The flexural deformation of connections greatly influences the overall response of steel structures. The behavior of steel connections is basically three-dimensional and nonlinear in nature, and involves the unilateral contact problem. A new finite element methodology is developed to investigate the characteristics of a bolted connection, especially the end-plate connection. Along with this main object, the paper is composed of three categories, namely, the development of an elasto-plastic three-dimensional element, the development of a contact algorithm with new gap elements, and the detailed investigation of the behavioral characteristics of the end-plate connection.
The iterative procedure to use the nonconforming elements in elasto-plastic problems is established and applied to the variable node transition solid element developed for the automated three-dimensional local mesh refinement. The validity and performance of the element are examined through the numerical tests. The most important strength of the element presented in this paper is such that in the elasto-plastic three-dimensional finite element analysis, it gives an economy in computation and a convenience in pre- and post-processing to achive a required degree of accuracy. As the nonlinear iterative procedure presented in this paper is accomplished for the general three-dimensional case, it could also be easily applied without major modifications to the two-dimensional elements such as membranes, plants and shells.
A simple yet efficient contact algorithms with gap element is developed to solve three-dimensional elasto-plastic contact problems without friction. A special gap element is proposed, together with a stress invariance principle, to model the contact process. The solution is achieved through an iterative procedure which adjust the modulus of the gap elements. The validity and performance of the proposed contact algorithm with gap elements are demonstrated through various numerical tests. The contact algorithm presented here is general in nature and can be used in conjunction with any finite element model to analyze three-dimensional elasto-plastic contact problems without friction. Due to simplicity and convenience in implementation on the computer, this method offers an attractive alternative to the use of the existing complicated algorithms. The proposed solution strategy is a trial-and-error method in the classical sense, but convergence to the solution of the unilateral problem is firmly assured.
The behavioral characteristics of the end-plate connections are investigated in detail to overcome the limitations of the previous finite element models. In order that the actual behavior could be simulated correctly and effectively, a three-dimensional modeling is established with nonconforming three-dimensional elements. The elasto-plastic nonconforming solid elements with variable nodes are used for the effective and economic three-dimensional finite element modeling and analysis. The effect of bolt pretensioning and the shapes of bolt shank, head and nut are taken into consideration in the modeling. A simple yet efficient contact algorithm with a new gap element is employed to simulate the interaction between the end-plate and column flange. The moment-rotation relationships, the variation of vertical displacement at beam tip, the contact phenomenon and the plastification of each component are investigated in detail. The comparsion of moment-rotation relationships obtained by the proposed scheme with the experimental results reveals that the modeling proposed in this study can properly simulate the actual behavior of the end-plate connection. The refined three-dimensional finite element model presented in this study can be used to generalize the behavioral characteristics of the end-plate connection through more extensive parametric studies. Extension of this methodology to the problems of various shapes, dimensions, and material properties may prove worthwhile for the accurate analysis and design of steel structures whereas the experimental studies become come expensive and time consuming.
