Design And Theoretical Research On Steel-Lightweight Aggregate Concrete Composite Beam

With the rapid economical and social development, modern architecture is developing rapidly, the orientation of the development are large span and high-level, which requires to reduce the self weight of high-level and large-span structure, and increase the thermal insulation properties of the structure, improve the seismic performance of buildings. The requirements on material are light-weight and high-strength. However, the disadvantage of ordinary concrete, such as heavy self weight and poor insulation performance, influence its application value in engineering, and limits its applications in some engineering. To meet such engineering requirements, the lightweight aggregate concrete structures are given rise.Steel-lightweight aggregate concrete composite beam is a new type of composite beam developed on the basis of the steel-concrete composite beam and lightweight aggregate concrete structure. Composite beam is able to make rational use of materials, gives full play to respective material properties of steel and concrete. Compared with steel structures, it can save steel by 20%～40%, and can save concrete than reinforced concrete beams, reduce self weight and the height of cross-section. The composite beam has good overall stability, shear performance and seismic performance. Steel-lightweight aggregate concrete beam inherits and plays the characteristics of composite beam more reasonable. Because light weight aggregate concrete has a light self weight, it can further reduce the dead load of the upper structure and the overall cross-section height, improve the load characteristics of beam and the high-span ratio of composite beam, increase headroom under the bridge, save the steel volume of steel girder, reduce the scale of substructure. It can reach the purpose of saving space, reducing costs and improving the overall economic benefits of the bridge.At the same time, from the construction point of view, steel- lightweight aggregate concrete composite girder bridge is facilitate to factory production, has a high quality of on-site installation, low construction cost and high construction speed, and can be applied to the situation which traditional masonry and concrete structure is difficult to apply. Based on the above advantages, steel-lightweight aggregate concrete beam can be widely used in bridge and building works. The study on lightweight aggregate concrete composite beam is at the initial stage, the research results are few. Although the "Technical Specification for Lightweight Aggregate Concrete" (JGJ51-2002) gives provisions for lightweight aggregate concrete, there isn't clear reference for calculation and test methods of lightweight aggregate concrete of composite beam. In engineering practice, because lightweight aggregate concrete has some differences with ordinary concrete distinction on many technical aspects, technical personnel either directly adopts the calculating formula derived by the test of medium and low-intensity shale haydite concrete structure, or uses the calculating formula with reduction or amplification by experience, which has larger blindness and is lack of theoretical basis. At present, there isn't a complete calculation theory and design methods of steel-lightweight aggregate concrete composite beam, deeply research on steel-lightweight aggregate concrete composite girder bridge is very necessary.This paper combined the scientific development plan project of Jilin province"Experimental Study on steel-lightweight Aggregate Concrete Composite Girder"(20050531), carried out the following research work:1. The design method of lightweight aggregate concrete mix from the theory is explored. The mix design process is identified. The physical and mechanical properties of lightweight aggregate concrete are studied by tests. The impact factors of physical and mechanical properties of lightweight aggregate concrete are analyzed by using regression analysis and probability and statistics and other modern math means.2. Based on elasticity theory, the shear lag effect of steel - lightweight aggregate concrete composite beam flange plate under different loads conditions is analyzed using the energy variational method. In order to simplify the analysis process of steel - lightweight aggregate concrete, on the basis of deep analysis of national norms calculation method of effective width ,the analysis results of shear lag effect is expanded to form the calculation method of effective width of the steel-lightweight aggregate concrete flange plate based on the variational method.3. The non-linear analysis of steel - lightweight aggregate concrete composite beam with different flexible shear connectors has been carried on using finite element method. Based on nonlinear results, the effects of three flexible shear connectors, i.e. stud, channel steel and bent up bars, on the performance of steel-lightweight aggregate beam performance are evaluated. The impact law of the strength and connect degree coefficient of stud to the performance of steel - lightweight aggregate composite beams was identified.4. Two pre-stressed steel-lightweight aggregate concrete simply supported beams ware produced, which ware tested by applying a concentrated and symmetric bending load. The strain distribution along the beam of cross-medium and 1/4 cross section, the relationship between the deformation of control cross-section and load, the shear lag of concrete slab, the shear slip strain difference between the steel and concrete, the stress increment, as well as strand steel flange under the strain distribution near the loading point, etc were measured. composite beams by a series of acts of force. From the measurements, the load law of composite beam was analyzed, the actual load carrying capacity of prestressed steel-lightweight aggregate concrete composite beam, as well as loading characteristics at various loading stage ware studied.5. The energy theory method for calculating the deformation of steel -lightweight aggregate concrete composite beam was formed by taking account of the slip effect of composite beams and using energy principle. From another theoretical point of view, according to the force balance of micro-element body on the interface of composite beams, and considering the slip as well as the curvature relationship between interfaces of composite beams, a steel - lightweight aggregate concrete composite beam deformation numerical algorithm was formed.6. Based on the plasticity theory, the load carrying capacity calculation formula of steel-lightweight aggregate concrete composite beam has been set up. The theoretical values and experimental values were compared and analyzed. Based on the load carrying capacity calculation formula of steel-lightweight aggregate concrete composite beam, by numerical calculation methods, the effects of various design parameters on load carrying capacity of steel-lightweight aggregate concrete beams ware analyzed.