抗土洞塌陷的低填方加筋路基荷载传递机制及设计方法

低填方加筋路基对地基承载力要求较低,同时利用水平加筋法跨越尺寸较小的土洞能有效预防路堤出现突发式局部沉陷,提高路堤抗工后沉降和失稳的安全系数,正被逐步应用于岩溶土洞地区道路工程;但其作用机理复杂,现存设计方法大都偏于保守,考虑抗土洞塌陷的低填方加筋路基荷载传递机制的设计方法亟待提出。通过揭示受土洞塌陷影响的低填方加筋路基荷载传递机制,推导了考虑路基差异沉降引起土体应力偏转的竖向应力计算方法,假定塌陷区上方加筋体作用抛物线荷载,从而明晰了加筋体应力-应变状态;应对岩溶区不同形态的土洞塌陷,同时考虑设计需要满足的正常使用极限状态与承载能力极限状态,提出了抗土洞塌陷的低填方加筋路基加筋体及路堤填方高度设计方法,通过与现有设计方法的对比进行了合理性及准确性验证,可为空洞上方低填方加筋路基设计提供参考。     

压型钢板-混凝土组合楼板粘结试验研究

文章对压型钢板与混凝土的交界面上是否涂有四环胶水泥砂浆的两种组合楼板进行了试验。经分析比较得出这种新型粘结剂作为抗剪措施的可行性。     

Seismic effects on reinforcement load and lateral deformation of geosynthetic-reinforced soil walls

Current design methods for the internal stability of geosynthetic-reinforced soil (GRS) walls postulate seismic forces as inertial forces, leading to pseudo-static analyses based on active earth pressure theory, which yields unconservative reinforcement loads required for seismic stability. Most seismic analyses are limited to the determination of maximum reinforcement strength. This study aimed to calculate the distribution of the reinforcement load and connection strength required for each layer of the seismic GRS wall. Using the top-down procedure involves all of the possible failure surfaces for the seismic analyses of the GRS wall and then obtains the reinforcement load distribution for the limit state. The distributions are used to determine the required connection strength and to approximately assess the facing lateral deformation. For sufficient pullout resistance to be provided by each reinforcement, the maximum required tensile resistance is identical to the results based on the Mononobe–Okabe method. However, short reinforcement results in greater tensile resistances in the mid and lower layers as evinced by compound failure frequently occurring in GRS walls during an earthquake. Parametric studies involving backfill friction angle, reinforcement length, vertical seismic acceleration, and secondary reinforcement are conducted to investigate seismic impacts on the stability and lateral deformation of GRS walls.     

On the design of geosynthetic-reinforced walls

An important design aspect of a geosynthetic-reinforced wall is specifying the reinforcement length. A simple limit equilibrium analysis, which considers two possible extreme inclinations of a reinforcement's resistance force, shows that predictions based on the K_a-analysis may not be safe. Although rules of thumb to determine embedment length are sometimes superimposed on the K_a-analysis prediction in design, it is demonstrated that such ‘rules’ may not always be safe. Design charts for granular backfill illustrate the effects of the reinforcement's force inclination showing quantitatively that the horizontal inclination required slightly larger tensile resistance force, while underestimating the embedment length.     

Variability of waste copper slag concrete and its effect on the seismic safety of reinforced concrete building: A case study

Proven research output on the behavior of structures made of waste copper slag concrete can improve its utilization in the construction industry and thereby help to develop a sustainable built environment. Although numerous studies on waste copper slag concrete can be found in the published literature, no research has focused on the structural application of this type of concrete. In particular, the variability in the strength properties of waste copper slag concrete, which is required for various structural applications, such as limit state design formulation, reliability-based structural analysis, etc., has so far not attracted the attention of researchers. This paper quantifies the uncertainty associated with the compressive-, flexural- and split tensile strength of hardened concrete with different dosages of waste copper slag as fine aggregate. Best-fit probability distribution models are proposed based on statistical analyses of strength data generated from laboratory experiments. In addition, the paper presents a reliability-based seismic risk assessment of a typical waste copper slag incorporated reinforced concrete framed building, considering the proposed distribution model. The results show that waste copper slag can be safely used for seismic resistant structures as it results in an identical probability of failure and dispersion in the drift demand when compared with a conventional concrete building made of natural sand.     

