Civil Engineering Reference
In-Depth Information
FEA of reinforced concrete structures is a highly nonlinear problem because of the nonlinear
constitutive relationships of reinforcement and concrete. The nonlinear problem can be solved
using the iterative solution algorithm until convergence is achieved with acceptable accuracy.
During the past 20 years many advanced algorithms
,
such as the line-searches method, the
quasi-Newton method with accelerations, the arc-length method, automatic increments and
the re-starts method have been developed for nonlinear analysis (Crisfield, 1997). By applying
the advanced solution algorithm, fast and stable convergence can be achieved, and acceptable
accuracy can be obtained. Today, the establishment of the material constitutive relationships,
improvement of the finite element method, and rapidly increasing computer power make it
possible to perform nonlinear FEA on reinforced concrete structures subjected to reversed
cyclic or dynamic loading.
The finite element computer programming of reinforced concrete structures represents an
enormous amount of work. Most nonlinear finite element computer programs involve three
similar procedures: (1) building finite element models such as nodes, elements, materials, and
loads; (2) solving nonlinear equations using the iterative solution algorithm; and (3) recording
the results of analysis. It would be an extremely laborious task for individual researchers
to develop their own finite element programs. Moreover, it would not be economical for
researchers to invest the time and effort in developing the general finite element code. Thus
,
an
increasing number of researchers tend to use general finite element programs or frameworks
such as FEAP, ABAQUS, or OpenSees, which offer users the ability to implement their own
elements and constitutive laws. Traditional general finite element programs, such as FEAP
(Taylor, 1999), were usually written in FORTRAN, which was characterized as a function-
oriented language. In recent years, however, object-oriented languages such as C
and Java
have been proven to significantly improve the extendability and usability of the software over
the function-oriented languages. Most notable was the finite element framework OpenSees
(Fenves, 2005) in applying objected-oriented languages to FEA.
++
9.1.2 OpenSees - an Object-oriented FEA Framework
OpenSees stands for Open System for Earthquake Engineering Simulation (Fenves, 2005).
It was developed at the Pacific Earthquake Engineering Center (PEER), the University of
California, Berkeley. OpenSees is an object-oriented framework for simulation applications in
earthquake engineering using finite element methods. Key features of OpenSees include the
interchangeability of components and the ability to integrate existing libraries and new com-
ponents into the framework without the need to change the existing code (Fenves, 2005). This
makes it convenient to implement new classes of elements, materials and other components.
Many advanced finite element techniques that are suitable for the nonlinear FEA have already
been implemented in OpenSees. As it stands, however, OpenSees is not readily applicable to
reinforced concrete plane stress structures because no suitable constitutive models for such
structures are included. That was the situation until recent studies done at the University of
Houston (Mo
et al
., 2008)
The OpenSees framework is adopted in this topic. The constitutive model CSMM is imple-
mented and a nonlinear finite element computer program, Simulation of Concrete Structures
(SCS), is developed. This program is capable of predicting the nonlinear behavior of reinforced
concrete structures subjected to static, reversed cyclic, and dynamic loading
s
. The program
is then validated with studies on different types of structures, as reported in the literature,
