工程结构在多灾害耦合作用下的研究进展

我国地处亚欧板块、太平洋板块和印度洋板块之间，且疆域辽阔、海岸线绵长，这就自然形成了我国地震、强风和降雨等自然灾害频发。工程结构，包括高层建筑、村镇低矮房屋建筑群、输电塔线体系等生命线工程，在其全寿命周期内会遭受地震、强风和降雨等多种灾害的单独或同时作用。传统设计方法基于最不利荷载对结构进行设计，忽略了多种灾害耦合作用对结构全寿命周期抗灾性能的影响。文章总结了该课题组近年来在多灾害研究领域所取得的主要成果，包括：①根据中国强震台网中心和中国气象局数据中心提供的地震、风和降水数据，开展了极端事件单独作用和耦合作用的危险性分析；同时，提出了基于Copula函数的联合概率模型分析方法；②提出工程结构在多种灾害耦合作用下的性能评估和荷载修正系数计算方法；③开展了高层建筑在地震和强风单独作用以及同时作用下的风险分析及荷载修正系数计算；进行了村镇低矮房屋在地震和洪水耦合作用下的风险分析；对风雨耦合作用下的输电塔线体系进行了易损性分析。结果表明：①在考虑灾害发生概率时，不同灾害(例如，地震、强风和降雨)同时作用对结构性能评估具有显著影响；②由本文方法计算的荷载组合系数均不小于规范值，建议对现行规范中地震和风荷载的设计强度进行适当修正。因此，在对工程结构进行抗多灾耦合作用的性能分析和设计方法研究时，应综合考虑多种灾害的耦合效应。     

轻型框架木结构在住宅中的应用

结合轻型框架木结构的国内外发展状况,介绍了轻型框架木结构基本框架的特点,为轻型框架木结构在国内的应用提供了一些信息。     

Fragility analysis of woodframe buildings considering combined snow and earthquake loading

This paper describes a study to evaluate appropriate percentages of design snow load (factors for use with nominal values provided by the current design load standard for structural design in the United States, ASCE 7-02) when snow load is being taken into account in a seismic fragility analysis. The procedure is illustrated through the development of seismic fragility curves for one and two-story woodframe structures in three locations (Memphis, TN; Carbondale, IL; and Boston, MA) having both moderate snow and seismic hazards. The fragilities are cast in terms of displacement criteria (maximum shearwall drift) with the snow load serving to add seismic weight to the structure. The structures are analyzed using a nonlinear dynamic time-history analysis procedure. The seismic hazard is defined using USGS seismic hazard maps and uncertainty in the seismic hazard at each location is characterized by a suite of ordinary ground motion records. The ground snow hazard is defined through an analysis of data from first-order weather stations at the sites considered. Through a series of multi-hazard convolutions, parametric studies, and the construction of fragility curves, percentages of design snow load are determined for use in constructing displacement-based seismic fragilities and calculating failure probabilities (by convolving with appropriate seismic hazard functions). Practical implications for fragility analysis considering multiple hazards and performance-based design of woodframe structures also are discussed.     

A probabilistic framework for multi-hazard risk mitigation for electric power transmission systems subjected to seismic and hurricane hazards

Abstract

Many areas of the world are prone to multiple hazards that can be concurrent/non-concurrent and dependent/independent. Infrastructure systems located in such areas will likely be subjected to more than one hazard in their lifetime. The damage due to such hazards on electric power systems is well documented. Over the years, strategies to mitigate single hazards have been proposed for electric power systems. However, accurate long-term decisions on investment in risk mitigation strategies require the consideration of multiple hazards that can impact a system over its lifespan. Therefore, there is a need to investigate the cost-effectiveness of mitigation strategies in reducing risks to infrastructure systems that are vulnerable to multiple hazards given the constraints on resources. This requires a comprehensive multi-hazard risk assessment approach. This paper presents a framework for investigating the effectiveness of multi-hazard risk mitigation strategies for electric power systems subjected to seismic and hurricane wind hazards. The framework includes probabilistically weighted deterministic hazard analysis model, component vulnerability models, topologically based system performance model, component importance measure appropriate for networked systems, and life cycle cost analysis. A notional electric power network assumed to be located in Charleston, SC, and New York, NY, is used to demonstrate the proposed framework.     

