Start of structural damage in stucco walls

A wealth of data about the performance of stucco shear walls under cyclic loading has become available since 2001. Stucco and drywall are the only earthquake and wind lateral force‐resisting systems in many existing residential buildings, especially single and multi‐family homes built before 1980. This paper presents the results of an analysis of cyclic tests conducted at the University of California, Irvine, on solid stucco walls to determine the start of structural damage. Copyright © 2010 John Wiley & Sons, Ltd.     

Performance of light-gauge cold-formed steel strap-braced stud walls subjected to cyclic loading

The performance of cold-formed steel (CFS) strap-braced walls is evaluated by experimental tests on full-scale 2.4 m×2.4 m specimens, and techniques to improve their behavior are presented. Different strap arrangements have been introduced, and their performance investigated by means of cyclic loading of a total of twenty full-scale walls. Several factors affecting the performance of cold-formed steel frame shear wall have been considered for each arrangement. This paper presents the failure modes of each system and the main factors contributing to the ductile response of the CFS walls to ensure that the diagonal straps yield and respond plastically with a significant drift and without any risk of brittle failure, such as connection failure or stud failure. Discussion of the advantages and disadvantages of including the non-structural gypsum board on lateral performance of the walls is also presented.     

Empirical validation and modelling of a naturally ventilated rainscreen façade building

In this paper the thermal behaviour of a rainscreen ventilated façade has been investigated both experimentally and numerically. Field measurements were performed during the 2009/10 winter season in a test building located in San Mauro Pascoli (Italy) having a squared base of internal dimension of 2.89 m and a total internal height of 7.75 m. The external walls of this tower are rainscreen ventilated façades with a 24 cm air cavity and an external side composed of stoneware with open joints. Ventilation grills are located at the top and at the bottom of the tower. In this work the modelling of the test building using a dynamic thermal simulation program (ESP-r) is presented and the main results discussed. In order to study the rainscreen ventilated façade three different multi-zone models were defined and the comparison with the experimental results has been used in order to select the best ESP-r air flow network for the modelling of this kind of envelope component. The thermal analysis of this envelope component evidenced that the ventilated façade is able to reverse the direction of the heat flux through the envelope in regions characterized by large solar irradiation during the winter and moderate wind velocity, when the indoor-outdoor air temperature difference is small, thereby reducing the energy consumption required for indoor heating.     

Fire tests of Magnesium Oxide board lined light gauge steel frame wall systems

Recently, Magnesium Oxide (MgO) board has been widely used in LSF wall systems because of its improved acoustic properties, impact resistance, structural strength and serviceability. However, their thermal properties and fire performance have not been fully investigated. Therefore, in this research study thermal properties of two different types of MgO boards available in Australia were measured and their fire performance was investigated using three full-scale fire tests of LSF walls lined with two types of MgO board. Although the tests were conducted on two different types of MgO boards with different configurations, the fire test results gave a fire resistance level (FRL) of 30 min, in which the failure was initiated by integrity of the board with either board cracking or board joint opening. This paper presents the details of the thermal property tests and the three full-scale fire tests, and their results. In addition, the effects of different MgO boards, joint configurations and compounds, noggings, screw fastening techniques and cavity insulation on the fire performance of LSF walls are also presented.     

Damaged masonry walls in two-way bending retrofitted with vertical FRP strips

Unreinforced masonry (hereafter termed ‘masonry’) structures comprise a significant proportion of the building stock in many countries worldwide, however their walls do not behave well under out-of-plane loading, such as that experienced during seismic events. Consequently, many existing masonry structures require some form of retrofit to comply with existing codes. As part of ongoing research at The University of Adelaide on the out-of-plane bending behaviour of masonry walls, eight full-scale walls (with window openings) were tested under reversed-cyclic loading. Four of the severely damaged walls were subsequently retrofitted using externally bonded (EB) (three walls) and near-surface mounted (NSM) (one wall) fibre-reinforced polymer (FRP) strips and tested again to quantify the increase in strength and ductility relative to the original capacities. A debonding mechanism not yet quantified for retrofitted masonry walls was observed and identified as displacement induced (DI) debonding. It is a result of a differential out-of-plane displacement at either side of a crack in the wall. NSM strips are more susceptible due to their orientation. This paper presents the results of the wall tests along with detailed accounts of the wall failure modes.     

