【正文】 l 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 behavior of t he abnormal joint s in re2 al st ructure and the seismic behavior of st ructure. Fig. 5 shows the p hoto of model . The test includes two step s. The fir st is the p seudo dynamic test . At t his step , El2Cent ro wave is inp ut and the peak acceleration varies f rom 50 gal to 1 200 gal . The seismic response is measured. The second is t he p seudo static test . The loading can’ t stop until t he model fail s. Fig. 7 Minor core The experiment shows t hat t he dist ribution and development of t he crack is influenced by t he rest rictive effect of the ort hogonal beam , and t he crack of joint core mainly dist ributes under t he orthogonal beam ( see Fig. 6) , which is different f rom t he result of t he plane joint test , but similar to J 4210. 3. 3 Analysis of test results 3. 3. 1 Mechanical analysis In t he experiment , t he location of the initial crack of t he exterior joint and the crushed position of concrete both appear in the middle of t he joint core , and t he position is near t he centerline of t he upper col2 umn. The initial crack and crushed position of t he concrete of the interior joint both appear in t he mi2 nor core ( see Fig. 4 ,Fig. 7) . For interior abnormal joint t he crack doesn’ t appear or develop in t he ma2 j or core out side of the mi nor core until t horough cracking takes place , while t he crack seldom appears in t he shadow region ( see Fig. 7) as the joint fail s. Therefore , for abnormal joint , t he shear capacity of t he joint core depends on t he properties of t he mi nor core , namely , on t he st rengt h grades of concrete , t he size and the reinforcement of t he mi nor core , get t he effect of t he maj or core dimension can’ t be neglected. Mechanical effect s are t he same will that of t he normal joint , when t he forces t ransfer to t he mi2 nor core t hrough column and beam and reinforcement bar . Therefore , t he working mechanisms of nor2 mal joint , including t russ mechanism , diagonal pression bar mechanism and rest rictive mechanism of stirrup , are also suitable for mi nor core of t he abnormal joint , but their working characteristic is not symmet rical when the load rever ses. Fig. 8 illust rates t he working mechanism of t he abnormal joint . When t he load t ransfer to mi nor core , t he diagonal pression bar area of mi nor core is bigger t han normal joint core2posed by small column and sma