Introduction - Design of Reinforced Concrete - page 6

turn in a length of not more than 12 times the bar diameter. 7 (The purpose of the twisting
was to provide better bonding or adhesion of the concrete and the steel.) In 1890 in San
Francisco, Ransome built the Leland Stanford Jr. Museum. It is a reinforced concrete
building 312 feet long and two stories high in which discarded wire rope from a cable-car
system was used as tensile reinforcing. This building experienced little damage in the 1906
earthquake and the fire that ensued. The limited damage to this building and other concrete
structures that withstood the great 1906 fire led to the widespread acceptance of this form
of construction on the West Coast. Since 1900-1910, the development and use of rein-
forced concrete in the United States has been very rapid. 8,9

1.5 COMPARISON OF REINFORCED CONCRETE AND

STRUCTURAL STEEL FOR BUILDINGS AND BRIDGES
When a particular type of structure is being considered, the student may be puzzled by the
question, “Should reinforced concrete or structural steel be used?” There is much joking
on this point, with the proponents of reinforced concrete referring to steel as that material
which rusts and those favoring structural steel referring to concrete as that material which
when overstressed tends to return to its natural state—that is, sand and gravel.
There is no simple answer to this question, inasmuch as both of these materials have
many excellent characteristics that can be utilized successfully for so many types of struc-
tures. In fact, they are often used together in the same structures with wonderful results.
The selection of the structural material to be used for a particular building depends on
the height and span of the structure, the material market, foundation conditions, local
building codes, and architectural considerations. For buildings of less than 4 stories, rein-
forced concrete, structural steel, and wall-bearing construction are competitive. From 4 to
about 20 stories, reinforced concrete and structural steel are economically competitive,
with steel having taken most of the jobs above 20 stories in the past. Today, however, re-
inforced concrete is becoming increasingly competitive above 20 stories, and there are a
number of reinforced concrete buildings of greater height around the world. The 74 story
859-ft-high Water Tower Place in Chicago is the tallest reinforced concrete building in
the world. The 1465-ft CN tower (not a building) in Toronto, Canada, is the tallest rein-
forced concrete structure in the world.
Although we would all like to be involved in the design of tall prestigious reinforced
concrete buildings, there are just not enough of them to go around. As a result, nearly all
of our work involves much smaller structures. Perhaps 9 out of 10 buildings in the United
States are 3 stories or less in height, and more than two-thirds of them contain 15,000 sq ft
or less of floor space.
Foundation conditions can often affect the selection of the material to be used for the
structural frame. If foundation conditions are poor, a lighter structural steel frame may be
desirable. The building code in a particular city may be favorable to one material over the
other. For instance, many cities have fire zones in which only fireproof structures can be

7 American Society for Testing Materials, 1911, Proceedings , 11, pp. 66-68.
8 Wang, C. K., and Salmon, C. G., 1998, Reinforced Concrete Design , 6th ed. (New York: HarperCollins), pp. 3-5.
9 “The Story of Cement, Concrete and Reinforced Concrete,” Civil Engineering , November 1977, pp. 63-65.