Influence of Charge Shape and Orientation on the Response of Steel-Concrete Composite Panels

Blast design codes usually generalize the shape of the charge as spherical or hemispherical. However, it was found that the blast overpressure of cylindrical charges differ greatly when compared with relevant analytical results generated with the charges assumed to be spherical. The objective is to use fully coupled 3D multi-material arbitrary Lagrangian Eulerian (MMALE) modelling technique in LS Dyna software to simulate the cylindrical charge blast loading. Comparison of spherical and cylindrical charge blast simulation was carried out to show the influence on peak overpressure and total impulse. Two steel-concrete composite specimens were subjected to blast testing under cylinder charges for benchmarking against numerical results. It was found that top detonated, vertical cylinder charge could give much higher blast loading compared to horizontal cylinder charge. The MMALE simulation could generate the pressure loading of various charge shape and orientation to be used for predicting the response of the composite panel

Dynamic behavior of reinforced concrete beams under varying rates of concentrated and impact loadings

Reinforced Concrete (RC) structures may experience various types of loading during their lifespan, which in turn induces a wide spectrum of strain rates. The materials involved in RC structures are strain-rate sensitive and thus, the behavior of structural members can be affected by the loading rates but only significantly when the rate differs by more than one order of magnitude. Majority of past research on RC beams have focused on assessing their behavior under static and relatively slow loading rates while limited attention has been paid to the high loading rates. Therefore, to shed some light in this field, an experimental program comprising twenty-four RC beams was carried out under four different loading rates ranging from slow (4 10-4 m/s) to fast (2 m/s) to cover the wide range of loading scenarios (quasi-static, earthquakes and low velocity impact regime). Comparative analyses of beams under these varying loading rates highlighted several important aspects of their dynamic behavior. Furthermore, the influence of various key parameters on dynamic increase factor (DIF) of maximum resistance and failure modes of beams under these loading conditions was summarized and discussed through numerical simulation parametric studies after successful validation of numerical models in an explicit finite element (FE) program. Although the loading rate effects covering low velocity impact regime were considered, however, it would be more practical to consider realistic impacts. Thus, a drop-weight impact test program was undertaken on thirty RC beams to evaluate their impact responses. The acquired data was then used in the development and verification of numerical and analytical methods. Two empirical equations have been proposed by analyzing a dataset which would aid in determining the required static bending and shear resistance for input impact energy by specifying the maximum midspan deflection for each limit state of beam. Moreover, to extent the knowledge beyond the range of parameters investigated experimentally, FE models of the beams were also developed. Maximum midspan deflection could be an important performance index to evaluate the damage levels of beam when subjected to impact loadings; hence simplified analytical models were employed to predict the same in less modeling effort and computational time. Residual performance assessment of damaged structures has been gaining enormous importance in engineering community to ensure that the damaged structures will not fail catastrophically and uphold structural integrity. However, to date no study has been documented in literature on residual performance of impact-damaged RC beams. Thus, the impact-damaged beams have been retested quasi-statically to determine their post-impact residual responses. Finally, the FE models developed earlier for drop-weight impact loading were modified by replacing the impactor with the loading plate to perform quasi-static simulation by utilizing resulting deformation and damages of beams from the impact stages. Thereafter, these models were used further to quantify the effect of various parameters on residual resistance index (RRI), which could be used effectively to delineate the extents of damage of beams after impact.Doctor of Philosophy (CEE

Strength and behavior in shear of reinforced concrete deep beams under dynamic loading conditions

Research on reinforced concrete (RC) deep beams has seen considerable headway over the past three decades; however, information on the dynamic shear strength and behavior of RC deep beams under varying rates of loads remains limited. This paper describes the experimental results of 24 RC deep beams with and without shear reinforcements under varying rates of concentrated loading. Results obtained serve as useful data on shear resistance, failure patterns and strain rates corresponding to varying loading rates. An analytical truss model approach proves its efficacy in predicting the dynamic shear resistance under varying loading rates. Furthermore, three-dimensional nonlinear finite element (FE) model is described and the simulation results are verified with the experimental results. A parametric study is then conducted to investigate the influence of longitudinal reinforcement ratio, transverse reinforcement ratio and shear span to effective depth ratio on shear behavior. Subsequently, two empirical equations were proposed by integrating the various parameters to assess the dynamic increase factor (DIF) of maximum resistance under varying rates of concentrated loading.Accepted versio

Predicting the punching shear failure of concrete slabs under low velocity impact loading

