Search

• Vehicle fire exposure degrades the performance of PC overlays. • Vehicle fires risk infrastructure with high heat flux and flame temperatures. • Measures should be developed to protect PC overlays from fire exposure. This study investigates the performance of polymer concrete (PC) overlays after short-duration vehicle fire exposure. A vehicle fire test was conducted on a reinforced concrete slab with polyester PC overlay. Test results show a notable decline in overlay performance after the fire. In high-exposure areas, average reductions ranged from 13.3% to 23.1% in skid resistance, abrasion resistance, chloride penetration resistance, and surface hardness. Heat exposure heightens the bond failure risk and causes overlay delamination. Water penetration tests, done separately, show extended fire worsens PC overlay damage. These findings guide future performance improvements of PC. [ABSTRACT FROM AUTHOR]

Highlights • Simplified nonlinear model for post-fire earthquake response of RC walls is presented. • Modification factors are applied to existing models for RC wall response. • Modification factors account for the change in stiffness, strength, and deformation. • Fire-damage indices (FDI) quantify the residual material properties due to fire. • Recommended modification factors are a function of axial load ratio and FDI. Abstract A potential multi-hazard scenario for buildings is the sequential occurrence of fire and earthquakes, with such a scenario possible if a fire is triggered by an initial seismic event and a subsequent aftershock occurs. With fire negatively influencing the stiffness, strength, and deformation capacity of structural components, the building may be at risk for local or global collapse. The key role of reinforced concrete (RC) walls as lateral load resisting components make them of particular importance in considering the post-fire earthquake performance of buildings. Since the risk of fire-earthquake hazards is low, simplified models are needed to efficiently evaluate building performance. In this paper, a framework for simplified nonlinear modeling of RC walls is presented. The models are defined by modification factors that account for the change in wall response relative to that of a wall without fire damage. Modification factors, established from the results of a parameter study of walls using a verified simulation method, are a function of fire damage indices that account for the effect of fire on the material properties of steel and concrete. The dependence of wall response on most wall characteristics is eliminated by use of the damage indices, with the recommended modification factors dependent on the fire damage index and axial load alone. [ABSTRACT FROM AUTHOR]

A potential but infrequently studied hazard is the sequential occurrence of earthquakes and fires. Fire hazards following an earthquake can be significant due to increased likelihood of fires igniting, increased demands on firefighting resources, and potential obstacles to timely response. Increased ignitions and longer burn times can have significant structural impacts on reinforced concrete (RC) structures which are usually considered to have superior performance in a fire. The impact of this fire induced structural damage on the lateral load resistance of RC structures, particularly RC structural walls, is not well understood but may be critical in the event of aftershocks and/or future earthquakes. Given the severity of the consequences of reduced lateral load resistance, it is important for engineers to better understand fire-earthquake hazards in RC walls. This paper presents numerical studies to investigate the impact of fire damage on the lateral load resistance of flexure-controlled RC structural walls, including a parametric study to identify influential wall characteristics. Results indicate that fire damage decreases the load-bearing capacity and the stiffness of RC walls under reversed-cyclic loads. Curvature is shown to be a better indication of fire induced failure. At failure, damage may shift to the web of a wall after fire exposure becomes more severe. Wall characteristics which significantly influence the residual wall response quantities were identified to be wall thickness, boundary element length, and axial load ratio. [ABSTRACT FROM AUTHOR]

The impact of fire induced structural damage on the lateral load resistance of RC structures, particularly RC structural walls, is not well understood, but may be critical in the event of sequential fire-earthquake hazards. A simple verified simulation procedure for the post-fire seismic analysis of RC structural walls is necessary to advance the understanding of the post-fire seismic performance of RC structural walls. However, individual software programs which can do well in both thermal analysis and seismic analysis are not currently available. In this paper, a simulation procedure combining SAFIR and OpenSees is proposed for the post-fire seismic analysis of RC structural walls. The thermal analysis of a wall section is conducted in SAFIR while the seismic analysis of the fire-damaged wall is conducted in OpenSees based on the temperature data from SAFIR. The simulation method is verified by test data of RC walls under sequential fire-earthquake loads. The comparison of the numerical and experimental data demonstrated the capabilities of the simulation procedure to capture temperature distribution, stiffness and strength of flexure-controlled RC structural walls. [ABSTRACT FROM AUTHOR]

