An evaluation of force-based design vs.direct displacement-based design of jointed precast post-tensioned wall systems

The unique features of jointed post-tensioned wall systems, which include minimum structural damage and re-centering capability when subjected to earthquake lateral loads, are the result of using unbonded post-tensioning to attach the walls to the foundation, along with employing energy dissipating shear connectors between the walls. Using acceptance criteria defined in terms of inter-story drift, residual drift, and floor acceleration, this study presents a multiplelevel performance-based seismic evaluation of two five-story unbonded post-tensioned jointed precast wall systems. The design and analysis of these two wall systems, established as the direct displacement-based and force-based solutions for a prototype building used in the PREcast Seismic Structural Systems （PRESSS） program, were performed at 60% scale so that the analysis model could be validated using the PRESSS test data. Both buildings satisfied the performance criteria at four levels of earthquake motions although the design base shear of the direct displacement-based jointed wall system was 50% of that demanded by the force-based design method. The study also investigated the feasibility of controlling the maximum transient inter-story drift in a jointed wall system by increasing the number of energy dissipating shear connectors between the walls but without significantly affecting its re-centering capability.

Seismic performance evaluation of steel frame-steel plate shear walls system based on the capacity spectrum method

This paper presents some methods that the standard acceleration design response spectra derived from the present China code for seismic design of buildings are transformed into the seismic demand spectra, and that the base shear force-roof displacement curve of structure is converted to the capacity spectrum of an equivalent single-degree-of-freedom （SDOF） system. The capacity spectrum method （CSM） is programmed by means of MATLABT.0 computer language. A dual lateral force resisting system of 10-story steel frame-steel plate shear walls （SPSW） is designed according to the corresponding China design codes. The base shear force-roof displacement curve of structure subjected to the monotonic increasing lateral inverse triangular load is obtained by applying the equivalent strip model to stimulate SPSW and by using the finite element analysis software SAP2000 to make Pushover analysis. The seismic performance of this dual system subjected to three different conditions, i.e. the 8-intensity frequently occurred earthquake, fortification earthquake and seldom occurred earthquake, is evaluated by CSM program. The excessive safety of steel frame-SPSW system designed according to the present China design codes is pointed out and a new design method is suggested.

Estimation of earth pressure against retaining walls with different limited displacement modes based on elastic theory

The earth pressure acting on retaining walls due to creep and consolidation is under limited equilibrium conditions(limited displacement). Linear elastic constitutive theory can be applied to determine earth pressure distribution along retaining walls under limited displacement condition. In addition,tangent modulus in Duncan-Chang nonlinear elastic model was introduced to reflect the variations of soil modulus with confining pressure, and boundary strains were derived from Rankine active earth pressure, Rankine passive earth pressure, static earth pressure and principal stress direction deflection.According to the above four boundary strains, earth pressure on retaining walls was divided into five state zones. By comparing the calculation results obtained from the equations proposed in this paper with those of experimental tests, the following conclusions can be drawn: earth pressure distribution was always nonlinear along retaining walls for translation displacement(T mode), rotation displacement around wall base(RB mode), and translation + rotation displacement around wall base(RBT mode). Also,calculated earth pressure distributions along with the depth of wall were found to be consistent with measured values under three displacement modes.Additionally, a parametric study was carried out to evaluate the effects of internal friction angle and backfill soil cohesion on earth pressure. It could be seen from the above series of studies that the earth pressure equations derived in this work could be well applied in practical engineering in designing retaining walls.

Die wall lubricated warm compaction of iron-based powder metallurgy material

Lubricant is harmful to the mechanical properties of the sintered materials. Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubricant. Iron based samples were prepared by die wall lubricated warm compaction at 175 ℃, using a compacting pressure of 550 MPa. Emulsified polytetrafluoroethylene(PTFE) was used as die wall lubricant. Admixed lubricant concentration ranging from 0 to 0.5% was tested. Extremely low admixed lubricant contents were used. Results show that in addition to the decrease in ejection forces, the green density of the compacts increases with the decrease of admixed lubricant content until it reaches the maximum at 0.06% of lubricant content, then decreases with the decrease of admixed lubricant content. The mechanical properties of the sintered compacts that contain more than 0.06% admixed lubricant are better than those of the samples that contain lesser lubricant. No scoring was observed in all die wall lubricated experiments.