Failure of web/flange welds during cold bending of tee sections

Cold forming of sections is an integral part of shipbuilding; however no detailed analysis has been carried out regarding the chances of failure of web/flange welds during the cold bending process. In this paper a theoretical analysis has been presented for predicting the possibility of such weld failures.For assessing the fillet weld strength, an index called the Fillet Weld Loading Factor (FWLF) has been introduced. Depending on the yield stress of the parent metal and the tensile strength of the weld deposit, limiting values of the FWLF have been assigned. By comparing the FWLF of the tee sections with that of the limiting ones it can be predicted whether the filler weld joining the flange to the web will be able to sustain the load during cold bending.The results of this investigation have been presented in the form of curves and simple formulae which can be directly used for predicting whether successful cold forming of a fabricated tee section to the required shape can be carried out.     

Effects of PET fiber arrangement and dimensions on mechanical properties of concrete

Concrete has low tensile strength and crack resistance. Its weaknesses could be enhanced with the addition of fiber. Polyethylene terephthalate (PET) fibers are generally used in concrete as discrete reinforcement in substitution of steel fiber. Fibers obtained by hand cutting of PET bottles are in the form of straight slit sheets, which impart weaker bonding in concrete matrix. The bonding of the fibers however may be improved by using other geometries such as flattened-end sheet pattern. So far, there are no guidelines for defining the geometry and dimensions of PET fibers. Therefore, this paper focuses on the use of fibers with different geometries and dimensions and investigates their effects on the mechanical properties of concrete. Test results show that geometry of fibers has a small effect on the workability of concrete. The use of smaller dimensions of fiber improves the workability. Enhancement in the strength and energy dissipation capacity of fiber concretes was observed from the use of flattened-end fibers of smaller dimensions. Furthermore, a higher ultrasonic pulse velocity value was observed for concrete made from smaller fibers as compared to fibers of larger dimensions.     

有机硅改性醋苯丙防水乳液的制备及性能研究

通过种子乳液聚合法制备了有机硅交联改性醋酸乙烯酯-苯乙烯-丙烯酸丁酯三元共聚核壳防水乳液。通过对乳液的透射电镜、涂膜的红外光谱分析,发现有机硅被成功地引入醋苯丙核壳乳液,起到室温自交联的作用,并且有机硅交联剂的加入可以有效抑制乳胶粒的相反转。粒径分析、涂膜吸水率分析以及涂膜力学性能的分析表明,随着有机硅交联剂用量的增加,乳胶粒的粒径减小、分布变窄,涂膜的吸水率降低、拉伸强度增大。所制得的共聚物乳液在防水性能和力学性能上优于传统苯丙乳液,具有更高的性价比。     

Prediction of fire resistance of concrete filled tubular steel columns using neural networks

A functional relationship between the fire resistance of a concrete filled steel column and the parameters which cause the fire resistance is represented using an artificial neural network. Experimental data obtained from previous laboratory fire tests are used for training the neural network model. The model predicted values are compared with actual test results. The results indicate that the model can predict the fire resistance with adequate accuracy required for practical design purpose. The developed neutral network can be used to predict the fire resistance of similar columns under fire by observing various factors influencing the resistance such as: (a) structural factors, (b) material factors, and (c) loading conditions. The structural engineer is required to provide the magnitude of these influencing factors as inputs to the neural network and the network will predict the fire resistance, based on the combined effect of these factors. This system can be used by structural engineers to predict the resistance of fire in similar concrete filled steel columns without conducting costly fire tests, by using the known parameters such as column dimensions, column height, and loading conditions.     

浅谈铝塑复合板幕墙

铝塑复合板的重量较轻、刚性适当,减震隔音和装饰效果较好;表面可以进行二次加工,如防腐、轧花、涂装、印刷等,加工后可与铝单板媲美,但却比铝单板造价低很多。铝塑复合板出厂前一般都要进行耐腐蚀、耐候、耐撞、抗折、抗压等加工处理,以保证使用过程中的安全性和可靠性,因此铝塑复合板可应用于高层建筑的外墙装饰。     

超大承载力端板连接节点试验研究

在大跨或重载钢结构中,当梁柱之间需要采用螺栓连接时,如果普通构造的端板连接节点和大承载力端板连接节点不能满足承载力要求,则需要采用受拉区布置12颗或16颗螺栓的超大承载力端板连接节点。为研究该类型节点受力性能,进行4个超大承载力端板连接节点足尺试件的单调加载试验,得到各节点试件的弯矩-转角曲线,分析不同螺栓直径、端板厚度和螺栓布置形式下各节点的抗弯承载力、转动刚度和受拉区螺栓拉应变增量分布的特点。结果表明,在试验试件构造条件下超大承载力端板连接节点的弯曲失效模式为端板屈服后螺栓失效,端板厚度对节点承载力影响明显;各螺栓的拉应变增量分布不均匀,角部螺栓对节点抗弯承载力影响较小,建议在设计中移除或仅按抗剪螺栓考虑;建议节点域屈服承载力仍按照现行规范计算,该类节点的等效受拉螺栓数量取为7。     

