Civil Engineering Reference
In-Depth Information
often specify a particular industry standard for design of particular materials. For exam-
ple, Section 1901.2 of the
International Building Code
requires that:
1901.2 Plain and Reinforced Concrete.
Structural concrete shall be designed and constructed
in accordance with the requirements of this chapter and ACI 318 as amended in Section 1908
of this code. Except for the provisions of Sections 1904 and 1911, the design and construction
of slabs-on-grade shall not be governed by this chapter unless they transmit vertical loads or
lateral forces from other parts of the structure to the soil.
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Because of this paragraph, we must use the requirements of ACI-318, except as specifi-
cally modified, when designing reinforced concrete structural systems conforming to the
IBC2000 building code.
Municipal and state governments adopt the model building codes or develop their
own codes based on the model building ones. Once adopted, these codes become legally
enforceable laws with which the design engineer must comply. The intention of the codes
is not to limit engineering creativity, as some people believe, but to provide a minimum
standard for loads and structural performance to safeguard the health and safety of the
public. When necessary, an engineer can, and should, go beyond the minimum specifica-
tions in the codes. In addition, the codes do not specify structural geometry. They only
specify a minimum standard for the performance of the system.
One other comment regarding building codes is appropriate. A structural system that just
satisfies the minimum requirements of the appropriate building code should not be consid-
ered a minimally safe or marginal structure that is on the verge of failure. A structural system
that satisfies the minimum requirements of the building code is a safe structural system that
complies with accepted professional standards for strength, serviceability, and durability.
Use of Computers in Structural Design
As you have become aware through other parts of this textbook, computer software has a
very important place in structural design. It is used extensively for determining the forces
in the structural system caused by the design loads as well as for selecting appropriate sizes
of structural components. Nevertheless, a computer is only a tool in the design process, just
as a hand calculator is a tool. It is, however, a very indispensable tool when designing sys-
tems because it can very quickly perform calculations that would otherwise require a con-
siderable number of hours. Throughout this chapter, we will be making heavy use of the
computer program
SAP2000
for analysis as we discuss building system design.
When using computers, an engineer should be aware of two considerations. First, all
computer programs are based on a set of assumptions on which formulation of the theo-
retical basis of the software was developed. Before using any computer program for
analysis and design, a prudent structural engineer must verify the assumptions, and
thereby the applicability of the software for the task at hand. Not doing so can quickly
lead to disaster if the software was not intended for the purpose for which it is being used.
Second, the precision afforded by a computer in calculations should not lull the de-
sign engineer into a false sense of security. Computers can calculate system response to
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International Code Council,
2000 International Building Code
, p. 451.
