Indian Concrete Journal

Determination of dynamic modulus of elasticity of concrete Priyaranjan Pal

An experimental investigation was carried out to determine the dynamic modulus of elasticity of pozzolana Portland cement concrete. Large numbers of concrete cubes were prepared in the laboratory for investigation. The destructive and non-destructive tests were conducted on concrete cubes at different ages. The destructive test was conducted to obtain the compressive strength of concrete cubes. Ultrasonic pulse velocity of cubes was measured according to IS 13311 (Part 1). The recorded values are used to determine the dynamic modulus of elasticity of concretes. Based on experimentally obtained data and analysis, a few relationships are proposed to correlate the water/cement ratio, compressive strength, and elastic moduli of concretes. Several interesting findings are observed from the correlations of the coefficients while analyzed by regression analysis. This study helps to determine the static properties of concrete from the dynamic ones.

Seismic performance analysis of outrigger structural system with dampers M. Rame Gowda, Shivie R. P. Goveas

Growth in economy leads to development in cities at a much higher rate and tall buildings are a direct effect of this growth. The cities with much higher seismic risk will have to develop new innovative concepts of designing tall structures and an outrigger structural system is one of many such design concepts which have made helped in constructing tall buildings. Outrigger structural system is easy to construct and they provide high lateral stiffness. Further this outrigger system is provided with dampers to improve the efficiency of the structure. This work presents the performance analysis of such outrigger structural system with dampers. Models consisting of one and two outriggers are developed and their performance is analyzed based on their response to dynamic analysis (time history) carried out to the past historical earthquakes in the California region. This work has been carried out using the ETABS software. The parametersdiscussed are lateral displacements, inter-story drifts, shear force and bending moment in the core for dynamic analysis. Also the performance of outrigger structural system with dampers is analysed varying flexural rigidity ratio from 0.25 to 2. From the analysis it is found that there is reduction in responses of the outrigger structure with dampers.

Design of Seismic Strengthening Technique for Soft-story RC Frames using Buckling-Restrained Braces Birendra K. Karaiya, Dipti Ranjan Sahoo, Ashok Gupta

This study is focused on the seismic strengthening of reinforced concrete (RC) frames with soft-stories using buckling-restrained braces (BRBs) in order to control the severe damages or complete collapse of these frames. A design procedure has been proposed to determine the BRB sizes required for the target design base shear of the study frames. The seismic performance of the strengthened frames is evaluated numerically using a computer software SAP2000. The modelling technique adopted for BRBs and frame members are discussed. Linear modal analyses are carried out to determine the mode shapes and time periods of the strengthened frames. Nonlinear static and dynamic analyses are carried out to investigate the lateral strength, failure mechanism, interstory drift response and residual drift response of the study frames. The seismic performance of the strengthened frames is also compared with those of the unstrengthened frames. The installation of BRBs significantly improved seismic performance of 4-story and 8-story RC frames with soft story. However, the lateral loadresisting potential of BRBs could not be fully utilized in the 20-story RC frame with soft ground story.

Assessment of Seismic Response Reduction Factor of RC Staging Elevated Water Tanks of Different Staging Height Jignesh A., Kashyap N. Patelaaa

Seismic design code for water retaining tanks IS 1893 (Part-II) 2014 indirectly consider the nonlinear behaviour of structures using ‘response reduction factor’ (R). The ‘R’ factor permits the use of linear elastic force based design for RC structures taking in to account the nonlinear behaviour and deformation limits. This study focus on the assessment of the realistic values of response reduction factor for RC frame staging elevated water tanks designed and detailed using the relevant Indian codes/standards. Twelve elevated RC frame staging water tanks of capacities 250 m3, 500 m3, 1000 m3, 1500 m3 and each having a staging height of 16 m, 24 m and 32 m are considered for analysis. RC staging elevated water tanks are analyzed using displacement controlled nonlinear static pushover analysis to obtain the capacity/pushover curve. The ‘R’ factor of elevated water tanks are evaluated at two performance limit viz. member level and structural level. The results of this study show that ductility factor and ‘R’ factor is considerably affected by the staging height and capacity of tanks. The evaluated values of ‘R’ factor corresponding to member level performance limit for the considered water tanks are either close to or higher than those specified in IS 1893 (Part-II) 2014 for special moment resistance RC frame staging water tanks.

Shape Effect of Columns on Structural Response of Flat Slab Systems in Non-Tower Area Chaithra P., Srinivasa Gowda, Divithkumar R. P

In modern cities due to the increase in vertical growth of structures, basement floors are mainly utilized for parking of vehicles and other utilities. The choice of structural framing for basement floors (mainly in non-tower areas) is strongly influenced by accommodation of parking spaces. The factors that are to be considered in deciding the structural form mainly includes the column locations, column spacing, column size and shape, beam depth and routing of the service systems. In the present work, flat slab system is considered for basement floors, as it offers several advantages such as providing minimum depth, large column free area, fast construction & flexible arrangements of services. A geometrically simple prototype of non-tower area with two basements and ground floor is considered from a realistic project of gated residential township. The numerical simulations of the models are carried out by finite element analysis program SAFE. Analysis is carried out on flat slabs supported on three types of column sections with circular, square and rectangular shapes. Furthermore, for rectangular columns the effect the L/B ratio (varied from 1 to 4) on structural response of flat slab systems in terms of punching shear ratio is presented.

Effect of infill in Composite shear wall RCC Building on Fragility Curve Punashri Prakash Phadnis, Vilas V. Karjinni

The present work aims to study the effect of masonry infill (MI) in reinforced concrete building with steel-concrete composite shear walls (SCCMSW) on seismic fragility curves using capacity spectrum method. Spectral displacement-based fragility curves and damage probability matrix under various damage states are developed for low-rise RCC frames using Barbat and HAZUS criteria. Comparison of both criteria shows good association between the results. It is concluded that the MI frame with SCCMSW have shown better performance during earthquake in all modes of different damage states.