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1. Effects of Axial Load and Tensile Strength on Reinforced UHPC Plastic Hinge Length

   https://doi.org/10.21838/uhpc.16658  

   Almeida, Joseph; Bandelt, Matthew (June 2023, International Interactive Symposium on UHPC)

   Aaleti, Sriram; Okumus, Pinar (Ed.)

   Researchers have explored the high energy absorption capacity and strength of UHPC materials to improve the seismic performance of structural components. Experimental results in the literature of reinforced UHPC members have indicated superior damage tolerance, higher strength and deformation capacities, and lower potential for collapse across a range of structural components. Investigations into the underlying failure mechanisms have highlighted the significance of the synergy between material tensile strength and reinforcement properties on member flexure response. Although research into the seismic application of reinforced UHPC continues to expand, relatively little is known about the effects of varying axial load on the plastic hinge response of beam-column elements across a range of UHPC tensile properties and reinforcement levels. Therefore, in this study, the effects of varying tensile properties on beam-column elements through numerical simulations across a range of axial load ratios were investigated. Two dimensional numerical models accounting for material nonlinearities (e.g., bond-slip, UHPC tensile strength and strain capacity) were used to capture component responses. Trends in the moment-drift responses and plastic hinge lengths have highlighted the diminishing returns of using higher fiber volume percentages (2%) as higher axial loads tend to relieve tensile demands. Additionally, existing plastic hinge length expressions for RC components were found to over-predict hinge length consistently while those developed for HPFRCC components accurately predict plastic hinge lengths at low axial load levels. 

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2. Understanding the behavior of HPFRCC columns subjected to axial and lateral loads

   Sthapit, Ronit; Bandelt, Matthew J (September 2025, Proceedings of the 3rd International Workshop on Durability and Sustainability of Concrete Structures (DSCS 2025))

   High-performance fiber reinforced cementitious composites (HPFRCC) are a class of novel cementitious materials which show pseudo-hardening behavior and multi-cracking in tension due to the use of steel and/or synthetic fibers. Reinforced HPFRCC (R/HPFRCC) flexural members show higher damage tolerance, deformation capacity and energy dissipation capacity compared to conventional reinforced concrete. Limited studies have been carried out to understand their behavior in the combined presence of axial and lateral loads. An experimental framework has been designed to fill this gap and test a set of R/HPFRCC columns subjected to axial and lateral loads. Experimental variables were selected based on a preliminary numerical study where the influence of reinforcement ratio, axial load ratio, and HPFRCC mechanical properties were studied. The preliminary numerical study, which is the main focus of this paper, showed that increasing the axial load ratio and longitudinal reinforcement ratio had a positive influence on the lateral load capacity. The deformation capacity also increased with the reinforcement ratio; however, high axial loads had a negative impact on the deformation capacity irrespective of the reinforcement ratio. The experiment aims to validate these findings by studying the results such as hysteresis response, crack pattern, longitudinal strain profile, and the failure mechanism. 

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3. Experimental Characterization of Plastic Hinge Behavior from Flexure and Axial Effects

   https://doi.org/10.21838/uhpc.16690  

   Sthapit, Ronit; Bandelt, Matthew (June 2023, International Interactive Symposium on UHPC)

   Aaleti, Sriram; Okumus, Pinar (Ed.)

   The unique mechanical properties of ultra-high performance concrete (UHPC) causes changes in failure modes and ductility in reinforced components. Numerous experiments have shown these materials, and others with similar ductile characteristics in tension, can improve the damage tolerance, strength, and ductility of members subjected to large deformations from seismic loading and similar extreme conditions. The use of these materials, however, has not been systematically studied to understand their application at a system-level performance and design procedures have been complicated due to their unconventional failure mechanism. This project aims to fill this gap by testing a targeted set of components subjected to combined effects of axial loads and bending with variations in axial load ratio and longitudinal reinforcement ratio. Additional experiments are planned to compare performance across other ductile concrete materials with variations in mechanical properties. The experimental results including load-deformation, reinforcement strain, concrete surface strain will be used to understand the parameters that have the highest influence on plastic hinge length and moment-rotation response which can ultimately help to validate analytical models against experiments based on these key parameters. 

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4. Influence of Reinforcement Ratio and Axial Load on Behavior of UHPC and HPFRCC Columns

   https://doi.org/10.21838/uhpc.25684  

   Sthapit, Ronit; Bandelt, Matthew J (June 2026, International Interactive Symposium on Ultra-High Performance Concrete Papers (Iowa State University Digital Press))

   Ultra-high-performance concrete (UHPC) and other high-performance fiber reinforced cementitious composites (HPFRCC) have shown promising results for use in seismic resistant flexural dominant structural members in terms of strength, deformation capacity, and energy dissipation capacity. Different studies investigating the flexural behavior of structural elements using these materials have found behaviors such as an increase in deformation capacity with increasing reinforcement ratio and failure of member due to reinforcing bar fracture, which directly contrast the behavior seen in conventional reinforced concrete structures. However, only a limited number of systematic studies have been conducted for members subject to axial and flexural loading. Hence, a study aiming to investigate the influence of reinforcement ratio and axial load on the behavior of column members subject to axial and lateral loads was designed. Eight specimens with variations in HPFRCC material, reinforcement ratio, and axial load ratio were subjected to axial and reversed cyclic lateral loads for experimental testing. The influence of the selected parameters on results such as load-displacement response, damage patterns, longitudinal reinforcement strain profiles, and failure mechanisms are discussed. 

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5. Behavior of Reinforced HPFRCC Columns Subjected to Axial and Lateral Loads

   Almeida, Joseph A; Bandelt, Matthew J (September 2023, ACI, Rilem, fib)

   Massicotte, Bruno; Mobasher, Barzin; Plizzari, Giovanni (Ed.)

   While widely adopted prescriptive-based design practices work to limit the probability of complete collapse, relatively little attention and emphasis is placed on the damage levels and functionality of structures after seismic events. High-performance fiber reinforced cementitious composites reinforced with steel (R/HPFRCCs) have been of growing interest for such seismic applications to improve structural level damage and performance. In order to progress the implementation of these materials at the structural level, a systematic approach toward understanding the mechanics of R/HPFRCC columns is warranted. Therefore, in this study, an existing numerical framework for R/HPFRCC beams was extended to the analysis of columns across a range of materials, reinforcement ratios, and axial load levels to evaluate the change in component level response. It was observed that axial load can considerably increase the nominal bending moment capacity of R/HPFRCC columns as well as affect the drift capacity. A shift from failure on the tension side of the element (e.g., reinforcement fracture) to the compression side (e.g., crushing of the HPFRCC) of the numerically tested column occurred between an axial load ratio of 10 and 20%. Lastly, changes in bond stress due to the material level tensile strength were shown to considerably impact the ultimate component drift capacity. 

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