Search

An experimental programme is undertaken to study the behaviour of vertical joints between precast wall panels. The parameters such as type of transverse reinforcement in the joint, amount and distribution of joint reinforcements, shape of the joint and strength of the joint grout are considered in this programme. The test setup, specimens, instrumentation are reported in this paper. The results of a typical test are presented.

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.

Shear walls in buildings are efficient under seismic load in terms of providing lateral strength and stiffness. A framed shear wall consisting of panels in a frame, can be constructed in a new building or in an existing building for seismic retrofitting. Their contribution needs to be verified by appropriate non-linear analysis. The present study investigated the different options of modelling a reinforced concrete framed shear wall in a pushover analysis of a regular low-rise building. Pushover analyses were carried out using two computational models. The refined model was developed using multi-layered membrane elements for the wall panels. A simplified model was proposed with equivalent column elements for the framed wall. The shear hinge properties for the equivalent column elements were developed using the softened truss model. The in-plane normal stresses generated in the panels of the refined model, due to the framepanel interaction, were considered in the analysis by the softened truss model. The pushover curve from the simplified model was close to that from the refined model. The simplified model was conservative in terms of predicting the lateral strength. However, the deformability was overestimated as the local stress concentrations at the corners of the panels were neglected. It was observed that a simplified model without considering the normal stresses in the generation of shear hinge properties for the equivalent column elements, provided reasonable results. Since, the later model was computationally less intensive, it is expected to be suitable for professional practice. � 2014 ACC Limited.

The in-plane shear stress versus strain behaviour of a finite element in a wall-type reinforced concrete (RC) structure can be predicted by the Modified Compression Field Theory (MCFT) and the Softened Membrane Model (SMM). In the formulation of the SMM, the Poisson's effect generated in a state of biaxial stresses is considered. The Poisson's effect refers to the generation of additional tensile and compressive strains, due to the orthogonal compression and tension, respectively, developed under in-plane shear. The biaxial tensile strain is substantial and is influenced by the cracking of concrete and reduction of the tension stiffening effect from the concrete. The present research quantified the biaxial strains in RC panels with the reinforcing bars inclined at 45� to the directions of applied tension and compression, a condition similar to that in the elements of a wall under in-plane shear. The loading was sequential to formulate the biaxial tensile strain in terms of the state of stress in each material individually. Based on the stress-based formulation, an alternate model to incorporate the Poisson's effect in the SMM is presented. The proposed formulation is validated through the prediction of the shear stress versus strain behaviour of a few panels available from the literature.

Corrosion of the reinforcing bars is one of the primary reasons for the deterioration of reinforced concrete bridges near the coast. There is a need for improved understanding and modelling of the influence of corrosion on the structural performance of such a bridge. 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 three dimensional 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 (IRC) specifications and the design rating of the bridge. The model was also simulated for a static proof loading using test vehicles, and for a dynamic loading generated by a shaker. Based on the corrosion due to chloride ions, a time-dependent reduction in the area of flexural reinforcement near the soffits of the girders, was considered in the model. The nonlinear effects of creep, cracking and spalling of concrete were also incorporated in the model with non-prismatic section properties and their stagewise variations. From the analysis of the time-variant response of the deck, it was observed that due to corrosion, the allowable moment capacity of a girder falls below the demand under rated service loads within the target service life of the bridge. However, as compared to creep, the effect of corrosion on the stiffness of the deck is not substantial to be accurately measured by a conventional sensor. The procedure of the computational analysis adopted in the present paper can be used by the practicing professionals for assessing longer span decks.

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.

An analysis procedure was developed to predict the moment versus rotation behaviour in the vicinity of the critical section of a simply supported beam, post-tensioned with unbonded tendons. For the post-cracking behaviour, the procedure was developed based on the concept of plastic zone of concrete deformation. The procedure satisfies not only the equilibrium condition, but also the compatibility of deformation of the tendons and the concrete, and the stress versus strain curves of the materials. The results for a few specimens from the literature on the above type of beams are presented. It was observed that the proposed procedure can reasonably predict the behaviour of a specimen up to failure. Finally, a parametric study was conducted to study the effects of the important design variables on the response of beams posttensioned with unbonded tendons.

