受腐蚀钢筋混凝土构件破坏过程的分形行为

本文根据试验资料，分析了受腐蚀钢筋混凝土构件在荷载作用下开裂及裂纹的演化、分布特性，证明了受腐蚀钢筋混凝土构件表面裂缝具有分形特征。利用分形几何学研究受腐蚀钢筋混凝土构件开裂及破坏过程,讨论了受腐蚀钢筋混凝土构件表面裂缝的分维数与构件中混凝土及钢筋的腐蚀损伤程度之间的关系及其延性系数降低量之间的关系。研究表明该分维数可作为构件受腐蚀程度的衡量指标,并可用来评估不同腐蚀程度钢筋混凝土构件的力学性能，从而为受腐蚀钢筋混凝土构件的剩余寿命评价提供了一个新的途径,为受腐蚀钢筋混凝土结构的承载力研究建立了一定的理论基础。     

CFRP筋增强ECC梁弯曲性能试验研究

为研究碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)筋/超高韧性纤维增强水泥基复合材料(Engineered cementitious composite,ECC)梁的抗弯性能,对3根CFRP筋/ECC梁、1根玻璃纤维增强树脂复合材料(Glass fiber reinforced polymer,GFRP)筋/梁和1根CFRP筋混凝土梁进行了四点弯曲试验,分析了配筋率、纤维增强树脂复合材料(Fiber reinforced polymer,FRP)筋类型和基体类型对梁抗弯性能的影响。试验结果表明:CFRP筋/ECC梁与GFRP筋/ECC梁和CFRP筋混凝土梁类似,均经历了弹性阶段、带裂缝工作阶段和破坏阶段;配筋率对CFRP筋/ECC梁的受弯性能影响较大。随着配筋率的增加,CFRP筋/ECC梁的承载能力不断提高,延性性能逐渐减弱;ECC材料优异的应变硬化能力和受压延性,使得CFRP筋/ECC梁的极限承载能力和变形能力均优于CFRP筋混凝土梁;由于ECC材料多裂缝开裂能力,CFRP筋/ECC梁开裂后,纵筋表面应变分布比CFRP筋混凝土梁更均匀; 由于聚乙烯醇(Polyvinyl alcohol,PVA)纤维的桥联作用,CFRP筋/ECC梁破坏时,其表面出现了大量的细密裂缝,且能保持较好的完整性和自复位能力;正常使用阶段,CFRP筋/ECC梁的最大弯曲裂缝宽度均小于CFRP筋混凝土梁。最后,根据试验结果,建立了基于等效应力图的CFRP筋/ECC梁弯曲承载力简化计算模型,确定模型中的相关系数。由简化模型计算的极限承载力与试验结果具有较好的相关性。      

CFRP加固火灾作用后圆钢管混凝土构件的侧向撞击性能研究

建立了火灾作用后和碳纤维增强复合材料(CFRP)加固受火后圆钢管混凝土构件的侧向撞击数值模型,通过不同试验分别验证了模型的准确性。分析了加固受火后构件的撞击全过程,对比了构件的撞击力、跨中挠度和截面弯矩。对构件的抗撞击承载力和抗弯承载力,塑性变形和吸能能力,以及内力分布与发展进行了分析,并给出构件在撞击荷载作用下跨中最大挠度简化计算公式,最后讨论了CFRP加固方式对受火后构件撞击性能的影响。结果表明:采用CFRP加固受火后构件的撞击力平台值和平均截面弯矩提高,跨中挠度和撞击持续时间明显减小,CFRP加固对构件的抗撞击性能和抗弯能力提升显著;构件的抗撞击承载力、抗弯承载力和吸能能力随着受火时间的增加逐渐降低;构件在跨中产生不同程度的塑性变形,其主要通过形成塑性铰吸收能量;在峰值阶段构件的弯矩和剪力分布形态与相应静态荷载作用时差异明显,但在平台阶段时其分布形态与静态荷载作用时一致;简化计算公式可以很好地计算构件撞击后的跨中最大挠度,CFRP加固方式对受火后构件的抗撞击性能影响明显。     

二次受力下自密实混凝土加固RC梁受弯性能研究

为模拟实际工程中加固构件的真实承载能力,实验在原混凝土构件持续受荷状态下,采用自密实混凝土对构件进行加固、养护。共进行了7根二次受力下自密实混凝土加固钢筋混凝土梁和2根对比梁的受弯性能试验,研究了不同初始受力水平、不同加固厚度及不同界面处理方式对加固钢筋混凝土梁抗弯承载力和截面刚度的影响。试验量测了构件裂缝分布形态、荷载-挠度曲线、钢筋应变发展规律等。结果表明:采用自密实混凝土加固钢筋混凝土梁,能有效地提高钢筋混凝土梁的抗弯承载力、截面刚度等性能;二次受力下自密实混凝土加固梁抗弯承载力随着初始受力水平的增大而降低。在试验结果的基础上,基于平截面假定,提出了二次受力下自密实混凝土加固梁钢筋滞后应变及抗弯承载力计算式,计算结果与试验结果吻合良好。     