The Effect of Biological Deterioration on the Seismic Performance of Woodframe Shearwalls

Abstract:  This article describes a combined experimental and analytical investigation of the effect of biological deterioration on the performance of light-frame wood shearwalls subject to seismic loading. Deterioration due to fungal attack is believed to have a significant effect on the displacement and capacity performance of light-frame shearwalls. Some studies have shown that fungi tend to degrade properties of nailed connections common in light-frame structures, however, the effect on shearwall assemblies has not yet been quantified. The effect of biological deterioration (due to fungal attack) on cyclic performance of light-frame shearwalls was evaluated in this study by, first, fitting sets of hysteretic model parameters to single fastener sheathing-to-framing connections exposed to different levels of decay from brown rot fungi. Next, these model parameters were used as an input to a numerical model used to evaluate the cyclic behavior of complete shearwall assemblies. Finally, the output from this model was used in a nonlinear dynamic time-history analysis to evaluate displacement response of the shearwalls subject to a suite of ground motion records. The results were presented in the form of peak displacement distributions and fragility curves.     

Load duration effects in wood members and connections order statistics and critical loads

Load duration behavior, arising from creep-rupture, is one of the most significant effects distinguishing wood materials from other structural materials. The phenomenon of creep-rupture has been widely studied over the past two decades. Recent experimental programs have focused on duration-of-load (DOL) effects in full-size lumber and a number of different cumulative damage models have been proposed. These models have been used in reliability analyses that take into account the stochastic nature of the loading process to evaluate appropriate load duration adjustment factors for use in design. More recently, the stochastic damage accumulation process itself has been investigated. This has resulted in proposals for simplified cumulative damage analyses and the re-emergence of the ‘killer pulse’ concept for load duration effects in wood. Other recent studies have focused on evaluating analogous load–time effects in mechanical connections in wood. While the mechanisms in connections are recognized as different from those in wood members, the treatment of time effects in design are (at least at the present time) similar. With the tendency toward engineered design of wood structures subject to natural hazards loadings, such as wind and seismic loads, load duration effects in both the primary framing members and the structural connections may be of particular importance. The evolution of the new LRFD standard for wood provides a good opportunity to re-visit this important issue. This paper will briefly review DOL research, with particular emphasis on the work used as the basis for the time effects factors in the LRFD standard, and describe some recent work in (a) a simplified approach to cumulative damage analysis using order statistics, and (b) load–time effects in simple wood connections. It is shown that reliability analyses including DOL behavior can be performed more simply (efficiently) using an order statistics approach or even a simple FORM analysis. Thus, it may be possible to evaluate load duration factors for design without having to perform complex stochastic cumulative damage analyses.     

北京市紫竹院公园竹结构茶楼结构设计

作为一种传统的建筑材料,竹材在我国有着非常广泛的用途。与其他结构体系相比,造价低廉、抗震性能优异、绿色环保的胶合竹结构房屋非常适合在地震区使用。但此种结构体系在我国属于一种新兴的结构形式,缺乏结构设计的规范和经验,这严重限制其在更大范围的推广应用。结合紫竹院公园竹结构茶楼工程项目,介绍了茶楼的施工概况、结构地震作用计算、抗侧力系统设计、连接计算及抗震构造措施等。本工程的设计方法可作为同类型结构设计的参考,最后给出相关建议和展望。     

Reliability of woodframe residential construction subjected to earthquakes

Most housing in the United States is light-frame wood construction (90% nationally, and 99% in California). Residential construction in the United States typically has received little or no structural engineering. The performance of wood residential construction to earthquake effects was apparent in the 1994 Northridge Earthquake, and underlines the need for new approaches to enhance building performance through improved prediction, evaluation and design methods. In this paper, methods of stochastic nonlinear dynamic analysis are used to simulate the behavior of lateral force-resisting shear wall systems typically found in residential construction subjected to earthquakes. The probability that shear wall drift limits are exceeded for uniform hazard earthquake ground motions with various return periods and intensities can be estimated from this analysis and can be related to performance levels for residential occupancy that have been suggested in concurrent research on performance-based engineering. The probability of failure under a spectrum of possible earthquakes is determined by convolving the structural fragility derived from the above analysis with the seismic hazard specified by the US Geological Survey.     

Database-assisted design methodology to predict wind-induced structural behavior of a light-framed wood building

This study investigates the applicability of the database-assisted design (DAD) methodology to predict structural reactions in a light-framed wood structure subjected to fluctuating wind pressures. Structural influence functions were determined on a 1/3-scale light-frame wood structure, which was then subjected to a wind flow, while the surface pressures and structural reactions at roof-to-wall and wall-to-foundation connections were simultaneously recorded. There was a good agreement between the DAD-predicted structural reactions and experimentally measured reactions, confirming that the DAD method is suitable for predicting the structural reactions in light-frame wood buildings. Subsequently structural reaction time histories at several connections within the building were generated using a 1:50 scale wind tunnel model of the structure and the peak structural reactions determined using the DAD method and previously obtained influence functions. When the DAD-estimated reactions were compared with reactions predicted by the ASCE 7-05 main wind force resisting system (MWFRS) method, they showed the ASCE 7 reactions were highly non-conservative(i.e. smaller than the DAD method predictions), by as much as 39% at the gable end truss. The components and cladding method showed reasonable agreement with the DAD method for the gable end and first interior truss reactions but it too underestimated the reaction loads at the second and third interior trusses by 30% and 12% respectively.     