Strap-braced, cold-formed steel framed walls are frequently used as the lateral force resisting system in cold-formed steel construction. While the behavior of these walls has been studied under lateral loading and (to a lesser extent) under fire conditions, there is a need to comprehend the influence of multi-hazard interactions, in particular the effect of fire pre-damage on the lateral load resistance of the walls. In this paper, a numerical model of a strap-braced cold-formed steel wall is developed to analyze the thermal and structural response when subjected sequentially to fire followed by shear deformation. The numerical model is validated against full-scale experiments. Coupon tensile tests are conducted to characterize the post-fire properties of the cold-formed steel that are used as inputs to the model. The results show that the numerical model can capture the post-fire response of the cold-formed steel walls including the wall strength, stiffness and ductile failure by yielding of the strap. The lateral behavior of the walls depends primarily on the maximum temperature reached in the cold-formed steel members and the resulting residual properties. Thermal analysis by the finite element method can be used to predict the maximum temperatures across a wall section under a variety of design-relevant fire scenarios, but the results are strongly affected by the quality of the data on thermal properties and by the loss of integrity of the gypsum sheathing. This study validates the numerical modeling strategy and suggests that the post-fire lateral capacity of the walls can be predicted from ambient temperature methods with use of the cold-formed steel residual mechanical properties. • Propose a numerical strategy to assess the post-fire lateral capacity of CFS strap-braced walls. • Conduct new material tests to obtain the post-fire retention factors for CFS. • Simulate four experimental tests to validate the proposed numerical strategy. • Capable to model the failure mode, stiffness and ultimate strength of fire-damaged CFS walls. [ABSTRACT FROM AUTHOR]

This paper presents an overview of selected issues in computational modeling for reinforced concrete structures in fire. The focus is on current modeling challenges, as well as aspects that are sometimes overlooked yet important for capturing the concrete material and structural behavior at elevated temperatures. Issues addressed include the consequences of realistic thermal exposures with cooling phases on the material properties and deformations, the uncertainties in material and structural response at elevated temperature, and the effect of the tensile fracture energy on the model response. The ability to capture membrane and shear failure modes is analyzed. The modeling of the residual response and potential failure during cooling is discussed. As an example, a five-story RC shear wall-frame building is modeled under natural fire. Finally, the paper ends with a discussion on the limits, research needs and opportunities with respect to computational modeling of concrete structures in fire. • The numerical modeling of concrete structures in fire is a complex endeavor. • Sensitivity of the predicted structural response in shear and membrane modes is discussed. • Tensile behavior and fracture energy are important yet insufficiently characterized. • Numerical failure (lack of convergence) must be distinguished from actual failure. • Still, (reasoned) adoption of numerical models offer great opportunities. [ABSTRACT FROM AUTHOR]

• A method to estimate economic loss due to fire in concrete buildings is presented. • The method is based on sequential analyses for fire hazard, response, damage, and loss. • Fire-specific EDP are proposed to measure thermal and structural damage states. • Fragility and consequences functions are given based on repair cost data. • A case study of a five-story RC building shows the potential of the method. A framework is proposed for the probabilistic estimation of yearly economic losses due to fire in concrete building structures. The fire loss estimation accounts for the uncertainties in the occurrence and growth of a fire as well as the response of the building. The assessment performs a fire hazard analysis, response analysis, damage analysis, and loss analysis. The response analysis relies on three-dimensional finite element modeling of the building structure. The expected direct loss for the building is determined by summing the expected losses under fires in different locations, weighted by the annual probabilities of fire occurrence in each location. To achieve this goal, we propose fire-specific engineering demand parameters (EDP) that are measurable and associated with damage states. One EDP addresses section damage due to temperature penetration, while a second EDP addresses component damage linked to deformations. We also define a set of fragility functions and consequence functions based on the selected damage states. The presented framework is applied to a case study of a five-story reinforced concrete frame building. Direct losses are evaluated at about 188 k$ for scenarios of single-compartment fire, conditional to the occurrence of severe fire. Losses are mostly related to nonstructural components and content. Although the case study focuses on single-compartment fires, losses in case of fire spreading within the building can be incorporated as well using event tree analysis with the conditional probability of the respective fire scenarios. The yearly fire loss framework presented in this paper can be adopted for other types of buildings and can be integrated into the workflow for the hazard vulnerability assessment of a community. [ABSTRACT FROM AUTHOR]

