FRP-混凝土界面模型及其应用

纤维增强复合材料FRP(Fiber Reinforced Polymer)已广泛应用于混凝土及其它结构的加固。从上世纪90年代初到现在,这项技术主要应用于结构抵抗静载、疲劳荷载和地震荷载的加固中,最新的研究开始涉及用外贴FRP加固技术增强结构抵抗爆炸和冲击荷载的能力。FRP与混凝土粘结界面是FRP加固混凝土结构中的薄弱环节。由FRP混凝土界面的粘结强度所决定的FRP有效应力是评价不同荷载条件下FRP加固效果的关键指标。本文对目前已有静/动态荷载条件下的FRP混凝土界面模型及其在数值分析中的应用进行了分类和总结。     

FRP加固钢筋混凝土柱经历模拟地震作用后的残余性能试验研究

本文对8根大比例的FRP加固钢筋混凝土桥柱模型在轴压比为0.2的恒定轴压力下进行拟静力试验,再对其中5根试验柱在经历有限的地震作用后进行长期荷载作用下的轴压试验。试验表明,FRP加固柱的徐变变形远小于对比柱的徐变变形;带损伤的加固柱在长期荷载作用下的变形发展受加固柱的损伤程度和持荷大小的控制,并与FRP的弹性模量有关;在试验条件下,带损伤的加固柱长期轴向变形呈稳定态势。采用AEMM和F ind ley模型为基础,考虑损伤程度、密封状态、三向应力状态和应力重分布等因素的影响,建立了损伤加固柱的徐变计算模型,并进行了验证。分析表明,损伤对加固柱的徐变发展和徐变破坏时限有显著影响。     

FRP混凝土结构研究进展

为解决钢筋混凝土结构中钢筋锈蚀的问题,建议将纤维增强复合材料(FRP)掺入混凝土中制成FRP混凝土,使FRP具有的轻质高强、耐腐蚀和耐疲劳等优良性能应用于混凝土结构修复加固工程中。从应力—应变关系、长期荷载下性能和抗震性能等方面阐述FRP约束混凝土力学性能在国内外的研究进展,从设计方法、计算模型和动力特性等方面分析了FRP约束混凝土研究中亟待解决的问题,为FRP修复加固混凝土结构的科学研究与工程应用提供了参考意见。     

盐溶液干湿交替作用下FRP加固梁长期挠度研究

通过5根试件研究盐溶液干湿交替作用下纤维增强聚合物（FRP）加固钢筋混凝土梁的长期变形性能,持载水平为未加固梁极限荷载的30%或60%,FRP种类考虑CFRP和GFRP,盐溶液干湿交替天数为360 d,分析不同持载水平、FRP种类对加固梁长期挠度、裂缝宽度等影响规律。试验结果表明：加固梁前期挠度增长较快,后期趋于稳定;其长期挠度随荷载水平的增加而增大;CFRP加固梁长期挠度小于GFRP加固梁;持载水平为60%极限荷载的CFRP加固梁裂缝宽度总体小于GFRP加固梁;基于试验结果,考虑盐溶液干湿交替作用对FRP材料性能的影响,给出了FRP加固混凝土梁长期挠度计算方法,其计算值与试验值吻合较好。     

FRP加固砖砌体的抗剪承载力研究

为了研究纤维增强复合材料(FRP)加固后砖砌体的抗剪承载力,对1片未加固带壁柱墙体及8片FRP加固的带壁柱墙体进行了抗震性能试验;在FRP与砖界面黏结-滑移本构关系基础上,考虑FRP与墙体的界面剥离,将界面黏结力转化为桁架模型中的拉力,并考虑FRP的直接加固作用与间接加固作用.建立了FRP加固砖砌体抗剪承载力的理论计算模型.结果表明:该模型所得结果与试验结果及其他研究结果吻合较好,且可以很好地计算FRP加固后砖砌体的抗剪承载力.     

