Vergleich des ETV Beton und DIN 1045‐1

Comparison of the ETV Beton and DIN 1045‐1 The paper compares the safety elements of the ETV Beton and the valid German reinforced concrete code DIN 1045‐1. The comparison is carried out in general for the characteristic values of the actions, for the partial safety factors of the actions and the resistance and for the action combination factors as well. Additionally the comparison has been done in terms of calculation of the required amount of reinforcement in an example. The comparison yields to the result that especially the partial safety factor for dead load is substantially lower in the ETV Beton compared to DIN 1045‐1. Newer developments in the Eurocode suggesting a lower partial safety factor for dead load are therefore backed by the presented investigation.     

索穹顶结构张拉找形与承载全过程仿真分析

索穹顶结构的预应力张拉过程是几何体系由机构变成结构的过程。首先,从预应力施工张拉方式实现既定结构成形态、确定结构成形态满足正常使用和安全要求、优化预应力度选定合理结构成形态三个方面,应用重启动计算分析方法,对索穹顶结构进行预应力张拉找形及承载全过程仿真分析。分析表明,采用不同的预应力张拉方式可以达到相同的既定成形态,这为制定预应力张拉施工方案创造了灵活的技术空间。其次,通过对索穹顶结构在不同预应力度下承载全过程仿真分析,得出工程采用的预应力度是安全合理的,并提出结构设计各阶段体系弹塑性性能指标。最后,针对不同跨度索穹顶结构,通过确定结构初始几何形态的初始预应力度P0,以P0为基本模数分析不同预应力度下结构的弹塑性性能,得出索穹顶结构初始预应力为（7.5～10）P0的设计方法。以上研究方法和结论在我国大陆地区首座大跨度索穹顶结构工程--内蒙古伊旗全民健身体育中心工程中实现应用。     

既有建筑结构构件的安全性分析

提出了基于目标使用期的既有建筑结构构件承载能力验算的极限状态表达式。根据适用于既有结构的荷载和抗力概率模型,考虑14种代表性的结构构件、不同的可变荷载效应与永久荷载效应的比值、3种可变荷载效应与永久荷载效应的简单组合,对不同目标使用期内的荷载分项系数进行了优化分析。结果为:永久荷载分项系数γG=1.0(当永久荷载对结构有利时,γG=0.6),可变荷载分项系数γQ=1.3。由荷载分项系数进一步优化分析得出不同构件的承载力分项系数为γR=1.1～1.8。按目标可靠指标增减0.25确定了既有建筑结构构件承载能力的等级评定标准。经工程实例验证,所提分析方法更加符合实际情况,合理实用。     

六角形柱网预应力24块拼板结构研究

本文结合常州纺织工业学校的服装、工艺美术展览厅工程，对六角形柱同预应力２４块拼块结构进行了研究，其中对上抬力的确定、预应力张拉阶段及使用阶段的内力计算、偏心预应力及预应力轴向压缩引起的次弯矩计算、节点构造、预应力张拉工艺以及荷载试验等均做了较详细的介绍，可供设计参考。     

GFRP筋的高温蠕变性能试验分析

通过对21组,共72根不同应力状态、不同温度下GFRP筋的蠕变性能进行的试验和分析,表明:随时间的延长GFRP筋的应变逐渐增大,而同一应力水平的GFRP筋试件随温度的升高,应变有增大的趋势。根据试验结果,可以确定预应力GFRP筋增强混凝土构件在火灾高温条件下GFRP筋的预应力损失值。     

我国预应力技术的现况与展望

改革开放以来，我国预应力技术取得了突飞猛进的发展。预应力材料供应充足，工艺逐步完善，工程应用不断扩大，专业队伍成长壮大。已有一大批预应力工程项目达到或接近国际水平。在新世纪到来之际，应抓好修订规程，开展国际交流，研究非金属预应力筋材等工作。     

Experimental load-carrying capacity evaluation of thermal prestressed H beam with steel brackets