冲击作用下CFRP修复损伤RC叠合梁动力性能试验研究

采用落锤冲击试验机,进行了现浇梁、叠合梁以及碳纤维增强复合材料(carbon fiber reinforced polymer,CFRP)修复的损伤梁的动力性能对比试验。冲击作用下试件破坏形态以及冲击力与变形时程曲线表明,叠合面在一定程度上抑制了跨中裂缝向上开展的趋势,损伤修复后的叠合梁在冲击荷载下的破坏程度明显减轻,初始损伤减弱了梁跨中位移的滞后现象;相比完好梁,现浇与叠合修复梁抗冲击承载力有着同等程度的提高。基于有效应变计算的修复梁承载能力提升与试验结果的对比显示,CFRP能有效改善并增强构件的整体受力性能,在冲击作用下对构件的实际抗力贡献大于原有构件承载力与FRP受拉能力简单叠加时的理论抗力贡献。     

模拟酸沉降环境混凝土梁承载性能研究

酸雨环境下钢筋混凝土梁力学性能的变化规律是揭示整个结构承载力和耐久性的前提和基础。参考我国典型城市酸雨的化学组成,分别配置PH1.5与PH2.5的硫酸、硝酸混合溶液来模拟不同酸度的酸雨;自行设计制作了人工降雨器模拟降雨;浇筑了11根120mm×200mm×1900mm的钢筋混凝土梁。分别采用完全浸泡、干湿交替、人工降雨等加速腐蚀试验方法,对10根钢筋混凝土梁进行加速腐蚀。对不同浓度溶液下经历不同腐蚀时间的钢筋混凝土梁,分别利用超声方法测试了混凝土损伤厚度和抗压强度,利用动力试验方法评价混凝土梁的整体特性,并对梁的抗弯性能进行了抗弯实验研究。得到了不同侵蚀状态混凝土梁混凝土损伤厚度、构件刚度、构件开裂荷载、极限承载等力学性能;对比分析了不同加速腐蚀条件下混凝土梁抗弯性能的退化规律,得到了混凝土强度、构件频率以及抗弯强度与混凝土梁损伤程度之间的定量关系。研究结果表明:人工降雨与干湿交替两种方法对混凝土梁抗弯性能的影响基本相似,较浸泡方法变化得到的混凝土梁抗弯性能的退化性能更为显著。     

CFRP布加固方案对RC梁剪切性能及尺寸效应影响分析EI北大核心CSCD

采用同时考虑混凝土材料非均质性、钢筋与混凝土之间的相互作用以及CFRP布与混凝土之间的相互作用影响的三维细观数值模拟方法,建立了CFRP布加固RC梁剪切破坏力学分析模型。在验证了细观数值方法合理性的基础上,设计并建立了12根CFRP布加固RC梁细观模型,探究相同CFRP配纤率(用布量)前提下,不同CFRP布加固方案对单调荷载作用下RC梁的剪切性能及尺寸效应的影响。结果表明:CFRP布应变分布与裂缝位置紧密相关,越靠近裂缝位置的CFRP布应变越大,提供的抗剪贡献越多;在CFRP配纤率一致的前提下,CFRP布宽度大厚度小的加固方案优于CFRP布厚度大宽度小的加固方案;CFRP布U型加固RC梁剪切强度存在尺寸效应现象,但相同CFRP配纤率下,不同CFRP布加固方案对名义抗剪强度尺寸效应的影响较小,可以忽略。     

高延性混凝土加固钢筋混凝土梁抗震性能试验研究

为研究高延性混凝土(HDC)加固钢筋混凝土(RC)梁的抗震性能,设计了8个RC梁试件,采用HDC和碳纤维布(CFRP)条带加固,通过低周反复荷载试验,研究剪跨比、加固方式对其破坏形态、变形和耗能能力等的影响。试验结果表明:采用HDC围套加固RC梁,HDC面层良好的拉伸应变硬化和多裂缝开展特性能有效控制剪切裂缝发展,明显改善构件的脆性破坏特征;HDC加固层与原构件协同工作良好,加固层对内部混凝土形成良好的约束作用,HDC加固梁的承载力、变形和耗能能力明显提高,其加固效果明显优于CFRP条带加固;剪跨比较大时,在HDC加固层配置钢筋网,试件的变形和耗能能力明显提高,但对承载力贡献较小。基于桁架-拱模型理论,提出HDC加固梁的抗剪承载力计算方法,计算结果与试验值吻合较好。     

