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

Structural deformations and soil displacements arising out of ground shaking are intertwined. This interplay is termed as seismic soil-structure interaction (SSI). Over last few decades, the conventionally perceived beneficial nature of SSI has been challenged with evidences of damaged sites from various earthquakes. This paper evaluates effects of SSI on seismic response of hardening single degree of freedom systems located in diverse geologies. The assessment is performed using substructure approach in terms of inelastic force reduction factor such that structure attains certain ductility levels. It is observed that soil-structure systems can afford a lesser reduction in design seismic forces compared to fixed-base structures. Components of total displacement arising out of structural deformation, footing translation and footing rotation are also evaluated. With increase in SSI effects, contribution of structural deformation is found to decline sharply. Footing rotation is observed to be very significant in structure-soil systems with larger SSI effects. The soil-structure system is modelled using a discrete physical model which enables inelastic response to be obtained in time domain while considering frequency dependence of impedance functions. © 2021, Springer Nature Switzerland AG.

Department Of Civil Engineering

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Innovative Infrastructure Solutions

Evaluation of seismic response of inelastic structures considering soil-structure interaction

Steel-concrete composite frames with semi-rigid connections can be designed to resist earthquakes in low to moderate seismic zones by ensuring that they have adequate strength, stiffness and ductility. However, the design of semi-rigid composite frames to ensure desirable seismic performance is a complex problem due to several issues such as calculation of flexural stiffness of the composite beam, evaluation of the storey drifts and defining the secant stiffness of the nonlinear connection. In this paper, issues in the design of semi-rigid composite frames are discussed and proposed preliminary design guidelines for semi-rigid steel-concrete composite frames to satisfy the drift limits and give acceptable performance. Seismic performance of frames designed as per the force based design and direct displacement based design is compared and found that direct displacement based design is not promising in low seismic zones in terms of utilisation of material. © 2020 Institution of Structural Engineers

Structures

Seismic performance of semi-rigid steel-concrete composite frames

Design of steel structures is an iterative process that often turns complicated when requires initial guess. A good initial design guess that comes from past design experience can considerably reduce the number of subsequent analysis and design cycles. It is difficult to form declarative rules to express human intuitions and past experience. Another problem in design process is arriving at optimal solution, where optimization process in most cases is computationally expensive and time consuming. Artificial Neural Network (ANN) is a promising computational model that can perform cognitive tasks, such as learning and optimization. This paper focuses on application of ANN in design so as to make design process more efficient. The aim is to train ANN to arrive at optimal solution by considering design constraints along with practical. This is illustrated with an example of design of compression member which primarily requires initial guess. The economy in design is tried to obtain by providing training set of optimal solutions to a multilayer neural network. The design process followed to generate training set is in accordance with IS: 800-2007. The solutions given by ANN are approximate but have reasonable agreement with the expected solutions. © Published under licence by IOP Publishing Ltd.

Fulltext

IOP Conference Series: Materials Science and Engineering

Use of Artificial Neural Network for Initial design of steel structures

The process of soil response influencing motion of the structure and vice-versa is termed as soil-structure interaction (SSI). SSI has been traditionally considered to be beneficial to seismic response of a structure. It has been suggested that ignoring SSI in design practice leads to a conservative design. It is evident from the design codes which either allow a reduction of the overall seismic coefficient on account of SSI or suggest it to be ignored altogether. However observations from some of the past seismic events such as 1989 Loma Prieta earthquake and 1995 Kobe Earthquake show evidences of detrimental nature of SSI in certain circumstances. Recent studies have also been able to justify such possibilities. As a consequence of this dissent among the research fraternity, there is a lack of adequately formulated design guidelines. Though advances have been made in developing methods to solve an SSI problem, incorporating SSI in design practice has been a rarity. The present paper attempts to summarize various approaches to include SSI in analysis of structures and guidelines outlined in prominent seismic codes. The significance of such a study lies in the need for selection of appropriate approach. A review of contemporary research in field of SSI is also presented at the end. © 2018 Institution of Structural Engineers

