钢纤维砼受弯构件荷载-变形全过程分析

通过对钢纤维砼单向拉仲与单向压缩应力-应变全曲线的试验,配筋钢纤维砼受弯构件荷载-变形试验及其全过程分析,本文提出了钢纤维砼的本构方程及其力学模式。并根据精确的计算结果,给出了便于设计的参数取值。理论计算与实验结果符合较好。     

高强凝灰岩轻骨料砼的特性

本文研究了利用约旦东北部的天然凝灰岩作骨料生产高强轻质砼的可能性。用标准的试验方法,根据不同砼配合比的试验结果,获得了高质量的轻质砼。九十天的抗压强度高达60MPa。为了研究这类高强砼的短期力学性能,对不同形状和尺寸的大量试件在不同龄期下进行了试验。所得到的性能包括容重、泊松比、静弹性模量、试件形状和尺寸的影响、抗压强度随龄期的变化以及不同养护条件下的劈拉强度和断裂模数。     

关于预应力砼空心板设计中几个问题的探讨

本文主要对预应力空心板(短向板)的抗裂度实际值皆高于规范允许值的原因进行了研究与分析,并根据冷轧带肋钢筋配筋的预应力空心板的受力特征与试验结果,提出了采用小直径、分散配筋的预应力砼空心板在计算抗裂度时,引入受拉区砼塑化能力系数C值的新概念,以使设计计算结果更能符合实际情况,从而可以减少预应力砼空心板的用钢量,具有较好的经济效益。此外本文还提出了预应力砼空心板在自重下挠度计算的新方法。     

陶粒砼剪力墙的试验研究

本文介绍8片陶粒砼剪力墙试件与4片普通砼剪力墙试件的对比试验研究结果,讨论了在低周反复荷载下单肢剪力墙的破坏形态、变形能力、构件延性,斜截面抗剪强度及水平和竖向分布钢筋的配筋构造等,证实了在低轴压比下的陶粒砼剪力墙可以满足延性要求,最后对轻砼剪力墙斜截面承载力计算与其配筋构造提出了一些设计建议。     

受弯构件砼强度等级的优选

一、从槽形板说起 图一为一预制槽形板横截面,换算为等效T形截面如图二所示;计算跨度L_0=3.84m,两纵助内各配φ12受拉钢筋一根,砼保护层厚度C=15mm,采用C20、C25、C30三种强度等级砼制成的板,能承受的弯矩值如表1所示: 不同强度等级砼槽板斜截面的受剪承载     

部分预备力砼结构的模糊优化设计

1、部分预应力砼结构的模糊优化数学模型: 在部分预应力砼结构设计中,设计约束条件有:强度约束、最小配筋约束、抗裂约束以及施工放张时的强度约束等等。     

高强轻砼的力学性能

本文论述了容重为1865kg/m~3、强度达100兆帕的高强轻砼的力学性能。我们研究了五种不同的轻集料,看来轻集料的强度是控制高强轻砼的强度之主要因素。高强轻砼的拉一压强度比率低于普通的高强砼,而弹性模量(等于17.8～25.9千兆帕)则比普通砼低得多。高强轻砼的峰值荷载时的极限应变为3.3～4.6mm/m,大于普通砼。高强轻砼的应力一应变曲线之上升部分之形状,比中,低强轻砼更加趋近于线性。原文为“mm/mm”,应为“mm/m”之误——译者注。     

粗骨料对高性能混凝土抗压强度的影响

抗压强度为３０ＭＰａ的砼中，砼受压破坏时粗骨料是完整的没受到破坏。而高性能砼则由于砼强度比较高，砼破坏时粗骨料几乎完全断裂破坏。本文对不同品种的粗骨料在砼中的体积含量、最大粒径对砼强度的影响进行了试验，并根据试验结果得到了数学模型，用以评价不同品种粗骨料的性能     

三向受拉及二拉一压状态下钢纤维砼的变形及强度特性

利用自制的砼三轴试验系统，对钢纤维砼在两拉一压及三拉应力状态下的变形及强度特性进行了试验研究。试件尺寸为１５ｃｍ×１５ｃｍ×１５ｃｍ和１０ｃｍ×１０ｃｍ×１０ｃｍ两种。在试验基础上分析了钢纤维砼应力一应变关系曲线的特点，计算了极限强度值，讨论了在两拉一压及三拉应力状态下不同应力比时钢纤维砼的抗拉、抗压强度的变化规律。     

