Research On Seismic Hybrid Testing Method Of Multi-span Bridge Based On MTS-NETSLAB System

Hybrid testing is an advanced testing method originated from substructure pseudo-dynamic testing, which integrates physical testing and numerical simulation. It can carry out a precise analysis similar to FEM, and can establish a strong functional networked collaborative hybrid testing method based on internet. This method is the hot topic in international academic circles of civil engineering, and several research institutions at home and abroad have carried out basic research.Based on the experimental resources and numerical resources of the present laboratories, the basic theory of hybrid testing method and it's applications in RC multi-span bridge are researched, the main research contents are described as following:1. Comparied with traditional subsructure pseudo-dynamic testing method, the greatest advantage of hybrid testing is that several nonlinear experimental elements are integrated, which can carry out integral analysis not component analysis. Several distributed laboratories are connected and carried out the large-scall even full-scall test cooperatively based on internet, then the more complex tests can be carried out collaboratively.2. Aiming at MTS structural testing system used in civil engineering widely, based on the hardware of FlexTest GT control box and software of MTS 793, an internal command control method for hybrid testing is put forward. VB_COM program is used to control the input and output, and then the control of GT is implemented. Three programs that named Monitor Station program, SinCycle Test program and RampControl Test program are developed respectively. The RampControl Test program is embed in NetSLab-Tester, and the connection between MTS and NetSLab is established based on a master-slaver network. A verification test with a cantilever steel column is carried out, and the testing results show that the connection is simplified and the speed is improved. The internal command control provides a new method for hybrid testing, but needs high requirement of hardware and software, and the system PC can be protected effectively by master-slaver network.3. Aiming at a column experimental element in hybrid testing of multi-span bridge, four reinforced concrete short columns are designed, and FRP strengthening calculation based on M. J. N. Priestley shear bearing capacity model are carried out. The mechanical properties testing of different materials are tested. The finite element simulation of unstrengthening and strengthening short column based on ANSYS and OpenSees are researched and nonlinear analysis of monotonic loading, quasi-static loading and seismic loading are carried out for investigating the specimens's mechanical properties beforehand. The numerical results show that the main effect of FRP strengthening is improving ductility not bearing capacity.4. The seismic quasi-static testing of unstrengthening and strengthening short columns are carried out respectively. The testing results show that the stiffness of FRP strengthening short columns has little improvement under small displacement. The primary function of FRP strengthening is increasing ductility and making the failure from shearing mode to bending mode.The numerical integral algorithms and loading control methods of hybrid testing are researched. An accumulated central difference method and Newmark combined algorithms, an external displacement loading control method under limit value protecting are researched, and a continuous ramp approach loading technique is implemented. Take a mulati-span bridge model structure for example, a CFRP strengthening short column is setted an experimental element, a verified hybrid testing is carried out at the stage of elastic behavior, plastic partial damage and post partial damage. The results show that a suitable diaplacemnet limit value and delay time are the effective means for satisfing the loading precision and decreasing the time. The specimen has stable 2nd order degradation stiffness at the range of some displacement, and the stiffness falls to be 1/3 of the initial value, which has consistence with the results from quasi-static testing. This work further provides a reference for settting of numerical elements in networked collaborative hybrid testing.5. In order to adapt the SDOF networked hybrid testing system, two simplified seismic testing scheme of multi-span bridge are designed. The networked environment test of NetSlab is carried out, the test results show that the proportion of communication time in the total testing time was very small, and the hybrid testing demand could be satisfied basically. Based on the simplified model of Santa Monica prototype bridge, associating with three universities, the hybrid testing of four spans three columns bridge structure in the action of small earthquake, medium earthquake and large earthquake is carried out based on domestic networked. Based on the simplified model of Russion River prototype bridge, associating with four universities, the hybrid testing of six spans five columns bridge structure in the action of small earthquake, medium earthquake, large earthquake is carried out based on international network. The networked environment and elapsed time are analyzed in detail, corresponding improvement measures are proposed. The analysis results show that the most testing time is spended on approach loading and waitting for stability of actuator, and the slow hybrid testing demand could be satisfied basically by the present network environment.6. The above two multi-span bridge hybrid testing are the first demonstrative multiple sites collaborative testing domestic, which can be extended as a standardization test platform. The testing results show that the networked collaborative hybrid testing method realizes the equipment sharing and provides a reference for seismic testing of complex bridge structure.