IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Open ground storey (OGS) buildings are known to be vulnerable under seismic loading due to early formation of collapse mechanism in the ground storey RC columns. The estimation of design forces in such buildings has not been adequately addressed in existing design codes and the literature. In the present study, four different methods are proposed, ranging from rigorous nonlinear dynamic analysis (NDA) of the infilled frame to simplified equivalent static analysis of the bare frame. All the methods proposed are found to result in similar estimates of the design forces in the ground storey columns. The linear analysis (static/dynamic) methods proposed are particularly simple to apply in practice, and will result in designs that are rational and economical, compared to the existing code-based methods.

Department Of Civil Engineering

GENERAL

Journal of Structural Engineering (Madras)

Earthquake-resistant design of open ground storey RC framed buildings

A study was conducted, to address the problem of estimating short-term deflections in reinforced concrete (RC) two-way slabs, using finite element analysis with appropriate stiffness modifiers. The study proposed a modified Branson's formulation, to account for the complex effects of flexural cracking and tension stiffening, along with a simple modification to account for torsional cracking. The parameters in proposed formulation are determined empirically and the procedure validated by 23 investigative loading-deflection data sets. The proposed formulation stated that the stiffness changes for an RC two-way slab, subjected to bi-directional bending and torsion throughout the slab. It was demonstrated that the stiffness changes throughout the slab, due to cracking, depending on the magnitude of the principal tensile stress. The study also demonstrated that the idea is, top retain the assumed isotropic behavior in the elasticity in the proposed approach.

Structural Engineering and Mechanics

Estimation of short-term deflection in two-way RC slab

Slenderness effects in reinforced concrete beams are not comprehensively accounted for in the prevailing design codes of concrete. Existing recommendations are prescriptions of limiting slenderness ratios, which are semi-empirical in nature. No reduction in flexural moment capacity is recommended for beams with moderate slenderness. Experimental studies on 15 RC beams reveal that, the existing design guidelines are not sufficient to ensure gradual failure and that a reduced ultimate flexural moment capacity results in beams of moderate slenderness. A simplified formulation for evaluating critical buckling moment in reinforced concrete beams is proposed in this paper. Authors highlight a theoretical basis for limiting slenderness and based on the experimemtal results, propose a conservative reduction factor for evaluating the ultimate flexural moment capacity of RC slender beams.

Indian Concrete Journal

Assessment of flexural strength of slender RC rectangular beams

Slenderness effects in reinforced concrete (RC) beams are not comprehensively accounted for in the prevailing design codes on concrete. The existing recommendations are limited to prescriptions of limiting slenderness ratios, which are semi-empirical in nature. No reduction in flexural moment capacity is recommended for beams whose slenderness approaches these limits. This paper attempts to address the aforementioned shortcomings for rectangular beams. In a recent paper, the authors proposed a formulation to predict the critical buckling moment, which is found to agree closely with experimental results. Based on this formulation, an expression for limiting slenderness ratio (to predict sudden buckling failure) is explicitly derived for under-reinforced rectangular RC beams. The proposed expression for limiting slenderness ratio accounts for beam end conditions, loading conditions, concrete strengths, and steel, as well as tension and compression reinforcement and transverse reinforcement ratios. It is found that a wide range of slenderness limits is feasible for different sets of design variables, in contrast to the constant value prescribed in the existing codes of practice for specified end conditions. Based on experimental studies carried out on eight moderately slender beams, it is observed that, like steel beams, RC slender beams also exhibit slenderness effects (lateral deflections and twist), even in beams with moderate slenderness. The ultimate moment capacity is found to reduce on account of these effects. An empirical reduction factor ? is proposed to account for such slenderness effects.&nbsp;

World University root node

ACI Structural Journal

Slenderness effects in reinforced concrete beams

The prevailing version of IS 1343 (1980) needs improvement with respect to the procedure for estimating the ultimate moment capacity of prestressed concrete (PSC) sections. There is a lack of clarity in the specified typical stress-strain curves for two different types of tendons specified in the code especially with regard to the manner in which the specified partial safety factor has to be applied. The code also suggests a simplified method in Appendix B, as an alternative to more rigorous strain compatibility method for estimating the ultimate moment capacity. However, it is seen that the IS 1343 simplified procedure invariably fails to satisfy the condition of force equilibrium and also overestimates the moment capacity. These shortcomings in the code are examined and reviewed in this paper, and suitable modifications are proposed in the form of modified stress-strain curves and simplified tables for incorporation in the forthcoming revision of the code.

