International Concrete Abstracts Portal

To constitute an alternative to ordinary fiber-reinforced polymer in the strengthening of existing structures, the tensile properties of polypropylene (PP) and polyethylene terephthalate (PET) fiber bundles in the outdoor thermal environment (80℃ and 105℃) were investigated. The fiber bundles were carefully removed from a woven textile and test specimens with a gauge length of 25 mm were fabricated. Based on the experiments, a Weibull distribution model of the tensile strength of the PP and PET fiber bundles was developed. Test results show that exposure temperature and time significantly affect the tensile strength, rupture strain, and elastic modulus of the PP and PET fiber bundles. The strength degradation of PP and PET fiber bundles is not obvious when exposed to 80℃. In contrast, on exposure to 105℃, The usage of them requires consideration of mechanical properties degradation. This study provides exact data for the use of PP and PET fiber bundles in outdoor thermal environments.

There is a need to model the complete responses of shear-critical beams strengthened with embedded through-section (ETS) fiber-reinforced polymer (FRP) bars. Here, a strategy is proposed to integrate two separate approaches, flexural‒shear deformation theory (FSDT) for element fields and a bonding-based method for ETS strengthening, into a comprehensive computation algorithm through localized behavior at the main diagonal crack. The use of force- and stress-based solutions in the algorithm that couple fixed and updated shear crack angle conditions for analyzing the shear resistance of ETS bars is investigated. The primary benefit of the proposed approach compared to single FSDT or existing models is that member performance is estimated in both the pre-peak and post-peak loading regimes in terms of load, deflection, strain, and cracking characteristics. All equations in the developed model are transparent, based on mechanics, and supported by validated empirical expressions. The rationale and precision of the proposed model are comprehensively verified based on the results obtained for 46 datasets. Extensive investigation of the different bond‒slip and concrete tension laws strengthens the insightfulness and effectiveness of the model.

This paper presents a statistically based expression derived from the existing ACI provision for determining the development and lap splice length of glass fiber-reinforced polymer (GFRP) reinforcing bars in concrete elements subjected to flexure. Missing parameters such as confining reinforcement and the differentiation between development and lap splice strength were incorporated into the base expression available in ACI CODE-440.11-22 to enhance its reliability. A database of 201 tests was used to formulate the proposed equation, aiming to prevent a splitting failure mode and resulting in a reduction in the required embedment length for typical values employed in a GFRP-reinforced concrete beam, as compared to the ACI 440 expression. The analysis of bond strength revealed an unconservative aspect in the current ACI 440 expression, particularly noticeable in lap splice tests. The proposed expression achieved an experimental-to-predicted ratio of 1.01 with a coefficient of variation of 0.180. Finally, recommendations for adoption in the next version of the Code are presented.

This paper presents the implications of creep-fatigue interactions for the long-term behavior of bulb-tee bridge girders prestressed with either steel strands or carbon fiber-reinforced polymer (CFRP) tendons. A large amount of weigh-in-motion data incorporating 194 million vehicles are classified to realistically represent live loads. Computational simulations are conducted as per the engagement of discrete autonomous entities in line with time- dependent material models. In general, the properties of CFRP tendons vary insignificantly over 100 years; however, the stress range of CFRP responds to fatigue cycles. Regarding prestress losses, the conventional method with initial material properties renders conservative predictions relative to refined approaches considering time-varying properties. The creep and fatigue effects alter the post-yield and post-cracking responses of steel- and CFRP-prestressed girders, respectively. From deformational capability standpoints, steel-prestressed girders are more vulnerable to fatigue in comparison with CFRP-prestressed ones. It is recommended that the fatigue truck and the compression limit of published specifications be updated to accommodate the ramifications of contemporary traffic loadings. Although the operational reliability of both girder types is satisfactory, CFRP-prestressed girders outperform their steel counterparts in terms of fatigue safety. Technical findings are integrated to propose design recommendations.