International Concrete Abstracts Portal

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.