 3-D model is 33.68kN which is almost the same as that obtained (33.44kN) from 2-D model under the same loading case of DL+LL+NHL2 (where LL = 4kPa and NHL2 = 6% LL). This shows that the adoption of 2-D model to obtain the design forces is generally satisfactory for this temporary grandstand. However, project officer should note that there may be difference in the analysis results between the 2-D and 3-D models. The location of the critical member of standard in the 3-D model is shown in Figure 15. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 40 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Standard (Axial force = 33.68 kN) Figure 15 Critical Members in the 3-D Model 7.5.2.3 We have also carried out an alternative structural analysis of the same temporary grandstand with a 3-D computer model by using the minimum imposed load of 5.0kPa as stated in the HK Loading Code (though the actual imposed load on this grandstand being 1.35kPa) to see if there are the difference between the results from two different analysis and design methods. Moreover, the member forces are also checked against the safe working loads as stated in the supplier’s catalogue. The major differences in the analysis and design method between the RSE’s submission and our subsequent calculations in the following sections are shown in Table 6. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 41 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Table 6 Model and parameters adopted in alternative analysis and design Model and Parameters Computer Model Design Method Design Imposed Load Design Submission from Specialist Contractor 2-D Working load against safe working load in supplier’s catalogue 4 kPa Alternative Analysis in this Paper 3-D Working load against safe working load in supplier’s catalogue 5 kPa 9.3% of the design imposed load along the line of seats; and 6.0% of the design imposed load perpendicular to the line of seats (from Section 4.3) Design Notional Horizontal Load 6% of the design imposed load (from IStructE 2007) Design Wind Load 0.41 kPa (the equivalent wind load 0.41 kPa (from Section 3.4) at tropical cyclone warning signal no. 3) 7.5.2.4 A 3-D computer model of the grandstand is shown in Figure 16. Sections of the computer model are shown in Figure 17. Structural analysis has then been carried out to evaluate the structural adequacy of the scaffold system with the use of computer software SAP2000. Figure 16 3-D Model of the Demountable Grandstand Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 42 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 (a) Perpendicular to the Line of Seats Direction (b) Along the Line of Seats Direction Figure 17 Typical Sections of the Demountable Grandstand 7.5.2.5 Section 2.6 states that scaffold system for the demountable grandstands has either column bucking mode or sway buckling mode depending on the bracing and the axial load on the standard, and that the lowest eigenvalue found by the eigenvalue analysis may not represent the first sway buckling mode λcr. In the present case, the maximum deflection of the grandstand is found to be 8.26mm, and the /H ratio is 1/1370, and it shows that the scaffold system has sufficient bracing members to become braced frame. Hence, the dominant buckling mode in the eigenvalue analysis is the local column buckling mode rather than sway buckling mode. 7.5.2.6 Both the deflection method and eigenvalue analysis were used to calculate the elastic critical load factor, λcr, of the structure under each load combination. The eigenvalue computed using the deflection method is 167, which is much greater than 10 while the eigenvalue analysis gives smallest eigenvalue of 1.997. From the deflected shape (shown in Figure 18), the mode of buckling with eigenvalue of 1.997 is a local column buckling mode. Hence, the eigenvalue of 1.997 obtained from the eigenvalue analysis is due to the large axial load on the members rather than the deflection due to the horizontal load, and the elastic Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 43 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 critical load factor, λcr, of the structure should be 167. The assumption in the original submitted design that 2nd order analysis is not required is therefore justified. Figure 18 Deflected shape of the scaffold system with eigenvalue of 1.997 7.5.3 Structural Design 7.5.3.1 In the 3-D model design, the dead load was assumed to be 1kPa, and the imposed load had been taken as 5kPa in accordance with the HK Loading Code for grandstand, though the actual imposed load on this grandstand was only 1.35kPa. Moreover, the following notional horizontal loads as stated in Section 7.5.2.3 had been adopted at floor level at each row of seats: (i) (ii) 9.3% of the design imposed load along the line of seats; or 6.0% of the design imposed load perpendicular to the line of the seats. The design wind pressure was taken as 0.41kPa. In addition, the force coefficient taking into account the shielding effect should be taken as 0.8 for a solidity ratio of 0.04 for 16 nos. of frames along the line of seats and 0.7 for a solidity ratio of 0.06 for 11 nos. of frames perpendicular to the line of seats. