Design Steps ofA Suspension Bridge (Based on SAP2000) Design Steps of Suspension Bridge. Er. Saroj Bhattarai 1 Design of Cable Elements: Possible load cases • Dead Load + Moving Load • Dead Load + Moving Load + Partial Wind • • Load + Braking Force Dead Load + Moving Load + Partial Wind Load Dead Load + Full Wind Load Select the critical Tensile Force on the cables Design Steps of Suspension Bridge. Er. Saroj Bhattarai Er. Saroj Bhattarai 2 1 Er. Saroj Bhattarai 3 Design of Cable Elements: • Tensile Resistance of the cable: F = Ks * Am * fu * Ka Where.76 – 0.0 for parallel wires Ka = Factor of safety for anchoring devices 0.85 for multiple strands 0.0 depending upon the type of anchorage Am = Net metallic area of the cable Design Steps of Suspension Bridge. 26. Saroj Bhattarai 4 2 . Saroj Bhattarai Er.55 for Multiple strand ropes f = 0. 32. fu = Ultimate tensile strength of cable (1500 – 1800 MPa) Ks = 0.8 – 1. 19… that forms a Hexagonal shape – The diameter and number of cables are adjusted as required • Net metallic area of the cables: Am = f * Gross area f = 0.93 – 1.75 – 0. 7. Er. 40 mm) • The possible number of cables: – 1.77 for open spiral ropes Design Steps of Suspension Bridge.Design of Cable Elements: • Select a diameter of the single cable and assume number of cables in the single rope (Nominal dia= 13. 36. Er.0 Frd should not be less than the Critical Tensile Force. fs = Overall factor of safety Usually taken as 3. Saroj Bhattarai Er.)) – Saddles – Pylons (steel or RCC) Design Steps of Suspension Bridge. Er. Saroj Bhattarai 6 3 . F The number and diameter of cables are adjusted to arrive at most economical combination Design Steps of Suspension Bridge. Saroj Bhattarai 5 Design of Cable Elements: • Other elements/parts – Anchoring devices: • End sockets and connections • Hangar connections – Anchor blocks (Gravity anchor / Dead Dead--man anchor / Anchor rods etc etc.Design of Cable Elements: • Design Tensile Resistance of the cable Frd = F / fs Where. 2) • Not necessary for tension members Design Steps of Suspension Bridge. cross members. Saroj Bhattarai 8 4 .). Er. cases The elements and their properties are predefined during the analysis in SAP2000 Design Steps of Suspension Bridge. Saroj Bhattarai 7 Design of Stiffening Girder (Steel truss) • Sectional pproperties required: p q – Cross section area – Moment of inertia (Ixx and Iyy) – Radius of gyration (RGxx and RGyy) • Different approach for elements in compression and • tension Find the effective length of the compression members – (IRC:24(IRC:24-2001. Select the critical forces from different load cases. Saroj Bhattarai Er. 5. Er. wind bracings etc.Design of Stiffening Girder (Steel truss) • Function of the Stiffeningg Girder • Load cases similar to the cable elements • Find the critical forces on different elements • (Top & Bottom chords. 511 or IS:800 IS:800--1984. vertical & inclined members. 511.3.1 – Allowable tensile stress can be taken as 0. • It may require several cycles of analysis & design Design Steps of Suspension Bridge. 5. Saroj Bhattarai 10 5 .6*fy Design Steps of Suspension Bridge. Er.Design of Stiffening Girder (Steel truss) • Find the slenderness ratio of the compression members: = Leff/RGmin Where. Saroj Bhattarai Er. Er.3 or IS:800 IS:800--1984. Saroj Bhattarai 9 Design of Stiffening Girder (Steel truss) • The actual Compressive/Tensile stresses in the elements should not exceed the allowable stress.5. • The Sections should be altered and analyzed--designed until the most analyzed economic sections are obtained. Leff = effective length RGmin = Minimum radius of gyration • Find the allowable compressive/tensile stress for f the h members: b – IRC:24IRC:24-2001. 0-07 07--462305 462305--2 IRC:24--2001. Tata McGrawMcGraw-Hill Publication. ISBNISBN. Er. 1986.0-471 471--90130 90130--X LS Negi.0-07 07--462366 462366--4 MS Troitsky Troitsky.Design of Stiffening Girder (Steel truss) • Other elements/parts: – Design of joints or welds – Design of Battens or lacings – Design of bearings Design Steps of Suspension Bridge. ISBN-. Cable Stayed Bridge – Theory and Design Design. Cable Supported Bridges – Concept & Design. Saroj Bhattarai 11 Some relevant literature/Reference • CS Reddy. Nepal Design Steps of Suspension Bridge. Basic Structural Analysis. General Construction in Steel IS:800 IS:1028--1979. • • • • • • • 1981. Saroj Bhattarai 12 6 . Design & Construction of Trial Suspension Bridges. Steel Road Bridges IRC:24 IS:800--1984. Design of Steel Structures. Suspension Bridge Project.0-258 ISBN 258--977034 977034--0 Niels J. 1977 1977. Gimsing. 1983. Saroj Bhattarai Er. ISBNISBN. Wire Ropes and Strands for Suspension Bridges IS:1028 Survey. Section V. ISBNISBN. Er. Tata McGrawMcGraw-Hill Publication. org www.icivilengineer. Saroj Bhattarai 13 7 .eng--tips.com (Discussion forum) www. Saroj Bhattarai Er.Relevant web resources: • • • • www.com Design Steps of Suspension Bridge.uk www. Er.eng www.co.brantacan.pbs.