• Numerical modeling of the fire response of a code-designed RC frame building. • Focus on post-fire damage and deformations as they affect resilience and recovery. • Large residual deformations and loss of capacity are observed in the columns. • Thermal deformations of beams and slabs have large effects on the RC columns behavior. • Models of the structural system are needed to capture these thermal restraint effects. Reinforced concrete (RC) structures often remain stable under fire, but exhibit damage and residual deformations which require repairs. While repair operations and building downtime are expensive, current fire design approaches do not consider post-event resilience. The first step to enable predicting the resilience of RC structures under fire is to develop capabilities to model the damage of these structures after various fire exposures. This paper focuses on the prediction of the residual (post-fire) deformations of RC columns within a code-designed five-story RC frame building. Computational modeling approaches to capture the fire behavior of the columns are investigated. The models range from isolated columns with linear springs at the boundaries to full building model coupling beam and shell elements, with intermediate approaches. The analyses highlight the critical nonlinear role of the thermal expansion-contraction of the surrounding beams and slabs on the column deformations. Large transversal residual deformations develop particularly in perimeter columns, combined with residual shortening. This invalidates models based on isolated column or 2D frame. A parametric study of the residual deformations of RC columns is then conducted, with due consideration of the 3D restraints and interactions, to investigate the effects of different design parameters and fire scenarios on the residual deformations after a fire event. The results of the parametric study indicate that fire load density and opening factor significantly influence the residual deformations of RC columns, compared to the thermal conductivity of concrete and live loads. This research improves the understanding and provides recommendations for numerical modeling of the effect of fire on the residual capacity and deformations in RC structures. [ABSTRACT FROM AUTHOR]

In the past decades, reducing and recycling of construction and demolition waste (CDW) has been gaining an increasing attention in infrastructure development for both economic and environmental benefits. Recycled concrete aggregate (RCA) from demolishing of old structures is one major type of construction waste. Many researchers have studied the resultant physical and mechanical properties of concrete made with RCAs. In a continued effort of material recycling, this study explored the feasibility of using demolished concrete blocks (DCBs) in the production of concrete. Compared to conventional RCA, DCB is characterized by its relatively large size. In this study, DCBs were used with self-compacting concrete (SCC) to produce DCB-filled-concrete (DCBFC) since SCC can easily fill up the voids between DCBs. The compression tests conducted in the study indicated that concrete with only SCC and DCB had low compressive strength – which, however, exhibited an increasing trend as the DCB was replaced with natural rocks. Among the three types of DCBFC, DCBFC60 (i.e., 60% DCBs with 40% natural rocks by mass) exhibited the highest compressive strength that was comparable to the compressive strength of SCC. Additionally, three reinforced concrete (RC) beams made of SCC with different proportions of DCBs and natural rocks were tested in the bending loading mode to characterize their flexural strength and cracking resistance potential. While the bending behavior was similar to normal RC beams, the yielding and ultimate moments of SCC beams increased with an increase in the natural rock content, which was consistent with the test results from the compression tests. Similarly, crack mapping also indicated an increase in more tortuous and secondary cracks with an increase in the ratio of the natural rock content. Life cycle assessment also yielded significant environmental benefits with the use of DCBs over conventional concrete. [ABSTRACT FROM AUTHOR]

The smoke back-layering length and the critical ventilation velocity in double fire scenarios where the fire sources were both inside and outside the tunnel were studied by small-scale tests and theoretical analysis. Results showed that the smoke back-layering length increased with an increase of the fire separating distance when the dimensionless fire separating distance was less than 3, and the values were larger than the results of a single internal fire at each fire separating distance. The dimensionless critical ventilation velocity segmentally increased with the increase of the dimensionless fire separating distance when the dimensionless fire separating distance was less than 10, and then remained constant. Moreover, the constant value was found to be close to that in the case of a single tunnel fire. In addition, an empirical model of dimensionless critical ventilation velocity was established for the double tunnel fire scenario both inside and outside a tunnel. • Tunnel fire scenarios occurring both inside and outside a tunnel were studied. • Critical velocity increased first and then remained stable with increasing spacing. • An empirical model of dimensionless critical ventilation velocity was established. [ABSTRACT FROM AUTHOR]

• State-of-the-art review of cost-benefit analysis in fire safety. • Minimum requirements for a cost-benefit analysis. • Cost-benefit ratios or benefit-cost ratios do not allow to compare designs. • Prototype methodology elaborated. • Fire protection in remote warehouse as illustrative example. Cost-effectiveness is a key consideration within fire safety engineering. Currently, different approaches are being applied in literature. These approaches differ in how cost-effectiveness is evaluated, which costs are considered, and how the preferred design solution is defined. Recognizing this issue, the Fire Protection Research Foundation enrolled an international team of researchers, supported by a broad stakeholder panel, to develop a reference methodology. In this paper, this reference methodology for cost-benefit analysis in fire safety engineering is presented following an extensive literature review. The methodology clarifies the minimum requirements for assessing cost-effectiveness, and highlights that only a present net value evaluation can be used to compare design alternatives. Commonly used cost-benefit ratios should only be used when deciding on the effectiveness of a single package of fire safety measures. An illustrative case study demonstrates the application of the methodology and shows how designs based on cost-benefit ratios can be sub-optimal when evaluating multiple possible fire safety measures. [ABSTRACT FROM AUTHOR]