【正文】 f 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 small beam of abnormal joint , which is due to t he pressive st ress diff usion of concrete pressive region of the beam and column , while at t he same time t he pression carried by the diagonal pression bar bees large. Because t he main part of bond force of column and beam is added to t he diagonal p ression bar but cont rasting wit h t he increased area of diagonal pression bar , t he increased action is small . The region in the maj or core but out of the mi nor core has less st ress dist ribution and fewer cracks. The region can confine t he expansion of t he concrete of t he mi nor core diagonal pression bar concrete , which enhances t he concrete pressive st rengt h of mi nor core diagonal pression bar . Making t he mi nor core as st udy element , the area increment of concrete diagonal pression bar in mi nor core is related to t he st ress diff usion of t he beam and column pressive region. The magni2 t ude of diff usion area is related to height difference of t he beam sections and column sections. Name2 ly , it is related to t he size of mi nor core section and maj or core section. Thus , the increased shear st rengt h magnit ude caused by mi nor core rest rictive effect on maj or core can be measured quantitative2 ly by t he ratio of maj or core area to mi nor core area. And it al so can be expressed that t he rest rictive effect is quantitatively related to t he ratio. Obviously , t he bigger t he ratio is and t he st ronger t he con2 finement is , t he st ronger t he bearing capacity is. The region in the maj or core but under the mi nor core still need stirrup bar because of t he hori2 zontal force t ransferred by bigger beam bar . But force is small . 3. 3. 2 load2displacement curves analysis Fig. 9 shows t he typical load2displacement curves at t he beam end of t he exterior and interior joint . The figure showing t hat t he rigidity of t he specimens almo st doesn’ t degenerate when t he initial crack appear s in t he core , and a turning point can be found at t he curve but it isn’ t very obvious. Wit h t he crack developing , an obvious t urning point can be found at t he curve , and at t his time , t he speci2 men yields. Then t he load can increase f urt her , but it can’ t increase too much f rom yielding load to ultimate load. When t he concrete at t he core collap ses and the plastic hinge occured at t he beam end , t he load begins to decrease rat her t han increase. The ductility coefficient of two kinds of joint s is basically more than 3 (except for J 3 9) . But it should be noted t hat the design of specimens is based on the principle of joint core failure. The ratio of reinforcement of beam and column tends to be lower t han practical project s. If t he ratio is larger , t he failure of joint is probably prior to t hat of beam and column , so t he hysteretic curve reflect s t he ductility property of joint core. Joint experiment should be a subst ruct ure test (or a test of posite body of beams and col2 umns) . So t he load2displacement curves at t he beam end should be a general reflection of t he joint be2 havior work as a subst ruct ure. Providing t hat the joint core fails af ter t he yield of beam and column (especially for beam) , t he load2displacement curves at t he beam end is plump , so the principle of “ st rong col umn and weak beam , st ron ger j oi nt should be ensured which conforms to t he seismic re2 sistant principle. The experiment shows t hat t he stiff ness of joint core is large. Before the joint reaches ultimate stage , t he stiff ness of joint core decreases a little and the irrecoverable residual deformation is very small under alternate loading. When joint core enter s failure stage , t he shear deformation increases sharply , and t he stiff ness of joint core decreases obviously , and t he hysteretic curve appears shrink2 age , which is because of t he cohesive slip of beam reinforcement . 3. 4 Influential Factors of Abnormal Joint Shear Capacity The fir st factor is axial pression. Axial pression can enlarge t he pression area of col2 umn , and increase t he concrete pression area of joint core[124 ] . At t he same time , more shears t ransferred f rom beam steel to t he edge of joint core concrete will add to t he diagonal pression bar , which decreases t he edge shear t hat leads to the crack of joint core concrete. So t he existence of axial p ression cont ributes to imp roving t he capacity of initial cracks at joint core. The effect of axial pression on t horough cracking load and ultimate load isn’ t very obvious[1 ] . The reason is t hat cont rasting wit h no axial pression , the accumulated damage effect of joint core under rever sed loading wit h axial pression is larger . Alt hough axial pression can improve t he shear st rengt h of concrete , it increases accumulated damage effect which leads to a decrease of the ad2 vantage of axial pression. Therefore t he effect of axial pression on t horough cracking load and ultimate load is not very obvious. Hence , considering the lack of test data of abnormal joint , t he shear capacity formula of abnormal joint adopt 0. 05 nf c bj h j to calculate the effect of axial pression , which is based on the result s of t his experiment and referenced to t he experimental st udy and statistical analy