THE APPLICATION OF AFRP FABRIC IN PIER
REINFORCING
Jian Liu1,2, Xinghua Wang1, Chuanxi Li2, Kebo Zhang2
1) School of Civil Engineering and Architecture, Central-South University, Changsha 410075
2) School of Civil Engineering and Architecture, Changsha Science and Technology University,Changsha 410076
Abstract: AFRP fabric is a kind of new type construction reinforcing material, which has some excellent characters including light weight, high strength, and resist fatigue. When it is used in concrete structures reinforcement, it can significantly increase the carrying capacity and anti-seismic capability of the structures. Reinforcing
mechanism, reinforcing design, and construction techniques with AFRP fabric in some pier reinforcing are introduced, and then, a simple beam bridge pier reinforcement project to explain the application of AFRP fabric in the pier reinforcement is presented in this paper.
Keywords: bridge, AFRP fabric, reinforcing, pier
With the rapid increase of the bridge structures and substantial growth of overloading in the transport, many old bridge structures cannot fit the current
requirements. It is very important and urgent to maintain and reinforce these bridges. At present, the traditional reinforcement methods are introduced such as increasing section, bonding plate, external prestressing and anchor spray. Using these methods is characterized by a relatively low cost, many mature reinforcement techniques and technologies. However, there are some shortcomings, such as environmental corrosion, increase in component weight, the construction process is relatively cumbersome and so on.
AFRP reinforcement is a reinforcing method that applies AFRP fabric to concrete and concrete structures to jointly undertake force. AFRP fabric is mainly used for military products in the early days, such as bullet-proof vests, aerospace equipment, etc. It has excellent impact resistance, anti-seismic capability, toughness
and fatigue resistance, as well as soft, lightweight, corrosion resistance, easy
construction technology, construction without affecting the normal use of the building characteristics, etc. When used in concrete structures reinforcement, it can
significantly increase its carrying capacity and anti-seismic capability.In this paper, a simple beam bridge pier reinforcement project to explain the application ofAFRP fabric in the pier reinforcement.
1. PROJECT PROFILE
A example is a 30m span prestressed concrete simply-supported T beam bridge, using φ1.2m double cylindrical pier, pier concrete design rating for a C25. Since the bridge was built in the mid-90s, with the subsequent sharp increase in traffic and overloading of vehicles increases, coupled with the corrosion of concrete under natural conditions, aging, the piers show many cracks, localized concrete spalling , many steel exposed , steel corrosion and other phenomena, Actual measure pier concrete intensity approximately C20,test results show that the bearing capacity and durability has reduced many. In order to ensure the safety and normal use of the
bridge and increase its service life, reinforcing these piers is a must. As the bridge is a city viaduct, its transportation both on the bridge and ground cannot be interrupted when being reinforced, its tight schedule demands and the demand for not to affect the appearance of the structure after reinforcement. Comprehensive consideration of the above factors, it can be decided to adapt to reinforce these piers.
2. REINFORCING MECHANISM OF AFRP FABRIC
AFRP fabric is a wholly aromatic polyamide fiber. It is a sheet that is made up of AFRP by one-way or two-way arrangement, the specific density for about 1/5 of the steel sheet, the tensile strength five times higher than steel sheet, so its texture is very soft; with a light-weight highstrength, high modulus of elasticity, corrosion resistance, non-conductive properties and other characteristics, particularly its anti-fatigue performance, impact resistance and its partial load resistance are the best of all FRP composite materials; thefailure mode of AFRP is plastic failure, so it is one of the best
materials to reinforce piers. Wrapping up AFRP fabric along the pier body, in the axial pressure the AFRP fabric has a “hoop effect” on concrete piers, making concretein three direction compression condition, thus significantly increasing
concrete compressive strength, to achieve the aim to improve the bearing capacity and anti-seismic capability of the bridge piers.
3. REINFORCEMENT DESIGN
The bridge piers use a one-way Lowie 2008 AFRP fabric to reinforce, which is a fully aromatic polyamide fibers produced by DuPont, whose main component is p-phenylene diamine terephthalamide polymers, and its performance parameters, see Table 1.
Table 1. Lowie 2008 AFRP fabric performance parameters
Bearing Capacity Analysis of the Original Piers
Pier cross-section shown in Figure 1, the longitudinal reinforcement for the 29 × φ28, u 'As =17855mm 2 , f ' sd = 280Mpa ；C25 Concrete f cd1=11.5Mpa , C20 Concrete f = cd 29.2Mpa ；Calculation of the length of the piers to take= L 0 5.0m ;
Eccentricity of axial force e ' 0=210mm.Piers as eccentric compression components, itsflexural capacity is calculated according to circularsection bias member, hat is to γ N ≤ Ar f +C ρ r f (1)
γ N e ≤ Br f + D ρ
In the formula:
γ ——structural importance coefficient, take 1;
A 、B ——the calculation coefficient about concrete bearing capacity, according to specifications [4] Appendix C, Table C.0.2 to check;
C 、D ——the calculation coefficient about longitudinal steel bearing capacity, according to specifications [4] Appendix C, Table C.0.2 to check;
r ——circular section radius, take 600mm;
g ——when concrete cover thickness to take 60mm, the ration of the radius of the circle where longitudinal steels are to circular cross-section radius is g r r s = /
=0.874；
ρ ——Longitudinal steel reinforcement ratio.
Piers bearing capacity to lower is mainly because of the decrease of concrete strength, the lower part can be calculated by the following formula ,that is to
⊿ N d = Ar 2 ( f cd 1 − f cd 2) (3)
According to calculation and analysis, the calculation of concrete bearing capacity obtained coefficient A=2.1387, B=0.5854,take the values of r, cd 1 f and cd 2 f to
substitute into (3), and calculate the value of dropping bearing capacity of bridge piers by 1771KN,thus in this pier reinforcement design project, the improved value of design carrying capacity to take 1771KN.
