International Concrete Abstracts Portal

Industrial facilities (such as offshore platforms, power plants, and treatment plants) are typically labyrinthine structures because they possess intricate layouts (resembling mazes or labyrinths), and most of their structural walls are interconnected. These reinforced concrete (RC) structural walls need to be designed for eight simultaneous demands. The existing US codes provide limited procedural guidance for the design of these walls. A novel Panel-based ACI (PACI) design approach for RC walls, rooted in the design concepts and formulations of ACI 349 and ACI 318.2, is proposed. The PACI approach is validated using two validation and verification (V&V) approaches. For the first V&V approach, existing experimental data is used to estimate PACI approach-based reinforcement areas, which are then compared against the reinforcements provided in the experiments (and against the reinforcement areas suggested by the EC2 sandwich model approach). Benchmarked numerical models are developed to compare the capacities of specimens using PACI-based reinforcements with experimentally observed capacities and with EC2-based reinforcement. For the second V&V approach, analytical data of publicly available design demands for real-world structures are used to estimate PACI-based reinforcements for a critical region of a nuclear power plant. Numerical models are developed to compare the capacities of the panels with PACI-based reinforcements against the design demands. The results from V&V1 approach showed that the PACI approach: (i) suggests similar reinforcement areas than those used in the experiments, with an average ratio of PACI suggested reinforcement areas over experimental provided areas of 0.97 for all 21 tests; and (ii) suggests similar reinforcement areas that those suggested by the EC2 approach, with an average ratio of EC2 based reinforcement areas, over PACI based reinforcement of 1.01 for all 21 tests as well. For the V&V2 approach, the numerical capacities of the models with PACI suggested reinforcements are greater than or equal to the design demands. The V&V studies illustrate that, despite its methodological simplicity, the PACI approach results in reinforcement recommendations that closely approximate the outcomes derived from the more rigorous procedures inherent to the EC2 approach. The design implementation of the PACI approach is also illustrated using a sample calculation.

Previous research studies have been conducted to study the seismic response of low-aspect-ratio 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 rebar congestion. However, the response of nuclear RC shear walls (i.e., aspect ratios of less than one) with both HSR and axial loads has not yet been 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 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 modelling assessment techniques. In this respect, two RC shear walls (i.e., 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, while 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 rebar strains. The test results are 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 are compared to the current ASCE 41-23 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 former 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 41-23 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.

Filling reinforced concrete (RC) frame spans with RC shear walls constitutes a strategic intervention to existing sub-standard buildings. The efficiency of this intervention depends, among other things, on the behavior of interfaces between the shear wall and the frame elements. The failure of critical interfaces that may lead to undesirable shear sliding of the wall at its base can only be prevented if the interfaces are adequately designed. To investigate the cyclic behavior of interfaces within the composite frame-to-wall members, four frames filled with RC walls, as well as two reference specimens (i.e., a bare frame and a monolithic frame/wall specimen), were subjected to cyclic horizontal displacements. The crucial effect of the interface reinforcement ratio, the detailing, the dowel distribution along the interface, and the embedment length on the behavior of the specimens, in terms of maximum capacity, drift, and failure mode, was confirmed.

Inverse analysis methods proposed by current standards for extracting the tensile properties of tension-hardening cementitious materials from indirect tension tests (e.g., flexural prism tests) are considered either cumbersome and can only be performed by skilled professionals 1,2 or apply to certain configurations and specimen geometries. Significant discrepancies are reported between the results of direct tension tests (DTT or DT tests) and inverse analysis methods. This has eroded confidence in flexural tests as a method of characterization of tension-hardening Ultra-High Performance Concrete (UHPC) and has motivated its abandonment in favor of DT testing. Additional concerns are size sensitivity, variability, and lack of robustness in the results of some methods. However, DT tests are even more difficult to conduct, and results are marked by notable scatter. This is why some codes allow for bending tests at least for quality control of UHPC. To address the limitations of the bending tests in providing an easy and quick method for reliable estimation of the tensile characteristic properties of UHPC, a new practical method is developed in this paper, based on a Forward Analysis (FA) of third-point bending tests. A unique aspect of the approach is that it considers the nonlinear unloading that occurs in the shear spans of the prism after strain localization in the critical region. The method was used to derive charts for direct estimation of the tensile properties from quality control bending tests, for the commonly used flexural specimen forms and material types. The goal of the study is to provide a practical alternative in the characterization of tension-hardening UHPC materials. Results obtained using the proposed FA method are in good agreement with the tensile response from DT tests. However, it is noted that due to the presence of a strain gradient in bending tests and the larger strain gauge lengths employed in some DT tests, the strain values at localization from DT tests tend to be more conservative.

The influence of alkaline aging on the basalt fiber-reinforced polymer (BFRP) bar reinforced concrete beam has not been thoroughly investigated, and the deterioration level can be further increased in seawater sea sand concrete (SSC) due to increased alkalinity. This study aims to unveil the coupled influence mechanism of accelerated sweater aging and impact loading on the impact resilience of BFRP-SSC beams. The influence of concrete strength, reinforcement ratio, falling weight height, and accelerated aging in seawater on the impact resistance of BFRP-SSC beam is examined. The results indicate that enhancing concrete strength can more obviously increase the peak impact force than enhancing the reinforcement ratio due to the higher strain rate sensitivity. The increased falling weight energy can increase the peak impact force while reducing the residual bearing capacity. The accelerated aging in seawater can reduce the peak impact force and increase the maximum midspan displacement. And the impact failure mode of the BFRP-SSC beam can be changed from concrete crushing to BFRP bar fracture due to the bar degradation. The peak impact force of beam specimens soaked in seawater at room temperature and 55°C conditions is reduced by 13.8% and 15.5%, while the maximum midspan displacements are increased by 32.2% and 47.1%, respectively. This study can serve as a solid base for the impact design of FRP bar reinforced seawater sea-sand and concrete beams.