使用加固纤维聚合物增强混凝土梁的延性（适用于毕业论文 中英文对照）

1、 使用加固纤维聚合物增强混凝土梁的延性作者Nabil F Grace George Abel-Sayed Wael F Ragheb摘要一种为加强结构延性的新型单轴柔软加强质地的聚合物 FRP 已在被研究开发和生产 在结构测试的中心在劳伦斯技术大学 这种织物是两种碳纤维和一种玻璃纤维的混合物而且经过设计它们在受拉屈服时应变值较低从而体现出伪延性的性能通过对八根混凝土梁在弯曲荷载作用下的加固和检测对研制中的织物的效果和延性进行了研究用现在常用的单向碳纤维薄片织物和板进行加固的相似梁也进行了检测以便同用研制中的织物加固梁进行性能上的比较这种织物经过设计具有和加固梁中的钢筋同时屈服的潜力从而和未加固

2、梁一样它也能得到屈服台阶相对于那些用现在常用的碳纤维加固体系进行加固的梁这种研制中的织物加固的梁承受更高的屈服荷载并且有更高的延性指标这种研制中的织物对加固机制体现出更大的贡献关键词混凝土延性纤维加固变形介绍外贴粘合纤维增强聚合物FRP片和条带近来已经被确定是一种对钢筋混凝土结构进行修复和加固的有效手段关于应用外贴粘合FRP板薄片和织物对混凝土梁进行变形加固的钢筋混凝土梁的性能一些试验研究调查已经进行过报告Saadatmanesh和Ehsani1991检测了应用玻璃纤维增强聚合物 GFRP 板进行变形加固的钢筋混凝土梁的性能Ritchie等人1991检测了应用GFRP碳纤维增强聚合物CFRP和

3、GCFRP板进行变形加固的钢筋混凝土梁的性能Grace等人1999和Triantafillou1992研究了应用CFRP薄片进行变形加固的钢筋混凝土梁的性能NorrisSaadatmanesh和Ehsani1997研究了应用单向CFRP薄片和CFRP织物进行加固的混凝土梁的性能在所有的这些研究中加固的梁比未加固的梁承受更高的极限荷载这些梁中大多数出现的一个缺陷是梁的延性有很大的损失然而通过对梁的荷载-挠度性能的测试可以发现大多数荷载的增加是在钢筋屈服后发生的也就是说极限荷载明显提高然而屈服荷载却没有太大提高因此在正常使用水平荷载的明显增加很难实现除去加固前混凝土构件条件的影响钢筋对加固梁的弯曲

4、反应有明显的贡献而可惜的是现有的FRP加固材料和钢材性能不同虽然FRP有很高的强度但是它们多数在提高足够的强度之前被拉伸而产生很大的应变因为同大多数FRP材料的极限应变相比钢材的屈服应变相对较低所以随着加固构件的变形钢材和FRP加固材料的贡献发生了变化结果钢筋可能会在加固构件取得任何可测荷载增加值之前就屈服了一些研究者在横截面布置了更强的FRP这通常会增加加固的成本进而提供可测的贡献尽管这时变形是受限制的在钢筋屈服之前但是加固材料从混凝土表面的剥落更多的时候是由于应力集中的原因发生的剥落是这项加固技术中不出现的一种脆性破坏尽管使用一些类似超高模量碳纤维的特别的低应变纤维看起来是一种解决方法但这

5、可能导致由于纤维破坏而产生脆性破坏本文旨在介绍一种新型伪延性FRP织物它在屈服时应变低从而具有与钢筋同时屈服的潜力能够实现期望中的加固水准研究意义FRP已经被越来越多地用做钢筋混凝土结构修复和加固的材料但是现在常用的FRP材料缺少延性并且与钢筋性能不一致结果经过加固处理的梁会体现出延性降低不能达到期待中的水平或者二者兼有本项研究介绍了一种新型的伪延性FRP加固织物这种织物可以使加固梁承受更高的屈服荷载并且有助于避免延性的损失而这在使用目前常用的FRP进行加固中是常见的混杂织物的研制为了克服前面所提的缺陷一种具有低屈服应变值的延性FRP材料是很必要的混杂的文献回顾为了研制这种材料考虑了各种不同纤

