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.

Post-fire cyclic behavior of reinforced concrete shear walls

The effects of fire exposure,reinforcement ratio and the presence of axial load under fire on the seismic behavior of reinforced concrete(RC) shear walls were investigated.Five RC shear walls were tested under low cyclic loading.Prior to the cyclic test,three specimens were exposed to fire and two of them were also subjected to a constant axial load.Test results indicate that the ultimate load of the specimen with lower reinforcement ratio is reduced by 15.8%after exposure to elevated temperatures.While the reductions in the energy dissipation and initial stiffness are 59.2%and 51.8%,respectively,which are much higher than those in the ultimate load.However,this deterioration can be slowed down by properly increasing reinforcement due to the strength and stiffness recovery of steel bars after cooling.In addition,the combined action of elevated temperatures and axial load results in more energy dissipation than the action of fire exposure alone.

高海拔穿破碎带大断面排水巷支护设计与数值模拟

目的:巨龙铜矿穿破碎带大断面排水巷道原采用锚杆+锚索+钢拱架联合支护的方式进行支护,但支护效果较差,急需解决该问题。方法:为解决该实际问题,针对围岩破碎区域提出了管片+壁后注浆的支护方式。管片采用C50混凝土浇筑,内置HPB300和HPB400E型号钢筋。每段巷道由6段管片进行拼接支护,每段管片留设注浆孔。利用数值模拟分析了穿破碎围岩大断面巷道支护效果。结果:结果表明,管片+注浆支护后巷道围岩变形均为毫米级变形,管片+注浆支护结构内最大应力为30.46 MPa。管片+壁后注浆的支护方式在巨龙铜矿穿破碎带大断面排水巷得到了成功应用,支护效果较好。意义:研究结果为类似巷道施工提供了理论参考。

深部区域破碎围岩开拓巷道控制技术研究

某矿+320m运输联络巷在掘进期间会揭露破碎围岩段,在破碎围岩段受地应力、构造应力以及破碎围岩等不利因素影响,导致运输联络巷围岩变形量整体较大、围岩支护难度高。结合+320m运输联络巷现场条件并基于让压支护原则,提出间隔使用锚网喷+锚索、钢架棚、壁后注浆支护方式,其中钢架棚支护滞后锚网喷+锚索支护7d、壁后注浆支护滞后钢架棚支护20d,通过允许围岩部分变形达到释放围岩应力、减少围岩控制难度以及提高围岩控制效果目的。现场应用后,+320m运输联络巷在破碎围岩段期间围岩变形均在允许范围内且变形量整体较小,其中顶底板、巷帮分别为57mm、66mm,表明现场采用的围岩控制技术实现了深部区域破碎围岩巷道变形有效控制,并为后续矿井其他类似条件巷道围岩控制工作开展提供了经验借鉴。

深中通道西人工岛现浇隧道后浇筑墙体控裂技术研究及应用

深中通道西人工岛处于外海环境,岛上现浇隧道结构尺寸大,断面宽度及墙身高度呈渐变形式。施工过程中,为确保隧道主线临时通行需求,对敞开段隧道结构墙体进行部分预留,待交通转换后进行浇筑封闭。因其龄期间隔时间长,新老混凝土间易因收缩不同步造成结构开裂。为降低混凝土开裂风险,确保海工混凝土结构耐久性,对外海现浇隧道后浇筑墙体开展系统性控裂研究,通过采用有限元仿真模拟分析、研发智能温控系统、辅以温控硬件措施投入等综合控裂措施,实现后浇筑墙体控裂目标,有效避免了墙体有害裂缝的发生。

建筑外墙干挂石材幕墙施工工艺研究

建筑外墙干挂石材幕墙可以满足复杂的施工要求、规避空鼓等质量风险,具有优良的耐久性。文章阐述了建筑外墙干挂石材幕墙的稳定性要求,介绍了干挂石材幕墙施工技术要点,并通过工程实例分析了该施工技术的控制要点,旨在为相关工作人员提供参考和借鉴。

