Structural response of large stadium roofs due to dynamic wind actions

The paper presents the experimental tests carried out in the Boundary‐Layer Wind Tunnel (BLWT) for the design of large roofs of the new Olympic stadium (Karaiskaki) in Pyraeus (Greece), Manfredonia (Italy) and “Delle Alpi” of Turin (Italy). In addition, a report about some results of the time domain (T. D.) dynamic response analyses performed on the Karaiskaki structure and on the Olympic stadium in Rome will be given. The peculiar shape of these large structures and their particular location (two of them are in the immediate sea vicinity) let arise the question about the actual distribution of the wind loads, i.e. on the pattern of pressure coefficients (c_p) over the entire roof. For every wind direction investigated, the following quantities have been evaluated: mean values of the aerodynamic coefficients c_p, standard deviation of c_p, maximum and minimum values of c_p. Finally, the recorded data have been used for the numerical simulation of the dynamic response of the structure in Time Domain, whose aim is the definition of the design loads of the steel lattice structures. A numerical model of the “Delle Alpi” stadium is also in preparation, allowing results of dynamic response analyses, which are still in progress.     

Long-term fatigue analysis of multi-planar tubular joints for jacket-type offshore wind turbine in time domain

Long-term fatigue analysis of welded multi-planar tubular joints for a fixed jacket offshore wind turbine designed for a North Sea site in a water depth of 70 m is performed. The dynamic response of the jacket support structure due to wind and wave loads is calculated by using a decoupled procedure with good accuracy (Gao et al., 2010). Hot-spot stresses at failure-critical locations of each reference brace for 4 different tubular joints (DK, DKT, X-type) are derived by summation of the single stress components from axial, in-plane and out of plane action, the effects of planar and non-planar braces are also considered. Both a 2-parameter Weibull function and generalized gamma function are used to fit the long-term statistical distribution of hot-spot stress ranges by a combination of time domain simulation for representative environmental conditions in operational conditions of the wind turbine. A joint probabilistic model of mean wind speed U_w, significant wave height H_s and spectral peak period T_p in the northern North Sea is used to obtain the occurrence frequencies of representative environmental conditions (Johannessen, 2002). In order to identify the contributions to fatigue damage from wind loads, wave loads and the interaction effect of wind and wave loads, 3 different load cases are analyzed: wind loads only; wave loads only; a combination of wind and wave loads. The representative environmental condition corresponding to the maximum contribution to fatigue damage is identified. Characteristic fatigue damage of the selected joints for different models is predicted and compared. The effect of brace thickness on the characteristic fatigue damage of the selected joints is also analyzed by a sensitivity study. The conclusions obtained in this paper can be used as the reference for the design of future fixed jacket offshore wind turbines in North Sea.     

大跨双层屋盖结构风洞试验与风振响应研究

对南太湖湿地奥体公园复杂体型体育场双层屋盖结构进行了风荷载的风洞试验与风致动力响应研究。屋盖由高低两个开口椭圆屋面叠合而成,两屋面之间设置观光走廊。利用风洞模型试验测定了双层屋盖上下表面的平均和脉动风压时程数据。通过计算分析得到了屋盖结构局部测点的极值风压以及平均风荷载整体合力与最不利风向角。然后基于有限元方法对该屋盖进行了风振响应的动力时程分析,获得了结构风振系数、等效静力风荷载的分布图以及考虑风振效应的最不利风向等数据和结论。     

BLWT tests and design loads on the roof of the new olympic stadium in Piraeus

The paper introduces some peculiar and innovative aspects by the experimental tests carried out in a boundary-layer wind tunnel (BLWT) for the design of the roof of the new Olympic soccer stadium in Piraeus, Greece, using simultaneous pressure measurements and state-of-the-art processing techniques. The wind tunnel data are then used for the numerical simulation of the quasi-static response of the structure in the time domain, so obtaining the time histories of the structural response. The extreme values of the wind effects are evaluated directly from the statistical analysis of the corresponding time histories and are compared with those from dead loads. Finally the uniform pressure distributions are identified which produce the same extreme values of wind effects.     

An evaluation exercise of a wind pressure distribution model

The wind pressure distribution (WPD) around a building is an important parameter for multi-zone airflow simulation. The input is usually in the form of pressure coefficients (C_p). The values of C_p are traditionally derived based on wind tunnel studies. However, since it is not possible to always conduct wind tunnel tests to obtain the C_p values, alternative approaches have been suggested. One approach involves the use of statistical regression analysis of data obtained from wind tunnel studies. In this paper, C_p values of a shophouse building under investigation are generated using wind tunnel, a WPD model, which is based on the regression analysis of wind tunnel data as well as based on wall averaged values from published data. Using the C_p values obtained from the wind tunnel as the reference, the accuracy of the C_p values generated by the WPD model and the wall averaged values are analysed and discussed. The effects of such accuracy on the computed air flow rates and age of air for the building using a multi-zone network airflow model are also considered.     

