192 REINFORCED CONCRETE CONSTRUCTION 



When bands or spirals are used, Table 14 gives the sectional area of 

 hooping for a maximum pitch of one-fourth the diameter of the enclosed 

 concrete also for a pitch somewhat less than this but which varies for the 

 different column diameters. The amount of hooped reinforcement taken 

 is 1 per cent of the volume of the column. This conforms to the recom- 

 mendations of the Joint Committee. 



Let D = diameter of enclosed concrete. 



Ah= sectional area of one strand of hooping for given pitch. 

 P = pitch allowed. 



lh = length of hooping in 1 ft. in height of column. 

 Then, for banded reinforcement 



Also, 



^U = ~ 



37.7Z) 



h=-p- 



Results for banded and spiral reinforcement will not differ appreciably and 

 Table 14 may be used for both bands and spirals. 



PROBLEMS 



In a certain building, it was necessary to space the columns 12 ft. centers 

 and to have beams in one direction only. The specifications called for the 

 following items: 



For slabs, M = l/I2wl 2 ; beams, M = l/Wwl 2 . 



Loadings: 



Dead load, actual weight, concrete weighing 150 Ib. per cubic foot. 



Live load, 250 Ib. per square foot. 



Unit stresses as recommended by Joint Committee. 



66. (a) What thickness (total) of floor slabs required? 



(b) What will be the spacing of the steel reinforcement if 1/2 in. 

 round bars are used? 



67. Design the beams to support the floor, making b' = 10 in. and assuming 

 weight of beam below slab = 210 Ib. per linear foot. Make b'd just large 

 enough to resist shear due to load, considering the web properly 

 reinforced. Required: b, b', d, o, and the number of 5/8 in. round 

 rods required. 



68. What will be the stress in the concrete at the bottom of the beam at 

 the column if one-half of the rods from each side are bent up and the 

 horizontal rods are lapped at the support? Use eight 5/8-in. round 

 rods at center of span. 



69. A beam 12 in. X22 in. in cross-section has four 7/8-in. round rods 

 placed 2 in. above the lower face of the beam. If the allowable stresses 



t as recommended by the Joint Committee are employed 



(a) What uniform load in pounds per linear foot could be applied to 

 the span? Span = 16 ft. M = 1 /8 wl 2 . 



(b) What is the maximum stress developed in the steel? 



