Engineering role in failure cost evaluation for buildings

Cost benefit analysis is a common tool for decision making on safety. The appropriate degree of safety in structural design can be discussed based on a simple formula for optimum reliability including parameters such as coefficient of variation of lifetime maximum load, cost-up constant and normalized failure cost. In many cases, the degree of safety is determined as specified in codes or regulations. However, when additional information is available, such as owner's demands, engineers are responsible for providing quantitative values for various parameters, in particular for failure cost. This paper examines sources of failure costs and relations between the engineer's role in structural safety and discusses failure costs.     

Schutzzielorientierte brandschutztechnische Bemessung für mehrgeschossige Gebäude

Performance – based fire safety design of multi‐storey buildings. In most countries fire design of multi‐storey buildings is still based on the standard temperature‐time curve (ISO 834) which is supposed to cover real fire scenarios on the safe side. A fire safety design considering more realistic natural fires and the redundancies of entire structural systems is risk‐oriented as well as economical. Using international experience and test results and ongoing research of iBMB, a design fire is developed and so‐called real fire curves are derived. They serve as a basis for general calculation methods (according to the Eurocodes) which are able to grasp the real behaviour of structural systems in a fire. A probabilistic safety concept guarantees the necessary reliability of the design taking the probability of fire development, the boundary conditions of life safety and the uncertainties of the design parameters into account.     

钢框架结构基于整体优化策略的非线性抗震设计

针对现有抗震优化设计很少考虑结构非线性反应的缺点,提出了整体优化策略,并运用到钢框架结构造价最小的抗震优化设计中。以结构构件截面尺寸为设计变量,结构构件的总体积为目标函数,整体优化策略在以结构弹性强度和弹性变形为约束条件的基础上,增加弹塑性变形为约束条件,与我国抗震设计规范两阶段设计方法相对应,因此基于整体优化策略的优化设计结果可以作为最终的结构设计方案。整体优化策略不仅能够考虑结构的非线性反应,而且可以采用我国抗震规范的相关规定作为约束条件,适用于钢框架结构造价最小的抗震优化设计。     

Practical valuations on the effect of two type uncertainties for optimum design of cable-stayed bridges

A procedure for the optimum structural design of cable-stayed bridges is proposed based on minimum expected life-cycle cost (LCC); the procedure is illustrated with the optimum design of a cable-stayed bridge subjected to static and earthquake loads. Reliability analysis of the bridge is performed taking into account the two types of uncertainty in the capacity and loads. The capacity of the bridge is assumed to be determined by its critical members; this is tantamount to the assumption that the capacities and load effects of the structural members are highly correlated. Various designs of a cable-stayed bridge are considered; namely, a standard design, plus several that are weaker as well as several that are stronger than the standard design. For the different alternative designs, the member sections are decreased or increased relative to those of the standard design. The LCC of a particular design is formulated assuming that the cost components (including the maintenance and social costs) are respectively fractions of the initial cost. Reliability of a design associated with the aleatory uncertainties is assessed for each design, and the corresponding expected LCC and safety index are evaluated. The results of the various designs provide the information, safety index vs expected LCC, for determining the design with the minimum expected LCC which can be presented graphically. Because of the epistemic type of uncertainty, the LCC as well as the safety index of the optimum design are random variables; the respective histograms are also generated, from which the various percentile values can be obtained. Especially, the 75% and 90% values of the LCC may be specified to minimize the chance of underestimating the actual LCC of the optimum design; similarly the 75% and 90% values of the safety index may be specified for a conservative design of the cable-stayed bridge.     

The J-Value and Its Role in Evaluating Investments in Fire Safety Schemes

Fire safety engineers endeavour to ensure that a design achieves an adequate level of fire safety. For uncommon buildings, adequate safety cannot be based on precedent and an explicit evaluation of the adequacy of proposed safety features may be required. Commonly, this requires demonstration that the residual risk associated with the design is as low as is reasonably practicable. In those situations, a measure for a safety scheme’s benefit relative to its cost is required, as more efficient safety schemes should be preferred over less efficient ones to maximize the number of lives saved under societal resource constraints. To this end, the J-value has been introduced in other engineering fields as a decision support indicator for assessing the efficacy of safety features. The J-value has been derived from societal welfare considerations (the Life Quality Index) and is adopted in the current paper for applications in fire safety engineering. It is demonstrated herein how the J-value can inform decisions on fire safety, and how it can provide a basis for assessing whether or not a proposed fire safety scheme should be implemented. Future work will focus on its implementation as a tool for assessing the benefit of real life fire safety scheme implementations, such as sprinkler installations.     

