A Beginner's Guide to the Steel Construction Manual, 13th ed. (old)

Chapter 8 - Bending Members

© 2006, 2007, 2008 T. Bartlett Quimby

Introduction

Flexure

Shear

Deflection

Misc. Limit States

Beam Design

Chapter Summary

Example Problems

Homework Problems

References

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Section 8.8

Example Problem 8.2

Given:  A 40 ft long, simply support W 18x35 beam supports a uniformly distributed load, w, over the whole span. The load consists of equal parts of dead, live, and snow loads.

Wanted:  Ignoring the self weight of the beam, determine the maximum load, ws,eq, that the beam can support for the given conditions:

a. The beam has full lateral support of the compression flange
b. The beam has lateral support of the compression flange at ends as quarter points only.
c. The beam has lateral support of the compression flange at ends and mid-point only.
d. The beam has lateral support of the compression flange at ends only.

Solution:  The solution to this problem is identical in approach to example problem 8.1, with the exception is that the applied load is now a uniformly distributed load instead of a point load.

The effect of changing the load is that different equations are used to compute shear, deflection, and moment on the span.  These equations can be found as case 1 on SCM pg 3-211.  In each case, the capacity of the beam is set equal to the applicable equation.  The resulting equation is solved for the distributed load that causes the internal force to equal the beam's capacity.

Table 8.8.2.1 summarizes the results of the computations.

Table 8.8.2.1
Example 8.2 Results Summary
ws,eq (k/ft)

  Flexure   Shear   Deflection   Controlling Controlling Limit State
part LRFD ASD LRFD ASD TL LL Only LRFD ASD LRFD ASD
a 0.984 0.996 6.29 6.37 0.62 0.68 0.62 0.62 TL Defl TL Defl
b 0.755 0.763 6.29 6.37 0.62 0.68 0.62 0.62 TL Defl TL Defl
c 0.0743 0.0751 6.29 6.37 0.62 0.68 0.07 0.08 Flexure Flexure
d 0.0257 0.0260 6.29 6.37 0.62 0.68 0.03 0.03 Flexure Flexure

All the same observations made about the solution to example problem 8.1 can also be made to this problem. In addition, note that the values of Cb in this version of the problem are different than those found in example problem 8.1. The difference stems from the change in shape of the moment diagram.

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