Improvement of IS 1343 procedure for estimation of ultimate moment capacity of PSC sections with bonded tendons

Precast concrete pipe racks are an economically advantageous alternative to steel pipe racks in industrial projects like refineries and petrochemical plants. One major reason for this is the elimination of fire proofing needs for the precast element. Optimal design of the concrete elements would further lower the cost. This paper deals with the optimal design of precast concrete pipe racks, considering design variables such as member sizes, grades of concrete and steel, and reinforcement area. Genetic algorithms (GA) have been used for optimisation and a program in VC++ has been developed to arrive at the optimal solution, which corresponds to overall cost, satisfying design criteria for strength and limiting deflection. Proposals for most favourable jointing mechanisms in terms of cost and constructability have also been given.

Optimal design of precast pipe racks

Glass fibre reinforced gypsum (GFRG) wall panel, a composite walling product, is made essentially of formulated gypsum plaster, reinforced with glass fibres. The behaviour of such wall panels under earthquake loading merits investigation. The hollow cores inside the walls can be filled with reinforced concrete to increase the strength and lateral load resistance. The results of experimental test on a full-scale GFRG wall panel, filled with reinforced concrete, and subjected to axial and in-plane reverse cyclic load, are presented in this paper. The experimental specimen is 1.02 m wide and 2.85 m high. Hysteretic behaviour of the wall panel, acting as a shear wall, is discussed. © 2008 Taylor & Francis Group.

Proceedings of the 4th International Structural Engineering and Construction Conference, ISEC-4 - Innovations in Structural Engineering and Construction

Behaviour of glass fibre reinforced gypsum wall panel under cyclic lateral loading

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.

Seismic retrofit strategies of buildings

The current scenarios of earthquake engineering research and practice in India in the aftermath of the Gujarat earthquake are discussed. The numerous building collapses and deaths in the Bhuj earthquake have highlighted the exposure to major Indian cities from future great earthquakes especially along the Himalayan frontal fault system. The existing building stocks pose a much graver problem of seismic safety in comparison with new constructions designed according to modern codes. The new seismic map of IS 1893, Zones I and II have been merged and new regions have been included in Zone III such as the Marathwada region of Maharashtra and the Chennai area in Tamil Nadu. The researches deals with post-earthquake reconnaissance studies, earthquake resistant design, structural control, component testing, seismic qualification, seismic retrofit, energy dissipation devices and field monitoring of buildings, with its research comprising both experimental and computational aspects.

Structural Engineer

Earthquake resistant design practice and research in India

Estimation of deflections in RC slabs is important in the limit state design approach, as deflection control is often the governing condition for slab thickness. Unlike the case of one-way slabs, there is presently no simple procedure available in design codes as well as in the published literature to estimate maximum deflections of RC two-way slabs. The present study attempts to address this problem, with regard to estimation of short-term deflections in RC two-way slabs for which deflection coefficients are available. A modified Branson's formulation is proposed to assess the flexural rigidity of the two-way slab in order to account for the complex effects of cracking and tension stiffening. The empirical formulation is based on 16 experimental load-deflection data sets reported in literature for uniformly loaded rectangular panels on unyielding supports with simply supported and restrained edges.

