سال:1388 | دوره: | شماره: |تعداد مقالات:7

This study investigates a time-domain method for modeling general transient elastodynamic problems using the spectral-based finite element method (SEM) which is based upon a conforming mesh of two-dimensional quadrilaterals. Employing the Galerkin weighted residual method, detailed formulation of the SEM is derived in which various aspects involving in elastodynamic problems are discussed. The accuracy and efficiency of the method is fully demonstrated by comparing results obtained from the SEM with those reported in other studies. For this purpose, a set of wave propagation and structural dynamic problems, subjected to various load forms such as triangular load, Heaviside step load, sinusoidal impulsive load, and ramped load are modeled using the SEM. Furthermore, support motion boundary conditions are examined using the SEM. Each problem is successfully modeled using a very small number of degrees of freedom in comparison with other numerical methods. The numerical results agree very well with the analytical solutions as well the results from other numerical methods.

In this paper, an energy formulation of the force method is developed and the analysis, design and optimization are performed simultaneously using ant colony algorithms. New goal functions are introduced for minimization, and ant colony algorithms are employed for continuous optimization. An efficient method is introduced using ant colony algorithms for designing structures with prescribed member stress ratios. Finally, minimum weight design of truss and frame structures is formulated using ant colony algorithms and applied to some benchmark problems from literature.

Wavelet analysis is a new mathematical technique and in the recent years enormous interest in application of engineering has been observed. This new technique is particularly suitable for non-stationary processes as in contrast to the Fourier transform (FT). The wavelet transform (WT) allows exceptional localization, both in time and frequency domains. The application of the WT to earthquake engineering is rare. In this paper the WT capability to give a full time–frequency representation of the earthquake record is demonstrated. In this method, the time series of the earthquake record, breaking at the tropical coral reefs and mechanically generated waves in the wave flume demonstrates the ability of the wavelet transform technique to detect a complex variability of these signals in the time–frequency domain. Various spectral representations resulting from the wavelet transform are discussed and their application for earthquake record is shown.

This paper attempts to calculate column shortening and differential shortening between columns and walls in concrete frames using a nonlinear staged construction analysis based on the Dirichlet series and direct integration methods. Prototype frame structures are idealized as two-dimensional and the finite element method (FEM) is used to calculate the creep and shrinkage strains. It is verified with respect to published experimental and analytical results. B3 model and methods such as AAEM, EMM, IDM, and RCM are used for verification purposes.For each frame, effects of creep and shrinkage parameters such as relative humidity percent, rate of construction, shrinkage parameter, and concrete strength have been taken into consideration separately. The manner in which creep and shrinkage can influence the behavior of concrete structures also has been discussed.

In this two-part paper, the response of restrained SIFCON two-way slabs is investigated. In part-1, different restrained SIFCON two-way slab specimens were loaded in flexure using the Whiffle-Tree loading arrangement and first crack loads, ultimate loads and load deflection responses were obtained. In part-2 results from punching shear tests performed on SIFCON two-way slabs are reported. Black steel wire fibres were used in the production of SIFCON slab specimens and the influence of fibre volume percentage on flexural and punching shear behavior is investigated.In this paper, the influence of volume percentage of steel fibres on strength and stiffness characteristics of slurry infiltrated fibrous concrete (SIFCON) slabs is investigated by testing nine numbers of SIFCON slabs under flexural loading. In order to compare the results, three numbers of fibre reinforced concrete (FRC) slabs and three numbers of plain cement concrete (PCC) slabs are taken as control specimens. The test results indicate that the SIFCON slabs exhibit high strength, high energy absorption and more ductility characteristics compared to the control specimens. SIFCON slabs with higher fibre volume fraction (12%fibre volume) exhibit superior performance among other slab specimens.Analysing the crack patterns noticed in the experimentation, yield line analysis has been performed and the bending moment coefficients for SIFCON slabs are calculated.

A finite element model based on the layer wise theory of Reddy is developed for the analysis of delamination in the [90.0] S cross-ply laminated beams. The Heaviside step function was adopted in the formulation to express the discontinuous interlaminar displacement fields of delaminated layers. Also, to accommodate the moderately large rotations of the beam, the von Karman type nonlinear strain field is used in the formulation. The finite element model is verified by comparing the present solutions with those available in the literature. It is shown that the present finite element model is able to capture accurate local stress fields and the strain energy release rates. Then the model is used to study delaminated cross-ply laminates under bending loads. The influence of boundary conditions and number of layers on the strain energy release rates is studied. Also, the growth of delamination is investigated for a pure bending case, and the mode of delamination growth is identified. The influence of geometric nonlinearity on the delamination growth is also investigated as the delamination advances. It is found that geometric nonlinearity does not significantly alter the delamination kinematics and strain energy release rates.

In part 1 of this paper, flexural tests conducted on restrained SIFCON two way slabs were described and the load-deflection responses under flexural loading were reported. Three different types of slabs i.e. SIFCON slabs, FRC slabs and PCC slabs were investigated. It was found that flexural performance of SIFCON slabs is quite superior when compared to FRC and PCC slabs. Among SIFCON slabs those containing twelve percent fibres by volume exhibited excellent load carrying capacities, ductility and energy absorption capacities.In part 2 of the paper, the effect of various volume percentage of steel fibre in SIFCON slab specimens subjected to punching shear was studied. The punching shear load was applied to simulate a column-footing connection. From experimentation, the failure loads, deflection and crack patterns in punching shear were studied. Fibre reinforced concrete (FRC) and plain cement concrete (PCC) slab specimens were used as control specimens.The results reported that SIFCON slabs with 12% fibre volume possess high performance than the other slab specimens in all respects. The experimental results are compared with the ACI and IS codes and the need for separate provisions for SIFCON in punching shear is emphasized. A regression model has been developed to predict the punching shear capacity of SIFCON slabs.