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.

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.

The results of an experimental program conducted to evaluate the performance of shear-critical post-tensioned I-girders with grouted and ungrouted ducts are presented. The experimental program involved the design, construction, and testing to failure of six fullscale specimens with different duct layouts (straight, parabolic, or hybrid) and using both grouted or ungrouted ducts. All tests resulted in similar failure modes, such as localized web crushing in the vicinity of the duct, regardless of the duct condition or layout. Furthermore, the normalized shear stresses at ultimate were similar for the grouted and ungrouted specimens. The current shear design provisions in the AASHTO LRFD Bridge Design Specifications (AASHTO LRFD) were reviewed, and updated shear-strength reduction factors to account for the presence of the duct in the web and its condition (that is, grouted or ungrouted) were proposed. The data generated from these tests served as the foundation for updated shear-strength reduction factors proposed for implementation in AASHTO LRFD.

This paper describes the experimental testing of a reinforced concrete tessellated shear wall. The wall specimen was tested as part of a National Science Foundation-funded research project designed to demonstrate the concept of tessellated structural-architectural (TeSA) systems. TeSA systems are constructed of topologically interlocking tiles arranged in tessellations, or repeating geometric patterns. As such, these systems are designed with easy repair and reuse in mind. The specimen discussed in this paper is a TeSA shear wall constructed from individually precast I-shaped tiles. This paper presents the results of reverse cyclic loading of the specimen, including load-displacement behavior, crack propagation, and energy dissipation. A simplified analytical model for predicting the wall’s flexural capacity is also discussed.

Unbonded post-tensioned rocking walls have demonstrated superiorseismic performance with greatly reduced damage and excellentself-centering behavior. Current design guidelines (ACI 550.7)and representative research on rocking walls are summarized inthis paper. Some inconsistencies and voids in the major designparameters for rocking walls are identified. A brief description isprovided for two rocking-wall specimens tested under quasi-staticcyclic loading. Force flow and failure mechanisms of rocking wallsobserved from the tests were studied, and it is discovered that theyare very different from those of special structural walls. The test datashowed that the concentration of compressive strain in concrete atthe corners of rocking walls was a local behavior such that theneed for confinement reinforcement higher above the toe regionwas diminished. Fiber grout weaker than concrete in rocking wallsused as ductile bearing materials at the wall-foundation interfaceis a reasonable alternative to ACI 550.7. Design recommendationsfor height and volumetric ratio of confinement reinforcementare provided. A requirement for the aspect ratio of rocking wallsstricter than that in ACI 550.7 is proposed to prevent shear slidingof the walls.