Now showing 1 - 10 of 22
  • Placeholder Image
    Publication
    A Methodology to Assess the Degradation in the Structural Response of the Deck of a Reinforced Concrete Road Bridge due to Corrosion of Reinforcing Steel
    (01-02-2012)
    Banerjee, Soumendra
    ;
    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.
  • Placeholder Image
    Publication
    Experimental investigation of shear-extension coupling effect in anisotropic reinforced concrete membrane elements
    (05-12-2022)
    Kosuru, Ratnasai
    ;
    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.
  • Placeholder Image
    Publication
    Evaluation of seismic vulnerability of multi-storeyed buildings having columns of different heights in a storey using pushover analysis
    (01-10-2016) ;
    Sarkar, Shubhayan
    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.
  • Placeholder Image
    Publication
    Seismic performance of strengthened reinforced concrete columns
    (01-10-2020)
    Murugan, Komathi
    ;
    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.
  • Placeholder Image
    Publication
    Assessment of effective joint width for exterior eccentric reinforced concrete beam-column joints
    (01-01-2015)
    Mahajan, Milinda Ashok
    ;
    Rao, G. Appa
    ;
    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.
  • Placeholder Image
    Publication
    Modelling of the behaviour of reinforced concrete columns retrofitted for flexure using concrete jackets
    (01-06-2012)
    Kaliyaperumal, Gnanasekaran
    ;
    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.
  • Placeholder Image
    Publication
    Determination of the causative mechanism of structural distress in the presidential palace of India
    (01-01-2019)
    Aranha, Chrysl A.
    ;
    ;
    The presidential palace of India was constructed between the years 1912 to 1929 CE in a novel architectural style resulting from an amalgamation of Colonial and traditional Indian styles. During a visual inspection of this double-domed structure, meridional cracks were spotted in two out of the four niches in the drum of the lower dome. The observed distress raised two important issues that needed to be resolved- the cause of the cracks and their impact on the structural response. The uncertainty in the actual geometry of the building and the variety of materials used in its construction, the complex layout, lack of prior knowledge of reinforcement details and the undocumented changes made to the structure prompted the adoption of a multi-disciplinary scientific investigation to evaluate the structure. The methodical approach encompassed a literature review of dome failures in the past, historical and geometrical surveys, foundation inspection and the use of relevant non-destructive and minor destructive tests in the evaluation of the superstructure. The information gained from the aforementioned investigation was useful in the development of a 3D finite element model of the structure. The findings of the investigation revealed that owing to its geometry, tensile stresses develop in the unreinforced brick masonry drum. The reduction in the thickness of the drum at the locations of the niches results in an inherent weakness in the structure. The opening for the stairwell in the north-eastern corner of the building, at the level of the drum, further reduces the tensile resistance of the abutment system of the dome and gives rise to the observed crack pattern
  • Placeholder Image
    Publication
    Formulation of a generalized truss analogy for the analysis of shear behavior of short jacketed columns
    (01-09-2023)
    Murugan, Komathi
    ;
    Short columns in a story of a reinforced concrete building tend to fail in shear during an earthquake. They can be strengthened using concrete jacketing. A performance-based evaluation requires the modeling of nonlinear lateral load versus deformation behavior of such a column. While previous studies are available to analyze the behavior of a flexure-critical column, computationally simple method of analysis of the shear behavior of a short column is lacking in the literature. A generalized truss analogy is proposed to predict the shear behavior of short columns beyond diagonal cracking and till failure. Its formulation satisfies equilibrium of forces in the concrete strut and reinforcing bar ties, compatibility of strains in the concrete and ties of the web region of a column, and suitable constitutive relationships of the materials. First, the formulation and computation algorithm as applicable to an original column, are presented in this paper. Next, the method is extended to columns strengthened by concrete jacketing. Its application to a composite jacketed section is implemented using a sandwich model. The validation of the proposed method is presented, comparing the predictions with the lateral load versus deflection behavior curves obtained from the tests of five large-scale shear-critical column specimens (two original and three jacketed), tested as part of this research. The good correlation of the predicted and test results confirmed the application of the proposed method for the nonlinear analysis of shear for short columns.
  • Placeholder Image
    Publication
    Seismic behaviour of concrete jacketed columns in buildings
    (01-09-2014)
    Kaliyaperumal, Gnanasekaran
    ;
    An existing reinforced concrete building with moment-resisting frames can be vulnerable during an earthquake owing to its deficient columns. The present paper reports a study on the enhancement of flexural strength and behaviour of columns, by concrete jacketing. First, the performance of the interface of additional concrete cast against the prepared surface of existing concrete was studied. Tests were then conducted on reference (without strengthening) and jacketed column specimens, to study the enhancement of strength of a retrofitted column section under the interaction of axial load and bending moment. Subsequently, interior beam–column–slab sub-assemblage specimens were tested under simultaneous vertical and lateral loading. It was observed that the selected jacketing scheme was effective in enhancing the flexural strength, as well as in retaining the ductility and energy dissipation in the behaviour. The moment–curvature behaviour of a retrofitted column section was predicted based on the layered analysis. The information was fed in the lateral load against drift analysis of a computational model of a retrofitted sub-assemblage specimen, using an incremental non-linear technique. The paper presents the method of analysis and guidelines for retrofitting of columns for seismic forces.
  • Placeholder Image
    Publication
    Evaluation of corrosion rates of reinforcing bars for probabilistic assessment of existing road bridge girders
    (01-06-2015)
    Firodiya, Payal K.
    ;
    ;
    The rate of corrosion of the reinforcing bars is one of the important parameters required to estimate the residual service-life of a reinforced concrete (RC) bridge deck. In the present study, first, the linear polarization resistance technique was used to measure the corrosion rates of plain mild steel and cold twisted deformed (CTD) bar specimens, which were typically used in the older existing bridges. To consider the variability of a corrosion rate, the frequency distributions of the corrosion rates for the two types of bars were determined. Next, a probabilistic approach was adopted for assessing an existing RC girder-and-slab road bridge deck, subjected to corrosion of bars attributable to air-borne chlorides. A computational model was developed using the Monte Carlo simulation method, to assess the reduction in the flexural capacity of a typical girder. It was observed that the reduction in the mean capacity and the dispersion of the capacity with respect to time, were high with the measured statistical parameters of the corrosion rate of CTD bars.