6、维的混杂多于一种纤维材料的混杂是许多材料科学研究的兴趣所在他们的工作多数集中于结合两种纤维以提高每种材料单独工作时的力学特性并且降低成本这已经在几本出版物中报道过例如Bunsel和Harris1974Philips1976Manders和Bader1981Chow和Kelly1980以及Fukuda和Chow1978做为一种能够克服FRP加固棒延性不足问题的工具混杂吸引了结构工程师NanniHenneke和Okamoto1994研究了用编织芳香尼龙纤维绕在钢筋核心的短棒Tamuzs和Tepfors报道了关于使用碳和芳香阻尼纤维进行组合而成的混合纤维棒的试验调查SomboonsongFrank和

7、Harris1998研制了一种用编织芳香尼龙纤维缠绕在碳纤维核心的混合FRP加固棒Harrissomboonsong和Frank1998使用这些棒对混凝土梁进行加固以得到用常规钢筋进行加固的混凝土梁的普通荷载-挠度特性设计思想和材料为了产生延性一种使用不同种类纤维的混杂技术已经被采用选用了在破坏时有不同延长量级的三种纤维图1显示了这些复合纤维在拉伸时的应力-应变曲线表1显示了它们的力学特性这项技术是建立在将这些纤维结合起来并控制配合比例的基础上的这样当它们被拉伸时共同承受荷载延伸小LE的纤维先破坏允许一定的应变松弛应变增加而混合材料的荷载却并未增加余下的延伸大HE的纤维被分配承担所有的荷载直到

8、破坏延伸小的纤维破坏时的应变值体现了混合材料屈服应变值而延伸大的纤维破坏时的应变值体现的是极限应变值延伸小的纤维破坏时对应的荷载体现的是屈服荷载值而延伸大的纤维承担的最大荷载体现的是极限荷载值超高模量碳纤维1号碳被用做延伸小的纤维它应有尽可能低的应变但不得小于钢筋的屈服应变60级钢筋大约为02另一方面型玻璃纤维被用做延伸大的纤维应能提供尽可能高的应变而产生高延性指标破坏时的变形和屈服时的变形的比例高模量碳纤维号碳被选做了延伸中等ME纤维它使在延伸小的纤维破坏后发生应变松弛时荷载的降低最小化并且能够提供从延伸小的纤维向延伸大的纤维逐渐传递荷载的途径基于这种思想生产了一种单向织物并进行了测试将它在

9、拉伸时的性能和理论预测的承载性能做了对比理论上的性能建立在混合物规则上根据这种规则混合物的轴向刚度是将各组成部分的相对刚度进行总合计算得到的这种织物的生产过程是将不同的纤维做为相邻的纱线结合起来并将它们用环氧树脂注入模具中图就是一个生产样品的照片编织而成的玻璃纤维片布置在试样的两端以消除测试中固定端的应力集中试样厚mm008in宽254mm1in在拉伸时根据美国材料实验协会3039规范进行测试四个测试样品的平均荷载-应变曲线见图3上面还有理论预测的曲线应该注意到直到应变值达到035荷载-应变性能都是线性的这时延伸小的纤维开始破坏在这一点上应变增长的速率高于荷载当应变值达到090时中等延伸的纤维

10、开始破坏导致应变有附加的增长直到由于延伸大的纤维破坏带来试样的彻底破坏可以测试到屈服荷载荷载-应变曲线上性能去不再为线性的第一点为046kNmm26kipsin极限荷载为078kNmm44kipsin梁的测试梁的详细情况一共浇筑了13根钢筋混凝土梁横截面尺寸为152254mm610in长2744mm108in梁的受弯钢筋由底部的两根5号16mm受拉钢筋和顶部的两根3号95mm的受压钢筋组成为防止发生剪切破坏使用162mm长的3号钢筋扎成闭合镫形对梁的抗剪进行进一步的加固有5根梁浇筑时角部做成半径25mm1in的圆角从而易于加固材料的安置图4显示了梁的尺度钢筋详图支座和加载点的位置使用的钢筋为6