To improve the load-carrying capacity of steel structures there are mainly two methods of using cover-plate which are the preflex method and multi-stepwise thermal prestressing method. However a prestress applied to the top flange of H beam is less than the bottom flange because these two methods have small eccentricity. It is necessary to develop an advanced feature of prestressing method which efficiently increases load-carrying capacity and prestressing efficiency. Therefore this study proposes a cover-plate prestressing method with increased sectional stiffness and prestressing efficiency, called multi-stepwise thermal prestressing with steel brackets. To evaluate the prestressing efficiency and load-carrying capacity of the proposed method, prestressing application tests and static loading tests were conducted on three H beams. The multi-stepwise thermal prestressing method with the steel brackets had higher displacement induced to the H beam and higher tensile stress in the top flange than in a case without the steel brackets. Also, when prestress is applied, the tensile stress in the cover-plate significantly decreased with the installation of the steel brackets. The static loading tests showed that the installation of the brackets increased the stiffness, the yield load, and ultimate load of the structure, compared with an unreinforced girder, which meant higher load-carrying capacity than a conventional thermal prestressed structure without brackets.     

高精度预应力混凝土梁的徐变控制技术研究

结合混凝土材料特性及预应力桥梁设计方法，研究了高精度线形要求的预应力混凝土梁在恒载、活载及预应力作用下的长期徐变机理和变形控制技术，提出了对高精度预应力混凝土梁的徐变控制的若干有价值的建议。     

Behavior of prestressed stayed steel columns under fire conditions

Prestressed stayed steel columns experience loss of strength and stiffness when exposed to fire conditions. This paper presents results from experimental studies on the behavior of prestressed stayed circular steel columns under fire conditions. Two full scale prestressed stayed steel columns were tested by subjecting the columns to simultaneous gravity (mechanical) loading and fire conditions. In these fire tests, the varied parameters include load level and level of prestressing. Cross sectional temperatures, axial deformations, as well as fire resistance during the fire tests were recorded and measured. The results indicate that prestressed stayed steel columns undergo various failures modes under different combinations of load and prestress ratios. Specifically, load level significantly influence the fire response of prestressed stayed steel columns with higher load level leading to higher contraction and lower fire resistance.     

2008奥运会羽毛球馆弦支穹顶预应力张拉模拟施工过程分析研究

对于大跨度弦支穹顶结构,预应力张拉施工过程实际上是几何体系由机构(准机构)变为可承担设计荷载的结构体系过程。该类结构体系的安全控制有别于常规结构体系,它需要对结构的设计状态即最终使用状态进行控制,同时应研究预应力张拉施工过程中结构的力学性能,并对结构几何成形过程中的安全性进行控制。本文以2008奥运会羽毛球馆弦支穹顶屋盖为研究对象,应用分步一次加载法和单元生死法两种不同的计算方法对弦支穹顶结构的预应力施工进行全过程模拟计算,分析了在预应力施工过程中结构位移、环索内力和径向拉杆内力变化规律,确认了张拉施工过程的安全性;得出分步一次加载法时结构力学响应大于单元生死法时结构力学响应的结论;证明弦支穹顶整体结构设计采用分步一次加载法是偏安全的。     

Simple approach for force finding analysis of circular Geiger domes with consideration of self-weight

A simple approach for force finding analysis of Geiger domes with a circle plan is proposed in this paper. The general equations are first deduced for computing the actual initial prestressing force of domes with consideration of self-weight. Following that, the process for prestress design of Geiger domes is presented. Taking two Geiger domes as illustrative examples, the prestress of the dome is designed and the difference between the ideal initial prestress and the actual initial prestress is investigated. The nodal displacements of domes under self-weight and external load are studied. The results show that the proposed simple approach is accurate and effective to obtain the actual initial prestress of Geiger domes.     