Inner and outer pressure forming of nickel based super-alloy thin-walled part with variable diameter sections

A novel forming method of nickel based super-alloy thin-walled part with variable diameter sections was proposed by using inner and outer pressure with the visco-elasto-plastic pressure-carrying medium at room temperature,and the principle of the method was provided.Experiments and FE simulations were carried out to analyze the deformation characteristics for the part with larger variable diameter ratio(35%).The results show that visco-elasto-plastic pressure-carrying medium can meet the requirements of the room-temperature deformation condition for nickel based super-alloy sheet.The inner and outer pressure forming with the visco-elasto-plastic pressure-carrying medium can meet the requirements of dimensional accuracy for the thin-walled part with variable diameter sections.The thinning of wall-thickness is less than 4%.This method provides a new approach for near-net shape forming of nickel based super-alloy thin-walled parts with variable diameter sections.

Structural model for the first wall W-based material in ITER project

The preparation, characterization, and test of the first wall materials designed to be used in the fusion reactor have remained challenging problems in the material science. This work uses the firstprinciples method as implemented in the CASTEP package to study the influ ences of the doped titanium carbide on the structural sta bility of the WTiC material. The calculated total energy and enthalpy have been used as criteria to judge the structural models built with consideration of symmetry. Our simulation indicates that the doped TiC tends to form its own domain up to the investigated nanoscale, which implies a possible phase separation. This result reveals the intrinsic reason for the composite nature of the WTiC material and provides an explanation for the experimen tally observed phase separation at the nanoscale. Our approach also sheds a light on explaining the enhancing effects of doped components on the durability, reliability, corrosion resistance, etc., in many special steels.

钻井利器的故事之“护壁堵漏材料”

近年来,作为入地最为关键手段的钻探所面临的地层越来越复杂,钻孔垮塌、掉块、缩径和超径等事故发生概率增加,严重制约了钻探工程质量与效率的提升。护壁堵漏材料是钻探工程不可或缺的关键性工程材料,护壁堵漏技术则是保证钻进工作安全、快速以及持续进行的重要技术环节,是复杂地层钻孔处理的主要内容。本文从科普的角度介绍了护壁堵漏材料的基本概念与组成、冲洗液护壁堵漏作用、水泥基材料护壁堵漏作用、护壁堵漏材料的进一步发展空间等,以期加深对护壁堵漏材料的认识,促进新型护壁堵漏材料的研发和应用。

井研地区筇竹寺组页岩储层水平井钻井井壁稳定性评价

川西南井研区块筇竹寺组页岩气具有良好的开发前景,但由于对其岩矿组分、力学性质、水化特征等认识程度较低,钻井井壁稳定性认识不清,导致出现掉块、阻卡等复杂情况。为了充分认识该区寒武系筇竹寺组地层的井壁稳定性,明确粉砂质页岩水化作用及其对坍塌压力的影响规律,在岩石力学实验的基础上,研究不同钻井液浸泡时间对岩石力学参数的影响规律,建立考虑水化作用的井壁稳定性预测模型,分析不同井斜方位下坍塌压力的差异。研究结果表明:筇竹寺组伊蒙混层含量高,具有一定膨胀性,水化作用后导致岩石强度降低,对井壁稳定性有较大影响;不同钻井液体系对井壁稳定性的影响有差异,总体上油基钻井液更有利于井壁稳定;考虑了水化作用的井壁稳定预测模型更加符合实际,以此为依据,通过优化钻井液设计可以有效降低井壁失稳风险,提高钻井时效。

镍基单晶高温合金近服役环境性能研究进展

航空发动机与燃气轮机作为国之重器,对保障国防安全和能源安全具有重要意义。随着发动机效率的不断提升,涡轮进气口温度不断提高。先进叶片往往采用高代次单晶高温合金材料制备,具有薄壁、多孔复杂冷却结构,且表面涂覆先进涂层,因而先进单晶叶片结构越来越精细复杂,服役过程中叶片不同部位温度场、应力场分布变化更大,其损伤机制无法通过传统棒状试样的变形损伤机制完全体现。基于先进单晶叶片的结构特点及服役环境特点,综述了叶片结构(薄壁、气膜孔)、二次枝晶取向(二次取向)及先进涂层等单一因素及多因素耦合作用对单晶合金拉伸、蠕变及疲劳等典型性能的影响规律及损伤机理研究,并对镍基单晶高温合金近服役环境性能研究的发展方向进行展望。

