Gaurav Srivastava

Numerical modeling of structural frames with infills subjected to thermal exposure: State-of-the-art review

Purpose Reinforced concrete structural frames with masonry infills (infill-frames) are commonly used for construction worldwide. While the behavior of such frames has been studied extensively in the context of earthquake loading, studies related to their fire performance are limited. Therefore, this study aims to characterize the behavior of infill-frames under fire exposure by presenting a state-of-the-art literature review of the same. Design/methodology/approach Both experimental and computational studies have been included with a special emphasis on numerical modeling (simplified as well as advanced). The cold behavior of the infill-frame and its design requirements in case of fire exposure are first reviewed to set the context. Subsequently, the applicability of numerical modeling strategies developed for modeling cold infill-frames to simulate their behavior under fire is critically examined. Findings The major hurdles in developing generic numerical models for analyzing thermo-mechanical behavior of infill-frames are identified as: lack of temperature-dependent material properties, scarcity of experimental studies for validation and idealizations in coupling between thermal and structural analysis. Originality value This study presents one of the most popular research problems connected with practical and reliable utilization of numerical models, as a good alternative to expensive traditional furnace testing, in assessing fire resistance of infill-frames. It highlights major challenges in thermo-mechanical modeling of infill-frames and critically reviews the available approaches for modeling infill-frames subjected to fire.

A novel method for prediction of truss geometry from topology optimization

An important task in designing a truss structure is to determine the initial configuration of the truss. In the absence of an efficient optimization technique, the selection of initial geometry is based on a trial and error procedure or standard truss configurations or past experiences. In this work, a fully automated algorithm is proposed which can be used to predict initial truss geometry from the grayscale images obtained from topology optimization of design domain. It predicts the locations of joints and the connectivity of members. It also estimates the approximate cross-sectional areas of the members. The interpreted truss geometry can be modified or directly used for structural analysis and design. Numerical examples are presented to demonstrate the functioning of the algorithm under various scenarios. The developed algorithm has been implemented as part of a web-based truss design application, previously developed by the same authors.

Nonlinear analysis of reinforced concrete plane frames exposed to fire using direct stiffness method

This article presents a framework based on the direct stiffness method for nonlinear thermo-mechanical analysis of reinforced concrete plane frames subjected to fire. It accounts for geometric nonlinearity, material nonlinearity, and nonlinear thermal gradients and incorporates two-way coupling between thermal and structural analyses. Force deformation relations are derived from classical Euler–Bernoulli beam theory and are expressed in terms of temperature-dependent stability and bowing functions. This is one of the unique features of proposed framework and allows a coarser spatial discretization to be used as opposed to full finite element–based approaches (such as SAFIR [registered trademark of the software SAFIR developed at the University of Liege]). The cross sections of the structural members are discretized with two-dimensional meshes for thermal analysis while structural analysis utilizes a line element based on direct stiffness method. Equivalent bending and axial rigidities of this line element are computed using several fibers along the length of the member, passing through the nodes of the two-dimensional mesh used for thermal analysis. The total strain at each fiber is decomposed into mechanical, thermal, creep, and transient thermal components. A discrete damage parameter is introduced at fiber level to ensure irreversibility of crushing and cracking in accordance with relevant constitutive laws. Five numerical examples are presented to demonstrate the accuracy and efficacy of the developed framework with respect to theoretical solutions, experimental observations, and some of the existing macro- and micro-finite element–based approaches. It is found that the developed framework can predict the response of reinforced concrete structures very well.

Numerical Modeling of Spalling in High Strength Concrete at High Temperature

High strength concrete (HSC) is predominantly used in high-rise reinforced concrete buildings. While excellent from strength point of view at room temperature, HSC is known to be prone to spalling, when exposed to high temperatures (e.g., in case of a fire). Fire resistance evaluated from building codes (CEN in Design of concrete structures. Part 1–2: general rules—structural fire design, Eurocode-2, Brussels, 2004; Bureau of Indian Standards in Indian code of practice for fire safety of buildings (General): details of construction code of practice. IS-1641, New Delhi, 1989) [1, 2] and simulation-based studies typically does not consider the effects of spalling. To alleviate these difficulties, a 2-D hydrothermal model has been developed for predicting the extent of spalling in HSC. The numerical model evaluates pore pressure inside the concrete as a function of time using the laws of thermodynamics. Spalling is said to occur when the pore pressure built-up within concrete exceeds its tensile strength. The model depends on several parameters such as permeability, initial moisture content, and thermomechanical properties of concrete. All of these parameters are considered by the model through a two-way coupling between the pore pressure analysis and thermal analysis, both implemented using the finite element method. Validity of the numerical example is established by comparing the spalling predictions obtained from the numerical model against standard experiments available in the literature. Parametric studies have also been performed using the numerical model to quantify the effects of model parameters such as permeability, grade of concrete, and type of fire scenario on the prediction of spalling.

Fire Safety in Offshore Structures

This chapter deals with fire safety in offshore structures. Process of fire, fire growth, and decay are discussed in detail. In addition, factors associated with fire-resistant design of structural members are dealt with reference to international codes. Examples are solved to illustrate the presented concept. Extracts of a few codal provisions are also given in this chapter for completeness of understanding.

Analysis and Design of Members in Fire

This chapter deals with aspects related to analysis and design of structures in fire. Detailed design procedure of steel members, reinforced concrete members, and steel–concrete composites under fire exposure are discussed. Design examples and solved following code provisions illustrate the presented concepts in detail.

Advanced Structural Analysis

Analysis of offshore structures is offset from the conventional methods due to the advanced geometric forms that are conceived. As design of offshore compliant structures is no more strength based but displacement controlled, knowledge about advanced analysis methods is inevitable for a designer. Sections on unsymmetrical bending and shear center are presented in a detailed manner with an objective to serve as reference guide for the designers. Design of curved beams, which is generally discussed as a topic in advanced strength of material is also included in this chapter to make the knowledge base complete and competent. In order to understand design philosophy and analysis methods, many numerical examples following the equations that are derived from first principles are included. This chapter highlights various advanced analysis methods, which are applicable to offshore structural design in various stages. A detailed understanding of analysis tools with a precursor about special environmental loads will make this chapter interesting and self-explanatory.