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 44 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 7.5.3.2 This paragraph intends to compare the difference in the results from the original design with those adopted values in the above paragraphs. The structure has been checked and designed by 1st order analysis with the loadings given in Section 7.5.2.3. Altogether 12 nos. of load combination have been considered. The section utilization ratios of the members of the structure under each load combination are shown in Table 8. Load cases 3 and 4 are the two most critical load combinations resulting in the maximum section utilization ratios of 1.26 for the standards, 0.41 for the ledgers and 1.24 for the bracings. The utilization ratios are obtained from comparing the member forces obtained from the computer program SAP2000 with the safe working load in supplier’s catalogue. As stated in Section 7.2.1, the safe working load in supplier’s catalogue has been used for comparison instead of that obtained from the computer program. The critical members (i.e. members with highest utilization ratios) are shown in Figure 19. 7.5.3.3 From the analysis results, it can be observed that the maximum section utilization ratio of standard and bracing had increased significantly from 0.90 to 1.26 (40% increase) and from 0.63 to 1.24 (97% increase) respectively with the adoption of the loadings given in Section 7.5.2. Under the critical load combination of DL + LL + NHL(±Y) for the standard and bracing, the changes in member forces of the critical standard and bracing member are shown in Table 7 for easy reference. Table 7 Comparison of member force obtained from alternative analysis Member Force (kN) DL + LL DL + LL NHL(Y) + NHL(Y) 24.45 9.17 33.62 Section Utilization 0.90 Model and Parameters Design Imposed Load: 4 kPa Design Notional Horizontal Load: 6% of the design imposed load (from IStructE 2007) Design Imposed Load: 5 kPa Design Notional Horizontal Load: 9.3% of the design imposed load (from HK Loading Code) Member Standard Bracing (Double) 0.07 7.04 7.11 0.63 Standard 28.99 17.74 46.73 1.26 Bracing (Double) 0.07 13.76 13.83 1.24 7.5.3.4 When compared with the member forces between the two different design loadings in Table 7, the member force of the standard due to DL + LL has only increased by 18.6% (from 24.45kN to 28.99kN) but the member force due to notional horizontal loads in the direction along the line of seats has increased substantially by 93.4% (from 9.17kN to 17.74kN). For the bracing, the member force due to DL + LL remains unchanged but the member force due to notional horizontal loads in the direction along the line of seats has increased substantially Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 45 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 by 95.5% (from 7.04kN to 13.76kN). Therefore, the maximum section utilization ratios of the standard and bracing have increased significantly from 0.90 to 1.26 (40% increase) and from 0.63 to 1.24 (97% increase) respectively mainly because of the increase in the adoption of the larger notional horizontal load in the direction along the line of seats as required by the new HK Loading Code. 7.5.3.5 However, it should be noted that the results are quite conservative because: a) b) the imposed load has been taken as 5.0kPa although the actual imposed load was 1.35kPa; and the wind load has been taken as 0.41kPa, which is the highest wind speed during the hoisting of typhoon signal no. 3, although the opening ceremony took place in December 2009 and the RSE had specified that the grandstand should not be occupied during typhoon signal no. 3 or above was hoisted. the design notional horizontal load along the line of seats is taken as 9.3% of the design imposed load instead of 6% as recommended by IStructE (2007). c) Among these factors, it can be noted that the increase in the design notional horizontal load will increase significantly the member force at the bracing. As stated in Section 4.3, the notional horizontal load in the Hong Kong Loading Code is larger than the nominal potential of spectator movement stated in IStructE (2007) (which is more reasonable in the present opening ceremony), and hence the inadequacy of the original design to cater for such large notional horizontal force is expected. Table 8 Maximum Section Utilization Ratio Load Case 1 2 3 4 5 6 7 8 9 10 11 12 Section Utilization Ratio Standard Ledger Bracing DL + LL + NHL (+X) 0.83 0.31 0.56 DL + LL + NHL (-X) 0.85 0.27 0.43 DL + LL + NHL (+Y) 1.23 1.26 0.41 DL + LL + NHL (-Y) 1.28 0.41 1.24 DL + LL + WL(+X) + NHL(+X) 0.54 0.22 0.39 DL + LL + WL(-X) + NHL(-X) 0.56 0.20 0.36 DL + LL + WL(+Y) + NHL(+Y) 0.86 0.40 0.98 DL + LL + WL(-Y) + NHL(-Y) 0.86 0.40 0.99 DL + WL(+X) 0.12 0.05 0.08 DL + WL(-X) 0.13 0.04 0.11 DL + WL(+Y) 0.17 0.15 0.27 DL + WL(-Y) 0.15 0.15 0.27 where DL= Dead Load, LL = Imposed Load, WL = Wind Load, NHL = Notional Horizontal Load Load Combination Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 46 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Standard (Section Utilization = 1.26) (a) Standard Ledger (Section utilization = 0.41) (b) Ledger Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 47 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Bracing (Section utilization = 1.24) (c) Bracing Figure 19 Critical Members 7.5.4 Dynamic Effect 7.5.4.1 Section 3.5.3 notes that where resonance is unlikely, the use of a nominal horizontal load approach can be used to include the dynamic effect due to crowd. A modal analysis should therefore be carried out to find out the fundamental frequency of the empty structure in order to eliminate the possibility of resonance due to such synchronized movement, which is one of the most common failure reasons of such demountable grandstand. The mode shapes of the structure at fundamental frequency along and perpendicular the line of seats directions are shown in Figure 20. The fundamental frequency of structure is found to be 10Hz which is much higher than the recommended minimum horizontal frequency of 4.0Hz as recommended by Ji and Ellis (1997) as discussed in Section 4.4. The fundamental frequency of the structure is therefore considered satisfactory and no further rigorous dynamic analysis is required. Hence, a check of the fundamental frequency in both sway direction is required to ensure that such demountable grandstands will not be susceptible to the resonance due to the dynamic load by spectators’ movement. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 48 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 7.5.4.2 The added Type 6 global bracing elements have also been included in the dynamic analysis to investigate their effects, and the results are shown in Table 9. It can be seen that the Type 6 global bracing elements have substantially improved the stiffness of the scaffold systems, confirming the conclusion from Ji and Ellis (2001). (a) Fundamental mode in perpendicular to the line of seats direction (Frequency = 15 Hz) (b) Fundamental mode in along the line of seats direction (Frequency = 10 Hz) Figure 20 Fundamental Mode Shapes of the Grandstands Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 49 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Table 9 Comparison of Fundamental Frequency With and Without Type 6 Global Bracing Members Direction Perpendicular to the line of seats Mode Shape Frequency 15 Hz 20 Hz Along the line of seats 10 Hz 12 Hz Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 50 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 7.5.5 Construction 7.5.5.1 It has been checked that all the standards are under compression in the working load condition with the minimum compression force of 0.66kN under all load combinations (Figure 21), and hence no ground anchors or kentledge are required to tie the standard onto the ground. Project officer should note that when there are any tensile force found in the standards from the structural analysis, it is necessary to check on site to ensure that all pins are installed to connect upper with lower standards and that the tensile force due to wind or lateral loads can be transmitted throughout the allround scaffold by using the pins. Standard Minimum compression = 0.66kN Figure 21 Member with the Minimum Compression Force 7.5.5.2 The RSE should be required to check the erection at the earliest moment, and should station himself or his supervisory staff on site when the erection of scaffold commences, such that any deviation from the approved drawings should be rectified immediately. Sufficient labour should be deployed by the specialist contractor to carry out the rectification works, and the programme of works, though tight, should allow the inspection by the RSE. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 51 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 8 References Blackmore, P (2004), BRE Special Digest SD 5: Wind Loads on Unclad Structures (Watford: BRE) (available: www.bre.co.uk, accessed: 24 October 2011). Bolton, A (1992), “Fatal Mix Caused Stand Fall”, New Civil Engineer, 14 May, pp. 5-6. Bolton, A (1997), “Correspondence: Effective Bracing Systems for Temporary Grandstands”, The Structural Engineer, 75(22), pp. 389-9 (available: www.istructe.org, accessed: 4 November 2011). BSI (1996), BS 6399: Part 1: 1996 – Loading for Buildings – Code of Practice for Dead and Imposed Loads (London: BSI). BSI (1997), BS 6399: Part 2: 1997 – Loading for Buildings – Code of Practice for Wind Loads (London: BSI). BSI (2005), BS EN 1993 1-1:2005: Eurocode 3 - Design Of Steel Structures - Part 1-1: General Rules and Rules for Buildings (London: BSI). Buildings Department (2004), Code of Practice on Wind Effects in Hong Kong 2004 (Hong Kong: Buildings Department) (available: www.bd.gov.hk, accessed: 1 September 2011). Buildings Department (2005), Code of Practice for the Structural Use of Steel 2005 (Hong Kong: Buildings Department) (available: www.bd.gov.hk, accessed: 1 September 2011). Buildings Department (2011), Code of Practice for Dead and Imposed Loads 2011 (Hong Kong: Buildings Department) (available: www.bd.gov.hk, accessed: 1 September 2011). Chandrangsu, T and Rasmussen, K (2006), “Structural Modelling of Support Scaffold Systems”, Journal of Constructional Steel Research, 67, pp. 866–75. Choi, E C C (1984), Wind Loading in Hong Kong: Commentary on the Code of Practice on Wind Effects Hong Kong 1983 (Hong Kong: Hong Kong Institution of Engineers). Crick, D and Grondin, G Y (2008), Structural Engineering Report No. 275: Monitoring and Analysis of a Temporary Grandstands (Edmonton, Alberta: Department of Civil and Environmental Engineering, University of Alberta) (available: www.uofaweb.ualberta.ca, accessed: 4 November 2011). De Brito, V L and Pimentel, RL (2009), “Cases of Collapse of Demountable Grandstands”, Journal of Performance of Constructed Facilities, 23, pp. 151-9(available: www.asce.org, accessed: 4 November 2011). Dickie, J F (1983), “Demountable Grandstand”, The Structural Engineer, 61A(3), pp. 81-6 (available: www.istructe.org, accessed: 4 November 2011). Ellis, B R and Ji, T (1997), “Effective Bracing Systems for Temporary Grandstands”, The Structural Engineer, 75(6), pp. 95-100 (available: www.istructe.org, accessed: 4 November 2011). Enright J, Harriss R and Hancock G J (2000), “Structural Stability of Braced Scaffolding and Formwork with Spigot Joints”, Proceedings of the Fifteenth International Specialty Conference on Cold-Formed Steel Structures, pp. 357–76. Godley, M H R and Beale R G (1997), “Sway Stiffness of Scaffold Structures”, The Structural Engineer, 75(1), pp. 4–12 (available: www.istructe.org, accessed: 4 November 2011). Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 52 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Godley, M H R and Beale R G (2001), “Analysis of Large Proprietary Access Scaffold Structures”, Structures and Buildings, 146(1), pp. 31–9. Grant, M (1975), Scaffold Falsework Design to BS 5975 (London: E and F N Spon). Harung, H S, Lightfoot, E and Duggan, D M (1975), “The Strength of Scaffold Towers under Vertical Loading”, The Structural Engineer, 53(1), pp. 23-30 (available: www.istructe.org, accessed: 4 November 2011). IStructE (2007), Temporary Demountable Structures: Guidance on Procurement, Design and Use (London: The Institution of Structural Engineers, 3rd ed). Ji, T (2003), “Concepts for Designing Stiffer Structures”, The Structural Engineer, 81(21), pp. 36-42 (available: www.istructe.org, accessed: 12 December 2011). King, C (2005), NCCI: Calculation of Alpha-cr (Ascot: SCI) (available: www.steelbiz.org, accessed: 14 November 2011). Labour Department (2001), Code of Practice for Metal Scaffold Safety (Hong Kong: Labour Department) (available: www.labour.gov.hk, accessed: 4 November 2011). Littler, J D (1996), “Measuring the Dynamic Response of Temporary Grandstands”, Proceeding of Structural Dynamics Eurodyn 1996, pp. 907-13. Peng J L, Chan S L and Wu C L (2007), “Effects of Geometrical Shape and Incremental Loads on Scaffold Systems”, Journal of Constructional Steel Research, 63, pp. 448–59. Rasmussen, K and Chandrangsu, T (2009), Research Report No. R905: Review of Past Research on Scaffold Systems (Sydney: The University of Sydney) (available: www.civil.usyd.edu.au, accessed: 31 October 2011). Rathbone, A J (2002), “Second-order Effects – Who Needs Them?” The Structural Engineer, 80(21), pp. 19-21 (available: www.istructe.org, accessed: 4 November 2011). Yu, W K (2004), “An Investigation into Structural Behaviour of Modular Steel Scaffolds”, Steel and Composite Structures, 4(3), pp. 211-26. Yu, W K, Chung, K F and Chan, S L (2004), “Structural Instability of Multi-storey Doortype Modular Steel Scaffolds”, Engineering Structures, 26, pp. 867–81. Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 53 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Annex A Sample Checking Certificate Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 54 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011 Structural Engineering Branch, ArchSD Information Paper on Demountable Grandstand Issue No./Revision No. : 1/- Page 55 of 55 File code : TemporaryGrandstand.doc CTW/MKL/CYK/LKN Issue/Revision Date : December 2011
Report "A Case Study of Using Metal Scaffold System for Demountable Grandstand: The Opening Ceremony of Hong Kong 2009 East Asian Games "