Design of Dissipative Braces for an Existing Strategic Building with a Pushover Based Procedure

The research presented in this paper deals with the seismic protection of existing frame structures by means of passive energy dissipation. An iterative displacement-based procedure, based on capacity spectrum, to design dissipative bracings for seismic retrofitting of the frame structures is described, and some applications are discussed. The procedure can be used with any typology of dissipative device and for different performance targets. In this work, the procedure has been applied, with both traditional pushover （load profile proportional to first mode） and multimodal pushover, to an existing RC （reinforced concrete） frame building. In the application, the buckling restrained braces have been used in order to prevent damages to both the structure and non structural elements. The use of multimodal pushover proves to be more effective than pushover based on single mode in case of medium rise RC frame building （higher than 30 m） but, once this building is retrofitted, and therefore regularized, with a bracing system, the difference between using monomodal or multimodal pushover becomes insignificant.     

Structural Retrofitting of Old Illyria Hote

Illyria hotel （formerly Bozhur） was built during the sixties in the heart of the actual Kosovo＇s capital Prishtina, according to former old Yugoslav standards in a Modernist architectural style. It represents a massive structural system with brick walls up to 54 cm thick and ＂avramenko＂ type reinforced concrete floors. The investor＇s aim was to add another two floors on the top of the existing ones and to build two level underground parking floors, a health spa centre, whilst at the vicinity of the existing building （the northern side） to erect a new 17 story-high brand new hotel and administration building. The retrofitting of the structure as well as construction of the new structure has been done in full accordance with the new structural Eurocodes＇ recommendations. 3D FEM （finite element method） modeling was used for the analysis and design, using ETABS v 9.5 nonlinear and ARSAP 2010 （Autodesk Robot Structural Analysis Professional 2010）. Response spectrum design according to EC 8,3.2.2.4 has been used for seismic analysis and design with a reference peak ground acceleration on type A ground Of AgR = 0.25 g.     

Existing Building Challenge and CONCERTO Project

If Europe is to achieve the planned transition to a low carbon economy by 2050, succeeding in improving the energy efficiency of the largely inefficient existing building stock will be pivotal. Certain energy efficiency retrofitting obligations have now emerged as part of the EU＇s Energy Performance in Buildings Directive and the Energy Efficiency Directive. Challenges for retrofitting currently include gaps in technical skills both amongst building trades and professionals, a lack of awareness of building owners and users, concerns about compromising cultural heritage as well as a lack of viable business models, comparatively high cost and resulting long pay-back periods currently hamper the progress. Lessons can be drawn here form the EU-funded initiative CONCERTO, which helped 58 communities in 23 countries to reduce their dependence on conventional energy supply by implementing energy efficiency measures and integrating renewable energy sources not at single building scale but community scale. Almost all of these entailed retrofitting activities bad to find solutions to the issues mentioned. This paper presents a selection of conclusions regarding retrofitting to be drawn from the analysis undertaken under the project CONCERTO premium, which analysed outcomes across the 58 projects on behalf of the European Commission and focuses in particular on the political relevance of outcomes.     

Comparative Analysis of Bridges with AASHTO and Florida I-Beam Girders

A comparative study of two pre-stressed girder bridges, one with AASHTO （American Association of State Highway and Transportation Officials） Type III girders and the other with new FIB （Florida l-beam） girders, is presented. FIB girders are expected to provide increased lateral stiffness, higher load carrying capacity, cost-efficiency and better reliability. In this paper, the first bridge that is analyzed is a 3-span bridge designed with six AASHTO Type III girders, and the second bridge has four FIB girders with the same span length, width and girder depth. The bridges are analyzed for Florida state legal loads SU4 and C5. Both bridges are analyzed using a sophisticated finite element method. The deflections, moment envelopes, section capacity and live load rating of the two bridges are obtained and compared. FIB girders have higher vertical stiffness, higher section capacity providing higher load rating than the AASHTO girders.     

Gross Pollutants Study in Urban Areas under Tropical Climates

Gross pollutants are the primary targeted pollutants in urban catchment management for urban water quality improvement as well as mitigation of flood. Apart from aesthetically unattractive because of its visibility, gross pollutants also contributes to degradation of river water quality and loss of aquatic habitat as it carries harmful pollutants such as oxygen demanding material, hydrocarbons and heavy metals. This study analyzed trend of gross pollutant generated from two urban residential areas located in Selangor, Malaysia. The median value of gross pollutant load obtained fi＇om the Amanah Apartment and Bandar Botanic are 347.41 kg/ha/year and 32.46 kg/ha/year, respectively. Relationship between gross pollutant wet load with rainfall depths was derived using regression equation. A significant trend of increasing gross pollutant wet load into drainage system with increasing rainfall depth was observed. The behavior of pollutant load is related to the one observed in Australia.     