Seismic Soil-structure Interaction: A State-of-the-Art Review

The present study analyses effects of soil-structure interaction (SSI) on the elastic response of moment resisting framed reinforced concrete structures founded on embedded raft in an elastic half-space to accelerograms compatible to design spectra conforming to diverse geology. Most structures are designed to remain elastic under design basis earthquake and are expected to exhibit inelasticity but no collapse under maximum credible earthquake. Moreover machine foundations subjected to harmonic excitations are supposed to respond in an elastic manner during its routine use. Hence there is a need to understand elastic response of structure-soil systems. The effect of SSI is to increase natural period and damping of the structure-soil system. Structure-to-soil stiffness ratio is the most significant parameter influencing extent of inertial SSI effects and has been selected as a metric of SSI and smaller values denote closeness to fixed-base structures. It is observed that SSI leads to reduced design forces in structures subjected to either harmonic excitation or ensembles of spectrum compatible design basis earthquakes. The results are expressed as response spectra plots which are quite familiar to structural engineers. Copyright © NCEE 2018: Integrating Science, Engineering, and Policy.All rights reserved.

11th National Conference on Earthquake Engineering 2018, NCEE 2018: Integrating Science, Engineering, and Policy

Elastic seismic response of moment resisting framed structures with soil-structure interaction

In general practice, composite beams are designed with either simple connections or fully rigid moment connections due to lack of information on semi-rigid connections. But, semi-rigid composite connections will offer several advantages like strength, stiffness and economy to the system when compared to simple or moment connection. Although, several researchers have reported the advantages of semi-rigid frames, information for their optimal design is currently not available. In this study, 4, 8 and 12 storey composite plane frames in different seismic zones are designed and their capacity curve is compared with corresponding curves for rigid frames to study the limitations and economy of semirigid frames. It is shown that semi-rigid frames perform better in low to moderate seismic zones but may not be advantageous in severe seismic zones.

Journal of Structural Engineering (India)

Design of semi-rigid steel-concrete composite frames for seismic performance

Steel-concrete composite frames offer several advantages such as efficient sections in terms of strength and stiffness, economy and speed of construction. Semirigid connections can also be easily achieved by providing additional rebars in the slab to resist hogging moments at beam ends. However, design of these frames is a complex problem as the minimum connection stiffness and strength required to satisfy seismic drift limitations are not easy to determine. Hence a comprehensive study is being undertaken with the objective of determining the most optimum connection properties for frames with various configurations such as spans and storey heights located in different seismic zones of India. In this study, regular plane frames of two, four and eight storeys are analysed under equivalent static and nonlinearstatic pushover analysis. The linear response of semi-rigid frames is characterisedin the form of ratios of roof drifts and time periods taken with respect to equivalent rigid frames. The moment-rotation curves for the semi-rigid connection are obtained from the results of an earlier study conducted by Smitha and Kumar (J Constr Steel Res 82:164-176, 2013) on stiffened flange plate composite connections.The variation of roof drifts and time periods with respect to connection stiffness is obtained. The roof drifts under equivalent static loads and time period sdecrease exponentially with increase in connection stiffness. The analyses results showed that significant reduction in design base shears can be achieved for practical semi-rigid frames as the time periods of these frames are higher than that of rigid frames. A design procedure is proposed to ensure that the frames satisfy code stipulated drift limitations. The seismic performance of a rigid and semi-rigid frame designed to satisfy current codal provisions are compared by carrying out non-linear static pushover analysis. The comparison indicates that, in low (zone II) to moderate (zone III) seismic areas, frames with semi-rigid connections can be designed to perform satisfactorily thereby reducing the overall cost of the structure. © Springer India 2015.