Calculation of Bearing Capacity after Reinforcement
Using a one-way Lowie 2008 AFRP fabric to reinforce bridge piers, according to “Lowie 2008 Kevlar fiber composite material design and construction reference manual for strengthening reinforced concrete structures” 【5】,for eccentric
compression of the reinforced concrete bridge piers, because of concrete fastened by AFRP fabric, the improved carrying capacity is as follows:
N =8 r Eεnt A/ d (4)
r 1 = 0.8 + (60 − c ) /150 (5)
In the formula:
f N ——increased value of carrying capacity
E ——AFRP fabric elastic modulus, take 118 Gpa;
ε ——allowable strain of AFRP fabric, to take0.0036 when compression reinforcement
d ——cylinder diameter;
1 r —— concrete Strength coefficient;
c ——concrete strength grade, C = 20.
According to formula (4)and (5) to calculate the increased values of carrying capacity when using different specifications, different layers oneway Lowie 2008 AFRP fabric
to reinforce bridge piers, the improved values are shown in Table 2
Table 2. The situation of improved values of carrying capacity by using different
specifications, different layers one-way Lowie 2008 AFRP fabric to strengthen bridge piers
According to Table 2 results, using two-layer AFS-60 unidirectional AFRP
fabric reinforce the piers (see Figure 2).
Figure 1. Steel layout of bridge pier Cross-section
Figure 2. Reinforced pier cross-section diagram
4. REINFORCEMENT TECHNICS
4.1 Construction Preparation
First of all, cleaning and flatting construction site to make the whole pier above the
ground, then building scaffolds around the pier.
4.2 Bridge Pier Surface Treatment
Because there are many concrete aging, spalling, cracks and exposed steels on the surface of bridge piers, the concrete surface if not treated, the combination strength of AFRP fabric and concrete will be reduced, thus failure to achieve their reinforcing effect. Therefore, surface treatment is a must before the bridge piers reinforced.
Firstly, cut out part of the spalling, loose, aging and broken concretes, inject epoxy glue into the cracks while derusting for exposed steels; and then using cement mortar to repair and level them; and finally smooth the uneven parts of the bridge piers wipe the piers surface with wet cloth, and clean greasy parts with acetone.
4.3 Smear Primer
According to the product specification to allocate primers in proportion, stir fully to mix evenly. Protection glasses, masks, gloves and other security tools must be wore when allocating primers, and pay attention to safety and fire safety. At the same time the construction should also be aware of the following aspects:
1) Ascertain the reinforced surface clean and dry, and then allocate primers;
2) With rolling brush or brush to smear epoxy primers on the surface of the reinforced surface, to make them fully saturated the concrete surface;
3) Coating temperature should be above 5 ℃.If the temperature is below 5 ℃, it is required to take appropriate measures of warming;
4) Every time the allocated primers should be used up as soon as possible within a specified time, and the expired primers cannot be used;
5) Primer standard dosage: 0.1 ~ 0.3 kg/m2, the specific amount is determined by the concrete
surface conditions.
4.4 Paste AFRP Fabric
4.4.1 The choice of AFRP fabric
According to calculation and analysis, this pro523 project uses two-layer AFS-60
unidirectional AFRP fabric to reinforce the bridge piers, its basic properties in Table 1.
4.4.2 Cut AFRP fabric
According to the reinforced pier shape, size(φ1.2m) draw AFRP fabric cutting diagram, cut paper into the required shape, winding AFRP fabric along the pier, fiber cloth lap length of not less than 100mm.
4.4.3 Mix impregnating resin
Put the main agent and hardening agent of impregnated resin into the container, according to a certain percentage, and in the same direction to stir evenly, and then use it after fully stirring with bubbles reduced.
4.4.4 Smear the bottom impregnating resins
With rolling brush to smear impregnating resin evenly on the surface of
reinforced concrete surface, the bottom impregnating resin standard dosage is 0.40 ~ 0.44kg / ㎡, the specific amount determined in accordance with the concrete surface conditions.
4.4.5 Paste AFRP fabric
Paste the first layer AFS-60 AFRP fabric by cutting diagram, with rollers rolling and pasting AFRP fabric repeatedly, in order to integrate closely with the concrete.
4.4.6 Smear the outer layer impregnating resins
smear the outer layer impregnating resins at a time after the bottom soaking the AFRP fabrics, using roller smearing resins evenly along the fiber direction and roll repeatedly to drive out the residual bubbles, making AFRP fabric soaked from inside and out, so that AFRP fabric, resin and concrete are bonded together.
4.4.7 Paste the second layer AFRP fabric
After layer 1 AFS-60 AFRP fabric paste completed, repeat 3,4,5,6 construction process, you can complete the second layer AFS-60 AFRP fabric paste.
4.5 Maintenance and Post-work
When moistures attaching to the early hardening resins, it will produce a
negative hardening layer, in order to prevent adhesion of water that can be used PVC
membrane covering conservation. Hardening process, if the rain erodes concrete
surface resins, special diluents to remove hardened layer should be used, and then the next step of construction. In order to prevent the surface of reinforced concrete
structures damaged, improve durability, we should brush a layer of cement mortar on the surface of the reinforced bridge piers.
4. CONCLUSIONS
The use of AFRP fabric to strengthen the bridge piers can effectively inhibit further crack to generate, while significantly increase the carrying capacity of bridge piers, to improve the deformation ability of the bridge piers, and increase the ductility of the piers and seismic capacity; construction convenient, easy to operate. Facts have proved that the use of AFRP fabric to strengthen the bridge piers is a success. In view of the history of AFRP fabric used in the domestic civil engineering structure reinforcement is not long, it is recommended to further improve strengthening operating procedures and strengthening quality evaluation standards, in order to further promote the use.
