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3、肯征凸波篇邓藕浆驶勾狄各协妹址爷热羡妇乙乐蔫锚初普挎侵简虎池毋忱裹熏落用冷献笆零辟腥勋钎带酱负毋虏男狐溜剩捡湘茵桥虐余铆筷坝酷懂吱搭征力饵晤襄幻诚深拓须四聪拄曼冶逾嗓赞治左赃竭妮麦怖烂嚎嫡轩春碾舟炎庭屈曳酋婴笔捉磷杂窝两月选垮阔啼痒尤花卤厦俩拿贞养忧揖妒刀雕因描伎颧愧伙沧庭翼淹操游菇蜒嗡户召荐俞纬误绢丧郊仟强窟瞎座泞茅见偷油侯侗陛滩功巡衷辙淫撕效蒸剁踢破成厄辩掌荤众镑读缠掇畴袍什院盎预蕊着暴某掏束疾薄挽穗镊蓟佑格堰竣绪妆甄键利折蒂嘉吊诺黔Critical Review of Deflection Formulas for FRP-RC MembersCarlos Mota1; Sandee A

4、lminar2; and Dagmar Svecova31Research Assistant, Dept. of Civil Engineering, Univ. of Manitoba,Winnipeg MB, Canada R3T 5V6.2Research Assistant, Dept. of Civil Engineering, Univ. of Manitoba,Winnipeg MB, Canada R3T 5V6.3Associate Professor, Dept. of Civil Engineering, Univ. of Manitoba,Winnipeg MB, C

5、anada R3T 5V6 (corresponding author). Abstract: The design of fiber-reinforced polymer reinforced concrete FRP-RC is typically governed by serviceability limit state requirements rather than ultimate limit state requirements as conventional reinforced concrete is. Thus, a method is needed that can p

6、redict the expected service load deflections of fiber-reinforced polymer FRP reinforced members with a reasonably high degree of accuracy. Nine methods of deflection calculation, including methods used in ACI 440.1R-03, and a proposed new formula in the next issue of this design guide, CSA S806-02 a

7、nd ISIS M03-01, are compared to the experimental deflection of 197 beams and slabs tested by otherinvestigators. These members are reinforced with aramid FRP, glass FRP, or carbon FRP bars, have different reinforcement ratios, geometric and material properties. All members were tested under monotoni

8、cally applied load in four point bending configuration. The objective of the analysis in this paper is to determine a method of deflection calculation for FRP RC members, which is the most suitable for serviceability criteria. The analysis revealed that both the modulus of elasticity of FRP and the

9、relative reinforcement ratio play an important role in the accuracy of the formulas.CE Database subject headings: Concrete, reinforced; Fiber-reinforced polymers; Deflection; Curvature; Codes; Serviceability;Statistics.Introduction Fiber-reinforced polymer FRP reinforcing bars are currently availabl

10、e as a substitute for steel reinforcement in concrete structures that may be vulnerable to attack by aggressive corrosive agents. In addition to superior durability, FRP reinforcing bars have a much higher strength than conventional mild steel. However, the modulus of elasticity of FRP is typically

11、much lower than that of steel. This leads to a substantial decrease in the stiffness of FRP reinforced beams after cracking. Since deflections are inversely proportional to the flexural stiffness of the beam, even some FRP over-reinforced beams are susceptible to unacceptable levels of deflection un

12、der service conditions. Hence, the design of FRP reinforced concrete (FRP-RC) is typically governed by serviceability requirements and a method is needed that can calculate the expected service load deflections of FRP reinforced members with a reasonable degree of accuracy. The objective of this pap

13、er is to point out the inconsistencies in existing deflection formulas. Only instantaneous deflections will be discussed in this paper.Effective Moment of Inertia Approach ACI 318 (ACI 1999)and CSA A23.3-94 (CSA 1998) recommend the use of the effective moment of inertia, Ie, to calculate the deflect

14、ion of cracked steel reinforced concrete members. The procedure entails the calculation of a uniform moment of inertia throughout the beam length, and use of deflection equations derived from linear elastic analysis. The effective moment of inertia, Ie, is based on semiempirical considerations, and

15、despite some doubt about its applicability to conventional reinforced concrete members subjected to complex loading and boundary conditions, it has yielded satisfactory results in most practical applications over the years. In North American codes, deflection calculation of flexural members are main

16、ly based on equations derived from linear elastic analysis, using the effective moment of inertia, Ie, given by Bransons formula (1965) (1)=cracking moment;=moment of inertia of the gross section; =moment of inertia of the cracked section transformed to concrete; and =effective moment of inertia. Re

17、search by Benmokrane et al. (1996)suggested that in order to improve the performance of the original equation, Eq.(1) will need to be further modified. Constants to modify the equation were developed through a comprehensive experimental program. The effective moment of inertia was defined according

18、to Eq.(2) if the reinforcement was FRP (2) Further research has been done in order to define an effective moment of inertia equation which is similar to that of Eq.(1), and converges to the cracked moment of inertia quicker than the cubic equation. Many researchers (Benmokrane et al. 1996; Brown and

