COBRtTGATED fiAR COMPANY. INC. 



column, the core of which shall be straight and well centered. The strength of hooped 

 columns depends very much upon the ratio of length to diameter of hooped core, and 

 the strength due to hooping decreases rapidly as this ratio increases beyond five. 

 The working stresses recommended are for hooped columns with a length of not more 

 than ten diameters of the hooped core. 



The Committee has no recommendation to make for a formula for working stresses 

 for columns longer than ten diameters. 



Bending stresses due to eccentric loads, such as unequal spans of beams, and to lateral 

 forces, must be provided for by increasing the section until the maximum stress does 

 not exceed the values above specified. Where tension is possible in the longitudinal 

 bars of the columns, adequate connection between the ends of the bars must be pro- 

 vided to take this tension. 



Reinforcing for Shrinkage and Temperature Stresses. When areas of con- 

 crete too large to expand and contract freely as a whole are exposed to atmospheric 

 conditions, the changes of form due to shrinkage and to action of temperature are 

 such that cracks may occur in the mass unless precautions are taken to distribute the 

 stresses so as to prevent the cracks altogether or to render them very small. The dis- 

 tance apart of the cracks, and consequently their size, will be directly proportional to 

 the diameter of the reinforcement and to the tensile strength of the concrete, and 

 inversely proportional to the percentage of reinforcement and also to its bond resis- 

 tance per unit of surface area. To be most effective, therefore, reinforcement (in amount 

 generally not less than one-third of one per cent of the gross area) of a form which 

 will develop a high bond resistance should be placed near the exposed surface and be 

 well distributed. Where openings occur the area of cross-section of the reinforcement 

 should not be reduced. The allowable size and spacing of cracks depends on various 

 considerations, such as the necessity for water-tightness, the importance of appearance 

 of the surface, and the atmospheric changes. 



The tendency of concrete to shrink makes it necessary, except where expansion is 

 provided for, to thoroughly connect the component parts of the frame of articulated 

 structures, such as floor and wall members in buildings, by the use of suitable rein- 

 forcing material. The amount of reinforcement for such connection should bear some 

 relation to the size of the members connected, larger and heavier members requiring 

 stronger connections. The reinforcing bars should be extended beyond the critical 

 section far enough, or should be sufficiently anchored to develop their full tensile 

 strength. 



Flat Slab. The continuous flat slab reinforced in two or more directions and 

 built monolithically with the supporting columns (without beams or girders) is a 

 type of construction which is now extensively used and which has recognized advan- 

 tages for certain types of structures as, for example, warehouses in which large, open 

 floor space is desired. In its construction, there is excellent opportunity for inspecting 

 the position of the reinforcement. The conditions attending deposition and placing 

 of concrete are favorable to securing uniformity and soundness in the concrete. The 

 recommendations in the following paragraphs relate to flat slabs extending over 

 several rows of panels in each direction. Necessarily the treatment is more or less 

 empirical. 



The co-efficients and moments given relate to uniformly distributed loads. 



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