A simplified analytical approach to predict the punching shear failure of a concrete slab under low velocity (<10 m/s) impact loading has been proposed. The proposed analytical approach has further been validated against a backdrop of experimental results available in the public domain. The efficacy of the proposed approach has further been tested against the results obtained by conducting numerical simulations designed by the authors. The results obtained from this simplified approach have on the whole shown good agreement with the experimental results. Furthermore, on the basis of extensive literature review, a state-of-the-art investigation to examine the structural response of concrete slabs under low velocity impact loading has also been presented in this paper. The paper aims to explore and present a quantum of the undertaken research under the sections dealing with the experimental studies, numerical simulations and the analytical modeling. Thus, in addition to the proposition of a simplified approach for predicting the punching shear failure of a concrete slab under low velocity impact loading condition, the paper also sets forth to establish the current knowledge base in this field and identify the key areas with a need for further research with regard to this domain.This research is supported by the Faculty Research Scheme of Indian Institute of Technology (Indian School of Mines)

Residual resistance of impact-damaged reinforced concrete beams

The behaviour of reinforced concrete (RC) beams under single or repetitive drop-weight impact loading has come under increasing attention within the engineering community in the past decades. However, until now, little effort has been sought towards examining the residual resistance of RC beams after impact damage. To contribute towards a better understanding in this area, both experimental and numerical investigations were carried out. The beams were first tested under drop-weight impact loading. Subsequently, quasi-static bending tests were conducted on the same specimens to obtain the residual behaviour. Thereafter, one beam from each series without any prior damage was tested under monotonic static loading to compare its behaviour with impact-damaged specimens. Furthermore, to investigate the structural response in detail, a numerical procedure was developed in an explicit finite-element program. Upon successful validation of the numerical results with the experimental outcomes, numerical case studies were carried out to quantify the variation of residual resistance index in terms of various parameters.Published versio

Dynamic behavior of reinforced concrete beams under varying rates of concentrated loading

The behavior under varying rates of concentrated loading of reinforced concrete (RC) beams was studied, aimed at attaining a better understanding of the effects of loading rates on RC beams. The test program was successful in providing a substantial volume of test data including load vs. mid-span displacement, crack profiles, strain at the mid-point of longitudinal tensile reinforcements and acceleration at several locations along the specimens. Peak load, stiffness, absorption energy and strain rate were found to increase with the enhancement of loading rates. LS-DYNA, an explicit finite element program widely used for three-dimensional nonlinear transient analysis of structures, was employed in this study to provide numerical simulations of RC beams under varying loading rates. Three-dimensional finite element (FE) models of RC beams have been described and verified with the experimental results, followed by a parametric study to investigate the influence of the longitudinal reinforcement ratio, the transverse reinforcement ratio and the shear span to effective depth ratio. Empirical equations are proposed in terms of various parameters to predict the Dynamic Increase Factor (DIF) of maximum resistance of RC beams under varying loading rates.Accepted versio

State-of-the-art review on low-velocity impact response of reinforced concrete beams

Based on a comprehensive literature review, a state-of-the-art report on the strain rate dependent mechanical properties of materials involved in reinforced concrete (RC) structures and the structural response of RC beams under low-velocity impact is presented. Due to the prevalence of plentiful equations to calculate the dynamic increase factor of concrete strength in compression and tension, future research is needed to reach a general consensus. Two empirical equations were derived based on previous test data, and the applicability of the proposed equations is demonstrated. With the interpretation of previous data in the light of authors' test results, the issue related to a change in failure mode from flexural failure under static loading to shear failure under impact loading is discussed. Finally, several issues related to the impact response of beams are raised, and the need for future research is identified.Published versio

Effects of high loading rate on reinforced concrete beams

The majority of past research on reinforced concrete (RC) beams has focused on their behavior under static and relatively slow loading rates, while limited attention has been paid to the corresponding behavior under high loading rates. Thus, a comprehensive literature review has been conducted on RC beams under varying loading rates to observe the overall trend of dynamic increase factor (DIF) of maximum resistance and failure modes. The wide range of data pertaining to DIF and the apparent changes in failure modes means, however, that general agreement has yet to be reached among researchers. To supplement the limited literature in this field, 24 RC beams were tested under four different loading rates ranging from slow (4 × 10–4 m/s) to fast (2 m/s) to cover the wide range of loading scenarios (quasi-static, earthquakes, and impact regime). Comparative analyses of RC beams under these varying loading rates highlighted several key aspects of their dynamic behavior.Published versio

Influence of Charge Shape and Orientation on the Response of Steel-Concrete Composite Panels

Blast design codes usually generalize the shape of the charge as spherical or hemispherical. However, it was found that the blast overpressure of cylindrical charges differ greatly when compared with relevant analytical results generated with the charges assumed to be spherical. The objective is to use fully coupled 3D multi-material arbitrary Lagrangian Eulerian (MMALE) modelling technique in LS Dyna software to simulate the cylindrical charge blast loading. Comparison of spherical and cylindrical charge blast simulation was carried out to show the influence on peak overpressure and total impulse. Two steel-concrete composite specimens were subjected to blast testing under cylinder charges for benchmarking against numerical results. It was found that top detonated, vertical cylinder charge could give much higher blast loading compared to horizontal cylinder charge. The MMALE simulation could generate the pressure loading of various charge shape and orientation to be used for predicting the response of the composite panel