Short-term deflections in two-way RC slabs using deflection coefficients

Simplified methods are generally preferred in practice for the transverse bending analysis of concrete box-girder bridges. The cross-section of the bridge is generally modelled as a frame of unit width with imaginary supports at the web locations and simplified frame analysis (SFA) is carried out. Alternatively, a method (ISM) using influences surfaces for elastic plates (Homberg's or Pitcher's Charts), as recommended by AASHTO, is adopted for simplified analysis. Because of the various assumptions made in the modelling, the SFA and ISM results are found to be erroneous. While the ISM results are generally very conservative, the SFA results are found to be sometimes unconservative in some cases of vehicular leading. In an earlier investigation, the authors have studied and quantifed the nature of the errors in SFA with reference to detailed 3-dimensional finite element analyses (3DFEA), for box-girder bridges (single rectangular cell) without flange overhangs, and a set of correction factors proposed for use in design practice. In the present study, the procedure is extended to box-girder bridges with flange overhangs. Based on extensive numerical studies by both SFA and 3DFEA, a set of correction factors are proposed, and their use demonstrated through an illustrative example. It is established that the use of conventional SFA gives erroneous results which are eliminated by applying the proposed modifications.

Transverse bending analysis of concrete box-girder bridges with flange overhangs

The design formulations of pavements and bridges are significantly influenced by the uncertainties associated with the prevailing vehicle weight characteristics. Accurate modelling of load spectra and the estimation of possible vehicle growth and composition are the main components in the safety assessment of transportation structures. The vehicle weights from the existing traffic form the basis for load spectra development, and the vehicle projections are subjective to the socio-economic conditions. In this paper, the methodologies of appropriate data consideration for such representation are discussed and demonstrated based on the data from India. The load spectra are also developed for vehicular data from Interstate 95 (I-95) in New York State. In lieu of the current status of the design codes for pavements and bridges worldwide, most of the developing countries are in need of analogous models for the calibration of the design basis. © 2007 Taylor & Francis Group, LLC. All rights reserved.

Transport

Axle load variations and vehicle growth projection models for safety assessment of transportation structures

The simplified equations available at present to predict the collapse loads of single-cell concrete box-girder bridges with simply supported ends are based on either space truss analogy or collapse mechanisms. Experimental studies carried out by various researchers revealed that, of the two formulations available to predict the collapse load, the one based on collapse mechanisms is found to be more versatile and better suited to box sections. Under a pure bending collapse mechanism, the existing formulation is found to predict collapse load with high accuracy. However, in the presence of cross-sectional distortion, there are significant errors in the existing theoretical formulation. This paper attempts to resolve this problem, by proposing a modification to the existing theory, incorporating an empirical expression to assess the extent of corner plastic hinge formation, under distortion-bending collapse mechanism. The modified theoretical formulations are compared with the experimental results available in the literature. New sets of experiments are also conducted to validate the proposed modified theory to estimate the collapse load. In all cases, it is seen that the modified theory to predict the collapse load match very closely with the experimental results. © 2007 ASCE.

Journal of Bridge Engineering

Estimation of collapse load of single-cell concrete box-girder bridges

A beam-column joint is a very critical element in reinforced concrete (RC) framed structure where the elements intersect in all three directions. Joints ensure continuity of a structure and transfer forces that are present at the ends of the members. The present provisions in IS 13920:1993 are inadequate, in terms of (i) minimum column width, (ii) column/beam flexure strength ratio, (iii) estimation of shear demand, (iv) assessment of shear strength, design and detailing of shear reinforcement, and needs to be upgraded regarding the beam-column joint under seismic loading. This paper reviews the design procedures for the RC beam-column joints under seismic loading reported in literature, with a special emphasis on three international codes of practice viz. ACI 318M-02, NZS 3101:1995 and prEN 1998-1:2003. It is pointed out that although there is a need for continuing research to resolve various disparities, there is an urgent need to revise IS 13920 suitably, in the interest of structural safety.

Design of RC beam-column joints under seismic loading - A review

Applications of Statistics and Probability in Civil Engineering - Proceedings of the 10th International Conference on Applications of Statistics and Probability, ICASP10

Correlation measures: Robustness and performance in simulations

At present, there are no recommendations in codes such as ACI 318 and BS 8110 to estimate the critical buckling moment in slender concrete beams. It is assumed that if the slenderness ratios of the beams are limited to the values prescribed by the codes, the failure moment of the beam will be dictated by flexure and not by buckling. Experimental studies carried out as part of the present study, however, show that the specified slenderness limits are not reliable, and failure by lateral instability can occur in slender beams designed according to the code. It is also shown that the existing formulations to predict critical buckling moments in beams, suggested by various researchers, grossly overestimate the capacities in the case of under-reinforced beams. In this paper, a modified formulation is proposed to predict theoretical buckling moment, and it is found to agree very closely with experimental results for both under-reinforced and over-reinforced beams. Copyright © 2006, American Concrete Institute. All rights reserved.

