Design Steps of (Based on SAP2000) Design Steps of Suspension Bridge.
Er. Er. S Saroj aroj Bhattarai Bhattarai
1
Design of Cable Elements: Possible load cases
• Dead Load + Movin Load • Dead Load + Moving Load + Partial Wind Load + Braking Force • Dead Load + Moving Load + Partial Wind Load
Select the critical Tensile Force on the cables Design Steps of Suspension Suspension Bridge. Bridge.
Er. Saroj Bhattarai
Er. Saroj Bhattarai
2
1
Design of Cable Elements: • Select a diameter of the single cable and assume number of cables in the single rope (Nominal dia= 13, 26, 32, 36, 40 mm) • The possible number of cables: – 1, 7, 19… that forms a Hexagonal shape shape – The diameter and number of of cables cables are are adjusted as required
• Am = f * Gross area f = 0.55 for Multiple strand ropes f = 0.75 – – 0.77 for open spiral ropes Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
3
Design of Cable Elements:
• Tensile Resistance of the cable: F = Ks * Am * fu * Ka Where, fu = Ultimate tensile strength of cable (1500 – 1800 MPa) Ks = 0.76 – – 0.85 for multiple strands 0.93 – – 1.0 for parallel wires 0.8 – – 1.0 depending upon the type of anchorage Am = Net metallic area of the cable
Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
Er. Saroj Bhattarai
4
2
Design of Cable Elements:
• Desi n Tensile Resistance of the cable Frd = F / fs Where, fs = Overall factor of safety Usually taken as 3.0
Frd should not be less than the Critical Tensile orce. The number and diameter of cables are adjusted to arrive at most economical combination Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
5
Design of Cable Elements:
• – Anchoring Anchoring devices: • End sockets and connections • Hangar connections – Anchor Anchor blocks (Gravity anchor / Dead Dead--man . – Saddles – Pylons (steel or RCC) Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
Er. Saroj Bhattarai
6
3
Design of Stiffening Girder (Steel truss) • Function of the Stiffenin Girder • Load cases similar to the cable elements • Find the critical forces on different elements (Top & Bottom chords, vertical & inclined members, cross members, wind bracings etc.). Select the critical forces from different . • The elements and their properties are predefined during the analysis in SAP2000 Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
7
Design of Stiffening Girder (Steel truss) • Sectional ro erties re uired: – Cross section area – Moment of inertia (Ixx and and Iyy) Iyy) – Radius of gyration (RGxx and and RGyy) RGyy)
• Different approach for elements in compression and •
tension Find the effective len th of the com ression members – (IRC:24(IRC:24-2001, 511 or IS:800 IS:800--1984, 5.2)
• Not necessary for tension members Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
Er. Saroj Bhattarai
8
4
Design of Stiffening Girder (Steel truss) • Find the slenderness ratio of the com ression members:
= Leff/RGmin Where,
Leff = effective length RGmin = Minimum radius of gyration
• Find the allowable compressive/tensile stress or t e mem ers: – IRC:24 IRC:24--2001, 511.3.3 or IS:800IS:800-1984, 5.5.1 – Allowable Allowable tensile stress can be taken as 0.6*fy Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
9
Design of Stiffening Girder (Steel truss)
• The actual Com ressive Tensile stresses in the elements should not exceed the allowable stress. • The Sections should be altered and analyzed--designed until the most analyzed economic sections are obtained. • It may require several cycles of analysis & design Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
Er. Saroj Bhattarai
10
5
Design of Stiffening Girder (Steel truss)
• – Design of joints or welds – Design of Battens or lacings – Design of bearings
Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
11
Some relevant literature/Reference • CS Reddy, Basic Structural Analysis, Tata McGraw McGraw--Hill Publication, • • • • • • •
1981, ISBN ISBN-- 0-07 07--462366 462366--4 , – , , ISBN-- 0-258ISBN 258-977034 977034--0 Niels J. Gimsing, Cable Supported Bridges – – Concept & Design, 1983, ISBNISBN- 0-471 471--90130 90130--X LS Negi, Design of Steel Structures, Tata McGrawMcGraw-Hill Publication, 1986, ISBNISBN- 0-07 07--462305 462305--2 IRC:24--2001, Section V, Steel Road Bridges IRC:24 IS:800--1984, General Construction in Steel IS:800 IS:1028--1979, Wire Ropes and Strands for Suspension Bridges IS:1028 Survey, Design & Construction of Trial Suspension Bridges, Suspension Bridge Project, Nepal
Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
Er. Saroj Bhattarai
12
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Relevant web resources: • • • •
www.brantacan.co.uk www.eng--tips.com (Discussion forum) www.eng www.pbs.org www.icivilengineer.com
Design Steps of Suspension Bridge.
Er. Saroj Bhattarai
Er. Saroj Bhattarai
13
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