Optimization for Maximum Nonlinear Buckling Load and Topics on Imperfection of Latticed Shells

The present paper represents comparison of continuum shells and latticed shells with qualitative analysis. For shells, the mechanical characteristics in the two perpendicular directions are continuous and related to each other, and any change in thickness will result in change in stiffness in any direction. In latticed shells, members are discrete and stiffnesses in two mutually perpendicular directions are discontinuous and independent of each other. Therefore, sensitivity of geometrical imperfection for buckling of latticed shells should be different from that of continuum shells. The author proposes a shape optimization method for maximum buckling load of a latticed shell. A single layer latticed dome is taken as a numerical example, and the results show that the buckling load parameter for full area loading case increases 32.75% compared to that of its initial shape. Furthermore, the numerical example demonstrates that an optimum latticed shell with maximum buckling load, unlike an optimum continuum shell, may not be sensitive to its geometrical imperfection.     

Seismic retrofit of GLD shear wall structures in Singapore

This study is concerned with the experimental investigation into the seismic behaviour and retrofitting of gravity-load-designed reinforced-concrete (RC) shear wall structures in Singapore. These structures are designed according to the British Standard (BS8110 1985 BS8110. 1985. Structural use of concrete parts 1, 2 and 3, London: British Standards Institution.  [Google Scholar]). For this purpose, 1/5 scaled models (with and without retrofitting), representing the lower critical regions of a 25-story RC shear wall structure, were tested under cyclic loadings. Test results showed that the shear wall failed at the base due to shear and that the pushover test provides a simplified representation of the cyclic test. Retrofitting the wall with GFRP (glass fibre reinforced polymer) system resulted in improved performances of up to 20% to 30% higher ultimate load capacity and displacement. The study provides an insight into the seismic behaviour of such structures and the mechanism of the proposed retrofitting scheme for improving the structural resistance to seismic loads.     

软土地基中超长PHC桩竖向静载荷试验研究

对四根软土地基中超长PHC桩进行抗拔和抗压载荷试验,分析软土地基中超长PHC桩的抗拔承载力和抗压承载力特性,为今后的设计和施工提供参考。抗拔试验结果表明,上拔荷载在超长PHC桩有效预压应力范围内,桩顶上拔量与荷载呈线性关系;抗压试验表明,超长PHC桩荷载-沉降曲线为缓变型,承载潜力较大,实际抗压承载力大于根据土工参数估算的承载力。     

软土地基超长桩静载试验中桩侧堆载影响分析

阐述了堆载法静载试验中桩侧堆载与地基变形对试桩的影响,为便于分析,定义了试桩沉降的实测值和真实值。对比分析了国家、行业及地方标准中关于试桩、锚桩(或压重平台支墩)和基准桩之间中心距离的相关规定,探讨了减小桩侧堆载对试桩沉降影响的方法。结合深圳填海区大直径超长桩静载试验工程实例,建立三维数值模型,分析了采用地基处理+“回”字形混凝土平台时,桩侧堆载和加/卸载方式对试桩受荷性状及测试结果的影响,包括桩土沉降、桩身轴力、监测点位移和试桩刚度等。研究结果表明:堆载法静载试验中,采用试桩沉降真实值时,桩侧堆载的加/卸载过程对试桩极限承载力和承载特性的影响可以忽略; 对于采用“回”字形混凝土平台的软土地基大直径超长桩静载试验,建议采用高精度水准仪或全站仪对试桩桩顶沉降真实值进行监测和校核,包括试验准备阶段桩侧堆载引起的沉降,以剔除桩侧堆载的加/卸载过程对沉降基准点竖向位移的影响。     

单桩静载试验的数值模拟及极限承载力确定

静载试验是确定单桩承载力最直接、可靠的方法,但对于大部分乙级和丙级桩基工程,往往只能采用规范提供的间接方法确定单桩极限承载力的大小,所得数值的可靠性不足、设计常偏于保守。将数值分析手段与现场勘察试验结果相结合,对单桩静载试验进行模拟,可以确定出单桩极限承载力。实例研究表明,该方法能较准确的模拟单桩静载试验过程,并得到破坏阶段时的极限承载力。     

载荷试验确定粉喷桩承载力的标准探讨

载荷试验确定粉喷桩承载力时 ,规范中没有明确的取值标准 ,故使得同一试验曲线 ,不同的试验人员会给出不同的承载力。本文根据 2 0余项载荷试验结果 ,对用载荷试验确定粉喷桩承载能力的标准进行了探讨与研究 ,并给出了较为具体的取值标准     

滚压成型灌注螺纹桩承载性能研究

采用静载荷试验及数值计算相结合的方法进行了螺纹桩承载性能的研究.分析了螺齿宽度、螺距等桩型参数对螺纹桩承载性能的影响,对外径相同的直径桩与螺纹桩的承载性能进行了静载荷对比试验研究.螺纹桩单桩极限承载力较相同桩外径的直型桩极限承载力稍高,螺齿宽度对螺纹桩的极限承载力影响非常明显,随螺齿宽度的增加螺纹桩的极限承载力增大;螺距对极限承载力影响也较为明显,随螺距的减小,螺纹桩的极限承载力增大.螺纹桩在低荷载水平下,桩侧阻力沿桩身均匀发挥,桩端阻力较小,随荷载水平的增大,桩端阻力大幅提高,并提出螺纹桩承载力的计算公式.     

