Design and Preparation of High Elastic Modulus Self-compacting Concrete for Pre-stressed Mass Concrete Structures

Requirements of self-compacting concrete （SCC） applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash （FA） substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC （with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation （Vs.~0 mm： V10-16 ram： V16.20 mm= 30%： 30%：40%）） with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d.

Initial pre-stress finding procedure and structural performance research for Levy cable dome based on linear adjustment theory

The cable-strut structural system is statically and kinematically indeterminate. The initial pre-stress is a key factor for determining the shape and load carrying capacity. A new numerical algorithm is presented herein for the initial pre-stress finding procedure of complete cable-strut assembly. This method is based on the linear adjustment theory and does not take into account the material behavior. By using this method,the initial pre-stress of the multi self-stress modes can be found easily and the cal-culation process is simplified and efficient also. Finally,the initial pre-stress and structural performances of a particular Levy cable dome are analyzed comprehensively. The algorithm has proven to be efficient and correct,and the numerical results are valuable for practical design of Levy cable dome.

Initial Pre-stress Finding and Structural Behaviors Analysis of Cable Net Based on Linear Adjustment Theory

The tensile cable-strut structure is a self-equilibrate pre-stressed system.The initial pre-stress cal- culation is the fundamental structural analysis.A new numerical procedure was developed.The force density method is the cornerstone of analytical formula,and then introduced into linear adjustment theory;the least square least norm solution,the optimized initial pre-stress,is yielded.The initial pre-stress and structural performances of a particular single-layer saddle-shaped cable-net structure were analyzed with the developed method,which is proved to be efficient and correct.The modal analyses were performed with respect to various pre-stress levels.Finally,the structural performances were investigated comprehensively.

Pre-Stressed Rope Reinforced Anti-Sliding Pile

Pre-stressed rope reinforced anti-sliding pile is a composite anti-sliding structure. It is made up of pre-stressed rope and general anti-sliding pile. It can bring traditional anti-sliding pile＇s retaining performance into full play, and to treat with landslide fast and economically. The difference between them is that the pre-stressed rope will transfix the whole anti- sliding pile through a prearranged pipe in this structure. The working mechanics, the design method and economic benefit are studied. The results show that the pre-stressed rope reinforced anti-sliding pile can treat with the small and middle landslides or high slopes well and possess the notable advantage of technology and economic.

Determination Method on Initial Pretension of Cables in Steel Mega Frame and Prestressed Composite Bracing Structure

Determining initial pretension values of pre-stressed cables is one of the key problems for a steel mega frame and pre-stressed composite bracing structure.Through the mechanical analysis of the composite bracing under vertical loading,the critical factors deciding the initial pretention value were found.According to these factors,a rule for the initial pretension value was put forward.The determination equations were acquired based on the principle of force equilibrium at nodes.The numerical results indicate that the internal force disequilibrium in composite bracings resulted from symmetrical load can be eliminated only in a symmetrical way,so that initial pretention values are decided only by vertical loads.The influencing coefficient leveling method,taking into account interactions between story and story,is accurate and feasible.

Stress Analysis of New Type Pre-Stressed Anchor Bearing Plate Combining Stamping with Welding Forming and Its Anchorage Zone

An anchor bearing plate transfers the anchoring force from anchor plate to the concrete and the pre-stress is formed in the concrete structure. Currently, the main type of anchor bearing plate is cast iron. It is brittle during transportation and tension process. This paper presents a new type of anchor bearing plate combined stamping with welding forming. The structure of the new type anchor bearing plate is introduced. The stress states of the anchor bearing plate and anchorage zone under work are studied. Various specifications of anchor bearing plate are studied by ANSYS finite element analysis software following the AASHTO specification. The analysis results are compared with the results of the same type of OVM round-shaped anchor plate. The study results show that the new pre-stressed anchor plates combined stamping with welding forming are feasible and more sturdy which can meet the engineering demand.

Decreasing of Ship Structure Mass by Active Counteraction to Bending Moment

Pre-stressed structure and its application for civil engineering.Specificity of external loads of ships.Corresponded specificity of controllable pre-stressing.An example of pre-stressed structure and an decreasing estimation of its mass(about 10%of the full displacement).Possibility of wider application.

Structural Systems Composed of Concentric Hoops and Designed for Lightweight Domes of Large Spans

The paper presents a selected group of tension-strut structural systems designed for the construction of lightweight dome covers of large spans, which can be comparatively easy to assembly and have rises of which can be relatively small. This will allow significant decrease costs of erection and maintenance of objects covered by these roof structures. The proposed systems have been obtained from the results of suitable transformations of a chosen type of double-layer space frame and an appropriate arrangement of tetrahedron modules in the space of each of the newly designed type of the structural system. All these systems are built by means of concentric hoops having their own integral spatial stiffness obtained after an appropriate pre-stressing. Particular hoops can be mounted on the ground level and then one by one will be hoisted to the designed positions where they will be connected by means of special sets of the tension members. Due to these structural features, the assembly process of each system should be relatively simple, fast and not expensive. The whole tension-strut structure has to be connected to the compression perimeter ring and suitably pre-stressed. There are presented visualizations of the proposed systems prepared on the basis of the appropriate numerical models especially defined for each particular structure.