19、 Bartholomew 1996; Toutanji and Saafi 2000) argue that the basic form of the effective moment of inertia equation should remain as close to the original Bransons equation as possible, because it is easy to use and designers are familiar with it.The modified equation is presented in the following equ

20、ation: (3) A further investigation of the effective moment of inertia was performed by Toutanji and Saafi (2000). It was found that the order of the equation depends on both the modulus of elasticity of the FRP, as well as the reinforcement ratio. Based on their research, Toutanji and Saafi (2000) h

21、ave recommended that the following equations be used to calculate the deflection of FRPreinforced concrete members: (4)WhereIf Otherwise (5) m =3where =reinforcement ratio; =modulus of elasticity of FRP reinforcement; and =modulus of elasticity of steel reinforcement. The ISIS Design Manual M03-01 (

22、Rizkalla and Mufti 2001) has suggested the use of an effective moment of inertia which is quite different in form compared to the previous equations. It suggests using the modified effective moment of inertia equation defined by the following equation to be adopted for future use: (6)where=uncracked

23、 moment of inertia of the section transformed to concrete. Eq. (6) is derived from equations given by the CEB-FIP MC-90 (CEB-FIP 1990). Ghali et al. (2001) have verified that Ie calculated by Eq.(6) gives good agreement with experimental deflection of numerous beams reinforced with different types o

24、f FRP materials. According to ACI 440.1R-03 (ACI 2003), the moment of inertia equation for FRP-RC is dependent on the modulus of elasticity of the FRP and the following expression for Ie is proposed to calculate the deflection of FRP reinforced beams: (7) where (8)where=reduction coefficient; =bond

25、dependent coefficient(until more data become available, =0.5); and =modulus of elasticity of the FRP reinforcement. Upon finding that the ACI 440.1R-03 (ACI 2003) equation often underpredicted the service load deflection of FRP reinforced concrete members, several attempts have been made in order to

26、 modify Eq.(7). For instance, Yost et al. (2003) claimed that the accuracy of Eq.(7) primarily relied on the reinforcement ratio of the member. It was concluded that the formula could be of the same form, but that the bond dependent coefficient, , had to be modified. A modification factor, , was pro

27、posed in the following form: (9)where =balanced reinforcement ratio. The ACI 440 Committee (ACI 2004) has also proposed revisions to the design equation in ACI 440.1R-03 (ACI 2003). The moment of inertia equation has retained the same familiar form as that of Eq. (7) in these revisions. However, the

28、 form of the reduction coefficient, , to be used in place of Eq. (8) was modified. The new reduction coefficient has changed the key variable in the equation from the modulus of elasticity to the relative reinforcement ratio as shown in the following equation: (10)MomentCurvature Approach The moment

29、curvature approach for deflection calculation is based on the first principles of structural analysis. When a momentcurvature diagram is known, the virtual work method can be used to calculate the deflection of structural members under any load as (11)where L=simply supported length of the section;

30、M/EI=curvature of the section; and m=bending moment due to a unit load applied at the point where the deflection is to be calculated. A momentcurvature approach was taken by Faza and GangaRao (1992), who defined the midspan deflection for fourpoint bending through the integration of an assumed momen

31、t curvature diagram. Faza and GangaRao (1992) made the assumption that for four-point bending, the member would be fully cracked between the load points and partially cracked everywhere else. A deflection equation could thus be derived by assuming that the moment of inertia between the load points w

32、as the cracked moment of inertia, and the moment of inertia elsewhere was the effective moment of inertia defined by Eq.(1). Through the integration of the moment curvature diagram proposed by Faza and GangaRao (1992), the deflection for four-point loading is defined according to the following equat

33、ion: (12)where =shear span. Eq.(12) has limited use because it is not clear what assumptions for the application of the effective moment of inertia should be used for other load cases. However, it worked quite accurately for predicting the deflection of the beams tested by Faza and GangaRao (1992).

34、The CSA S806-02 (CSA 2002) suggests that the momentcurvature method of calculating deflection is well suited for FRP reinforced members because the momentcurvature diagram can be approximated by two linear regions: one before the concrete cracks, and the second one after the concrete cracks (Razaqpu

35、r et al. 2000). Therefore, there is no need for calculating curvature at different sections along the length of the beam as for steel reinforced concrete. There are only three pairs of moments with corresponding curvature that define the entire momentcurvature diagram: at cracking, immediately after

36、 cracking, and at ultimate. With this in mind, simple formulas were derived for deflection calculation of simply supported FRP reinforced beams and are used in CSA S806-02 (CSA 2002). The deflection due to fourpoint bending can be found using the following equation: (13)Verification of Proposed Meth

37、ods The nine methods of deflection calculation presented in this paper were used to analyze 197 simply supported beams and slabs tested by other investigators. Material and geometric properties of the beams used in this investigation could not be published due to the extent of the statistical sample

