Research On Mechanical Model Of Beam-Column-Slab Joints In Reinforced Concrete Frame Structures

Beam-column joint in reinforced concrete frame structure belongs to discontinuity regions. It is well recognized as the extremely weak part of seismic system. Currently, with application of the negative bending, slab will influence the flexural strength of beam as the tensile flange by research at home and abroad, but our code provisions have not carried on explicitly. Then, current design code for beam-column joint are based on empirical considerations from the plane joint experiment, without considering the effect of cast-in-place slab, nor establishing mechanical model. Based on these, this thesis adopts the method of experimental study and theoretical analysis to study the beam-column-slab joint, the main content of study are listed as follows:(1) Reversed cyclic quasi-static loading experiment on the beam-column joint assembly with or without cast-in-place slab was conducted separately. The anti-seismic behavior involving bearing capacity, shearing capacity and deformation, energy dissipation etc was analyzed. The experimental results indicated Strong Column Weak Beam could be achieved by the present design code, regardless of slab. The negative flexural strength of beam would be improved because of slab, evoked column end to form plastic hinges. But not all of the slab bars were able to fully work.(2) On the basis of experimental study, the strengthening of the negative flexural capacity caused by cast-in-place slab was researched. From the perspective of capacity, the analytic model and proposed calculation formula were put forward, which about the effective tensile flange width of beam in reinforced concrete frame structure. The results were in good agreement with the experimental results, which can provide reference for engineering design.(3) The mechanic behavior of beam-column-slab joint was analyzed. Then, the formula about horizontal shear increment value in the joint core area was established through the tie and strut theory in cast-in-place slab. In addition, the softened strut-and-tie model was modified by considering the effect of cast-in-place slab bars and orthogonal beam. The results by modified softened strut-and-tie model could more precisely predict the joint shear strength as well as more truthfully reflect the shear behavior of joint more than unmodified.