Department of Civil Engineering
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Item Investigation of fatigue crack growth after a single cycle peak overload in IS 1020 steel(Elsiever, 1992) Singh, Shamsher BahadurCrack propagation experiments were conducted on IS 1020 steel for various overload ratios (1·2, 1·3 and 1·4). On the basis of these experiments one power law is developed to predict the crack propagation delay period. The delay period after application of a single overload was found to increase as the magnitude of the overload increased. Crack growth also decreased after the application of an overload cycle but after a certain number of cycles it tended to return to the crack propagation rate for constant amplitude loading (CAL).Item A study of fatigue crack growth IS-1020 steel under constant-amplitude loading(Elsiever, 1992) Singh, Shamsher BahadurCrack propagation experiments were performed on IS-1020 steel for various load ranges and stress ratios. At constant maximum load, the life of the specimen increased as the load ratio increased. The crack growth data were analysed in terms of as a function of stress ratio R. The data covered R values of 0, 0·1, 0·2, and 0·3, and a good relation was obtained for . A crack growth rate equation was also developed.Item Experimental observations of fatigue crack growth in IS-1020 steel under constant amplitude loading(Elsiever, 1993) Singh, Shamsher BahadurCrack propagation experiments were performed on a 0·2% C 0·9% Mn (IS-1020) steel for various load ranges and stress ratios. At constant load range, the life of the specimen decreased as the load ratio increased. The crack growth data were analysed in terms of as a function of stress ratio R. The data covered R values for 0, 0·15, 0·30, 0·35 and 0·40 and a good relation was obtained for . A crack growth rate equation was also developed.Item Progressive failure of symmetrically laminated plates under uni-axial compression, Structural Engineering and Mechanics(Korea Institute of Science and Technology Information, 1997) Singh, Shamsher BahadurThe objective of this work is to predict the failure loads, associated maximum transverse displacements, locations and the modes of failure, including the onset of delamination, of thin, flat, square symmetric laminates under the action of uni-axial compression. Two progressive failure analyses, one using Hashin criterion and the other using Tensor polynomial criteria, are used in conjunction with the finite element method. First order shear deformation theory and geometric nonlinearity in the von Karman sense have been employed. Five different types of lay-up sequence are considered for laminates with all edges simply supported. In addition, two boundary conditions, one with all edges fixed and other with mixed boundary conditions for (+45/−45/0/90)2s quasi-isotropic laminate have also been considered to study the effect of boundary restraints on the failure loads and the corresponding modes of failure. A comparison of linear and nonlinear results is also made for (±45/0/90)2s quasi-isotropic laminate. It is observed that the maximum difference between the failure loads predicted by various criteria depend strongly on the laminate lay-ups and the flexural boundary restraints. Laminates with clamped edges are found to be more susceptible to failure due to the transverse shear and delamination, while those with the simply supported edges undergo total collapse at a load slightly higher than the fiber failure load.Item Progressive failure of symmetric laminates under in-plane shear: Il-Negative shear(Korea Institute of Science and Technology Information, 1998) Singh, Shamsher BahadurThe objective of the present work is to estimate the strength and failure characteristics of symmetric thin square laminates under negative shear load. Two progressive failure analyses, one using the Hashin criterion and the other using a Tensor polynomial criterion, are used in conjunction with the finite element method. First-order shear-deformation theory along with geometric nonlinearity in the von Karman sense has been incorporated in the finite element modeling. Failure loads, associated maximum transverse displacements, locations and modes of failure including the onset of delamination are discussed in detail; these are found to be quite different from those for the positive sheer load reported in Part I of this study (Singh et al. 1998).Item Progressive failure of symmetric laminates under in-plane shear, Part I-Positive Shear, Structural Engineering and Mechanics(Korea Institute of Science and Technology Information, 1998) Singh, Shamsher BahadurThe objective of this present work is to estimate the failure loads, associated maximum transverse displacements, locations and the modes of failure, including the onset of delamination, of thin, square symmetric laminates under the action in-plane positive (+ve) shear load. Two progressive failure analyses, one using the Hashin criterion and the other using a Tensor polynomial criterion, are used in conjunction with finite element method. First order shear deformation theory along with geometric non-linearity in