Asian journal of civil engineering
Volume:10 Issue: 3, Jun 2009

Tension stiffening, is attributed to the fact that concrete does not crack suddenly andcompletely but undergoes progressive microcracking(strain softening). Immediately afterfirst cracking, the intact concrete between adjucent primary cracks carries considerabletensile force due to the bond between the steel and the concrete. The bending stiffness of the member is considerably greater than that based on a fully cracked section, where concrete in tension is assumed to carry zero stress. This tension stiffening effect may be significant in the service load performance of beams and slabs. This phenomenon is also effective in longterm behaviour of concrete members due to the creep and shrinkage of the concrete.Various methods have been proposed to account for tension stiffening in the analysis ofconcrete structures. An approach for modelling tension stiffening is to assume that an area of concrete located at the tensile steel level is effective in providing stiffening. In this paper a simple formulation is proposed for study of short-term and long-term behaviour of reinforced concrete beams and one-way slabs considering tension stiffening effect. The proposed formula is validated with experimental results and some numerical examples are worked out

Laterally loaded reinforced concrete beams may fail in shear before their full flexural strengths are attained if they are not adequately designed for shear. Unlike flexural failures, shear failures are very sudden and unexpected. A thorough knowledge of the different modes of shear failure and the mechanisms involved is necessary to prevent them. Shear strength of concrete is an important consideration in the design of RC members. In situations, where use of steel stirrups becomes impractical or difficult to provide such as RC slab, the intrinsic shear strength of the concrete becomes all important. For concrete of low shear strength, quite often the concrete cross-section size needs to be enhanced only to provide for the high shear demand. It is, therefore, pertinent to study the shear strength of concrete. The present describe the experimental investigation on shear strength of concrete beams reinforced with longitudinal tension steel. The primary design variables were the shear span-to-depth ratio in terms of depth of beam and amount of longitudinal reinforcement. The study aims to investigate the effect of increasing percentage of longitudinal reinforcement and depth of beams in terms of shear span-to-depth ratio on shear strength of concrete. Test results show that, the depth of beam in terms of shear span-to-depth ratio is highly influencing parameter of shear strength of concrete in addition to the amount of longitudinal reinforcement and concrete compressive strength. This aspect is not reflected in the Indian Standard [4]

In this paper an efficient method is developed for the formation of null bases of finiteelement models comprised of four-node quadrilateral plane stress and plane strain elements corresponding to highly sparse and banded flexibility matrices. This is achieved byassociating special graphs to the finite element models and using an element with newequilibrium tractions and stress field for the formation of localized self-equilibrating stresssystems. The efficiency of the present method is illustrated through some examples.

In this paper an efficient method is developed for the formation of null bases of finiteelement models comprised of four-node quadrilateral plane stress and plane strain elements corresponding to highly sparse and banded flexibility matrices. This is achieved byassociating special graphs to the finite element models and using an element with newequilibrium tractions and stress field for the formation of localized self-equilibrating stresssystems. The efficiency of the present method is illustrated through some examples.

This paper proposes a refined version of particle swarm optimization technique for the optimum design of steel structures. Swarm is composed of a number of particles and each particle in the swarm represents a candidate solution of the optimum design problem. Design constraints in accordance with ASD-AISC (Allowable Stress Design Code of American Institute of Steel Institution) are imposed by the particle swarm optimization based optimum design algorithm developed. A constraint handling method called the ‘penalty function method’ is introduced to maintain acceptable solutions. The refined version of the particle swarm optimization algorithm proposed in this paper is easy to implement and the results and convergence performance are better than the simple particle swarm optimization algorithm and some other meta-heuristic optimization techniques. The effect of different inertia weight parameters in finding the optimum design is also tested in two numerical examples.

Now a days high strength and high performance concrete are being widely used all over the world. Most applications of high strength concrete have been in high rise buildings, long span bridges and in some special applications in structures. In developed countries, using high strength concrete in structures today would result in both technical and economical advantage. In high strength concrete, it is necessary to reduce the water/cement ratio and which in general increases the cement content. To overcome low workability problem, different kinds of pozzolanic mineral admixtures (fly ash, rice husk ash, metakaoline, etc. and chemical admixtures are used to achieve the required workability.In the present experimental investigation, the mechanical properties of high-strengthconcrete of grades M40 and M50, at 28 days characteristic strength with different replacement levels of cement with silica fume or micro silica of grade 920-D are considered. Standard cubes (150mm x 150mm x 150mm), standard cylinders (150mm dia x 300mm height) and standard prisms (100mm x 100mm x500mm) were considered in the investigation. In all, 144 specimens were cast with and with out silica fume. The mechanical properties viz., compressive strength, flexural strength and splitting tensile strength, and stress-strain characteristics of high strength concrete with various replacement of silica fume viz., 3%, 6%, 9%, 12% and 15%, has beenconsidered. The investigations revealed that the use of waste material like silica fume improved the mechanical properties of high strength concrete witch is other wise hazardous to the environment and thus may be used as a partial replacement of cement.