Performance of Flexure-Controlled Reinforced Concrete Structural Walls Under Sequential Fire-Earthquake Loads

The performance of reinforced concrete (RC) structural walls under individual hazards has been well studied. However, little is known regarding the behavior of RC structural walls under sequential hazards. The research presented here seeks to address the performance of RC structural walls under sequential fire-earthquake loads (both post-earthquake fire and post-fire earthquake). Longer burn times of post-earthquake fire and initial seismic damage can have significant structural impacts on RC structures which are usually considered to have superior performance in a fire. An 8-inch wall with characteristics representative of typical construction in seismic regions was utilized as the basis of the simulations. The wall with non-uniform layout of reinforcement provides a complex deformed shape under fire. Individual typical earthquake damage states were introduced to the wall to assess impact on fire resistance. The fire resistance of a wall was discussed according to thermal-insulation and load-bearing criteria in codes. The results show that crack does not impact the fundamental response of a wall under fire while cover loss decreases its load-bearing capacity significantly. Moreover, the location of cover loss has remarkable impact on the deformed shape of a wall and its load-bearing fire resistance. While the thermal-insulation capacity decreases below code requirements, the load-bearing fire resistance of earthquake-damaged walls is still acceptable. Another potential but infrequently studied hazard is the post-fire earthquake scenario. The impact of fire damage on the earthquake behavior of RC walls is not well understood, which leads to some safety concerns in earthquake after fire or aftershocks after post-earthquake fire. A simulation procedure combining SAFIR and OpenSees is proposed and validated for the PFE analysis of RC structural walls. Based on the validated the simulation procedure, a parametric study on the PFE performance of RC walls was conducted. Results indicate that fire damage decreases the load-bearing capacity and stiffness of RC walls under reversed-cyclic loads while fire damage decreases the deformation capacity in most cases. Severe fire exposure may shift damage from the boundary element to the web. Wall characteristics which significantly impact the residual wall response quantities are wall thickness, boundary element length, and axial load ratio. In addition, a framework for simplified nonlinear modeling was proposed for the PFE performance of RC walls. 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 the parametric study, are a function of fire damage indices that account for the effect of fire on the material properties of steel and concrete. Results indicate that the model is generally able to predict the response of a fire-damaged wall

Lifetime economically optimum position of steel reinforcement in a concrete column exposed to natural fire

This paper incorporates a probabilistic fire loss assessment method for reinforced concrete structures into a cost-benefit analysis to optimize a structural fire design. Economic losses in case of failure and survival of the structure are both quantified with, in the latter case, an estimate of the damage and repairs costs. As a case study, a cost-benefit optimization of the position of rebars in a concrete column is investigated. The column response in fire is evaluated using finite element simulations in SAFIR. Variations in cover thickness result in variations in failure probabilities and, for cases where no failure occurs, variations in repair costs due to heat penetration and residual out-of-plane deformation of the column. The optimum cover thickness is the one that offers the best trade-off between the various repair costs across the range of likely fire intensity levels. This optimum is sensitive to repair decisions such as the tolerance on the acceptable residual out-of-plane deformation after a fire. For the studied cases, the optimum cover thickness is smaller in slender columns than in stocky columns due to greater out-of-plane deformations in the former

Sensitivity studies of the resilience of RC columns to various fire scenarios

Reinforced concrete (RC) structures generally remain stable under fire, but exhibit damage and residual deformations which require repairs. Besides the repair cost, the building downtime can also be expensive. However, current fire design approaches focus solely on life safety, and do not consider resilience. To improve post-fire performance of buildings and facilitate fast reuse, an important step is to develop a predictive capability for the effect of a fire event on residual deformations and load-bearing capacity in structures. This research investigates the residual deformations in RC buildings after a fire, with a focus on the columns as one of the key structural members. The case study is a five-story RC frame building with a fire developing on the first story. Thermo-structural finite element analyses were used to analyze the columns performance under various fires. The sensitivity of the RC columns responses to main parameters related to fire characteristics, material properties and mechanical loading was analyzed. Based on the sensitivity studies, the most critical parameters were determined for the vulnerability of the RC columns to the different fire scenarios. These critical parameters will be used for the subsequent probabilistic damage evaluation of the RC columns and their design alternatives. The results will contribute to improve understanding of the effects of fire on resilience of RC buildings and infrastructure, as well as the identification of designs which provide enhanced post-fire performance

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

Effects of antiplatelet therapy after stroke due to intracerebral haemorrhage (RESTART): a randomised, open-label trial