REFERENCES
Liu Laijun, Zhao Xing, Bridge Reinforcement Designand Construction Technology, Beijing:People's Communications Press, 2004
He Weiping, Cheng Xiaofang, The Application of Technology of Lowie 2008 AFRP
Fabric in The Reinforced Concrete Pier Columns, Railway Construction, 2004 Issue 4
Zhang Shuren, etc., Reinforced Concrete and Prestressed Concrete Bridge Structure
Design Principle, BeiJing: People's CommunicationsPress, 2004
Highway of Reinforced Concrete and Prestressed Concrete Bridge and Culvert
Design Specification (JTG D62-2004), Industry Standard of People's Republic of China.
Oceanpower Engineering Science and Technology Co., Ltd., Lowie 2008 Kevlar Fiber Composite Material Design and Construction Reference Manual of Strengthening Reinforced Concrete Structures (2003 ~ 2004 version), June 2003
芳纶纤维在建筑中的应用
Jian Liu1,2, Xinghua Wang1, Chuanxi Li2, Kebo Zhang2
1）土木建筑与环境工程，中南大学，长沙410075 2）土木建筑与环境工程，长
沙理工大学，长沙410076
摘要：芳纶纤维面料是一种新型骨架材料，它具有重量轻，强度高，抗疲劳等特性。当它应用在钢筋混凝土结构中时，它可使结构提高承载能力和抗震能力。本文提出了结构与芳纶纤维织物增强机制，介绍了芳纶纤维在一简支梁桥桥墩加固工程中的应用，并做了解释了。
关键词：桥梁，芳纶纤维布，加固，墩
随着桥梁结构的迅速增加，对运输超载的大幅增长，许多旧桥结构不能满足目前的需求。保持和加强这些桥梁是非常重要和迫切的，。目前有许多传统的加固方法，例如增加一节，接骨板，体外预应力和锚喷。使用这些方法的特点是成本相对较低，加固技术也比较成熟。但是，也有诸如环境腐蚀，重量增加了一些组件缺点，施工过程比较繁琐等。
芳纶纤维加固是一种新型的加固方法，适用于混凝土结构中，以共同承担的力量。在早期的时候芳纶纤维织物主要用于军工产品，例如防弹背心，航空航天设备等，具有优良的耐冲击，抗震性能，韧性和抗疲劳性能，以及软，重量轻，耐腐蚀。在施工技术中，在不影响建筑物的特性的情况下，使用在钢筋混凝土结构建筑，它可以大大提高其承载能力和抗震能力。在此提出了一种将其应用在一简支梁桥桥墩中，解释了芳纶纤维布在桥墩加固中的应用。
1． 工程项目简介
一个例子是一个30米大跨度预应力混凝土简支T 梁桥，采用双圆柱墩φ1.2m ，桥墩为C25的混凝土设计等级。由于大桥建于90年代中期，withthe 随后在交通急剧增加，超载车辆的增加，再加上自然条件下混凝土腐蚀，抗老化，码头呈现出许多裂缝，局部混凝土剥落，露出许多钢铁，钢腐蚀等现象，实测码头约C20的混凝土强度，测试结果表明，承载能力和耐用性减少
了许多。为了确保大桥的安全和正常使用，提高其使用寿命，加强这些码头是必须的。由于大桥是城市高架桥，其运输都在桥上和地面不能中断时得到加强，它的紧迫要求，是不影响需求的结构加固后的外观。综合上述因素的考虑，它可以决定，以适应加强这些码头。
2． 芳纶纤维织物加固机理
芳纶纤维织物是一种全芳香族聚酰胺纤维。可惜的是，是由芳纶纤维的1 / 5的钢板，其拉伸强度高出五倍单向或双向的安排，具体的密度大于钢板板材，因此其质地非常柔软; 用轻重量高强度，弹性，耐腐蚀，高模量，非导电性能等特点，尤其是其抗疲劳性能，耐冲击及部分负载电阻是所有玻璃钢复合材料的最佳; 故障模式芳纶纤维是塑料故障，所以它是最好的材料，以加强码头之一。结束了沿墩身芳纶纤维织物，芳纶纤维的轴向压力的织物具有“箍效应”混凝土桥墩，使得三个方向的压状态下混凝土，从而大大提高混凝土的抗压强度，达到目标，提高承载能力和抗震能力的桥墩。
3． 加固设计
表1。路威2008芳纶纤维织物的性能参数
3.1原桥墩承载力分析
桥墩截面如图1所示，纵筋为29 × φ28，u 'As =17855mm 2 , 'sd f = 280Mpa ；；C25混凝土cd 1 f =11.5Mpa , C20 Concrete cd 2 f =9.2Mpa ；长度计算采取L=5.0M, e' =210mm.
