CHAPTER XIX

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METHODS AND COST OF REINFORCED CONCRETE BUILDING CONSTRUCTION.

If we set aside concrete block construction, virtually all concrete used in building construction is reinforced; plain monolithic or mass concrete now, as in the past, is one of the secondary building materials. It is reinforced concrete building construction that is discussed in this chapter. In no class of concrete work is the contractor's responsibility for the successful outcome of the work greater than in reinforced concrete building construction. No degree of excellence in design can make up for incompetent, careless or dishonest work in construction. This is true not merely in the general way that it is true of all engineering construction--it is true in a special way peculiar to the material. Except for the reinforcing steel, the contractor for concrete building work has no guarantee of the quality of any element of his work except his own faithful care in performing every task that combines to produce that element. The quality of his concrete depends upon the care with which he has chosen his cement, sand and stone, and on the perfection with which he has incorporated them into a homogeneous mixture. The quality of his beam or column, then, depends upon the care with which the concrete is placed in position with the reinforcement and with which the supporting forms are maintained until the member is amply strong to do without support. There is no certainty of any detail except the certainty that is had by performing every part of the work as experience has taught that it should be performed if perfect results are to be attained. We have dwelt thus emphatically on the responsibility in concrete building work of the contractor for the reason that in the past it has been upon the contractor that the burden of failure has been generally shifted.

The construction work of buildings is divided into (1) construction, erection and removal of forms; (2) fabrication and placing of reinforcement; (3) mixing, transporting and placing concrete.

CONSTRUCTION, ERECTION AND REMOVAL OF FORMS.

The stereotyped text-book statement that forms must be true to dimensions and shape and rigid enough in construction to maintain this condition under all loads that they have to sustain mentions only one of the factors that the constructing engineer or the contractor has to keep in mind in designing such forms. His design must be made true and rigid at the least possible cost for first construction of lumber and carpenter work; it must be made with the plan in mind of using either the same forms as a whole or the same form material several times in one structure; it must be made with a view to convenience in taking down, carrying and re-erecting the forms the second or third time; and it must be made with the object in sight of securing the greatest salvage value either in forms fit for use again or in form lumber that can be sold or worked up for other purposes.

The general conditions governing the computation and design of economic form work are discussed in