Background: Antiplatelet therapy reduces the risk of major vascular events for people with occlusive vascular disease, although it might increase the risk of intracranial haemorrhage. Patients surviving the commonest subtype of intracranial haemorrhage, intracerebral haemorrhage, are at risk of both haemorrhagic and occlusive vascular events, but whether antiplatelet therapy can be used safely is unclear. We aimed to estimate the relative and absolute effects of antiplatelet therapy on recurrent intracerebral haemorrhage and whether this risk might exceed any reduction of occlusive vascular events. Methods: The REstart or STop Antithrombotics Randomised Trial (RESTART) was a prospective, randomised, open-label, blinded endpoint, parallel-group trial at 122 hospitals in the UK. We recruited adults (≥18 years) who were taking antithrombotic (antiplatelet or anticoagulant) therapy for the prevention of occlusive vascular disease when they developed intracerebral haemorrhage, discontinued antithrombotic therapy, and survived for 24 h. Computerised randomisation incorporating minimisation allocated participants (1:1) to start or avoid antiplatelet therapy. We followed participants for the primary outcome (recurrent symptomatic intracerebral haemorrhage) for up to 5 years. We analysed data from all randomised participants using Cox proportional hazards regression, adjusted for minimisation covariates. This trial is registered with ISRCTN (number ISRCTN71907627). Findings: Between May 22, 2013, and May 31, 2018, 537 participants were recruited a median of 76 days (IQR 29–146) after intracerebral haemorrhage onset: 268 were assigned to start and 269 (one withdrew) to avoid antiplatelet therapy. Participants were followed for a median of 2·0 years (IQR [1·0– 3·0]; completeness 99·3%). 12 (4%) of 268 participants allocated to antiplatelet therapy had recurrence of intracerebral haemorrhage compared with 23 (9%) of 268 participants allocated to avoid antiplatelet therapy (adjusted hazard ratio 0·51 [95% CI 0·25–1·03]; p=0·060). 18 (7%) participants allocated to antiplatelet therapy experienced major haemorrhagic events compared with 25 (9%) participants allocated to avoid antiplatelet therapy (0·71 [0·39–1·30]; p=0·27), and 39 [15%] participants allocated to antiplatelet therapy had major occlusive vascular events compared with 38 [14%] allocated to avoid antiplatelet therapy (1·02 [0·65–1·60]; p=0·92). Interpretation: These results exclude all but a very modest increase in the risk of recurrent intracerebral haemorrhage with antiplatelet therapy for patients on antithrombotic therapy for the prevention of occlusive vascular disease when they developed intracerebral haemorrhage. The risk of recurrent intracerebral haemorrhage is probably too small to exceed the established benefits of antiplatelet therapy for secondary prevention

Effects of antiplatelet therapy after stroke due to intracerebral haemorrhage (RESTART): a randomised, open-label trial

Background: Antiplatelet therapy reduces the risk of major vascular events for people with occlusive vascular disease, although it might increase the risk of intracranial haemorrhage. Patients surviving the commonest subtype of intracranial haemorrhage, intracerebral haemorrhage, are at risk of both haemorrhagic and occlusive vascular events, but whether antiplatelet therapy can be used safely is unclear. We aimed to estimate the relative and absolute effects of antiplatelet therapy on recurrent intracerebral haemorrhage and whether this risk might exceed any reduction of occlusive vascular events. Methods: The REstart or STop Antithrombotics Randomised Trial (RESTART) was a prospective, randomised, open-label, blinded endpoint, parallel-group trial at 122 hospitals in the UK. We recruited adults (≥18 years) who were taking antithrombotic (antiplatelet or anticoagulant) therapy for the prevention of occlusive vascular disease when they developed intracerebral haemorrhage, discontinued antithrombotic therapy, and survived for 24 h. Computerised randomisation incorporating minimisation allocated participants (1:1) to start or avoid antiplatelet therapy. We followed participants for the primary outcome (recurrent symptomatic intracerebral haemorrhage) for up to 5 years. We analysed data from all randomised participants using Cox proportional hazards regression, adjusted for minimisation covariates. This trial is registered with ISRCTN (number ISRCTN71907627). Findings: Between May 22, 2013, and May 31, 2018, 537 participants were recruited a median of 76 days (IQR 29–146) after intracerebral haemorrhage onset: 268 were assigned to start and 269 (one withdrew) to avoid antiplatelet therapy. Participants were followed for a median of 2·0 years (IQR [1·0– 3·0]; completeness 99·3%). 12 (4%) of 268 participants allocated to antiplatelet therapy had recurrence of intracerebral haemorrhage compared with 23 (9%) of 268 participants allocated to avoid antiplatelet therapy (adjusted hazard ratio 0·51 [95% CI 0·25–1·03]; p=0·060). 18 (7%) participants allocated to antiplatelet therapy experienced major haemorrhagic events compared with 25 (9%) participants allocated to avoid antiplatelet therapy (0·71 [0·39–1·30]; p=0·27), and 39 [15%] participants allocated to antiplatelet therapy had major occlusive vascular events compared with 38 [14%] allocated to avoid antiplatelet therapy (1·02 [0·65–1·60]; p=0·92). Interpretation: These results exclude all but a very modest increase in the risk of recurrent intracerebral haemorrhage with antiplatelet therapy for patients on antithrombotic therapy for the prevention of occlusive vascular disease when they developed intracerebral haemorrhage. The risk of recurrent intracerebral haemorrhage is probably too small to exceed the established benefits of antiplatelet therapy for secondary prevention

Local and global response data from post-fire earthquake simulations of RC structural walls

Data are provided from simulation studies of post-fire earthquake (PFE) of reinforced concrete (RC) structural walls. Local response data describe material peak temperatures and residual stiffness and strength, as well as quantification of the extent of seismic damage. Global response data provide load-deformation envelopes, as well as stiffness, strength, and deformation capacity. The data can support development of simplified modeling tools for PFE analysis of buildings, as well as to support development of and interpretation of future experimental tests. For further theory behind the modeling approach and full interpretation of the data, the reader is referred to the article entitled “Post-fire seismic behavior of reinforced concrete structural walls” (Ni and Birely, 2018) [1]

Economic Impact of Fire: Cost and Impact of Fire Protection in Buildings

The objective of the work is to establish and apply a methodology for evaluating the total benefits and costs related to fire protection features in buildings. An important component to reducing economic loss from fire is the ability to measure this loss. The work focuses on identifying the various dimensions of the economic impact of fire. It also seeks to measure these dimensions so that the cost of fire prevention and other interventions can be weighed against their benefits. Specifically, the project addresses four tasks which are summarized in this report: (i) literature review on methods to measure costs and losses from fires, and methods for cost-benefit evaluation from fire protection features in buildings, (ii) critical analysis of the identified methods including the data needs, advantages and limitations, (iii) recommendation of a holistic calculation method for evaluating the total benefits and costs related to fire protection features in buildings, and (iv) presentation of five case studies