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1.
因混凝土收缩与徐变引起的预应力损失在总损失中占的比重很大,我国规范中对这部分损失的求解给出了经验公式,本文提出了分段逼近法可求解先张法预应力混凝土轴心受拉构件,任一时间因收缩和徐变引起的预应力损失,并同时考虑了非预应力筋的影响;方法中,把总时间分段,各时段中设应力为常数,求解各时段因收缩和徐变引起的预应力损失,再叠加求总损失,这样,可求出预应力损失较精确值,混凝土收缩与徐变求解采用了作者导出的一组公式。/ 相似文献
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预应力混凝土桥梁徐变分析的全量形式自动递进法 总被引:8,自引:3,他引:5
首先将预应力混凝土桥梁中考虑收缩、徐变影响的任意时刻混凝土应力、应变关系在持荷时段内写成代数形式,引入内力平衡方程及变形协调条件后,提出了计入截面上钢筋位置、配筋率、预应力钢筋松弛、混凝土弹性模量随时间变化等影响的徐变效应分析的全量形式自动递进法,并建立了计算式,适用于任何形式的收缩、徐变特性表达式;基于建立的全量形式公式,可方便地求解任意时刻混凝土、钢筋的应力与应变和梁体竖向变形。理论分析与试验结果比较表明,公式可方便地控制计算精度,直至给出满意的结果。将计算式编程后极易与目前桥梁设计中常用的杆系有限元软件接口,进行可靠的徐变分析。 相似文献
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与部分预应力混凝土梁相比,全预应力混凝土梁全截面受压且压应力较高,由于混凝土收缩徐变产生的梁长期变形也更大。该文从按龄期调整的有效模量法出发,将梁沿长度方向细分单元,细分单元长度为截面高度的1倍~2倍,锁定单元节点,分别计算混凝土的收缩、徐变以及预应力筋的松驰对其产生的强迫力值;释放强迫力,并将其反向作用于节点上,求出此时的截面时随应变和附加曲率,进而推导出可用于求解任意时刻的全预应力混凝土梁长期变形的计算公式。基于该课题组和其他研究者试验结果,对该文及国内外规范的计算公式进行了对比分析,结果表明:该文公式计算值与试验结果吻合良好;国内外规范计算值与试验结果的平均误差则明显偏大,且计算结果偏于不安全。 相似文献
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预应力组合梁桥的时效分析 总被引:1,自引:0,他引:1
本文根据组合梁桥的施工过程,采用按龄期调整的有效模量,结合有限单元步进法,对组合梁的时效行为进行了分析探讨,并编制了相应的计算程序,在程序中考虑了单元的分层建造,张拉预应力筋,结构体系转换,施工外荷载的影响以及各节段混凝土龄期的不同所导致的收缩,徐变差异,可以计算组合梁结构从施工到成桥这一整个过程中任一时刻的截面应力与变形,还可预测成桥后若干年收缩,徐变引起的组合截面应力与变形的变化,文末以一座两 相似文献
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无粘结预应力高性能粉煤灰混凝土桥梁收缩与徐变变形试验研究 总被引:4,自引:0,他引:4
结合洛湛线的建设,以8根不同掺量的高性能粉煤灰混凝土无粘结预应力桥梁的收缩、徐变试验为基础,研究了不同掺量高性能粉煤灰混凝土在荷载长期作用下收缩、徐变性能及其上拱随时间的变化规律,探讨了温度、湿度等环境因素对不同掺量高性能粉煤灰混凝土收缩、徐变的影响。300多天的实验观测结果表明:高性能粉煤灰掺量20%~40%混凝土梁不但具有良好的工作性能和力学性能,而且长期性能良好,与同强度的未掺高性能粉煤灰的梁相比,其后期强度和抗压弹性模量增大,收缩徐变减小,具有良好的社会和经济效益。 相似文献
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预应力混凝土桥梁时变效应分析的钢筋约束影响系数法 总被引:1,自引:0,他引:1
系统地提出了预应力混凝土桥梁结构中钢筋对徐变和收缩时变效应的约束影响系数的概念,并给出了影响系数的计算公式,籍此提出了时变效应分析的钢筋约束影响系数法,建立了一套理论公式,可计算时变的钢筋和混凝土应力、应变及梁体竖向变形。不仅适用于静定桥梁结构,亦适用于超静定桥梁结构,可计算时变结构内力重分布。计算式物理意义明确,使用方便;理论分析与试验结果比较表明,公式具有较高的计算精度。 相似文献
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本文应用三维空间有限元单元法,结合斜桥桥的实际施工过程,同时考虑斜拉桥的缆索垂度效应,梁柱效应,结构大位移效应,以及混凝土收缩徐变,预应力及其损失,施工中结构体系转换等各种因素的影响,编制了大跨度预应力混凝土斜拉桥的空间非线性分析软件,并提供了前后处理功能,可以结合拉桥的实际施工过程,很方便地跟踪分析各种方法施工的预应力斜拉桥从施工开始到成桥这一整个过程任一时刻的内力变形。 相似文献
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预应力混凝土斜拉桥的时效行为分析 总被引:3,自引:0,他引:3
就预应力混凝土斜拉桥而言,无论其施工方法如何,其在施工到成桥的过程中,结构的几何特性,材料特性,承受的荷载等均随时间的推移而不断的变化,混凝土的收缩徐变必将影响到结构的内力和变形,因此对混凝土斜拉桥进行有效分析以了解其在施工中及成桥后真实的内力和变形是非常必要的,本文根据斜拉桥的结构特点编制了斜拉桥时效分析软件,并运用该软件,对某一预应力混凝土斜拉桥的时效行为和进行了分析。 相似文献
11.
L. J. van der Meer D. R. W. Martens A. T. Vermeltfoort 《Materials and Structures》2013,46(12):2091-2108
Data on creep and shrinkage of high-strength calcium silicate element masonry with thin-layer mortar (CASIEL-TLM masonry) is not currently available in international literature. A novel application of this material in unbonded post-tensioned shear walls requires creep and shrinkage data to predict prestress loss. Therefore, creep and shrinkage were measured on 38 large-scale high-strength CASIEL-TLM specimens, including a TLM bed joint or a wall-floor connection, for a period of 300 days. Initial moisture content of the specimens and temperature and relative humidity of the environment were carefully controlled. Creep and shrinkage data were used to predict prestress loss by means of visco-elastic finite element simulations as well as a simple analytical expression. These predictions were validated by prestress loss experiments, conducted simultaneously with the creep and shrinkage experiments. Predictions for final prestress loss due to creep and shrinkage are below 16 or 24 % for CASIEL-TLM masonry with prestressing strands or prestressing bars respectively. 相似文献
