CORRUGATED BAR COMPANY, 



than the distance center to center of columns in that direction. Continuous bars 

 should not all be bent up at the same point of their length, but the zone in which this 

 bending occurs should extend on each side of the assumed point of inflection, and 

 should cover a width of at least one-fifteenth of the panel length. Mere draping of the 

 bars should not be permitted. In four- way reinforcement the position of the bars in 

 both diagonal and rectangular directions may be considered in determining whether 

 the width of zone of bending is sufficient. 



(m) Reinforcement at Construction Joints. — It is recommended that at construction 

 joints extra reinforcing bars equal in section to 20 per cent of the amount necessary 

 to meet the requirements for moments at the section where the joint is made be added 

 to the reinforcement, these bars to extend not less than 50 diameters beyond the joint 

 on each side. 



(n) Tensile and Compressive Stresses. — The usual method of calculating the tensile 

 and compressive stresses in the concrete and in the reinforcement, based on the assump- 

 tions for internal stresses given in this chapter, should be followed. In the case of the 

 dropped panel the section of the slab and dropped panel may be considered to act 

 integrally for a width equal to the width of the column-head section. 



(o) Provision for Diagonal Tension and Shear. — In calculations for the shearing 



stress which is to be used as the means of measuring the resistance to diagonal tension 



stress, it is recommended that the total vertical shear on two column-head sections 



constituting a width equal to one-half the lateral dimensions of the panel, for use in 



the formula for determining critical shearing stresses, be considered to be one-fourth 



of the total dead and live load on a panel for a slab of uniform thickness, and to be 



three-tenths of the sum of the dead and live loads on a panel for a slab with dropped 



25 IF 

 panels. The formula for shearing unit stress may then be written v= '., for slabs 



of uniform thickness, and v= —rn — for slabs with dropped panels, where W is the 



sum of the dead and live load on a panel, b is half the lateral dimension of the panel 

 measured from center to center of columns, and jd is the lever arm of the resisting 

 couple at the section. 



The calculation of what is commonly called punching shear may be made on the 

 assumption of a uniform distribution over the section of the slab around the peri- 

 phery of the column capital and also of a uniform distribution over the section of the 

 slab around the periphery of the dropped panel, using in each case an amount of 

 vertical shear greater by 25 per cent than the total vertical shear on the section under 

 consideration. 



The values of working stresses should be those recommended for diagonal tension 

 and shear in the section on "Working Stresses." 



(p) Walls and Openings. — Girders or beams should be constructed to carry walls 

 and other concentrated loads which are in excess of the working capacity of the slab. 

 Beams should also be provided in case openings in the floor reduce the working strength 

 of the slab below the required carrying capacity. 



{q) Unusual Panels. — The co-eflBcients, apportionments, and thicknesses recom- 

 mended are for slabs which have several rows of panels in each direction, and in which 

 the size of the panels is approximately the same. For structures having a width of one, 



203 