新尤文图斯体育场结构设计

为了1990年世界杯而兴建的意大利都灵阿尔卑斯体育场,在建成约19年后被一座称为新尤文图斯的新体育场所代替。新体育场的设计以最新的体育场及体育设施的设计规范为依据。本文介绍了该新体育场建筑设计和结构设计所采用的方法。主要阐述了基础系统、大型看台的框架体系、悬挂屋顶结构体系、边界风洞实验室的试验测试工作以及施工安装等。     

Back-analysis and finite element modeling of jacking forces in weathered rocks

Prediction of jacking forces has been well-established for pipe-jacking drives traversing soils. However, the accrual of jacking forces for drives negotiating weathered rock formations has not been well understood. Three pipe-jacking drives in Kuching City, Malaysia spanning weathered lithological units of sandstone, phyllite and shale were studied. In the absence of in-situ pressuremeter testing during the investigation stage, tunneling rock spoils were collected and characterized through direct shear testing. The “generalized tangential” technique was applied to the nonlinear direct shear test results to obtain linear Mohr–Coulomb parameters, c′_p and ϕ′_p. This allowed for back-analysis of frictional coefficient, μ_avg through the use of a well-established predictive jacking force model. The reliability of using c′_p, ϕ′_p and μ_avg was assessed through 3D finite element modeling of the studied pipe-jacking drives. Based on these parameters, the results obtained from the numerical analyses of the studied pipe-jacking drives show good agreement with the jacking forces measured in-situ. The outcome of this research demonstrates that the derived strength parameters from direct shear testing of tunneling rock spoils has the potential to be used as reliable input parameters in finite element modeling to predict pipe-jacking forces in highly weathered geological formations.     

The influence of realistic mean wind loads on the static response and the design of high cooling towers

The dominating load of natural draught cooling towers is induced by the action of turbulent wind. It is usual to describe the wind load $\text{p(z,θ) =}\text{c}{}_{\mathrm{p}}\text{·q}$ by the velocity pressure $\text{q(z)}$ and the pressure distribution $\text{c}{}_{\mathrm{p}}$. Based on measured data from wind tunnel test in homogeneous flow it has become common practice to use a simplified height-constant pressure distribution $\text{c}{}_{\mathrm{p}}\text{(θ)}$, where θ is the angle in circumferential direction. Tests in shear flow show, that this is no longer true, as $\text{c}{}_{\mathrm{p}}$ also depends on the height $\text{z, c}{}_{\mathrm{p}}\text{= c}{}_{\mathrm{p}}\text{(z, θ)}$. The aim of this paper is to elaborate the differences between the simplified approach with $\text{c}{}_{\mathrm{p}}\text{(θ)}$ and the realistic pressure with $\text{c}{}_{\mathrm{p}}\text{(z, θ)}$ for the pressure coefficients $\text{c}{}_{\mathrm{p}}$, for the response of the shell, the columns and the foundation loads, and finally for the influence on the dimensioning of the shell and the supports.     

液体黏滞阻尼器在盘古大观高层建筑上的抗震应用

盘古大观钢结构写字楼是毗邻2008奥运会主场馆的45层、高191m的超高层建筑,通过与美国John Martin公司配合,进行结构抗震、抗风分析。结合是否需要和怎样安置作为结构保护系统的黏滞阻尼器,进行设计和验算的反复迭代、全面计算和优化。按我国规范和超高限审查要求的大、中、小,水平和竖向地震作用下结构的全面地震反应进行研究,对越来越引起人们注意的结构附属结构的地震反应进行初步探讨。本工程使用了带刚度的黏滞阻尼器,采用穿越式安装支撑的方法。结果表明,液体黏滞阻尼器对该超高层建筑抗震具有系统、全面的改进作用。     

国家体育馆设计中运用的高新技术

以在北京举办的奥林匹克运动会的主体育场“鸟巢”为例，介绍在奥运建筑中运用的新方法、新技术、新材料，为相关各方面积累了宝贵的经验，从而为中国建筑水平的实质性提高作出贡献。     

