Dynamic Responses Of Beam Bridges And Cable-stayed Bridges Under Vehicular Loads

The vibration of bridge structures and vehicles can be easily induced when the vehicles travel across the bridges. The dynamic responses of the bridge structures induced by the moving vehicle loads are generally larger than those induced by the static vehicle loads. In the bridge design codes, the dynamic responses are generally been considered as a factor named as Impact Factor. Due to the impact factors are different with the different bridge structures; it should be significant to obtain the accurate responses of the bridge structures induced by the moving vehicle loads for evaluating loading-response of these structures.The dissertation is the part of the two projects:one is supported by Hubei Province Communications Department, and which name is "the design methodology and construction technology of the High-pier Long-span Continuous Concrete Rigid Bridge"; the other is supported by Ministry of Transport of the People's Republic of China, and which name is " The Research on the Key Technology of Jingyue Yangtze River Bridge". The main contents and results of this dissertation are shown as follows:(1) Based on the studies of the bridge-vehicle coupled system, the differential equations of motion for different degree-of-freedoms (DOFs) vehicle models were obtained. Using the methodology of solving the non-stationary vibration, the non-stationary road surface inputs of the four tires were simulated. Based on the numerical simulations, the following conclusions can be drawn:the non-stationary road surface inputs may increase with the vehicle speeds increase; it can be obtained the more rational responses using the non-stationary road surface inputs.(2) A single-span beam was given as an example for creating the differential equations of motion of the vehicle-bridge coupled system. The program solving the equations was established by the software Matlab and was verified by comparing the simulations and the others studies. The effects of the non-stationary inputs, stationary inputs, concrete pavement, and asphalt pavement on the responses of the beam induced by the moving vehicle loads. Numerical results indicate that:the effects of non-stationary inputs and stationary inputs on the impact factors are different, the amplitudes of non-stationary random responses of the wheels increase as the vehicle velocity increases; factors including the road surface, vehicle initial speed (10m/s), and acceleration (5m/s2) are the same, the impact factor corresponding to the concrete pavement is aboutl.35 times of that to the asphalt pavement.(3) A continuous beam was given as an example for studying the dynamic responses of the damaged beams under the moving vehicle loads. Numerical results indicate that:the frequencies may change with the different crack categories, and using vibration behaviors corresponding to the open crack zone to interpret those of the breathing crack zone may lead to the incorrect conclusion. factors such as crack categories, crack factors, vehicle frequencies and the number of the vehicles can change the frequencies of vehicle-bridge coupled system; the impact factor generally increase with the presence of the open crack zones or breathing crack zones.(4) A high-pier continuous beam bridge, named Luping Bridge, was used to test the responses for different situations of testing loads. A road roughness measured device, named LXPL-1 Highway Continuous Roughness Device, was used to test the bridge road roughness. The vertical and lateral vibration frequencies were performed using the ambient vibration method. Based on the responses corresponding to static loads and vibration frequencies, the numerical model of the bridge was updated using the response surface method. It can be seen from the results of the measurement and numerical model process that the vertical and lateral vibration models can be tested using the ambient vibration method and the identification peak method. The lateral vibration can be easily induced due to the first two natural frequencies are lateral direction. The response surface method can be used to update the structural numerical model.(5) To study the effect of patch contact on the vibration of the vehicle-bridge coupled system, a new vehicle-bridge coupled numerical model was established. The comparison of the effects of the two inputs (point contact and patch contact) on the mid-span deflection and the impact factors were compared with different parameters including the coefficient of surface roughness, vehicle acceleration, and vehicle braking. The numerical results show that:If the road surface classification is zero-roughness, the patch contact can be simplified as the point contact; If the road surface classification ranges from the Good to Poor, the difference of the effect of the patch contact and point contact on the mid-span deflections increases as the road roughness classification increases; treating the contact condition between the tire and road surface as a point contact may overestimate the dynamic deflection of the bridge; when studying the faulting condition effect where the simulation using the point contact may result in significant errors. For example, the simulated solution corresponding to the patch contact is the 1.3times of the test solution; however, the simulated solution corresponding to the point contact is the 1.06times of the test solution.(6) To study the lateral vibration of the high-pier continuous bridge structures, a new vehicle-bridge coupled numerical model considered the lateral degree-of-freedoms (DOFs) was established. The comparisons of the theoretical simulations and field measurements show that the proposed method can be applied to study the bridge lateral vibration induced by moving vehicles with good accuracy. For the studied bridge, the passengers may feel a little uncomfortable, and both lateral and longitudinal vibrations of the high-pier bridge can significantly affect the drive comforts and can bring up safety concerns from the passengers. The lateral displacement does generally increase with the increase of vehicle speeds; the displacement reaches a peak at the speed of 110km/h.(7) A long-span cable-stayed bridge named Jingyue Yangtze River Bridge was given as an example for studying the vibration responses and impact factors using the statistical methodology. Numerical results indicate that:the 15 samples of the road surface inputs is enough to calculate the vertical displacement, however, the number of the samples equals 25 for calculating the lateral displacement. If the vehicle travels about at 900m, the vertical displacement may reaches a peak and equals 32.7mm; however, the lateral displacement may reaches a peak and equals 7.34mm when the vehicle moves at 715m. Based on the specifications, the impact factor equals 0.05. However, numerical results indicate:in the situation that the vehicle moves less than 10m/s, the impact factor of displacement where location at both at the mid-span and 1/4span may be less than 0.05; but for the other situations, the impact factor may be more than 0.05, therefore, the impact factor calculated follow from the code may be more conservative.