Life-cycle reliability assessment of reinforced concrete bridges under multiple hazards

This paper proposes a novel probabilistic methodology for estimating the life-cycle reliability of existing reinforced concrete (RC) bridges under multiple hazards. The life-cycle reliability of an RC bridge pier under seismic and airborne chloride hazards is compared to that of a bridge girder under traffic and airborne chloride hazards. When conducting a life-cycle reliability assessment of existing RC bridges, observational data from inspections can provide the corrosion level in reinforcement steel. Random variables related with the prediction of time-variant steel weight loss can be updated based on the inspection results using Sequential Monte Carlo Simulation (SMCS). This paper presents a novel procedure for identifying the hazards that most threaten the structural safety of existing RC bridges, as well as the structural components with the lowest reliability when these bridges are exposed to multiple hazards. The proposed approach, using inspection results associated with steel weight loss, provides a rational reliability assessment framework that allows comparison between the life-cycle reliabilities of bridge components under multiple hazards, helping the prioritisation of maintenance actions. The effect of the number of inspection locations on the updated reliability is considered by incorporating the spatial steel corrosion distribution. An illustrative example is provided of applying the proposed life-cyle reliability assessment to a hypothetical RC bridge under multiple hazards.     

Shake table testing of a full-scale seven-story steel-wood apartment building

In July 2009, a full-scale mid-rise light-frame wood apartment building was subjected to a series of earthquakes at the world’s largest shake table in Miki, Japan. The test program consisted of two major phases: the building tested in the first phase consisted of a single-story steel special moment frame (SMF) with six stories of wood on top, and the second phase consisted of locking down the steel story and testing the six-story light-frame wood building by itself. This paper focuses on the test results for the seven-story steel-wood building tested to earthquakes having return periods of 72 and 665 years. The objective of this phase of the test program was to investigate the performance of a mid-rise light-frame wood building with a first-story moment frame when subjected to a major earthquake, essentially providing a landmark data set to the seismic engineering research community. The building consisted of 225 square meters for retail space at the first story and 1350 square meters of multi-family residential living space with 23 apartment units above. The building was instrumented with just over 300 sensors and 50 LED optical tracking points to measure the component and global responses, respectively. In this paper the seven-story test specimen is described and the resulting seismic response and behavior is summarized. Detailed damage inspection was performed following each of these tests, and representative images are presented and discussed. The building was found to perform excellently, with very little damage following an event that was slightly larger (×1.16) than the design-level event for the city of Los Angeles, California. The peak global drift at roof level was 166 mm, and the peak inter-story drifts were approximately 1.3%.     

中外荷载规范雪荷载取值及控制影响因素对比分析

基于对当今中外荷载规范雪荷载章节的梳理，以雪荷载对应取值及控制因素的差异为视角进行了深入的对比剖析，得出各国规范体系构架存在较高相似性，均采用由地面雪荷载（基本雪压）乘上一系列用以量化计算的控制因素系数而获得屋面雪荷载值，而屋面雪荷载按作用效应又可划分为基本雪荷载、漂移雪荷载与滑落雪荷载三类，且各类别在不同规范中取值具有差别。由此建议在中国新版建筑荷载规范雪荷载章节继承完善基本雪荷载和漂移雪荷载，并补充对屋面滑落雪荷载取值规定。另外，总结了各国规范中雪荷载控制影响因素，可归为外界环境与建筑本身两大类，并依据国外规范对控制因素的考虑权重，选取影响较大且我国规范尚未考虑的因素进行详细探讨。由此建议引入考虑降雨量与坡屋顶特性的雨雪联合因素，考虑宏观地貌气候与周围环境的建筑暴露状态因素，考虑室内采暖温度与屋面热阻的建筑采暖因素及考虑屋面光滑程度的屋面材料因素，以达到优化规范体系构架的目的。     

FEMA approaches in seismic assessment of jacket platforms (case study: Ressalat jacket of Persian gulf)

