公路桥梁加固采用体外预应力方法的探讨

桥梁结构在使用期间受环境因素的影响,材料将逐渐产生劣化,性能下降因车辆超载等因素也使建成后的桥梁出现不同程度的损伤甚至痛害.有些病害严重的桥梁已经不能正常运营,因此必须对其进行加固与修复.体外预应力方法,是将预应力钢筋布置于梁体截面外,并通过锚固块及转向块来对桥梁结构施加预应力的一种加固结构体系.本文根据多年的桥梁加固设计工作经验,介绍了采用体外预应力法加固桥梁在设计方面所应注意的问题,并通过典型案例分析,为推广体外预应力加固同类桥梁提出了借鉴.     

介绍无粘结预应力技术在高层星级酒店中应用

根据无粘结预应力混凝土结构技术特性,介绍其在某高层星级酒店客房层楼盖设计与施工应用中,使客房层高度降低至2.9m,有效控制建筑物总高度,并有利于星级酒店管道设施布置,取得较好的经济效益。     

预应力砼超静定结构次弯矩的直接计算法

本文从结构力学的一般原理出发，提出一种不需计算等效荷载，不需计算综合弯矩，应用预应力砼超静定结构一般原理直接计算次弯矩。该法还能准确计算预应力因损失引起的沿预应力筋变化时的次弯矩；此外，对于预应力筋布置成各种不同曲线的次弯矩也能准确计算。并能编成电算程序，供工程设计应用。     

局部单层浅网壳的设计分析

局部单层浅网壳的设计关键在于在满足网壳刚度与整体稳定的条件下,确定经济合理的单层部分的可能布置区域和面积。为了满足网壳的刚度与整体稳定,施加预应力是一种常用且有效的方法,而预应力的施加对网壳单层部分的确定有直接影响。本文通过分析比较,寻找单层部分范围和预应力值之间的相对关系。     

矿山钢井架结构设计问题研究

钢井架作为矿山开采中的重要设施,其结构设计是否可靠合理直接关系到钢井架的安全性,必须引起设计人员的足够重视。基于此,本文首先分析了矿山钢井架结构布置设计的原则,然后从斜架布置、立架布置和构件截面布置三个方面分析了矿山钢井架结构布置设计,结合钢井架荷载及荷载效应组合,对钢井架结构计算和斜架基础设计进行了分析和研究,为矿山开采中钢井架的设计提供了一定的参考。     

有粘结预应力混凝土连续梁的极限承载力研究

预应力混凝土连续梁结构的极限承载能力直接影响结构的安全性,是结构工作性能评价中重要指标之一。本文以典型试验梁为例,建立了预应力混凝土连续梁的有限元分析模型,并进行试验加载全过程模拟分析,由此验证有限元分析方法的准确性。合理设计25个考虑受拉区纵向钢筋面积、受压区纵向钢筋面积、混凝土轴心抗压强度、预应力比率和有效预应力等因素的三跨有粘结预应力混凝土连续梁模型,以研究各因素对梁极限承载能力及变形的影响,为该种梁的设计和分析提出相关建议。     

浅谈高层建筑结构转换梁的选型优化

本文对带梁式转换层的高层建筑结构进行了整体受力分析,利用ANSYS结构分析软件对预应力混凝土转换梁和型钢混凝土转换梁进行截面设计,并分别对带普通混凝土、预应力混凝土及型钢混凝土转换梁的结构进行了动力分析与比较.     

钢筋混凝土单层厂房结构形式和布置特点分析

钢筋混凝土单层结构是厂房结构形式的一种，在厂房建筑中广泛运用，其结构形式和布置特点是该类厂房结构建筑施工的设计的主要内容，直接影响到厂房的稳定性和实用性。文章将就钢筋混凝土单层厂房结构形式和布置特点进行分析。     

预应力宽厚板轧机机架的设计与制造

国内外特大宽厚板轧机机架有两种结构,即整体式机架和组合式机架。通过对整体式机架和组合式机架的结构、制造难度和使用状况的比较分析后,引入了预应力机架的设计思想,并对预应力机架的可行性进行了分析,对机架的结构形式、制造方法等方面进行了论述。由于重型预应力机架为分块式结构,制造的难度也随之降低,零件质量容易得到保证,制造周期也会因单件重量降低而大大缩短,更加符合重型机械制造低碳化的发展趋势。     

论预应力技术在建筑工程中的应用

通过对各种预应力结构形式的分类说明,和对预应力平板结构优点的重点阐述,分析和比较预应力结构的竞争力所在及其适用范围,达到预应力技术在建筑工程中推广的目的.     

