| The mechanical properties of special-shaped nodes such as variable beam sections and staggered floors formed by modern civil building shapes and industrial building production process requirements are different from conventional nodes.The performance of special-shaped middle nodes of PEC column-steel beam frames is studied to guide application of special-shaped middle nodes.The research has a certain engineering significance.In this paper,two 1/2 scale test specimens were designed and produced,one of which is specimen YX1 with equal height beams on the left and right of the middle node,and the other is the specimen YX2 with unequal height beams on the left and right,but its beams linear stiffness i is the same on both sides.Through low-cycle repeated load tests,the seismic performance indexes of the joints,such as hysteretic performance,skeleton curve,bearing capacity degradation coefficient,stiffness degradation,ductility,energy dissipation capacity,and joint core area deformation,were analyzed,and compared with related studies.The research results show that specimen YX1 forms plastic hinges at the roots of the beams on both sides,which belongs to ductile failure and meets the seismic design requirements of "strong column and weak beam".The specimen YX2 occurs cracks along the long diagonal line in the core area of the concrete firstly,and the cracks along the short diagonal line are relatively lagging,and finally an X-shaped crack is formed.A large amount of concrete in the core area is spalled,and the web and flanges of beam are deformed,and the core area is mainly sheared.Compared with the test piece YX3 with equal height beams on the left and right,the average ultimate bearing capacity of the specimen YX1 has an increase of 5.8% in the positive and negative,and the average displacement has a decrease of 7.1% in positive and negative.Compared with the test piece YX4 with unequal height beams on the left and right of the node,the average ultimate load-bearing capacity is increased by 2.8%,and the positive and negative displacement is increased by 24.7% on average.The bearing capacity degradation coefficient of each test piece is between 0.916 and 1.000,and the bearing capacity degradation is relatively stable.Comparing test piece YX1 with YX3,the stiffness degradation trend is the same and the former has a greater degree of degradation than the latter.When test piece YX2 is compared with YX4,The initial stiffness degradation is severe,and the former is more stable than the latter in the later stage of loading.The displacement ductility coefficients of the specimens YX1,YX2,YX3,YX4 are 5.55,6.13,4.47,and 4.96,respectively,and the average equivalent viscous damping coefficients are 0.38,0.39,0.45,0.44,respectively.Compared with YX3,the ductility of YX1 is increased by 24.2%,but the energy consumption capacity is weakened,compared with YX4,the ductility coefficient of YX2 is increased by 40.0%,and the energy consumption capacity is also reduced.Based on the test results,a formula for the shear bearing capacity of the special-shaped mid-joint of the PEC column-steel beam frame is proposed.Numerical simulations were carried out on the basis of the test with the height of the staggered layer as a parameter.The height of the staggered layer is increased from 150 mm to 200 mm,the ultimate bearing capacity increased by 9.8%,the ultimate deformation increased by 20.5%,and the ductility coefficient increased by 6.3%.When the height of the staggered layer is increased from 200 mm to 250 mm,its ultimate bearing capacity increased by 5.3%,ultimate deformation decreased by 16.3%,and ductility coefficient increased by 2.0%.But the height of the staggered layer is increased from 250 mm to300mm,its ultimate bearing capacity increased by 2.1%,ultimate deformation decreased by 2.8%,and ductility coefficient,a decrease of 57.6% indicates that when the height of the staggered layer of the joint specimen reaches 1.5 times the beam height,the bearing capacity increases little,and the deformation and ductility decrease. |
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