预应力混凝土小箱梁预应力阶段预应力损失分析

通过对20m预应力混凝土小箱梁张拉过程中预埋于箱梁中钢筋应变计进行实测,并对实测数据、公桥规范（JTG D62-2004）给出的锚固损失计算值、及midas有限元模型计算值对比分析,结果表明：小箱梁采用后张法张拉时跨中截面各损失在短期损失（短期损失加上50％钢筋松弛引起损失）中所占的百分比基本相同,在L/4截面处σ12能达到总损失的一半,σ14和σ15占到20％,σ11占10％左右,锚具变形、钢筋回缩和接缝压缩是引起梁端截面应力损失的主要原因;跨中截面、L/4截面和梁端截面的短期损失占预加力的比重均较大,所以设计时必须对各截面预应力损失都进行计算;影响小箱梁上拱度的因素较多,建议施工时根据预制梁实测上拱值修正反预拱度.     

推广应用“无粘结预应力砼结构”

推广应用“无粘结预应力砼结构”郭力伟（正阳河木材厂）赵京南（哈尔滨第三工程公司）宋野（哈尔滨建材工业设计院）郭长源（黑龙江森工总局）后张法无粘结预应力工艺，系在预应力钢筋表面涂以专用防腐油脂的涂料层，外包聚乙烯或聚丙烯的塑料管的外包层；将这种特制加工...     

桥梁无粘结预应力钢筋的极限应力分析

根据无粘结部分预应力混凝土梁的受力特点，采用弯矩-曲率法计算无粘结预应力钢筋的极限应力，计算结果与现有的试验数据符合得较好。建立了系统的无粘结部分预应力混凝土简支空心板梁桥设计理论和方法，有助于UPPC梁桥设计理论的完善及发展，并为“公桥规”的修订和完善提供有益的参考。     

预应力技术的发展及常用预应力锚固体系

本文回顾了预应力体系的起源与发展，介绍了几种常用的预应力锚固体系，并阐述了每种锚固体系的特点。为预应力混凝土结构设计者和施工人员提供参考。     

后张法预制箱梁预应力损失的计算和控制探析

指出了预应力筋的预加应力并不是常量,而是瞬时或随着时间的增加而逐渐减少,预应力筋这种预加应力逐渐减少的现象称为预应力损失。结合石武客运专线驿城制梁场在箱梁预应力施工过程中总结出的经验,全面分析了后张法预应力混凝土铁路桥简支箱梁在施工中预加应力损失的因素。根据预应力损失的原理提出了减少损失应采取的措施,以保证预应力构件的抗拉强度。     

预应力钢结构的发展及应用

通过介绍预应力钢结构的特点和受力机理，表明预应力钢结构具有良好的结构性能和良好的经济实用性，并对预应力钢结构的发展进行了展望。     

预应力混凝土空心板"蒸养"裂纹产生与防范

在预应力空心板冬季“蒸养”过程中，混凝土初期养护管理、升降温梯度、板粱上下散热速度差以及梁内是否配置防裂钢筋等都将对粱的浇注质量产生影响，本文以伊嘉公路五汤段的预应力空心板粱为例，对粱的“蒸养”裂纹作了详细分析，提出了相应的防范措施。     

无粘结预应力钢箱索梁桥的设计

本文介绍了钢箱索的计算理论;钢箱索梁桥的模型实验,其模型实验解决了钢索梁张力对梁的刚度的贡献及外力荷载引起的张力增量索梁自振频率等;详细介绍了预应力钢筋索梁的结构设计、钢箱索梁桥实桥测试。     

环形预应力束的有效预应力分布及回缩量计算

对环形预应力束的有效预应力及回缩量计算公式进行了推导 ,并将其用于哈尔滨松花江公路大桥索塔锚固区预应力有效预应力分布及回缩量计算中。计算结果显示该计算公式能够准确地算出环形预应力束的有效预应力分布     

预应力简支钢箱梁基频分析

以预应力简支钢箱梁模型试验的测试结果为基础，应用有限元分析软件ANSYS建立普通简支钢箱梁和预应力简支钢箱梁模型并对其进行模态分析，将有限元计算结果和模型试验测试结果进行对比，从而验证预应力简支钢箱梁有限元模型的正确性。分析结果表明，预应力简支钢箱梁基频都比普通简支钢箱梁小；预应力简支钢箱梁的基频随着锚固位置的增大而减小；双折线型布索的预应力简支钢箱梁基频最大，曲线型布索的预应力简支钢箱梁的基频最小。     

曲线预应力的有限元模拟

采用面切割体的方法,利用Matlab生成相应的切割曲面程序,在ANSYS中直接调用该命令生成相应的预应力曲线,加载求解.同时对摩阻损失进行了模拟,提出了解决办法,为后续预应力的模拟提供参考.     