一步法计算钢筋砼受弯构件的配筋As及ρ,ξ值

根据钢筋砼矩形截面单筋受弯构件正截面受拉钢筋的计算方式,推导出不同标号砼不同的等级钢筋的配筋公式,给出ＣＡＳＩＯｆｘ－１８０Ｐ计算器计算程序。     

High Strength Polypropylene Fibre Reinforcement Concrete at High Temperature

Concrete is an inherently brittle material with a relatively low tensile strength compared to compressive strength. Reinforcement with randomly distributed short fibres presents an effective approach to the stabilization of the crack and improving the ductility and tensile strength of concrete. A variety of fibre types, including steel, synthetics, and natural fibres, have been applied to concrete. Polypropylene (PP) fibre reinforcement is considered to be an effective method for improving the shrinkage cracking characteristics, toughness, and impact resistance of concrete materials. Also, the use of PP fibre has been recommended by all of the researchers to reduce and eliminate the risk of the explosive spalling in high strength concrete at elevated temperatures. In this study, constitutive relationships are developed for normal and high-strength PP fibre reinforcement concrete (PPFRC) subjected to high temperatures to provide efficient modelling and specify the fire-performance criteria for concrete structures. They are developed for unconfined PPFRC specimens that include compressive and tensile strengths, elastic modulus, modulus of rupture, strain at peak stress as well as compressive stress–strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results. These results are used to establish more accurate and general compressive stress–strain relationships prediction. Further experimental results for tension and the other main parameters at elevated temperature are needed in order to establish well-founded models and to improve the proposed constitutive relationships, which are general, rational, and fit well with the experimental results.     

Constitutive Relationships for Steel Fibre Reinforced Concrete at Elevated Temperatures

Steel fibre reinforced concrete (SFRC) is an advanced cementitious composite where fibres can act as a profitable replacement for diffused reinforcement, like welded steel mesh, especially for thin cross sections. In this case fire becomes a very important condition in the design. Previous experimental research has shown the benefits in fire resistance of steel fibres, when structural elements are bent. The proper understanding of the effects of elevated temperatures on the properties of SFRC is necessary. In this study, constitutive relationships are developed for high-strength FRSC subjected to fire, with the purpose of given that capable modelling and to specify the fire-performance criteria for concrete structures. They are developed for unconfined FRSC specimens that include compressive and tensile strengths, modulus of elasticity, modulus of rupture, strain at peak stress, and compressive stress–strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results. These results are used to establish compressive stress–strain relationships. Further experimental results for tension and the other main parameters at elevated temperature are needed in order to establish well-founded models and to improve the proposed constitutive relationships, which are general, rational, and fit well with the experimental results.     

锈蚀后钢纤维和钢纤维混凝土的力学性能

通过对剪切型、铣削型、切断型3种钢纤维和钢纤维混凝土的快速锈蚀试验,研究了锈蚀前后钢纤维的外观、弯折性能和抗拉强度的变化,以及钢纤维混凝土经过不同锈蚀时间后的抗压强度和抗拉强度的变化规律.结果表明:随锈蚀时间的增加,钢纤维的锈蚀程度逐渐增大,弯折性能和抗拉强度逐渐降低,钢纤维混凝土的抗压强度和抗拉强度随之减小.但是抗压强度和抗拉强度的变化规律有所不同,当锈蚀时间较短时,抗压强度变化不明显,在锈蚀时间超过60d以后,抗压强度显著降低.而抗拉强度随锈蚀时间的增加逐渐下降.锈蚀时间相同时,抗拉强度的降低幅度比抗压强度的降低幅度小.切断型钢纤维的抗锈蚀能力相对较好,剪切型和铣削型钢纤维的抗锈蚀能力相对较差.     

钢筋混凝土剪力墙轴拉试验和轴拉刚度理论分析

文章完成截面纵筋率为17%、25%的钢筋混凝土剪力墙轴拉试验。试验结果表明：剪力墙轴拉刚度在混凝土开裂前由钢筋和混凝土共同提供,并随轴拉力的增加逐渐下降;在混凝土开裂时轴拉刚度迅速下降;在开裂后混凝土退出工作,轴拉刚度逐渐趋于截面纵筋刚度。基于试验结果,完成剪力墙的轴拉受力特性和刚度变化特征的理论分析,提出能够描述钢筋混凝土剪力墙轴拉刚度变化特征的二阶段计算方法：在混凝土开裂前及开裂时根据混凝土本构模型获得的受拉弹性模量进行计算,在开裂后则引入纵向受拉钢筋应变不均匀系数进行计算。由此得到的理论值与试验结果更为吻合,更能反映剪力墙在轴拉阶段的受力和刚度变化特征。     

GFRP筋活性粉末混凝土梁受力性能试验研究

为了研究GFRP筋活性粉末混凝土梁的受力性能,对8根梁进行三分点加载试验,获得了试验梁的开裂弯矩、极限弯矩以及各级荷载作用下的变形及裂缝分布与开展。试验结果表明：活性粉末混凝土试验梁纯弯区段开裂应变 (750×10-6) 约为普通混凝土梁的7倍,开裂弯矩及截面塑性系数计算应考虑纵向受拉GFRP筋的有利影响。GFRP筋活性粉末混凝土梁正截面受弯破坏形式可分为纵向受拉GFRP筋被拉断而受压边缘活性粉末混凝土未被压碎的受拉破坏,受压边缘活性粉末混凝土被压碎(5500×10-6)而纵向受拉GFRP筋未被拉断的受压破坏,以及纵向受拉GFRP筋被拉断的同时受压边缘活性粉末混凝土被压碎的界限破坏等三种。对于受压破坏可按拉区应力为0.25倍活性粉末混凝土抗拉强度来考虑拉应力对正截面受弯承载力的贡献。对于受拉破坏则基于材料应力-应变关系通过数值积分迭代计算正截面受弯承载力。刚度及裂缝宽度计算的关键是合理计算使用阶段GFRP筋的拉应力,在计算GFRP筋拉应力时所用弯矩应为外荷载弯矩减去拉区活性粉末混凝土拉应力合力对压区合力点的弯矩。图9表12参10     