Advances in Structural Engineering: Dynamics, Volume Two

Performance based seismic design of semi-rigid steel concrete composite multi-storey frames

To prevent disaster in future earthquakes, one way of retrofitting the members in reinforced concrete buildings is concrete jacketing. The present study investigates the effect of jacketing on the flexural strength and performance of beams. First, slant shear tests are conducted to study the interface between old and new concrete. Second, beam specimens are tested to study the effect of jacketing on the positive bending of the span region. Third, beam-column-joint sub-assemblage specimens are tested to study the effect of jacketing on the positive bending of the beams adjacent to the joint. Further, analytical investigations are carried out to predict the experimental results. A layered approach is used for the prediction of the moment versus rotation curves for the retrofitted beam specimens. An incremental nonlinear analysis is adopted to predict the lateral load versus displacement behaviour for the retrofitted sub-assemblage specimens. Finally, guidelines are provided for the retrofitting of beams by concrete jacketing.

GENERAL

ISET Journal of Earthquake Technology

Seismic retrofit of beams in buildings for flexure using concrete jacket

Fracture behaviour of piping components used in pressurised heavy water reactors of nuclear power plants are of great importance to ensure safety and integrity against the extreme load conditions. Fracture mechanics approach predicts crack growth behaviour under normal operating conditions and failure load under accidental conditions. Leak-Before-Break concept is used to investigate the structural integrity of the piping components. Experimental investigations were carried out on straight pipes to study their fatigue and fracture behaviour under bending. Fatigue tests were conducted on 406 mm outer diameter straight pipes to study the crack growth with various notch configurations. Fracture tests were also conducted on the pipes, which were tested in fatigue, under monotonic loading for their fracture resistance. A new database on fatigue life of large size carbon steel pipes has been created which will be very useful for integrity assessment of power plant structures. The details of the studies are presented in this paper.

Journal of Structural Engineering (Madras)

Fatigue crack growth and fracture studies on straight pipes with circumferential surface notch

The concept of leak before break (LBB) has now replaced the traditional design basis of a double ended guillotine break (DEGB) to design the piping systems for new generation of nuclear reactors. The LBB aims at the application of fracture mechanics principle to demonstrate that pipes are, in general, unlikely to experience DEGB without prior indication of leakage due to through the thickness crack. Pipe elbows are the most critical components in any piping system under earthquake loading. Three cyclic load experiments have been conducted on 90° elbows of two different diameters to investigate their fatigue crack growth and leak before break behavior. A detectable leak before break was observed in all the three pipe elbows tested. Details of this experimental study and the results are presented in this paper. © 2007 Elsevier Ltd. All rights reserved.

International Journal of Fatigue

Experimental study on LBB behaviour of LMFBR pipe elbows

Piping elbows are one of the critical components of the cooling piping systems in power plants. This paper presents the details of fatigue crack propagation analysis based on code procedure and FEM and compares the results with experimental observations. The fatigue crack propagation was evaluated based on the inelastic range J integral, Js, which was obtained by applying the plastic correction factor (from RCC-MR code) to the elastic J-integral values obtained from the code as well as from the elastic finite element analysis. The fatigue crack propagation was also studied directly using the elastic-plastic J-integral value obtained from the finite element analysis. It was observed that the fatigue life calculated based on the modified Js-integral values was closer on the conservative side to the experimental results, than that from J-integral obtained directly from elastic-plastic finite element analysis. © 2007 Elsevier Ltd. All rights reserved.

Fatigue crack propagation analysis of surface cracks in pipe elbows

The energy dissipation capacity of conventional concentric braced frames in multi-storeyed buildings degrades drastically under earthquake loading, due to buckling of bracings under the compression regime. Non-Buckling bracing is an innovative patented system, in which the buckling of the bracing is prevented and the energy is dissipated by plastic deformation under tension-compression cycles, with stable hysteresis. The strength and stiffness of Non-Buckling bracing can be tailored to obtain the desired level of storey drift limit and energy absorption. A single-bay ten-storey concentric braced frame with diagonal Non-Buckling bracing is chosen for studying their effect during earthquake loadings. Non-linear time history analysis was carried out using SAP2000 to study the variation of maximum base shear, roof displacement, inter-storey drift, Damage Index and stresses in various members due to the El Centro earthquake accelerogram. It is observed that Non-Buckling bracings are effective in dissipating energy and controlling inter-storey drift. © 2006 Elsevier Ltd. All rights reserved.