Assessment of seismic vulnerability of reinforced concrete buildings can be carried out by various approaches. In this paper, an approach based on push-over analysis was used for generating vulnerability indices. The indices quantify the deficiencies in lateral load resistance and lateral drift of a building, the performance ranges of the hinges formed in the beams and columns, and the inter-storey drift. First, a regular mid-rise building was analysed to evaluate the vulnerable indices. The modelling and analyses were performed using SAP 2000. Next, variations of the building with typical vertical irregularities were studied. It was observed that for the buildings with soft and weak storey or vertical geometric irregularity or in-plane discontinuity in the vertical elements of the lateral load resisting system, the indices based on the performance of columns in a storey and the storey drift ratio showed the maximum deficiency. It was concluded that the indices can indeed be used to identify such typical deficiencies in existing buildings.

The softened membrane model is used for the prediction of post-cracking non-linear response of reinforced concrete panel elements subjected to in-plane shear. The model includes the Poisson's effect of compression in the orthogonal tensile strain. The present research quantified the Poisson's effect by testing eight reinforced concrete panel specimens under in-plane biaxial tension-compression. The strains in the two orthogonal directions were decomposed into the uniaxial and biaxial components. Expressions were developed for modelling the Poisson's effect in terms of apparent Poisson's ratios. The results can be used in refined prediction of the shear response of reinforced concrete panel elements.

To prevent disaster in future earthquakes, the existing deficient buildings need to be retrofitted. One way of retrofitting the columns in reinforced concrete multistoreyed buildings is concrete jacketing. The present study has investigated the effect of jacketing on the flexural strength and performance of columns. First, slant shear tests were conducted to study the interface between the old and new concrete. Second, column specimens were tested to study the strength. Third, beam-column-joint sub-assemblage specimens were tested to study the ductility (or energy absorption) and energy dissipation. Analytical investigations were carried out to predict the experimental results. A lamellar approach and a simplified method of analysis were used for the prediction of the axial load versus moment interaction curves and moment versus curvature curves for the retrofitted columns. An incremental nonlinear analysis was adopted to predict the lateral load versus displacement behaviour for a retrofitted sub-assemblage specimen. Guidelines for the retrofitting of columns by concrete jacketing are provided.

The present paper proposes indices for assessing seismic vulnerability of multi-storeyed reinforced concrete buildings with moment resisting frames based on the equivalent static analysis and push-over analysis. Based on the push-over analysis, indices for the lateral load resistance of a building, drift of a building, overall performance of the beams and columns (referred to as members), performance of the columns in individual storeys are proposed. Based on the equivalent static analysis, an index for the storey drifts, an overall index for the demand-to-capacity ratios of the members and an index for the demand-to-capacity ratios of the columns in individual storeys are proposed. The purpose of the indices is to have quantitative and objective measures of the observations from the analyses, which otherwise remain subjective. The indices can be used to compare alternative retrofit schemes. A case study is reported to demonstrate the applicability of each index. From the results it can be concluded that the indices indeed reflect the deficiencies as per the respective analysis. From a push-over analysis, an index can detect a soft storey mechanism and other indices can check the lateral load resistance and drift of the building based on the required performance level. If a pushover analysis cannot be performed, indices based on the equivalent static analysis can detect the high demand in the columns of an open ground storey, and check the storey drifts.

In the seismic analysis of a framed building with masonry infill walls, it is necessary to model the effect of the walls on the lateral stiffness, strength and ductility of the building. The equivalent strut method is a convenient method for modelling the walls. Out of the two approaches of equivalent strut method, the one based on elastic analysis is suitable for linear methods of seismic analysis such as equivalent static and response spectrum methods. The approach based on ultimate load is suitable for nonlinear methods of seismic analysis such as pushover analysis. The present study proposes a nonlinear axial load versus deformation behaviour for the equivalent strut to be used in conjunction with a pushover analysis.

The Department of Civil Engineering, Indian Institute of Technology Madras, has developed a Handbook on Seismic Retrofit of Buildings under the sponsorship of the Central Public Works Department and under the aegis of Indian Buildings Congress. The Handbook contains seventeen chapters covering different aspects of seismic retrofit The first chapter is a stand-alone chapter that explains the concepts of seismic design and retrofit in a language suitable for the lay person. Besides the introductory chapters, there are chapters on evaluation and retrofit of various types of buildings. The types of buildings cover non-engineered, masonry, reinforced concrete, steel buildings and historical and heritage structures. The geotechnical seismic hazards and retrofit of foundations are placed as separate chapters. Retrofit using fibre reinforced polymer composites, energy dissipation and base isolation devices are introduced. A chapter on quality assurance and control is included. This paper presents the content of the Handbook and two case studies briefly.