急倾斜薄矿体采场围岩及假底应力分布规律研究

急倾斜极薄矿脉是有色、黄金矿山常见的矿体形态,多采用人工假底的留矿法或削壁充填法回采,研究采动过程中围岩和人工假底的受力分布对于设计假底参数和安全开采具有重要意义。以某金矿削壁充填采场为工程背景,模拟研究了人工假底及围岩采动过程中应力变化规律。上、下盘围岩采动后最大主应力和最小主应力减小,回采区域顶板应力集中。假底中心处垂直压力最小,越靠近上、下盘边壁垂直压力增加,随着采高增加,假底各部位的垂直压力增加,最后呈收敛趋势。人工假底主要是剪应力破坏,假底破坏主要是上、下盘高水平应力未作用在同一轴线而产生的剪应力造成的。根据散体侧压力和采动应力变化规律,提出在采场内每隔10m利用混凝土铺底,增加人工假底中混凝土强度及垂直方向的配筋,提高假底抗剪强度,从而提高深部采场回采的安全性和人工假底的稳固性。

Ni/Al叠层薄壁筒形构件热态气压成形工艺

NiAl基合金性能优异,具有成为下一代高温结构材料的潜力。然而,难变形NiAl基合金薄壁筒形构件的成形是阻碍其应用的主要难题。本文基于叠层材料的成形-反应制备工艺,以Ni、Al箔材为原料,首先制备了Ni/Al叠层圆柱筒坯,而后完成了Ni/Al叠层圆柱筒坯两端扩口密封,获得了质量良好、微观组织优异的扩口叠层圆柱筒坯。最终采用热态气压成形方法,制备了Ni/Al叠层圆-方变截面薄壁构件,为Ni/Al叠层薄壁复杂异形构件的成形提供了参考。

外保温系统高空坠落风险的热湿渐进性微损伤研究

基于断裂相场法的数值分析,构建细观-宏观尺度的计算模型,模拟外墙表面遭受炎热暴晒后突然降温情况下内部温度场与微观应力场,建立了热湿渐进性微损伤的评价模型,并通过粘接砂浆拉拔试验进行验证。结果表明:外保温系统外表面夏季升温至88.6℃再突然遭遇冰雹及强降雨降温至20℃时,细骨料和净浆受到的最大主应力值可达15 MPa,其厚度方向5 mm深度约100μm宽的裂纹已发展贯通,表明极端气候变化对保温系统结构完整性造成了实质性损害,外保温系统高空坠落风险迅速增大。

高承压水地层深基坑抗突涌技术

为了防止高承压水地层深基坑突涌破坏,以韩江-榕江-练江水系连通后续优化工程GX12号井深基坑为依托,采用有限元软件建立三维数值模型,对考虑地连墙深度以及布设减压井的5种技术方案进行模拟分析,研究各方案的抗突涌效果,并通过综合考虑基坑抗突涌效果及地连墙施工技术难度和工程造价等,确定基坑工程抗突涌的优化方案。结果表明:1)地连墙深度可由原设计的91.8m优化为78m;2)坑内增设减压井可有效减小坑底隆起和地连墙水平位移,但是增加了基坑周边地表沉降,而增加地连墙深度可显著减小基坑周边地表沉降和坑底隆起;3)增大地连墙深度的抗突涌效果优于增设减压井的效果。本文成果可为类似高承压水地层深基坑工程抗突涌技术提供一定的借鉴。

绕墙底转动模式下装配式挡土墙土压力研究

墙背土压力分布及大小是装配式挡土墙设计的关键依据。设计并开展新型装配式混凝土挡土墙现场试验,研究挡土墙在加载条件下的位移模式和土压力分布规律。以现场试验为原型,建立无黏性填土、墙背倾斜且粗糙的挡土墙理论计算模型,同时考虑挡土墙位移模式与大小、土拱效应和土层间剪应力的影响,采用水平层分析法推导了绕墙底转动(RB)模式下挡土墙的土压力计算公式。结果表明:①该装配式挡土墙整体性能良好,绕墙底刚性转动。在RB模式下,墙顶处土体最先达到主动极限状态,土体从上至下逐渐达到极限状态;任意深度处的土体位移S_(c)达到7 mm时将达到极限状态,即S_(c)=0.16%H(H为墙高)。②本文理论解与试验值吻合较好,计算公式可用于求解挡土墙绕墙底转动过程中的土压力分布及大小。③随着挡土墙转动幅度的增大,土压力分布曲线凹向逐渐明显,土压力合力作用点高度呈现先降低后回升的现象;挡土墙转动角度η=0.007 rad为挡土墙达到主动状态的临界值。

