Stud reinforcement in dapped ends of concrete beams
Date
2008
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Abstract
The ends of precast girders often have a reduced depth over short lengths in the form of dapped ends. This simple shape allows for quick and cost-effective assembly of the structural elements on a construction site. Girders with dapped ends are normally used in parking structures, pedestrian bridges, and long-span bridges. Dapped ends also serve as popular detail for expansion joints in buildings and bridges. The design of dapped ends requires special consideration, because the shear and bending at the end of the beam must be carried by a much smaller section. In addition, the geometric discontinuity of a dapped end causes high stress concentrations, which often result in wide cracks at the re-entrant comer. Furthermore, the mechanism of load transfer through dapped ends is difficult to analyze using conventional design procedures. Dapped ends are typically reinforced with conventional stirrups and longitudinal reinforcing bars which require hooks and bends and even welded plates to ensure sufficient anchorage to the concrete. The present research investigates the efficiency of studs with single or double heads for reinforcing the dapped ends. Three stud reinforcement layouts are investigated. A comparison is made with the behaviour of conventionally reinforced dapped ends. Three analytical methods are employed in this investigation. Strut-and-tie models are used to develop different layouts of the reinforcement. The shear friction method is used to calculate the ultimate shear strength. A diagonal bending method is developed and used to determine the flexural capacity of dapped-end beams as it is affected by diagonal cracking within the shear span. The latter two methods give information on the location and inclination of the critical crack at shear or flexural failure and are used to examine the effectiveness of the stud reinforcement in enhancing the strength of beams with dapped ends. An experimental program is conducted on a series of dapped-end beams to corroborate the analytical study. The use of studs in dapped ends is shown to provide an efficient and reliable solution that prevents premature failure caused by inadequate anchorage of conventional reinforcement.
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Bibliography: p. 269-274
Some pages are in colour.
Some pages are in colour.
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Citation
Herzinger, R. (2008). Stud reinforcement in dapped ends of concrete beams (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/1815