USEFUL DATA 



When the depth of a restrained beam is greater at its ends than at midspan and the 

 slope of the bottom of the beam at its ends makes an angle of not more than 15 degrees 

 with the direction of the axis of the beam at midspan, the span length may be measured 

 from face to face of supports. 



The length of columns should be taken as the maximum unstayed length. 



(c) Stresses. — The following assumptions are recommended as a basis for calculations: 



1. — Calculations will be made with reference to working stresses and safe loads 

 rather than with reference to ultimate strength and ultimate loads. 



2. — A plane section before bending remains plane after bending. 



3. — The modulus of elasticity of concrete in compression is constant within the 

 usual limits of working stresses. The distribution of compressive stress in beams is, 

 therefore, rectilinear. 



4. — In calculating the moment of resistance of beams the tensile stresses in the 

 concrete are neglected. 



5. — The adhesion between the concrete and the reinforcement is perfect. Under 

 compressive stress the two materials are, therefore, stressed in proportion to their 

 moduli of elasticity. 



6. — The ratio of the modulus of elasticity of steel to the modulus of elasticity of 

 concrete is taken at 15, except as modified in section on "Working Stresses." 



7 — Initial stress in the reinforcement due to contraction or expansion of the concrete 

 is neglected. 



It is recognized that some of the assumptions given herein are not entirely borne out 

 by experimental data. They are given in the interest of simplicity and uniformity, 

 and variations from exact conditions are taken into account in the selection of formulas 

 and working stresses. 



The deflection of a beam depends upon the strength and stiffness developed 

 throughout its length. For calculating deflection a value of 8 for the ratio of the 

 moduli will give results corresponding approximately with the actual conditions. 



T-Beams. In beam and slab construction an effective bond should be provided at 

 the junction of the beam and slab. When the principal slab reinforcement is 

 parallel to the beam, transverse reinforcement should be used extending over the 

 beam and well into the slab. 



The slab may be considered an integral part of the beam, when adequate bond and 

 shearing resistance between slab and web of beam is provided, but its effective width 

 shall be determined by the following rules : 



(a) — It shall not exceed one-fourth of the span length of the beam; 



(6) — Its overhanging width on either side of the web shall not exceed six times the 

 thickness of the slab. 



In the design of continuous T-beams, due consideration should be given to the com- 

 pressive stress at the support. 



Beams in which the T-form is used only for the purpose of providing additional 

 compression area of concrete should preferably have a width of flange not more than 

 three times the width of the stem and a thickness of flange not less than one-third of 

 the depth of the beam. Both in this form and in the beam and slab form the web 

 stresses and the limitations in placing and spacing the longitudinal reinforcement will 

 probably be controlling factors in design. 



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