Fire Behaviour Of Concrete Slabs And Testing Study On Continuous Panels In A Whole Structure

Building fires remain frequent in recent years, resulting in local damage or destruction even catastrophic collapse of massive buildings subjected to fire. Thus, the safety of structures under fire and subsequent damage detecting, strengthening and repair of the structures post-fire attract more and more attentions of researchers and engineers. In order to further understand the mechanical properties of reinforced concrete(RC) slabs, the thesis adopts the self programming to carry out the nonlinear analysis of the single isolated RC slabs under fire and post-fire, which have been demonstrated in the literature published. However, in real building fires RC slabs present better the fire behavior compared to the standard fire tests due to complex interaction between different structural elements. Based on above consideration, this thesis further studies the fire-resistance of contiouous RC slabs(2×3) in a complete building. Moreover, the vibration properties of 2×2 continuous RC slabs located in above complete building are studied exploringly. The specific contents are summarized as follows:(1) Transient temperature fields(TTF) of the structures under fire are simulated through self-made finite element thermal analysis programming. During the simulation water evaporation is considered, thus the simulation results are more accurate compared to classical analysis of temperature field. Example analyses also confirm the validity and accuracy of temperature field simulation. Study on TTF lays the foundation for subsequent nonlinear analysis of RC slabs in fire and post-fire.(2) Based on TTF analysis, self-made nonlinear finite element procedure is used to predict the structural behavior of the RC slabs at ambient and elevated temperatures. The procedure adopts layered plate element with large deflection and elasto-plastic theory to establish two-dimensional thermal elasto-plastic constitutive model of concrete or reinforcement at each layer. In this way the crush and crack of concrete, as well as the yield and strengthen behavior of reinforcement are computered more accurately. Simulation results indicate that above analytical model can analyze the fire behavior of RC slabs exactly.Fire resistance analysis shows that specifications stipulate a similar fire resistance of one-way RC slabs as judged by deformation criteria and temperature criteria used in the thesis; but for two-way RC slabs, the specifications are too conservative, thus the fire resistance needs to be modified. However, fire tests performed on single isolated RC slabs do not reflect the real behavior of the slab in the whole structure under fire. In real buildings the slab has better fire performance due to its stronger boundary constraints. Thus further studies of fire resistance of RC slabs should be continued.(3) The assessment of the residual strength of post-heated RC slabs in a professional way is a prime factor to take a decision about the reinstatement or demolition of fire-damaged slabs. The thesis presents the calculation of residual load-bearing capacity based on the finite element simulation. The method depends on estimation of the peak temperature and duration, calculation of thermal gradient within the slabs and assessment of the residual strength of post-heated slabs. The theoretical results are in good agreement with the testing results, which verify the reliability and rationality of the finite element model.(4) Fire behavior of six continuous panels(2×3), located in a three-storey steel-framed building with three bays long and three bays wide, was tested by use of self-made furnace. In this thesis, the test building, specially designed furnace and relevant testing program were briefly introduced; the experimental phenomena including failure patterns were also described. The furnace temperatures, temperature distributions, failure patterns as well as horizontal and vertical displacements of some structural components during the heat-up and cool-down phases were recorded and discussed in detail. The testing results were also compared with the other fire testing results. The test produced lots of valuable experimental data and leaded to better understand the real fire behaviour of RC slabs.(5) The vibration properties of RC slabs in above real building under fire were studied. Hilbert Transform can be as an effective method to extract instantaneous frequency of engineering strucutres. Vibration intensity has important relationships with boundary constraints. The frequency changes are closely with cracks propagation and show significant decreasing trend during the heat-up stage. Through the frequency analysis the fire behavior of the panels can be monitored.