Experimental Research On Fire Resistance Performance Of Reinforced Concrete Composite Slabs With Boundary Constraints

In order to learn the fire resistance performance of reinforced concrete co-mposite slabs(RCCS) with boundary constraints and the mechanical properties of fire-damaged RCCS with boundary constraints,7 RCCS with boundary constraints were studied in static tests under ambient temperture, in fire endurance experiment and in bearing capacity tests after fire. The comparision of finite element(FE) simulation and theoretical calculation were carried out. The main conclusions are as follows:(1) The boundary constraints of RCCS under working conditions include-s:vertical support of beams, embedded restraint supported by adjacent plates and beam torsional rigidity, horizontal restraint supported by adjacent plates and the uneven deformation of beam by fire.This test through pouring edge beams to simulate the negative moment rotational restraint. The vertical displacement of the side beam were constraints, at the same time when the beam under theuneven fire, will produce laminate secondary constraints.(2) The bearing capacity of 1 RCCS with boundary constraints was tested under ambient temperature. The cross strains, crack development, cracking load, ultimate load, failure mode of the specimen, and the shear properties of laminated surface were studied in the experiment. It shows that RCCS with boundary constraints has a larger earring capacity and safety margin, steel truss played a significant role in suppressing relatively slip at laminated surface. The results are prepared for the experiments under and after fire as the comparativedata.(3) FE simulation on the flexural behavior of RCCS with boundary constraints were carried out by using software ABAQUS. The cracking load, ultimate lode were calculated by theoretical method. Both of the results are coincide with the experiments data.(4)3 RCCS were carried out fire endurance test under load. S2 and S3 were RCCS with boundary constraints, which of the load ratio were 0.3 and 0.5. S4 was RCCS with no boundary constraints, which has the same load with S2.The temperature field, fire performance and failure characteristics in different time under fire were comparatively studied. The results indicated that boundary constraints can significantly improve the fire resistance of speciments and inhibited horizontal peeling cracks between the panels and laminated layer.(5) The results of FE simulation of temperature field which achieved byusing software ABAQUS are coincide with the experiment results. According to this, the nonlinear coupled thermal mechanical analysis of RCCS were done.Specimens analytical results of fire endurance,displacement time curve, agreed well with experiment results.(6) In this paper, Flexural members'fire resistance of different load ratios was carried out regression analysis. The data was obtained from test of this paper and others'test and FE simulation. It found that the regularity between ordinary concrete member with holding charge ratio was strong. The fire resistance of different parameters affected varies with load ratio was obtained by regression. This has a strong guiding significance to predicting the fire resistanceof reinforced concrete.(7) Using theoretical analysis method and considering the tensile membrane effect of slabs, the ultimate bearing capacity of RCCS under high temperature was calculated. The relationship between different boundary constraints of RCCS and time under fire were obtained. Considering the effect of high-temperature tensile strength damage and specimen deformation on shear properties at laminated surface, the shear capacity were calculated by theoretical method.(8) The flexural behavior of 3 RCCS with boundary constraints which were exposed to fire with different time (30min,60min and 90min) then cool under load were tested under ambient temperature. The cross temperature field during heating and cooling, flexural deformation under and after fire, and residual bearing capacity of specimens were studied in the experiments. The results indicate t-hat with the increase of time under fire, the ultimate lode, stiffness of RCCS decrease signficantly, while the residual deflection increses. The relationship be-tween maximum dispalcement, stiffness and ultimate load with time under fire were obtained by regression analysis.(9) The cross temperature field of specimens were simulated during heating and cooling process and the flexural ability of RCCS with boundary constraints after fire were analyzed all by ABAQUS. It shows that the cross temperature field during cooling are huge different with heating process. The simulation of ultimate load of RCCS with boundary constraints after different timeunder fire are consistent with experiment data.(10) Based on the experimental studies, numerical simulations and theoretical analysis, The fire resistance of RCCS with different constraints and load ratio was obtained. The deteriorated formulas of residual bearing capacity of RCCS after fire then cool was also obtained. All of this provide a scientific basis of fire safety design and evaluation after fire with RCCS.