CFRP布端绕双杆自锁加固混凝土窄梁抗弯试验

为了抵抗粘贴碳纤维增强聚合物基复合材料（CFRP）加固钢筋混凝土结构中常见的剥离破坏,发明了将CFRP布端部以特定方式绕平行双杆实现自锁的方法。鉴于窄梁截面宽度有限,提出将CFRP布贴梁受拉底面布置后,用安装在梁侧面的双L形端锚装置固定双杆,形成侧锚底贴加固方案。完成了5根混凝土强度较低的矩形截面梁四点弯曲试验,其中4根采用上述锚固方式抗弯加固,检验了锚固效果,考察了CFRP布宽度及其沿全长与梁底面是否粘结对加固效果的影响。试验结果表明,采用本文方法进行加固后,端部剥离得以避免,中部剥离即使发生,或在无粘结加固梁受力后期,CFRP布仍能承担较大拉力,因此,极限荷载较对比梁有明显提高。比较而言,CFRP布与梁底有粘结时加固效果更好,CFRP布宽度加大也对提高承载力有益。     

预应力型钢超高强混凝土梁抗弯性能试验研究

预应力型钢超高强混凝土梁是融合了超高强混凝土材料、钢结构和预应力技术所形成的一种新型组合构件。为了研究预应力型钢超高强混凝土梁的抗弯性能,进行了14根预应力型钢超高强混凝土简支梁在竖向静力荷载作用下的受弯性能试验,分析了试件受力过程、破坏形态、裂缝开展与分布规律等相关试验数据。结果表明:超高强混凝土脆性破坏显著,导致预应力型钢超高强混凝土梁极限状态后承载力骤降,但内置型钢有效提高了试验梁极限状态后的持载能力;预应力型钢超高强混凝土梁以普通受拉纵筋屈服作为试验梁进入屈服阶段的标志,以受压区混凝土崩裂作为试验梁达到极限状态的标志;荷载达到0.9t up之前,试验梁跨中控制截面基本符合平截面假定。在不考虑型钢与混凝土粘结滑移的基础上,采用ANSYS有限元程序对预应力型钢超高强混凝土梁进行数值模拟计算,试验梁开裂荷载、屈服荷载以及极限荷载的计算值与试验值吻合较好,验证了有限元模型的正确性。     

Optimal efficiency factor in strut-and-tie model for FRP-reinforced concrete short beams with (1.5 < <Emphasis Type="Italic">a/d </Emphasis>< 2.5)

A new model for the efficiency factor of the concrete strut in the strut-and-tie model is proposed in this study for FRP-reinforced concrete short beams with (1.5 < a/d < 2.5). The ultimate load capacity of tested FRP-reinforced short beams was evaluated using the proposed model along with other models for the efficiency factor used in strut-and-tie models of design codes such as the ACI, CSA, and AS3600. It was found that efficiency factor models used in existing reinforced concrete design codes do not predict the ultimate load capacity of FRP-reinforced short beams as accurately as they do for steel-reinforced short beams. This can be attributed to not accounting for the effect of the shear span to effective depth ratio, a/d and the axial stiffness of the flexural reinforcement on the efficiency factor of the concrete strut in reinforced concrete short beams. Ultimate shear load capacity predictions by the proposed model were in agreement with experimental data obtained on 15 GFRP and CFRP-reinforced concrete short beams tested in the laboratory. The proposed model for the efficiency factor was shown to be statistically more accurate yielding the lowest standard deviation and coefficient of variation compared to those of the ACI, AS3600, and CSA A23.3 models. It was also found that shear equations recommended for FRP-RC beams by design guidelines such as the CSA S806-02, ISIS, JSCE, and ISE render very conservative predictions of the ultimate load capacity of FRP-reinforced short beams.     

Response of steel fiber reinforced high strength concrete beams: Experiments and code predictions

The shear-flexure response of steel fiber reinforced concrete (SFRC) beams was investigated.Thirty-six reinforced concrete beams with and without conventional shear reinforcement (stirrups) were tested under a four-point bending configuration to study the effectiveness of steel fibers on shear and flexural strengths, failure mechanisms, crack control, and ductility.The major factors considered were compressive strength (normal strength and high strength concrete up to 100 MPa), shear span-effective depth ratio (a/d = 1.5, 2.5, 3.5), and web reinforcement (none, stirrups and/or steel fibers).The response of RC beams was evaluated based on the results of crack patterns, load at first cracking, ultimate shear capacity, and failure modes.The experimental evidence showed that the addition of steel fibers improves the mechanical response, i.e., flexural and shear strengths and the ductility of the flexural members.Finally, the most recent code-based shear resistance predictions for SFRC beams were considered to discuss their reliability with respect to the experimental findings. The crack pattern predictions are also reviewed based on the major factors that affect the results.     

