. Engineering and Contracting. ltiplying the unit lateral and the longitudinal strain. This isknown ordinarily as Poissons ratio and formost materials of construction is about 1-3or Vi. Let us assume a concrete column re-inforced with hoops and with longitudinalrods. When it is stressed by loading a longi-tudinal shortening takes place which sets upstresses in both steel and concrete, the ratiobetween them being the ratio of theirrelative rigidities. If the hoops wereabsent, a lateral expansion would havetaken place, which, per unit of diameter materials locally, is very inadequately af-forded
. Engineering and Contracting. ltiplying the unit lateral and the longitudinal strain. This isknown ordinarily as Poissons ratio and formost materials of construction is about 1-3or Vi. Let us assume a concrete column re-inforced with hoops and with longitudinalrods. When it is stressed by loading a longi-tudinal shortening takes place which sets upstresses in both steel and concrete, the ratiobetween them being the ratio of theirrelative rigidities. If the hoops wereabsent, a lateral expansion would havetaken place, which, per unit of diameter materials locally, is very inadequately af-forded. In the hooped columns, the tests on whichare referred to below, a 1 :1 mixture of smallsize trap rock and cement was used. Thehoops were welded from steel flats and wereof tvyo thicknesses, and ins. Thequantity of metal relative to the core withinthe hoops varied from to Nolongitudinal metal was employed save threestrips of thin hoop iron which were employedas spacers for the hoops. In order to measure. ^?^ii ^ Si/a 1 ??1 5 5/ress mc /? / i i,-- .,,N;:|UntiT5ttl!l --»ii--m+lt7il!i !iH:liill|-iltrtttti O / ^ j ^ S 6 /> S :} /i> 1/ /2^yw-Con/a Sfress //? Sfee/-fftsi/sa/toj of/is /ler Fig. 5—Typical Behavior of Hooped Concrete Under High Compressive Stress. ? 7 g 3 /O // // /S Fig. 6—Curve Showing Ratio of Steel Stressto Axial Compressive Stress in a 1 : 1Hooped Column. deformation by the elastic modulus of thatmaterial. This method of graphical segrega-tion is always possible and it will be evidentthat the steel curve will be steepest where thequantity of metal is greatest. Table IIIshows in a few other representative cases,the magnitude of the stress in the longi-tudinal reinforcement accompanying a stressof 1,250 lbs. per sq. in. in the concrete. On account of the increased working stressin the concrete, the average stress in the steelis substantially greater. The attainment of mrfi TABLE nr- SIMULTANEOUS STRESSES IN CONCRETE AND STEE
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