Influence of external post-tensioning on the behavior of long-span steel mega trusses
Date of Issue2016-04-13
School of Civil and Environmental Engineering
Land shortage has always been a challenge in any metropolis with numerous buildings occupying every piece of useful land. Under such circumstances, the Bridging Mega-truss System (BMS), which is located above busy expressways or roads, may create space for buildings such as offices and commercial facilities besides serving the function of a bridge. The aim of this study is to investigate (1) the feasibility of such BMS; (2) the necessity of external tendons; (3) the influence of the external tendons on the behavior of long-span steel mega trusses; (4) proposing a simplified design guide for steel truss with external tendon. This high performance steel bridging structure is intended to support stack-up buildings on top as well as other facilities. In the numerical investigation, a mega-truss bridge model consisting of shallow steel truss and external post-tensioned tendon, was built with its girder simply supported. The analysis results on the real-time influence of external post-tensioning answered the question on (1) whether post-tensioning helps decrease the downward deflection of the steel mega-truss; (2) how this technique can be deployed to a steel structure in a practical and efficient manner. The analysis result shows that the post-tensioning technology can effectively achieve staged construction which controls the steel mega-truss’s deflection, increases the load-carrying capacity of the shallow steel truss and equalizes the section sizes of the truss members at the cost of complicating the stress situation at the area around deviators and anchoring points. In this case, it is concluded that external tendons are necessary for the BMS as they provide great flexibility towards the BMS. Furthermore, it is demonstrated that high strength material can be used in many projects since the deflection problem can be solved by the application of the external tendons. With the introduction of high strength material, the weight of the structure decreases and thus facilitates the construction process and saves both human labor cost and material consumption. All of the above indicate that there is a possibility of building such BMS over busy expressways or roads in metropolis. Finally, a simplified design guide for a steel truss with external tendon is proposed.
DRNTU::Engineering::Civil engineering::Structures and design