Engineering Wonders of the World
Volume I

 426 ENGINEERING WONDERS OF THE WORLD. Fig. 18.—DIAGRAM REPRESENTING A SUDDEN AND COMPLETE FRAC- TURE OF A PLAIN CONCRETE BEAM, WHICH WOULD OCCUR AT STRESSES RANGING FROM 200 TO 300 LBS. PER SQUARE INCH. Disposition of Steel Bars in Columns. and at the same time to resist the outward bulging of the con- crete. The brac- ing can be ap- plied in the form of links, as rep- resented in Fig. 23, which shows that the vertical bars cannot bend very much so long as the links remain intact. As a matter of fact the bars can only bend between the links instead J?ig. 19.—REINFORCED CONCRETE BEAM INTACT UNDER CONDITIONS CAUSING STRESS IN THE STEEL EQUIVALENT TO THE TENSION OF 2,000 LBS. PER SQUARE INCH IN THE CONCRETE. of bending as a whole (see Fig. 24), and under ordinary working conditions the curvature is in- that the effects of the pressure are to shorten the column and to cause it to bulge laterally. In the other diagram we have a thin column upon which the force Px acts at the top and the force P2 acts against one side, the result being that the column assumes a curved form, and is subject to stresses distributed like those in a beam. The curvature is exaggerated in Fig. 21. In actual practice the column would be very little bent, and so it would be called upon to resist direct compression as in Fig. 20, as well as the stresses occasioned by bending. We have next to see how these fundamental principles affect the design of reinforced con- crete columns. Let us first take the case of a very short column like that in Fig. 20, but with the addition of four vertical reinforcing steel bars, disposed as shown by the cross section in Fig. 22. Then the compression and bulging of the concrete are accompanied by bending of the steel bars, partly because the bars are so long in proportion to their thick- ness, and partly because the outward thrust of the concrete is a very powerful force. To use steel in this way would evidently be in- effective and uneconomical. We will now show how the same four bars can be rendered more effective by the addition of bracing intended to keep the bars straight, finitesimal. Consequently, the vertical bars are of great assistance to the concrete, pre- venting the excessive shortening of the columns, and reducing the tendency of the concrete to bulge laterally, of further value in resisting The links are the small amount of bulging that ac- tually takes place, and the resistance so afforded in turn helps the concrete and the vertical bars to stand up against the pressure acting on them at the top of the column. The upshot of this con- certed action is to make the column ex- ceedingly strong, and to bring into play that union of forces which underlies genuine reinforced concrete construction. Reinforced concrete piles are very much like columns of the same ma- terial, except at the head and _ Reinforced , , . , , Concrete Piles, toe. The head is more strongly reinforced transversely than the body of the pile, because it has to withstand the force