Development and mechanical properties of HDPE/PA6 blends: Polymer-blend geocells

Geocells are three-dimensional expandable panels composed of polymers such as polyolefin polymers. Currently, geocells are being extensively used in various geotechnical engineering applications; however, its applications are limited because of the sizeable long-term deformation under constant loading and poor tensile strength. Owing to the rapid growth rate of geocells, it has become necessary to develop a polymer material with excellent creep resistance and tensile strength. To this end, a polymer-blend geocell (PBG) is developed in this study using a twin-screw extruder with high-density polyethylene (HDPE), polyamide 6, and compatibilizer. The polymer formula is determined by the tear fracture surface and scanning electron microscopy. The tensile properties of the blends with different formulas are studied in terms of yield strength, tensile strength, and elongation at break. Finally, three types of PBG and HDPE geocells are selected to study the long-term creep behavior using accelerated creep tests. The analysis results of raw creep data, master creep curve, and isochronous creep curves indicated that the PBG had a better creep resistance than the HDPE geocells.     

Analysis of installation damage tests for LRFD calibration of reinforced soil structures

North American design codes are now committed to the development of load and resistance factor design (LRFD) for reinforced soil structures including internal stability limit states. Reliability-based analysis is required to carry out these calibrations. A framework for LRFD calibration has been proposed by the writers that requires bias statistics for load and resistance terms for each limit state function. In this paper the formulation of the limit state for reinforcement tensile rupture is developed and the component strength-reduction bias statistics identified. The paper describes how to compute bias statistics from project-specific installation damage trials for use in reliability-based design for the reinforcement rupture limit state or using data from multiple sources for LRFD calibration. A database of results from field installation damage trials on 103 different geosynthetic products was collected from 20 different sources. A total of 799 and 2248 in-air tensile test results were reviewed for undamaged and damaged geosynthetic specimens, respectively. This database is used to compute installation damage bias statistics for six different categories of geosynthetic and four categories of backfill soils classified according to the D₅₀ particle size. A practical outcome is that for analysis purposes, bias statistics can be grouped into two ranges for each geosynthetic type based on D₅₀ of the soil greater than or less than 19 mm. The paper shows how bias statistics together with load and resistance factors for the geosynthetic rupture limit state function recommended by AASHTO (2010) can be used to calculate probability of failure using Monte Carlo simulation and demonstrates the sensitivity of probability of failure to magnitude of installation damage bias statistics. The installation damage data is valuable for future LRFD calibration to select resistance factors for use in design codes for the geosynthetic rupture limit state in reinforced soil structures.     

纤维加筋土的动力特性试验研究

研究用聚丙烯纤维加筋粘性土抵抗静动荷载作用下土体发生张拉裂缝的功能。试验研究结果表明，纤维加筋土的静动力抗张拉、抗断裂性质，诸如极限拉应力、极限技应变、动强度、动模量、临界断裂韧度等，与素土相比都有很大的提高。由此说明纤维加筋粘性土是一种比较理想的土坝防渗抗震填料。     

设防地震作用下受拉剪力墙设计方法

针对设防地震作用下受拉剪力墙的设计方法，结合JGJ 3—2010《高层建筑混凝土结构技术规程》指出了我国目前广泛采用等效弹性方法设计存在的问题，介绍了弹塑性时程分析法的设计流程、设计软件和地震波选取以及墙铰模型的开裂后刚度取值。对于设防地震下弹塑性时程分析法，弹塑性模型的初始配筋采用多遇地震作用下的配筋结果，剪力墙单元可以采用墙铰单元、纤维截面壳单元、S4R壳单元等模拟，设计地震动可采用拟合设计反应谱的人工波，并控制设防地震作用下剪力墙受拉不屈服来调整受拉配筋设计。此外，设防地震作用下受拉剪力墙是否设置型钢应根据其所受剪力大小确定，还应复核罕遇地震作用下受弯屈服剪力墙的边缘拉应变。采用工程实例验证了上述方法的可行性，且偏于安全考虑，建议采用考虑开裂后抗拉刚度退化至15%初始抗拉刚度的墙铰模型进行受拉剪力墙的抗震设计。     

