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Analytical Modeling of Nonlinear Behavior of Composite Stub-Girders
Raafat E. S. Ismail,Mohamed T. H. El-Katt,Hesham A. Zien Eldin,Younis M. Y. Kasem 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.4
This paper presents an inelastic analytical model for modeling the nonlinear behavior of partially composite stub-girder under midspan concentrated load with partially end joint stiffness. The method treats the stub-girder as a beam with three distinct layers, the top and bottom layers behave according to the normal beam bending theory, while the middle layer is a shear layer without any bending stiffness. At the interface between the steel and concrete elements, the headed stud shear connectors are modeled as linear elastic built-in cantilevers. The present method smears the effects of all the contributing shear elements, stubs and studs, along the span. The differential equation for the stub-girder is solved to obtain the general expression of elastic deflection for the case when one concentrated load is applied at the mid-span. Based on the present approach a computer program called “PZA” is developed. The program accounts for nonlinear behavior of concrete and steel materials. The accuracy and reliability of the program are demonstrated by the analysis of three stub girders and one composite beam over the entire loading range up to ultimate load and the results are compared with published experiments.. A relatively good agreements with the experimental findings are found. Then a parametric study is carried out to discuss the effect of the initial stiffness of shear connector and the stub height on the behavior of stub-girder.
Numerical Investigations on Dynamic Performance of Stiffened Box Steel Bridge Piers
Raafat E. S. Ismail,Fahmy A. Fathelbab,Hesham A. Zien Eldin,Sameh I. Zenhom 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.2
The aim of this paper is to carry out extensive numerical investigations about the effect of various structural parameters on the dynamic performance of stiffened box steel bridge pier under a strong earthquake ground motion. The considered structural parameters are the local slenderness ratios of stiffener and stiffened wall as well as the global slenderness ratio of the pier. In the present study, all investigated piers are made of high tensile steel with high yield ratio. The non-linear time history analyses are carried out using in-house Finite Element Program DYNAPSS, recently developed by the first author. This program is verified by comparing its results with the results obtained by the general FE program. In this program, the geometrical nonlinearity is considered on the bases of Total Lagrangian formulation, while the non-linearity of structural steel material is considered through implementation of modified multisurface cyclic plasticity model by which real characteristics of high tensile steel material such as, Plateau, Massing type of Bauschinger’s effect, disappearing of Plateau and cyclic strain hardening, are accurately modeled. The results are closely examined in respect with the damage index criterion. From this study, it is found that the increase in slenderness ratios of stiffener does not only increase the damage index, but also may lead to the full collapse. Furthermore, the damage index increases with the increase of local slenderness ratio of stiffened wall and the global slenderness ratio. Also, it is found that when the loacal buckling is not the dominant eigen mode and the pier behave as a single degree of freedom, the natural period has destructive effects when it is close to predominant period of the earthquake. Finally, contour plots of damage index values are presented. These contour plots may be greatly useful for the design of stiffened box steel bridge piers, where, critical values of structural parameters corresponding to certain value of damage index could be determined.