11、0等级屈服强度415MPa800psi加固材料研制中的混合织物用于加固8根梁使用了两种不同厚度的织物第一种H体系t 10mm厚度10mm004in第二种H-体系t 15mm厚度15mm006in其他四根梁使用现在常用的碳纤维加固材料进行加固1一层单向碳纤维薄片极限荷载034kNmm195kipsin2两层单向碳纤维织物极限荷载131kNmm75kipsin3一层固体玻璃谈碳纤维板极限荷载为28kNmm16kipsin对这些材料测试得到的荷载-应变图见图5表2给出了包括研制中的织物在内的加固材料的特性粘结材料对这种混合织物使用一种环氧树脂环氧A注入纤维并做为织物和混凝土表面的粘结材料这种环氧材料

12、极限应变为44从而保证不至于在纤维破坏之前破坏对于使用碳纤维薄片板和织物加固的梁使用的是极限应变为20的环氧树脂环氧B由生产商提供的粘结材料的力学特性见表3加固在梁的底部和两侧喷砂以使其表面粗糙然后使用丙酮除去污物对梁进行清洁采用两种加固构造1只在梁底面布置加固材料A组梁2除对梁底部外在梁两侧各伸长152mm16in大概能覆盖住梁的受弯拉伸部分B组梁加固材料沿梁长度布置在中心长达224m88in环氧在对梁进行测试前要进行两周的养护对研制中的混合织物H-体系加固的梁制备了两根并对各种构造进行测试来证实结果表4对梁的检测进行了汇总仪器跨中FRP的应变通过布置在梁底面的三个应变片测量测量A组梁钢筋拉

13、伸应变是通过监控在梁的侧面与钢筋棒平行处测量点设置的DEMC可拆式机械计量器而B组梁使用的是应变片跨中挠度是通过使用串行电位计测量的使用液压器对梁加载荷载有一种荷载电池测量所有的传感器同数据采集系统相连以扫描并记录读数试验结果和讨论控制梁控制梁的屈服荷载823kN185kips极限荷载957kN215kips梁由于钢筋屈服而破坏随之跨中混凝土受压破坏控制梁的试验结果见加固梁的试验成果图上图6至15A组梁A组梁已在底面进行了加固图6至11显示了这些梁的试验结果H-50-1梁和H-75-1梁分别和H-50-2梁和H-75-2梁各自的结果非常接近因此关于这些梁的讨论就集中于后两者以避免重复梁的延性通

14、过计算延性指数来考察即计算破坏时与屈服时的挠度之比图6a显示了C-1梁的荷载-跨中挠度关系图C-1梁使用碳纤维薄片进行加固梁在荷载为859kN193kips时屈服在荷载为1019kN229kips时由于碳纤维薄片的开裂而破坏值得注意的是从这幅图中看来虽然有了延性性能但是同控制梁比起来屈服荷载只提高了4延性指数为215图6b显示了跨中荷载-碳纤维应变关系图图7a显示了C-2梁对应的荷载-挠度曲线这根梁使用固体玻璃碳纤维板进行加固它没有屈服台阶延性指数为1在荷载为1326kN298kips时由于板端部的受剪-受拉破坏而突然破坏尽管荷载提高了61但破坏仍是脆性的图7b显示了跨中荷载-碳纤维应变关系碳

15、纤维破坏时记录的最大应变为033这意味着板的承载力发挥了24C-3梁的荷载-挠度关系见图8a该梁由两层碳纤维织物加固它在荷载为1077kN242kips时屈服在荷载为1344kN3021kips时由于织物的剥落而破坏此时它并未如控制梁那样显示出任何明显的屈服台阶延性指数是164值得注意的是在图8b中破坏时记录到的碳纤维应变的最大值为067这意味着纤维承载力大约发挥了48图9a显示了H-50-2梁的荷载-挠度关系这根梁使用研制中的厚度为1mm厚的混合织物进行加固屈服荷载为979Kn220kips同控制梁比起来提高了19在图9b中值得注意的是当梁屈服时织物应变为040它的延性指数为233当荷载最终

