REENFORCED CONCRETE 



167 



Therefore the distance between ties should be 



1750. 



= 18 in. 



V6750 



98. Radially reenforced flat slabs. A system of floor construction 

 without the use of beams or ribs, called the " mushroom system," 

 has been devised by Mr. C. A. P. Turner (Fig. 111). The essen- 

 tial features of this system are that the floor slab is of uniform 

 thickness throughout, the reenforcement is radial, and the col- 

 umn top is enlarged and reenforced with hoops. This type of con- 

 struction is best adapted to large areas with few large openings. 

 The following is a simple analysis 

 of the chief features of the design. f* D--- 



T 



FIG. Ill 



99. Diameter of top. In the case of a continuous floor slab sup- 

 ported by several columns, it is obvious that the slab will be con- 

 cave downwards over the columns and concave upward in the center 

 of each panel. Between these two extremes there must be a bound- 

 ary at which there is no curvature, that is, a line of inflection. In 

 a restrained beam of length I, bearing a uniform load, the two 

 points of inflection occur at a distance of 0.212 I from each support 

 (article 45). For a continuous slab, therefore, the line of inflection 

 for square panels may be assumed to be approximately a circle of 

 radius between \ I and \ Z, where I denotes the span, or distance 