FRP网格约束混凝土圆柱的抗震性能

对纤维增强聚合物(FRP)网格约束混凝土圆柱进行了轴压荷载试验;给出了FRP网格侧向约束强度和侧向约束刚度计算公式及FRP网格约束混凝土圆柱的应力-应变关系模型确定方法.在此基础上,进一步完成了FRP网格加固钢筋混凝土圆柱在低周反复荷载作用下的试验,重点探讨了FRP网格加固用量及FRP网格中纵筋是否锚入柱底座对试件承载力和变形能力的影响.结果表明,FRP网格约束后混凝土圆柱的强度和延性有明显提高,约束后的应力-应变关系曲线有无软化段主要与FRP约束量有关,FRP网格加固能明显提高钢筋混凝土结构的承载力和延性等抗震性能.     

FRP加固钢筋混凝土受弯构件裂缝计算模式

本文主要讨论了外贴FRP加固钢筋混凝土梁的开裂性能,对我国现行钢筋混凝土设计规范GB50010-2002中的裂缝计算公式进行了适当的修正,提出了适用于加固构件的裂缝计算模型,该模型考虑了钢筋—混凝土和FRP—混凝土界面间粘结力的影响。文中对裂缝间距和裂缝宽度的模型预测结果和试验结果进行了比较,对比结果表明文中提出的计算模型是合理的。     

地震荷载作用下FRP用量对加固RC圆柱变形能力影响研究

纤维增强复合材料(FRP)加固钢筋混凝土(RC)圆柱可以有效提高其抗震性能。本文研究地震荷载作用下FRP用量对加固圆柱变形能力的影响。运用数值计算方法对加固柱截面曲率进行计算,发现FRP用量对屈服曲率影响很小,但对极限曲率有显著的影响。试验结果显示,加固柱顶点侧向位移角并不随FRP加固用量的增加一直增加,当FRP用量达到一定值后进一步增加会降低侧向位移角。理论分析表明,这是由于加固柱塑性铰长度也受FRP用量的影响,随着FRP用量的增加塑性铰长度变小。最后讨论了具有良好加固效果的FRP用量上限范围。     

FRP-ECC加固钢筋混凝土梁受弯性能研究

桥梁、房屋服役时间过长,通过加固的方式可以提高建筑使用寿命。文中使用FRP-ECC复合材料对钢筋混凝土梁进行加固,通过有限元分析未加固梁和FRP的配筋率为0.94%、1.41%的加固梁,有限元分析结果与试验结果吻合较好,验证有限元模型准确性。拓展0%、1.67%、1.88%和2.51%FRP配筋率的加固效果。得到FRP-ECC加固梁的屈服荷载与极限荷载以及相应位移。FRP-ECC复合材料加固效果要明显优于仅使用ECC材料加固,FRP-ECC加固梁屈服荷载比控制梁提高18.4%～27.7%,FRP配筋率对屈服荷载影响不明显。FRP-ECC加固梁的极限抗弯承载力比控制梁提高27.4%～59.6%,FRP配筋率为1.41%、1.67%、1.88%和2.51%加固梁极限抗弯承载力比FRP配筋率为0.91%加固梁分别提高7.5%、13.3%、19.0%和25.2%。提出FRP-ECC加固梁抗弯承载力计算方法,与有限元模拟结果相差-5.0%～0.2%,可为FRP-ECC加固结构工程应用提供参考。     