16、达到1148kN258kips时由于织物的彻底开裂而破坏图9c即为破坏时的梁图10a显示了H-75-2梁的荷载-屈服关系这根梁使用厚度为15mm厚的研制中的混合织物它在荷载为1139kN256kips时屈服在1308kN294kips的极限荷载下由于织物剥落而导致彻底破坏之前体现出的延性指数为213值得注意的是尽管最终破坏是由于织物的剥落但这是在取得了令人满意的延性之后发生的从图10b中可见当梁屈服时的应变为035图10c是梁破坏时的照片图11和表5对A组梁的试验结果进行了比较可以观察出如下现象1C-1梁和H-50-2梁体现了较好的延性特征但是H-50-1梁比C-1梁体现了更高的屈服荷载这是因

17、为经过设计这种研制中的混合织物比碳纤维片有更高的初始刚度因此在钢筋屈服前它比碳纤维对加固的贡献更大2尽管碳纤维织物的极限荷载比15mm厚的混合织物屈服时对应的荷载大几倍但是直到屈服时H-75-2体现着和C-3相似的性能但是H-75-2梁有令人满意的屈服台阶而C-3梁却没有3相对于现在常用的碳纤维加固材料这种研制中的织物屈服时的应变和钢筋的屈服应变接近尽管仍然较高但是混合织物的应变值和梁屈服时的应变值接近这意味这它和钢筋同时屈服这一部分要归功于将植物安置在梁的外表面这样比安置在梁的内部要承受更大的拉应变结果织物的屈服应变设计值看起来是可以接受的4当使用有较高承载能力的碳纤维板正如在C-2梁中使用

18、的时能够提供高的破坏荷载同时也会产生脆性破坏B组梁这组梁除对梁底部外在梁两侧向上延伸152mm16in的范围也进行了加固改组试验结果见表5和图12至15H-S50-1梁和H-S75-1梁分别和H-S50-2梁和H-S75-2梁各自的结果非常接近因此关于这些梁的讨论就集中于后两者以避免重复图12a显示了CS梁的荷载-挠度关系这根梁是使用碳纤维薄片体系加固的它在荷载达到992kN223kips时由于钢筋的屈服而屈服屈服荷载增加了20梁在达到1233kN277kips的极限荷载时由于跨中混凝土的受压破坏而破坏从图12b可以看出当梁屈服时碳纤维的应变为035因此在这段承载阶段发挥了它的大约30的能力在

19、梁破坏之前记录到的最大应变为10取得的延性指数为204H-S50-2的试验结果见图13这根梁使用研制中的厚度为1mm厚的混合织物进行加固图13a显示了它的荷载-挠度曲线当荷载达到1139kN256kips时由于钢筋和织物的破坏梁发生破坏屈服荷载增加了38梁在达到1466kN329kips的极限荷载时由于混凝土的受压破坏而破坏延性指数为225图13b显示了跨中荷载和织物应变的关系梁屈服时记录到的应变值是035结论基于本研究所介绍的研究调查可以得出如下结论1目前常用的FRP材料作为弯曲加固体系用于混凝土结构并不能总是在加固梁中提供类似未加固梁的屈服时的屈服台阶在一些情况下加固可能导致加固梁的脆性破

20、坏或着是屈服荷载增加很不明显或者是二者兼有2选择的几种类型的纤维的混杂被用于研制伪延性的织物它在屈服时的应变低035经过设计这种织物具有同加固梁中的钢筋同时屈服的潜力3同那些应用碳纤维进行加固体系相比使用研制中的混合织物进行加固的梁通常会显示出在屈服荷载上有更高的增长有些用混合织物进行加固的梁会显示出类似未加固梁的屈服台阶这在结构破坏之前保证足够的警示作用是特别重要的4使用研制中的混合织物体系进行加固的梁并没有显示出明显的延性损失使用碳纤维加固的梁也没有明显的延性损失但是屈服荷载较低参考文献ASTM D 3039 2000 Standard Test Method for Tensile Pr