西咸自由贸易企业服务中心超高层建筑结构设计

西咸自由贸易企业服务中心地处高烈度区,与渭河断裂之间的距离约2km,应考虑近场效应。项目采用钢管混凝土框架(钢梁)+钢筋混凝土核心筒混合结构,存在扭转不规则、刚度突变、有加强层和通高层等不规则项。为提高结构刚度,在避难层设置了2道伸臂桁架加强层。采用YJK、MIDAS Building软件进行了小震弹性对比分析,采用YJK进行了小震弹性时程分析。根据设定的抗震性能目标,对主体结构主要部位和关键构件进行了性能化设计;采用SAUSAGE软件进行了罕遇地震作用下的动力弹塑性时程分析;采用ANSYS软件对伸臂桁架关键节点进行有限元分析。结果表明:各项指标均符合设计要求,结构及构件均达到预设性能目标,结构体系合理,安全可靠。本工程部分墙体为钢板混凝土剪力墙,设计中应注重钢板混凝土剪力墙的构造措施,施工中应采取措施控制钢板变形。

苏州某大型复杂商业连体结构设计

苏州某大型商业综合体项目位于7度抗震设防烈度区,为体型重叠建筑。通过5道防震缝将建筑整体划分为购物中心A区、购物中心B区、停车楼、商业街A区、商业街B区五个独立结构单元。购物中心A区为复杂连体高层建筑,1~5层采用框架-剪力墙结构,两个单体在3~5层中区由钢桁架相连,顶部(6层)钢桁架结构与两个单体通过成品球铰支座连接,形成强连体结构。充分考虑了周期比、位移比双指标平衡后对购物中心A区剪力墙布置进行了优化;屋顶钢桁架结构支座采用变刚度设计,局部设置滑动支座解决恒载下杆件应力比较高的问题。通过性能化设计,该复杂结构连体部位可以满足中震弹性、大震不屈服的性能目标要求。性能化设计及专项分析表明,影院钢结构具有良好的抗震性能、楼盖舒适度及防倒塌性能。

浅析不同环保认证标签的水性内墙涂料中挥发性有机化合物含量

随着人们环保意识的增强,室内空气质量愈发受到广泛关注。目前针对室内装饰涂料引发的空气污染问题,研究较多的为挥发性有机化合物(VOC),事实上一些半挥发性有机化合物(SVOC)同样会引发室内空气污染,并对人体健康造成危害。由于普通消费者缺乏相关专业知识,因此在选购水性内墙涂料时往往仅根据涂料包装上的环保认证标签进行识别。本研究抽选了52个不同渠道、厂商、等级的具有代表性的水性内墙涂料样本,对其VOC和SVOC含量水平进行了实测分析,结果显示,具有不同环保认证标签的涂料产品在VOC和SVOC含量方面有很大的差异。

HL-3装置碳基第一壁系统地震响应谱分析

针对HL-3碳基第一壁系统进行了地震工况分析。建立了包含装置主体系统的整体模型,通过模态分析获得第一壁系统的基本动力学特征。采用响应谱法对第一壁分析模型进行地震分析,计算出第一壁结构在工况下的变形和应力分布。分析结果表明,碳基第一壁满足结构设计安全性要求。

HL-3装置碳基第一壁螺栓预紧力分析

通过对HL-3装置第一壁基本模块进行高温下的螺栓预紧力分析,获得第一壁结构的应力分布及螺栓预紧力的变化情况,为碳基第一壁结构的现场安装提供数据支撑。

从BIPV(光伏建筑一体化)到BIPVES(光伏储能建筑一体化)

[目的]随着光伏、储能、新型建材及装配式建筑产业的发展,将光伏组件与屋面、墙体、遮阳等构件进行一体化设计与制造的光伏建筑一体化(Building Integrated Photovoltaic,BIPV)技术开始延伸为光伏储能建筑一体化(Building Integrated Photovoltaic and Energy Storge,BIPVES)技术。[方法]文章提出世界首个可充电水泥电池,将建筑墙体与光伏发电装置、储放电装置相融合;对设备和材料进行跨界创新,在玻璃表面打印高清晰度、高透光率花纹图案,制造高效光伏建材;研发预制式储能墙体,与各类钢结构装配式建筑体系进行结合,实现订制式生产、装配式施工,形成建筑构件与光伏、储能一体化的变革趋势。[结果]水泥基电池实现了建筑墙体具有光伏发电、储电以及供电等多种功能;新一代光伏建材可节省建筑外立面装饰材料的成本,降低建筑物碳排放;光伏和储能等可再生能源技术在建筑中的一体化集成,可取得最大化收益。[结论]新型光伏建材技术和水泥电池等新型储能技术具有发展前景,将可充电电池构件、光伏外墙板与装配式建筑墙体及预埋件进行组合集成并推广应用具有可行性。