摘要
基于文献数据,采用假设检验法,开展纤维增强复合材料(FRP)箍筋强度保留率分布规律研究. 通过Kolmogorov‑Smirnov(K‑S)检验对比了Weibull分布、正态分布及对数正态分布这3种模型对FRP箍筋强度保留率的拟合优度.结果表明:当FRP箍筋弯折半径(R)与箍筋直径(D)之比(R/D)在常规范围内(3~5)时,对数正态分布为最优分布模型,据此得到95%和50%保证率下FRP箍筋强度保留率分别不小于32.46%和43.79%;中国、美国、日本和加拿大四国规范保留率预测公式计算结果的保证率仅为24.1%~40.3%,偏于不安全.根据中国FRP纵筋与箍筋的强度保证率要求,当R/D=3、4、5时玻璃纤维增强复合材料(GFRP)箍筋强度保留率不小于38.86%、35.68%、46.09%.
纤维增强复合材料(FRP)筋质量轻、强度高、耐腐蚀性优,可用来替代钢筋,解决混凝土结构中的钢筋锈蚀问
鉴于此,本文通过文献调研建立FRP箍筋弯拉强度及强度保留率(S)的数据库,并通过假设检验法确定FRP箍筋强度保留率的最优分布模型.在此基础上进行可靠性分析,并以工程中最为常用的玻璃纤维增强复合材料(GFRP)箍筋为例,提出基于箍筋强度设计要求的箍筋强度保留率的合理取值.
国内外学者自21世纪初即开展了众多FRP箍筋强度试验研究.本文在公开发表的论
Imjai
由于影响FRP箍筋强度保留率的参数众多,本研究基于Pearson相关性理论,先对FRP箍筋强度保留率与各影响因素之间的相关性进行分析.
Pearson相关系数(r)又称积差相关系
(1) |
式中:、分别表示变量X和Y的每个具体值;、分别表示变量X、Y的所有数据的平均值;n表示变量X与Y的数据量.
r是一个无量纲的统计指标. r > 0表明变量X与Y正相关;r < 0表明变量X与Y负相关;r = 0表明变量X与Y不相关.|r|越接近1,两变量之间的相关程度就越密切.变量间相关程度与r的对应关系如
Correlation degree | ∣r∣ |
---|---|
Uncorrelation | [0,0.3) |
Weak correlation | [0.3,0.5) |
Significant correlation | [0.5,0.8) |
Strong correlation | [0.8,1] |
Factor | r |
---|---|
Type of FRP stirrup | 0.12 |
Test method | -0.28 |
Section shape of stirrup | 0.07 |
Fiber content | 0.07 |
Diameter | -0.24 |
Bend radius | 0.19 |
R/D | 0.63 |
Tensile strength | 0.24 |
Elastic modulus | 0.28 |
基于试验数据的筛选原则与相关性分析结果,筛选出的59组数据涵盖了工程中常用的FRP箍筋类型(GFRP、BFRP、CFRP)及箍筋的R/D范围(3~5).详细数据来
Author | Type of stirrup | Section shape | D/mm | R/mm | R/D | Bend strength/ MPa | Tensile strength/MPa | S/% |
---|---|---|---|---|---|---|---|---|
Li, et al | CFRP | Rectangle | 2.0 | 8 | 4 | 1 086 | 2 480 | 43.8 |
Ahmed, et al | GFRP | Circular | 9.5-19.1 | 38-76 | 4 | 240-712 | 533-1 538 | 32.9-58.3 |
Imjai, et al | GFRP | Rectangle/circular | 3.0-13.5 | 9-54 | 3-5 | 271-464 | 690-720 | 36.6-64.4 |
Shehata, et al | CFRP | Rectangle/circular | 5.0-12.0 | 20-50 | 4 | 345-793 | 713-1 800 | 44.1-56.1 |
El‑Sayed, et al | CFRP | Circular | 9.5-12.7 | 38-51 | 4 | 539-761 | 1 224-1 328 | 44.0-57.3 |
WANG, et al | GFRP | Circular | 7.0 | 20 | 3 | 387 | 1 045 | 37.0 |
L | BFRP | Circular | 6.0-8.0 | 24-32 | 4 | 347-594 | 1 096-1 604 | 31.6-39.1 |
本文采用Weibull分布、正态分布和对数正态分布3种分布模型,对不同R/D情况下FRP箍筋强度保留率数据进行拟合.并通过线性回归分析及Kolmogorov‑Smirnov(K‑S)检验确定最优分布模型.
先将以上3种分布模型的概率累积分布函数表达式线性变换为y=ax+b形式,如
Distribution model | Cumulative distribution function | y | x | a | b |
---|---|---|---|---|---|
Weibull | |||||
Normal | |||||
Lognormal |
Note: F(S) represents the cumulative distribution function of Weibull distribution, normal distribution and lognormal distribution; μ and σ are the mean and standard deviation of different distribution models; a,b represents the slope and intercept of the linear function after linear regression,respectively.
R/D | Weibull | Normal | Lognormal | Critical value of significant level | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|
=0.01 | =0.05 | ||||||||||
3 | 46.22 | 9.98 | 0.917 | 44.04 | 5.42 | 0.952 | 44.11 | 5.33 | 0.966 | 0.575 | 0.456 |
4 | 48.04 | 6.63 | 0.941 | 44.84 | 8.28 | 0.970 | 44.92 | 8.44 | 0.980 | 0.440 | 0.345 |
5 | 56.45 | 8.95 | 0.957 | 53.59 | 7.14 | 0.968 | 53.72 | 7.36 | 0.958 | 0.684 | 0.553 |

