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Abstract: Nonlinear Analysis of Reinforced Concrete StructuresReturn to previous page
By Sashi Kunnath, University of California at Davis, US
Reinforced concrete (RC) structural systems subjected to severe dynamic stress resulting from high winds, strong earthquakes, impact or shock loading, and other extreme events, can undergo sufficiently large deformations so as to cause structural members and connections to respond in the nonlinear range. An accurate prediction of this behavior is essential to facilitate the development of design guidelines to ensure satisfactory performance of structures subjected to these loads. It is also becoming increasingly important, in the wake of recent efforts to advance performance-based design of structures, to evaluate systems at various stages up to its collapse limit so that issues related to damageability and survivability of the structure at prescribed “performance levels” can be addressed.
The primary objective of any analysis, linear or nonlinear, is to determine locations of maximum stress and estimate deformation demands at critical regions due to the imposed loading. When the loading is deterministic and the system is expected to respond linearly, the modeling tasks are significantly simplified. However, for transient non-deterministic loads and structural systems that exhibit degrading inelastic behavior, the variables and uncertainties associated with selecting model variables or choosing an analysis method are much more difficult. The consequences of choosing a simple model to carry out a complex nonlinear analysis or using a complex model to conduct a simple linear static analysis can be far-reaching. It is always important to ascertain the level of complexity required to achieve a desired solution.
The range of modeling options available to a designer is diverse. If the purpose of an analysis is to determine the state of stress or strain at a particular location in a structural component or connection, then it is necessary to resort to finite element models that incorporate detailed constituent material behavior. However, if the quantities of interest are more global in nature such as member rotation or inter-story drift in a building, then the use of approximate member models may be sufficient. Since the inelastic behavior of RC structures is mostly concentrated at known locations in an element, a macromodel approach can often be used with remarkable reliability. Macromodels are computationally efficient and offer a great deal of flexibility in modeling. Since it is possible to account for a variety of behavior patterns in an equivalent sense, they are often used to model the global response of reinforced concrete structures.
The purpose of this paper is to provide an overview of essential modeling and analytical techniques that can be used to arrive at an understanding of the post-elastic behavior of concrete structures using a variety of techniques that can be used to model complex nonlinear behavior using relatively simple approaches. Every effort is made to identify available and relevant resources in the literature on each of the topics presented in this chapter so that the reader may explore specific topics in greater depth.
Sashi Kunnath is Professor of Structural Engineering in the Department of Civil & Environmental Engineering at the University of California at Davis. He served as Chair of the department from 2009-2015. He is also Distinguished Adjunct Professor at the Asian Institute of Technology in Bangkok, Thailand, Distinguished Visiting Professor at Nanjing Tech University in China, and has been honored as one of the Thousand Talent Foreign Experts in China.
He formerly served as the Editor-in-Chief of the ASCE Journal of Structural Engineering and also chaired the ASCE Technical Administrative Committee on Dynamic Effects and the Committee on Seismic Effects. Currently, he chairs the Executive Committee of the Technical Activities Division of the Structural Engineering Institute (SEI) of ASCE. He has received various national and international honors including: the 2012 Norman Medal and the 2008 Raymond Reese Research Prize from ASCE, and the American Concrete Institute (ACI) Structural Research Award in 2001. He is Fellow of the American Concrete Institute (2007), the American Society of Civil Engineers (2010) and the ASCE Structural Engineering Institute (2013).