Civil Engineering Reference
In-Depth Information
These specifications will on many occasions clearly prescribe the loads for which
structures are to be designed. Despite the availability of this information, the designer's
ingenuity and knowledge of the situation are often needed to predict what loads a particu-
lar structure will have to support in years to come. Over the past several decades, insuffi-
cient estimates of future traffic loads by bridge designers have resulted in a great amount
of replacement with wider and stronger structures.
1.25
CALCULATION ACCURACY
A most important point, which many students with their amazing computers and pocket
calculators have difficulty in understanding, is that reinforced concrete design is not an
exact science for which answers can be confidently calculated to six or eight places.
The reasons for this statement should be quite obvious: The analysis of structures is
based on partly true assumptions; the strengths of materials used vary widely; and
maximum loadings can only be approximated. With respect to this last sentence, how
many users of this topic could estimate to within 10% the maximum live load in
pounds per square foot that will ever occur on the building floor they are now occupy-
ing? Calculations to more than two significant figures are obviously of little value and
may actually be dangerous because they may mislead students into a false sense of
accuracy.
1.26
IMPACT OF COMPUTERS ON REINFORCED
CONCRETE DESIGN
The availability of personal computers has drastically changed the way in which rein-
forced concrete structures are analyzed and designed. In nearly every engineering school
and office, computers are routinely used to handle structural design problems.
Many calculations are involved in reinforced concrete design, and many of these cal-
culations are quite time consuming. With a computer, the designer can reduce the time re-
quired for these calculations tremendously and thus supposedly have time to consider
alternative designs.
Although computers do increase design productivity, they do undoubtedly tend at the
same time to reduce the designer's “feel” for structures. This can be a special problem for
young engineers with little previous design experience. Unless designers have this “feel,”
computer usage, though expediting the work and reducing many errors, may occasionally
result in large mistakes.
It is interesting to note that up to the present time, the feeling at most engineering
schools has been that the best way to teach reinforced concrete design is with chalk and
blackboard, supplemented with some computer examples.
Inside the back cover of this topic is a CD-ROM containing a design program
SABLE 32, which is initially discussed in Section 2.6 of this topic. This software is fre-
quently used to solve example problems in the chapters to follow. In addition, a student
version of a nationally used commercial program, SAP2000, is included on the CD-ROM.
Its application is illustrated in Chapter 21.