装配式后浇竖缝剪力墙结构计算及有限元分析

针对装配式后浇竖缝剪力墙的结构性能表现,文章制备了四组剪力墙试件,对L型和凸型竖缝形式进行了正交试验,探究了不同轴压比(0.2和0.3)下的性能,计算得到墙体与地梁、加载梁连接的强度,通过施加荷载作用,模拟弹性至弹塑性状态的转变,分别对剪力墙的正截面和斜截面的刚度和承载力进行计算分析,采用ANSYS有限元软件,模拟分析了荷载作用下的开裂行为和峰值荷载响应,为装配式后浇竖缝剪力墙的工程实践提供了技术支撑。

房建施工中的地下室后浇带防水技术研究

以某房建工程地下室外墙后浇带防水施工为案例,在其项目概况及技术难点分析的基础上,对施工流程中多个环节进行研究,并对地下室后浇带防水性能进行测试。试验结果表明,随着水压试验的进行,在24 d时的渗水量显著低于临界值2.0 mm。此次地下室外墙后浇带防水施工技术措施有效。

Influence of fiber posts on the fracture resistance of endodontically treated premolars with different dental defects

This study aimed to evaluate the influence of quartz fiber post placement on the fracture resistance of endodontically treated premolars with different dental defects under dynamic loading.Fifty extracted single-rooted mandibular premolars were randomized into five groups.Each group was prepared according to numbers of residual walls ranged from 0 to 4.Then each group was divided into two subgroups with one restored with quartz fiber posts and the other without posts.In no-post groups,gutta percha point 2 mm below cemento-enamel junction was removed.Composite resin was adapted to the well and used to shape the core directly.Each tooth was restored with a complete metal crown.Dynamic loading was carried out in a masticatory simulator with a nominal load of 50 N at 2 Hz for 300 000 loading cycles.Then a quasi-statically load was applied in a universal testing machine 306 to the long axis with a crosshead speed of 1 mm？min21until fracture.Data were analyzed with one-way analysis of variance and pairwise comparison（P,0.05）.No specimens failed during dynamic loading.The fracture resistance enhanced with the increase of numbers of coronal walls and the differences were significant（P,0.05）.Placement of fiber posts had a significant effect when fewer than two walls remained（P,0.05）,but it had no significant influence in groups with two,three or four walls（P.0.05）.Fiber post did not change failure mode,and the fracture pattern was mainly favorable.More dentin walls need to be retained in clinic.When no less than two walls remained,a fiber post is not always necessary.

Effect of fiber angle on LYP steel shear walls behavior

Steel shear wall(SSW) was properly determined using numerical and experimental approaches.The properties of SSW and LYP(low yield point) steel shear wall(LSSW) were measured.It is revealed that LSSW exhibits higher properties compared to SSW in both elastic and inelastic zones.It is also concluded that the addition of CFRP(carbon fiber reinforced polymers) enhances the seismic parameters of LSSW(stiffness,energy absorption,shear capacity,over strength values).Also,stress values applied to boundary frames are lower due to post buckling forces.The effect of fiber angle was also studied and presented as a mathematical equation.

Shake-table testing of a self-centering precast reinforced concrete frame with shear walls

The seismic performance of a self-centering precast reinforced concrete （RC） frame with shear walls was investigated in this paper. The lateral force resistance was provided by self-centering precast RC shear walls （SPCW）, which utilize a combination ofunbonded prestressed post-tensioned （PT） tendons and mild steel reinforcing bars for flexural resistance across base joints. The structures concentrated deformations at the bottom joints and the unbonded PT tendons provided the self-centering restoring force. A 1/3-scale model of a five-story self-centering RC frame with shear walls was designed and tested on a shake-table under a series of bi-directional earthquake excitations with increasing intensity. The acceleration response, roof displacement, inter-story drifts, residual drifts, shear force ratios, hysteresis curves, and local behaviour of the test specimen were analysed and evaluated. The results demonstrated that seismic performance of the test specimen was satisfactory in the plane of the shear wall; however, the structure sustained inter-story drift levels up to 2.45%. Negligible residual drifts were recorded after all applied earthquake excitations. Based on the shake-table test results, it is feasible to apply and popularize a self-centering precast RC frame with shear walls as a structural system in seismic regions.

