Flexural Rigidity And Seismic Performance Analysis Of Reinforced Concrete Frame Beam Considering The Boundary Beam Effect

Reinforced concrete frame structure may suffer from larger deformation and displacement than other structures under a strong seismic action due to its low lateral stiffness and high overall structural flexibility, while frame structure dissipates seismic energy mainly through the plastic deformation of beam and column members, so the location and sequence of plastic hinge in the members have a huge impact on the response and overall deformation of structure under a horizontal seismic action. According to reports on the previous several disastrous earthquakes, lots of frame structures collapsed due to the earlier destruction of column than beam. An important cause for this is that the flexural stiffness of beam wasn't considered in the time of internal force calculation. The impact of floor slabs on beam stiffness cannot be ignored, while a boundary beam of frame structure may twist under a load action from floor slabs, but the corresponding boundary beam will produce a restriction effect on floor slabs to restrict their deformation, so as to exert an effect on the flexural stiffness of beam through floor slabs.At present, when the constraints of floor slabs on frame beam are considered in research,the impact of the boundary beam formed from integrated cast-in-site on floor slabs are usually neglected, neither is there an accurate calculation formula for the values of beam rigidity amplification coefficient. By considering the amplifying action of floor slabs on the stiffness of frame beam under the influence of boundary beam, this paper researched the stiffness and seismic performance of frame beam:(1) Researched various countries' regulations on the amplifying action of floor slabs on beam stiffness, and the fundamental principle of pushover analysis.(2) Used PKPM and SAP2000 for modeling and calculation, obtaining data related to beam rigidity amplification coefficient in different conditions, and carried out a data analysis,devising a formula for the relationship between beam rigidity amplification coefficient and boundary beam depth, middle beam depth as well as slab thickness.(3) Validated the beam rigidity amplification coefficient calculation formula with consideration to beam action, calculated the reinforcement in various frame structures using this formula, and then adopted SAP2000 for a pushover analysis.(4) Obtained data on floor displacement and inter-storey displacement in the frame structure by way of pushover analysis to evaluate the seismic performance of the frame structure beam to which the rigidity amplification coefficient calculation formula with consideration to beam action is applied, and judge whether the structure reinforcement is rational, whether the structural distortion is within the code limit, and whether the structure is consistent with the"strong column-weak beam" mechanism in accordance with the location and sequence of plastic hinge.A pushover analysis was made of the frame structure reinforced according to beam rigidity amplification coefficient calculation formula with consideration to boundary beam action. The result shows: the use of this formula can help calculate the rigidity amplification coefficient of frame bream more accurately; the structure has higher lateral stiffness and ductility; the location and sequence of plastic hinge are also consistent with the "strong column-weak beam" mechanism,and the structure has good seismic performance.