Mechanical Property Research Of Reinforced Concrete Beam Bridges Under Automobile Load Spectrum

With the increase of reinforced concrete bridges' operation time, concrete has cracked, and reinforcing steel bar has been rusted, and their load-carrying capability has decreased unceasingly. Many existing bridges include prestressed concrete bridges, which were designed obeying the rule of cracking strength, cracked and their cracks propagate unceasingly under automobile loading. In the aspect of design, bridge's design loads are the worst combination of activity loads and constant load, which are static loads. But the loads in existing bridges are automobile loading. Bridges' whole life is a course of cumulative damage under automobile loading. Under the loads bridge's structure will give birth to cumulative damage, and so much as be destroyed. So it is very important and necessary that we study the mechanical properties of reinforced concrete beam bridges under automobile load spectrum. This paper firstly discusses the problem of coming into being automobile load spectrum. Making use of others study fruits, author writs the program of VLS, vehicle load spectrum, and gets vehicle load spectrum in different traffic condition. Using ANSYS, a familiar finite element program, this paper analyzes the simply supported T-beam bridge's space dynamic response under different loading condition, such as symmetric vehicle load spectrum, non-symmetric vehicle load spectrum, two-lane vehicle load spectrum in uniform direction, and two-lane vehicle load spectrum in opposite direction, and studies the effect of automobile speed on the dynamic coefficient. At the same time the paper establishes the solid finite element model of T-beam, and analyses the fatigue cracks, and the time-stress history of the reinforcement in tensile region and of the concrete in compressive zone under automobile load spectrum.The study indicates these conclusions. It is viable that we analyse the mechanicalproperties of reinforced concrete beam bridges by using computer to simulate automobile load spectrum and acting them on FEM model. The effect of automobile speed on the dynamic coefficient is complex. There is a peak value when the automobile speed is high or low. It has a fluctuating ascend direction as a whole. The side beam has stronger vibration than main beam under automobile load spectrum. The transverse vibration of highway reinforced concrete beam bridges is weak. Train flow direction has a weak effect to the bridge's vibration. The T-beam's dynamic deflection under automobile load spectrum is bigger than its static deflection under design loads and under checking computation loads. Their fatigue live is bigger than 2 X 106, but less than 2X 107. The stress of the concrete in compressive zone is in the range of Code for Design of Concrete Structures GB 50010-2002, but the stress of the reinforcement in tensile region is out of the range of this code. So the reinforced concrete beam bridges, which are designed obeying Specifications for Design of Reinforced Concrete and Prestressed Concrete Highway Bridges and Culver JTJ 023-85 and JTG D62-2004 should be checking computed.