| Eccentrically braced steel frames have high rigidity and good ductility.They can not only meet the requirements of current specifications for lateral drift angle between stories under moderate and small earthquakes,but also exhibit good plastic energy dissipation capacity under large earthquakes.However,there are obvious disadvantages in the integrated design of the energy-consuming beam section and the steel frame beam:(1)the section of the energyconsuming beam section is too large,which leads to the energy-consuming area not being concentrated after the structure enters the plastic state,making the safety evaluation of the postearthquake structure more difficult;(2)After the earthquake,the repair cost of the structure and the replacement cost of the energy-consuming beam section are very high and the engineering cost is relatively high.Based on the above defects,the design idea of separating the energy dissipation beam section from the steel frame beam is put forward,and the two sections are connected into a whole by high-strength bolts.In order to further optimize the plastic energy dissipation performance of the structure,the steel brace is replaced by a double steel tube bucklingrestrained brace with a contact ring.The improved eccentrically braced steel frame structure has the following advantages:(1)the replaceable energy dissipation connection can centrally bear most of the plastic damage under a large earthquake,not only the safety evaluation of the structure after the earthquake becomes simple and efficient,but also the target that the main frame structure will not collapse under the large earthquake can be realized,and the safety degree of the structure after the earthquake is improved;(2)The separated design enables the section and length of the replaceable energy dissipation connection to be specifically adjusted according to different design requirements,thus widening the applicable scope of the structure.In this paper,a finite element model of 30 web-connected K-eccentrically braced steel frames with composite floors was established by using finite element software ABAQUS.The load-displacement curves of the structures under monotonic and cyclic loading were obtained.The effects of cross-sectional area,cross-sectional size(width-to-thickness ratio of plates),stiffener spacing and length on the stiffness,bearing capacity,ductility and plastic energy dissipation capacity of the web-connected K-eccentrically braced steel frames with composite floors were analyzed.Subsequently,six 1/3-scale web-connected replaceable connector Kshaped eccentrically braced steel frame specimens with composite floors were designed and tested under low cyclic loading.Through finite element analysis and experimental research,the following conclusions are obtained.(1)Under the influence of composite floor slab,the hysteretic circle of the K-shaped eccentrically braced steel frame with web connection type replaceable connection piece with composite floor slab is full and fusiform,the initial stiffness in the elastic stage is large,the stiffness degradation in the elastic-plastic stage is obvious,and the minimum plastic rotation angle still meets the minimum limit requirement of 0.08 rad in the specification,which indicates that the structure still has good plastic deformation capability and energy dissipation capability under the action of composite floor slab.(2)Test data and finite element stress nephogram show that when the interlayer displacement angle approaches 1/250,the replaceable energy dissipation connector first enters the yield energy dissipation stage.With the increase of displacement,the stress of the bucklingrestrained brace gradually approaches the yield stress value.Under the influence of shear dislocation of the replaceable energy dissipation connector,the stress value of the concrete in the middle area of the composite floor is significantly larger,and the vertical through crack develops from here at the earliest.This shows that the finite element simulation is consistent with the experimental research.(3)Through detailed analysis of the influence rules of web height-thickness ratio and flange width-thickness ratio on the mechanical properties of the structure,it is found that the flange width-thickness ratio has little influence on the bearing capacity and ductility energy dissipation capacity of the structure.Therefore,in the design,the flange plate width-thickness ratio only needs to meet the requirements of the current specification,and no further detailed design is needed.(4)The cross-sectional area and length of the replaceable energy dissipation connector are the main factors that affect the mechanical and seismic performance of the web-connected replaceable connector K-eccentrically braced steel frame with composite floors.The influence of the spacing of stiffening ribs is relatively weak,but its influence exceeds the height-thickness ratio of the web.After comprehensive analysis of the length and cross-sectional size,it is suggested that when the length ratio is around 1.2,the bearing capacity and plastic denaturation capacity of the structure are better.(5)The site verified the post-earthquake replaceability of the replaceable energy dissipation connector.By comparing the test data before and after replacement,it is found that the bearing capacity and ductility of the replaced structure are still very good.The whole replacement process takes about half an hour and can be completed by three people.This fully illustrates the operability and economy of the structural design idea. |
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