Evaluation of the static and dynamic structural performance of segmental pre-stressed concrete box girder bridge after repairing and strengthening

The objectives of this study are to explain the repairing and strengthening methods which are used to improve the structural performance of the bridge structure,to analyze the static and dynamic responses after strengthening,and to evaluate the performance of the bridge structure after repairing and strengthening.The methods of repairing and strengthening include reconstruction the deck of the bridge by casting 10 cm layer of concrete,strengthening the web and bottom floor of box girders of middle spans and side spans by sticking the steel plates,strengthening the whole bridge structure by using external pre-stressing tendons,and treatment the cracks.The results of theoretical analysis show that the values of tensile stress and vertical deflection are decreased and the compressive stress is increased after strengthening.There are not tensile stresses are appeared in the sections of the bridge structure.The modal analysis results show that the value of natural frequency is equal to 2.09 Hz which is more than the values before strengthening which is equal to 1.64 Hz,indicating that the stiffness of the bridge structure is improved and the strengthening process is effective to improve the cracks resistance and bearing capacity of the bridge structure.

新型非黏结柔性管接头的设计和分析研究

针对传统非黏结柔性管接头安装时,由外管套扣压变形而引起的接头排气孔变形问题,研制了新型非黏结柔性管接头,不仅避免了排气孔的变形,而且提高了排气孔处的结构强度。运用ABAQUS有限元分析软件对管接头的扣压过程进行仿真分析,通过对比分析结果,验证了新型管接头的结构设计合理有效,从而为非黏结柔性管接头设计提供技术参考。

闸墩预应力锚索新形式的探索

本文结合大推力预应力闸墩的现状 ,提出了布置一种新型的无粘结弯曲预应力锚索的想法 ,并对其进行了研究。文章以喜河电站表孔闸墩设计参数为基本数据 ,应用大型商用结构分析软件MSC/Nastran ,对闸墩在弧门推力作用下的应力状况进行了分析 ;同时 ,根据墩体及锚块内的最大主应力迹线进行无粘结弯曲锚索的布置 ,对以闸墩颈部 (闸墩与锚块连接处 )为主的受拉区混凝土进行预压。对于这种新型的无粘结弯曲锚索 ,利用MSC/Nastran软件 ,从对混凝土的预压效果方面将其与传统的有粘结直锚索的做法进行了对比、研究。结果表明 ,无粘结弯曲锚索的效果更好一些。

非粘结柔性软管失效模式与控制措施研究进展

非粘结柔性软管是海洋油气田与海上平台连接的重要纽带,随着世界海洋油气开发逐步迈入深水和超深水区,其应用也更加广泛。由于柔性软管结构形式和所受载荷复杂,加上海洋环境恶劣,使柔性软管的失效模式更加多样。为此,通过梳理非粘结柔性软管国内外相关研究成果,系统分析了其运行过程中存在的8种典型失效模式,并且有针对性地提出了失效控制措施。研究结果表明:①椭圆度、侵蚀、腐蚀会削弱骨架层抵抗压溃的能力,引起压溃失效;②内压过大、管内气体无法通过排气系统正常排出,会引起抗压铠装层和外包覆层的爆破失效;③过大的轴向拉力载荷同腐蚀、疲劳共同作用会引起抗拉铠装层钢带断裂,骨架层也可能因拉力载荷发生解锁失效;④抗压铠装层钢带缠绕角度过大、外包覆层破裂,轴向压缩载荷易造成抗拉铠装层产生压缩屈曲失效;⑤过度弯曲会导致外包覆层发生破裂、金属层发生屈曲;⑥过度扭转主要导致抗拉铠装层的屈曲或断裂;⑦柔性动态立管常受到风浪流循环载荷作用,易发生疲劳失效;⑧管内流体的渗透或外包覆层破裂导致的海水倒灌会引发柔性软管内部发生腐蚀。结论认为,所提出的降低柔性软管失效风险的预防和控制措施,可以为柔性软管设计和运行管理提供参考。

