Amlan Kumar Sengupta

This paper illustrates the effect of chloride-induced corrosion in the flexural capacity of a pretensioned concrete girder in an existing girder-and-slab deck bridge. The numerical study of the time-wise variation of the flexural capacity is based on a proposed model for the loss of cross-sectional area of the prestressing strands. It was observed that almost 46% of the total area of strands can get affected due to chloride-induced corrosion of the girder, by the end of its service life. The corresponding flexural capacity of the girder gets reduced by 50% of its initial capacity.

Well designed and detailed reinforced concrete shear walls in a building can provide the required lateral stiffness and strength, as well as ductility, for resisting seismic loads. A pushover analysis is preferred to an equivalent static analysis to estimate the non-linear behaviour of a building under seismic loads. The present study investigated the different options for modelling a tall and solid shear wall in a pushover analysis of a regular multi-storeyed building. Two approaches were adopted for modelling the non-linear behaviour of a shear wall. The first one was based on lumped (point) plasticity, where the shear wall was modelled using column elements (Model 1). The second one was based on spread (distributed) plasticity, where the wall was modelled using fibre-based wall elements (Model 2). The analyses of Models 1 and 2 were compared based on the pushover curves, demand and capacity spectra plots, and formation of hinges. The observed non-linear behaviours of the two models were very similar. It is concluded that the modelling of a tall and solid shear wall using column elements is adequate for pushover analysis, provided the hinge properties are defined properly.

The present paper provides a methodology to analyse the effect of corrosion on the strength and stiffness of the slab-and-girder deck of a road bridge. A linear finite element model of a typical medium span deck of an existing bridge was developed as per the as-built drawings. The vehicular loadings were as per the recommendations of the Indian Roads Congress specifications and the design rating of the bridge. Based on the phenomenon of corrosion, a time-dependent reduction in the area of flexural reinforcement near the soffits of the girders, was considered in the model. The effects of flexural cracking, creep and spalling of concrete were incorporated in the model with non-prismatic section properties and their stage-wise variations. From the analyses of a girder section and the computational model, it was observed that due to corrosion, the allowable moment capacity of a girder falls below the demand under dead load plus the rated live load, within the target service life of the bridge. However, the effect of corrosion on the stiffness of the deck is not substantial to be accurately measured by a conventional sensor. It is recommended that the procedure adopted in the paper can be used by the practicing professionals for numerically assessing longer span decks, to have a’priori estimates of the quantities that can be measured in a field test.

Performance based analysis under seismic loads using the finite element method for wall-type reinforced concrete (RC) members in buildings and in important structures like liquid retaining structures, nuclear containment structures, offshore concrete gravity structures etc., necessitates the understanding of the non-linear behaviour of the constituent membrane elements. The current orthotropic formulation of the softened membrane model (SMM) can be strictly used only when the reinforcement is symmetric to the principal axes of applied stresses. When the reinforcement is asymmetric, shear strain is generated due to the normal stresses in the principal axes of applied stresses, which is referred to as shear-extension coupling. An anisotropic formulation is required to capture the generated shear strain. The current study quantifies the shear strain due to asymmetry in reinforcement, by testing panels under biaxial tension-compression using a large-scale panel testing facility. A model for the shear strain is proposed based on the tests data. The paper presents the experimental programme, important test results and the modelling of shear strain. Expression developed for the shear strain can be incorporated in the solution algorithm of the SMM for improved prediction of the shear behaviour of a membrane element. This further aids in accurate prediction of the seismic performance of the important structures mentioned earlier.

The variation of the height of the columns in a storey of a multi-storeyed building increases their vulnerability to seismic forces. Assessment of seismic vulnerability of buildings can be carried out by various approaches. In this paper, an approach based on pushover analysis was used for generating vulnerability indices. The indices quantify the deficiencies in lateral load resistance and lateral drift of a building, storey drift, and the performance ranges of the hinges formed in the beams and columns. First, a regular mid-rise reinforced concrete building was analysed to evaluate the vulnerability indices. Next, the study investigated the effects of increased height of the open ground storey, foundations on sloping levels, split-level floors, and partial height infill walls in similar buildings. It was observed that the increase in vulnerability due to the variation of the height of the columns in a storey could be quantified by the indices for lateral load resistance, storey drift, and the performance of the columns in a storey.

