Experimental Study On Fire Resistance Of Restrained Monolithic Laminated-slab Composite Beams

The monolithic laminated-slab composite beam is a structural form of overall stress that is composed of monolithic laminated slabs,steel beams and studs.The pre-fabricated slab is made in the factory,and steel structure is a natural type of assembled structure,so the monolithic laminated-slab composite beam is one of assembled buildings.The monolithic laminated-slab composite beam is accorded with orientation that popularizes assembled structure by nation.Besides the monolithic laminated-slab composite beam has good mechanical properties and economic advantages,so the monolithic laminated-slab composite beam has been widely used in building structures.As an important transverse load-bearing member,fire resistance of the monolithic laminated-slab composite beam can influence safety of the whole structure.When a fire breaks out,the restraint of peripheral members on composite beams can affect directly the failure form of the composite beam.So it is essential that an experimental study on fire resistance is carried out about restrained monolithic laminated-slab composite beams.It is found by study results of fire resistance of steel-concrete composite beams at home and abroad that there is not any study about restrained monolithic laminated-slab composite beams.So considering three parameters,thickness of post-poured layer of laminated slabs,the space of studs,constraint mode,experimental studies that five restrained monolithic laminated-slab composite beams and a cast-in-place concrete slab composite beam as contrast and finite element analysis that five restrained monolithic laminated-slab composite beams are carried out.The main conclusions drawn by experimental studies and finite element analysis as follows:(1)A temperature gradient appears along the direction of thickness of laminated slab,and temperature of underside is tallest.The regions of laminated slab below 40 mm are influenced by fire more seriously.And it can as a basis for increasing the thickness of concrete protective layer.Distributions of laminated slab are the same as distributions of cast-in-place concrete slab.The surface between pre-fabricated slabs and post-poured layer has little influence on temperature field.(2)Both monolithic laminated-slab composite beams and cast-in-place concrete slab composite beams undergo vertical deflection under the action of thermal-mechanical coupling.The change laws of the two composite beams are basically the same.Cracks on the top of the laminated slab are distributed along the central axis,and cracks extend from both ends to the mid-span with cracks narrowing from wide to narrow.The laminated surface between the pre-fabricated slab and the post-poured layer in the laminated slab is not cracked and still works together cooperatively.There is no crack at the bottom of the slab,but local concrete burst occurs,with the burst location concentrated at the bottom of the pre-fabricated slab.The cracks also appear at the top of cast-in-place concrete slab along the direction of central axis,but the cracks are relatively short.There is no crack at the bottom of the slab and no concrete burst.(3)The thickness of the post-poured layer of the composite slab has little influence on the fire resistance of monolithic laminated-slab composite beams.The stud spaces of 150 mm and 200 mm are both completely shear resistant designs,which has little effect on the fire resistance of monolithic laminated-slab composite beams.Different connection modes have their own influence on fire resistance of monolithic laminated-slab composite beams,but under rigid connection composite beams are more prone to out-of-plane instability.(4)The macroscopic failure characteristics of the monolithic laminated-slab composite beam and the cast-in-place concrete slab composite beam are similar,which shows that the fire resistance of the monolithic laminated-slab composite beam is not obviously reduced due to the existence of a large number of new and old combined sections.(5)The finite element model of restrained monolithic laminated-slab composite beams is established by using finite software ABAQUS.Through the finite element analysis of the temperature field and thermal-mechanical coupling,it is found that the results of finite element analysis are in good agreement with the experimental measurement results.The correctness of the finite element model is indicated,which can be used for further research on monolithic laminated-slab composite beams.