Durability design of prestressed concrete structures

Based on the durability characteristics of prestressed concrete structures,the durability limit states of carbonation and chloride ion attack are defined, respectively.Durability predicting models on the basis of reliability mathematics and stochastic processes areconstructed, and the pure theoretical formulae of failure probability of prestressed concretestructures are analyzed. In addition, a simple durability design method for carbonation ofstructures is put forward. According to the analysis, the durability of prestressed concretestructures is superior to that of traditional structures. The research also indicates that theconcrete cover prescribed in the current code (GB 50010-2002) is not adequate. The rational coverthickness should notbe less than 35 or 45 mm according to carbonation or chloride ion attack,respectively.

Three-dimensional Analysis of Prestressed Concrete Offshore Wind Turbine Structure Under Environmental and 5-MW Turbine Loads

A concrete gravity base structure may not be suitable for offshore weak soil because of its heavy weight. Therefore, a conceptual model for a concrete offshore wind turbine structure suitable for weak soils is proposed. The proposed model is composed of a prestressed concrete(PSC) supported by a pile foundation. For a three-dimensional analysis of the large concrete structure, wave pressures based on the diffraction wave theory are developed using a three-dimensional solid finite element method. Static and dynamic analyses were performed to achieve the conceptual model of a PSC structure subjected to ocean environmental loads and a 5-MW turbine load on southwest coast in Korea. From the analysis, the maximum displacement and stresses of the proposed model did not exceed the allowable values from design standard, and the first mode of natural frequency of the structure was in a safe range to avoid resonance. The proposed model has enough structural stability to withstand external loads, and it is expected to be used in locations suitable for concrete gravity structures.

Probabilistic Assessment of Pitting Corrosion Effect on Flexural Strength of Partial Prestressed Concrete Structures in a Chloride Environment

Like reinforced concrete （RC） structure, Prestressed concrete （PC） structures cannot escape from corrosion related problems, especially when they are subjected to very aggressive environment, such as chloride environment. The corrosion of PC and RC structures can take place if the concrete quality is not adequate, the concrete cover is less than that specified in the design, poor detailing during design and construction. For RC structures, corrosion in the reinforcing steel generally leads to serviceability problems （staining, cracking and spalling of concrete）. By contrast, for PC structures, corrosion of prestressing strands may initiate structural collapse due to higher stress levels in the steel and smaller diameter of the prestressing steel. Research on corrosion effect on concrete structure has mainly considered the effect of corrosion have on reinforced and full prestressed concrete structure. In this study, a structural framework will be developed to predict the flexural strength of partial prestressed concrete structures in a chloride environment. The corrosion model previously developed for reinforced and prestressed concrete structures will be combined to predict the effect of corrosion has on partial prestressed concrete structures. Note that in partial prestressed concrete structures, both non prestressing steel （passive） and prestressing （active） reinforcement are utilized to carry the load. The framework developed will be combined with probability analysis to take into account the variability of parameters influencing the corrosion process. This approach allows more accurate prediction of service life of partial prestressed concrete structures in a chloride environment.

Shear Behavior of Novel Prestressed Concrete Beam Subjected to Monotonic and Cyclic Loading

Prestressed steel ultrahigh-strength reinforced concrete(PSURC) beam is a new type of prestressed concrete beam, which not only has a considerable compressive strength attributed to the ultrahigh strength concrete, but also ensures a certain degree of ductility at failure due to the existence of structural steel. Five of these beams were monotonically tested until shear failure to investigate the static shear performance including the failure pattern, loaddeflection behavior, shear capacity, shear crack width and shear ductility. The experimental results show that these beams have superior shear capacity, crack control ability and shear ductility. To study the shear performance under repeated overloading, seven PSURC beams were loaded in cyclic test simultaneously. The overall shear performance of cycled beams is similar to that of uncycled beams at low load level but different at high load level. The shear capacity and crack control ability of cycled beams at high load level are reduced, whereas the shear ductility is improved. In addition, the influences of variables including the degree of prestress, stirrup ratio and load level on the shear performance of both uncycled and cycled beams were also discussed and compared, respectively.

