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Chapter: Civil : Design Of Steel Structures

Important Question And Problems With Answer: Beam

Civil - Design Of Steel Structures

Important Question And Problems With Answer: Beam


1.What is a Beam?

A beam is a structural member, which carries a load normal to the axis. The load produces bending moment and shear force in the beam.


2.       What is meant by castellated beam?

A rolled beam with increased depth is to be castellated. To obtain such sections, a zigzag line is cut along the beam by an automatic flame-cutting machine. The two halves thus produced are rearranged so that the teeth match up and the teeth are then welded together.


3. How the beams are failed? Bending failure Shear failure

Deflection failure

The designs are based on these three failures which are to be determined.


4.       What do you mean by bending failure?

Bending failure may be due to crushing of compression flange or fracture of the tension flange of the beam. Instead of failure due to crushing, the compression flange may fail by a column like action with side ways or lateral buckling. Collapse would follow the lateral buckling.


5.       What is the maximum deflection that to be allowed in steel beams?

The deflection of a member, shall not be such as to impair the strength or efficiency of the structure and lead to finishing. The deflection is generally should not exceed 1/325 of the span.


6. What is web crippling?

Web  crippling  is  the  localized  failure  of  a  beam  web  due  to  introduction of an excessive load over a small length of the beam. It occurs at point of application of concentrated load and at point of support of a beam. A load over a short length of beam can cause failure due to crushing and due to compressive stress in the web of the beam below the load  or  above     the  reaction.  This      phenomenon  is    also known  as  web  crippling  or    web crushing.                         


7.  What are laterally supported beams?                      

The  beams   which        are  provided        with   the  lateral  supports   either   by embedding the compression flange in the concrete slab or by providing effective intermediate (support) restraints at a number of points to restrain the lateral buckling is called laterally supported beams.


8. Mention the advantages of using rolled steel wide flange section as beams More section modulus

Lesser area Economical


9. Why does buckling of web occur in beams? Diagonal compression due to shear Longitudinal compression due to bending

Vertical compression due to concentrated loads


11.     Under what situations the plated beams are used?

When a bending moment is large which cannot be resisted by the largest available rolled beam section

The depth of the beam is restricted due to headroom requirements. 12. Why intermediate stiffeners are required for plate girders?

The web of the plate girder relatively being tall and thin it is subjected to buckling. Hence it is stiffened both vertically and horizontally using intermediate stiffeners.


13. What do you mean by curtailment of flanges?

The section of a plate girder is to be designed first at mid span. The bending moment will goes on decreasing towards the supports. Hence the flange plates, provided at the maximum section can be curtailed.


14. What is the purpose of providing the bearing stiffener?

It prevents  the web from crushing  and buckling  sideways,  under the action of concentrated loads

It relieves the rivets connecting the flange angles and web, from vertical shear.


15. Name the components of a plate girder.

Web plate Flange plate Flange angles

Web splice plates Flange splice plates Vertical or transversestiffeners Bearing stiffeners

Longitudinal or horizontal stiffeners End bearings or end connections


16. Mention the basic design assumptions of a plate girder?

The web plate resists the shear force.

The shear stress is uniformly distributed over whole cross sectional area of web.

The flanges resist the bending moment


17. Where the plate girders are used?

The plate girders are used in the buildings where the span is more and heavy

loads are expected and in the bridges. Most commonly they are used in the bridges.


18. What are the methods that are adopted to determine the flange design?

Flange area method

Moment of inertia method

The former method is an approximate method, which is used for determining the trial section. In this method, it is assumed that the stress distribution in the tension and compression flanges  is  uniform,  whereas  in  the  latter  case  it  is  the  exact  method  and  is recommended by the IS code. Generally, the section designed by the flange area method is checked by this method.


20. The pitch of the rivets connecting cover plates with flanges of rolled steel beam is designed for what force?

These rivets are designed for horizontal shear between the flange plate and flange angles. Since the vertical load is transferred by the flange plates to the flange angles by direct bearing, there will be no vertical shear due to the vertical load. Here the rivets will be in single shear.

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