Estimation of critical buckling moments in slender reinforced concrete beams

Safety assessment and rational design of bridge structures requires the uncertainty associated with vehicle loads to be modeled as accurately as possible. This modeling is rendered difficult by the presence of vehicle axle weights that involve different combinations of unimodal and multimodal probability distributions with different dependence structures. In this paper, a transformation invariant approach using copula functions is proposed for the multivariate simulation of dependent axle weights of different vehicle classes. Copula based dependence modeling, which is widely used in the financial risk analysis, is applied to model and simulate three different vehicle cases with different combinations of marginal probability distributions for axle weights. The database of observed vehicle weights is based on the data collected at five locations on national highways in India. The dependence between multimodal distributions of axle weights is accurately considered and simulations are carried out. The simulated axle weights are found to be in very good agreement with the observed data. This type of simulation is useful in carrying out simulation-based reliability analysis of bridges and pavements. © 2006 ASCE.

Journal of Transportation Engineering

Multivariate simulation and multimodal dependence modeling of vehicle axle weights with copulas

Of the various methods available for the analysis of box-girder bridges subject to vehicular loading, threedimensional finite element analysis (3DFEA) gives accurate results, compared to the other methods. However, 3DFEA is not commonly adopted in practice, and simplified methods of frame analysis are preferred. In this paper, a new simplified method (Modified Fixed Beam Method) is presented for the transverse bending analysis of box-girder bridges without overhangs. The results of extensive three-dimensional finite element analysis have been quantitatively assessed to provide a logical basis for the proposed 'Modified Fixed Beam Method' suitable for design practice. In the proposed method, the top flange of the box-girder bridge is modeled as a beam with fixity at the web-top flange junctions (fixed beam model), and the transverse bending moments so generated are suitably modified to yield the actual distribution of transverse moments. Modification factors are proposed based on extensive numerical studies, to account for the influence of type and location of loads, wheel contact dimensions, spacing of webs and the relative thickness of flange and web. Finally, the application of this proposed simplified method is demonstrated by means of two illustrative examples.

Simplified method for transverse bending analysis of concrete box-girder bridges

This paper presents a reliability-based analysis of reinforced concrete slab culverts constructed as per the design recommendation of the Ministry of Road Transport and Highways (MORTH) at the flexural limit states. Hasofer and Lind's technique is employed to evaluate reliability index, β, which is a measure of probability of failure. The results indicate that the nominal probability of failure of slab culverts designed as per MORTH's recommendations at the limit state of collapse in flexure lies in the order of 10 -5 to 10 -8, which reveal that the designs are conservative (in comparison with AASHTO's recommendations), and the degree of conservatism is not uniform for all spans.

Reliability of RC slab culverts

Glass fiber reinforced gypsum (GFRG) wall panel is made essentially of gypsum plaster reinforced with glass fibers. The panels are hollow and can be used as load bearing walls. The hollow cores inside the walls can be filled with in-situ plain or reinforced concrete. This paper presents guidelines for the use of GFRG wall panel as a lateral load resisting component in buildings based on a numerical analysis procedure to arrive at its capacity estimation under axial compression, compression with inplane bending and shear. Variation of buckling load of unfilled GFRG wall panels for various widths is reported. The axial load carrying capacity of 1.02 m wide and 2.85 m high wall panel, obtained from the numerical analysis and the test results are comparable for this load case. While assessing the axial load capacity for design under compression, a minimum possible eccentricity (causing out-ofplane bending) is accounted for. An engineering model is proposed to assess the strength of unfilled and concrete filled GFRG wall panels in multi-storied building system subjected to lateral load such as earthquake.