International Concrete Abstracts Portal

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.

While evaluating the stiffness properties is crucial for developing the response spectra of structures, none of the North American codes/standards—including ACI 318-19, ASCE/SEI 41-06, ASCE/SEI 43-05, and CSA A23.3-19—offer an explicit analytical approach for estimating the shear stiffness of cracked concrete squat walls. Furthermore, the paucity of experimental research has led to the lack of seismic design provisions for concrete structures reinforced with fiber-reinforced polymer (FRP) bars. Therefore, this study is focused toward investigating the stiffness characteristics of concrete squat walls reinforced with glass FRP (GFRP) bars, aiming at proposing a straightforward method of analysis that can be used to estimate the post-cracking shear stiffness. Four wall specimens with an aspect ratio (height-to-length ratio) of 1.14 were constructed and tested under simultaneous axial and reversed-cyclic lateral loads. Test results were analyzed in terms of stiffness degradation trends and decoupled flexural and shear deformations. An analytical model was developed for evaluating the secant shear stiffness at any load level in the post-cracking range. The model was achieved by idealizing the shear-transfer mechanism of the web reinforcement using a variable-angle truss, and that of the web concrete using a direct strut-and-tie system representing the tied arch action developed through the web. A simple analytical expression was formulated for predicting the magnitude of average strain in the web horizontal reinforcement at failure. The validity of the derived model and expressions was examined by reproducing the load-shear displacement response of the tested walls. Further verification was also conducted by reproducing the response of steel-reinforced concrete squat walls available in the literature, considering only their pre-web yielding range.

Impact-echo’s history is an interesting story of how a real need for nonde-structive test methods for flaw detection in concrete structures led to a sys-tematic and sustained basic and applied research effort to develop such a method, beginning in 1983, at the National Bureau of Standards, and con-tinued since 1987 at Cornell University. This paper discusses the contributions of the people and the organizations who carried out the theoretical, numerical, laboratory, and field studies that established the method and who developed the software and instrumentation that gave rise to a patented impact-echo field system. It also documents how this effort was undertaken and sustained with government and industry funding. Subsequently, this paper draws on knowledge gained over twelve years of research to provide, for the first time, a unified explanation of impact-echo theory as it applies to the testing of structural elements, including plates (slabs, walls, bridge decks, pavements, etc.), bars (beams and columns), and hollow cylinders (pipes and tunnel and mine shaft liners) and to the detection of flaws within these elements. The last key pieces fell into place in 1995, and it is now possible to explain in a concise and coherent way the principles upon which impact-echo testing is based.

When slenderness ratios of load-bearing reinforced concrete walls resting on either continious or isolated footings exceed the limits of ACI 318-71 (klu/r 100), a detailed evaluation of slenderness is needed. Using numerical analysis procedures, a systematic accounting of the various factors affecting the behavior of wall panels is presented here, based on a column model of the panel. Also presented in this paper is a typical design aid of a slender wall having a thickness of 5 1/2 in. (14 cm) and resting on continious footings. A rational means of evaulating the effects of isolated footings on the ultimate capacity of the slenderness walls is also indicated along with a design example.