Application of laminated vierendeel truss in high-position transfer story structure

To meet the demands for large space and flexible compartmentation ofbuildings, laminated vierendeel trasses are adopted in high-position transfer story structures.First the bearing characteristics are analyzed, in which reasonable stiffness ratio of the upperchord, middle chord, and lower chord is derived. Then combined with an actual engineering model (1:8similar ratio), the static loading and pseudo-dynamic tests of two models for laminated vierendeeltrass used in transfer story structures are conducted, in which one model adopts reinforcedconcrete, and the other adopts prestressed concrete and shape steel concrete. Seismic behaviors areanalyzed, including inter-story displacement, base shear-displacement skeleton curves, andequivalent viscosity-damping curves. A program is programmed to carry out the elasto-plastic dynamicanalysis, and displacement time-history curves of the two models are derived. The test and analysisresults show that the laminated vierendeel trass with prestressed concrete and shape steel concretehas excellent seismic behaviors. It can solve the disadvantages of laminated vierendeel trussesused in transfer story structures. Finally, some design suggestions are put forward, which can bereferenced by similar engineering.

Seismic Performances of Large-Span Prestressed Concrete Frame Structure by Shaking Table Tests

The seismic performances of the large-span prestressed concrete frame structure of bunker bay of thermal power plant under different intensity level was investigated by shaking table tests.A 1/8 microconcrete nonfull weight scaled model was designed according to the prototype structure and the conditions of laboratory.Three kinds of scaled ground motion accelerations were employed as seismic excitations.White noise was input in the structure through each seismic wave applied.The experimental results indicate that the structure is safe to endure seven degree intensity as required in Chinese codes.The natural vibration frequency of the structure is decreasing with the increasing of the seismic intensity,the natural vibration frequency of the structure decreases by about 24.5%,and the structural stiffness reduces by nearly 44% in seven degree intensity of seldom occurred earthquake.The damage at the top of column in the first floor is the most serious,the weak part of the structure is at the first floor,and the strong beam/weak column phenomenon appeared obviously,so this kind of large-span prestressed concrete frame should not be used in a high intensity district.

3D fracture modelling and limit state analysis of prestressed composite concrete pipes

In this manuscript,we study fracture of prestressed cylindrical concrete pipes.Such concrete pipes play a major role in tunneling and underground engineering.The structure is modelled fully in 3D using three-dimensional continuum elements for the concrete structure which beam elements are employed to model the reinforcement.This allows the method to capture important phenomena compared to a pure shell model of concrete.A continuous approach to fracture is chosen when concrete is subjected to compressive loading while a combined continuous-discrete fracture method is employed in tension.The model is validated through comparisons with experimental data.

预应力在我国大跨度结构中的应用研究综述

为了提高大跨度结构的正常使用性能,通常在混凝土结构中施加预应力.结果表明,预应力混凝土结构具有更好的使用性、耐久性和大跨度适用性,其中预应力混凝土空心板结构在不显著降低承载力和刚度的前提下明显减小结构自重,预应力型钢混凝土梁(板)结构采用较小的截面尺寸即可满足承载力和刚度的需求.开发城市地下空间是解决城市用地紧张的有效手段,我国地下大跨空间常用的结构形式主要包括密排框架(肋梁)结构、折板或拱形结构、变截面(加腋)板结构、预应力混凝土结构、型钢-混凝土组合结构和Y形柱结构6种形式,相比之下,跨度较大时宜采用预应力结构.

横向静载作用下轨道交通预应力混凝土U型梁裂缝开展研究

为探究轨道交通预应力混凝土U型梁结构在腹板横向受力情况下的裂缝开展状况,通过回顾总结其裂缝开展成因,并以实际工程中的某标准梁段为例,进行了横向静载破坏试验,分析了U型梁结构在横向受力下的应变、挠度变化规律以及裂缝发育和损伤状况。研究结果表明,在横向对称荷载作用下,随着加载级的增大,U型梁展现出良好的整体性能和横向抗裂性能;该梁的裂缝损伤首先出现在腹板和底板处,随后逐步扩展到底板与腹板的连接部位;在破坏加载级下,腹板与翼缘发生破坏性裂缝损伤和明显的外扩变形;在高于规范撞击力建议值2倍的横向静载作用范围内,试验梁能够保持弹性工作状态,验证了采用美国ACI规范中对于列车脱轨撞击力的建议值进行U型梁横向抗撞设计的合理性。该研究成果可为轨道交通预应力混凝土U型梁的力学性能研究和结构优化设计提供更多参考。

