Experimental Study And Theoretical Analysis Of Steel - Concrete Continuous Composite Beams

Compared with simply-supported composite beams, continuous composite beams have the advantages of large stiffness, high strength, large-span space. There are not only cross-section plastic strength reserve but also statically indeterminate structural plastic strength reserve. Although great achievements have obtained, the load-carrying mechanism of continuous composite beam with web openings has not been adequately investigated. Also, no guidelines for the design of continuous composite beams with web openings are provided in current codes. On the other hand, if we can fully grasp the characteristics of the beams, the losses caused by the reduction of stiffness and strength can be resolved, and holes can be made on the web of the beams, or even large holes. So as to achieve the purpose of reducing the story and saving a lot of funds for construction. In this paper, experimental study, Finite element and theoretical methods were used to analyzing the behavior of continuous composite beams with web openings. The main research contents and conclusions are concluded as follows:1. In order to investigate the mechanical performance and load-carrying capacity of continuous steel-concrete composite beams with web openings, Five continuous composite beams with web openings and one without web openings were tested. The test results show that web openings not only decrease the stiffness and ultimate load-carrying capacity but also give rise to the redistribution of shear force of steel beams and concrete slabs at the web opening region. The plane hypothesis is not satisfied to the web opening area. The failure mode is the shear failure of concrete slab in the region near the opening, the result also indicates that the shear bearing capacity at the span with web openings increases as the main factors for design. Additionally, by increasing the thickness and reinforcement ratio of a concrete slab, the ultimate load-carrying capacity and deformability of continuous composite beams increased, which can be used to the enhancement of web opening area.2. In order to investigate the mechanical performance of continuous steel-concrete composite beams with web openings, The behavior of plastic hinges and internal force redistribution in continuous composite beams are studied emphatically. The test results show that web openings decrease the stiffness and ultimate load-carrying capacity. The plane hypothesis is not satisfied to the web opening area. The failure process of five continuous composite beams is a shear force plastic hinge first formed and ultimately a kinematical mechanism generated in the region of the web opening. The continuous composite beams with web openings have already existed redistribution phenomenon compared to the composite beams without web openings in elastic stage. Additionally, The results indicate that there is not only moment redistribution but also shear redistribution between the concrete and steel components for continuous composite beams with web openings.3. The finite element package ANSYS was used in order to investigate their mechanical behavior and load-carrying capacity. The main points were the concrete slab thickness, reinforcement ratio,the opening size, the location of web openings, the opening eccentricity and multi-openings. The results show that with the increase of slab thickness and the reinforcement ratio, the load carrying capacity and the deformation capacity of beams with web openings increased, respectively. With the increase of the width and height of the hole, the load carrying capacity of the beams reduced and the deflection of web opening region increased accordingly.4. The finite element package ANSYS was used in order to investigate the internal force redistribution of continuous composite beams with web openings, the main parameters were the opening size and the location of web openings.The results show that there are not only plastic moment redistribution, but also moment redistribution caused by opening. With the increase of slab thickness, the moment modulation of beams decreased. On the contrary, with the increase of reinforcement ratio, the moment modulation of beams increased. With the increase of the width and height of the opening, the moment modulation of composite beams increased,accordingly. In addition, the results also indicated that the location of openings have a significant impact on the load carrying capacity and moment redistribution of continuous composite beams.5. Several reinforcing methods are introduced and mechanical properties are compared with FEM results in different reinforced continuous composite beam.The result indicates that the bending and vertical shear capacity of continuous composite beam with web opening can be effectively enhanced to a certain extent. In addition, stiffness and local stability at web opening area are also increase. Effective reinforcing method is presented and can be used in engineering practice.6. The development and application of the plastic design method was introduced first, and then the calculation of ultimate bearing capacity of dangerous section of composite beams was briefly introduced. For composite beam which has a mode of shear failure (plastic hinges were formed in the four corners of the web opening), four secondary moment functions at hogging moment area of the web opening were derived, which provide a theoretical reference to the design of composite beam with web openings.