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S. Benyoucef A. Tounsi K. H. Benrahou E. A. Adda Bedia 《Mechanics of Time-Dependent Materials》2007,11(3-4):231-248
External bonding of fibre reinforced polymer (FRP) composites has becomes a popular technique for strengthening concrete structures
all over the world. An important failure mode of such strengthened members is the debonding of the FRP plate from the concrete
due to high interfacial stresses near the plate ends. For correctly installed FRP plate, failure will occur within the concrete.
Accurate predictions of the interfacial stresses are prerequisite for designing against debonding failures. In particular,
the interfacial stresses between a beam and soffit plate within the linear elastic range have been addressed by numerous analytical
investigations. In this study, the time-dependent behavior of RC beams bonded with thin composite plate was investigated theoretically
by including the effect of the adherend shear deformations. The time effects considered here are those that arise from shrinkage
and creep deformations of the concrete. This paper presents an analytical model for the interfacial stresses between RC beam
and a thin FRP plate bonded to its soffit. The influence of creep and shrinkage effect relative to the time of the casting
and the time of the loading of the beams is taken into account. Numerical results from the present analysis are presented
to illustrate the significance of time-dependent of adhesive stresses. 相似文献
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钢骨混凝土柱结构在过去几十年间已得到广泛的运用。但是目前关于这种柱结构在长期荷载作用下由于徐变和收缩引起的与时间相关的力学性能研究还开展得很少。该文开展了钢骨混凝土短柱的长期轴向荷载试验研究,还进行了这些柱的极限承载力破坏试验。试验监测了由徐变和收缩引起的柱的轴向长期变形。基于该实测曲线的分析表明,采用ACI 209R-92的收缩模型和CEB-FIP90的徐变模型,利用龄期调整有效模量法可以较好地模拟钢骨混凝土柱在长期轴向荷载作用下的变形发展。经历了长期加载后的试验柱的极限承载力破坏试验还表明,长期轴向荷载对柱的轴压承载力没有显著影响。 相似文献
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钢管混凝土小偏心受压构件的徐变分析 总被引:8,自引:1,他引:7
通过对钢管混凝土偏心受压构件的受力特性进行分析,结合核心混凝土的徐变特点,采用继效流动理论及多轴应力状态下混凝土的徐变理论,构造了计算钢管混凝土偏心受压构件徐变的计算方法。此方法较为合理地考虑了多轴应力状态下核心混凝土的特点及钢管混凝土构件徐变的影响因素(如含钢率、材料等级、应力级别等),并引入迭代来计算构件的徐变。计算算例结果与试验结果的对比表明:本文所提出的方法理论可靠、合理。 相似文献
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K. Balaji Rao M. B. Anoop P. Sreeshylam S. Sridhar K. Kesavan K. Ravisankar 《Strain》2011,47(Z1):e175-e188
Abstract: In this study, stochastic analyses of pre‐stress losses in two pre‐stressed concrete beams are carried out, and the results of the analyses are compared with those obtained from the laboratory experimental investigations. The deterministic models given in ACI 209 (with modelling error) are used for predicting the pre‐stress losses. The compressive strength of concrete, water–cement ratio, coarse aggregate–cement ratio, fine aggregate–cement ratio, cement content, initial stress in steel and relative humidity are considered as random variables. Monte Carlo simulation technique is used to