Simplified Analysis of the Effect of Soil Liquefaction on the Earthquake Pile Response

The time-history response of a structure-pile system during soil liquefaction is highly complicated and several analytical methods have been proposed through the accuracy verification based on the comparison with the experimental works. However, the analytical methods with higher accuracy often require large computational loads and are not necessarily preferred in the actual design practice. On the other hand, while the response spectrum method is not accurate compared to the aforementioned methods, it can provide useful design guidelines in the preliminary stage for structure-pile systems under soil liquefaction with acceptable accuracy. In this paper, the previously proposed response spectrum method for a structure-pile-soil system is used where the effect of soil liquefaction is taken into account by introducing the so-called p-multiplier method. It is shown that, while in the case of inner partial liquefaction with a non-liquefied layer at the top, the demand on the pile moment is large due to the inertial effect of that non-liquefied layer at the top, in the case of overall liquefaction near the ground surface, the demand is smaller than the case of inner partial liquefaction.     

横向荷载作用下扩底桩弯曲破坏性状分析

扩底桩因其承载能力强而越来越多地应用于工程实践中,对扩底桩的研究多集中在竖向荷载作用下的工作性状研究,承受横向荷载作用的扩底桩受力性能研究较少。对大尺寸、承载力强的扩底桩开展原型破坏试验非常困难,而模型试验可以在有限试验条件下模拟原型试验的真实试验过程。本文通过对扩底桩进行横向逐级加载模型试验,得到扩底桩在横向加载作用下桩顶位移、桩身应力、桩侧土抗力、桩底土压力的变化规律以及弯曲破坏时桩体的破坏形态,并对其承载性能进行分析和总结。模型试验得到的扩底桩在横向受荷作用下呈现的承载性能规律和破坏形式可以为今后扩底桩的横向受力机理研究和应用提供依据和参考。     

锤击PHC管桩的荷载传递试验

根据地质工程勘察报告所提的土层摩阻力及端阻力来设计锤击PHC管桩的承载力是不充分的。本文根据锤击PHC管桩的现场预埋件试验,介绍了土层摩阻力及端阻力的变化规律,提出了针对锤击PHC管桩的土层参数。     

长沙湾特大桥基桩单桩承载力分析

介绍了长沙湾特大桥桥墩的工程地质条件、试桩的桩位以及竖向抗压静载试验和水平静载试验的装置和试验方法。通过对试验数据的分析比较认为:三个典型桥墩下的桩基础的竖向极限承载力均大于试验的最大荷载,各试桩水平临界荷载值离散性较小,可取其平均值作为单桩水平承载力特征值,m值随水平力或桩顶水平位移的增加而减小。     

预制桩水平承载性能研究

结合预制桩水平静载试验结果,确定水平承载力特征值和地基土水平抗力系数的比例系数m值,研究预制桩的水平承载性能。     

两种静载试验确定大直径扩底桩竖向承载力

工程上通常用一种静载试验确定扩底桩的竖向承载力 ,而本文用两种静载试验方法 (即直接试验法和间接试验法 )确定扩底桩的承载力 ,据此对端承于粗砂层的埋深 1 4.5m左右的扩底桩竖向承载性状进行了分析。结果表明 ,两种试验方法得到的SD1、SD2桩的极限承载力值分别相差 5 %和 1 0 %。扩底直径为 3.40m的SD1桩的极限承载力为 960 0kN ,端阻力达86% ;扩底直径为 3.0 0m的SD2桩的极限承载力为 685 0kN ,端阻力占 81 %。当桩顶沉降 1 8.72mm左右时 ,SD1、SD2桩摩阻力已充分发挥 ;而端阻力充分发挥时 ,SD1、SD2桩顶沉降分别达 31 .85 5mm和 2 9.34mm。直径相同时 ,扩底桩的竖向承载力远大于纯摩擦桩和直身墩     

摩擦型预制桩有效桩长对单桩承载力影响

介绍武汉某综合楼顶制桩桩基工程,从多次静载试验结果对比中获得一些有益的结论,对今后类似此类型桩单桩极限承载力的确认有借鉴意义和指导作用.     

后注浆超长灌注桩竖向承载特性载荷试验研究

现场载荷试验是确定单桩竖向承载力常用方法之一,基于现场试桩静载试验和桩身轴力测试试验,分析了后注浆超长灌注桩的竖向极限承载力性状、桩身轴力传递特性及桩侧阻力,桩端阻力发挥特性。研究结果表明:在竖向荷载作用下,桩身轴力随着深度的增加而增量减小,且随荷载的增加而逐渐增大;超长灌注桩表现出摩擦桩特性,荷载-沉降曲线没有明显破坏点,其竖向荷载主要靠侧摩阻力进行传递;桩侧阻力和桩端阻力非同步发挥并且相互影响。根据实测数据对计算单桩承载力的侧摩阻力和桩端阻力的系数进行修正,修正后为类似桩基础工程设计提供技术参考。