Example Problems

A Beginner's Guide to the Steel Construction Manual, 16^th ed.

Chapter 8 - Bending Members

Introduction

Flexure

Shear

Deflection

Misc. Limit States

Beam Design

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Section 8.8.2

Example Problem 8.2

The example problems presented in this section have a spreadsheet solution. You will need this file to follow along with the presented solutions. You can click on the following link to get the file:

Chapter 8: Excel Spreadsheet Solutions

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, w_s,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 3-208. 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
w_s,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 C_b 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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