锈胀钢筋混凝土拱肋承载力试验与模拟

为研究锈胀损伤对钢筋混凝土拱肋极限承载力的影响,制作了4片钢筋混凝土圆弧拱肋,通过电化学快速锈蚀使其表面产生不同程度的锈胀裂缝,讨论了初始锈胀裂缝的分布情况,研究了锈胀拱肋的裂缝发展、不同位置处位移和应变、极限承载力及失效模式。试验结果表明:锈胀削弱了混凝土截面尺寸和刚度,降低了钢筋与混凝土间的粘结性,是承载力退化的主要原因之一;锈胀导致的拱肋极限承载力下降率约为60%;锈胀未改变拱肋的失效模式,所有拱肋均在一侧拱脚发生脆性破坏。在试验的基础上,建立了锈胀钢筋混凝土拱肋的有限元计算模型,由于RC拱肋存在大面积锈胀,模型中未考虑混凝土保护层的影响,计算结果和试验值较为接近,为日后有限元建模提供一定参考。     

Flexural strengthening of concrete beams with CFRP laminates bonded into slits

Near surface mounted (NSM) strengthening technique using carbon fibre reinforced polymer (CFRP) laminate strips was applied for doubling the load carrying capacity of concrete beams failing in bending. This objective was attained and the deformational capacity of the strengthened beams was similar to the corresponding reference beams. The NSM technique has provided a significant increment of the load at serviceability limit state, as well as, the stiffness after concrete cracking. The maximum strain in the CFRP laminates has attained values between 62% and 91% of its ultimate strain. A numerical strategy was developed to simulate the deformational behaviour of RC beams strengthened by NSM technique. Not only the load carrying capacity of the tested beams was well predicted, but also the corresponding deflection.     

Flexural strength and cracking behavior of hybrid strength concrete beams

The flexural and cracking behavior of hybrid strength concrete beams cast with two concrete compressive strengths of 20 and 70 MPa were compared with 20 MPa normal and 70 MPa high strength beams. The hybrid beams showed an improvement in the load carrying capacity at cracking, yielding and ultimate loading as compared to normal strength beams. The increase in load carrying capacity was (1.80–70.8%) higher than normal strength beams and only (3.3–9.8%) lower than corresponding high compressive strength beams. Also from experimental results the crack spacing of hybrid beams were between those of normal strength and high strength beams, but the crack width in the hybrid beams were narrower than both types of beams at all loading stages. At service and ultimate loading stages, the crack width in the hybrid beams were 19.5–26.0% narrower than those of corresponding normal strength beams, and 9.2–15.1% narrower than high strength beams.     

Effect of steel and synthetic fibers on flexural behavior of high-strength concrete beams reinforced with FRP bars

Six high-strength concrete beam specimens reinforced with fiber-reinforced polymer (FRP) bars were constructed and tested. Three of the beams were reinforced with carbon FRP (CFRP) bars and the other three beams were reinforced with glass FRP (GFRP) bars as flexural reinforcements. Steel fibers and polyolefin synthetic fibers were used as reinforcing discrete fibers. An investigation was performed on the influence of the addition of fibers on load-carrying capacity, cracking response, and ductility. In addition, the test results were compared with the predictions for the ultimate flexural moment. The addition of fibers increased the first-cracking load, ultimate flexural strength, and ductility, and also mitigated the large crack width of the FRP bar-reinforced concrete beams.     

钢板混凝土复合梁在爆炸荷载作用下的损伤评估研究

为满足钢板混凝土复合梁爆炸损伤评估的实际需要,完成了钢板混凝土复合梁与钢筋混凝土梁承载性能的比较试验,研究了两种梁的承载性能与破坏特点,获得了二者的抗力试验曲线、抗弯变形限值及抗力函数。基于钢板混凝土复合梁的等效单自由度运动方程,采用数值求解方法,得出了评估其在爆炸荷载作用下破坏状态的超压-冲量（P-I）等损伤曲线。研究结果表明：钢板混凝土复合梁的承载力、变形限值、临界超压以及临界冲量比钢筋混凝土梁的都要高,前者的抗爆性能更好。