Earthquake Resistant Behavior Study And Nonlinear Finite Element Analysis Of Knee Joints On The Top Story In R.C.Frame With Special-Shaped Columns

In this paper, beam-column knee joints on the top story in reinforcement concreteframe were tested under low reversed cyclic loading, on this basis, the nonlinear finiteelement analysis on the beam-column knee joints on the top story in reinforcementconcrete frame were performed, which possessed important theoretical andengineering purposes.At first, the importance of beam-column joints and transfer mechanism andfactors affecting seismic behavior of beam-column knee joints were generalized. Then,five full-scale beam-column knee joints on the top story in reinforcement concreteframe were tested under low reversed cyclic loading. One of the column'scross-section of the test specimens is a rectangle with h/b=3. The column's cross-section of the other 4 specimens are L-shaped, in which the flange width of thecolumn's cross section are in two groups. That is the primary variable is the flangewidth of the column's cross-section. Through the experiment, based on measurementof load-displacement of beam end and strains in the joint core and beam head in initialcrack stage, 0.2 mm crack stage, yielding stage extremity and ultimate stage, theearthquake-resistant characteristics such as dissipation of energy, stiffness, crack andductility of each member were analyzed. On this basis, the joint core shear on mainstages was calculated. Finally, based on the Darwin-Pecknold's orthotropic materialmodal, the nonlinear finite element analysis on the beam-column knee joints on thetop story in reinforcement concrete frame was presented with separating mode.Kupfer-Gerstle failure criterion modified for concrete was adopted on account of hesoftened compressive strength for cracked concrete and concrete confined was takeninto consideration. Stress-strain relationship for steel reinforcement is elastic-perfectlyplastic model. Nonlinear finite element analytical procedure adopted incrementalmethod, and the influence of flange was taken into account. Load-displacementskeleton curves, steel reinforcement strain of beam head, the joint core shear, stirrupstress and strain of the joint core and bonding element strain under the nonlinear finiteelement analysis on the beam-column knee joints was analyzed The results indicatethat the finite element analysis results agreed with the experiment ones. In addition,mathematical representation of stirrup and concrete of flanges participating inshearing strength of core was obtained, which conduced to extend experiment resultsto longer flanges.