Carbon fiber-reinforced polymer (CFRP) sheets can be used to strengthen existing reinforced concrete members. However, debonding (separation of the CFRP sheet from the concrete surface) may occur at less than 50% of CFRP sheet’s tensile capacity, implying that half of the CFRP material is ineffective in increasing the strength of a concrete member. The use of carbon fiber anchors can increase the amount of tension carried in the CFRP sheets. Forty specimens were tested to develop initial design parameters of carbon fiber anchors. Tests showed that by providing anchors with a total cross-sectional area at least two times greater than that of the longitudinal sheet, it was possible to fracture the CFRP sheets. The best results were obtained using a greater number of smaller anchors. Further, surface preparation is unimportant when the CFRP sheets were well anchored and a 1:4 transition slope can manage any offsets in surface level. The general anchor design was then implemented on a series of long beams and...

This paper documents the findings from a dynamic collapse experiment carried out on a single-story two-by-two bay reinforced concrete flat-plate substructure. The test specimen had a 0.4 scale, represented older flat-plate buildings designed without structural integrity reinforcement in slabs, and was subjected to an instantaneous removal of an exterior supporting column. Tests were conducted three times with different levels of gravity load until a progressive collapse occurred. The specimen survived a gravity load corresponding to 42% of the normal loading capacity defined by the direct design methods but collapsed at a load of 49% of the design loading capacity. The collapse of the specimen was initiated by the punching failure at an interior slab-column connection carrying the most redistributed load after the exterior column removal. The tests confirmed the existence of slab compressive membrane action and examined the strain rates of material under dynamic response. The tests also indicated that a slab-column connection without continuous slab bottom reinforcement through the column has limited post-punching resistance. The experiment indicated that an older flat-plate building is vulnerable to a progressive collapse when it is subjected to a sudden exterior column removal. Numerical simulations of the experiments using a macromodel were conducted and its effectiveness was confirmed.

Under a collapse scenario, the sudden loss of support causes a dynamic response that can amplify the internal forces in the members and lead to greater damage. This study considered a one-quarter scale, 2-bay, 2-story RC frame that was axially restrained at the beam locations. The frame was loaded with dead weights, and the support under the center column was kicked out to initiate the dynamic test. The results from four dynamic tests of a reinforced concrete frame with discontinuous reinforcement under various levels of applied load are presented. The fourth drop, with a load corresponding to 42% of the design (1.2×dead load+0.5×live load), did result in a catenary action range of response. A simple single degree of freedom (SDOF) analysis showed that there is a snap-through effect, i.e., a very fine tipping point at which the structure is pushed past the compressive arch or flexural range of response into the catenary action range of response. At this point, the loads in the structure increase s...

The experimental results of dynamically removing an interior column in a single-story, 2-bay-by-2-bay reinforced concrete flat-plate substructure are presented. The test specimen represented pre-1971 designed flat-plate buildings. The specimen was loaded with dead weight at a load level equal to 78% of the unfactored design load and the support under the interior column suddenly removed by means of a collapsing jack. The test specimen experienced punching failures at four neighboring slab-column connections, but did not fully collapse due to postpunching capacity. Because the gravity load acting on the slab was only slightly greater than a typical service load in a flat-plate building, an older flat-plate building may be at risk for progressive punching failures under a sudden column removal scenario. The measured axial force in two adjacent columns at punching failure was 36% less than the punching load in an isolated column test due to the effects of unbalanced moment, in-plane restraint, and dynamic loading. However, the slab rotation at punching was consistent with predicted rotation capacity and previous test data. The measured lateral expansion of the specimen indicated the presence of compressive membrane forces in the slab at the time of punching failure. The experimental results validated a macro model developed for simulating the behavior of plate-plate structures.

In this paper, the live load factor in the Strength I Limit State in the AASHTO LRFD Bridge Design Specifications is calibrated based on state-specific traffic environments and bridge configurations. As the initial development of the live load factor in the LRFD specifications was intended to be applied at the national level, state-specific traffic conditions, such as traffic volume, truck load, or bridge configurations, were not considered in the development process. In addition, due to the lack of reliable U.S. truck weight data in the early 1990s, truck data from Ontario, Canada, collected in the 1970s were used for the initial AASHTO calibration. Hence, the application of the live load factor in the LRFD specifications may result in over- or under-designed bridges for a specific state. Through reliability analysis of bridges based on state-specific traffic and bridge conditions, the live load factor can be recalibrated to achieve both reliable and economical bridge design. In this study, the traffic d...

This paper presents experimental and numerical studies of reinforced concrete flat-plate structures. Experiments were performed on six interior slab-column connections without structural integrity reinforcement to examine their punching and postpunching behaviors. The test variables included slab tensile reinforcement ratio and lateral restraint at the slab boundary. The experiments indicated that, under the level of restraint achieved in the tests, the compressive membrane action could enhance the punching resistance by as much as 9.5%. The tests also showed the slab-column connections without continuous compressive bars at the columns had a postpunching loading capacity of about 50% of the failure load, but this residual capacity cannot be maintained under large deformations. It was found that anchoring the slab tensile reinforcement into slab by hooks provided an alternative approach to achieve stable postpunching capacity. The numerical simulations confirmed the effectiveness of a macromodel f...