50-Year-Old Prestressed Segmental Concrete Bridges

The first prestressed segmental concrete bridge in the United States opened to traffic was a small bridge in Madison County, Tennessee. The bridge was constructed using prestressed concrete segments and was opened to traffic in October 1950. Prestressed concrete beams were placed side by side to form the superstructure of the bridge. The construction of this bridge and several other similar prestressed concrete bridges are described herein. The existing condition of eleven prestressed concrete bridges remaining in Tennessee is given. Only minor spalling, leaching, and horizontal cracking are present in the superstructure after fifty years of service. Many of the design features introduced in this design can be found in today’s modern precast segmental concrete bridges.     

Design and Construction of a Bridge in Very High Performance Fiber-Reinforced Concrete

The design, technology, and construction of a small road bridge made of very high performance fiber-reinforced concrete is described in this paper. The bridge consists of precast prestressed concrete beams with a cast-in-place ordinary concrete deck. A preliminary experimental investigation was conducted to define the mix design, to establish the properties of the material and its durability, and to study the flexural behavior of the prestressed concrete beams with and without the concrete deck. The effect of steel fibers at the structural level, where there is an influence of constitutive behavior and size effects, was analyzed by testing a prestressed beam using very high performance fiber-reinforced concrete without fibers. The establishment of the structural properties of the material then allowed the design of the final section of the bridge beams and the definition of a model to justify the design rules adopted. This project represents an attempt to demonstrate the industrial feasibility of very high performance concrete structural elements manufactured with conventional raw materials and usual production techniques and to evaluate the production technology when utilizing steel fibers.     

New Earth Retention System with Prestressed Wales in an Urban Excavation

This study discusses the new earth retention system with prestressed wales. The prestressed wale provides a high flexural stiffness that resists bending caused by lateral earth pressures. The prestressed wale system consists of wales, steel wires, H-beam support legs, and hydraulic jacks. The system allows for a wider spacing between supports and is more economically efficient than conventional systems. In addition, the construction process is relatively simple and the system demonstrates excellent performance. This paper explains the basic principles, mechanisms, and design procedure, as well as the advantages and limitations of this new earth retention system. It also presents the results for the performance of the field application and the measured performance is investigated and discussed. These results demonstrated that this new earth retention system with prestressed wales performed successfully in an urban excavation.     

Deflection Control of Concrete Beams Pretensioned by CFRP Reinforcements

Use of carbon fiber reinforced polymers (CFRP) reinforcement for prestressing concrete structures introduces a promising solution for deterioration of concrete structures due to corrosion of steel reinforcements. Due to the low elastic modulus and limited strain at failure of CFRP reinforcement, partial prestressing could be the most appropriate approach to enhance deformability and reduce the cost in comparison to fully prestressed concrete structures. For members reinforced or prestressed with fiber reinforced polymers reinforcements, serviceability requirements may be the governing criteria for the design; therefore, deflection under service loading conditions should be well defined. This paper introduces simplified methods to calculate the deflection of beams prestressed by CFRP reinforcement under short-term and repeated loading. It also examines the applicability of current approaches available to calculate the deflection. Based on an experimental program undertaken at the University of Manitoba, bond factors are introduced to account for tension stiffening of concrete beams prestressed by CFRP. A procedure to determine the location of the centroidal axis of cracked prestressed sections is also proposed. The proposed methods for deflection calculation are calibrated using the results obtained from different experimental programs. Design guidelines are proposed to predict the deflection of beams partially prestressed by CFRP reinforcement.     

