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Chapter: Civil - Structural Analysis - Space And Cable Structures

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Important Questions and Answers: Space And Cable Structures

Civil - Structural Analysis - Space And Cable Structures


CABLE AND SPACE STRUCTURES

 

 

 

1. What are cable structures?

 

Long span structures subjected to tension and uses suspension cables for supports. Examples of cable structures are suspension bridges, cable stayed roof.


 

Suspension bridge- cable structure

 

2. What is the true shape of cable structures?

 

Cable structures especially the cable of a suspension bridge is in the form of a catenary. Catenary is the shape assumed by astring/cable freely suspended between two points.

 

 

 

3. What is the nature of force in the cables?

 

Cables of cable structures have only tension and no compression or bending.

 

4. What is a catenary?

 

Catenary is the shape taken up by a cable or rope freely suspended between two supports and under its own self weight.

 

 

 

5. Mention the different types of cable structures.

 

Cable structures are mainly of two types: (a) Cable over a guide pulley (b)Cable over a saddle

 

 

 

6. Briefly explain cable over a guide pulley.

 

Cable over a guide pulley has the following properties:

       Tension in the suspension cable=Tension in the anchor cable

       The supporting tower will be subjected to vertical pressure and bending due to net horizontal cable tension.

 

7. Briefly explain cable over saddle.

 

Cable over saddle has the following properties:

 

        Horizontal component of tension in the suspension cable=Horizontal component of tension in the anchor cable

 

        The supporting tower will be subjected to only vertical pressure due to cable tension.

 

 

 

8. What is the degree of indeterminacy of a suspension bridge with two hinged

 

stiffening girder?

 

The two hinged stiffening girder has one degree of indeterminacy.

 

 

 

9. What are the main functions of stiffening girders in suspension bridges?

 

Stiffening girders have the following functions.

 

They help in keeping the cables in shape

 

They resist part of shear force and bending moment due to live loads.

 

 

 

10.            Differentiate between planetruss and spacetruss.

 

Planetruss

 

       All members liein one plane

 

       All joints are assumed to be hinged.

 

Spacetruss

 

       This is a three dimensional truss

 

       All joints are assumed to be ball and socketed.

 

 

 

11.            Define tension coefficient of a truss member.

 

The tension coefficient for a member of a truss is defined as the pull or tension in the member divided by its length, i. e. the force in the member per unit length.

 

 

 

12.            Give some examples of beams curved in plan.

 

Curved beams are found in the following structures.

 

Beams in a bridge negotiating a curve

 

       Ring beams supporting a water tank

 

       Beams supporting cornerlintels

 

       Beams in ramps

 

13.            What are the forces developed in beams curved in plan?

 

Beams curved in plan will have the following forces developed in them:

 

       Bending moments

 

       Shear forces

 

       Torsional moments

 

 

 

14.            What are the significant features of circular beams on equally spaced supports?

 

       Slope on either side of any support will be zero.

 

       Torsional moment on every support will be zero

 

 

 

15.            Give the expression for calculating equivalent UDL on a girder.

 

Equivalent UDL on a girder is given by We:


 

16.            Give the range of central  dip of a cable.

 

The central dip of acablera nges from 1/10 to 1/12 of the span.


 

 

17.            Give the horizontal and vertical components of a cable structure subjected to UDL.


 


18. Give the expression for determining the tension T in the cable.

 

The tension developed in the cable is given by 


Where H=horizontal component and V=vertical component.

 

 

 

19.            Give the types of significant cable structures

 

Linear structures

 

       Suspension bridge s

 

       Draped cables

 

       Cable-stayed beams or trusses

 

       Cable trusses

 

       Straight tensioned cables

 

Three-dimensional structures

 

       Bicycle wheel roof

 

       3D cable trusses

 

       Tensegrity structures

 

       Tensairity structures

 

 

20.            What are cables made of?

 

Cables can be of mild steel, high strength steel, stainless steel, or polyest er fibres. Structural cables are made of a series of small strandstwistedor bound together to form a much larger cable. Steel cables are either spiral strand, where circular rodsaretwisted together or locked coil strand, where individual interlocking steel strands form the cable (often with aspiral strand core).

 

Spiral strand is slightly weaker than locked coil strand. Steel spiral strand cables have a Young's modulus, Eof150 10kN/mm and come in sizes from 3 to 90 mm diameter. Spiral strand suffers from construction stretch, where the strands compact when the cable is loaded.

 

 

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