Search results

This paper examines the level of detail and complexity that one needs to incorporate in a computational finite element (FE) model to predict the thermal and structural response of steel high-rise building frames to fire. Comparisons are made between these models in terms of accuracy and efficiency. Performance related to three parameters was examined: (1) the representation of the structural system as a 3-D full frame model versus a 2-D plane-frame model, both of which include the steel frame and the floor slab; (2) the representation of the slab in the 2-D plane frame model; and (3) the effects of modeling the temperature profile of each steel member cross-section as non-uniform (i.e. allowing a thermal gradient to develop) versus uniform. Results indicate that the 2-D plane frame model can be reasonably used in some cases to predict the performance of the perimeter column and floor beams framing into them in a fire-exposed high-rise moment-resisting frame (MRF) with a significant savings in analysis run time. The slab has little influence on the structural analysis of a 2-D plane frame; however, the slab influences the thermal profile through the depth of the beams, and these temperature changes will produce a non-negligible change when calculating the behavior of the frame and should be accounted for. Results also indicate that models whose members have uniform temperature can be used to obtain reasonable estimates of the interaction between connected beams and columns. However, thermal gradients produce significant changes in the deflection mechanics and plastic P-M limit state behavior exhibited by non-uniformly heated beam-columns that experience a severe decrease in capacity; therefore, it is recommended that thermal gradients be included in models that are used to predict deflections or plastic limit state behavior.

Mild steel plates used in buildings and offshore platforms are prone to fire accidents. These plates being ductile are designed effectively for buckling and ultimate strength characteristics under static loads. These characteristics get drastically affected due to reduction in stiffness of the stress strain characteristics of mild steel with increase in temperatures. This paper presents a numerical study conducted on clamped plates at elevated constant temperature for the assessment of reduced buckling and ultimate strengths. Coupled Nonlinear static thermal analysis on clamped plates was performed using standard FE software ANSYS®. Both geometric and material nonlinearities are considered in the analysis. The study comprises of plates with varying aspect ratio (1 to 4) and breadth to thickness (28 to 128) at constant elevated temperatures of 0 °C, 200 °C, 400 °C, 600 °C and 800 °C. Nondimensional plate slenderness ratios based on AISC and Eurocode at elevated temperature was evaluated. Several charts showing normalised buckling stress vs temperature and normalised ultimate strength vs temperature for varied nondimensional plate slenderness ratio and plate aspect ratios are drawn. The buckling and ultimate strengths from this study are found to be underestimated in comparison to Eurocode and AISC calculations. The reduction in buckling and ultimate strength was found to be significant beyond 400 °C. It is observed that for all plate aspect ratios, the effect of plate breadth to thickness ratio is important for temperatures below 500°C and at 800°C ultimate strength of plate is only about 10% of that of at normal temperature.

This paper aims to present a literature review on the problem of fire following earthquake (FFE) as a potential hazard to communities in seismically active regions. The paper is important to work toward resilient communities that are subject to extreme hazards.

The paper lists and reviews the historical FFE events (20 earthquakes from 7 countries), studies the available analytical tools to evaluate fire ignition and spread in communities after an earthquake, discusses the available studies on performance of individual buildings under post-earthquake fires and summarizes the current literature on mitigation techniques for post-earthquake fires.

FFE can be considered a potential hazard for urban communities that are especially not prepared for such conditions. The available analytical models are not yet fully up to the standards that can be used by city authorities for decision-making, and therefore, should be further validated. Limited structural analyses of individual buildings under FFE scenarios have been completed. Results show that the drift demand on the building frame increases during post-earthquake fires. Despite the mitigation actions, there are still urban cities that are not prepared for such an event, such as certain areas of California in the USA.

The paper is a complete and an exhaustive collection of literature on different aspects of FFE. Research in earthquake engineering is well advanced, while structural analyses under fire load and performance of communities under FFE can be further advanced.

This paper aims to investigate the need for active boundary conditions during fire testing of structural elements, review existing studies on hybrid fire testing (HFT), a technique that would ensure updating of boundary conditions during a fire test, and propose a compensation scheme to mitigate instabilities in the hybrid testing procedure.

The paper focuses on structural steel columns and starts with a detailed literature review of steel column fire tests in the past few decades with varying axial and rotational end restraints. The review is followed with new results from comparative numerical analyses of structural steel columns with various end constraints. HFT is then discussed as a potential solution to be adapted for fire testing of structural elements. Challenges in contemporary HFT procedures are discussed, and application of stiffness updating approaches is demonstrated.

The reviewed studies indicate that axial and rotational restraints at the boundaries considerably influence the fire response of steel columns. Equivalent static spring technique for simulating effect of surrounding frame on an isolated column behavior does not depict accurate buckling and post-buckling response. Additionally, numerical models that simulate fire performance of a column situated in a full-frame do follow the trends observed in actual test results up until failure occurs, but these simulations do not necessarily capture post-failure performance accurately. HFT can be used to capture proper boundary conditions during testing of isolated elements, as well as correct failure modes. However, existing studies showed cases with instabilities during HFT. This paper demonstrates that a different stiffness updates calculated from the force-displacement response history of test specimen at elevated temperature can be used to resolve stability issues.

The paper has two contributions: it suggests that the provision of active boundary conditions is needed in structural fire testing, as equivalent static spring does not necessarily capture the effect of surrounding frame on an isolated element during a fire test, and it shows that force-displacement response history of test specimen during HFT can be used in the form of a stiffness update to ensure test stability.