International Concrete Abstracts Portal

Corrosion of prestressing steel can threaten the durability of prestressed concrete. To ensure the durability of unbonded post-tensioning (PT) systems, it is crucial to investigate the effects of construction defects such as grease leakage and high-density polyethylene (HDPE) sheath damage. This study quantified the thickness of grease coating (PT-coating) and HDPE sheath damage as experimental variables. An accelerated corrosion test was conducted in two environments: 1) chloride ions only (Cl-) and 2) both chloride ions and dissolved oxygen (Cl- + DO). The corrosion current density and weight loss of prestressing strands and the suspended concentration density of corrosion cell solution were measured to quantify the corrosion performance. Increasing the grease coating thickness over 0.3 mm (0.012 in.) did not significantly enhance corrosion resistance. Realistic levels of HDPE sheath damage had no significant detrimental effects on durability; however, excessive HDPE sheath area loss must be avoided for long-term durability. It was examined to quantify the interrelationship between three data: electrochemical measurement, weight loss, and suspended concentration density as quantitative corrosion data. The findings of this study can serve as a basis for developing durability-related provisions, as well as controlling the construction defects of unbonded PT systems in field applications.

This study introduces a new anchorage strategy using ultra-high-performance concrete (UHPC) to attach unbonded post-tensioning (PT) strands to existing foundations. This solution complements a seismic retrofit scheme investigated by the authors, which transforms non-ductile cast-in-place reinforced concrete (RC) shear walls into unbonded post-tensioned rocking shear walls, following concepts of selective weakening and self-centering. In the proposed PT anchorage scheme, mild steel reinforcements are inserted through the shear wall thickness and into the foundation. Subsequently, UHPC is cast around the wall base, forming a vertical extension connected to the foundation, which is used to anchor the unbonded PT strands. The feasibility and performance of the anchorage scheme were investigated through a combination of laboratory testing and numerical simulations. Pull-out testing on four scaled-down anchorage specimens was conducted in the laboratory. Hairline cracks were observed in the UHPC during testing. Additionally, 3D finite element (FE) models were created, validated, and used to study the performance of the proposed anchorage scheme under lateral loading. The simulation results support the effectiveness of the proposed anchorage strategy.

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.

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.