Seismic Responses And Control Measures Of Underground Large Scale Frame Structures

Underground large scale frame structures(ULSFS)have the large structural span between the two external walls and frame columns along two structural horizontal directions.With the development of economy,the 3-D expansion of underground space has become one of the important contents of modern urban planning.ULSFS have gradually become an important part of modern urban infrastructure in China.China is located in an earthquake-prone area,and the seismic safety of underground large space structures will be the main content of urban infrastructure earthquake resistances and disaster prevention projects.Underground large space structures,such as the ULSFS,are usually constructed in crowded and prosperous urban central areas.The damage of the ULSFS under earthquakes would cause immeasurable unfavorable effects on the life and property.Moreover,the underground structures are surrounded by the soil,which makes the restoration of the damaged underground structures more difficult than aboveground structures;the indirect economic and engineering costs are enormous.Therefore,it is very necessary to carry out relevant research works on the ULSFS.This paper focuses on the vibration effects and dynamic responses of the ULSFS under earthquakes.Based on significant vibration effects of the ULSFS,a new simplified Pushover analysis method is proposed.Furthermore,reasonable and applicable seismic control measures are developed for seismic responses and dangerous positions of the ULSFS.The main research contents and conclusions are as follows:(1)The dynamic responses of underground structures with different scales under earthquake are studied.The vibration effects of the ULSFS on the structure and the whole soil-structure system are analyzed quantitatively by the Dynamic Participation Factor.The effects of relative stiffness(between soil and structure)and the buried depth on the structural vibration effects are also discussed.The results show:the vibration of the ULSFS is obvious,which not only increases the deformation and internal forces of the structure itself but also enlarges the dynamic response of the whole soil-structure system;moreover,the vibration effects of the ULSFS would be more significant when the surrounding soil is soft and the buried depth is small.(2)The seismic response of the ULSFS under the near-fault ground motion with the long-period velocity pulse is studied.The laws of deformations and internal forces and dangerous positions of the structure are obtained.The influences of soil displacement and structural vibration effect on the ULSFS are evaluated by correlation coefficient.The typical near-fault ground motion is decomposed,and the influences of long-period velocity pulse and high frequency earthquake component on the ULSFS are compared.The results show:the internal force and deformation of bottom columns would increase gradually from outside to inside,and the top outer columns perform great reverse bending deformation and the bottom floor slab and bottom outside walls have significant tensile damages where the soil-structure interaction(SSI)is intense;moreover,the long-period velocity pulse in the near-fault ground motion tends to cause the mentioned law of bottom columns and the reverse bending of top columns,and the high-frequency earthquake component makes the outer linings vulnerable.(3)The seismic responses of underground structures with different structural scales under earthquakes with different incident angles are analyzed.To investigate the failure mechanism of the ULSFS under different input incidents earthquakes,the stress and strain of frame columns and the tensile damage of floor slabs and outer walls are studied.The results show:the SV wave is more likely to cause larger seismic responses of the ULSFS than the P wave;in the oblique seismic waves,the damage of the fragile internal slabs and frame beams would reduce the overall seismic performance of underground structures;under the combined asynchronous earthquake waves,the internal frame columns perform adverse reactions such as mutation and uneven distribution of internal forces.With the increase of incident angle of seismic wave,the maximum seismic response of the ULSFS will increase gradually.(4)A Pushover analysis method for the ULSFS is proposed.The applicability of the traditional Pushover method for underground structures with different structural scales is verified.The structural dynamic coefficient of the ULSFS relative to the structural vibration mode is obtained,and according to the acceleration of free-field,the new Pushover method considering structural vibration effects and site characteristics is proposed.Comparing results with dynamic time history analysis,the new Pushover method is applicable for the ULSFSs without and with structural joints and complex above-underground structures.The proposed Pushover method is proved to be reasonable,accurate and applicable for complex underground structures with different scales.(5)Based on the vulnerable positions and failure mechanism of the ULSFS,the seismic control measures are developed in view of the soil displacement and structural vibration effect.The results show:the separation seismic control measures proposed in this paper are aimed to reduce internal forces of dangerous positions in the ULSFS and improve the overall structural resistance performance;the seismic measures could significantly reduce the impact of soil displacement on the structure,and adverse effects of the structural vibration effects on the seismic response of ULSFS can be effectively controlled by the energy dissipation layer.