体内外预应力混合配索桥梁设计中分阶段预应力配置设计

体内外预应力筋混合配索的桥梁设计方案,可利用体内索承担悬臂浇注施工荷载,又可利用体外索承担二期恒载和使用阶段荷载,并可发挥体外预应力筋在使用阶段易于检测与更换的优点。但在预应力筋混合配索中,不同的配索方案会导致体内体外预应力的布置和用量存在差异,也决定桥梁的应力状态。本文以实际工程为背景,以体内索承担施工阶段荷载,体外索承担二期恒载和使用荷载为原则,完成了施工过程中的不同配索优化,重点介绍了不同体内预应力索的设置方案,以及相应的体外预应力索的设计,确定了最终的桥梁设计方案与桥梁应力状态。相关设计过程可为类似混合配索的预应力连续梁或连续刚构桥提供参考。     

缓黏结预应力混凝土梁耐久性能试验研究#br#

为研究缓黏结预应力混凝土梁在长期荷载与腐蚀共同作用下的耐久性能,文章进行了14根缓黏结预应力混凝土梁及普通混凝土梁在荷载与氯盐干湿循环共同作用下的侵蚀试验,总结了荷载比、预应力度、干湿循环时间对不同受力部位的氯离子浓度沿深度分布和钢筋锈蚀的影响规律,以及荷载比和干湿循环时间对氯离子输运速度的影响规律。结果表明：在混凝土梁中施加预应力能有效减缓氯离子的渗透速度,增强构件的抗氯盐腐蚀能力;相同深度处的氯离子浓度随荷载比的增大而增大、干湿循环时间的增加而增大、与跨中距离的减小而增大;缓黏结预应力混凝土氯离子扩散系数与荷载比之间呈指数函数关系;荷载作用加速了钢筋锈蚀的进程;在裂缝控制等级相同的情况下,承担更大荷载比的缓黏结预应力混凝土梁的钢筋锈蚀程度与无预应力梁相当,体现出更佳的耐久性能。     

Transient high-temperature stress relaxation of prestressing tendons in unbonded construction

Unbonded post-tensioned (UPT) flat plate concrete slabs are popular for modern continuous multiple bay floor assemblies due to economic and sustainability benefits (reductions in slab thickness and building self-weight) and structural advantages (decreased deflections over larger spans). Only limited research has been conducted on the performance of UPT flat plate slabs under fire conditions, yet the inherent fire endurance of these systems is sometimes quoted as a benefit of this type of construction. One concern for these structures in fire is that high-temperature stress relaxation of the unbonded prestressed reinforcement may cause considerable and irrecoverable prestress loss, with subsequent structural consequences. This paper uses a computational model which has been developed to predict the transient high-temperature stress relaxation (i.e., prestress loss) for typical UPT multiple span flat plate slabs in fire, to study the potential prestress relaxation behaviour under various plausible temperature conditions as might occur during exposure to a standard fire. The model is validated using experimental data from relaxation tests performed on locally heated unbonded seven-wire prestressing stand. The initial prestress level, concrete cover to the prestressed reinforcement, and ratio of heated length to overall tendon length are varied to investigate the potential implications for prestress loss, and subsequently for flexural and punching shear capacity. The results highlight the need for particular care in the construction of UPT slabs to ensure adequate concrete cover for structural fire safety.     

Experiments on the residual load-bearing capacity of prestressed confined concrete columns

This paper is an experimental study of the prestressed external confinement (as opposed to the unstressed external confinement) of concrete compression members as a means of influencing load-deformation behaviour and residual capacity. Residual capacity is understood to be the load which can be absorbed in the event of ineffective or removed external confinement by a column which has previously been subjected to high loading in a confined state. The prestress and tensile stiffness of the confinement, as well as the loads on the confined system, were systematically varied in order to evaluate influences on residual capacity. 45 cylindrical confined specimens, as well as reference specimens, were subjected to concentric and eccentric, single and cyclic loading. The experiments confirmed the beneficial influence of confinement prestressing on concrete residual capacity. Prestressed confinement proved to be particularly effective in the case of cyclic loading and low confinement modulus, especially when compared to the unstressed variant. Analysis of the experimental results goes on to show that safety considerations are indispensable in the case of ineffective unstressed external confinement.     