Post-earthquake reconnaissance studies have reported severe damage to reinforced concrete buildings. In a moment resistant framed building, columns are the critical members of the load path. Shear failure of a column is brittle, leading to quick degradation of the lateral strength and vertical load carrying capacity. The reported study focuses on seismic strengthening of a short shear-critical column by concrete jacketing technique. For a shear-critical jacketed column, the integrity of the new and old concrete depends on any slippage at their interface. The investigation on the effects of three different interfaces such as surface roughening, providing dowel bars or bent shear connector bars in addition to surface roughening, on the seismic performance of jacketed columns, is presented in this paper. Large-scale column specimens were tested to shear failure under lateral monotonic and cyclic loads, in presence of estimated service level axial loads. The details of the experiments and the comparison of their results in terms of shear strength, stiffness and behavior are included. The specimens with different interfaces were found to be similar in their lateral load resistance, showing negligible difference in strength. However, the specimens with bent bars showed higher stiffness compared to the specimens with other two types of interfaces. The strengths of the specimens were predicted using codal provisions and a strut-and-tie model. Their behavior was traced using a piecewise linear model. The predictions were compared with the test results. The proposed method of analysis for shear deformation can be used in developing non-linear shear hinge properties for short jacketed columns, in a pushover analysis of a building.

The response of reinforced concrete (RC) framed structures under the action of lateral loads depends on the type of joints between the framing beams and columns. The design specifications developed for concentric joints are inadequate to be used for the design of eccentric beam-column joints. This study investigated the shear deformation and strength of non-seismically detailed RC concentric and eccentric exterior joints, through experiments and nonlinear finite element analysis. From the tested specimens it was observed that in the eccentric joint, the effect of torsion increased the joint shear deformation by more than 50%, and reduced the joint shear strength by about 20%. A parametric study was carried out using the finite element analysis to model the effects of beam-to-column width ratio, joint eccentricity and joint aspect ratio on the effective width of a joint. It is found that the proposed expression of the effective width of joints predicts reasonably well, when compared with numerical and experimental values.

The increased use of shear walls in buildings has necessitated the study for a better understanding of the modelling aspects of a wall and its behaviour under lateral loads. In a framed shear wall, the behaviour of the infill wall panels under lateral loads is governed by shear deformation and the frame-panel interaction. In the present study, a reinforced concrete low-rise multistoreyed building with a centrally located framed shear wall was investigated for two approaches of modelling the non-linear behaviour of the wall. In the first approach, the wall was modelled using multi-layered membrane elements (refined model). In the second approach, the wall was modelled using equivalent column elements (simplified model) with lumped plasticity at the ends. Pushover analysis and incremental dynamic analysis (IDA) were performed using these models. It was observed that the pushover curves and the IDA plots for both the models are reasonably close. From the pushover analyses, the prediction of lateral strength by the simplified model was slightly lower than the refined model due to the idealisation of the equivalent column elements. Nevertheless, the modelling of a framed shear wall using equivalent column elements is adequate in terms of quantifying the lateral stiffness, strength and overall behaviour of the structure under lateral loads, provided the hinge properties are defined properly.

The present paper provides methods for analyzing reinforced concrete column sections strengthened with concrete jacket. First, the prediction of the axial load versus moment interaction curve is presented based on a lamellar analysis and a simplified method of analysis. The predicted results are compared with experimental results of jacketed columns. Second, the prediction of the moment versus curvature behaviour of a retrofitted column section under an axial load, is presented based on both the methods of analysis. Finally, the lateral load versus displacement behaviour of a beam-column-joint sub-assemblage with retrofitted columns, is predicted using an incremental non-linear analysis. The predicted behaviours are compared with experimental results. It is concluded that the lamellar analysis provides good prediction of the strength, as well as the moment versus curvature behaviour of a retrofitted column section. The simplified analysis gives a conservative value of the strength. It cannot predict the ductility in the behaviour reasonably well. The incremental non-linear analysis provides substantial better prediction of the behaviour of a retrofitted sub-assemblage specimen, as compared to a conventional pushover analysis.

A parametric study was conducted on a model 7-storey reinforced concrete building as per the Indian code IS 1893: 2002 and the International Building Code IBC: 2006. Four different locations in India and USA were selected with different soil conditions to study the variations of the base shear, overturning moment and the member forces. The results of base shear and overturning moment are provided as bar charts for comparison. From the results it can be observed that the forces or moments can increase substantially when the local site effects are considered. Hence, it is important to include the latter in the code for seismic analysis.