Abstract Structural fire safety requirements implicitly balance up-front investments in materials (protection or element sizing) with improved performance (loss reductions) in the unlikely event of a fire. For traditional prescriptive fire safety recommendations, the underlying target safety levels are not clear to the designer, nor is the associated balancing of risk and investment costs. It is discussed that traditional (structural) fire safety design is deterministic, with the safety foundation premised upon the collective experience of the profession. However, it is noted that building forms are increasingly uncommon in nature, due to material choice, height, failure consequences, etc. Within the framework presented in PD 7974–7:2019 there is an expectation that probabilistic risk assessment (PRA) methods be employed to demonstrate adequate safety for cases where the collective experience of the profession cannot be called upon to guide design approaches. In doing so, any design must be demonstrated to be tolerable to society, and the residual risk as low as is reasonably practicable (ALARP). In support of the PD 7974–7:2019 framework, the paper assesses the failure probabilities of isolated steel elements in function of insulation thickness, utilization, load ratio and (mean) fire load. In support of a generalized definition of target safety levels for structural fire safety engineering, optimum target safety levels for insulated steel beams are then determined as a function of the fire characteristics by applying life-time cost optimization (LCO) techniques. The LCO results in an assessment of the optimum investment level as a function of the fire, and damage and investment cost parameters characterizing the building. It is intended that the current contribution can be a steppingstone towards rational and validated reliability targets for performance-based design (PBD) in structural fire safety engineering.

中文翻译：

---

基于生命周期成本优化的结构钢构件的充分防火安全

摘要 结构防火安全要求隐含地平衡了材料（保护或元件尺寸）的前期投资与在不太可能发生的火灾时提高性能（减少损失）。对于传统的规范性消防安全建议，设计人员不清楚潜在的目标安全水平，也不清楚相关的风险和投资成本的平衡。讨论了传统（结构）消防安全设计是确定性的，安全基础以专业的集体经验为前提。然而，值得注意的是，由于材料选择、高度、破坏后果等，建筑形式在本质上越来越不常见。 在 PD 7974-7 中提出的框架内：2019 年，预计在无法利用专业的集体经验来指导设计方法的情况下，采用概率风险评估 (PRA) 方法来证明足够的安全性。在这样做时，任何设计都必须被证明是社会可以容忍的，并且剩余风险尽可能低（ALARP）。为支持 PD 7974-7:2019 框架，本文评估了隔离钢元件在绝缘厚度、利用率、载荷比和（平均）火灾载荷方面的失效概率。为了支持结构消防安全工程目标安全水平的广义定义，然后通过应用寿命成本优化 (LCO) 技术，将绝缘钢梁的最佳目标安全水平确定为火灾特性的函数。LCO 会根据建筑物的火灾、损坏和投资成本参数对最佳投资水平进行评估。目前的贡献旨在成为结构消防安全工程中基于性能设计 (PBD) 的合理且经过验证的可靠性目标的垫脚石。