International Concrete Abstracts Portal

The calculation of the nominal flexural strength of concrete members prestressed with hybrid (i.e., a combination of bonded and unbonded (steel and/or carbon fiber reinforced polymer (CFRP)) tendons is dependent on determining the stress in the unbonded prestressed reinforcement. Current provisions in the ACI CODE-318-25 are only applicable to members with either unbonded or bonded steel tendons. Additionally, while ACI PRC-440.4R-04 is adopted for unbonded CFRP tendons, neither ACI provisions address the use of hybrid tendons. This paper presents a closed-form analytical solution for the stress at ultimate derived based on the Modified Deformation-Based Approach (MDBA) that is applicable to beams prestressed with unbonded, hybrid (steel or FRP), external with deviators or internal tendons, with and without non-prestressed reinforcement. An assessment of its accuracy and applicability in calculating the nominal flexural strength is examined using a large database of 330 beams and slabs (prestressed with steel and/or CFRP tendons) compiled from test results by the authors as well as those available in the literature. Results predicted by the proposed approach exhibited excellent accuracy when compared to those predicted using ACI CODE-318 or ACI PRC-440 stress equations. They also show that the approach is universally applicable to any combination of bonded and/or unbonded (steel and/or CFRP) tendons, span-to-depth ratio, as well as loading applications.

To improve the ductility of fiber-reinforced polymer reinforced concrete structures, the hybrid reinforcement with glass fiber-reinforced polymer (GFRP) and stainless steel (SS) is selected in this paper. Nine seawater sea sand concrete beams were designed and tested. The effects of concrete strength, effective reinforcement ratio ρ₂, and reinforcement type in the tensile zone on the flexural behavior of the beams were analyzed. The test results show that with the same concrete strength and the same effective reinforcement ratio ρ₂, the ductility of hybrid reinforced beams is higher than GFRP reinforced beams; the comparison of mid-span deflection of the GFRP bars and hybrid reinforced beams are not only depend on the reinforcement type, but also depend on the total stiffness of reinforcement before SS bars yield in the tensile zone and whether the SS bars are yielding in the tensile zone. Meanwhile, theoretical analysis was conducted for cracking moment, ultimate flexural load-carrying capacity, and mid-span deflections. A new ultimate flexural load-carrying calculation equation was proposed, which predicted the experimental values in good agreement.

Previous research studies have been conducted to study the seismic response of low-aspect-ratio reinforced concrete (RC) shear walls when designed using normal-strength reinforcement (NSR) versus high-strength reinforcement (HSR). Such studies demonstrated that the use of HSR has the potential to address several constructability issues in nuclear construction practice by reducing the required steel areas and subsequently reinforcing bar congestion. However, the response of nuclear RC shear walls (that is, aspect ratios of less than 1) with both HSR and axial loads has not been yet evaluated under ground motion sequences. As such, most nuclear design standards restrict the use of HSR in nuclear RC shear wall systems. Such design standards do not also consider the influence of axial loads when the shear-strength capacity of such walls is calculated. To address this gap, the current study investigates the influence of axial load on the performance of nuclear RC shear walls with HSR when subjected to ground motion sequences using hybrid simulation testing and modeling assessment techniques. In this respect, two RC shear walls (that is, W1-HSR and W2-HSR-AL) with an aspect ratio of 0.83 are investigated. Wall W2-HSR-AL had an axial load of 3.5% of its axial compressive strength, whereas Wall W1-HSR had no axial load. The test walls were subjected to a wide range of ground motion records, from operational basis earthquake (OBE) to beyond design basis earthquake (BDBE) levels. The experimental results of the walls are discussed in terms of their damage sequences, cracking patterns, ductility capacities, effective periods, and reinforcing bar strains. The test results were then used to develop and validate a numerical OpenSees model that simulates the seismic response of nuclear RC shear walls with different axial load levels. Finally, the experimental and numerical results were compared to the current ASCE 41 backbone model for RC shear walls. The experimental results demonstrate that Walls W1-HSR and W2-HSR-AL showed similar crack patterns and subsequent shear-flexure failures; however, the former had wider cracks relative to the latter during the different ground motion records. In addition, the axial load reduced the displacement ductility of Wall W2-HSR-AL by 18% compared to Wall W1-HSR. Moreover, the ASCE 41 backbone model was not able to adequately capture the seismic response of the two test walls. The current study enlarges the experimental and numerical/analytical database pertaining to the seismic performance of low-aspect-ratio RC shear walls with HSR to facilitate their adoption in nuclear construction practice.

This study examines the lateral cyclic response of a repaired damaged bridge pier originally reinforced with fiber-reinforced polymer (FRP) bars, particularly glass FRP (GFRP), as a corrosion-resistant and durable alternative to traditional steel. An as-built large-scale hybrid (GFRP-steel) reinforced concrete (RC) column had an outer cage reinforced with GFRP bars and an inner cage reinforced with steel reinforcing bars. The columns were first tested under cyclic lateral loading, where the hybrid specimen demonstrated ductility and energy dissipation capacity comparable to the conventional single-layer steel RC column. Following these initial tests, both specimens were repaired using FRP wraps and retested under the same loading protocol, resulting in a total of four tests. Enhanced structural integrity and energy dissipation demonstrate the effectiveness of innovative repair techniques in seismic engineering. These findings provide a blueprint for resilient infrastructure in earthquake-prone areas and contribute to advancements in bridge design and repair strategies.

Integrating real-time sensor data with physics-based models enhances the accuracy and efficiency of structural simulation and prognosis. In this study, a sensing-based simulation method is introduced to compute bending moments in reinforced concrete bridge columns subjected to seismic motions, based on the measured strains continuously fed to plasticity models. The experimental program included hybrid testing of scaled reinforced concrete bridges under consecutive seismic events. The experimental columns were instrumented with embedded as well as surface-adhered fiber-optic Bragg grating (FBG) sensors for real-time monitoring of strains reflecting degradation of the columns during the formation of damage. The fundamental assumption of strain compatibility in reinforced concrete members was investigated for the successive progression of damage in the cross sections of the columns. The stress distributions within the concrete core and cover were computed through the confined and unconfined concrete stress-strain relations for loading, unloading, and reloading scenarios. The bending moments in the cross-section were computed and compared with the corresponding experimental values calculated based on direct measurements of forces. The results from this study revealed that the cross-sectional strains exhibit three primary features during the seismic events that need to be considered for the accurate calculation of bending moments. Computation of the bending moments requires considering the shifts in cyclic reference, post-event residual strains, and the real steel strains. By using these features, the computed bending moments during the column tests mimicked the experimental results based on the measured seismic forces on the columns.