Analysis Of Impact Collapse Of Precast Slab Floor In Multistory Brick Buildings

The multi-storey brick-concrete structure with sintered ordinary brick as vertical bearing structure and precast concrete slab as horizontal floor has a long service history in China.Under the long-term external environment and loads,this kind of structure which can bear vertical loads well but is prone to damage or even collapse under horizontal loads,especially under seismic loads,is facing security challenge.Different external disturbances may lead to partial drop of prefabricated concrete slabs at the top and consecutive collapse of multi-storey brick-concrete structures from the top to the bottom floor.Therefore,taking the typical floor collapse engineering structure as the research object,the collapse analysis of precast concrete slabs based on the concrete structure system and its mechanical characteristics has important theoretical significance and application value for putting forward reasonable treatment measures and ensuring the safety of such structures.The following work has been done in this paper:Firstly,the main factors affecting the falling of roof prefabricated panels are analyzed.At first,it is found that the additional surface load caused by high water content expanded perlite insulation layer is far greater than the design requirements,and the long-term deformation effect experienced by roof precast slab concrete leads to the reduction of the stiffness,and the increase of deflection of precast slab and the deflection of the end of slab also make the supporting length of the slab reduces.Secondly,there is no brick masonry wall above the end of the prefabricated slab of the roof,which can improve the integrity of the cast-in-situ concrete surface layer without pouring between the prefabricated slabs of the roof.Thirdly,due to the long-term effect of load,seasonal temperature difference,earthquake and strong wind disturbance during use,there is a certain out-of-plane deformation of the inner and outer longitudinal walls supporting roof prefabricated panels.The erosion of external environment makes the performance of wall materials deteriorated and the bearing capacity reduced.The cumulative effect of various reasons makes the supporting conditions of precast prestressed concrete hollow slabs and surrounding supporting walls worse,and eventually falls off.Secondly,it is found that the falling precast slab continuously breaks down to the first floor,and the surrounding supporting beam produces obvious transverse cracks in the middle of span and shear inclined cracks near the support at the end of the beam.The surrounding columns and walls are also damaged to varying degrees,and the bearing structures in this area have been basically destroyed.Based on the measured material strength,it is analyzed that the ultimate bearing capacity of four-storey precast hollow concrete slabs are not enough to resist the impact load of falling floor slabs.For the following floors,with the improvement of impact quality and height,it is difficult for the lower floors to bear the impact effect of increasing layer by layer,which eventually leads to the continuous collapse of the area.Finally,the strategies for rebuilding the collapsed areas and strengthening the integrity and improving the integrity of the remaining areas are proposed.For cast-in-situ concrete slabs which do not meet the safety requirements,the reinforced concrete surface layer is used to reinforce,and the reinforced concrete surface layer is cast upon the precast concrete slab area;for brick masonry walls,the composite wall composed of the reinforced concrete surface layer is used to reinforce the brick masonry walls,and the roof and wall adopt reliable connecting measures.It meets the requirement of the project to continue safe service.