SHEAR BEHAVIOUR OF HIGH - STRENGTH CONCRETES

Abstract

Shear strength of concrete is an important consideration in the design of RC floor. In situations where use of steel stirrups become impractical or difficult to provide (thin slab, flat plate, flat slab etc.) , the intrinsic - shear strength of concrete becomes all te- important. For concretes of low shear strength, quite often the concrete section size needs to be increased only to provide for the high shear requirement. It is, therefore, pertinent to study the shear strength of concrete, particularly in the high strength range, 40 MPa and above. In the present workt, attempts have been made to experimentally investigate the role of cement content, water-cement ratio and presence of tension steel bars on the shear resisting capacity of concrete. These shear strength contributing parameters are to be studied for their dominating or otherwise effects. Cement content in a concrete mix is an important parameter since sufficient cement particles should be available to cover the total surface area of coarse and fine aggregates. Both, less than the required amount as well as the availability of excess amount of cement would be disadvantageous. Cement percentage of 17,18,20 and 22 of the weight of hardened concrete have been adopted to cover the entire range of cement content, from deficient to excess. Water-cement ratios adopted are in the low range, 0.35, 0.32 and 0.30, so as to obtain concretes of high compressive strength. Superplasticizer has been used- to impart adequate workability to fresh concrete. For shear strength determination, the concrete has been tested in the form of 100 x 150 mm beams of 1.2 m length. 4-point loading system has been adopted so as to obtain a small part of the span under constant shear (shear span). Since concrete is weak in tension, small amount of tension steel needs to be provided to ensure failure in shear instead of flexural tension. Two used numbers of 10, 12 or 16 mm diameter deformed steel bars haveb for this purpose. Based on the above test results, appropriate processing of the data has been done to arrive at suitable conclusions. Key words : High Strength Concrete, Shear Strength, Concrete Mix Proportion, Dowel Action. (vi