The assessment of existing platforms under past environmental (wave, wind, current and etc.) loads and probable future loads (earthquake) is a relatively new process and has not yet been standardized as the design has. This lack of standardization creates some difficulty in establishing performance requirements which must be developed depending upon the risks (i.e., hazards, exposures and consequences) associated with the future operation of the platform. The present criteria of the offshore structure standards for seismic assessment can be improved using Building prestandards. Recently some documents such as FEMA-356 and ATC-40 are developed for seismic assessment of buildings. However there is advice in API documents (API RP 2A) in order for seismic assessment of jacket platforms, but because of brief existing comments in this field, it is necessary to use more appropriate (pre)standards for seismic assessment of these structures. In this paper rough and global comments of API are compared with a detailed method of FEMA. As an example seismic assessment of the existing 4 legged Service platform placed in the Ressalat Oil Field (Persian gulf) is presented. It is very useful and efficient to use of FEMA for seismic assessment of jacket platforms.     

A step forward towards a comprehensive framework for assessing liquefaction land damage vulnerability: Exploration from historical data

The unprecedented liquefaction-related land damage during earthquakes has highlighted the need to develop a model that better interprets the liquefaction land damage vulnerability (LLDV) when determining whether liquefaction is likely to cause damage at the ground’s surface. This paper presents the development of a novel comprehensive framework based on select case history records of cone penetration tests using a Bayesian belief network (BBN) methodology to assess seismic soil liquefaction and liquefaction land damage potentials in one model. The BBN-based LLDV model is developed by integrating multi-related factors of seismic soil liquefaction and its induced hazards using a machine learning (ML) algorithm-K2 and domain knowledge (DK) data fusion methodology. Compared with the C4.5 decision tree-J48 model, naive Bayesian (NB) classifier, and BBN-K2 ML prediction methods in terms of overall accuracy and the Cohen’s kappa coefficient, the proposed BBN K2 and DK model has a better performance and provides a substitutive novel LLDV framework for characterizing the vulnerability of land to liquefaction-induced damage. The proposed model not only predicts quantitatively the seismic soil liquefaction potential and its ground damage potential probability but can also identify the main reasons and fault-finding state combinations, and the results are likely to assist in decisions on seismic risk mitigation measures for sustainable development. The proposed model is simple to perform in practice and provides a step toward a more sophisticated liquefaction risk assessment modeling. This study also interprets the BBN model sensitivity analysis and most probable explanation of seismic soil liquefied sites based on an engineering point of view.     

高跨为双坡屋面的高低屋面低跨平屋面积雪分布研究

高低屋面对雪荷载较为敏感，通过模型试验对高跨为双坡屋面形式的高低屋面低跨平屋面积雪分布形式进行研究。模型试验在哈尔滨工业大学自主研发的户外风雪联合系统中进行，该设备可在试验段内模拟自然降雪过程。根据高跨坡屋面坡度不同共设置4个模型，并针对每个模型进行了不同风速、不同风向下的试验研究。通过高跨为平屋面形式的高低屋面积雪分布的实测与试验结果的对比，验证了试验结果的可靠性。结果表明：风速越大，积雪分布不均匀现象愈加显著，但屋面积雪分布系数并未随风速增加而增大；高跨双坡屋面坡度对变跨处积雪分布影响显著，高跨为60°双坡屋面，迎风向3m/s风速时变跨处积雪分布系数最大值达到7.9，超出欧洲EU规范取值。     

Machine learning-based seismic assessment of framed structures with soil-structure interaction

The objective of the current study is to propose an expert system framework based on a supervised machine learning technique (MLT) to predict the seismic performance of low- to mid-rise frame structures considering soil-structure interaction (SSI). The methodology of the framework is based on examining different MLTs to obtain the highest possible accuracy for prediction. Within the MLT, a sensitivity analysis was conducted on the main SSI parameters to select the most effective input parameters. Multiple limit state criteria were used for the seismic evaluation within the process. A new global seismic assessment ratio was introduced that considers both serviceability and strength aspects by utilizing three different engineering demand parameters (EDPs). The proposed framework is novel because it enables the designer to seismically assess the structure, while simultaneously considering different EDPs and multiple limit states. Moreover, the framework provides recommendations for building component design based on the newly introduced global seismic assessment ratio, which considers different levels of seismic hazards. The proposed framework was validated through comparison using non-linear time history (NLTH) analysis. The results show that the proposed framework provides more accurate results than conventional methods. Finally, the generalization potential of the proposed framework was tested by investigating two different types of structural irregularities, namely, stiffness and mass irregularities. The results from the framework were in good agreement with the NLTH analysis results for the selected case studies, and peak ground acceleration (PGA) was found to be the most influential input parameter in the assessment process for the case study models investigated. The proposed framework shows high generalization potential for low- to mid-rise structures.     

