International Concrete Abstracts Portal

An approach to improve the progressive collapse resistance of conventional RC frame structure was put forth by using unbonded post-tensioning strand (UPS). Two UPSs with a straight profile are mounted at the bottom of the beam section. A static loading test was conducted on an unbonded prestressed RC (UPRC) beam-column sub-assemblage under a column removal scenario. The structural behaviors of the test specimen, such as the load-carrying capacity, failure mode, post-tensioning force of the UPSs, and rebar strain, were captured. By analyzing the results of the tested substructure, it was found that the compressive arch action (CAA) and catenary action (CTA) were sequentially mobilized in the UPRC sub-assemblage to avert its progressive collapse. The presence of UPSs could significantly improve the load-carrying capacity of conventional RC structures to defend against progressive collapse. Moreover, a high-fidelity finite element (FE) model of the test specimen was built by using the software ABAQUS. The FE model was validated by the experimental results in terms of the variation of vertical load, horizontal reaction force, and post-tensioning force of the UPSs against middle joint displacement (MJD). Finally, a theoretical model was proposed to evaluate the anti-progressive collapse capacities of UPRC sub-assemblages. It was validated by the test result as well as by the FE Models of the UPRC sub-assemblages which were calibrated using the available experimental data.

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.

This paper examines the inaccuracy of the initial strain method that is generally adopted in three-dimensional (3-D) finite element prestressing analysis and discusses the merits of a newly developed method to calculate 3-D prestressing effects. The new method considers friction loss of the tendon force as well as pseudo- centripetal forces, allowing a wide range of functional forms for the prestressed concrete (PC) steel force distribution assumption. This study examined the basic concepts for adopting the functional form of the PC steel force distribution at the prestressing and seating stages, after which the observed and calculated values of pulled-out lengths of PC steel were compared to assure the credibility of the assumed functional form of the PC steel force distribution. A three-span continuous bridge model was used to compare results obtained by the conventional method and the new 3-D method. The equilibrium of a free body was used also to evaluate the accuracy of results by the new method. The importance of the new method being able to calculate a pulled-out PC steel length considering concrete deformation was stressed because this value may be adopted to confirm assumptions of the PC steel force distribution.

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.

This study examined how tendon configuration affects the temperature behavior of post-tensioned concrete structures during fire exposure using finite element analysis. The thermal behavior of various tendon configurations was modeled, showing good agreement with experimental data. Parametric studies found that unbonded single-strand tendon (S) and prestressing (pre-tensioned) strand (R) had lower thermal resistance compared to bonded post-tensioned tendon (B), unbonded post-tensioned tendon (U), and grouted extruded-strand tendon (G). The S and R specimens stayed at or below the critical temperature for one-way slabs, validating current safety codes. The B, U, and G specimens remained well below critical temperatures, indicating thinner concrete cover might suffice. These findings highlight the need to consider tendon configuration in structural fire resistance evaluation and incorporate heat resistance assessment to ensure the safety and efficiency of prestressed concrete structures during fires.