【正文】 Experimental research on seismic behavior of abnormal joint in reinforced concrete frame Abstract :Based on nine plane abnormal joint s , one space abnormal joint experiment and a p seudo dynamic test of a power plant model , the work mechanism and the hysteretic characteristic of abnormal joint are put to analysis in this paper. A conception of minor core determined by the small beam and small column , and a conclusion that the shear capacity of ab2 normal joint depends on minor core are put forward in this paper. This paper also analyzes the effect s of axial pres2 sion , horizontal stirrup s and section variation of beam and column on the shear behavior of abnormal joint . Finally , the formula of shear capacity for abnormal joint in reinforced concrete f rame is provided. Key words : abnormal j oint 。 minor core 。 seismic behavior 。 shear ca paci t y CLC number :TU375. 4 。 TU317. 1 Document code :A Article ID :100627930 (2020) 0220208210 1 Int roduction For reinforced concrete f rame st ructure , t he joint is a key ponent . It is subjected to axial p ression , bending moment and shear force. The key is whet her the joint has enough shear capaci2 ty. The Chinese Code f or S eismic Desi gn of B ui l di ngs ( GB5001122020) adopt s the following formula to calculate t he shear capacity of the reinforced concrete f rame joint . V j = 1. 1η j f t bj h j + 0. 05η j N bj bc + f yv Asvj hb0 a′ s s (1) Where V j = design value of t he seismic shear capacity of the joint core section 。 η j = influential coefficient of t he orthogonal beam to the column 。 f t = design value of concrete tensile st rength 。 bj = effective widt h of the joint core section 。 hj = dept h of the joint core section , Which can be adopted as t he depth of the column section in t he verification direction 。 N = design value of axial pression at t he bot tom of upper column wit h considering the bi2 nation of the eart hquake action , When N 015 f c bc hc , let N = 0. 5 f c bc hc 。 bc = widt h of t he column section 。 f yv = design value of t he stirrup tensile st rengt h 。 Asvj = total stirrup area in a set making up one layer 。 hb0 = effective dept h of t he beam. If t he dept h of two beams at the side of t he joint is unequal , hb0 = t he average depth of two beams. a′ s = distance f rom the cent roid of the pression beam steel bar to the ext reme concrete fiber . s = distance of t he stirrup . Eq. 1 is based on t he formula in t he previous seismic code[1 ] and some modifications made eavlicr and it is suit2 able to the normal joint of reinforced concrete f rame , but not to t he abnormal one which has large different in t he section of t he upper column and lower one (3 600 mm and 1 200 mm) , lef t beam and right beam (1 800 mm and 1 200 mm) . The shear capacity of abnormal joint s calculat2 ed by Eq. 1 may cause some unsafe result s. A type of ab2 normal joint which of ten exist s in t he power plant st ruc2 t ure is discussed ( see Fig. 1) , and it s behavior was st ud2 ied based on t he experiment in t his paper 2 Experimental work According to the above problem , and t he experiment of plane abnormal joint s and space abnormal joint , a p seudo dynamic test of space model of power plant st ruct ure was carried out . The aim of t his st udy is to set up a shear force formula and to discuss seismic behavior s of t he joint s. According to the characteristic of t he power plant st ruct ure , nine abnormal joint s and one space abnormal joint were designed in t he experiment . The scale of the model s is one2fif t h. Tab. 1 and Tab. 2 show t he dimensions and reinforcement detail s of t he specimens. Fig. 2 shows the typical const ruction drawing of t he specimen. Fig. 3 shows the loading set up . These specimens are subjected to low2cyclic loading , the loading process of which is cont rolled by force and displacement , t he preceding yield loading by force and subsequent yield by t he displacement . The shear deformation of the joint core , t he st rain of the longit udinal steel and t he stirrup are main measuring items. 3 Analysis of test result s 3. 1 Main results Tab. 3 shows t he main result s of t he experiment . 3. 2 Failure process of specimen Based on t he experiment , t he process of t he specimens’ failure includes four stages , namely , t he initial cracking , t he t horough cracking , the ultimate stage and t he failure stage. (1) Initial cracking stage When t he first diagonal crack appears along t he diagonal direction in t he core af ter loading , it s widt h is about 0. 1mm , which is named initial cracking stage of joint core. Before t he initial cracking stage , t he joint remains elastic performance , and the variety of stiff ness is not very obvious on t he p2 Δ curve. At t his stage concrete bear s most of the core shear force while stirrup bears few. At t he time when t he initial crack occur s , t he st ress of t he stirrup at t he crack increase sharply and t he st rain is a2 bout 200 10 6 — 300 10 6 . The shear deformation of t he core at t his stage is very small (less than 1 10 3 radian ,generally between 0. 4 10 3 and 0. 8 10 3 radian) . (2) Thorough cracking stage Wit h the load increasing following t he initial cracking stage , the second and t hird crossing diago2 nal cracks will appear at t he core. The core is cut into some small rhombus pieces which will bee at least one main inclined crack across t he core diagonal . The widt h of cracks enlarges obviously , and t he wider ones are generally about 0. 5mm , which is named core t horough cracking stage. The st ress of stirrup increases obviously