The Preliminary Study On Reinforcing Adjustment About Concrete Frame Beam When Considering The Impact Of Slab

One of the basic principles of concrete structural seismic design is guaranteed to achieve"strong column and weak beam". That is, under the action of strong earthquakes the framebeams first yield to consume a large amount of seismic energy and so as to achieve thepurpose of the whole structure’ earthquake safety. But the damage of Wenchuan earthquakeshow that many frame structures did not achieve the expected "strong column and weakbeam" failure modes, and they presented as "strong beam and weak column" failure modes.The related research shows that no reasonable considering the contribution of cast-in-placefloor to frame beam’s flexural bearing capacity is an important reason for the emergence ofthese problems. Therefore, it is necessary to adjust the frame beam reinforcement, in order toensure that the frame beam yields earlier than the frame column. This paper has conducted apreliminary study, the specific work is as follows:1、As the three level framework in7degree zone has more common application scope,we used the first layer of midspan beam and column as the research object. According todifferent standard width of a room size grouping, we did the Push-over analysis on a total of44three-layer frame structures. By adjusting the beam negative moment reinforcement wemade the beam and column to hinge the same time, and we investigated the adjustment ofbeam reinforcement under the "critical state". Research shows that:(1) When the PKPMsoftware calculates, it reinforces more about the frame beam’s negative bending moment anddoesn’t considering the contribution of the slab reinforcement, this may lead to "strong beamand weak column" failure mode.（2）Under the "critical state", the adjustment of the beamreinforcement amount decreases with the increase of the beam and column’s cross-sectionheight. At the same time it increases with the increase of the span. The adjustment coefficientof the beam reinforcement fitted with better accuracy;（3）This coefficient is suitable for thefirst layer midspan frame beam of the three-layer four level framework, it isn’t suitable forthe two lever framework with the same number of layers.2、In the condition of7degree seismic intensity, we analyzed the beam reinforcementadjustment coefficient of two eight-layer structures and three six-layer structures as a total of five multi-storey frame structures. Then we investigated the effect of structural layers toaffect this coefficient. Research shows that:（1）For the two level frame, the beam hingeappears earlier than the column hinge and it doesn’t need to adjust the frame beamreinforcement;（2）For the three and four level frame, in order to make the beam hinge aheadof the column hinge, we need to adjust the frame beam’s reinforcement of the negativemoment. But the adjustment coefficient of the beam reinforcement should be aimed atdifferent floors and multiplied by the corresponding coefficient of correction.3、In the condition of7degree seismic intensity, we analyzed the hinge sequence of onefifteen-layer structure and three eleven-layer structures as a total of four frame shear wallstructures. We discussed the necessary adjustment of beam reinforcement and theapplicability of the adjustment coefficient of the beam reinforcement. Research shows that:（1）When the column cross-section doesn’t change from bottom to top, it’s easy to satisfythe requirements that the beam hinge appears earlier and we doesn’t need to adjust the framebeam reinforcement;（2）When the column cross-section decreases along the verticaldirection, in order to make the beam hinge appears earlier than the column hinge, we need toadjust the frame beam’s reinforcement. But the adjustment coefficient of the beamreinforcement should be aimed at different floors and multiplied by the correspondingcoefficient of correction.