构件偏心受压构件，其抗弯承载力的计算按照圆形截面偏压计算。 γ N ≤ Ar f +C ρ r f (1) γ N e ≤ Br f + D
在公式：0γ - 结构重要性系数，取1，A B - 关于具体的计算承载力系数，根据规格[4]附录C ，表C.0.2检查; 的C ，D - 的计算约纵向钢筋承载力系数，根据规格[4]附录C ，表C.0.2检查和r - 圆截面半径，以600毫米; 克 - 当混凝土保护层厚度60mm 的采取，对半径比纵向的循环，即钢圆形的横截面半径grrs = / = 0.874; ρ - 纵向钢筋配筋率
承载能力降低，主要是因为混凝土的强度下降的状态下，部分可通过下列公式计算
⊿Nd = Ar2（ f1 − f2）
经计算和分析，混凝土承载能力计算得到系数a = 2.1387，b= 0.5854，取R 的值，CD1的F 和F 到光盘2代入（3），并计算出承载力值下降桥墩由1771KN ，因此，在这个码头加固设计项目中，承载能力，采取1771KN 设计改进的价值。
3.2计算加固后的承载力
使用单向路威2008芳纶纤维织物，以加强桥墩，按照“路威2008芳纶纤维复合材料的设计和加强钢筋混凝土结构施工参考手册”【5】，为钢筋混凝土桥墩的偏心受压，因为由芳纶纤维织物固定混凝土，提高承载能力如下 N =8 r E ε nt A d (4)
1 r = 0.8 + (60 − c ) /150 (5)
式中：F n的 - 提高承载能力f e将价值 - 芳纶纤维织物的弹性模量，以118千兆; 发ε - 芳纶纤维织物允许应变，采取压缩时0.0036加固ñ - 芳纶纤维布层; 英尺 - 单芳纶纤维织物纤维布的厚度; c比率 - 混凝土横截面面积d- 气缸直径 - 混凝土强度系数; 的C - 混凝土强度级，C = 20。根据式（4）及（5）计算
承载能力时，使用不同规格，不同层次单向路威2008芳纶纤维织物加固桥墩的增加值，改善值见表2
表2。对携带使用不同规格，单向不同层次路威2008芳纶纤维织物的能力得到加强桥墩值情况
根据表2的结果，使用两层的AFS 60单向芳纶纤维织物加固桥墩（见图2）。
图1。钢布局桥墩截面
图2。加固桥墩截面图
4． 加固工艺
4.1施工准备
首先，清理和平整施工现场，使整个码头地面，然后围绕码头支架。
4.2桥墩表面处理
因为有很多具体的老化，剥落，裂缝和对桥墩，混凝土表面如不及时治疗地表出露钢，芳纶纤维织物与混凝土的结合强度会降低，从而达不到应有的补强作用。因此，表面处理是必须的前桥桥墩钢筋。首先，把他的剥落，松散，破碎的混凝土老化，部分裂缝注入环氧树脂胶而暴露钢材除锈，然后用水泥砂浆修补和水平他们，终于顺利桥墩部分擦拭不均桥墩表面用湿布，并用丙酮清洗油腻的部分。
4.3涂片底漆
根据产品规格按比例分配的引物，充分搅拌混合均匀。防护眼镜，口罩，手套和其他安全工具必须分配时穿引物，并注意安全和防火安全。在建设的同时，也应该意识到以下几个方面：1）确定了钢筋表面的清洁和干燥，然后分配引物; 随着滚刷或刷子涂抹在表面上的钢筋环氧底漆，2）使他们充分饱和的混凝土表面; 3）涂布温度应高于5℃。如果温度低于5℃时，需要考虑到气候变暖的适当措施; 4）每所分配的引物被用完规定时间内尽快的时间，过期的引物不能使用;
5）引物标准用量：0.1〜0.3 kg/m2，具体数额由混凝土表面的条件决定的。
4.4粘贴芳纶纤维织物
4.4.1选择芳纶纤维织物
经计算和分析，pro523项目采用两层的AFS 60单向芳纶纤维织物，以加强桥墩，在表1的基本属性。
4.4.2切芳纶纤维织物
据码头的钢筋形状，大小（φ1.2m ）绘制芳纶纤维面料裁剪图，切成需要的形状纸，沿着蜿蜒的码头，纤维布不小于100毫米的搭接长度芳纶纤维织物。
4.4.3混合浸渍树脂
放入容器中的主剂和硬化剂浸渍树脂，按一定的比例，并在同一个方向搅拌均匀，然后使用与减少泡沫后充分搅拌它。
4.4.4涂片底部浸渍树脂
随着滚刷涂抹浸渍的钢筋混凝土表面树脂表面均匀，浸渍树脂底标准剂量为0.40〜0.44千克/㎡，具体数额的规定确定具体的表面状况。
4.4.5粘贴芳纶纤维织物
粘贴第一层战地服务团- 60芳纶纤维的切割和粘贴芳纶纤维轧辊布反复，为了与混凝土紧密结合图，面料。
4.4.6涂片外层浸渍树脂
涂抹外层浸渍后浸泡芳纶纤维织物底部一次树脂，采用辊涂树脂均匀地分布在纤维方向和滚一再赶走残留的气泡，使芳纶纤维织物浸泡从内到外，使芳纶纤维织物，树脂和混凝土粘合在一起。
4.4.7第二层粘贴芳纶纤维织物
可供出售后1层- 60芳纶纤维布粘贴完成，重复3,4,5,6建设过程中，您可以完成第二层战地服务团- 60芳纶纤维布粘贴。
4.5维护和会后工作
当水分附加到早期硬化树脂，它会产生负硬化层，以防止水，可用于PVC 膜覆盖保护粘连。硬化过程中，如果下雨侵蚀混凝土表面树脂，特殊稀释剂去除硬化层应使用，那么下一步施工。为了防止损坏，提高耐久性，我们应该刷上的钢筋混凝土桥墩表面的水泥砂浆面层钢筋混凝土结构。
5． 结论
芳纶纤维织物的利用，加强桥墩能有效地抑制进一步打击生成，同时
显着增加桥墩的承载能力，改善桥墩变形能力，提高抗震能力的码头和延性; 建设方便，易于操作。事实证明，芳纶纤维面料来加强桥墩是成功的。鉴于在国内土木工程结构加固用芳纶纤维织物历史观不长，建议进一步完善加强作业程序，强化质量评价标准，以进一步推广使用。
参考文献
刘来君，赵星，《桥梁加固设计和施工技术》，北京：人民交通出版社，2004 赫委乒，郑小芳，路威 《芳纶纤维织物的技术在钢筋混凝土桥墩柱中的应用》，2004年第4期
章书饪等，《钢筋混凝土和预应力混凝土桥梁结构设计原理》，北京：人民交通出版社，2004
《公路钢筋混凝土及预应力混凝土桥涵设计规范》（JTG D62 - 2004），业界人士对中国共和国标准。
海川工程科技有限公司，《芳纶纤维复合材料加固钢筋混凝土结构设计》（2003〜2004年版），2003年6月
THE APPLICATION OF AFRP FABRIC IN PIER
REINFORCING
Jian Liu1,2, Xinghua Wang1, Chuanxi Li2, Kebo Zhang2
1) School of Civil Engineering and Architecture, Central-South University, Changsha 410075
2) School of Civil Engineering and Architecture, Changsha Science and Technology University,Changsha 410076
Abstract: AFRP fabric is a kind of new type construction reinforcing material, which has some excellent characters including light weight, high strength, and resist fatigue. When it is used in concrete structures reinforcement, it can significantly increase the carrying capacity and anti-seismic capability of the structures. Reinforcing
mechanism, reinforcing design, and construction techniques with AFRP fabric in some pier reinforcing are introduced, and then, a simple beam bridge pier reinforcement project to explain the application of AFRP fabric in the pier reinforcement is presented in this paper.