水工混凝土结构修补加固关键技术探析

我国多数水库大坝建设年代早,水工混凝土结构存在各种老化安全问题,亟待采取修补加固处理。针对水工混凝土结构缺陷类型较多,缺陷修补加固技术复杂,本文根据水工混凝土结构的运行环境和常见缺陷类型,对其修补加固方案、加固材料及施工工艺等进行了技术总结,结合漳河水库水工混凝土结构缺陷问题,详细阐述混凝土裂缝、混凝土表面剥蚀、局部结构强度不足等缺陷产生原因和最新加固技术,相关研究成果和实践经验可供类似工程借鉴。

预应力混凝土框架梁中预应力效应分析研究

针对预应力混凝土框架梁预应力效应开展理论和数值分析,指出了将预应力混凝土框架梁简化为固定翼缘宽度线性构件的方法存在局限性。建立了梁板结构实体模型,分别施加竖向荷载和轴向等效集中力,对楼板内的正应力分布情况展开分析。结果表明:在框架梁承受轴向力时,楼板承受正应力的范围沿梁长度方向存在显著的不均匀分布现象,常用的线框模型无法准确反映梁正应力分布。分别建立了梁板结构的实体模型、固定翼缘宽度梁线框模型和梁板结合模型,对模型施加预应力等效荷载,并进行预应力效应对比分析。结果表明:固定翼缘宽度梁线框模型无法考虑楼板约束引起的梁内次轴力,导致其在变形和裂缝宽度分析中存在较大误差;实体模型分析准确但时间成本过高;梁板结合计算模型可以充分考虑肋梁在板约束下产生的次轴力效应,可实现以较小的分析成本准确计算内力和变形。

某带空腹桁架的科研楼结构设计

该结构采用框架-剪力墙结构体系,该项目存在竖向抗侧力构件不连续、楼板局部不连续、扭转不规则特点。针对项目扭转不规则,设置了屈曲约束支撑,取得了较好的抗扭转效果。针对竖向抗侧力构件不连续,同时为实现通高大堂,在4层设置了空腹桁架;基于“强化转换层及其下部,相对弱化转换层上部”的设计思想,定量给出了空腹桁架控制指标和内力调整措施。空腹桁架下弦杆采用了预应力型钢混凝土梁的设计,给出了该梁的抗弯、抗剪计算公式。

深中通道泄洪区非通航孔桥主梁设计

深中通道泄洪区非通航孔桥总长6.05 km,分布于伶仃洋大桥及中山大桥2座通航孔桥两侧。泄洪区非通航孔桥采用等跨连续梁布置,4~6跨一联。主梁设计过程中,首先进行110、120、130 m三种跨径方案比选,确定采用最经济的110 m跨径方案。然后针对结构形式,提出预应力混凝土梁、钢-混组合梁和钢箱梁3种方案,从力学性能、经济性和施工风险等方面综合考虑,最终推荐采用钢箱梁方案。钢箱梁采用外形简洁流畅的封闭式断面,有利于后期维养;考虑全线景观效果,主梁高度取4 m,高跨比为1/27.5;横隔板间距取2.5 m,采用实腹式横隔板和框架式横肋的组合式设计,使箱室内部通透性更好;钢箱梁采用Q420qD钢和Q345qD钢2种材料。钢箱梁施工采用适合海上长大桥梁的大节段预制+现场拼装的施工方案。

基于预应力法的钢筋混凝土结构施工加固方法研究

当前钢筋混凝土结构施工加固结构多为单向,加固层级受限制,导致预应力差不断提升,为此提出对基于预应力法的钢筋混凝土结构施工加固方法的设计与实践研究。工程通过放线测定及钻孔清孔处理、支撑构件预应力测算,采用多阶的方式打破加固层级受到的限制,部署多阶支撑结构点位。设置粘钢预应加固梁,并完成钢管支撑的简化,采用混凝土桁架搭接实现结构加固处理。最终的测试结果表明:经过对5个随机选定区域的比对,最终得出的预应力差被较好地控制在40MPa以下,说明当前所设计的混凝土内置结构加固方法的针对性与稳定性较高,故其具有较好实际的应用价值。

