Structural fire design represents one important aspect of the design of reinforced concrete buildings. The work presented in this thesis seeks to elucidate the structural behaviour of reinforced concrete slabs during exposure to heating from below, as would occur in the case of a building fire, with a particular focus on structural fire modelling using finite element analysis. The focus in on validating finite element models against experimental results and quantifying the sensitivity of model outputs to relevant thermal and mechanical input parameters. A primary goal of the work is to provide recommendations to structural fire engineering analysts and designers considering the performance-based design of reinforced concrete slabs for structural fire resistance using available finite element software. A critical review of the available knowledge of the structural fire response of reinforced concrete structures in general and concrete slabs in particular is presented, along with an awareness as to the importance of understanding structural response of concrete structures exposed to fires. Current techniques for structural fire design of concrete structures are reviewed, and shortcomings highlighted. Available experimental data are presented, and various finite element models of these slabs are developed and interrogated to identify important aspects for understanding, as well as for future improvement of similar studies (both experimental and numerical) with the intention of supporting future progress in structural fire engineering, in particular as regards performance based structural fire design of concrete slabs. A range of thermal and mechanical parameters that are potentially important and influential in the structural fire design of reinforced concrete slabs is then studied, including: fire scenario, thermal properties of materials (thermal conductivity and specific heat), heat transfer parameters (coefficient of convection and emissivity) and assumptions, restraint conditions at the supports, variations of span-to-depth ratio, reinforcement detailing, as well as plan aspect ratio are all investigated; their influence on the structural fire response of reinforced concrete slabs is studied and discussed. A key issue in validating finite element models against experimental results lies in defining the temperature inputs to the structural finite element models correctly. Variation of available thermal and mechanical input parameters, as recommended in Eurocodes, influences the predictive performance of thermal and structural finite element models, however these are not the main contributing factors in obtaining a credible prediction of response from the finite element models. The most challenging aspect in performing heat transfer analysis for fire furnace tested reinforced concrete slabs lies in defining the correct thermal boundary condition. For simply supported one-way spanning and two-way spanning slabs, increasing slab's thickness (lowering span-depth ratio) does not improve fire resistance rating for the slabs when both limiting deflection criteria and limiting tensile plastic strain are set as acceptance criteria. Two-way slabs with higher span-depth ratio have better fire resistance ratings, judging from the overall trends and magnitudes of mid-span deflections. The formation of plastic hinges is likely to occur for one-way spanning slabs modelled with finite rotational spring stiffness at supports, but not for two-way spanning slabs. A yield line mechanism in two-way slabs means that the behaviour is more complex as compared to the simple flexural mechanism for one-way slabs. In one-way slabs, plastic hinges potentially occur at the location where top reinforcement is curtailed, highlighting the importance of properly understanding the nuances in response of concrete slabs in fire. Investigation of the influence of aspect ratio in two-way spanning slabs confirms that slabs with lower aspect ratios have better structural fire resistance than slabs with higher aspect ratios when both limiting deflection criteria and limiting tensile strain in reinforcing steel were used as the performance indicators. A combination of both limiting mid-span deflection criteria as well as limiting tensile plastic strain is recommended for specifying acceptance criteria for both one-way and two-way slabs, since it gives more accurate and comprehensive assessment on the structural response of the slabs under exposure to severe heating from below.

