یادداشت فنی بررسی رفتار غیرخطی عرشه پلهای بتن‌آرمه به کمک روش اجزاء محدود

Many bridges built in the past 50 years are reinforced concrete. Because of their normal deterioration, the introduction of new safety standards, and the increasing traffic volume and loads, a high percentage of the older bridges require rehabilitation or expansion. Often, the choice between constructing a new bridge and rehabilitating the existing one must be made. An essential factor in making a sound decision is knowledge of the strength of the bridge in its existing form. Unfortunately, the inelastic response, load distribution characteristics, and ultimate strength of bridges can not be realistically assessed by use of simplified procedures currently used for design and evaluation. Prediction of this behavior ultimately requires extensive experimental tests or advanced analytical techniques. In many cases, analytical methods are more economical and expedient than laboratory or field testing, and a number of researchers have extolled the potential of using finite element analysis to predict bridge response.The primary objective of this study is to establish and demonstrate a convenient, reliable, and accurate methodology for analyzing reinforced concrete structures with particular emphasis on reinforced concrete bridge and develop a capability for predicting stress and strain distribution through the thickness of bridge decks. A secondary objective of the analytical evaluation include the development of a finite element model that could correctly represent global bridge behavior and accurately predict strains, stresses and displacements in the deck. A specific objective is to investigate the enhancing effects of compressive membrane action on the ultimate flexural strength of bridges.A nonlinear finite element program, NONLACS2, developed by Kheyroddin, was selected as the basic platform for this study. The next step was to demonstrate how reinforced concrete is modeled within NONLACS2 and to validate the results predicted by the NONLACS2 program by comparing them with relevant experimental data and accepted design calculations. The finite element model of a reinforced concrete beam, simply supported, and subjected to a uniformly distributed load, was initially investigated. Further verification of the validity of finite element models of reinforced concrete components were demonstrated by comparing the predicted response of the model with experimental results obtained from laboratory tests of a two-way reinforced, simply supported, concrete slab. Tests on existing slab and beam bridges around the world have shown that many of these structures possess a greater load capacity than current design codes predict they should have. Many researchers attribute the additional capacity to a phenomenon known as compressive membrane action. Compressive membrane action occurs as a result of in plane restraints that restrict the horizontal expansion of the bridge deck as it deflects vertically. For this purpose, finite element modeling of slabs with idealized end restraints has been carried out.With the information acquired through the research proposed in this paper, a more complete understanding of the nonlinear behavior of RC bridges was obtained. This would allow a more realistic assessment of the flexural strength of these bridge types to be made. Some important points can be noted. The type of end restraint imposed on a slab significantly affects its load-deflection behavior. The ultimate load capacity of a slab with fully restrained ends is almost five times greater than that of a simply supported slab. The stiffness of the horizontally restrained slabs is also significantly greater. The behavior of slabs with pinned ends depends greatly on the height at which the horizontal support acts. T-shape beam have a high lateral strength rather than rectangular beam and cause decreasing of deflection of deck. The stiffness of the T-shaped beams was largely responsible for the mode of failure.