模糊综合评价法在施工前隧道塌方风险分析中的应用

修建于崇山峻岭之中的山岭隧道,由于其复杂的地质条件和施工扰动,造成坍塌、突泥、涌水等地质灾害频发。在此方面,为了达到减轻灾害的目的,普遍开展隧道施工前的安全风险评估和施工开挖后的稳定性评价工作,取得了显著的进展,但是鲜有施工过程中对此类灾害的潜在危险性和危害性的辨识和评估。本文采用模糊综合评价法对碑仔头隧道断层破碎带塌方风险性进行分析,详细阐述模糊综合评价法的具体应用,为隧道穿越断层破碎带时施工风险性做出定量分析,对指导施工具有重要经济意义和安全意义。     

Bacterial-based additives for the production of artificial snow: What are the risks to human health?

For around two decades, artificial snow has been used by numerous winter sports resorts to ensure good snow cover at low altitude areas or more generally, to lengthen the skiing season. Biological additives derived from certain bacteria are regularly used to make artificial snow. However, the use of these additives has raised doubts concerning the potential impact on human health and the environment. In this context, the French health authorities have requested the French Agency for Environmental and Occupational Health Safety (Afsset) to assess the health risks resulting from the use of such additives. The health risk assessment was based on a review of the scientific literature, supplemented by professional consultations and expertise. Biological or chemical hazards from additives derived from the ice nucleation active bacterium Pseudomonas syringae were characterised. Potential health hazards to humans were considered in terms of infectious, toxic and allergenic capacities with respect to human populations liable to be exposed and the means of possible exposure. Taking into account these data, a qualitative risk assessment was carried out, according to four exposure scenarios, involving the different populations exposed, and the conditions and routes of exposure. It was concluded that certain health risks can exist for specific categories of professional workers (mainly snowmakers during additive mixing and dilution tank cleaning steps, with risks estimated to be negligible to low if workers comply with safety precautions). P. syringae does not present any pathogenic capacity to humans and that the level of its endotoxins found in artificial snow do not represent a danger beyond that of exposure to P. syringae endotoxins naturally present in snow. However, the risk of possible allergy in some particularly sensitive individuals cannot be excluded. Another important conclusion of this study concerns use of poor microbiological water quality to make artificial snow.     

Experimental testing of tall reinforced masonry walls under out-of-plane actions

This paper presents the results of experimental tests on tall reinforced masonry walls. Systems made with vertically perforated clay units for building mainly tall, load-bearing, reinforced masonry walls for commercial and industrial purposes were studied for applications in areas characterised by low to high seismic risk. Tests aimed at obtaining basic mechanical characterisation of the construction systems, and reproducing the behaviour of single-storey reinforced masonry buildings provided with deformable roofs. For this structural configuration, a special set-up for out-of-plane cyclic tests was designed and built. In particular, this paper presents: (a) systems used for tall reinforced masonry wall construction; (b) test set-up to reproduce the behaviour under out-of-plane loads and P–Δ effects; (c) experimental results obtained. The final aim is validating the effectiveness of the proposed construction systems and achieving complete mechanical characterisation for modelling and structural assessment purposes.     

钢框架-轻木剪力墙混合结构抗震性能振动台试验研究

为研究钢框架-轻木剪力墙混合结构的抗震性能,设计了缩尺比为2/3的钢木混合结构模型,并对其进行了振动台试验。试验中选取汶川、Canterbury、El Centro和Kobe共4条地震波,并考虑多遇、设防和罕遇3个地震水准,相应的地震加速度峰值分别为0.14g、0.40g和0.80g。通过振动台试验获得了钢木混合结构的地震响应和破坏模式。结果表明：钢木混合结构在多遇地震作用下最大层间位移角为0.15%,罕遇地震作用下最大层间位移角为0.85%,均能满足规范对结构变形的要求;在试验过程中,结构的钢框架部分和钢木连接没有出现损伤,其主要破坏模式表现为轻木剪力墙面板钉节点的破坏,破坏部位主要位于墙体覆面板的边缘;多遇地震作用下,轻木剪力墙承担了结构地震剪力的55.1%以上,有效地提高了结构抗侧承载力;随着输入地震加速度峰值的增大,剪力墙刚度逐渐退化,其分担的地震剪力有所降低,但即使在罕遇地震作用下,轻木剪力墙分担剪力的比例仍能达到39.9%以上。