International Concrete Abstracts Portal

Door or window openngs in masonry infill panels can reduce the lateral strength and stiffness on infill-frame systems. In an effort to study these effects, a series of tests were conducted on half-scale test structures consisting each of three stories and three bays. Infill panels of the control structure were solid with no openings while panels of the second structue were perforated with window and door openings of varying size and location. The test structures were designed to replicate typical building practice of the early 1950's with little or no seismic detailing of frame reinforcement. The test structures were subjected to cyclic in-plane lateral forces to study their strength and deformation capacity under seismic excitation. The cyclic loading was chosen to apply displacemet demands on the structures, representative of those that are expected to occur during strong earthquake motions. Test results discussed in this paper are presented in terms of observed changes in strength, stiffness and deformation capacity of both test structures. Damage patterns and propagation of cracks in the concrete frame and masonry infill during loading are illustrated and discussed in terms of measured histories of force and deflection. Experimental results supported by analytical studies are used to estimate overall reductions in strent, deformation capacity and stiffness due to the presence of openings in the panels.

The seismic performance of repaired reinforced concrete framed shear walls with openings is quantitatively investigated in this study. Ten large-scale repaired framed wall specimens subjected to reversed cyclic lateral loading had been tested, and a simple prediction model was proposed to analyze the test specimens. According to the failure mechanism of the prototypes, three specimens were repaired with epoxy and the other specimens were repaired by various methods, such as enlargement of the column size, additon of wing walls adjacent to the boundary columns, jacket addition to the joints of beam-column, and use of steel bracings on the wall. The experimental results show that the maximum strength of framed shear walls repaired with epoxy is close to the prototype specimen. However, their lateral displacement obviously increases and rigidity tends to be smaller. The maximum strength and energy dissipation of most other repaired specimens are greater than those of the prototype specimens, and their cyclic resistance capacities are better than those of the prototypes.

A common connection between steel outrigger beams and reinforced concrete walls involves a shear tab welded onto a plate that is conncected to the wall through headed studs. Previous studies focused on behavior of headed studs have ignored a number of major issues, e.g., (a) cyclic behavior of studs under multiple loads was not studied, (b) the concrete around studs was not reinforced or the reinforcement did not represent what would commonly be present in wall boundary elements, and ( c) effects of cracking and yielding of reinforcement around headed studs were not included. To remedy these deficiencies and to develop seismic design guidelines for outrigger beam-wall connections, a coordinated experimental and analytical research program was conducted. Through a number of tests, involving a wall subassembly and an outrigger beam, the behavior of studs subjected to cyclic tension and constant gravity shear was examined, and a design methodology was developed to control the mode of failure. To further investigate the cyclic performance of outrigger beam-wall connections and to validate the design guidelines, two 1/4-scale walls with two outrigger beams were tested. The wall reinforcement details around the connection were selected according to the anticipated level of cracking and plastic hinge formation. The two outrigger connections were subjected to constant gravity loads and cyclic tensile forces, which were controlled as a function of the wall shear. This paper provides an overview of the experimental program, testing procedures, relevant test results, and design implications. The design methodology followed in this research resulted in connections that could develop and exceed the design forces despite extensive cracking and yielding of wall reinforcement around the headed studs. Presence of heavily confined wall boundary elements around headed studs increases the capacity. A simple method to account for strengthening effects of boundary elements was develped. This model could accurately assess the expected mode of failure and capacity of outrigger beam-wall connections. Test results indicate that the outrigger beam transfers the majority of diaphragm forces directly to the core wall, and participation of floor slab toward transferring the loads to the core wall is negligible. Therefore, floor diaphragm-wall connections can be based on simplle details, and designed to resist only gravity loads.

Axial compression test results for square RC columns incorporation Taiwanese construction practice in the placement of stirrups and various kinds of jacketing schemes are presented. The jacketing schemes include circular, octagonal and square shapes. The jacketing materials vary from stell plate to carbon fiber reinforced polymer (CFRP) COMPOSITES. It is found from the monotonic axial load test results that the failure mode of the benchmark non-retrofitted specimen is identical to that observed in real damage cases subsequent to the 1999 Chi-Chi Taiwan earthquake. The benchmark specimen developed its design strength but a non-ductile failure mode occurred soon after the peak load was reached. Among the retrofitted specimens, the steel jacketed specimens exhibit not only greatly enhanced load carrying capacity but also excellent ductility performance. Test results show that CFRP sheets are effective in increasing the column axial strength, but the sheets could fracture suddenly in high strain conditions due to their brittle material characteristics. Test results indicate that CFRP sheet wrapping in general is not as effective as steel jacketing in improving the axial ductility capacity of RC columsn. However, the proposed octagon-shaped CFRP wrapping scheme exhibits an improved performance compared to rectangular-wrapped columns using the same layers of CFRP sheets. Tests confirm that all octagonal stell or CFRP jacketed specimens have axial load capacities more that 2 time the nominal capacity.

The structural behavior of reinforced concrete framed shear walls subjected to reversed cyclic lateral loading were studied by testing ten large-scale specimens, including high-, middle-, and low-rise shear walls. An analytical model was also proposed to predict the behavior of the tested specimens. The parameters of concrete strength and vertical stell ratio of walls were investigated. The predicted maximum load and corresponding displacement, and load-displacement curves satisfactorily agreed with the experimental results. In addition, the experimental results showed that the failure mode of high-rise shear walls was flexural; their ductility factors were greater than those of low-rise shear walls; their displacements were also greater. The mid-rise shear walls failed by a combination of both flexure and shear. The experimental results also showed that the maximum loads were greater for specimens with higher concrete strength or higher verical stell ratio. The vertical stell ratio of walls has more significant effect on flexure-predominant walls. However, it is insensitive to shear-critical walls. It was found that the simple model develped from previous small-scale tests could not closely reflect the experimental results of all specimens. This suggests that the size effect needs to be taken into account in the analytical model.