预应力技术在桥梁工程施工中的应用研究

预应力技术可提高工程的耐久性和抗裂性,具有较强的实践价值。文章阐释了预应力施工技术的基本原理和应用优势,从混凝土构件施工、梁段预制、受弯构件施工等方面探究了预应力施工技术在道路桥梁施工技术中的具体应用,分析了预应力施工技术应用于桥梁施工技术出现的问题,并提出了相应的施工质量控制措施。

服役15年大跨跨海预应力混凝土梁桥荷载试验及结构性能评价

大跨预应力混凝土梁桥因其结构刚度大、行车平顺舒适、抗震性能好、施工技术成熟等优势得到广泛应用,该类桥梁在服役较长时间后,由于自然环境和超载的长期影响可能导致结构出现裂缝,并影响结构的安全承载能力,这一问题对于跨海桥梁显得尤为突出。因此,为准确评估在役跨海混凝土桥梁的实际工作状态与承载能力,通过对一座已服役15年的大跨跨海预应力混凝土梁桥进行现场静载、动载试验,并结合有限元对其振型等特性进行了分析。研究结果表明,桥梁结构的工作性能仍保持良好,但由于所处海域环境及长期服役导致的结构损伤和裂缝的影响,使其实际承载能力有所下降。研究成果可为在役同类桥梁的维修加固提供参考。

预应力波纹钢-混凝土组合板力学性能分析

为充分发挥波纹钢混凝土组合板力学性能,本文提出预应力波纹钢混凝土组合板结构。在利用试验结果验证数值模型准确性的基础上,对不同类型组合板进行了力学性能比较分析,研究了结构受荷历程和破坏模式,明确了上波纹钢板和预应力的作用机制,二者组合后显著提高了组合板弹性工作范围和抵抗破坏能力。进一步通过参数化分析,研究了预应力双层波纹钢混凝土(PSCS)组合板力学性能变化规律,结果表明:波纹钢板型号、核心混凝土厚度、栓钉间距及预应力水平对PSCS组合板抗滑移能力和抗破坏能力影响重大,其中核心混凝土厚度和波纹钢板波形影响更为明显,恰当的预应力水平能够更好发挥PSCS组合板力学特性。研究结果可为预应力波纹钢混凝土组合板结构的设计和优化提供参考和指导。

PK梁板在装配整体式框架结构中的应用

针对PK预应力混凝土叠合梁、预应力混凝土叠合梁同时在一个工程中应用遇到的模板设计与计算、起重设备的选型和吊具选择以及施工工艺等问题,结合工程实际情况,形成了PK预应力混凝土叠合梁板组合的施工工艺流程,确保PK预应力混凝土叠合板吊装的精确定位及受力性能,满足工程质量要求。

装配式GRC-PC复合墙板收缩性能的试验研究

文中开展了不同工艺条件下装配式GRC-PC复合墙板收缩性能的研究,并与单一材料墙板进行了对比。结果表明,GRC墙板与C30混凝土墙板的收缩应变随着时间的延长,呈现先快速降低后平稳的趋势;C30混凝土墙板的收缩应变稳定在-80×10^(-6)μm,较GRC墙板的收缩应变降低93.2%。与GRC墙板收缩应变相比,GRC-PC墙板的表面收缩应变及内部收缩应变的降低幅度分别为89.2%、94.9%;与C30墙板收缩应变相比,复合墙板内部的收缩应变降幅达到33.3%。加入钢丝网后,GRC-PC复合墙板+钢丝网的表面收缩应变开始下降,具有更好的抗裂性能。

某金融大厦托梁拔柱改造工程设计与施工研究

托梁拔柱技术设计难度大、施工复杂,施工过程中安全风险较高,因此尚未形成完整的托梁拔柱设计理论和施工技术。结合某金融大厦改造工程,对托梁拔柱实践进行探讨,该大厦项目拟拆除两根框架柱,依据功能布局的需求及相应的计算结果,采用新增简支预应力上翻梁的加固改造措施。从实施方案对比、可行性论证和现场监测验证等方面阐述了简支上翻梁的优越性,并详述托梁拔柱的施工方案。施工过程中框架梁监测点变形量在-4.6mm~2.5mm之间,大厦改造后可以满足预定的使用功能,可为同类型的工程提供参考。