The Research On The Rational Structural Forms Of The Semi-integral Abutment Jointless Bridge

Jointless bridge is one kind of bridges which using integral abutment, semi-integral abutment or continuous spans cancelling all the expansion devices. Hunan University research team had put forward one new form of integral abutment jointless bridge in1998. The bridge connects the approach slab and approach pavement with the main girder of the bridge. And the main mechanism of the bridge is using the cracks produced in the approach pavement to absorb the shrink deformation caused by the temperature effect of the main girder. In2008one new form of integral abutment jointless bridge had been put forward based on some improvement of the old integral abutment jointless bridge. The main difference between these two forms is one anchor beam has been added at the end of the approach pavement. Here the anchor beam is used to control the length of the approach pavement. After one year study, the basic performance of the integral abutment jointless bridge with anchor beam had been grasped. At the beginning of2009, a new bridge form named’integral abutment jointless bridge with pre-cut cracks’ has been put forward. And the main improvement of the bridge is the pre-cut cracks have been added in the approach pavement. Here the pre-cut cracks in the approach pavement are to control the development of the cracks along the approach pavement when the temperature of the main girder changes. After the cracks have been made in the approach pavement, the space of the cracks could be control in allowable value and also the tensile force between the approach pavement and the approach slab could be decreased. This paper mainly focuses on the theoretical and experimental research of these two new bridge forms. The main research results are shown as follows:1. In order to control the length of the approach pavement, the integral abutment jointless bridge with anchor beam had been put forward. The internal force and deformation calculation formula of the integral abutment jointless bridge had been deduced. The reinforcement calculation program of the reinforced approach pavement had been complied. The crack spaces and the crack widths had been calculated when all kinds of the experimental parameters had been inputted the program. High absorbing ability of the temperature deformation of the main girder had been approved by the temperature effect simulation experiment of the integral abutment jointless had been carried out in the lab. But also some drawbacks had been found, such as the crack spaces of the cracks in the approach pavement are too small to satisfy with the highway standard allowance. So the bridge form could not be used to absorb the big temperature change of the main girder. At the same time, the bigger displacement of anchor beam toward the end of main girder appeared when the bigger temperature change had been considered. So the design of anchor beam should be pay more attention to.2. In order to control the cracks development along the approach pavement, to reduce the tensile force between the approach slab and the approach pavement and to make the cracks transform from the frist one of the approach pavement to the last one of the approach pavement as well, a new bridge form named integral abutment jointless bridge with pre-cut cracks had been put forward. The cracks distribution pattern had been received through the temperature effect simulation experiment of the new bridge form in the lab. All the cracks widths are satisfied with the allowance of the highway specification. High crack load transfer capacity of the crack with the biggest crack width has been found through the theory analysis of the deflection value between the cracks. Small influence of the soil pressure at the end of abutment has been found when the temperature deformation had been considered, so the design and construction requirement of the abutment could be lower. Also high absorbing ability of the temperature deformation of the main girder had been found. In the end, the19m long approach pavement of the experimental model had been approved that it could be used to absorb the total length of90m and considering20degree temperature change of the integral abutment jointless bridge.3. The stresses calculation model and differential equation formula of force balance of the reinforced approach pavement had been established according to the linear constitutive bond-slip relationship between the reinforcement steel and the concrete. The calculation formula of crack width, the internal force and the deformation had been deduced. The calculation formula of crack width only considers the temperature change of the main girder also had been deduced. In order to get the crack width of the surface of the approach pavement, the surface crack width transform parameter was recommended in this paper. The construction items of the pre-cut cracks in the approach pavement which should be pay attention to had been put forward by combining with the pavement construction procedures.4. The performance of the reinforced approach pavement considered the temperature load, lane traffic load and embankment settlement at the end of the abutment had been studied. Also experiment model considered the temperature load, lane traffic load and embankment settlement at the end of the abutment had been simulated in the lab. The3D ANSYS software had been used to simulate the same situation. The whole stiffness of integral abutment jointless bridge was bigger than the non jointless bridge for the connection among the main girder of the bridge, the approach slab and the approach pavement. Big influence of the crack width had been found when considered the settlement at the end of the bridge abutment. In order to control the crack width, the settlement at the end of the abutment should be controlled strictly.5. The experimental and the theoretical analysis of the cycle temperature load experiment which added at the integral abutment jointless bridge experimental mode had found that the friction forces and the anchor forces are smaller with load cycle number increased. And big influence of the crack width at the pre-cut joints also had been found. So cycle temperature load should be taken into the crack width calculation theory of the integral abutment jointless bridge with pre-cut cracks. Also high anti-seismic ability of the jointless bridge had been found in the experiment.