Keywords: bridge, AFRP fabric, reinforcing, pier
With the rapid increase of the bridge structures and substantial growth of overloading in the transport, many old bridge structures cannot fit the current
requirements. It is very important and urgent to maintain and reinforce these bridges. At present, the traditional reinforcement methods are introduced such as increasing section, bonding plate, external prestressing and anchor spray. Using these methods is characterized by a relatively low cost, many mature reinforcement techniques and technologies. However, there are some shortcomings, such as environmental corrosion, increase in component weight, the construction process is relatively cumbersome and so on.
AFRP reinforcement is a reinforcing method that applies AFRP fabric to concrete and concrete structures to jointly undertake force. AFRP fabric is mainly used for military products in the early days, such as bullet-proof vests, aerospace equipment, etc. It has excellent impact resistance, anti-seismic capability, toughness
and fatigue resistance, as well as soft, lightweight, corrosion resistance, easy
construction technology, construction without affecting the normal use of the building characteristics, etc. When used in concrete structures reinforcement, it can
significantly increase its carrying capacity and anti-seismic capability.In this paper, a simple beam bridge pier reinforcement project to explain the application ofAFRP fabric in the pier reinforcement.
1. PROJECT PROFILE
A example is a 30m span prestressed concrete simply-supported T beam bridge, using φ1.2m double cylindrical pier, pier concrete design rating for a C25. Since the bridge was built in the mid-90s, with the subsequent sharp increase in traffic and overloading of vehicles increases, coupled with the corrosion of concrete under natural conditions, aging, the piers show many cracks, localized concrete spalling , many steel exposed , steel corrosion and other phenomena, Actual measure pier concrete intensity approximately C20,test results show that the bearing capacity and durability has reduced many. In order to ensure the safety and normal use of the
bridge and increase its service life, reinforcing these piers is a must. As the bridge is a city viaduct, its transportation both on the bridge and ground cannot be interrupted when being reinforced, its tight schedule demands and the demand for not to affect the appearance of the structure after reinforcement. Comprehensive consideration of the above factors, it can be decided to adapt to reinforce these piers.
2. REINFORCING MECHANISM OF AFRP FABRIC
AFRP fabric is a wholly aromatic polyamide fiber. It is a sheet that is made up of AFRP by one-way or two-way arrangement, the specific density for about 1/5 of the steel sheet, the tensile strength five times higher than steel sheet, so its texture is very soft; with a light-weight highstrength, high modulus of elasticity, corrosion resistance, non-conductive properties and other characteristics, particularly its anti-fatigue performance, impact resistance and its partial load resistance are the best of all FRP composite materials; thefailure mode of AFRP is plastic failure, so it is one of the best
materials to reinforce piers. Wrapping up AFRP fabric along the pier body, in the axial pressure the AFRP fabric has a “hoop effect” on concrete piers, making concretein three direction compression condition, thus significantly increasing
concrete compressive strength, to achieve the aim to improve the bearing capacity and anti-seismic capability of the bridge piers.
3. REINFORCEMENT DESIGN
The bridge piers use a one-way Lowie 2008 AFRP fabric to reinforce, which is a fully aromatic polyamide fibers produced by DuPont, whose main component is p-phenylene diamine terephthalamide polymers, and its performance parameters, see Table 1.
Table 1. Lowie 2008 AFRP fabric performance parameters
Bearing Capacity Analysis of the Original Piers
Pier cross-section shown in Figure 1, the longitudinal reinforcement for the 29 × φ28, u 'As =17855mm 2 , f ' sd = 280Mpa ；C25 Concrete f cd1=11.5Mpa , C20 Concrete f = cd 29.2Mpa ；Calculation of the length of the piers to take= L 0 5.0m ;
Eccentricity of axial force e ' 0=210mm.Piers as eccentric compression components, itsflexural capacity is calculated according to circularsection bias member, hat is to γ N ≤ Ar f +C ρ r f (1)
γ N e ≤ Br f + D ρ
In the formula:
γ ——structural importance coefficient, take 1;
A 、B ——the calculation coefficient about concrete bearing capacity, according to specifications [4] Appendix C, Table C.0.2 to check;
C 、D ——the calculation coefficient about longitudinal steel bearing capacity, according to specifications [4] Appendix C, Table C.0.2 to check;
r ——circular section radius, take 600mm;
g ——when concrete cover thickness to take 60mm, the ration of the radius of the circle where longitudinal steels are to circular cross-section radius is g r r s = /
=0.874；
ρ ——Longitudinal steel reinforcement ratio.
Piers bearing capacity to lower is mainly because of the decrease of concrete strength, the lower part can be calculated by the following formula ,that is to
⊿ N d = Ar 2 ( f cd 1 − f cd 2) (3)
According to calculation and analysis, the calculation of concrete bearing capacity obtained coefficient A=2.1387, B=0.5854,take the values of r, cd 1 f and cd 2 f to
substitute into (3), and calculate the value of dropping bearing capacity of bridge piers by 1771KN,thus in this pier reinforcement design project, the improved value of design carrying capacity to take 1771KN.