FRP-ECC加固钢筋混凝土梁受弯性能研究

桥梁、房屋服役时间过长,通过加固的方式可以提高建筑使用寿命。文中使用FRP-ECC复合材料对钢筋混凝土梁进行加固,通过有限元分析未加固梁和FRP的配筋率为0.94%、1.41%的加固梁,有限元分析结果与试验结果吻合较好,验证有限元模型准确性。拓展0%、1.67%、1.88%和2.51%FRP配筋率的加固效果。得到FRP-ECC加固梁的屈服荷载与极限荷载以及相应位移。FRP-ECC复合材料加固效果要明显优于仅使用ECC材料加固,FRP-ECC加固梁屈服荷载比控制梁提高18.4%～27.7%,FRP配筋率对屈服荷载影响不明显。FRP-ECC加固梁的极限抗弯承载力比控制梁提高27.4%～59.6%,FRP配筋率为1.41%、1.67%、1.88%和2.51%加固梁极限抗弯承载力比FRP配筋率为0.91%加固梁分别提高7.5%、13.3%、19.0%和25.2%。提出FRP-ECC加固梁抗弯承载力计算方法,与有限元模拟结果相差-5.0%～0.2%,可为FRP-ECC加固结构工程应用提供参考。     

FEA on bearing behavior of cuplok scaffold based on tri-linear semi-rigid joint model

利用三折线半刚性节点模型,结合碗扣式脚手架竖向承载力足尺试验,对碗扣式脚手架的竖向失稳问题进行了有限元模拟、结果对比和性能分析。模拟中重点考虑碗扣节点的材料非线性和构件的初始几何非线性。结果表明,三折线半刚性节点模型精度可靠,适用于碗扣式脚手架的精细化数值模拟。此外,对影响碗扣式脚手架受力性能的因素进行了研究,包括底端边界条件、碗扣式半刚性节点初始刚度和伸长段长度。研究发现：以上因素对碗扣式脚手架受力性能有不同程度影响,中间立杆离地对承载力影响较大,承载力随碗扣节点初始刚度增大而增大并呈现三段式变化,承载力随伸长段长度增大而减小并呈现两段变化。     

A numerical model of fully grouted bolts considering the tri-linear shear bond–slip model

A numerical model of fully grouted bolts is proposed in this study by implementing the tri-linear bond–slip relationship of bolts into the numerical framework presented by Hyett et al. (1996). The bond–slip relationship of bolt–rock interface is simplified and represented by the tri-linear model. The proposed numerical model is characterized by (1) its ability in modeling decoupling mechanism of bolt–rock interface, i.e. the degradation of the interfacial shear bond stress along bolts; (2) its easy implementation in a numerical code. The proposed numerical model is verified with the pullout tests, and good agreements with the experimental results can be observed in terms of axial stress distributions in the bolt, shear stress distributions along the bolt and load–displacement relationship. The proposed model also gives a reasonable prediction on the behavior of bolts installed in the field.     

上海浦东国际机场T2航站楼静力弹塑性分析

上海浦东国际机场T2航站楼结构为复杂大跨混合结构,采用NosaCAD2005有限元程序建立其结构分析模型.模型主要由非线性杆单元组成,包括梁、柱和二力杆单元,梁、柱采用三段变刚度杆模型,以受弯为主的梁单元截面弯矩-曲率关系采用二折线和三折线模型,柱和二力杆截面采用纤维模型.参照试验所得参数,选用模态和均匀加速度组合惯性力加栽方式进行了弹塑性推覆分析,研究了该结构的变形、内力、破坏情况的发展历程,对该结构的抗震性能进行了评价.     

新型组合结构梁柱节点滞回性能试验研究

为研究新型组合梁与钢管混凝土柱连接节点的抗震性能,开展了新型组合梁与钢管混凝土柱连接节点低周反复荷载作用下的试验研究,对这种类型节点的滞回性能进行了研究,在实验研究的基础上,提出了新型组合梁与钢管混凝土柱连接节点的三折线恢复力模型,结果表明,试件具有良好的耗能能力,建立的恢复力模型骨架曲线与试验值接近。     

A new analytical solution to the mechanical behaviour of fully grouted rockbolts subjected to pull-out tests

A new analytical approach able to predict the mechanical behaviour of fully grouted rockbolts subjected to pull-out tests is proposed in this paper. Input parameters of such approach are: bolt radius, bolt’s Young modulus, displacement of the free end of the bolt and the constitutive law of the rockbolt–grout joint interface. The limited circumstances under which it is accurate to determine such constitutive law from pull-out tests are also presented. A solution for the load–displacement curve obtained during pull-out tests has been developed and is detailed in the case of a tri-linear bond-slip model. Comparison with experimental results obtained via in situ pull-out tests has led to the validation of this approach.     