基于全寿命环境成本的工程结构维护方案优化

工程结构全寿命过程中存在有害气体、污水和固体废弃物排放等环境问题,但是由其造成的经济损失却很少在结构设计或工程决策过程中予以考虑。为此,将三类污染物排放的防治成本计入工程活动的环境成本中,得到了多种建筑材料、能源消耗、运输方式和建筑机械使用的环境成本。通过将环境成本与经典全寿命成本模型相结合,建立了包含环境成本的全寿命总成本模型。根据所提出的环境成本模型和全寿命总成本模型,以某一沿海高速公路桥梁结构为例,通过设置预防性维护措施和必要性维护措施,对其进行维护方案的多目标优化,分析环境成本对工程决策的影响。并对直接成本和环境成本的不确定性进行了分析,研究了环境成本折现率对环境成本影响。结果表明,在结构优化过程中考虑环境成本能够得到经济效益和环境综合性能更佳的工程方案。     

滑坡加固方案优化的并行进化神经网络方法研究

提出了一种新的滑坡治理优化设计方法。首先在极限平衡法结合有限单元法的基础上，初步设计出数十种不同的加固方案的设计参数，并分别分析其治理后的稳定性以及防治工程造价；继而运用进化神经网络建立设计参数与稳定性及加固方案造价之间的非线性映射关系；最后以此关系模型输出的造价为目标函数，以预测的安全系数大于某一要求值为约束条件，再利用并行遗传算法在全局范围内快速地搜索出最优的设计参数，优化选择合理的滑坡加固方案。该方法已应用于三峡库区滑坡防治工程中，并取得了良好的经济效益和社会效益。     

Multi-stage production cost optimization of semi-rigid steel frames using genetic algorithms

The response of a steel structure is closely related to the behavior of its joints. This means that it is necessary to take explicit account of joint properties in order to ensure a consistent approach to design optimization of steel frames. Semi-rigid design has been introduced into steel construction standards such as Eurocode 3 and AISC. However, in the absence of appropriate guidelines, engineers encounter difficulties when bringing in semi-rigid design to everyday engineering practice. Moreover, connection design significantly affects the production cost of steel frame structures. Thus, a realistic optimization of frame design should take into account the effective costs of different stages of production including manufacturing and erection activities. This paper presents a Genetic Algorithm based method for multi-stage cost optimization of steel structures. In the objective function, the total cost of different production stages is minimized. A new cost model is presented that itemizes costs of all stages of production (material supply, manufacturing, erection and foundation). Design examples are used to validate the proposed methodology. Numerical validation shows that the multi-stage design optimization results in substantial cost benefits between 10% and 25% compared to traditional design of steel frames. Furthermore, the developed methodology is shown to be capable of measuring the possible impact of design choices in the early design stage thus assisting designers to make better design decisions.     

A group-AHP decision analysis for the selection of applied fire protection to steel structures

Decisions related to selecting the most suitable fire protection for steel structures subject to fully developed fires are critical to addressing design and construction uncertainties. Fire design stakeholders are faced with the challenge of managing their divergent opinions to make design decisions given the many options or engineered solutions available to meet performance objectives. This paper demonstrates the viability of a group-Analytic Hierarchy Process (AHP) as a multi-criteria decision analysis (MCDA) technique for managing fire design stakeholder opinions on economic, safety, environmental and societal considerations toward selecting suitable fire protection for steel structures. Based on 22 structural fire design decision criteria gathered from literature and expert opinion, 36 New Zealand stakeholders from 12 fire design stakeholder categories have been interviewed to elicit ratings from their relative comparisons of the structural fire design decision criteria. The Geometric Mean Method-Analytic Hierarchy Process (GMM-AHP) is used to assess four applied fire protection options or alternatively to use unprotected steel. The results show the seamless aggregation of multiple stakeholder desires, the importance levels of different stakeholder opinions and the systematic approach in ranking the proposed fire protection options. The ranking shows that given a general selection of passive fire protection by stakeholders having equal weights, there is a stronger preference for the concrete encasement of steel.     