A Post-Mastectomy Radiation Therapy Dose Distribution Study

Purpose: For post-mastectomy radiation therapy, skin dose must be accurately estimated to assess skin reactions, such as: erythema, desquamation, and necrosis. Even with advanced algorithms, planning systems do not always provide accurate dosimetry for target volumes distal to skin. Methods and Materials: In this study, a female anthropomorphic (ART) phantom and the newest generation of optically stimulated luminescence dosimeters (OSLD) (nanoDots, Landauer Inc.) were deployed to measure chest wall dose distribution. Since actual dose to patients’ lung and heart cannot be measured using in-vivo dosimetry, film was also used to verify the dose distribution to the left lung and heart. The treatment planning was performed using tolerance limits of 95% to 107% of prescription dose. The ART phantom was irradiated according to 3 three-dimensional (3D) conformal radiotherapy plans for 200 cGy dose per fraction using 6 MV medial and lateral tangential photon beams. The dose distribution provided by treatment planning was studied using nanoDots and film. Results: Results show that the largest surface dose difference between nanoDots measurement and prescribed dose for medial and lateral tangential beams, are 3.8% and 9.8%, respectively. This difference may be due to higher effective point of measurement and angular dependence of the nanoDots. The maximum differences in measured dose compared with prescribed dose, using film for heart and the left lung, were 6.2% and 7.5% respectively. Conclusions: Both nanoDots and film provided reasonable estimation of dose distribution in post-mastectomy radiation therapy.

Seismic retrofi tting of RC columns with RC jackets and wing walls with different structural details

An original reinforced concrete(RC) column and four strengthened specimens, two with RC jackets and two with wing walls, were tested in this study. The original column specimen was designed to comply with older(pre-1999) design standards so that the usual detailing defi ciencies in existing school buildings in Taiwan could be simulated. Two different structural details were chosen to fabricate the full-scale specimens for each retrofi tting technique. The study confi rmed that either RC jacketing or the installation of wing walls with two different structural details can effectively improve the stiffness and strength of an existing column. RC jacketing shows a better improvement in energy dissipation and ductility when compared to the columns with wing walls installed. This is because the two RC jacketed columns experienced a fl exural failure, while a shear failure was found in the two columns with the wing walls installed, and thus led to a drastic decrease of the maximum lateral strengths and ductility. Since many factors may affect the installation of a post-installed anchor, it is better to use standard hooks to replace post-installed anchors in some specifi c points when using RC jacketing or installing wing walls.

A Rare Interstitial Type of Post Appendectomy Incisional Hernia

Intraparietal Hernias are hernias occurring in the anterior abdominal wall at different anatomical planes. An interparietal hernia has a hernial sac that passes between the layers of the anterior abdominal wall. Appendectomy is a very common surgical procedure, and post appendectomy incisional hernia is a very rare complication. Here we present a case of a 24-year-old male with swelling in the right hypochondrium and lumbar region with an open appendectomy scar. He was diagnosed to have an interparietal hernia in the anterior abdominal wall. After obtaining consent patient was taken up for surgery. At surgery, the patient was found to have a defect in the transverse abdominis muscle with a medial leaf far from the incision site. Open repair of the defect along with double breasting of external oblique done. Interparietal hernias are rare in post appendectomy scar and this case is of significance since it Highlights a rare interstitial type incisional hernia, as a complication of post appendectomy scar, and not many cases reports are mentioned in literature.

变开缝长自复位剪力墙截面设计及抗震性能

为研究不同开缝长度下自复位剪力墙的抗震性能,对自复位剪力墙截面进行受力分析,量化不同开缝长度下墙体理论承载力.基于四水准中第三水准下的性能目标,对自复位剪力墙进行截面设计,并与已有试验结果及不同开缝长自复位剪力墙的静力弹塑性结果进行比较验证.结果表明:理论推导的承载力表达式与已有试验及有限元结果均吻合良好;随着开缝长度增加,墙体自复位能力增强,耗能能力减弱;开缝长度系数为0.2~0.3能满足残余位移角限值,同时保持较好的耗能能力.