Simplified nonlinear progressive collapse analysis of welded steel moment frames

In this study, two nonlinear analysis methods are proposed that can be used for a simplified but accurate evaluation of progressive collapse potential in welded steel moment frames. To this end, the load-resisting mechanism of the column-removed double-span beams in welded steel moment frames was first investigated based on material and geometric nonlinear parametric finite element analysis. A simplified tri-linear model for the vertical resistance versus chord rotation relationship of the double-span beams was developed. The application of the developed model to energy-based nonlinear static progressive collapse analysis was then proposed. The relationship between the gravity loading and the maximum dynamic chord rotation or the concept of collapse spectrum was also established for a quick assessment of the maximum deformation demands.     

An analytical analysis of the full-range behaviour of grouted rockbolts based on a tri-linear bond-slip model

This paper presents an analytical solution for predicting the full-range mechanical behaviour of grouted rockbolts in tension based on a realistic tri-linear bond-slip model with residual bond strength at the grout–bolt interface. The full-range behaviour consists of five consecutive stages: elastic stage, elastic–softening stage, elastic–softening–debonding stage, softening–debonding stage and debonding stage. For each stage, closed-form solutions for the load–displacement relationship, interfacial shear stress distribution and bolt axial stress distribution along the bond length were derived. The ultimate load and the effective anchor length were also obtained. The analytical model was calibrated and validated against two pullout experimental studies. The predicted load–displacement curves as well as the distributions of the interfacial shear stress and the bolt axial stress are in close agreement with test results. A parametric study is also presented, providing insights into the behaviour of the rockbolts.     

Size-independent fracture energy in plain concrete beams using tri-linear model

The boundary effect or the size effect on the fracture properties of concrete has been studied assuming a bi-linear model for the distribution of local fracture energy concept. Boundary effect is observed not only near the back boundary but also near the notch tip, where a fictitious boundary seems to exist, separating the linear and non-linear fracture zones. In this paper a tri-linear function is assumed for the local fracture energy distribution along the ligament and expressions relating RILEM fracture energy and the size-independent fracture energy are developed. Transition ligament length measurements based on the acoustic emission (AE) histogram of events are used to obtain size-independent fracture energy. Length of the fracture process zone is identified in the AE histogram and compared with the value obtained from softening beam model. There seems to be a good agreement between the results.     

基于有效惯性矩的预应力混凝土梁的挠度计算

针对预应力混凝土梁计算所存在的问题,推导了基于有效惯性矩法的挠度计算公式,并编制了Matlab程序对公式中参数进行研究,通过与试验结果进行对比,发现该公式能较好地模拟预应力混凝土梁的三折线荷载挠度曲线,弥补了规范公式的不足.     

空间结构半刚性C型节点优化及转动性能试验研究

提出了一种新型空间半刚性C型节点。为使该节点具有较好的转动能力及耗能能力,基于“强节点、弱构件”的抗震基本原则,提出了“强连接、弱板件”的空间半刚性节点。首先根据规范及理论分析初步确定节点各组件的合理尺寸;然后运用ABAQUS有限元软件建立非线性有限元模型,对节点各组件的尺寸进行优化,确定合理的组件尺寸。通过有限元分析和试验对该节点的性能进行研究。结果表明：该空间半刚性C型节点在弯矩荷载作用下表现出了较好的受弯承载能力和延性;节点刚度及承载力均随锥头侧连接板厚度、前端板厚度的增加而增大。节点锥头部分的材料本构模型选取对有限元分析结果的影响显著,采用三折线模型模拟所得结果更为精确。