某体育会展中心大跨屋盖系统风荷载试验研究

介绍了某体育会展中心会展馆和体育场的大跨屋盖系统模型风洞试验的概况和主要试验结果,通过分析典型测点方法详尽研究了挑篷上平均风压和脉动风压的分布,讨论了脉动风压对总设计风荷载的贡献,并对比了计算围护结构风荷载的规范方法和统计方法;结果表明,正面迎风时,体育会展馆和体育场屋盖边缘的平均风压和脉动风压系数均较大,采用规范方法算得的会展馆围护结构风荷载大部分小于采用统计方法算得的风荷载,而用规范方法算得的体育场围护结构风荷载均小于采用统计方法算得的风荷载,在大跨屋盖设计中应分区域选用两者中较大值作为风荷载设计标准值。     

Uncertainty in airflow rate calculations due to the use of surface-averaged pressure coefficients

Mean wind pressure coefficients (C_p) are key input parameters for air infiltration and ventilation studies. However, building energy simulation and stand-alone airflow network programs usually only provide and/or use a limited amount of C_p data, which are based on several assumptions. An important assumption consists of using surface-averaged C_p values instead of local C_p values with a high resolution in space. This paper provides information on the uncertainty in the calculated airflow rate due to the use of surface-averaged C_p data. The study is performed using published empirical data on pressure coefficients obtained from extensive wind tunnel experiments. The uncertainty is assessed based on the comparison of the airflow rate (?) calculated using the surface-averaged C_p values (?_AV) and the airflow rate calculated using local C_p values (?_LOC). The results indicate that the uncertainty with a confidence interval of 95% is high: 0.23 ?_AV < ?_LOC < 5.07 ?_AV. In cases with the largest surface-averaged ΔC_p, the underestimation or overestimation is smaller but not negligible: 0.52 ?_AV < ?_LOC < 1.42 ?_AV. These results provide boundaries for future improvements in C_p data quality, and new developments can be evaluated by comparison with the uncertainty of the current methods.     

Occupants’ interactions with windows in 8 residential apartments in Beijing and Nanjing,China

Occupants’ interactions with windows influence both building energy consumption and exposure to airborne pollutants indoors. Occupants’ window opening behavior varies from region to region due to physical environmental factors and social reasons. China is now confronting severe atmospheric pollution, which may affect occupants’ window opening behaviors. A field study was conducted in 8 naturally ventilated residential apartments in Beijing and Nanjing, China. This involved periodically monitoring window states of eight residential apartments within each season from October 2013 to December 2014 by magnetic induction devices (TJHY, CKJM-1). Relationships between the probability of window opening (p) and explanatory variables, including outdoor air temperature (t _o), outdoor relative humidity (RH), outdoor wind speed (V _s), and ambient PM2.5 (particles with aerodynamic diameter less than 2.5 microns) concentrations (C _p), were analyzed. Stochastic models of occupants’ interactions with windows in monitored residences were established via univariate and multivariate linear logistic regression for both cities. According to the results, t _o is the most important explanatory variable affecting occupants’ interactions with windows in monitored residences. The best multivariate linear logistic model result from the “backward selection” procedure based on “Akaike Information Criterion” (AIC) includes t _o, RH, V _s and C _p as explanatory variables, which implied that outdoor air quality, represented by C _p, has become a concern affecting Chinese residents’ interactions with windows.     

Mechanisms of quasi-preconsolidation stress development in clays: A rheological model

This paper deals with the development of a mechanistic model for the ageing consolidation behavior of clays with the focus on aspects related to the development of quasi-preconsolidation pressure. The initial use of such pressure in design met with criticism, but field and laboratory evidence, which highlights its significance, continues to accumulate. A nonlinear rheological model is used to numerically simulate the consolidation process of clay in laboratory tests and to identify the basic mechanical parameters that contribute to the development of the quasi-preconsolidation phenomenon. Methods to identify the parameters of the model from oedometer tests are described. It is shown that while the variation in soil modulus can be characterized by a linear form in the virgin compression region, it is nonlinear in the recompression region and is best characterized by a hyperbolic function. Changes to the modulus in the recompression region, due to ageing, is shown to be the dominant cause of the development of the quasi-p_c phenomenon. Observed results as well as numerical simulations demonstrate that specimens that had aged longer show increased quasi-p_c values. While the variation in soil modulus controls the EOP curve of clays, the observed time effects, such as the “vanishing p_c” phenomenon, are controlled primarily by changes in soil viscosity. However, this has no bearing on the development of the quasi-p_c phenomenon.     

