Reconsideration of the Environmental Reduction FactorCEfor GFRP Reinforcing Bars in Concrete Structures

Design guides for fibre-reinforced polymer-reinforced concrete (FRP-RC) require that the design tensile strength of FRP bars be determined by multiplying the guaranteed tensile strength by an environmental reduction factor (C-E), to account for the long-term effects of environmental exposure. The recommendedC(E)values in the American Concrete Institute (ACI) design guide are based on a consensus of the opinion of ACI 440 Committee members and believed to be conservative. The ACI design guide notes the expectation that, with continued research,C(E)values will become more reflective of observed environmental performance. In this study,C(E)values were estimated for a compiled database of glass FRP (GFRP) bars based on short-term results from accelerated aging tests. TheC(E)values were calculated with a prediction model considering the effects of seasonal temperature fluctuations, service year, and relative humidity (RH) of exposure. The analysis shows that the calculated values ofC(E)depend to a certain extent on the mean annual temperatures and RH. In all cases, however, the calculated values were higher than those recommended in the ACI design guide. The authors recommend aC(E)value of 0.85 for an assumed service life of 75-100 years to be applied to the guaranteed tensile strength as the basis for determining the design tensile strength. This value is recommended for GFRP bars complying with ASTM Standards, whether exposed or unexposed to earth and weather in cold temperatures and climates encountered in most regions of the world.

纤维增强聚合物（FRP）增强混凝土（FRP - RC）的设计指南要求，FRP筋的设计抗拉强度应通过将保证抗拉强度乘以环境折减系数（C - E）来确定，以考虑环境暴露的长期影响。美国混凝土学会（ACI）设计指南中推荐的C(E)值是基于ACI 440委员会成员的共识，并且被认为是保守的。ACI设计指南指出，随着研究的不断深入，C(E)值将更能反映所观察到的环境性能。在本研究中，基于加速老化试验的短期结果，对一个汇编的玻璃纤维增强聚合物（GFRP）筋数据库估算了C(E)值。C(E)值是通过一个考虑季节温度波动、使用年限和暴露环境相对湿度（RH）影响的预测模型计算得出的。分析表明，C(E)的计算值在一定程度上取决于年平均温度和相对湿度。然而，在所有情况下，计算值都高于ACI设计指南中推荐的值。作者建议，对于假定的75 - 100年使用寿命，将0.85作为C(E)值应用于保证抗拉强度，以此作为确定设计抗拉强度的基础。对于符合美国材料与试验协会（ASTM）标准的GFRP筋，无论在世界大多数地区所遇到的寒冷温度和气候条件下是否暴露于土壤和天气中，都推荐使用该值。