Seismic response of precast reinforced concrete wall subjected to cyclic in-plane and constant out-of-plane loading

This paper provides insight into the seismic behavior of a full-scale precast reinforced concrete wall under in-plane cyclic loading combined with out-of-plane loading replicated by sand backfill to simulate the actual condition of basement walls. The tested wall exhibited flexural cracks, owing to the high aspect ratio and considerable out-of-plane movement due to lateral pressure from the backfill. The wall performed satisfactorily by exhibiting competent seismic parameters and deformation characteristics governed by its ductile response in the nonlinear phase during the test with smaller residual drift. Numerical analysis was conducted to validate experimental findings, which complied with each other. The numerical model was used to conduct parametric studies to study the effect of backfill density and aspect ratio on seismic response of the proposed precast wall system. The in-plane capacity of walls reduced, while deformation characteristics were unaffected by the increase in backfill density. An increase in aspect ratio leads to a reduction in in-plane capacity and an increase in drift. Curves between the ratio of in-plane yield capacity and design shear load of walls are proposed for the backfill density, which may be adopted to determine the in-plane yield capacity of the basement walls based on their design shear.     

冷弯薄壁型钢开洞组合墙体抗剪性能研究

对4片足尺冷弯薄壁型钢组合墙体的抗剪性能进行了水平加载试验.通过建立考虑材料和几何非线性影响的有限元模型对试验试件的抗剪性能进行数值模拟.采用有限元方法对开有不同尺寸洞口的组合墙体的抗剪性能进行数值分析,提出了开洞组合墙体抗剪承载力的建议计算方法.结果表明:开洞组合墙体的破坏主要发生在洞口处;开有门、窗洞口的试件在墙面板角部出现45.方向的压溃和撕裂现象;当构造相同时,开洞组合墙体的抗剪承载力和抗侧刚度均随开洞率的增大而逐渐降低;提出的开洞组合墙体抗剪承载力的建议计算方法计算结果与ANSYS计算结果吻合较好,可供实际工程设计参考.     

密实砂土层中H型锤击桩的试验研究

进行了2根H型钢桩的现场原型试验,桩长分别为39．6m和55．4m,单桩设计承栽力为3540kN。沿桩身布设了应变计后,桩通过锤击方式打入到密实砂土层中。观测了桩在不同荷载水平下的荷载传递及沉降特性。并用土力学原理对实测桩侧摩阻力的大小和分布进行了检验。     

气屏刚度非线性雨幕墙的频域解法

通过对气屏非线性刚度、空气柱非线性阻尼力等的线性化,获得了气屏刚度非线性雨幕墙压力传递的频域解法,基于设计风压下具有常规尺寸及气屏刚度的该类雨幕墙的算例对频域法进行了检验,计算发现:气屏刚度线性化是引起频域求解误差的主要原因,气屏刚度越大或其非线性越弱,频域法精度越高。     

我国高层建筑结构综述(上)

本文介绍我国高层建筑的发展概况、一些结构体系的特点和适用范围(包括楼板体系)。文中还扼要介绍了高层建筑结构的一些科研成果和设计经验,其中包括:剪力墙的形式及其设计,地震区底层大空间剪力墙结构,框架一剪力墙结构中剪力墙的合理数量及柱截面的选定,楼板变形对高层建筑结构内力的影响,筒体结构的试验研究,高层建筑结构动力特性,高层建筑风荷载体型系数及沿高度分布的研究。     

高层建筑钢结构基于风振响应和动力特性的优化设计

高层建筑的风致响应和等效静力荷载虽然可以通过风洞试验和动力分析有效的加以确定,在结构设计的整个过程中这些等效风力却往往被当作常数来应用。本文提出了一个结合气动风力分析和结构刚度优化的自动化技术。在结构设计中利用这个技术,可以在优化结构刚度和最小化结构造价的同时,实时检查和更新作用在建筑结构上的等效风荷载。一个几何尺度与航空研究共同顾问理事会(CAARC)建议的建筑模型一致的钢框架结构被用来进行风力分析和结构优化的例子。结果表明这个技术不但能在满足位移设计要求的情况下优化结构刚度降低造价,而且也降低了作用在结构上的等效风力。     