Journal of Constructional Steel Research

Behaviour of frames with Non-Buckling bracings under earthquake loading

Connections between Rectangular Hollow Sections (RHS) have been a long-standing problem in steel construction but have received little attention from researchers. To ameliorate the situation, a new and efficient connection was proposed and evaluated by cyclic tests and finite element analysis. The connection consists of a channel connector welded to a column and bolted to a beam through a web opening. The validity of finite element analysis of the connection has also been established by comparing with test results in a companion paper. In this study, the necessary information for design is generated by finite element analyses and the influence of the various parameters is explained. The connection moment-rotation behaviour is represented by three parameters, namely, initial connection stiffness, ultimate moment capacity and the shape parameter. The variation of these parameters with the dimensions of the connecting element is presented. It is shown that the depth and thickness of the channel connectors are the primary parameters affecting the connection characteristics. It is also shown that the width-to-thickness ratio of the column web has a significant effect on the initial connection stiffness and should not be ignored in design. Other effects such as shear lag and stress intensity have a profound influence on the ultimate moment capacity of the connection. Empirical equations are presented to evaluate modal parameters based on a parametric study using finite element analysis. For the connection to be employed in seismic resistant frames, it is important to evaluate its ductility and energy dissipation capacity. Guidelines for their evaluation are also given. The results of finite element analyses are compared with simplified analysis to enable a better understanding of the distribution of forces and deformations at the initial and ultimate stages. This will be of great use in designing suitable connections between RHS sections. © 2006.

RHS beam-to-column connection with web opening-parametric study and design guidelines

Rectangular Hollow Sections (RHS) have superior structural performance compared to conventional steel sections. However, the application of RHS in structural steel framework is limited because suitable connection configurations have not been developed between such members. Also adequate information on the moment-rotation characteristics of connections between RHS members is not available for design. To overcome these problems, a new and efficient connection is proposed which is easy to fabricate and convenient for erection. The connection employs channel connectors welded to the column flange and bolted to the beam to transfer beam flange forces into the column webs thereby avoiding the need to provide internal diaphragms in the column. An opening in the web facilitates the installation of bolts and can be used to pass service lines. The bolts are loaded in shear, so as to obtain improved performance of the connection under cyclic loading. By choosing suitable dimensions for the channel connectors, the strength and stiffness of the connection can be varied. The behaviour of the connection is evaluated by cyclic tests and non-linear finite element analysis. Test results are presented in the form of hysteretic curves and failure modes. In the case of channel connectors of high strength, failure occurs at the beam net section away from the face of the column, similar to beams with Reduced Beam Sections (RBS). It is shown that the connection has adequate ductility and hysteretic energy dissipation capacity. The moment-rotation characteristics of the connection can be expressed in terms of the three-parameter power model, for semi-rigid frame analysis. © 2006.

RHS beam-to-column connection with web opening-experimental study and finite element modelling

Reinforced concrete frames are designed to withstand severe earthquakes by developing flexural plastic hinges in beams, away from the beam-to-column joint. To preclude shear and bond failures, additional shear reinforcement and anchorage lengths are advocated leading to congestion in the joint region. To clarify the effect of joint detailing on the seismic performance of lightly reinforced concrete frames, an experimental study was undertaken. The parameters studied were the effect of joint rotation, column axial load, cross-reinforcement in the joint and percentage of longitudinal reinforcement in the beam. The test results and qualitative evaluations are reported. It was found that joint rotation and axial load in the column are beneficial. The cross-reinforcement in the joint reduced the damage in the joint region but had an adverse effect on the cyclic performance.