International Concrete Abstracts Portal

Design recommendations are presented for calculating the immediate deflection of cracked prestressed concrete members under service load. Inconsistency and sometimes confusion regarding the calculation of immediate deflection for the different approaches presently available highlight the need for a rational approach to computing deflection. The ACI 318-19 approach for reinforced (nonprestressed) concrete is broadened to include prestressed concrete. This involves the implementation of an effective moment of inertia taken together with an effective eccentricity of the prestressing steel used to define the effective curvature and/or camber from the prestressing force. Proposed revisions to ACI 318 are presented for prestressed Class T and Class C flexural members and clear steps are provided for calculating immediate deflection. The effectiveness of the new approach is validated against an extensive database of test results, showing reasonable accuracy and reliability in predicting deflections. The paper concludes with practical recommendations for implementation and a worked-out example to illustrate the proposed methodology. These findings aim to enhance the accuracy and consistency of deflection predictions in prestressed concrete design, contributing to better serviceability and performance of concrete structures.

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 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.

Prediction of immediate deflection is evaluated for cracked prestressed concrete members using integration of curvature. Integration accounts for changes in member stiffness and strand eccentricity along the member length when applicable. Several approaches are considered, including a bilinear momentdeformation response and those using an effective moment of inertia based either on an effective prestress moment defined by an effective eccentricity of the prestress force or an offset in the cracked response with tension stiffening. Comparison is also made with deflection computed directly, assuming a uniform member stiffness based on the effective moment of inertia at the critical section where the moment is greatest. Results are evaluated using an extensive database for beams either fully or partially prestressed. The beams are simply supported under two-point loading and have a straight tendon profile with constant eccentricity. Integration of curvature is observed to improve prediction of immediate deflection in general and depends not only on the approach used but on several factors that include the cracking moment, elastic modulus of concrete, and the effect of approximating uncracked section properties with gross section properties.

This study investigated the serviceability behavior and strength of polypropylene-fiber (PF) reinforced self-consolidating concrete (PFSCC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. Five full-scale concrete beams measuring 3100 mm long × 200 mm wide × 300 mm deep (122.1 × 7.9 × 11.8 in.) were fabricated and tested up to failure under four-point bending cyclic loading. Test parameters included the longitudinal reinforcement ratio (0.78, 1.18, and 1.66%) and polypropylene fiber (PF) volume (0, 0.5, and 0.75% by concrete volume). The effect of these parameters on serviceability behavior and strength of the test specimens is analyzed and discussed herein. All the beams were evaluated for cracking behavior, deflection, crack width, strength, failure mode, stiffness degradation, and deformability factor. The test results revealed that increasing the reinforcement ratio and PF fiber volume enhanced the serviceability and flexural performance of the beams by effectively restraining crack widths, reducing deflections at the service and ultimate limit states, and decreasing residual deformation. The stiffness exhibited a fast-to-slow degradation trend until failure for all beams, at which point the beams with a higher reinforcement ratio and fiber volume evidenced higher residual stiffness. The cracking moment, flexural capacities, and crack width of the tested beams were predicted according to the North American codes and design guidelines and compared with the experimental ones. Lastly, the deformability for all beams was quantified with the J-factor approach according to CSA S6-19. Moreover, the tested beams demonstrated adequate deformability as per the calculated deformability factors.