Research On The Ultimate Bearing-capacity And Dynamic Response Of The Cooperated System Incorporating The Concrete Cable-stayed Bridge And The T-framed Structure

Jinma Bridge, as a result of successful design and construction, draws a significant attention from the bridge industry.It features an innovative structural system incorporating a large-span concrete cable-stayed main structure cooperative with its adjacent rigid-framed spans. As the longest of single-tower concrete cable-stayed bridge in the world nowadays, Jinma Bridge presents a unique bridge structure adopting a cooperative system including a cable-stayed and a rigid T-frame structure.It significantly saves the amount of deep water foundation, reduces the overall cost, and improves the ease of traffic and the resistance to crashing. The efficient design of this bridge results in a saving of up to one hundred million RMB compared to other design alternatives.The available references, however, do not allow for a deep understanding with respect to the structural behavior analysis of this type of unique structure, not even mentioning a developed research on its ultimate bearing capacity random vibration dynamic characteristic analysis and the seismic reactions.This dissertation presents a detailed research on all mechanical behaviors of the cooperative system.The primary work is summarized as follows:(1) This paper summarizes the design technology in Jinma Bridge using the large-span concrete cable-stayed main structure cooperative with the rigid-framed system.It focuses on the detailed finite-element analysis on the tendon strengthening techniques in the main tower as well as the staged post-tensioning technology in the transverse diaphragms.Through the comparison with the light-elastic experiments, it is believed that this innovative technology can provide guidance for the design and construction of similar projects.(2) This dissertation in order to ananlyze the ultimate bearing capacity of cooperated system with concrete cable-stayed bridge and T-shape rigid structure the reduced stiffness method for 2D beam element considering the nonlinearity of material is given , Furthermore, an equation has been derived to calculate the concrete creep in a format of force method.This dissertation proposes a refined method which is incorporated into a finite element program to precisely account for the concrete creep.Then, through analysis of ultimate bearing capacity of jinma bridges,prove that the influence of the ratio of reinforcement of stiffening girder, the safety coefficients of cable, and the concrete shrinkage and creep on the ultimate bearing capacity is not significant.attention should be paid to selection of the safety coefficient of the cable,furthermore it is found that for the condition of loading on the entire bridge and half bridge, the safety coefficients of ultimate bearing capacity of jinma bridges are respectively 21.40 and 9.67,proved the ultimatebearing capacity of jinma bridge is very fine.(3) According to the generalized variation principle in the large deformation nonlinear elastic theory, this dissertation takes into account the coupling effect of axial and flexural action, shear strain energy as well as the torsional strain energy in the stiffening girder.It establishes the large deformation incomplete generalized potential energy function of space coupling free vibration in a cooperative system incorporating the single-tower concrete cable-stayed main bridge and a T-framed structure.Through the constraint variation, fundamental differential equations are derived for the main bridge accounting for the vertically flexural vibration, the laterally flexural vibration, and the longitudinal vibration.Also presented are the equations for the main tower with respect to the longitudinal and lateral vibrations.By considering the most complicated vertical vibration equation in the main girder, this dissertation sets up the unique boundary conditions from the T-framed structures in the cooperative system, which further derives the vibration frequency differential equation of the system.lt takes an example of the Jinma Bridge and results in the analytical solutions of the free frequency in the vertical vibration equation by the means of nonlinear approach.The results are compared with the numerical solutions and ends up with a significant match, which provides a reliable theory basis to analyze the natural vibration characteristics of similar cooperative structure types.(4) The dynamic characteristics of the cooperative system mainly consist of its natural vibration frequency and principal mode, which are the basis and precondition of its dynamic analysis.This dissertation presents Jinma Bridge as an example, performs the dynamic characteristic analysis of the innovative cooperative system, and gives the first 20 frequencies and corresponding vibration modes by the use of the space finite element models.Through the comparative study of cable-stayed bridges with similar span level as well as the characteristic analysis of the most advanced shear hinge design scheme, this dissertation proves that Jinma Bridge features the advantageous dynamic characteristics.In addition, it investigates the impact of various structural parameters on the dynamic behavior of the cooperative structure and presents the detailed discussion and analysis.The numerical results offer a theoretical basis for the natural vibration analysis and the anti-seismic design of the cooperative system.(5) By the use of four groups of artificial seismic waves, this dissertation accounts for the impact of non-linearity of the structure and the wave passage effect.lt presents a detailed study of the seismic response of concrete cable-stayed bridge and T-frame cooperative system in terms of the vertical, longitudinal, and lateral seismic excitation.lt also presents the comparative analysis including the multiple-support linear uniform,nonlinear uniform and wave passage effect excitation, and the response time histories of internal force and displacement of critical sections in the main beam, tower, and the side pier.The effect regulation is discussed in details.(6) By the use of the pseudo excitation method (PEM) and the HPD (High Precision Direct integration) method, This dissertation analyzes the random seismic response of the cooperative system under the P-wave, SH-wave and SV-wave.It is special considered that multiple-point non-uniform excitation (spatial effect); non-stationary excitation, quasi-static displacement and damping ratio effect can impact on the peak response of the internal force of structure.The dissertation proposes an effective model allowing significantly reducing the amount of computation and improving the calculation efficiency of the simple-bearing cooperative system.lt takes the Jinma Bridge as an example and gives a detailed discussion on various excitation parameters on the seismic response principle of the cooperative system used in Jinma Bridge. The results provide valuable references for the research on the random response of similar bridges.