determine the statistical properties of pre‐stress losses at different times. From the results obtained, it is noted that while the relaxation strain can be assumed to follow a normal distribution, the frequency distributions of creep and shrinkage strains are not uni‐modal. A relation for estimating total losses is also proposed in the article. The stochastic analysis approach presented in the article would be useful in the assessment of pre‐stress losses in existing pre‐stressed concrete members in a more rational way. 相似文献
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Darius Bacinskas Gintaris Kaklauskas Viktor Gribniak Wen-Pei Sung Ming-Hsiang Shih 《Mechanics of Time-Dependent Materials》2012,16(2):117-127
A numerical technique has been proposed for the long-term deformation analysis of reinforced concrete members subjected to
a bending moment. The technique based on the layer approach in a simple and rational way deals with such complex issues as concrete cracking and tension-stiffening as well
as creep and shrinkage. The approach uses the material stress-strain relationships for compressive concrete, cracked tensile
concrete and steel. Such effects as linear and nonlinear creep, cracking, tension-stiffening as well as the reduction in concrete
tension strength due to sustained loading have been taken into account. The shrinkage effect has been modeled by means of
adequate actions of axial force and bending moment. A statistical deflection calculation analysis has been carried out for
322 experimental reinforced concrete beams reported in the literature. The comparative analysis of the experimental and the
modeling results has shown that the proposed technique has well captured the time-deflection behavior of reinforced concrete
flexural members. The results of the predictions by ACI 318 and Eurocode 2 design codes have been also discussed. 相似文献
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Creep and drying shrinkage characteristics of concrete produced with coarse recycled concrete aggregate 总被引:1,自引:0,他引:1
Gholamreza Fathifazl A. Ghani Razaqpur O. Burkan Isgor Abdelgadir Abbas Benoit Fournier Simon Foo 《Cement and Concrete Composites》2011,33(10):1026-1037
Laboratory tests are performed to investigate the effects of a new method of mixture proportioning on the creep and shrinkage characteristics of concrete made with recycled concrete aggregate (RCA). In this method, RCA is treated as a two component composite material consisting of residual mortar and natural aggregate; accordingly, when proportioning the concrete mixture, the relative amount and properties of each component are individually considered. The test variables include the mixture proportioning method, and the aggregate type. The results show that the amounts of creep and shrinkage in concretes made with coarse RCA, and proportioned by the new method, are comparable to, or even lower than, those in similar concretes made entirely with natural aggregates. Furthermore, it is demonstrated that by applying the proposed “residual mortar factor” to the existing ACI and CEB methods for calculating creep or shrinkage of conventional concrete, these methods could be also applied to predict the creep and shrinkage of RCA-concrete. 相似文献