Calculation of Bearing Capacity after Reinforcement
Using a one-way Lowie 2008 AFRP fabric to reinforce bridge piers, according to “Lowie 2008 Kevlar fiber composite material design and construction reference manual for strengthening reinforced concrete structures” 【5】,for eccentric
compression of the reinforced concrete bridge piers, because of concrete fastened by AFRP fabric, the improved carrying capacity is as follows:
N =8 r Eεnt A/ d (4)
r 1 = 0.8 + (60 − c ) /150 (5)
In the formula:
f N ——increased value of carrying capacity
E ——AFRP fabric elastic modulus, take 118 Gpa;
ε ——allowable strain of AFRP fabric, to take0.0036 when compression reinforcement
d ——cylinder diameter;
1 r —— concrete Strength coefficient;
c ——concrete strength grade, C = 20.
According to formula (4)and (5) to calculate the increased values of carrying capacity when using different specifications, different layers oneway Lowie 2008 AFRP fabric
to reinforce bridge piers, the improved values are shown in Table 2
Table 2. The situation of improved values of carrying capacity by using different
specifications, different layers one-way Lowie 2008 AFRP fabric to strengthen bridge piers
According to Table 2 results, using two-layer AFS-60 unidirectional AFRP
fabric reinforce the piers (see Figure 2).
Figure 1. Steel layout of bridge pier Cross-section
Figure 2. Reinforced pier cross-section diagram
4. REINFORCEMENT TECHNICS
4.1 Construction Preparation
First of all, cleaning and flatting construction site to make the whole pier above the
ground, then building scaffolds around the pier.
4.2 Bridge Pier Surface Treatment
Because there are many concrete aging, spalling, cracks and exposed steels on the surface of bridge piers, the concrete surface if not treated, the combination strength of AFRP fabric and concrete will be reduced, thus failure to achieve their reinforcing effect. Therefore, surface treatment is a must before the bridge piers reinforced.
Firstly, cut out part of the spalling, loose, aging and broken concretes, inject epoxy glue into the cracks while derusting for exposed steels; and then using cement mortar to repair and level them; and finally smooth the uneven parts of the bridge piers wipe the piers surface with wet cloth, and clean greasy parts with acetone.
4.3 Smear Primer
According to the product specification to allocate primers in proportion, stir fully to mix evenly. Protection glasses, masks, gloves and other security tools must be wore when allocating primers, and pay attention to safety and fire safety. At the same time the construction should also be aware of the following aspects:
1) Ascertain the reinforced surface clean and dry, and then allocate primers;
2) With rolling brush or brush to smear epoxy primers on the surface of the reinforced surface, to make them fully saturated the concrete surface;
3) Coating temperature should be above 5 ℃.If the temperature is below 5 ℃, it is required to take appropriate measures of warming;
4) Every time the allocated primers should be used up as soon as possible within a specified time, and the expired primers cannot be used;
5) Primer standard dosage: 0.1 ~ 0.3 kg/m2, the specific amount is determined by the concrete
surface conditions.
4.4 Paste AFRP Fabric
4.4.1 The choice of AFRP fabric
According to calculation and analysis, this pro523 project uses two-layer AFS-60
unidirectional AFRP fabric to reinforce the bridge piers, its basic properties in Table 1.
4.4.2 Cut AFRP fabric
According to the reinforced pier shape, size(φ1.2m) draw AFRP fabric cutting diagram, cut paper into the required shape, winding AFRP fabric along the pier, fiber cloth lap length of not less than 100mm.
4.4.3 Mix impregnating resin
Put the main agent and hardening agent of impregnated resin into the container, according to a certain percentage, and in the same direction to stir evenly, and then use it after fully stirring with bubbles reduced.
4.4.4 Smear the bottom impregnating resins
With rolling brush to smear impregnating resin evenly on the surface of
reinforced concrete surface, the bottom impregnating resin standard dosage is 0.40 ~ 0.44kg / ㎡, the specific amount determined in accordance with the concrete surface conditions.
4.4.5 Paste AFRP fabric
Paste the first layer AFS-60 AFRP fabric by cutting diagram, with rollers rolling and pasting AFRP fabric repeatedly, in order to integrate closely with the concrete.
4.4.6 Smear the outer layer impregnating resins
smear the outer layer impregnating resins at a time after the bottom soaking the AFRP fabrics, using roller smearing resins evenly along the fiber direction and roll repeatedly to drive out the residual bubbles, making AFRP fabric soaked from inside and out, so that AFRP fabric, resin and concrete are bonded together.
4.4.7 Paste the second layer AFRP fabric
After layer 1 AFS-60 AFRP fabric paste completed, repeat 3,4,5,6 construction process, you can complete the second layer AFS-60 AFRP fabric paste.
4.5 Maintenance and Post-work
When moistures attaching to the early hardening resins, it will produce a
negative hardening layer, in order to prevent adhesion of water that can be used PVC
membrane covering conservation. Hardening process, if the rain erodes concrete
surface resins, special diluents to remove hardened layer should be used, and then the next step of construction. In order to prevent the surface of reinforced concrete
structures damaged, improve durability, we should brush a layer of cement mortar on the surface of the reinforced bridge piers.
4. CONCLUSIONS
The use of AFRP fabric to strengthen the bridge piers can effectively inhibit further crack to generate, while significantly increase the carrying capacity of bridge piers, to improve the deformation ability of the bridge piers, and increase the ductility of the piers and seismic capacity; construction convenient, easy to operate. Facts have proved that the use of AFRP fabric to strengthen the bridge piers is a success. In view of the history of AFRP fabric used in the domestic civil engineering structure reinforcement is not long, it is recommended to further improve strengthening operating procedures and strengthening quality evaluation standards, in order to further promote the use.
