| The RC frame structure has the advantages of good durability,flexible space arrangement,meeting people's use of space requirements easily and so on,so it has a large proportion of the total construction volume.However,multiple earthquake damage surveys have shown that the RC frame presents the “strong beam weak column” destruction phenomenon,contrary to the original intention of “strong column weak beam”.This form of destruction will lead to the collapse of the integrity or locality of the frame structure,which is detrimental to the earthquake resistance of the frame structure and is not conducive to ensuring the safety of people's lives.Therefore,exploring how to improve the “strong beam weak column” damage phenomenon has considerable positive significance.According to previous studies on this issue,one of the main reasons for the “strong beam weak column” phenomenon is that the cast-in-situ slab and its slab reinforcement have a significant effect on the end of the frame beam.In this paper,based on the idea of weakening beam and slab connection,the constraints of the cast-in-situ slab on the beam end were released.The experimental frame was used as a prototype,and a pure frame,actual frames with different thickness cast-in-situ slab,and frames with different thickness 200 mm corner-hole cast-in-situ slab finite element models were built with ABAQUS.The static analysis under the action of an inverted triangle load and the dynamic analysis under the action of the El-Centro seismic wave were carried out for these models,and the following conclusions are drawn:(1)During the first stage of the test loading,under the action of the vertical load,the longitudinal steel bars at the end of the cast-in-situ slab top are under tension,and the longitudinal steel bars at the end of the cast-in-situ slab bottom are under pressure.The steel strain values along the transverse beam show small in two sides and large in the middle.And the steel bar strain value of cast-in-situ slab top is bigger than that of cast-in-situ slab bottom.(2)The presence of cast-in-situ slab reduces the stress of the steel bar at the beam end of negative moment,alleviates the damage to the concrete,and delays the plastic hinges.When the ratio of the thickness of the cast-in-situ slab to the height of the beam reaches a certain value,it should also be taken into account to positive bending moment beam end properly.In addition,the beam ends of different types of nodes are affected differently by the cast-in-situ slab,and the effect of it on the beam ends of the middle node is greater than that of the edge nodes.(3)Under the action of an inverted triangle load,the stress of rebar at the longitudinal beam end increases,the concrete damage is aggravated,and the yield time at the column end is delayed,after the 200 mm hole is opened in the cast-in-situ slab.It is indicated that the phenomenon of “strong beam weak column” of RC frame is improved after cast-in-situ slab hole opening,which is beneficial to realize the original design of “strong column weak beam”.However,the rebar of cast-in-situ slab with corner-hole frame column ends is still yielding before the beam rebar,and the frame column concrete damage has not been significantly improved.These show that in terms of the analysis model,opening a 200 mm corner hole in the cast-in-situ slab cannot guarantee to realize “strong column weak beam” of RC frame.The response of RC frame under the El-Centro seismic wave is similar to the static analysis.(4)A large number of cracks occurred at the junction between the cast-in-situ slab and the transverse beam after opening corner hole,and the interaction between the cast-in-situ slab and the transverse beam is strengthened.The concrete damage of transverse beam end is aggravated due to the twisting. |
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