索-混凝土板预应力组合网架可靠度分析

文章将网架上弦用混凝土板代替、下弦用拉索代替并施加预应力,形成索-混凝土板预应力组合网架。利用ANSYS有限元软件建立该结构的模型,分别分析其基于结构最大位移和腹杆最大应力两种性能下的正常使用极限可靠度,其中建立模型时将结构离散成板单元、梁单元、杆单元和索单元,各单元之间通过节点彼此相连。经软件分析得出在所给几何尺寸、材料特性、预应力、恒荷载以及活荷载等随机变量作用下,结构分别基于位移和腹杆应力正常使用极限状态下的可靠度都是良好的;对结构位移和腹杆应力影响最大的变量都是荷载,影响最小的变量都是混凝土板厚度以及肋的厚度与宽度;预应力荷载和外荷载对结构位移和腹杆应力起相反的影响作用。     

大直径无粘结预应力钢套筒混凝土涵管的试验研究

通过试验,对无粘结预应力张拉施工中混凝土内钢绞线的应力、预应力损失和混凝土管壁中的应力分布,以及充水条件下混凝土管壁中的应力分布等问题进行了研究。试验结果表明,一端张拉时,预应力筋单圈布置管的预应力损失小于双圈布置管;预应力张拉完毕后,混凝土管环向形成闭合的压应力环,有效地提高了混凝土涵管的抗裂能力;张拉后管壁的抗拉强度远大于1.0MPa水压所产生的拉应力。     

基于储煤筒仓结构中无粘结预应力技术的应用

以山西某煤矿储煤筒仓为例,介绍了无粘结预应力在储煤筒仓结构中的设计方案,从预应力材料控制、无粘结筋的铺设、张拉端预埋处理等方面阐述了无粘结预应力技术在储煤筒仓结构中的施工控制措施,以保证储煤筒仓的安全性和可靠性。     

Teilsicherheitsfaktoren für die Berechnung von Großkraftwerken

Die Baustrukturen von Großkraftwerken werden in Deutschland u. a. auf Basis der VGB‐Richtlinie R 602 U berechnet und bemessen. In dieser Richtlinie sind unter Berücksichtigung der Besonderheiten des Großkraftwerksbaus Einwirkungen und Teilsicherheitsfaktoren definiert. Während die Lasten auf diese Randbedingungen abgestimmt wurden, hat man die Teilsicherheitsfaktoren auf der Lastseite aus der DIN 1055‐100 entnommen und lediglich die Kombinationsbeiwerte angepasst. Diese Sicherheitsbeiwerte tragen jedoch den speziellen Randbedingungen eines Kraftwerks oder Schwerindustriebaus nur bedingt Rechnung. Im Rahmen des Beitrags werden die Teilsicherheitsbeiwerte auf der Einwirkungsseite – insbesondere für das Konstruktionseigengewicht – für die Bemessung von Stahlbetonteilen vor diesem Hintergrund kritisch diskutiert und ein optimierter, wissenschaftlich abgesicherter Vorschlag unterbreitet. Partial Safety Factors for the Design of Power Plants In Germany power plants are designed in accordance to VGB regulation R 602 U. In this code load actions and partial safety factors are applied taking the special characteristics of power plants into consideration. The actions are defined regarding these circumstances, however the safety coefficients are assumed according to DIN 1055‐100 and only the combination coefficients are adjusted. However it has to be recognized that the partial safety factors in DIN 1055‐100 are calibrated for building constructions and thus do not consider the specialities of power plants in an adequate manner. In this paper the partial safety factors for the design of power plants and other heavy industry buildings are discussed for structural concrete elements and a scientific based optimized approach for the safety factor for dead load is presented.     

三类简支梁非线性有限元分析

利用ANSYS软件对三类不同情况的简支梁进行了非线性有限元分析,介绍了有限元模型在预应力阶段、开裂和达到极限时的形态。通过有限元分析可以看出施加体外预应力后无缝梁与带缝梁承载能力都得到了提高,可见施加体外预应力来提高梁的承载能力是一种切实可行的加固措施。