• G Appa Rao

      Articles written in Sadhana

    • Influence of interface properties on fracture behaviour of concrete

      G Appa Rao B K Raghu Prasad

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      Hardened concrete is a three-phase composite consisting of cement paste, aggregate and interface between cement paste and aggregate. The interface in concrete plays a key role on the overall performance of concrete. The interface properties such as deformation, strength, fracture energy, stress intensity and its influence on stiffness and ductility of concrete have been investigated. The effect of composition of cement, surface characteristics of aggregate and type of loading have been studied. The load-deflection response is linear showing that the linear elastic fracture mechanics (LEFM) is applicable to characterize interface. The crack deformation increases with large rough aggregate surfaces. The strength of interface increases with the richness of concrete mix. The interface fracture energy increases as the roughness of the aggregate surface increases. The interface energy under mode II loading increases with the orientation of aggregate surface with the direction of loading. The chemical reaction between smooth aggregate surface and the cement paste seems to improve the interface energy. The ductility of concrete decreases as the surface area of the strong interface increases. The fracture toughness (stress intensity factor) of the interface seems to be very low, compared with hardened cement paste, mortar and concrete.

    • Evaluation of size dependent design shear strength of reinforced concrete beams without web reinforcement

      G Appa Rao S S Injaganeri

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      Analytical studies on the effect of depth of beam and several parameters on the shear strength of reinforced concrete beams are reported. A large data base available has been segregated and a nonlinear regression analysis (NLRA) has been performed for developing the refined design models for both, the cracking and the ultimate shear strengths of reinforced concrete (RC) beams without web reinforcement. The shear strength of RC beams is size dependent, which needs to be evaluated and incorporated in the appropriate size effect models. The proposed models are functions of compressive strength of concrete, percentage of flexural reinforcement and depth of beam. The structural brittleness of large size beams seems to be severe compared with highly ductile small size beams at a given quantity of flexural reinforcement. The proposed models have been validated with the existing popular models as well as with the design code provisions.

    • Evaluation of size effect on shear strength of reinforced concrete deep beams using refined strut-and-tie model

      G Appa Rao R Sundaresan

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      This paper reports on development of size-dependent shear strength expression for reinforced concrete deep beams using refined strut-and-tie model. The generic form of the size effect law has been retained considering the merits of Siao’s model and modified Bazant’s size effect law using the large experimental data base reported in the literature. The proposed equation for predicting the shear strength of deep beams incorporates the compressive strength of concrete, ratios of the longitudinal and the web reinforcement, shear span-to-depth ratio and the effective depth.

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