21、operties of Polymer Matrix Composite Materials Annual Book of ASTM Standards V 1503 pp 106-118Bunsell A R and Harris B 1974 Hybrid Carbon and Glass Fibre Composites Composites V 5 pp 157-164Chow T W and Kelly A 1980 Mechanical Properties of Composites Annual Review of Composite Science V 10 pp 229-2

22、59Fukuda H and Chow T W 1981 Monte Carlo Simulation of Strength of Hybrid Composites Journal of Composite Materials V 16 pp 371-385Grace N F Soliman K Abdel-Sayed G and Saleh K 1999Strengthening Reinforced Concrete Beams Using Fiber Reinforced Polymer CFRP Laminates Journal of Composites for Constru

23、ction ASCE V 2 No 4Harris H G Somboonsong W and Frank K K 1998 New Ductile Hybrid FRP Reinforcement Bar for Concrete Structures Journal of Composites for Construction ASCE V 2 No 1 pp 28-37Manders P W and Bader M G 1981 The Strength of Hybrid GlassCarbon Fibre Composites Part 1Failure Strain Enhance

24、ment and Failure Mode Journal of Materials Science V 16 pp 2233-2245Nanni A Henneke M J and Okamoto T 1994 Tensile Properties of Hybrid Rods for Concrete Reinforcement Construction and Building Materials V 8 No 1 pp 27-34Norris T Saadatmanesh H and Ehsani M R 1997 Shear and Flexure Strengthening of

25、RC Beams with Carbon Fiber Sheets Journa of Structural Engineering ASCE V 123 No 7 pp 903-911Philips L N 1976 The Hybrid EffectDoes it Exist Composites V 7 pp 7-8 Ritchie P A Thomas D A Lu L and Connelly G M 1991 External Reinforcement of Concrete Beams using Fiber Reinforced Plastics ACI Structural

26、 Journal V 88 No 4 July-Aug pp 490-500Saadatmanesh H and Ehsani M R 1991 RC Beams Strengthening with GFRP Plates I Experimental Study Journal of Structural Engineering ASCE V 117 No 11 pp 3417-3433Somboonsong W Frank K K and Harris H G 1998 Ductile Hybrid Fiber Reinforced Plastic Reinforcing ACI Mat

27、erials Journal V 95 No 6 Nov-Dec pp 655-666Tamuzs V and Tepfers R 1995 Ductility of Nonmetallic Hybrid Fiber Composite Reinforcement for Concrete Proceedings 2nd International RILEM Symposium FRPRCS-2 pp 18-25Triantafillou N P 1992 Strengthening of RC Beams with Epoxy-Bonded Fiber-Composite Material

28、s Materials and Structures V 25 pp 201-211附录表1 复合纤维的力学特性纤维材料描述弹性模量GPaMSi抗拉强度MPaksi表4 试验梁的汇总梁的组别梁的称号加固材料NA控制梁NAA组梁C-1碳纤维薄片C-2碳纤维板C-3碳纤维织物H-50-1H体系t 1mmH-50-2H-75-1H体系t 15mmH-75-2B组梁CS碳纤维薄片H-S50-1H体系t 1mmH-S50-2H-S75-1H体系t 15mmH-S75-2表5 试验结果汇总梁的名称加固体系屈服荷载kN kips屈服时的挠度mmin破坏时的荷载kNkips破坏时的挠度mmin 延性指数 第6

29、列第4列破坏时FRP的应变最终破坏类型控制梁NA823185140055957215495195355NA钢筋屈服后混凝土破坏C-1碳纤维薄片8591931320521019229284112215110钢筋屈服后FRP断裂C-2碳纤维板1326298160063100033剪切拉伸破坏C-3碳纤维织物10772421350531344302221087164067钢筋屈服后FRP剥落H-50-2H体系t 1mm979220152061148258356140233155钢筋和FRP屈服后FRP断裂H-75-2H体系t 15mm11392561370541308294292115213074钢