结构设计阶段优化工程造价成本的思路及对策

工程造价成本的控制不仅是对建筑方案阶段和建筑设计阶段的造价进行控制,还应当对结构设计阶段等进行优化。通过分析结构设计方案、结构设计过程和结构设计质量对工程造价成本影响,提出基于全生命周期的工程造价成本控制和形成系统化工程造价管控模式的两点优化思路,并提出应用价值工程设计优化、建立结构方案内部评审机制等具体优化对策。以期为实现工程目标价值与实际价值的最小偏离提供帮助。     

Optimising design decision-making for steel structures in fire using a hybrid analysis technique

Steel structures can be protected against the effects of fully-developed fires by the use of sprayed on materials, board systems and intumescent paints, etc. or by using sufficiently large unprotected elements. This paper presents how optimum decisions for the protection of steel structures in fires can be achieved in a performance-based design environment, given conflicting structural fire design decision criteria and multidisciplinary fire design stakeholder views. In particular, a novel hybrid analysis approach is proposed for combining stakeholder views on the different fire protection options and the numerical outcomes of structural fire analysis. As for the stakeholder views, reference is made to benefits and costs criteria priorities for assessing competing options resulting from a previous study from the same authors. The fire protection structural performance is numerically and probabilistically assessed according to a parametric study. The proposed approach is exemplified by making reference to a limit state structural fire design of single steel elements. A synthesis and ranking technique is then applied to integrate the qualitative results obtained in terms of benefits and costs priority scores; and the quantitative measures of failure probabilities and costs for the different fire protection options. The results show that the ranking technique accounts for multidimensionality in synthesising the structural fire design decision problem. The results also show that intumescent paints and board systems are the most cost-effective options in different stakeholder influence scenarios, given a general selection of steel structural fire protection. The hybrid technique is proposed to support an optimal and cost-effective structural fire design decision-making for buildings in a performance-based design environment.     

钢结构抗火设计在“上海水立方”中的应用

随着性能化结构抗火设计的发展,结构的抗火能力和相应的结构防火保护措施可以通过对结构在真实火灾温度场下的实际性能分析来确定。对于大空间结构,根据其内部的可燃物、通风条件和空间大小等特性,采用性能化结构抗火设计往往可以不影响结构抗火安全水平的前提下降低对结构进行防火保护的要求,实现安全、美观且经济的建筑设计。本文将介绍工程设计实践中行之有效的性能化结构抗火设计方法,并以上海东方体育中心的大空间结构抗火设计为例,证明该钢结构抗火方法的切实有效性。     

Development of a Risk Assessment Method for Life Safety in Case of Fire in Rail Tunnels

The present paper describes the development of a risk assessment methodology to quantify the life safety risk for people present in a rail tunnel in the context of the creation of a fire safety design. A bow-tie structure represents the risk assessment model, starting from major contributing factors leading to disastrous events. Using past accidents for the construction of the event tree part of the bow-tie, the most important factors are determined to be: human behaviour; fire growth; ventilation conditions; safety system (e.g. Smoke & Heat Exhaust, detection, voice communication, etc.); population density. These factors are incorporated into the event tree using pathway factors. Frequencies are calculated for each branch outcome based on data from research projects, fault tree analysis and engineering judgement. For the determination of the consequences, the method makes use of three integrated models: the smoke spread, the evacuation and the consequence model. The models can take into account all types of geometry and materials, human behaviour and different susceptibilities of people for smoke. Together, they determine the possible number of fatalities, by means of an FID (Fractional Incapacitation Dose) value, in case of a fire in a rail tunnel. The final risk is presented by the expected number of fatalities, the individual risk and the societal risk. The societal risk is demonstrated by means of an FN-curve (Frequency/Number of Casualty-curve).     

