International Concrete Abstracts Portal

It can be demonstrated that performance-based seismic design of post-installed anchors in accordance with ACI 318 is not possible by using the anchor qualification information provided by ACI 355. The current state-of-the-art anchor qualification does not provide capacities that reflect actual earthquake responses in seismic design scenarios. This paper provides a comprehensive analysis and highlights the gaps in the current approach. A performance-based framework is proposed as the basis of future developments in seismic design and qualification of post-installed anchors. It is demonstrated that the approach is fully transparent and provides the possibility to identify key driving parameters that need further experimental investigation. The approach acknowledges that performance-based seismic design of post-installed anchors needs an understanding of the seismic damage of the concrete-anchor system. Currently, no design tools are available to predict this damage. The proposed framework adopts the theory of the accumulated damage potential (ADP) as a damage parameter. It is demonstrated that the selected damage parameter is simple but meaningful enough to represent the seismic damage of the concrete-anchor system at the design level. Possibilities for future development of the approach is explored, and directions for the next steps are suggested. It is highlighted that a definition of a framework for realistic seismic performance objectives of post-installed anchors is needed for the development of design tools in the future. The proposed framework has great practical significance and may help fill a gap in the seismic design of post-installed anchors. Promoting a transparent framework that is driven by the needs of performance-based seismic design may help develop a feasible qualification system and replace the currently used pass-or-fail assessment approach that is not suitable to provide anchor capacities for performance-based seismic design.

Two large-scale exterior beam-column connections with beam longitudinal headed bars were tested to evaluate their susceptibility to breakout failures. The specimens were designed following the strength and transverse reinforcement detailing provisions in Chapter 15 of ACI 318-19. The variable investigated was the headed bar embedment length, which was determined based on either Chapter 25 of ACI 318-19 or recent research at The University of Kansas, the latter leading to a 22% shorter embedment length. Both specimens exhibited beam flexural yielding, but the specimen with the shorter bar embedment length experienced significantly more connection damage, followed by a concrete breakout failure. Based on the limited test results, it is recommended that nominal joint shear strength be calculated based on a joint effective depth equal to the headed bar embedment length and a shear stress of 1.0λ√fc'​​ MPa (12λ​​√fc' psi). A method for calculating headed bar group anchorage strength in exterior beam-column connections was proposed, which led to reasonable and conservative strength estimates in the test specimens.

Inner surface reinforcement is one of the most widely adopted techniques for upgrading or strengthening shield tunnels. An important failure mode in this method is the debonding of the thin plates from the segments, resulting in less reinforcement effect than expected. A shield tunnel lining is a discontinuous curved structure formed by connecting segments with bolts, and its structural form and internal force state are essentially different from reinforced concrete beams. However, there are few reports on the evolution process of debonding failure of similar structures. Therefore, to develop a thorough understanding of the debonding failure, a three-dimensional refined numerical model for a shield tunnel strengthened by a thin plate at the inner surface based on the mixed-mode cohesive method was proposed. The validity and rationality of the model were corroborated by a full-scale experiment. Then, the model was applied to other inner surface reinforcement schemes commonly used in practice to explore the debonding mechanism of the adhesive layer. Finally, anti-debonding measures were proposed, and their effectiveness was elucidated by numerical analysis. The results show that the proposed numerical model can accurately predict the failure process of the adhesive interface of the shield tunnel strengthened by a thin plate. There are obvious interfacial stress concentrations at the joints and the plate ends, which are the essential reasons for the debonding failure initiating from those places. Anchoring the thin plate only at the plate ends and joints can significantly and sufficiently increase the debonding load. Therefore, it is not necessary to add anchoring measures elsewhere.

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 nonductile cast-in-place reinforced concrete (RC) shear walls into unbonded PT 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 was investigated through a combination of laboratory testing and numerical simulations. Pullout testing on four scaled-down anchorage specimens was conducted in the laboratory. Hairline cracks were observed in the UHPC during testing. Additionally, three-dimensional (3-D) 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.

During past earthquakes, failures of beam–column joints have commonly been observed on the exteriors of buildings. However, only one side of these joints can be retrofitted because of the presence of beams on the other three sides. Therefore, this study aims to test four exterior beam–column joints with transverse beams, leaving the rear side as the only viable location for placing fiber-reinforced polymer (FRP) laminate. All four test specimens are designed with insufficient joint shear strength, as determined by ACI 318 equations, while satisfying the criteria for a strong-column–weak-beam mechanism and sufficient development length for bar anchorage. A total of two un-retrofitted specimens, with and without joint hoops, are constructed as controls. Subsequently, two similar specimens are retrofitted by applying an FRP laminate on the rear side. The results show that sufficient FRP laminate can enhance the seismic performance of joints in terms of deformability, energy dissipation, and failure delay.