30、筋和FRP屈服后FRP剥落CS碳纤维薄片9922231420561233277ACI STRUCTURAL JOURNAL TECHNICAL PAPER Title no99-S71Strengthening of Concrete Beams Using Innovative Ductile Fiber-Reinforced Polymer FabricBy Nabil F Grace George Abel-Sayed Wael F RaghebabstractAn innovative uniaxial ductile fiber-reinforced polymer FRP fabr

31、ic has been researched developed and manufactured in the Structural Testing Center at Lawrence Technological University for strengthening structures The fabric is a hybrid of two types of carbon fibers and one type of glass fiber and has been designed to provide a pseudo-ductile behavior with a low

32、yield-equivalent strain value in tension The effectiveness and ductility of the developed fabric has been investigated by strengthening and testing eight concrete beams under flexural load Similar beams strengthened with currently available uniaxial carbon fiber sheets fabrics and plates were also t

33、ested to compare their behavior with those strengthened with the developed fabric The fabric has been designed so that it has the potential to yield simultaneously with the steel reinforcement of strengthened beams and hence a ductile plateau similar to that for the nonstrengthened beams can be achi

34、eved The beams strengthened with the developed fabric exhibited higher yield loads and achieved higher ductility indexes than those strengthened with the currently available carbon fiber strengthening systems The developed fabric shows a more effective contribution to the strengthening mechanismkeyw

35、ordConcrete ductility textile fiber reinforcement distortionINTRODUCTIONThe use of externally bonded fibcr-rcinforccd polymer FRP sheets and strips has recently been established as an effective tool for rehabilitating and strengthening reinforced concrete structures Several experimental investigatio

36、ns have been reported on the behavior of concrete beams strengthened for flexure using externally bonded FRP plates sheets or fabrics Saadatmancsh and Ehsani 1991 examined the behavior of concrete beams strengthened for flexure using glass fiber-reinforced polymer GFRP plates Ritchie ct al 1991 test

37、ed reinforced concrete beams strengthened for flexure using GFRP carbon fibcr-rcinforccd polymer CFRP and GCFRP plates Grace et al 1999 and Trian- tafillou 1992 studied the behavior of reinforced concrete beams strengthened for flexure using CFRP sheets Norris Saadatmancsh and Fhsani 1997 investigat

38、ed the behavior of concrete beams strengthened using CFRP unidirectional sheets and CFRP woven fabrics In all of these investigations the strengthened beams showed higher ultimate loads compared to the nonstrcngthcncd ones One of the drawbacks experienced by most of these strengthened beams was a co

39、nsiderable loss in beam ductility An examination of the load- deflection behavior of the beams however showed that the majority of the gained increase in load was experienced after the yield of the steel reinforcement In other words a significant increase in ultimate load was experienced without muc

40、h increase in yield load Hence a significant increase in service level loads could hardly be gainedApart from the condition of the concrete element before strengthening the steel reinforcement contributes significantly to the flcxural response of the strengthened beam Unfortunately available FRP str

41、engthening materials have a behavior that is different from steel Although FRP materials have high strengths most of them stretch to relatively high strain values before providing their full strength Because steel has a relatively low yield strain value when compared with the ultimate strains of mos

42、t of the FRP materials the contribution of both the steel and the strengthening FRP materials differ with the deformation of the strengthened element As a result steel reinforcement may yield before the strengthened element gains any measurable load increase Some designers place a greater FRP cross

43、section which generally increases the cost of the strengthening to provide a measurable contribution even when deformations arc limited before the yield of steel Debonding of the strengthening material from the surface of the concrete however is more likely to happen in these cases due to higher str

44、ess concentrations Debonding is one of the nondesired brittle failures involved with this technique of strengthening Although using some special low-strain fibers such as ultra-high-modulus carbon fibers may appear to be a solution it would result in brittle failures due to the failure of fibers The