上海松江新城交通枢纽暨购物中心钢结构穹顶风振分析

大跨度钢结构穹顶为风敏感结构,准确得到平均风荷载和风振力对工程设计非常重要.本文通过数值风洞模拟方法得到了各风向下穹顶结构的平均风压,尤其是给出了有效分析风激动力响应和等效风荷载的理论方法.通过分析松江新城钢结构穹顶的风振实例看出,对该工程风振影响最大的是整体水平与竖向运动的前八阶振型,动力部分大体占总响应的25%.本文为大跨度屋盖结构的风振分析提供了一种有效的计算方法.     

High strength thin-walled rectangular concrete-filled steel tubular slender beam-columns,Part II: Behavior

Experimental and numerical research on full-scale high strength thin-walled rectangular steel slender tubes filled with high strength concrete has not been reported in the literature. In a companion paper, a new numerical model was presented that simulates the nonlinear inelastic behavior of uniaxially loaded high strength thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns with local buckling effects. The progressive local and post-local buckling of thin steel tube walls under stress gradients was incorporated in the numerical model. This paper presents the verification of the numerical model developed and its applications to the investigation into the fundamental behavior of high strength thin-walled CFST slender beam-columns. Experimental ultimate strengths and load-deflection responses of CFST slender beam-columns tested by independent researchers are used to verify the accuracy of the numerical model. The verified numerical model is then utilized to investigate the effects of local buckling, column slenderness ratio, depth-to-thickness ratio, loading eccentricity ratio, concrete compressive strengths and steel yield strengths on the behavior of high strength thin-walled CFST slender beam-columns. It is demonstrated that the numerical model is accurate and efficient for determining the behavior of high strength thin-walled CFST slender beam-columns with local buckling effects. Numerical results presented in this study are useful for the development of composite design codes for high strength thin-walled rectangular CFST slender beam-columns.     

Interpretation of full-scale strain data from wind pressures on a low-rise structure

This paper presents a study on the structural performance of a low-rise building under high-wind action, derived from the data analysis of a long-term full-scale monitoring program (1997–2000). Experimentation and full-scale measurements are critical in the study of wind-pressure-induced loading associated with complex phenomena such as three-dimensional flow fields and non-stationary winds. Recorded pressure data and corresponding deformations (strains) on selected portions of the structural frame in the proximity of the pressure transducers are evaluated and compared. The system under investigation is unique since it is located in a complex topography (coastal) environment, for which even the interpretation of basic wind and pressure data becomes challenging.The correspondence of the observed data with the United States wind load specifications (ASCE-7) is investigated both from the perspective of the loads (pressures) and of the deformation response predictions. The structural performance is evaluated through the comparison of the recorded strains with predicted deformations, derived from the application of the corresponding external wind pressure loading to a simplified structural model simulating the behavior of an instrumented region of the building.Results show good agreement between measured pressure coefficients and selected values estimated through the ASCE-7 specifications, especially in areas of positive pressures where the predictions are consistently larger than the recorded data. Reasonable and consistent correspondence was also found from the analysis of the strains in structural members.     

Field measurement and wind tunnel simulation of hurricane wind loads on a single family dwelling

During landfall of Hurricane Ivan on the Florida ’panhandle’ in 2004, pressure time-history data were recorded on multiple pressure sensors installed on the roofs of six single-family homes. An analysis approach was developed to determine the peak negative, mean, peak positive, and standard deviation of pressure coefficients for these datasets. This paper presents a comparison of the full scale pressure coefficients from one of these homes, which experienced sustained hurricane force winds, with the results of wind tunnel experiments on a 1:50 scale model of that home. It was determined that the wind tunnel and full-scale mean and rms pressure coefficients matched very closely at almost every monitored location on the roof, while the peak negative pressure coefficients in the wind tunnel study generally underestimated the full-scale values, consistent with observations from previous full-scale/wind tunnel comparative studies. Field-measured hurricane wind loads may prove useful for evaluating existing wind load provisions. However, recommendations in that regard are premature without the analyses of multiple homes in multiple storms, performed by more than one wind tunnel facility. Future work will focus on building such a joint study.     

