| It is popular that the strength of the concrete in the column is higher than that in the beam in the reinforced concrete high-rise frame structures. In construction, if the column-beam joints is poured with the same strength concrete as columns, there are some difficult in solving such as formwork planning, construction joint, quality of construction and construction technology. It is useful and effective that the column-beam joints are poured with the same strength concrete as beams. The column-beam joints poured with the same strength concrete as beams need improve by special measures in order to meet load-carrying ability and deflection. One of restrained joint and three full-scale specimens representing lower strength concrete with different improved measures in the column-beam joints interior joints were test under cyclic load, through it, we investigated the seismic behavior of lower strength concrete beam-column joints .The specimens were constructed according to Code for Design of Concrete Structures (GB50010-2002), it was emphasized that much data were studied in disadvantage condition of higher shear-compression ratio, axial load ratio and ratio of beam concrete strength to column concrete strength with improved measures, these data were performance of specimens consisting of failure mode, load-carrying capacity, beam bar anchorage capacity and slip character, the capacity of the improved measures, ductility, energy dissipation capacity and stiffness degradation, etc. The following conclusions may be drawn from the results of this limited investigation on lower strength concrete joints.①Orthogonal beam supplies stronger restraint to original joint and reduces the deflection in the joint region caused by shearing of the specimens, it reinforces the seismic behavior of the frame's joint that the core concrete strength is inferior to that of column.②When the strength of the concrete in joint region is less than half of the strength of the concrete in column, that is to say, the ratio of beam concrete strength to column concrete strength is less than 0.5, it is proposed that corresponding improved measures should be token and the concrete in joint region should be checked.③In disadvantage condition of higher shear-compression ratio, axial load ratio and ratio of beam concrete strength to column concrete strength, the column-beam joints poured with the same strength concrete as beams with X bar not only improve shearing ability, but also significantly reduce the deflection in the joint region caused by shearing of the specimens, and reach the level of the traditional column-beam joints, it is an effective measure of the column-beam joints poured with the same strength concrete as beams with X bar. X bars are substitute for stirrup when the stirrup is too dense to construct and design.④The short bars in joint region can reduce effectively axial load ratio and improve the ductility of specimens.⑤To the column-beam joints poured with the same strength concrete as beams with improved measures, Slip of beam bars and the deflection due to bar slip of the specimens exceed to these of traditional specimens.⑥Slip of beam bars is a noticed problem in the column-beam joints poured with the same strength concrete as beams. It is showed by tests that bonding degradation and stiffness degradation become faster, slip of beam bars becomes serious in the condition of higher shear-compression ratio and ratio of beam concrete strength to column concrete strength. To the column-beam joints poured with the same strength concrete as beams, the proportion of the diameter of beam bars to the length of beam bars through the joint( d b/ D≤1/20), provided by present code to the traditional specimens, should be properly limited. It is proposed that the ratio should be appropriately less and not more than d b/ D≤1/25.
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