Study On Seismic Behavior Of Linked Column Steel Braced Frame With Spring Column Base

Linked column steel braced frame with spring column base is a new type of replaceable component structural system.A spring is set at the foot of the linked column,which is equivalent to releasing part of the constraint.Under the action of frequent earthquake and basic earthquake intensity,the foot of linked column can move upward,and the two ends of the link beam are staggered.The link beams enter the seismic energy dissipation stage preferentially,while the main frame members remain elastic state or rarely reach the yield state.After the earthquake,only replacing the link beam can quickly restore the structure's function,and will not have an obvious impact on the lateral stiffness,bearing capacity and ductility of the structure.Under the action of rare earthquake,the lifting height of foot reaches the limit,which improves the bearing capacity of the structure.Since the foot of the column can move upward and link beam enters plastic state,the dynamic response of the structure is reduced and the direct collapse of the building structure can be avoided.In order to study the seismic performance of the linked column steel braced structure,the following work is mainly done in this paper.(1)A three-story single-span and two-story single-span linked column steel braced frame with spring base were designed and fabricated for low-cycle reciprocating loading experiments.The link beams were replaced on each experiment.The results show that it is an ideal component replaceable structure system.Under the earthquake action,one foot of linked columns moves upward,and the foot of the other side functions as a hinge.The structure saways and the energy consumption of link beams developes fully.Before vertex displacement ratio is up to 1.5%,the main structure maintains its elastic state basically.The replacement of link beams has little effect on the bearing capacity,stiffness and ductility of the structure,achieving the goal of quick recovery of structural functions.Different cross-section forms of link beams have great influence on the seismic performance of the whole structure.The seismic performance of link beams with web stiffeners is better than that of link beams with openings.It is more reasonable to design bolt holes on the column base according to short slots,which can help column base avoid being stuck by bolt shank.It is unreasonable to design the lifting height of column base according to the rotational capacity of link beam.(2)The process of establishing test model by finite element software ABAQUS is introduced in detail.The column spring is simulated by non-linear spring element,and the beam and column are simulated by solid or shell elements.Comparing the calculation results of the model with expermients,the refined model and the experimental results are well fitted,verifying the rationality and feasibility of the model establishing method.Based on the bottom shear method,the influence of different seismic intensity and the aspect ratio on the linked column foot are studied.The results show that when the aspect ratio is greater than 1.93,the horizontal overturning moment increases under rare earthquakes,and foot has the tendency to move upward.The typical yielding mechanism of linked column braced steel frame with lift column is analysed in the limit state,and the formula of ultimate bearing capacity is deduced.(3)Three groups of models are established by finite element software ABAQUS,and study the influence of the length of link beam,inelastic angle of link beam and aspect ratio on seismic performance.The results show that if the length of link beam is longer,the structural energy dissipation performance,bearing capacity and lateral stiffness will be significantly reduced.The recommended length e is in the range of(0.95~1.54)M_p/V_p.The inelastic angle of link beam has a significant influence on the energy dissipation capacity of the structure.The rotation angle is larger,the plastic development of link beam is more sufficient.It is recommended that the rotation angle be?_p=0.06~0.08rad.With the increase of the aspect ratio of the structure,the bearing capacity and lateral stiffness of the structure decrease,and the ductility and deformation capacity get improved.(4)The collapse criteria of multi-story steel structures at home and abroad are summarized,and a collapse criterion for LCBF structures is proposed.When the story drift ratio reaches 2.6%,the structure is considered to be in collapse state.The anti-collapse capacity of LCBF structures is evaluated by CMR(Collapse Margin Ratio)method.The results show that the collapse margin capacity of LCBF structure is strong,and the collapse probability under rare earthquake is less than 10%,which meets the requirement of no collapse in violent earthquake.