the von Karman sense have been employed. Variation of failure loads and failure characteristics with five type of lay-ups and three types of boundary conditions has been investigated in detail. It is observed that the maximum difference between failure loads predieted by various criteria depends strongly on the laminate lay-up and the flexural boundary restraint. Laminates with clamped edges are found to be more susceptible to failure due to transverse shear (ensuing from the out of plane bending) and delamination, while those with simply supported edges undergo total collapse at a load slightly higher than the fiber failure load. The investigation on negative (-ve) in-plane shear load is in progress and will be communicated as part-II of the present work.Item Postbuckling response and strength of laminates under combined in-plane loads(Elsiever, 1999-04) Singh, Shamsher BahadurThe objective of this work is to study the postbuckling behaviour and progressive failure response of thin, symmetric laminates under uniaxial compression and uniaxial compression combined with in-plane shear loads (positive and negative). First-order shear deformation theory and geometric non-linearity in the von Karman sense are used with a finite-element procedure. The 3-D Tsai-Hill criterion is used to predict failure of a lamina and the maximum stress criterion is used to predict onset of delamination at the interface of two adjacent layers. The effect of plate aspect ratio and ply lay-ups on the load deflection response is presented. Load interaction diagrams for (±45/0/90)2s, (±45)4s and (0/90)4s laminates are obtained in terms of the buckling, the first-ply and the ultimate failure loads. In addition, progressive failure response of the (±45/0/90)2s laminate is also presented to show the buckling loads, failure loads, maximum transverse displacements associated with the failure loads and failure modes and locations at various load ratios.Item Design Approach for CFRP Prestressed Concrete Bridge Beams,(ACI, 2003) Singh, Shamsher BahadurThis paper presents a design approach for carbon fiber-reinforced polymer (CFRP) concrete bridge beams prestressed using bonded pretensioning and unbonded post-tensioning tendons arranged in multiple vertically distributed layers along with non-prestressing CFRP rods. Design equations to determine the flexural capacity and to compute the stresses and strains in concrete and tendons are provided. In addition, based on parabolic stress-strain relation for concrete and linear stress-strain relation for tendons, a computer program was developed to compute the overall response of the beam such as deflections, strains, cracking loads, and post-tensioning forces. The design equations and the accuracy of the nonlinear computer program were validated by comparing the analytical results with experimental results from a full-scale double-T (DT) test beam. The difference in the analytical and experimental values of the ultimate moment capacity of the DT-test beam is negligible, whereas the corresponding difference in the ultimate forces in unbonded externally draped post-tensioning strands is approxi- mately 4.1%. A detailed parametric study was conducted to examine the effect of the reinforcement ratio and the level of pre- stressing forces on the deflections and ultimate load-carrying capacity of the full-scale DT-beam. It is observed that the reinforce- ment ratio and the level of prestressing have significant effect on the moment-carrying capacity and ultimate load deflection of the beam. The combination of bonded and unbonded prestressing levels (0.3 to 0.6) can significantly increase the ultimate moment capacity of an over-reinforced beam.Item Flexural Response of CFRP Prestressed Highway Bridge Box-Beams(Precast/Prestressed Concrete Institute, 2004-02) Singh, Shamsher BahadurThis paper presents an experimental and analytical investigation of the flexural response of box beams reinforced and prestressed using carbon fiber reinforced polymer (CFRP) tendons. Two one-third scale box beams were prestressed using seven bonded pretensioning tendons and six unbonded post-tensioning tendons. A third beam was prestressed with seven bonded pretensioning tendons and six non-prestressed unbonded posttensioning tendons. Beams were reinforced with carbon fiber composite cable stirrups and tested to failure. A computer program was developed to predict deflection, strain, and post-tensioning forces at various loads. A parametric analysis examined the effects of the level of pretensioning and post-tensioning forces on the overall flexural response. Results showed that the beam prestressed using both pretensioning and unbonded post-tensioning tendons had a 26 percent higher ultimate load capacity and 36 percent lower energy ratio than the beam with non-prestressed unbonded post-tensioning tendons. Levels of initial pretensioning and posttensioning forces significantly affect the flexural response and beam failure mode.Item Concrete Beams Reinforced with CFRP: Investigating the Shear Performance of Box-Beams Strengthened with Carbon Fiber-Reinforced Polymers(ACI, 2005-01) Singh, Shamsher Bahadur