Most Dangerous Internal Forces Of Seismic Structures With Viscous Dampers

Fluid viscous dampers as a kind of velocity-dependent energy dissipation devices, provide no damping force to the structure at maximum drift of the building and provides maximum damping force at maximum velocity and zero drift. This 90 o phase difference between the damping force and the story drift is an advantage of viscous dampers others among. But at the same time because of the 90 o phase difference, it becomes difficult to determine when the structure is most dangerous during the earthquake. This paper works on this problem and the main contents are as follows:(1)The method calculating the maxmum axis force of the column that connects to the viscous damper is presented. The procedure in FEMA273, the method proposed here and the method that adds the damping force directly are compared. The analysis of the axis force of the column of the linear single-degree of freedom(SDOF) system undergoing harmonic motion at the frequency of the structure and under earthquake show that, during harmonic motion, the proposed method provides the exact solution, and the result of FEMA273 is close to the proposed method; under earthquake input, both methods underestimate the axis force; the method that adds the damping force directly overestimates the axis force in all cases.(2)The characteristics of absolute acceleration response spectrum(AARS) and pseudo acceleration response spectrum(PARS) are studied. The relationship between AARS and PARS is obtained through analysis of harmonic motion. According to this relationship, the AARS of national seismic code of China is transformed to PARS. The accuracy of the PARS is investigated through spectrum analysis of earthquake records.(3)Considering characteristics of the force of columns of viscous damped structures, four kinds of combinations of axis force and bending moment are consided for the section design of the columns. The areas of steel bars of RC columns with the four combinations are compared in different conditions. The results show that the combination at the maximum drift gives the most accurate solution. (4)The methods to get the most dangerous forces is validated by a 3-story reinforced concrete structure. The result shows that the accuracy of the methods comply with the previous studies.