| Curved bridge with single column pier is widely used in highways and upright pivots because of its structural advantage and low cost. However, with the increasing numbers of overfreight and the complex mechanical behavior of substructure, there are many cases about cracks found in both superstructures and substructures of curved bridge with single column pier. This thesis deals with problems about mechanical behavior of curved bridge with single column pier, and mainly focuses on the design theory of substructure, the single column pier, through both the theoretical analysis and experimental analysis. And result could be found in ultimate strength analysis, reinforcement design method, cracking width calculation and so on, as follows:1) For the mechanical behavior of superstructure, the curved bridge, the longitudinal stress distribution in transverse direction of bridge is not symmetrical even in the symmetrical load case, and the shear lag effect in curved bridge is also not symmetrical. This is mainly because eccentrical load could lead to additional torsion as well as bending moment in curved bridge. Through the deliberately assigned support offset, the additional torque moment could be partly balanced by the torque moment produced by the support offset. Moreover, the overturn safety factor is studied considering the effect of beam-end reinforcement. Result shows that the support reaction distribution at beam end section becomes uniform when widening the diaphragm in beam end and installing additional support, increasing the overturn safety factor, but this reinforcement shows little improvement of mechanical behavior of curved bridge itself.2) By comparing different codes, the author believes that the Strut and Tie Model (STM) is the most suitable model in calculating the shear capability of the reinforced concrete cap beam. Moreover, a modified STM model based on Mohr-Coulomb’s failure criterion is proposed by considering contribution from the up steel bar, the stirrup and tensile strength of concrete for calculating the shear capability of the reinforced concrete cap beam. It describes the real behavior feature of cap beam in the failure stage. Compared with other theories, the effectiveness and applicability of the model used in different shear-span ratio is also discussed. As a result, it accords well with the results obtained by FEM.3) Based on the topology optimization, this thesis incorporates both the traditional SIMP method and SIMP based on nodal density, to obtain the rational STM model for single column piers under different shear-span ratio and different bearing-reaction ratio. The result shows a triangle truss-like shape STM when shear-span ratio λ<2. So a triangle truss-like STM model is suitable in analyzing single column pier with λ<2. Meanwhile this paper presents an optimized reinforcement design method in terms of the principle of minimum complementary potential energy which achieves the optimized rebar layout. A case study is presented, and the result shows good agreement with FEM analysis.4) Based on the design data of a typical cracking pier, seven large scaled reinforced concrete models are designed through orthogonal test design method by considering the experimental condition. Three factors are primary studied:shear-span ratio, ratio of reinforcement and types of reinforcement layout. The experiment result shows that typical failure begins when the shear crack develops from the support area and finally reaches the base of cantilever part, forms a failure plane. And shear-span ratio is the key factor for the ultimate strength of single column pier. Increasing reinforcement ratio could increase the ultimate strength in a certain range. When the reinforcement ratio reaches a certain level, continuing increasing reinforcement ratio may not lead to corresponding improvement of strength. Also the result shows a significant role of bentup bar in restricting shear crack development, but excessive bentup bar layout could lead to bending failure at the bending point of bentup bar because of the deficiency of tensile strength of Tie.5) Both ANSYS, based on smeared crack model, and ABAQUS, based on damaged plasticity model, are incorporated to numerically simulate the real experiment. The result shows that both models do well in simulating the actual loading process, but both models overestimate the stiffness of model with small shear-span ratio and model without bentup bar. ANSYS result shows a plastic strain zone near the base of cantilever part which causes the failure of whole structure. ABAQUS result shows good agreement with experiment, and the equivalent plastic strain distribution meets well with the real crack zone.6) This thesis compares the bending crack width calculated in different codes with the experimental bending crack width, and shows that the formula in JTJ267-98shows good aggrement with the experimental result. But when calculating nominal steel stress, author suggests using STM model by treating Tie as axial tension member, and also considering equivalent height modified coefficient of Tie. For calculating shear crack width, this thesis derives the formula for calculating shear crack width of single column pier based on basic theory of bending crack width calculation. Experimental datas are used for parameter fitting.7) A design and crack control guideline for bridge with single column pier is drawn up based on the research result above and relevant researches and codes, hoping to be useful for reference. |
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