| Fabricated structures and composite structures are two major trends in the development of bridges.Based on the basic research project of the Ministry of Transportation "Research on the Basic Construction Theory of Super-Span Steel TrussConcrete Composite Continuous Rigid Frame Bridge"(No.2013 319 814 040),this paper explores a fully prefabricated steel truss-concrete composite(ab.PSTC)continuous rigid frame bridge,which needs no cast-in-situ concrete construction.The specific construction,the structural performance and the calculating method of the steel truss-concrete composite structure under negative bending moment are systematically studied by experiment and theoretical analysis.The main research work and achievements are as follows.1)Considering the problems of later stage cracking and heavy weight of concrete continuous rigid frame bridge,this paper explores a fully prefabricated steel trussconcrete composite continuous rigid frame bridge,which is formed as follows: firstly install the prefabricated concrete slabs,then prestress the longitudinal high strength steel strands through the slabs and then consolidate the slabs,finally connect the slabs and the steel truss beam.The general layout and the key construction of PSTC continuous rigid frame bridge are studied,and the construction procedures and methods are preliminarily constructed.It provides a feasible way for the continuous rigid frame bridge to be constructed with larger span,better quality,higher efficiency and environmental protection.2)The prefabricated composite shear studs(ab.PCSS)are improved,in which the vertical steel plates with horizontal shear studs are embedded in the concrete slab,and then welded with the top slab of the steel beam.The push-out tests of 32 PCSS small specimens and 2 PCSS large components are carried out,and the shear transfer mechanism of PCSS shear connectors is studied.Based on the parametric FEM analysis of PSTC beam,the distribution characteristics of PCSS are revealed under the influence of structural discontinuity caused by the cracking of the slab seams.Based on the bond-slip theory and the characteristics of the discontinuous crack between the seams,a method for calculating the PCSS' slip and load distribution is established for the whole process.3)Three assembling steel truss-concrete composite test beams with three prestressing degrees and two arrangements of shear studs were designed and manufactured.Experimental study on load performance under two loads and negative bending moment is carried out.The elastic restoring capacity,cracking load and cracking development of PSTC beams under static cyclic loading with different upper bound loads are investigated.The strain,displacement and slippage of the joints between steel truss girder and concrete are tested,and the effects of prestress and precast concrete slab joints on cracking load and crack width are analyzed and coMPared.The load-slip laws of PCSS shear studs in PSTC beams are studied,and the influence of the shear studs arrangement direction on load-slip characteristics is coMPared.The feasibility of construction and the controllability and designability of load-bearing performance of PSTC beams are demonstrated by experiments.4)The strain history of PSTC beam from the construction to the cracking limit state of the steel truss beam and the concrete roof is analyzed,the formula for calculating the section strain of PSTC composite beam with cracking effect is established,and the formula for calculating the cracking moment of PSTC composite beams with slip effect is deduced under two loading conditions.The crack development characteristics of PSTC beams at various loading stages are analyzed,the influence of concrete roof cracks on the change of neutral axis and curvature of composite beams is studied,and the formula for calculating the crack width of the concrete slab in the PSTC beam considering the influence of the cracks between plates and the cracks in the plates is established.Three main failure modes of PSTC beam under negative bending moment are analyzed,the corresponding formula for calculating ultimate bearing capacity is established according to the internal force balance condition.Considering the lack of shear connection,the calculation method of ultimate bearing capacity considering the influence of PCSS shear bond slipping is discussed.5)Based on the ABAQUS finite element program,the finite element modeling method of PSTC beam fining is explored.The mechanical behavior of PSTC1 test beam during construction and loading to failure is simulated and analyzed,and the occurrence and development of cracks in PSTC beam and slab are simulated effectively by introducing concrete damage constitutive model.Considering the simulation analysis of long-span PSTC composite continuous rigid frame bridge,the whole process nonlinear modeling method based on MIDAS-Pushover is discussed.Based on this,the nonlinear whole-process mechanical behavior of PSTC2 test beam is analyzed,and the mechanical behavior of composite beam from construction to loading to failure is simulated.The analysis results are in good agreement with the test results.6)The design and research work of fully assembled steel truss concrete composite continuous rigid frame bridge are carried out for the Qingqiyong Bridge of Guangzhou-Foshan-Zhaoqing Expressway.Using the modeling method proposed in this paper,the whole process of construction,operation and failure of the bridge is simulated and analyzed.Based on the formulas for calculating the crack resistance moment,the crack width and the bearing capacity proposed in this paper,the resisting ability of the bridge to the negative bending moment at the top of the pier under normal and overloaded service is checked.The key structural details of the bridge are studied and improved,and the main construction process and its reasonability are proved.Practice shows that a 152 m long and 16.8 m wide continuous rigid frame main bridge has been built in only 25 days from the beginning of hoisting steel truss girder to the completion of the main structure of the bridge,which fully reflects the advantages of high efficiency in "fully prefabricated". |
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