Torsional Design of Hybrid Concrete Box Girders

Hybrid concrete box-girder bridges that include prestressed slabs and corrugated steel webs provide a major improvement over traditional prestressed concrete box-girder bridges. To reduce the self-weight, high strength concrete is used for the top and bottom slabs and corrugated steel webs are employed for the webs. Because the weight of the girders has been reduced, the span length can be increased for more cost-effective design. A series of systematic tests on hybrid concrete box girders subjected to torsion has been performed. According to the test results, an analytical model was developed. Using the developed analytical model, a step-by-step procedure for torsional design of such bridges is presented in this article. Based on the design procedure proposed, a girder is designed by the analytical model and checked to satisfy structural codes.     

超大跨度预应力混凝土梁施工技术

文章以赤峰国际会展中心工程为背景,深入探讨本工程超大跨度预应力混凝土梁施工的关键技术,详细介绍了施工过程中的材料准备、混凝土梁模板及支撑体系的设计、预应力钢筋安装、混凝土浇筑及养护、孔道灌浆等主要环节,对大跨预应力混凝土梁的施工具有较高的参考价值。     

Fatigue Behavior of Externally Strengthened Concrete Beams with Fiber-Reinforced Polymers: State of the Art

This paper presents the recent progress and achievement in the application of fiber-reinforced polymers (FRP) on strengthening reinforced/prestressed concrete beams subjected to fatigue loading. Although the performance of FRP-strengthened structures under monotonic loading has been intensively investigated, fatigue behavior is relatively less known to date. This paper summarizes most of the currently available literature, including the codes and design manuals, on reinforced/prestressed concrete beams externally strengthened with FRP. The review focuses specifically on the fatigue life as a function of the applied load range, bond behavior of externally bonded FRP, damage accumulation, crack propagation, size effects, residual strength, and failure modes. Research needs including considerations for design guidelines are presented.     

架空导线用特强预应力钢芯制备与性能表征

随着以新能源为主体的新型电力系统逐步构建,架空输电线路对大规模清洁能源的大容量、安全高效输送能力的提升成为电力行业关注的热点。基于优化成分的高碳钢盘条以及适配的加工工艺,制备出抗拉强度大于2 100 MPa、伸长率不小于4.8%、锌铝合金镀层质量不低于320 g/m²的特高强度预应力镀锌铝钢线。绞合制成的预应力钢芯1 000 h应力松弛率为4.178%。在此基础上开展了特强高导预应力钢芯软铝增容导线的设计研制,为该新型增容导线产品的国产化开发与工程应用提供了技术支撑。     

Repair of Bridge Girder Damaged by Impact Loads with Prestressed CFRP Sheets

A sound repair on a 40 year old four-span prestressed concrete girder bridge is performed with an innovative strengthening method using prestressed carbon fiber reinforced polymer (CFRP) sheets. In fact, this application is the first North American field application of its type. An adequate repair design is conducted based on the American Association of State Highway and Transportation Officials Load Resistance Factor Design (AASHTO LRFD) and the Canadian Highway Bridge Design Code. To ensure the feasibility of the site application using prestressed CFRP sheets, tests are conducted and closed-form solutions are developed to investigate the behavior of the anchor system that is necessary for prestressing the CFRP sheets. A full-scale finite-element analysis (FEA) is performed to investigate the flexural behavior of the bridge in the undamaged, damaged, and repaired states. The AASHTO LRFD exhibits conservative design properties as compared to the FEA results. The repaired bridge indicates that the flexural strength of the damaged girder has been fully recovered to the undamaged state, and the serviceability has also been improved. An assessment based on the AASHTO rating factor demonstrates the effectiveness of the repair.     

Charged-particle interaction with liquids: Ripplon excitations

This paper presents results of structural analyses and a preliminary design of a precast, prestressed concrete lunar base subjected to one atmosphere internal pressure. The proposed infrastructure measures 120 ft in diameter and 72 ft in height, providing 33,000 sq ft of work area for scientific and industrial operations. Three loading conditions were considered in the design: (1) During construction; (2) under pressurization; and (3) during an air‐leak scenario. A floating foundation, capable of rigid body rotation and translation as the lunar soil beneath it yields, was developed to support the infrastructure and to ensure the air‐tightness of the system. Results reveal that it is feasible to use precast, prestressed concrete for construction of large lunar bases on the moon.