45、 objective of this paper is to introduce a new pseudo-ductile FRP fabric that has a low strain at yield so that it has the potential to yield simultaneously with the steel reinforcement yet provide the desired strengthening levelRESEARCH SIGNIFICANCEFRPs have been increasingly used as materials for

46、rehabilitating and strengthening reinforced concrete structures Currently available FRP materials however lack the ductility and have dissimilar behaviors to steel reinforcement As a result the strengthened beams may exhibit a reduced ductility lack the desired strengthening level or both This study

47、 presents an innovative pseudo-ductile FRP strengthening fabric The fabric provides measurably higher yield loads for the strengthened beams and helps to avoid the loss of ductility that is common with the use of currently available FRPDEVELOPMENT OF HYBRID FABRICTo overcome the drawbacks mentioned

48、previously a ductile FRP material with low yield strain value is neededACI Structural Journal V 99 No 5 September-October 2002MS No 01-349 received October 23 2001 and reviewed under Institute publication policies Copyright ? 2002 American Concrete Institute All rights reserved including the making

49、of copies unless permission is obtained from the copyright proprietors Pertinent discussion will be published in the July-August 2003 ACl Structural Journal if received by March 1 2003ACI StructuralJournalSeptember-October 2002ACI member Nabil F Grace is a professor and Chair of the Structural Testi

50、ng Center Department of Civil Engineering Lawrence Technological University Southfield Mich He is a member of ACI Committee 440 Fiber Reinforced Polymer Reinforcement and Joint ACI-ASCE Committee 343 Concrete Bridge Design His research interests include the use of fiber-reinforced polymer in reinfor

51、ced and pre stressed concrete structuresGeorge Abdel-Sayed is Professor Emeritus in the Department of Civil and Environmental Engineering University of Windsor Windsor Ontario Canada His research interests include soil-structure interactionWael F Ragheb is a research assistant in the Department of C

52、ivil Engineering at Lawrence Technological University He is a PhD candidate in the Department of Civil and Environmental Engineering University of Windsor Windsor Ontario CanadaTable 1Mechanical properties of composite fibersFiber materialDescriptionModulus of elasticity GPa Msi Tensile strength MPa

53、 ksi Failure strain Carbon No IUllra-high-modulus carbon fibers379 55 1324 192 035Carbon No 2High-modulus carbon fibers231 335 2413 350 09 to 10GlassE-glass fibers48 7 1034 150 21 Composite properties are based on 60 fiber volume fractionLiterature review on hybridizationTo develop this material hyb

54、ridization for different fibers was considered Hybridization of more than one type of fibrous materials was the interest of many materials science researchers Most of their work was concerned with combining two types of fibers to enhance the mechanical properties of either type acting alone and to r

55、educe the cost This has been reported in several publications such as Bunsell and Harris 1974 Philips 1976 Manders and Bader 1981 Chow and Kelly 1980 and Fukuda and Chow 1981 Hybridization interested structural engineers as a tool to overcome the problem of a lack of ductility in FRF reinforcing bar

56、s Nanni Henneke and Okamoto 1994 studied bars of braided aramid fibers around a steel core Tamuzs and Tcpfcrs 1995 reported experimental investigations for hybrid fiber bars using different combinations of carbon and aramid fibers Somboonsong Frank and Harris 1998 developed a hybrid FRP reinforcing

57、bar using braided aramid fibers around a carbon fiber core Harris Somboonsong and Frank 1998 used these bars in reinforcing concrete beams to achieve the general load- deflection behavior of concrete beams reinforced with conventional steelDesign concept and materialsTo generate ductility a hybridiz

58、ation technique of different types of fibers has been implemented Three fibers have been selected with a different magnitude of elongations at failure Figure 1 shows the stress-strain curves in tension for the selected composite fibers and Table 1 shows their mechanical propertiesThe technique is based on combining these fibers together and controlling the mixture ratio so that when they arc loaded together in tension the fibers with the