File:Handbook for architects and builders (1898) (14779493965).jpg

Identifier: handbookforarchi14illi (find matches)
Title: Handbook for architects and builders
Year: 1898 (1890s)
Authors: Illinois Society of Architects
Subjects: Architecture Building Architects
Publisher: Chicago
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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witli square ends:50,000 1 +■ (12L)- 36000 r^ In tliese formulas 1 = length of column ininches. r = least radius of gyration ininclies. To use the diagram look up in the liandbooks the size of column of the requiredlength to carry the load. The value of r isgiven in a column in the tables. Using thelengtli in inches find the value of 1/r andthen find on the diagram the line represent-ing the formula by which the table was com-puted. Starting from the 1/r on this linedrop vertically to the line of the Chicagoformula and then go horizontally to the leftand ascertain the fiber stress permitted un-der tlie Chicago ordinance. Divide the loadby this fiber stress and thus obtain the crosssectional area of the column. Find a columnin the tables having the desired area andfollow the load line to the left until the re-quired length is obtained. The load foundwill usually be considerably greater than theload to be carried, for the fiber stress underthe Cliicago requirements will be less tlian
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<5 Mo with lihci- stresses in tlie tables for columns(i\i r 7(» radii. For c:olumns under 50 radiithe Chicago ordinance undoubtedly permitstoo high values. Beinforced Concrete. In Section 547, Chicago Building Ordinance,the factors to use in reinforced concrete arefound. Let M = bending moment = resisting mo-ment. If this is in incli poundsthen b is in inclies. If tliemoment is in foot pounds thenb Is in feet.b = breadth in inches = 12 for slabs.d =: depth from top of concrete to cen-ter of steel,k = depth to neutral axis (percentageof d). j = moment arm 1 — R = a moment factor. Ap = steel ratio = —bdA ~ area of steel in sq. ins.n = ratio of deformation. Kbd-; b M / M -; d = V It is R d- R b economy to use a deformed steel having a high elastic limit. Witli such steela fiber stress of ISOOO lbs. per sq. in. maybe used and the following table gives fac-tors to use in reinforced concrete designwith an 18000 lb. steel fiber stress. Con- Steel crete Mix stress stress t f R P 1 k n

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