Analysis And Experimental Investigation Of Cracking And Slipping Behaviour Of Accelerated Constructed Steel-Concrete Composite Small Box Girder

Bridge construction in the form of steel-concrete composite beams is among the most efficient methods to construct highway bridges.With the development of urbanization and the rapid progress of civil engineering,the problem of urban congestion has become increasingly prominent.Therefore,it is necessary to improve the construction of urban transportation infrastructure methods and expand urban expressway networks.In order to build,replace,and repair a bridge,or a series of bridges,in areas with heavy traffic,traditional construction methods are usually used in current engineering projects.These methods generally include field activities,such as the installation of supports,formwork,binding of reinforcement bars,pouring and curing of concrete,etc.These onsite construction activities not only consume a great deal of time but also lead to traffic congestion,which weakens the safety and efficiency of the traffic network.On the other hand,due to the constraints of the construction site and climatic conditions,the components of onsite construction are prone to quality problems,which may potentially affect the durability of the structure.Accelerated bridge construction(ABC)is a promising approach to reduce the impact of construction on traffic,improve the quality of materials and durability of products,and minimize the construction time.A combination of steel beams and a concrete deck with shear connectors,known as steel-concrete composite beams,are widely used in the ABC approach.The composite beam usually consists of a steel section jointly acting with one(or two)flange(s)made of reinforced concrete that is mainly subjected to bending.These two materials are interconnected by means of mechanical shear connectors.The concrete bridge slab of the composite beam is reserved with a connection hole to connect steel beams and shear studs,and post pouring concrete is used to realize the shear connection of these two materials.Therefore,a composite beam,even with small steel sections,has high stiffness and carries heavy loads on long spans.However,by increasing the load intensity,additional issues such as slip and deflection occur along the beam,which will affect the performance of steel beams and concrete.Based on this,this research has carried our relevant experimental research and numerical simulation analysis of simply supported and continuous steel-concrete composite beam structure with ABC technology.The main work and some valuable conclusions are as follows:(1)In this research,the key technical problems of the accelerated construction of the high-performance steel-concrete composite small box-girder bridge is elaborated.Generally,the concrete grade is below C50 in traditional construction,while high-performance concrete with a grade higher than C60 is used in the ABC process.Therefore,due to the high mechanical strength and durability,high-performance concrete in the composite beam receives much attention.(2)To simulate the accelerated construction of high-performance steel-concrete composite small box girder,three models with 4.2m span of simply supported and two models with 6.3m span of continuous high-performance steel-concrete composite small box girder were designed and fabricated Based on the experimental study,the influence of the spacing,quantity of the different group stud and the geometric size of welding stud on the mechanical behavior is obtained.(3)The numerical model of simply supported as well as the continuous beam were established in the ABAQUS software.The main objective is to develop a convenient and reliable analysis method by a finite element test model that can accurately predict load-deflection curve,ultimate bearing capacity and shear connection of simply supported and continuous steel-concrete composite beams.The development of the finite element analysis model of the steel-concrete composite small box girder and some key issues are described in detail.(4)A semi-empirical model was proposed to predict the size of cracks in terms of small box girder deflection and intensity of load applied to the structure.To this end,an experimentally tested model under different caseloads was used to create a dataset of the box girder response in terms of beam deflection and crack width.The obtained dataset was then utilized to develop a simplified formula providing the maximum width of cracks.The results showed that the cracks initiated in the hogging moment region when the load exceeded 80 kN.Additionally,it was observed that the maximum cracked zone occurred in the center of the beam due to the maximum negative moment.Moreover,the crack width of the box girder at different loading cases were compared with the test results obtained from the literature.A good agreement has been found between the proposed model and experiment results.(5)This research also investigated the influencing behavior of group studs in simply supported and continuous box girders.To this end,three sets of simply supported steel-concrete composite small box girders and two continuous steel-concrete composite small box girders were made with different groups of shear studs,and the slip generated along the beams was recorded under different caseloads.On this basis,the estimation of slip on simply supported high-performance steel-concrete composite small box girder and two spans continuous small box girder was put forward respectively for the simplified formula.The results show that the slip value of the test beam is inversely proportional to the degree of shear connection.The slip of Simply Supported Prefabricated Beam-3(SPB3)is 1.247 times more than Simply Supported Prefabricated Beam-1(SPB1),and 2.023 times more than Simply Supported Prefabricated Beam-2(SPB2).Also,the slip value of Experimental Continuous Beam-1(ECB1)is 1.952 times more than Experimental Continuous Beam-2(ECB2).The higher the degree of shear connection,the smaller the maximum slip value.