| Whether in the structure and construction method, or in the mechanical behavior, the self-anchored suspension bridge has significant differences with the ground-anchored suspension bridge. It has the advantages of novel structure, reasonable stress and beautiful landscape, the advantages of the self-anchored suspension bridge can be protruded in the soft soil foundation and the gully area, so it is very competitive in the large span bridge selecting. At present, researches on the mechanical performance of self-anchored suspension bridge are still inadequate at home and abroad, related research results are very small. Thus, take the main bridge of Songhuajiang Bridge in Harbin third-ring west section as practical engineering background, relied on Harbin construction system key science and technology project "Experimental Study on the Structure Performance and the Full-bridge Model of Self-anchored Suspension Bridge with Steel-concrete Composite Beam"(201107), carried on research on the static and dynamic properties of the massive structure based on model test.The fatigue performance of steel bridge welded joint at low temperature is an important branch of mechanics research field. The "Railway Steel Bridge Manufacturing Specification"(TB10212-2009) which is widely used for bridge construction in our country specifies that we must stop welding operation when the temperature is less than5degrees centigrade. The welding researches which aim to break the lower limit of that temperature have shown that the conventional mechanical properties of low temperature welding seam can meet the specification requirements if adopt reasonable welding process and manufacturing specifications. In the study on the durability of the welding structure, the study on the local fatigue property of welding seam at low temperature is extremely rare in the literatures. The research object of this thesis is the first self-anchored suspension bridge in the high latitude cold area, the fatigue properties of the bridge welding seam at low temperature have no precedents to imitate. In order to ensure the safe use of low temperature welding joints, relied on Harbin construction system key science and technology project "Experimental Study on the Fatigue Performance of Welded Structure of Bridge under Low Temperature in winter"(201106), carried out test study on the fatigue properties of weldment at the-5degrees centigrade.The main research contents are as follows:Firstly, we carried out bridge1:50reduced scale model design research. The model static similar relation is on the principle of equal stiffness, take equation analysis to deduce the similar indexes between test model and structure prototype in multiphase medium conditions. Established the power triangular matrix of criterion factors based on the dimension harmony principle in quality system, and obtained dynamic similarity criterion between test model and structural prototype. Designed and manufactured the bridge model according to the similarity analysis the results.According to the FEM analysis, formulated static test conditions and loading scheme of test model. The static test had focused on the stress and deformation characteristics of bridge, at the same time, take the checking method between calculated test value and real bridge theoretical calculated value to confirm the rationality test model design. Finished bridge dead load test results showed that:the axial force make the stress distributed unequally in the stiffening girder under the action of single bending moment, the stress change to full span pressure uniformly distributed under the action of bending moment and axial force coupling effects, this illustrates the axial force has a favorable impact on the stiffening girder; under the most unfavorable loading condition, the measured displacement and deformation characteristics of the main beam have agreement with calculated values of the finite displacement theory, the load verification coefficient is between0.88to1.15, the roof and floor stress of the composite beam are less than the material allowable stress, the girder has large safety reserve; the measured values of unloading residual deformation and residual strain are close to zero, demonstrate that the main girder is in a good elastic working condition when the self-anchored suspension bridge is under the action of finished bridge loading; based on the evaluation and analysis of key component under the test working condition, the safety coefficient of main cables and suspender of the bridge are respectively2.81and3.75, the rigidity of girder is7/10000, all satisfy the code requirement, the structure has enough safety storage.In the dynamic test, employed the ambient excitation method supplemented by attenuation vibration test technique and the stochastic subspace method supplemented by parameter identification technique successfully obtained the first six order frequency of self-anchored suspension bridge test model. The results showed that:in the larger frequency range, the main vibration mode distributes clearly; the tested first-order vibration mode is stiffening girder first-order antisymmetric longitudinal floating accompanying with bridge pylon bending, that coincide with the longitudinal semi-floating system characteristic self-anchored suspension bridge, in the first six order vibration mode besides the first-order, the lateral vibration mode occur in the forth-order and fifth-order, indicate that the main span of the bridge has sufficient lateral stiffness, the other vibration modes are vertical vibrating, and the main express form of the first-order vertical vibration is the bending of the main span, reflect that the main span of long-span composite beams self-anchored suspension bridge has relatively soft characteristics.In dynamic frequency testing, due to the reduced scales ratio of model is smaller, there is a larger error between experimental values and theoretical values, employed large bridge reduced scale model test for the first time, adopted the finite element model updating technology base on the response surface method, obtained the finite element dynamic updating model which coincides with the true state of structure. Selected a second degree polynomial as the mathematical model of response surface function, based on the significance analysis of corrected parameters and the central composite experiment design, employed the least squares method to fit the sample space data of experimental design, obtained explicit function expressions for response surface of self-anchored suspension bridge with the iterative standard of achieving target, and intuitively provided the spatial curved surface model of typical responses. R2and root mean square error model verifying results showed that:the dynamic updating finite element model based on the response surface methodology is accurate and reliable; besides the lateral second-order frequency, the peak value errors of each order frequency are significantly cut down after updating, the updating results are well, and the measured errors of the fundamental frequency is only0.96%. The updated finite element model can be used as the reference model of the structure further analysis.Combined with the real bridge welding station, designed two sets equal thickness butt welding sample and two sets cross butt welding sample at-5degrees centigrade, meanwhile, designed corresponding compared sets sample at normal temperature, S-N fatigue curves and fatigue cracking characteristics results show that:after polished process, the butt weld experimental data at-5degrees centigrade is almost as same as equal thickness butt weld experimental data at ambient temperature; the standard deviation of data regression reflects that sample’s fatigue strength of relatively easy flat weld is superior to erect weld, and the sample’s fatigue data discreteness of flat weld is better than erect weld; the polished processing can significantly improve fatigue strength of weld joint; to the equal thickness butt weld joint at low temperature, preheating before weld, slow cooling after weld and choosing reasonable weld process at the-5degrees centigrade have no obvious effect on fatigue strength; to the complex structure as different thickness cross butt weld, the fatigue data discreteness is large, the fatigue strength is unstable and the fatigue strength after regression less than the standard limit, it is not recommended carrying out weld processing at-5degrees centigrade. |
PDF Full Text Request