In recent years, high performance concretes (HPC) are finding increasing applications in buildings and infrastructure due to numerous advantages, such as higher strength and durability, these HPC offer over conventional concretes. Structural members made of HPC, when used in buildings, have to satisfy the fire resistance requirements specified in building codes and standards. Although conventional concrete members have good fire resistance, same may not be true for HPC members due to faster degradation of strength with temperature and occurrence of fire induced spalling. Spalling in HPC columns can be overcome either through the addition of fibers in the concrete mix or through the provision of 135° bent ties. For evaluating the fire resistance of HPC columns, as well as to account for the beneficial effects of fibers and 135° tie configuration on spalling mitigation, high temperature properties of HPC and numerical models that can take in to account the effect of tie configuration is required. At present, there is lack of data on high temperature properties specific to different types of HPC (plain and with fibers). Also, there is no methodology to account for the effect of tie configuration on fire resistance of RC columns. To overcome these knowledge gaps, an experimental and numerical study is undertaken as part of this thesis. Performance characterization of high performance concretes under fire conditions is carried out at both material and structural level (specifically columns). As part of material characterization, thermal and mechanical property tests were carried out in 20-800°C temperature range on different HPC mixes (plain and with different combinations of fibers). Data from measured property tests was utilized to develop empirical relations for high temperature properties. As part of structural characterization, fire resistance tests were carried out on two fly ash concrete (FAC) and two high strength concrete (HSC) columns with different fiber combinations. As part of numerical study, a macroscopic finite element (MFE) model, originally developed to evaluate fire resistance of RC columns, was extended to include the effect of tie configuration. The proposed tie sub-model is based on the approach used in seismic design and involves calculation of force acting on ties by evaluating stresses resulting from pore pressure, mechanical loading and thermal effects in RC columns under fire exposure. The force acting on ties is compared against temperature (time) dependent bond strength (tie-concrete interface) to evaluate the failure of ties. The model is validated by comparing response predictions against test data and the model was applied to carry out parametric studies to quantify the influence of HPC properties and tie configuration on fire response of HPC columns.Results from high temperature material property tests show that HPC exhibit thermal properties similar to that in conventional concrete. However, mechanical properties of HPC degrade at faster rate (much severe) than that in conventional concretes. Results from fire resistance tests show that plain HPC columns exhibit lower fire resistance due to occurrence of fire induced spalling and faster degradation of strength. However, presence of different fiber combinations in HPC columns can significantly enhance the fire resistance of the columns. In addition, presence of 135° bent ties in HPC columns can significantly enhance the fire resistance of these columns through confinement action.
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