Finite element modelling of the pyrolysis of wet wood subjected to fire

The modelling of the pyrolysis of wet wood provides more realistic fire scenarios for structural fire design by taking into account variable thermal properties of wood which are beyond the scope of conventional structural fire design codes. The proposed numerical methodology has been written in MATLAB environment. A 2D nonlinear finite element analysis (FEA) is performed to model the pyrolysis of wet wood subjected to high temperature. The varying of thermal proprieties of wood are discussed from the point of view of changes of structure and chemical composition under fire condition. The validity of the model is established by comparing the predicted results with results from fire resistance tests presented in literature. Qualitatively, the model provides good agreement with the experimental data. It is shown that the model can handle layers of a wooden composite structure. Temperature profiles at different points in the wood sample and the two-dimensional charring depth of Laminated Veneer Lumber (LVL) panels are calculated and compared with experimental data.     

双排桩支护的优化设计分析

本文主要阐述了关于优化结构设计的步骤和基本原理;并选取双排桩结构为研究对象,通过数学优化理论,以结构工程造价为优化的目标函数,选择支护结构整体抗弯强度以及最大偏移量为优化分析的约束条件,建立了某支护结构优化分析数学模型;利用MATLAB7．0计算分析并实现双排桩支护结构的优化分析。并通过某工程验证表明该优化分析方法的可行性,可以为类似工程设计中提供应用参考。     

PPP‐Projekte: Strukturelle Kostenvergleichsuntersuchungen zwischen Eigenrealisierung der öffentlichen Auftraggeber und PPP‐Anbietern

Manufacturing and utilization costs as well as additional factors in private construction versus public construction were compared with the costs of a public private partnership (PPP) provider, based on a review of published studies and own data. The costs were calculated and compared according to the discounted cash‐flow method. At typical rates, PPP providers achieve a price advantage of more than 30% without even taking into account all price disadvantages (construction time, post‐building improvements) of the public construction industry. An expansion of the public private partnership market beyond the currently 5% of public construction activity is necessary not only from an economic perspective, but also in light of the limited budget situation on the communal, state and federal level. Using the same financing, 30% more construction projects can be realized.     

Multiobjective optimization under uncertainty in tunneling: application to the design of tunnel support/reinforcement with case histories

In this paper, two questions common in tunnel design are addressed: (i) how to choose an optimum solution when more than one conflicting objective must be achieved; (ii) how to deal with data affected both by imprecision and randomness. Fuzzy Set Theory and Random Set Theory are used to develop a general interactive multiobjective procedure, which is then applied to the design of tunnel support/reinforcement. A case history illustrates how the procedure was successfully used in the preliminary design of a total of 40 km of tunnels in Central Italy. It is shown that the procedure allows the designer to become a knowledgeable decision maker because his interaction is required at the key points of the process, and because the trade-offs among the objective functions can be easily assessed. The designer's personal input is valued and clearly defined in its impact on the solution. The case history demonstrates that, without an optimization procedure, it is extremely likely (probability of 99%) that a solution is chosen, which either increases the costs without increasing safety, or decreases the safety without decreasing the costs. Finally, it is shown that both imprecision and randomness can be easily taken into account in tunnel design.     

Life‐cycle cost assessment of mid‐rise and high‐rise steel and steel–reinforced concrete composite minimum cost building designs

The traditional trial‐and‐error design approach is inefficient to determine an economical design satisfying also the safety criteria. Structural design optimization, on the other hand, provides a numerical procedure that can replace the traditional design approach with an automated one. The objective of this work is to propose a performance‐based seismic design procedure, formulated as a structural design optimization problem, for designing steel and steel–reinforced concrete composite buildings subject to interstorey drift limitations. For this purpose, eight test examples are considered, in particular four steel and four steel–reinforced concrete composite buildings are optimally designed with minimum initial cost. Life‐cycle cost analysis (LCCA) is considered as a reliable tool for measuring the damage cost due to future earthquakes that will occur during the design life of a structure. In this study, LCCA is employed for assessing the optimum designs obtained for steel and steel–reinforced concrete composite design practices. Copyright © 2011 John Wiley & Sons, Ltd.     

Outline of a stochastic decision-making model for building fire safety and protection

An outline is given of stochastic state-transition models that have been developed to predict life loss and monetary loss for multi-storey, multi-compartment buildings subject to fire. The stochastic models consider the extent and the effects of smoke and flame spread. Results obtained from the stochastic models can be used to select an appropriate design strategy for the provision of fire safety and protection in buildings, based on the dual attainment of a satisfactory level of predicted life loss and an optimum level of fire-cost expectation. The fire-cost expectation considers costs due to fire losses and the provision of fire-safety and protection measures.