REFERENCES
Liu Laijun, Zhao Xing, Bridge Reinforcement Designand Construction Technology, Beijing:People's Communications Press, 2004
He Weiping, Cheng Xiaofang, The Application of Technology of Lowie 2008 AFRP
Fabric in The Reinforced Concrete Pier Columns, Railway Construction, 2004 Issue 4
Zhang Shuren, etc., Reinforced Concrete and Prestressed Concrete Bridge Structure
Design Principle, BeiJing: People's CommunicationsPress, 2004
Highway of Reinforced Concrete and Prestressed Concrete Bridge and Culvert
Design Specification (JTG D62-2004), Industry Standard of People's Republic of China.
Oceanpower Engineering Science and Technology Co., Ltd., Lowie 2008 Kevlar Fiber Composite Material Design and Construction Reference Manual of Strengthening Reinforced Concrete Structures (2003 ~ 2004 version), June 2003
芳纶纤维在建筑中的应用
Jian Liu1,2, Xinghua Wang1, Chuanxi Li2, Kebo Zhang2
1）土木建筑与环境工程，中南大学，长沙410075 2）土木建筑与环境工程，长
沙理工大学，长沙410076
摘要：芳纶纤维面料是一种新型骨架材料，它具有重量轻，强度高，抗疲劳等特性。当它应用在钢筋混凝土结构中时，它可使结构提高承载能力和抗震能力。本文提出了结构与芳纶纤维织物增强机制，介绍了芳纶纤维在一简支梁桥桥墩加固工程中的应用，并做了解释了。
关键词：桥梁，芳纶纤维布，加固，墩
随着桥梁结构的迅速增加，对运输超载的大幅增长，许多旧桥结构不能满足目前的需求。保持和加强这些桥梁是非常重要和迫切的，。目前有许多传统的加固方法，例如增加一节，接骨板，体外预应力和锚喷。使用这些方法的特点是成本相对较低，加固技术也比较成熟。但是，也有诸如环境腐蚀，重量增加了一些组件缺点，施工过程比较繁琐等。
芳纶纤维加固是一种新型的加固方法，适用于混凝土结构中，以共同承担的力量。在早期的时候芳纶纤维织物主要用于军工产品，例如防弹背心，航空航天设备等，具有优良的耐冲击，抗震性能，韧性和抗疲劳性能，以及软，重量轻，耐腐蚀。在施工技术中，在不影响建筑物的特性的情况下，使用在钢筋混凝土结构建筑，它可以大大提高其承载能力和抗震能力。在此提出了一种将其应用在一简支梁桥桥墩中，解释了芳纶纤维布在桥墩加固中的应用。
1． 工程项目简介
一个例子是一个30米大跨度预应力混凝土简支T 梁桥，采用双圆柱墩φ1.2m ，桥墩为C25的混凝土设计等级。由于大桥建于90年代中期，withthe 随后在交通急剧增加，超载车辆的增加，再加上自然条件下混凝土腐蚀，抗老化，码头呈现出许多裂缝，局部混凝土剥落，露出许多钢铁，钢腐蚀等现象，实测码头约C20的混凝土强度，测试结果表明，承载能力和耐用性减少
了许多。为了确保大桥的安全和正常使用，提高其使用寿命，加强这些码头是必须的。由于大桥是城市高架桥，其运输都在桥上和地面不能中断时得到加强，它的紧迫要求，是不影响需求的结构加固后的外观。综合上述因素的考虑，它可以决定，以适应加强这些码头。
2． 芳纶纤维织物加固机理
芳纶纤维织物是一种全芳香族聚酰胺纤维。可惜的是，是由芳纶纤维的1 / 5的钢板，其拉伸强度高出五倍单向或双向的安排，具体的密度大于钢板板材，因此其质地非常柔软; 用轻重量高强度，弹性，耐腐蚀，高模量，非导电性能等特点，尤其是其抗疲劳性能，耐冲击及部分负载电阻是所有玻璃钢复合材料的最佳; 故障模式芳纶纤维是塑料故障，所以它是最好的材料，以加强码头之一。结束了沿墩身芳纶纤维织物，芳纶纤维的轴向压力的织物具有“箍效应”混凝土桥墩，使得三个方向的压状态下混凝土，从而大大提高混凝土的抗压强度，达到目标，提高承载能力和抗震能力的桥墩。
3． 加固设计
表1。路威2008芳纶纤维织物的性能参数
3.1原桥墩承载力分析
桥墩截面如图1所示，纵筋为29 × φ28，u 'As =17855mm 2 , 'sd f = 280Mpa ；；C25混凝土cd 1 f =11.5Mpa , C20 Concrete cd 2 f =9.2Mpa ；长度计算采取L=5.0M, e' =210mm.