Vibrations and aerodynamic stability of a prestressed pipeline cable bridge

A method is presented for analysing the vibrations and aerodynamic stability of a prestressed pipeline cable bridge structure. The structure of the bridge and the method for calculation of the natural vibration frequencies are described. Some of the natural vibration frequencies were tested by measuring dynamic quantities on a bridge structure in situ.A sectional model was designed for testing in a wind tunnel of diameter 1.8 m; the model was investigated by means of a drag balance, and the aerodynamic coefficients C_L, C_D and C_M were determined. The same model was suspended elastically in a wind tunnel and its response to an airstream studied. The results of the measurements for the rigidly and elastically suspended model are used in calculating the critical flutter velocity and in analysing the model's aerodynamic stability.     

大跨屋盖结构下压风荷载确定方法与实例分析

介绍了几种大跨度屋盖结构下压风荷载的计算方法,并以某大型体育场屋盖为例,通过引入峰值因子和位移匹配度判据,分析了等效荷载作用下位移响应值和空间分布的合理性。研究结果表明,按比例放大的阵风荷载因子法和动力放大系数法,当计算基准值较小时,得出的放大倍数过高,将导致除等效目标之外的响应值被高估。采用准静态荷载与均匀分布附加风振力的线性叠加方法得出的等效荷载将给出较为合理的位移响应值,其中又以结合LRC方法的等效荷载位移匹配度最高。此外,研究表明若不考虑风洞试验结果,按体型系数+0.2在半跨屋盖上作用均匀风荷载,也能给出基本合理、工程上可用的下压风荷载。     

Active control for a benchmark building under wind excitations

The tall building proposed in the benchmark problem is a concrete office tower, which is wind sensitive due to its slenderness. The wind loads acting on the building are defined by the results of wind tunnel tests conducted at the Sydney University and an active mass driver can be designed for installation on the top floor in order to reduce the structural response under strong wind gusts. In this paper, the control strategy presented for the third generation benchmark control problem for wind-excited buildings (J. Eng. Mech. (1999), submitted for publication) is the simultaneous treatment of both H₂ performance criteria and H_∞ attenuation constraints that demonstrates design tradeoffs and can be applied to the AMD system based on acceleration feedbacks. This control problem can be formulated by linear matrix inequalities in terms of a common Lyapunov function. Solving linear matrix inequalities is a convex optimization problem and efficient interior-point algorithms are now available to solve this problem. Simulation and design results demonstrates that, decreasing H_∞ attenuation constraint can be used to reduce the structural response under wind excitations at the expense of increasing H₂ performance index.     

多风向多目标等效静风荷载分析方法及应用

针对大跨空间结构中多振型参与风振响应特点和工程应用需要,提出针对多个风向的多目标等效静风荷载分析方法。根据所有风向的平均风荷载（或者风振响应极值）分布之间的相似性指标,将所有风向分为若干个风向区,计算各风向区的风振包络响应;在每个风向区内,选择平均风荷载分布和结构主导振型惯性力作为构造多目标等效静风荷载的基本向量,根据最小二乘法,得到基本向量的最优组合系数,从而得到针对多个风向、多个等效目标的等效静风荷载。将该方法用于某大型科技新馆,分析结果表明：根据各风向下屋面平均风压系数分布间的相关系数,36个风向角仅需分成3个风向区,且各风向区等效静风荷载作用下的静力响应与实际动力响应包络响应吻合较好,验证了所提方法的计算精度和工程应用的便利性。     

Characterization of Yangsan Clay,Pusan, Korea

It has been reported by previous researchers that the preconsolidation pressure (p_c) of Kimhae (Yangsan) clay, which is thickly deposited along the Naktdong River, Pusan, Korea, is considerably less than its in-situ effective overburden pressure (p'_vo)-The question has arisen whether such a low p_c value is due to underconsolidation or to the unreliability of laboratory tests, including the use of low quality sample. As a cooperative research program between PHRI (Port and Harbour Research Institute) and Pusan National University, extensive in-situ and laboratory investigations were carried out at Yangsan, using a Japanese sampler and Japanese sampling technique. It is found that the p_c values at the site are slightly greater than p'_vo, which is different from the test results from the previous researchers. However, the overconsolidation ratio (OCR) at this site is quite small compared to similar aged normally consolidated clays deposited in Japan.     

体育场屋盖结构静动力风荷载实用分析方法

本推导了体育场屋盖结构静动力风荷实用计算公式,并以上海虹口体育中心足球场大悬挑钢屋盖结构体系为例,分析和研究了它的位移风振分布规律。