不同FRP增强混凝土梁断裂性能试验研究

为了探讨不同种类纤维增强复合材料（FRP）增强带裂缝混凝土的断裂性能,开展了芳纶纤维增强复合材料（AFRP）、碳纤维增强复合材料（CFRP）和玻璃纤维增强复合材料（GFRP）增强带裂缝混凝土梁的三点弯曲试验,分析了其断裂性能参数.结果表明：相对于普通混凝土梁试件,FRP对带裂缝混凝土梁的阻裂加固效果更明显;CFRP增强混凝土梁的起裂荷载和失稳荷载均大于AFRP与GFRP增强混凝土梁,CFRP的阻裂增强效果最佳;AFRP增强混凝土梁和CFRP增强混凝土梁的破坏形式均为试件底部混凝土 FRP界面的剥离破坏,GFRP增强混凝土梁的破坏形式为试件底部GFRP的拉断破坏;通过对不同FRP增强混凝土梁阻裂加固机理的分析,计算得出CFRP增强混凝土梁的起裂韧度和失稳韧度最大,且CFRP价格适中,因此使用CFRP对带裂缝混凝土梁进行增强加固的性价比最优.     

Upper and lower bounds for structural design of RC members with ductile response

In the present paper, some of the complex phenomena characterizing the flexural behaviour of reinforced concrete beams, such as hyper-strength and snap-back and snap-through instabilities, are interpreted under a unified approach based on nonlinear fracture mechanics concepts. In particular, they are analysed by means of a numerical algorithm adopting the cohesive crack model for concrete in tension and the overlapping crack model for concrete in compression. According to the latter constitutive law, a fictitious interpenetration is assumed to describe the concrete damage, analogously to the fictitious crack opening used for tension.Such an integrated cohesive-overlapping crack model is applied to assess the minimum reinforcement amount necessary to prevent unstable tensile crack propagation and to evaluate the rotational capacity of plastic hinges. The main novelty is given by the capability to predict the size-scale effects evidenced by several experimental programmes available in the literature. According to the numerical results obtained, new practical design formulae and diagrams are proposed, as well as, upper and lower bounds to the reinforcement amount, the material properties and the structural dimensions are defined in order to avoid brittle failures.     

Tension stiffening model for nonlinear analysis of GFRP-RC members

An analytical approach is presented to capture the tension stiffening effect of reinforced concrete member subjected to tensileforces. In this model, the tensile stiffening is described through an analytical relationship of stress–strain law in the cracking range which differs from the CEB-tension stiffening model that is based on the stress–strain curve of reinforcing bars using a bi-linear relationship. The bi-linear relation does not quite capture the post-cracking behaviour of reinforced concrete structures. In view of this, a parabolic branch is selected in the post-cracking phase possessing as asymptotic line to the stress–strain line of the bare bar that minimises the tension stiffening effect at the ultimate load level. This assumption is taken into account in view of material nonlinearities, the bond character and the tension stiffening effect. Analytical results are obtained and compared with experimental data for direct tensile load. In general, the computed results agree well with experimental results. Moreover, the effects of concrete strength, reinforcement ratio and bar diameter on tension stiffening are studied.     

采用ANSYS分析FRP约束素混凝土方柱强度

在试验的基础上,采用ANSYS对BFRP约束素混凝土方柱强度对加固效果的影响作了研究,并将ANSYS分析得出的强度与试验结果进行了比较。分析结果表明:通过合理选择有限元分析数值模型,可较好地预测纤维布加固混凝土柱的轴心受压性能,且分析所得强度与试验吻合良好。     

复杂动荷载作用下全级配混凝土损伤机理细观数值试验

提出了一种适用于复杂应力状态下的双折线弹性损伤模型,对混凝土试件进行了轴向拉压细观数值模拟试验,同时探讨了复杂应力状态下混凝土损伤破坏机理。然后基于实际工程采用的混凝土细观动态参数试验实测值,利用细观数值模型对循环荷载作用下全级配大坝混凝土试件进行了弯折损伤破坏模拟。其数值计算结果与材料试验测的数据吻合较好,进一步验证了在循环动荷载作用下预静载对动弯拉强度也存在强化现象。本文轴向拉压细观数值模拟试验表明,细观界面黏结强度是控制混凝土宏观抗压强度和宏观抗拉强度的关键参数,而黏结面泊松比的大小对混凝土宏观抗压强度影响很大。这个研究结果表明,混凝土材料受拉破坏机制与剪切破坏机制在本质上可统一为受拉破坏机制。