无黏结曲线锚索式预应力衬砌结构数值建模方法研究

无黏结曲线锚索式预应力衬砌结构是有压水工隧洞采用的一种新型衬砌型式,因结构体系受力机理较复杂,造成结构设计存在困难。为此,本文首先根据无黏结曲线锚索式预应力衬砌结构受力特征分析其数值建模的关键点;然后,提出相应的建模方法:通过设置接触关系实现模拟围岩对衬砌不同的约束作用,利用等效荷载和实体模型相叠加的方法模拟锚索变化的预应力状态,采用梯度荷载分段施加方式模拟预应力损失的非线性分布;最后,基于有限差分软件FLAC3D,以小浪底有压排沙洞为工程案例建模分析,选取衬砌变形、衬砌局部和整体预应力效果、受力最不利位置和衬砌薄弱环节潜在破坏特征等最能反映预应力衬砌结构力学特性的四个方面,将数值计算结果与监测数据对比分析,验证了本文建模方法的正确性。研究表明,本文提出的建模方法原理明确、建模快捷、结果可靠,对工程设计具有指导意义。

后张无粘结预应力混凝土空心板-柱结构的振动台试验研究

通过一个四层现浇无粘结预应力混凝土空心板柱结构的1/4比例模型的模拟地震振动台试验,对其在弹性和弹塑性阶段的动力特性以及该结构在El-Centro地震波不同峰值加速度作用下的地震反应进行了研究。试验结果表明,现浇无粘结预应力混凝土空心板柱结构具有一定的抗震能力,但其抗侧移性能较差;对地震反应起控制作用的是低阶振型;在地震加速度峰值较小的弹性阶段,模型的一阶振型呈剪切形变形,随着裂缝的开展和损伤的积累,结构阻尼比显著增加,一阶振型的剪切特征越来越不明显。基于试验结果,并考虑空心管孔洞对楼板刚度的影响,建立了改进的空间框架"板带-柱"结构分析模型,通过ANSYS软件对该结构进行的弹性阶段时程地震反应分析结果表明,计算结果与试验数据吻合较好。

小浪底排沙洞混凝土衬砌不同阶段预应力变化实测分析

小浪底排沙洞是我国首例采用双圈环绕无粘结预应力混凝土衬砌的水工隧洞 ,本文对这一新型结构形式和特点进行了简单介绍 ,并根据观测仪器所获得的大量实测数据 ,对不同阶段 (预应力施加、回填灌浆和过水运行 )混凝土衬砌和锚索中的有效预应力变化及混凝土徐变变化规律进行了探讨。实测资料表明 ,采用双圈环绕无粘结预应力技术 ,可实现理想的预应力效果和均匀的环向应力分布。围岩开挖的质量对环向预应力分布的均匀性具有重要影响 ;对预应力施加需时较长的实际结构 ,混凝土的徐变应变在观测仪器的总应变变化中占有不容忽视的比例 ,其大小与预压应力和持荷时间成线性关系 ,可按ε0 =α∑σiti 进行计算。过水运行阶段的实测数据表明 。

无粘结预应力混凝土平板的结构性能

现行行业标准无粘结预应力混凝土技术规程JGJ/92- 93 没有对平板结构不同布筋形式的性能作出详细规定;应用等代框架法计算出的无粘结预应力筋随意布置,忽略跨中板带预应力筋的不利作用;在应用有限元等较为精确的方法验算时部分区域不满足抗裂度设计要求.本文应用有限元法并通过模型试验分析布筋形式的影响。

《无粘结预应力混凝土结构技术规程》修订简介

介绍了《无粘结预应力混凝土结构技术规程》修订的主要内容 ,包括材料及锚具系统、结构设计和施工工艺的改进和提高、新增加体外预应力混凝土梁的设计与施工。

低周反复荷载下装配式框架连接的性能

通过三个框架节点在低周反复荷载下的试验,对无粘结预应力装配式混凝土框架连接的破坏形态、滞回曲线、变形恢复能力、位移延性、能量耗散等性能进行了研究。结果表明,无粘结预应力装配式混凝土框架连接具有良好的耗能能力,在延性和变形恢复能力上比现浇连接更优。

疲劳荷载作用下无粘结部分预应力混疑土梁的受力行为

本文根据六片无粘结部份预应力混凝土梁在静力与疲劳荷载作用下的试验结果,研究了试验荷载作用下各片梁的受力行为,分析了梁的应力、挠度与裂缝宽度的计算方法。该方法与试验结果较为一致,可供今后的设计与研究工作参考。

预应力自复位装配式混凝土框架节点抗震性能研究

提出一种新型装配式混凝土框架梁柱节点,其具有震后自主复位,低损伤等特点。为了解该新型节点的抗震性能,进行了新型装配式节点与现浇节点的拟静力对比试验研究,并与Open Sees有限元分析结果进行了对比。试验结果表明,新型装配式节点在梁端位移角达到1/18时,仍保持承载力不降低,结构构件基本完好,仅在梁端出现少量弯曲裂缝,且在荷载卸除后实现自主复位,裂缝基本闭合。有限元分析结果表明,该装配式节点的承载能力随初始预应力的增大而增大,同时也随耗能钢筋截面面积的增大而增大,耗能能力则主要来源于耗能钢筋。