67 



To determine for negative moment find your moment 

 at the support and see whether you have enough steel at 

 the top to take it. 



To determine vertical shear, take the cross section of 

 the beam from top of slab to center of steel. Deduct this 

 from the total shear and the remainder of the shear will 

 determine how many straight bars at 10,000 Ib. per sq. In. 

 you must have at the bottom of the beam at supports. 



To determine the horizontal shear, figure what your 

 concrete takes per effective depth; then place U's in each 

 effective depth to take the remaining shear. 



In the following examples from the booklet Issued by 

 the Ransome Machinery Co., (which have been checked) 

 are given formulae used in the Ransome System. 



"If the Ransome system is used, the following formulas 

 will facilitate the calculations necessary to properly de- 

 sign concrete steel structures. In the examples the safe 

 strength of the steel is taken from the following table 

 which gives a factor of safety of four. For important 

 work it is advisable to consult a competent concrete 

 engineer. 



WALL AND PIER FOOTINGS. 



Plates I and II illustrate the general form and arrange- 

 ment of tension bars in our standard wall and pier foot- 

 ings. 



FORMULA FOR WALL FOOTINGS. 



We have Riven in all cases the width of the wall TT, the 

 load per linear foot L, and the width of the footing Wl. 

 The total stress in the tension bars or the total compres- 

 sion in the concrete per linear foot is 



. 2XLXP 

 Stress- 



in which L equals the total load in tons, P equals the 

 projection in inches and D equals the distance In Inches 

 from the top of the footing to the center of the bars. We 

 have two unknown quantities, Stress and D. It Is there- 

 fore necessary to impose another condition, and it Is that 

 when the safe compresslve strength of the concrete equals 

 36 tons per sq. ft. there shall be 16 sq. In. of concrete in 

 the area above, the bars for each ton stress or 16 x stress 

 li 1 x D from which stress % D. This condition is 

 necessary in order that the concrete shall not be strained 



