Experimental Study On Seismic Performance Of Knee Joint With Anchoring Plate And 500MPa Reinforcement Overlapping In Pillar

Construction of steel bars for beam and pillar negative moment in end node of frame top layer specified in Code for design of concrete structures (GB50010-2002) include two measures of"Overlap in beam"and"Overlap in pillar". The two measures may lead to difficulty in concrete placement and construction, therefore, improvement of connection of steel bars for beam and pillar negative moment in end node of frame top layer is highly expected. This paper expects to reduce overlap length of steel bars by additional anchoring end, so as to improve the connection of steel bars for negative moment in end node of frame top layer and to facilitate construction. Connection of steel bars for beam and pillar negative moment in four specimens of the experiment adopts the measure as follows: Stretch the outside pillar bar to the pillar top at first. Stretch the upper longitudinal bars of the beam to the outside of the node and then bend downward. Anchoring ends are added at the end of steel bars in beams and pillars.Aseismic performance of connection measure mentioned above is inspected and verified by reversed cyclic loading tests of four nearly full-size end node of reinforced concrete frame top layer in which 500MPa steel bars are adopted. Problems may appear in the application of this connection measure are analyzed. The main points and conclusions of this paper are summarized as follows:①Connection measure mentioned above is adopted in four specimens and stirrups in nodal region are designed according current code, evenly spaced, intensively spaced or spaced with additional U-style reinforcement. The conclusion that the aseismic performance of specimens is unfavorable is obtained by analysis of test results and comparison with specimens of other connection measures. However, under a certain value of shear-compression ratio the ductility of specimens can meet the need with some constructional measures.②Anchoring plates are adopted for steel bars in positive moment zone of beams. According to test results, slide of steel bars with anchoring plates is less than that with 90°hooked anchorage. The provision that anchoring plates are adopted in nodal region for steel bars in positive moment zone of beams and the horizontal projection length is not less than 0.4 l aE can meet the aseismic demand.③To promote the understanding of the design of the end node of top layer in foreign codes, this paper compares aseismic shearing bearing capacity formulas and limits of shear-compression ratio in design codes of different countries. A deep understanding of provisions on mechanical anchorage of steel bars in different countries is obtained, and then, basic anchoring length and anchoring length of steel bars with anchoring plates in different countries are compared.