作为媒介的“驿壁”:精神交往与地理想象

作为一种“地方性媒介”或“地理媒介”,驿壁是借助中国古代强大的驿传系统而衍生的独特媒介形式,是公共性、地方性的意见表达场所。驿壁传播是独具中国文化特色的传播现象,唐诗宋词依托驿壁而流传四方。驿壁也是古代文人精神交往的媒介,他们在这里实现跨越时空的对话与交流。在驿壁之上出现了“媒介—人—地理”的互动与重合,驿壁让成千上万的陌生人在不同时空完成一种共同阅读的“仪式”,形成新的共识感,构建起一块充满文化元素和心理期待的想象空间。

特高压直流穿墙套管绝缘支柱在高地震烈度下的机械应力仿真

特高压直流穿墙套管由于其结构细长,在地震中极易受损,然而其内部支柱绝缘子的受力情况未见报道。此外,新型陶瓷材料作为高机械强度的绝缘材料,具备替代环氧材料的应用潜力。为此,该文首先设计了3种基本形状的陶瓷绝缘支柱。其次,通过有限元法计算了9级地震烈度下纯SF_(6)气体绝缘直流穿墙套管中绝缘支柱的应力分布,基于静力法分析了绝缘支柱的受力情况。最后,对比了新型陶瓷支柱与现有环氧支柱的裕度。结果表明:陶瓷支柱中凹线形结构的应力最小,分布最均匀。应力主要在顶部和底部金属嵌件附近的圆弧位置处集中,分别由竖直方向和水平方向的载荷引起,最大应力为105.1 MPa。由于新型陶瓷材料具备了优异的机械强度,地震工况下陶瓷支柱的裕度显著大于环氧支柱,为2.85。因此,相比于环氧支柱,陶瓷支柱可以提供更好的机械支撑,可以为高烈度地震区中SF_(6)气体绝缘设备内部的绝缘支柱的选择和研制提供参考。

船闸闸室墙开裂机理及防裂方法研究

船闸闸室墙在中间浮式系船柱附近的混凝土易产生裂缝,影响船闸工程整体稳定性。通过对闸室混凝土的温度应力展开仿真分析和实际船闸工程混凝土裂缝调研,发现整浇闸墙中间系船柱附近和上下游侧墙中间下部混凝土在施工期易产生竖向裂缝。因此,考虑闸墙中部采用后浇带的方式,并且比较了后浇带不同施工方案,发现采用后浇带能降低闸室上下游侧墙混凝土的最大主应力,防止裂缝的产生;但仅采用后浇带的方式,会导致中间浮式系船柱附近的后浇混凝土开裂风险增加;因此,可通过改变后浇带浇筑顺序和采用微膨胀混凝土的方式,提高中间浮式系船柱附近混凝土的抗裂能力。

修复后两边连接钢板剪力墙抗震性能研究

使用带型钢加劲肋的内嵌钢板对震后受损的两边连接钢板剪力墙结构进行修复可以为两边连接钢板剪力墙结构的震后修复提供依据。通过有限元软件对修复后单跨2层钢板剪力墙结构进行了抗震性能研究,主要探讨了修复结构与未修复结构的面外变形、承载力、刚度和能量耗散量的差异。结果表明:用带型钢加劲肋的内嵌钢板修复两边连接钢板剪力墙是可行的,修复后的结构在遭遇第2次拟静力荷载时,内嵌钢板的面外变形得到了约束,十字加劲修复和斜加劲修复结构承载力分别提升了12.17%和23.10%,累积耗能分别提升了45.93%和57.22%;相较而言,2种修复结构中十字加劲修复结构刚度与未修复结构首次加载时更接近。

沉降后浇带临时加固对毗邻高层建筑挡土墙稳定性影响的研究

为解决毗邻高层建筑的挡土墙加固问题,创新设计了一种低成本、便于施工的挡土墙加固方法,对与挡土墙相邻的车库筏板、楼板沉降后浇带进行加固。通过ANSYS有限元软件对沉降后浇带加固与未加固条件下的各种工况进行结构数值模拟分析,验证了该加固方法的可行性,研究了随着高层建筑层数的增加,挡土墙、筏板及车库楼板的变形及应力的变化规律。结果表明,对毗邻挡土墙的沉降后浇带采用该种简易的临时加固方法后,不影响沉降后浇带的两侧结构的沉降变形,同时也能满足结构稳定的要求,无需改变挡土墙结构形式或大幅增加挡土墙及筏板结构的配筋量,大大降低了工程成本。