International Concrete Abstracts Portal

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.

Compared to conventional reinforced concrete (RC) flat-plate systems, post-tensioned (PT) flat-plate systems lack experimental studies on shear strength, and there are no studies that have been analyzed and collected with clear criteria (for example, calculation of effective depth, unbalanced moment, and measured shear strength) about experiments conducted so far. As a result, the current ACI 318-19, Section 22.6.5, for prestressed members has many restrictions based on the lack of experimental data on the nominal shear-strength equation. In this study, to reevaluate the nominal shear strength of the PT flat-plate system more reasonably and provide a reference for future studies, a total of 120 experimental data on the shear strength of the PT flat-plate system without shear reinforcement that have been conducted so far were recalculated and recompiled with clear criteria (the experimental data consists of 74 interior connections, 41 edge connections, and five corner connections). In addition, the factors affecting the shear strength and the validity of restrictions in the nominal shear-strength equation of ACI 318-19 were analyzed. The factors affecting the shear strength include: 1) method of loading; 2) presence of nonprestressed reinforcement; and 3) reinforcement ratio along the lateral load direction. The restrictions in the nominal shear-strength equation of ACI 318-19 include: 1) fc′ ≤ 4900 psi (34 MPa); 2) fpc ≥ 125 psi (0.9 MPa) (in each direction); 3) fpc ≤ 500 psi (3.5 MPa) (average in the two directions); and 4) it is applicable only for interior connections.

In tall core-wall buildings with concrete unbonded post-tensioned flat-plate gravity framing, modeling the behavior of the slab-wall-column framing under earthquake loading can be crucial to determining structural response quantities for the design of the flat-plate framing. The outrigger action of the gravity system also affects the overall dynamic properties of the building and may affect wall moment and shear demands. The outrigger effect can be modeled using a slab-beam model, which uses linear-elastic frame elements with concentrated nonlinear hinges at each end. In this study, the slab-beam model is calibrated using results from a slab-wall-column laboratory test. Recommendations suitable for design office practice are presented.

Post-tensioned concrete flat slabs with high span-depth ratios are susceptible to vibration problems. Although the issue was addressed in previous research, there is no final agreement on the effect of prestress level on the fundamental frequency of post-tensioned concrete slabs. Through numerical modeling using Abaqus software, this paper presents the effect of prestressing forces on the fundamental frequencies of slabs. This paper also examines the applicability and accuracy of the available mathematical models to estimate the fundamental frequency of concrete slabs. Finally, the paper presents two newly proposed mathematical models created by a neural designer program. The first model estimates the fundamental frequencies of uncracked concrete slabs, and it is more accurate than the currently available equations. The secondproposed model estimates the peak acceleration of uncrackedconcrete slabs, and it is applicable for the dynamic motion of aforcing frequency of 2 Hz and a damping ratio of 2%.

With the development and commercialization of post-tensioned (PT) concrete structures, concerns pertaining to structural safety for disasters and diverse conditions, such as fire and high temperatures, have emerged. To better understand fire-resistance performance, effects associated with cover thickness and tendon configurations for six unbonded PT concrete slabs were evaluated in regardto temperature changes, deflection, tendon tensile forces, and fire endurance/time. In addition, the factors and relationship between the extent of damage caused by concrete cracking/delamination and tendon force at post-tensioning were evaluated. Thermal resistance and deflection rates for materials such as galvanized steel duct or high-density polyethylene (HDPE) sheathing were also examined. It is the authors’ hope that the aforementioned informationidentifying parameters affecting fire-resistance performanceof PT slabs may be helpful to the practitioner when consideringtendon configurations for unbonded PT concrete structures.