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Abstract
Beam-to-column joints are very important parts of steel frames and have great influence on the strength, stiffness, ductility and stability of the whole structure, especially in seismic zones. After the earthquake of Northridge (January 17th. 1994), in which, the failure of beam-to-column welded connections was the most failure type that occurred in steel structures during this earthquake, a resolution was announced in every thing related to beam-to-column joints, i.e. fabrication, execution, analysis, proposals of new types, and modeling.
Modeling of beam-to-column joints in steel frame, especially, in seismic areas is a challenging target. It is, in fact, a microscopic modeling which has to take care of the details of the joints, i.e. welds, bolts, prying forces and contact, and, at the same time, this modeling is required to be as simple and accurate as possible. Adding to this, some new seismic codes and provisions oblige the designers to carry out experimental tests for the connections that will be used in seismic areas. This is very expensive process and, hence, it is required to replace the experimental models by alternative types that have the reliability in representing the behavior of beam-to-column joints. This behavior is mainly represented by the moment-rotation (M —0) curve which is generally nonlinear.
From another point of view, extended end-plate connections were proposed and focused as an alternative to the pre-Northridge welded connections since they have the ability to dissipate energy safely. From the modeling point of view, it is one of / or the most complex connection due to the number of connection components and their nonlinear behavior.
The purpose of this research is to obtain an approximate model for extended end-plate beam-to-column joints in seismic areas. This model has to be both simple and accurate.
Another important feature of the target model is to have the ability to be easily implemented in a frame analysis program.
In this thesis, two methods of modeling were proposed and verified. The first is the finite element method; it is the most accurate method alternative to the experimental modeling. At first, two extended end-plate joints (previously tested experimentally) were modeled and the results show excellent agreement with the experimental results. After that, many fully-detailed joints (about 600) were modeled for three different configurations of the extended end-plate connections using the ANSYS finite element package. To save both time and effort required for FE modeling, three command files (programs) were made for the modeling of the three configurations of the extended end- plate connections using the APDL (ANSYS Parametric Design Language). Using these programs, the only effort required is to introduce the dimensions and the material properties of the studied connection.
The other proposed method of modeling is the mathematical modeling. It is more preferable than the finite element method since it can be easily implemented in a frame analysis program. An extensive parametric study was done and its results were curvefitted to the equation of the four-parameter power model of Richard-Abbott using the statistical software ORIGINPRO-8. This equation was chosen since its four parameters are of real physical meaning. Again the results of the curve fitting process with the