(1)Systems of reinforcing concrete for strength and ductility, (2) serviceability of concrete structures

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1) Systems of Reinforcing Concrete for Strength and DuctilityA steel reinforcing bar in concrete can resist a force equal to its full yield strength only when it is positively anchored to the concrete. Conventional stirrups and crossties rely on hooks or bends for anchorage. However, where there is demand for the yield strength of the bar adjacent to a hook or a bend, experiments typically exhibit crushing or splitting of the concrete at the interface, accompanied by anchorage slip. Systems of steel reinforcement are developed for use in concrete in lieu of conventional stirrups and crossties. The basic component of the new systems is a stud with an anchor head at each end, capable of developing the full yield strength of the stud without slip. This anchorage quality makes the studs more efficient than conventional stirrups in providing strength and particularly ductility (essential for earthquake-resistant structures). Examples of applications of studs are: punching shear reinforcement in slabs, crossties in columns, walls and bridge piers, longitudinal bars in deep (or short) beams and corbels, and anti-splitting reinforcement at bearings and ends of prestressing tendons.(2) Serviceability of Concrete StructuresThis project aims at development of robust techniques of computing stresses and strains due to temperature, creep and shrinkage of concrete and relaxation of prestressing reinforcement and, accordingly, design the minimum reinforcement and its detailing to ensure satisfactory service life and durability. The work involves considering material and geometric nonlinearities, caused by cracking of concrete, yielding of reinforcement, presence of axial forces and use of unbonded or external prestressing tendons. The analysis considers the deformation up to failure of concrete members subjected to increasing load introduced after occurrance of creep, shrinkage and relaxation.