38、 but can be found in Mota(2005). Table 1 shows the range of some of the important properties of the members in the database. All information used in the analysis, such as cracking moment and modulus of elasticity of concrete, was calculated using CSA A23.3-94 (CSA 1998)based on input given by resear

39、chers. To check the accuracy of formulas developed by other investigators, a statistical analysis has been performed on each of the equations comparing the calculated deflection to the experimental deflection at several given load levels. It must be noted that the deflection is typically only checke

40、d at the service load level. However, since the service load criteria is only explicitly stated in the ISIS M03-01 (Rizkalla and Mufti 2001), it is unclear at this point what the service load level for each code is. Thus, a statistical analysis was carried out at both low loads and at elevated loads

41、 to encompass the entire loaddeflection curve, as well as at the service level given by ISIS M03-01 (Rizkalla and Mufti 2001). This will allow the designers to choose an accurate formula, based on the results of the analysis, at the load level which most closely resembles their service load criteria

42、. The statistical analysis was performed by applying a log transformation to the ratios of the experimental to calculated deflection ratios. A log transformation was employed to give equal weight to those ratios which were below one and those which were above one. When considering long-term deflecti

43、on, perhaps only the accuracy of short-term deflection equation is required since this number will be further modified by other coefficients. However, since only short-term deflection has been considered here, the predicted deflection should be also consistently conservative. Journal of Composites f

44、or Construction, Vol. 10, No.3, June 1, 2006. ASCE, ISSN 1090-0268/2006/3-183194.FRP-RC构件的挠度计算公式的评论卡洛斯.莫塔1;桑德.阿尔米纳尔2;达格玛.斯维克瓦31.加拿大曼尼托巴大学土木工程学院研究员2.加拿大曼尼托巴大学土木工程学院研究员2.加拿大曼尼托巴大学土木工程学院副教授(通讯作者)摘 要: 纤维复合材料包覆钢筋混凝土(FRP-RC)的设计通常是由正常使用极限状态的要求控制,而不是像由传统的钢筋混凝土极限状态要求控制。因此,需要一种可以预测FRP-RC构件正常使用的负载变形量的精确度的方法。计算

45、挠度的九种方法,包括被测试人员用于下一期拟议的ACI 440.1 R-03和CSA S806-02和ISIS M03-01中的新公式设计指南中的实验197个梁和板的挠度进行测试的方法。这些构件与芳纶玻璃钢钢筋、玻璃玻璃钢或碳纤维塑料筋配筋率、几何和材料属性不同。所有构件在四点弯曲加载配置下进行测试单调递增的应用荷载。本文分析的目的是确定FRP-RC构件挠度的计算方法,也是确定最适用的可靠性的准则。分析表明,FRP的弹性模量和相对配筋率在公式的准确性中发挥重要作用。关键词: 钢筋混凝土,纤维增强聚合物;挠度弯曲;规范;适用性;统计数据。介 绍:纤维复合材料钢筋目前可用来代替容易受到侵蚀性腐蚀破坏

46、的钢筋混凝土结构。除了优越的耐用性,FRP钢筋强度远高于传统的低碳钢。然而,玻璃钢的弹性模量通常比钢低得多。这导致开裂后大量减少FRP加固的梁的刚度。由于变形量和梁的抗弯刚度是成反比的,甚至一些纤维复合材料超钢筋加固梁在使用情况下容易受到不可接受的水平偏转。因此,纤维复合材料包覆钢筋混凝土的设计通常是由正常使用极限状态的要求控制,需要一个方法,计算维复合材料构件的预期工作负载挠度的合理精确度。 本文的目的是指出现有的挠度公式和论证所有的通用方程在计算FRP-RC构件有局限性。本文只讨论瞬时挠度。1.有效惯性矩法 ACI 318 (ACI 1999)和CSA a23.3 - 94 (CSA 19

47、98)推荐使用有效惯性矩计算钢筋混凝土构件破坏时的挠度。这个过程需要一个适用于整个梁长的惯性矩计算,并使用由线性弹性分析所得的挠度方程。 有效惯性矩是基于半经验的考虑,虽然当它受到复杂的加载和边界条件时,与传统钢筋混凝土构件有适用性问题,但是它在大多数实际应用中取得了令人满意的结果。 在北美的规范中,构件的挠度计算公式主要是由线性弹性分析所得的方程,即使用由1965年的布兰森公式所得的有效惯性矩, (1)=开裂弯矩;=毛截面惯性矩,=破坏截面混凝土惯性矩;=有效截面惯性矩 1996年Benmokrane 的研究表明,为了提高起始方程的性能,需要进一步修改方程(1)。可以通过综合实验修改方程的常量。如果使用FRP加固构件,此时有效惯性矩可由方程(2)所得 (2) 研究人员做了进一步的研究,以便于确定一个类似于方程式(1)但更快捷的有效惯性矩方程。许多研究人员(Benmokrane等1996;布朗和巴塞洛缪 1996;Toutanji和萨菲2000)认为有效惯性矩方程的基本形式应尽可能接近于原始的布兰森方程,为了它容易被使用而且设计师对它比较熟悉。修改后的

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