构件偏心受压构件，其抗弯承载力的计算按照圆形截面偏压计算。 γ N ≤ Ar f +C ρ r f (1) γ N e ≤ Br f + D
在公式：0γ - 结构重要性系数，取1，A B - 关于具体的计算承载力系数，根据规格[4]附录C ，表C.0.2检查; 的C ，D - 的计算约纵向钢筋承载力系数，根据规格[4]附录C ，表C.0.2检查和r - 圆截面半径，以600毫米; 克 - 当混凝土保护层厚度60mm 的采取，对半径比纵向的循环，即钢圆形的横截面半径grrs = / = 0.874; ρ - 纵向钢筋配筋率
承载能力降低，主要是因为混凝土的强度下降的状态下，部分可通过下列公式计算
⊿Nd = Ar2（ f1 − f2）
经计算和分析，混凝土承载能力计算得到系数a = 2.1387，b= 0.5854，取R 的值，CD1的F 和F 到光盘2代入（3），并计算出承载力值下降桥墩由1771KN ，因此，在这个码头加固设计项目中，承载能力，采取1771KN 设计改进的价值。
3.2计算加固后的承载力
使用单向路威2008芳纶纤维织物，以加强桥墩，按照“路威2008芳纶纤维复合材料的设计和加强钢筋混凝土结构施工参考手册”【5】，为钢筋混凝土桥墩的偏心受压，因为由芳纶纤维织物固定混凝土，提高承载能力如下 N =8 r E ε nt A d (4)
1 r = 0.8 + (60 − c ) /150 (5)
式中：F n的 - 提高承载能力f e将价值 - 芳纶纤维织物的弹性模量，以118千兆; 发ε - 芳纶纤维织物允许应变，采取压缩时0.0036加固ñ - 芳纶纤维布层; 英尺 - 单芳纶纤维织物纤维布的厚度; c比率 - 混凝土横截面面积d- 气缸直径 - 混凝土强度系数; 的C - 混凝土强度级，C = 20。根据式（4）及（5）计算
承载能力时，使用不同规格，不同层次单向路威2008芳纶纤维织物加固桥墩的增加值，改善值见表2
表2。对携带使用不同规格，单向不同层次路威2008芳纶纤维织物的能力得到加强桥墩值情况
根据表2的结果，使用两层的AFS 60单向芳纶纤维织物加固桥墩（见图2）。
图1。钢布局桥墩截面
图2。加固桥墩截面图
4． 加固工艺
4.1施工准备
首先，清理和平整施工现场，使整个码头地面，然后围绕码头支架。
4.2桥墩表面处理
因为有很多具体的老化，剥落，裂缝和对桥墩，混凝土表面如不及时治疗地表出露钢，芳纶纤维织物与混凝土的结合强度会降低，从而达不到应有的补强作用。因此，表面处理是必须的前桥桥墩钢筋。首先，把他的剥落，松散，破碎的混凝土老化，部分裂缝注入环氧树脂胶而暴露钢材除锈，然后用水泥砂浆修补和水平他们，终于顺利桥墩部分擦拭不均桥墩表面用湿布，并用丙酮清洗油腻的部分。
4.3涂片底漆
根据产品规格按比例分配的引物，充分搅拌混合均匀。防护眼镜，口罩，手套和其他安全工具必须分配时穿引物，并注意安全和防火安全。在建设的同时，也应该意识到以下几个方面：1）确定了钢筋表面的清洁和干燥，然后分配引物; 随着滚刷或刷子涂抹在表面上的钢筋环氧底漆，2）使他们充分饱和的混凝土表面; 3）涂布温度应高于5℃。如果温度低于5℃时，需要考虑到气候变暖的适当措施; 4）每所分配的引物被用完规定时间内尽快的时间，过期的引物不能使用;
5）引物标准用量：0.1〜0.3 kg/m2，具体数额由混凝土表面的条件决定的。
4.4粘贴芳纶纤维织物
4.4.1选择芳纶纤维织物
经计算和分析，pro523项目采用两层的AFS 60单向芳纶纤维织物，以加强桥墩，在表1的基本属性。
4.4.2切芳纶纤维织物
据码头的钢筋形状，大小（φ1.2m ）绘制芳纶纤维面料裁剪图，切成需要的形状纸，沿着蜿蜒的码头，纤维布不小于100毫米的搭接长度芳纶纤维织物。
4.4.3混合浸渍树脂
放入容器中的主剂和硬化剂浸渍树脂，按一定的比例，并在同一个方向搅拌均匀，然后使用与减少泡沫后充分搅拌它。
4.4.4涂片底部浸渍树脂
随着滚刷涂抹浸渍的钢筋混凝土表面树脂表面均匀，浸渍树脂底标准剂量为0.40〜0.44千克/㎡，具体数额的规定确定具体的表面状况。
4.4.5粘贴芳纶纤维织物
粘贴第一层战地服务团- 60芳纶纤维的切割和粘贴芳纶纤维轧辊布反复，为了与混凝土紧密结合图，面料。
4.4.6涂片外层浸渍树脂
涂抹外层浸渍后浸泡芳纶纤维织物底部一次树脂，采用辊涂树脂均匀地分布在纤维方向和滚一再赶走残留的气泡，使芳纶纤维织物浸泡从内到外，使芳纶纤维织物，树脂和混凝土粘合在一起。
4.4.7第二层粘贴芳纶纤维织物
可供出售后1层- 60芳纶纤维布粘贴完成，重复3,4,5,6建设过程中，您可以完成第二层战地服务团- 60芳纶纤维布粘贴。
4.5维护和会后工作
当水分附加到早期硬化树脂，它会产生负硬化层，以防止水，可用于PVC 膜覆盖保护粘连。硬化过程中，如果下雨侵蚀混凝土表面树脂，特殊稀释剂去除硬化层应使用，那么下一步施工。为了防止损坏，提高耐久性，我们应该刷上的钢筋混凝土桥墩表面的水泥砂浆面层钢筋混凝土结构。
5． 结论
芳纶纤维织物的利用，加强桥墩能有效地抑制进一步打击生成，同时
显着增加桥墩的承载能力，改善桥墩变形能力，提高抗震能力的码头和延性; 建设方便，易于操作。事实证明，芳纶纤维面料来加强桥墩是成功的。鉴于在国内土木工程结构加固用芳纶纤维织物历史观不长，建议进一步完善加强作业程序，强化质量评价标准，以进一步推广使用。
参考文献
刘来君，赵星，《桥梁加固设计和施工技术》，北京：人民交通出版社，2004 赫委乒，郑小芳，路威 《芳纶纤维织物的技术在钢筋混凝土桥墩柱中的应用》，2004年第4期
章书饪等，《钢筋混凝土和预应力混凝土桥梁结构设计原理》，北京：人民交通出版社，2004
《公路钢筋混凝土及预应力混凝土桥涵设计规范》（JTG D62 - 2004），业界人士对中国共和国标准。
海川工程科技有限公司，《芳纶纤维复合材料加固钢筋混凝土结构设计》（2003〜2004年版），2003年6月