Light gauge steel cassette wall construction — theory and practice

Light gauge steel cassette wall construction is an interesting alternative to the conventional method of constructing light steel framing for low-rise buildings using wall studs. This paper demonstrates that this method of construction is shown to particular advantage when wall panels are subject to in-plane shear forces, which generally arise from wind loading but can also arise from seismic loading or mining subsidence. Some deficiencies in current design codes are noted. The paper also includes detailed consideration of the appropriate way to carry out the stressed skin (diaphragm) design of cassette walls with window and door openings.     

矩形塔式高层建筑满足人舒适要求的三维抗风设计

本文探讨了矩形塔式高层建筑满足人舒适要求的三维抗风设计方法。文中,确定了满足人舒适要求抗风设计的风荷载取值;建立了考虑结构顺风向短周期风振加速度、横风向风振加速度和扭转风振加速度的满足人舒适要求三维抗风设计的计算公式及相应数表。应用文中公式的工程实例设计验算表明,本文方法是十分简明和方便的。     

Full-scale wind pressure measurements on a twin-span 12.2 × 12.2 m inflated roof greenhouse

In recent years plastic film has been extensively used for cladding low cost greenhouses. A limitation of the material is its susceptibility to wind storm damage and its wider use is dependent on good design through a knowledge of wind loads.Results of a limited programme of measurements of wind pressure on a film clad inflated roof greenhouse are presented. The measurements were made on the full-scale structure under natural wind conditions. The shape of the roof was modified by the wind and has been calculated for the measured wind load pattern assuming inviscid uniform flow. The application of these results to design is discussed.     

Lateral drift constrained structural optimization of an actual supertall building acted by wind load

Recent trends towards constructing taller and increasingly slender buildings imply that these structures are more sensitive to wind excitation. This paper presents a technique for the wind‐resistant optimal design of supertall buildings with a complex structural system including concrete‐filled steel tube columns, shear walls, and various types of beams and columns. In each optimal design cycle, the dynamic wind load acting on a building is transformed into a set of multiple‐oriented equivalent static wind loads, which converts the optimal design for a building acted by dynamic loads into a simpler optimal design problem that considers only static loads. The objective function and constraint functions are explicitly formulated for various types of frame and area members, and consequently, the optimal design problem is mathematically modeled. The optimality criteria method is employed to seek a solution to the optimal design problem. A 68‐story actual supertall building with a height of 303 m is considered for a case study. The obtained results show that the presented technique is capable of giving a good numerical optimal solution for practical use. The technique and results obtained from this study are valuable for academic and professional engineers involved in wind engineering and structural design.     

Full-scale measurements of wind effects on the Jin Mao building

The Jin Mao Building located in Pudong New Area, Shanghai, which has a height of 420.5 m and 88 floors, is currently the tallest building in Mainland China. This paper presents some selected results obtained from the full-scale measurements of wind effects on the Jin Mao Building during the passage of Typhoon Rananim in August, 2004. The field data including acceleration responses, wind speed and wind direction were simultaneously and continuously recorded during Typhoon Rananim. Detailed analysis of the field data was conducted to investigate wind effects on the super tall building. The characteristics of typhoon-generated wind and wind-induced responses of the 88-storey building are presented and discussed. Dynamic properties of the building are determined based on the field measurements, and comparison with those calculated from the finite element model of the building is made. The amplitude-dependent characteristics of damping that were obtained using the random decrement technique on the basis of the field measurements are investigated. Furthermore, wind tunnel experiment is conducted to study wind effects on the Jin Mao Building through force balance model test, and the full-scale measurements are compared with the wind tunnel test results for verification of wind tunnel test techniques. Finally, the serviceability of the super tall building under typhoon conditions is discussed.