Experimental And Numerical Analysis Of Beam-column Connections In Steel Frames Subjected To Impulsive Loading

Beam-column joints, as significant components of steel frames, play a crucial role in the mechanical properties of the whole structure, which could cause huge financial loss once they are broken. A variety of researches about beam-column connections in steel frames have been taken, but concentrating in static force fields. However, many extreme loads,such as explosion and impact of falling objects, whose effects to steel structures are quite different from that under static force, pose a threat to our built buildings around us. On the other hand, there are few studies associated with the dynamic response of beam-column connections in frame subjected to dynamic loads (impact loads as a example), and few relevant steel structure design specifications are made in domestic design codes, thereby making it necessary to give an intensive study and analysis. The experiment about steel frames’impact resistance properties was the first one conducted interiorly, in which three different connection styles, involving flush endplate connection, extended plate connection and welded connection and two different impact energy were considered. At the same time, numerical simulation was adapted to explore such questions. The research work can be summarised as following:(1)The steel frame structures were designed according to 《Code for design of steel structure 》GB50017-2003 and numerical simulation results. Then the impact experiment was taken using the high-performance drop hammer test machine, during which the beams’vertical and lateral displacements and internal forces across sections were measured, as well as the connections feature behaviors captured by high-speed camera. Failure models of different connection styles are analysed. The failure of bolt in extended endplate connection frame is ductile with fibroid fracture section for it suffers more tensile force, while that in flush endplate connection frame is brittle with flat and smooth profile and it suffers more shear force.(2)Using the nonlinear finite element simulation program ABAQUS/Explicit, the beam-column connection numerical models of steel frames are developed to simulate the dynamic response of steel frame during the impact processes. And the technical details of the finite element modeling process are introduced, such as the choice of element style, material model and the definition of contact pairs. The ratio of artificial strain energy and total internal energy plus the comparison of the results of numerical calculation and that of impact experiment illuminate the correctness of the numerical models.(3) This paper analyses the impact force time history curve, dynamic moment-rotation curve and impact force-displacement curve to study the dynamic response in the impact processes. The results illustrate that the process of dynamic response of steel frame can be divided into three periods according to the impact force time history curve:impact, stable and bounce. In impact period, the impact force and joint moment that work on steel frames shoot up to its peak value and the displacement and rotation increase dramatically correspondingly. The stable period is the main time for rotation and displacement development, as well as the most important one for impact force producing work and joints assuming energy. Then the curve experiences the bounce period after the hammers departure from the beam, and the elastic strain return to zero for its ductile property.(4) This paper analyses the impact resistance properties of steel frame with different connec-tion styles in the perspective of energy transformation. The conception of energy transformation ratio(ET) is put forward to characterize the frames-ability of absorbing impact energy and trans-forming it into plastic strain. Besides, the contribution of each component to the impact resistance ability of the whole structure is studied. The results are as following:①the ET of steel frame has no business with its connection styles. The amount of energy absorbed by steel frames with different connection styles is almost the same when they are expos-ed to the same initial kinetic energy, even though that for each component is quite different②The beam of flush endplate connection frame has more plastic deformation and bigger ET value for its weak restriction action, followed by that of extended endplate connection frame and welded connection frame, whose ET value is minimal. Besides, both ET values of columns in semi-rigid connection steel frame is quite small that can be neglected while that in rigid steel frame is bigger (about 1/5 of the whole)③ Equal impact energy would be absorbed and transformed into plastic deformation by the steel frame when it is subjected to the same initial kinetic energy. However, the ET value would be bigger when it suffers more kinetic energy. When it comes to the endplate and bolts individu-ally, we could figure out that the endplate’s plastic deformation constitutes the main part when the impact subject has low initial kinetic energy, while the bolts experience more plastic deformation than its counterparts conversely when the impact subject has more high initial kinetic energy,④ the ET value of beam, who is the main energy dissipation element, can be considered as a constant value approximately.