含中心裂纹薄壁型钢的又一组应力强度因子解

首先根据无限大中心裂纹板在Ⅰ型荷载作用下应力分布的全场解析解,构建薄壁杆件在均匀拉伸时沿裂纹所在截面的正应力的分布模型;然后利用平衡条件确定无量纲应力强度因子Y(ξ)获得含中心裂纹拉伸薄壁型钢的又一组无量纲应力强度因子Y(ξ)的近似解析解。与现有的数值结果比较表明,该方法不仅简单实用,而且结果可靠。文中给出的几种常见薄壁杆件含Ⅰ型中心裂纹时的无量纲应力强度因子的近似简单解析表达式,既适用于焊接组合薄壁杆件,也适用于冷弯薄壁杆件。     

碳纤维布加固混凝土梁的有限元分析

通过建立复合材料的有限元模型，对碳纤维布加固钢筋混凝土（RC）梁进行了抗弯有限元仿真与计算，表明了采用有限元方法计算由多种材料组成的非线性复合材料是一种有效的方法，碳纤维布可以有效地抑制梁受拉区混凝土应力的发展，提高混凝土梁的承载刚度。     

张力补偿计算法在预应力空间网格结构张拉施工中的应用

提出的张力补偿计算法能计算预应力空间网格结构中索的施工张力控制值 ,同时还能计算结构在张拉施工任一阶段时的杆件内力与节点变位。当采用简单的分组分批张拉施工方法时 ,每批索只要一次张拉到计算所得的施工张力控制值即可 ,当最后一批索张拉完毕 ,所有索的实际内力将达到它们各自的张力设计值。这样 ,目前通常所采用的分阶段分组分批张拉 ,逐阶段多次张力调整的施工方法将得以改善 ,张拉工作效率将大幅提高 ,施工成本大幅降低。     

Anwendung der Fließgelenktheorie auf Baugruben

Application of plastic design to retaining walls. Design approaches that take the occurrence of plastic hinges into account are generally known as a smart way to determine the ultimate load of statically indeterminate systems. The ultimate state is reached, when the hole system or several parts of it become kinematical. Thus this kind of design approach takes advantage of the plastic reserve of the cross-section and of the static system. The application of plastic design to retaining walls leads to a few interesting questions. There are several failure mechanisms that arise from the following failure types and combinations of them: plasticizing of the sheet pile wall – plasticizing of the anchorage or support – failure of the area of soil resistance. Further on it's not clear how the plasticizing of the system shall be induced, because unlike in structural analysis the soil is not only a load in the form of the earth pressure acting on the retaining wall but also a structural element. Thus it's the often described characteristic of geotechnics that has to be taken into account. There are six approaches introduced, of which two are further examined by the finite element method. The first approach consists of the reduction of the plastic bending moment resistance of the sheet pile until plastic hinges occur. The idea of the second approach is to increase the water pressure incremental. The calculations show, that the earth pressure is redistributing with the increasing displacement of the sheet pile wall in dimensions that are generally greater than covered by the recommendations of EAB (2006) and EAU (2004). This could lead to an underestimation of the supporting force. The EAB (2006) allows the plastic design of sheet pile walls if certain conditions are considered. The EAU (2004) does not include such recommendations yet.     

不对称发育深卸荷地质力学模式

揭示不对称发育深卸荷空间分布规律、变形破坏类型及地质力学模式。以白鹤滩水电站深卸荷为典型实例,基于现场调查、精细描述,分析深卸荷空间分布特征、变形破坏特征、变形破坏类型,结合河谷演化历史,揭示深卸荷岩体能量演化过程,从能量存储、释放角度建立不对称发育深卸荷地质力学模式。研究表明：深卸荷分布于距边坡表面水平、垂向深度均为50～150 m空间范围,均处于历次谷底高应力集中影响范围;深卸荷变形破坏类型可划分为3类：继承性拉张型、新生性张剪型与错动扩展型;偏移-下切河谷演化使左岸岩体经历多次循环加卸载过程,能量演化过程具有区别于右岸的三高特点：储存量高,耗散量高,强度劣化程度高,这是深卸荷不对称分布的根本原因;深卸荷地质力学模式可概括为先期沿结构面与岩桥拉裂,以及后期沿缓倾角错动带产生的滑移-拉裂;深卸荷形成过程可概括为3阶段：损伤加剧与强度劣化阶段、局部拉应力形成阶段、错动扩张阶段。