图1 不同R/D情况下3种分布模型的线性回归结果
Fig.1 Linear regression results of three distribution models with different R/D values
K‑S检
(2) |
式中:j为按照强度保留率由小到大排序的序号;Sj为序号为j的FRP箍筋强度保留率;N表示样本数据总量;Fj(Sj)为由累计分布函数计算得到的强度保留率达到Sj时的失效概率理论值;F(Sj)为通过中位秩法计算所得箍筋强度保留率达到Sj时的失效概率,.
选取工程上常用的显著性水平α=0.01和α=0.05,进行不同R/D情况下K‑S检验,结果如
R/D | N | DN | DN,α | ||||
---|---|---|---|---|---|---|---|
Weibull | Normal | Lognormal | =0.01 | =0.05 | |||
3 | 17 | 0.107 | 0.086 | 0.081 | 0.381 | 0.318 | |
4 | 31 | 0.101 | 0.070 | 0.061 | 0.285 | 0.240 | |
5 | 11 | 0.094 | 0.097 | 0.077 | 0.468 | 0.391 |
本文基于FRP箍筋强度保留率最优分布模型——对数正态分布模型,采用
(3) |

图2 不同R/D情况下FRP箍筋强度保留率-保证率曲线
Fig.2 Strength retention rate‑reliability curves of FRP stirrup under different R/D values
根据试验值,将采用中位秩法得到的保留率-保证率曲线也绘于
中
(4) |
式中:ffb表示FRP箍筋弯拉强度;ffu表示FRP箍筋直线段抗拉强度.
基于FRP箍筋强度保留率满足对数正态分布规律,本文对各国现行规范中的FRP箍筋强度保留率进行可靠性分析,结果显示:当R/D=4时,各国规范中FRP箍筋强度保留率计算值的保证率仅为24.1%;当R/D=3、5时,FRP箍筋强度保留率计算值的保证率分别为40.3%、39.5%,均小于50%,总体上偏于不安全.
当FRP箍筋强度保留率服从对数正态分布时,在某一保证率下的保留率可按
(5) |
式中:z为将对数正态分布转换为标准正态分布时对应的参数,可查表确定.
R/D | R(S)/% | S/% | /% | ||
---|---|---|---|---|---|
3 | 44.11 | 5.33 | 95 | 35.90 | 44.04 |
50 | 43.79 | ||||
5 | 53.41 | ||||
4 | 44.92 | 8.44 | 95 | 32.46 | 44.85 |
50 | 44.15 | ||||
5 | 60.04 | ||||
5 | 53.72 | 7.36 | 95 | 42.50 | 53.58 |
50 | 53.22 | ||||
5 | 66.66 |
本文基于上述提出的FRP箍筋强度保留率分布模型和已有的工程应用最多的GFRP纵筋抗拉强度分布模

图3 GFRP箍筋弯拉强度分布规律
Fig.3 Distribution law of bend strength of GFRP stirrups
(1)在159组影响FRP箍筋强度保留率试验数据的基础上,基于有效数据筛选原则与相关性分析结果,得到由59组数据构成且按弯折半径R与箍筋直径D之比R/D分组的FRP箍筋强度保留率数据库,用于确定分布模型.
(2)综合线性回归分析和K‑S检验结果,研究发现Weibull分布、正态分布和对数正态分布模型均可表征FRP箍筋强度保留率的分布规律,且对数正态分布为最优分布模型.
(3)中国、美国、日本和加拿大现行规范中FRP箍筋强度保留率计算值的保证率均小于50%. 当R/D=3、5时,保证率为40.3%、39.5%;当R/D=4时,保证率仅为24.1%,总体上偏不安全.
(4)根据中国FRP纵筋与箍筋的强度设计要求,当R/D=3、4、5时GFRP箍筋强度保留率分别为38.86%、35.68%、46.09%.
需要说明的是,本文中FRP箍筋强度保留率的相关结论仅适用于采用连续纤维拉挤工艺生产的FRP箍筋,采用模压工艺成型的FRP箍筋强度保留率的可靠性仍需进一步开展相关研究.
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