预应力混凝土管桩基础设计应注意的问题

从岩土工程观点来探讨预应力管桩的应用条件,提出设计中应注意的问题。     

无粘结部分预应力、有粘结预应力及碳纤维布对砼梁抗弯设计配筋的比较分析

通过对一根简支梁抗弯配筋设计的计算，分析研究无粘结部分预应力，有粘结预应力以及碳纤维加固技术对受弯构件配筋量及抗裂性能的影响，可供工程应用参考。     

无风撑钢管混凝土拱桥建模分析

结合康复南路跨线桥工程实例,阐述了利用A nsys建立钢管混凝土拱桥模型的一般方法,即首先建立拱桥的空间杆系单元模型,对复杂截面采用写截面的方法,同时在建模过程中使用数组来增强程序的可读性,并提出了施加预应力和吊杆初张力的方法.理论计算与实测结果对比分析表明,本建模方法正确可靠.     

预弯预应力混凝土梁的施工

该文所介绍的是目前国内最大跨径预弯梁的施工概况,提出的一些关键工序应注意的问题。     

Effects of pretension in bolts on hysteretic responses of moment-carrying timber joints

The adoption of a concept similar to the prestressing technique used in laminated wood decks of bridge structures might increase the initial stiffness or ultimate resistance of dowel-type timber joints by applying pretension to their bolts. This study investigated the effect of pretension in bolts on hysteretic responses and ultimate properties of moment-carrying timber joints with steel side plates. A pretension of 20 kN that yielded a prestress level of 1600 kPa or about 90% of the allowable long-term end-bearing strength of spruce species was applied to the bolts of prestressed joints. The superiority of the prestressed joint over the non-pre-stressed joint was proved by very high hysteretic damping, equivalent viscous damping ratio, and cyclic stiffness. At any given rotation level, hysteretic damping reduction and moment resistance decrement due to continuously reversed loads were found to be small because bolt pretensioning minimized the pinching effect. This study showed that the hysteresis loop of the prestressed joint can be obtained by adding the frictional hysteresis loop due to pretension force into the hysteresis loop of the non-pre-stressed joint. Despite a great increase of initial stiffness, only slight increments in ductility coefficient and ultimate moment resistance were found in the prestressed joint.     

牡丹江市报业大厦预应力梁板的设计及施工要点

本文以牡丹江市报业大厦无粘结预应力梁板为例,详细论述了设计与施工要点及采用的新技 术、新工艺。     

森林资源型经济转型中的社会福利损失:特征、内容及出路

森林资源型经济转型是在国有林业经济领域应对中国全面深化改革要求的深刻实践,而转型期间产生的社会福利损失则是资源型经济“改革之殇”的具体体现,具有政策性、周期性和阶段性、广泛性、相对性等本质特征。经济转型中的福利损失包括传统森工企业承受的生存困境及不断弱化的企业贡献力（经济贡献力、资源管护力、生态服务力）、林业职工生计的每况愈下、林区福利体系的碎裂化及其应对国家生态战略需求的妥协性和政策依赖性、国有林区社会认同危机以及国有森工企业的群体价值威胁等。只有通过转变观念,加深认识,以包容性增长理念统筹兼顾经济转型与社会福利建设,才能在分别实现以产业多元化破解资源型经济转型、以供给与保障多元化减小社会福利损失的前提下确保森林资源型经济转型和林区社会福利体系建设的协调与统一。     

One-year stress relaxation of timber joints assembled with pretensioned bolts

In our previous study, great increases of hysteretic damping and initial slip resistance of timber joints were attained by applying axial pretension to the steel fasteners. To evaluate the effectiveness of this method, 1-year stress-relaxation measurement was carried out. Nine prestressed joints were prepared and three of them were restressed after 3 and then 6 months after the initial prestressing. All joints were exposed to indoor conditions, and relaxation of the pretension was regularly measured from time-dependent decreases of axial strain of the bolts. After measurement, the joints were subjected to cyclic and monotonic loading tests until failure. The average ratio of residual stress to the initial prestress after 1 year was about 0.23 and 0.66, respectively, for joints without restressing and those with restressing. A simulated stress-relaxation curve developed from the four-element relaxation model predicted 3% of the initial stress after 5 years. Without a regular restressing program, the initial prestressing effect therefore must be considered negligible. However, about 20% of the pre-stress level can be reasonably assumed if restressing is carried out annually. This small residual stress was found to introduce suffi cient frictional damping to signifi cantly increase the equivalent viscous damping ratio of the joints. Part of this study was presented at the 10th World Conference on Timber Engineering, Miyazaki, June 2008