【正文】 a of shear capacity for abnormal joint in reinforced concrete f rame is provided. Key words : abnormal j oint 。 minor core 。 shear ca paci t y CLC number :TU375. 4 。 η j = influential coefficient of t he orthogonal beam to the column 。 bj = effective widt h of the joint core section 。 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 。 f yv = design value of t he stirrup tensile st rengt h 。 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 , and the stirrup in t he middle of t he core is near to yielding or has yiel2 ded. The joint core shows nonlinear property on t he p2Δ curve , and it enter s elastic2plastic stage. The load at t horough cracking stage is about 80 % — 90 % load. (3) Ultimate stage At t his stage , t he widt h of t he cracks is about 1mm or more and some new cracks continue to oc2 cur . The shear deformation at t he core is much larger and concrete begins to collap se. Af ter several cyclic loading , the force reaches the maximum value , which is called ultimate stage. The load increase is due to t he enhancing of the concrete aggregate mechanical f riction between cracks. At t he same time t he st ress of stirrup increases gradually. On t he one hand stirrup resist s t he horizontal shear , and on t he ot her hand the confinement effect to t he expanding pression concrete st rengthens continuous2 ly , which can also improve t he shear capacity of diagonal pression bar mechanism. (4) Failure stage As the load circulated , concrete in t he core began to collap se , and t he deformation increased sharply , while the capacity began to drop . It was found t hat t he slip of reinforcement in t he beam was very serious in t he experiment . Wit h t he load and it s circulation time increasing , t he zoon wit hout bond gradually permeated towards t he internal core , enhancing t he burden of t he diagonal pression bar mechanism and accelerates the pression failure of concrete. Fig. 4 shows t he p hotos of typical damaged joint s. A p seudo dynamic test of space model of power plant st ruct ure was carried out to research t he working