The essence of performance-based structural fire safety design of steel building structures is the ability to predict thermal and structural response to fire. An important aspect of such predictions is the ability to evaluate strength of columns at elevated temperatures. Columns are critical structural elements, and failure of columns can lead to collapse of a structure. The ability of steel columns to carry their design loads is greatly affected by timeand temperature-dependent mechanical properties of steel at high temperatures due to fire. It is well known that structural steel loses strength and stiffness with temperature, especially at temperatures above 400 °C. Further, the reductions in strength and stiffness of steel are also dependent on the duration of exposure to elevated temperatures. The time-dependent response or creep of steel plays a particularly important role in predicting the collapse load of steel columns subjected to fire temperatures. Specifically, creep of steel leads to the creep buckling phenomenon, where the critical buckling load for a steel column depends not only on slenderness and temperature, but also on duration of exposure to fire temperatures. The main focus of the research summarized in this dissertation is on a testing program to investigate the effects of time-dependent material behavior or creep on buckling of steel columns subjected to fire. Material characterization tests were conducted at temperatures up to 1000 °C to evaluate tensile and creep properties of ASTM A992 steel at elevated temperatures. In addition, buckling tests on W4×13 wide flange columns under pin-end conditions were conducted to characterize short-time and vii creep buckling phenomena at elevated temperatures. The column test results are further used to verify analytical and computational tools developed to model the time-dependent buckling of steel columns at elevated temperatures. Test results are also compared against code-based predictions such as those from Eurocode 3 and the AISC Specification. Results of the research study presented in this dissertation clearly indicate that thermal creep of steel has a very large effect on strength of steel columns at high temperatures due to fire. The effect of creep on column capacity at high temperatures can be predicted using analytical and computational approaches presented in this dissertation. / text

The average intensity and frequency of wildland fires have been on the rise over the years, leading to an increase in the risk to homes located in the Wildland-Urban Interface (WUI). Fire suppression is the most used method of wildland fire control, but this suppression can cause wildland fires to become more frequent and devastating. Increased development in the WUI also puts these homes at greater risk. Current methods of passive fire protection are effective, but these methods are expensive, time consuming to set up, and not fully effective. This research proposes a permanent passive fire protection system that is built into the structure. A flame- resistant material would be attached to the sheathing with the roofing and siding attached over the material. This system would allow the easily replaceable exterior components of the structure to burn, and the interior of the structure would be protected. This system protects the structural supports of the building, so the house does not collapse, and the exterior components can be replaced. To test this permanent passive fire protection system 21 small-scale specimens were constructed with five different flame-resistant materials and three different types of siding. The flame-resistant materials include structural wrap, Kaowool, ceramic fiber insulation, Pyrogel, and intumescent paint. The sidings include wood siding, vinyl siding, and hardie board. The testing took place in a burn room to simulate the conditions of a wildland fire. Post-burn charring evaluations and temperature analyses were conducted to determine which type of material and siding were most effective at protecting the small-scale models. The charring evaluation included determining the percent charring of the OSB face of the specimens, and the temperature analysis included determining the percent difference between the internal and external temperatures of the specimens. The performance, cost and installation, constructability, and replaceability of each of the materials were considered in deciding which materials were most effective. Overall, the Pyrogel outperformed the other materials, but this material is by far the most expensive. The ceramic fiber material was overall the second most effective flame-resistant material, and this material could be as effective as the Pyrogel if used in conjunction with the other materials tested. Further testing of material combinations is required to determine if different flame-resistant material combinations could be as effective as the Pyrogel material on its own. The results of this project did prove the feasibility of a permanent passive fire protection system, but further testing of large-scale specimens is required to test the effectiveness of the system in more complex circumstances.

This project involves a failure analysis of the internal structural collapse that occurred in World Trade Center 5 (WTC 5) due to fire exposure alone on September 11, 2001. It is hypothesized that the steel column-tree assembly failed during the heating phase of the fire. The results of this research have serious and far-reaching implications, for this method of construction is utilized in approximately 20,000 existing buildings and continues to be very popular. Catastrophic failure during the heating phase of a fire would endanger the lives of firefighters and building occupants undergoing extended egress times (e.g., high-rise buildings), or relying upon defend-in-place strategies (e.g., hospitals). Computer software was used to reconstruct the fire event and predict the structural performance of the assembly when exposed to the fire. Results from a finite element, thermal-stress model confirms this hypothesis, for it is concluded that the catastrophic, progressive structural collapse occurred approximately 2 hours into the fire exposure.