Seismic behavior of hollow concrete columns
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Hollow reinforced concrete columns have been used in the past in place of their solid counterparts in the construction of bridges. These hollow columns have several benefits over solid columns, including the reduction of vertical load applied to the foundation as well as the reduction of seismic mass. Despite the benefits of hollow reinforced concrete columns, little is known about the effectiveness of transverse reinforcement to confine the concrete in these columns when only one layer of transverse reinforcement is provided.
The goal of this research is to develop design procedures and modeling techniques which can accurately describe the behavior of hollow columns with one layer of transverse reinforcement. To achieve this goal, a review of previous research was conducted and the findings were used to propose an adjustment to an existing confined concrete model. A modeling technique for hollow columns was then described, which utilizes the proposed confinement model adjustment. The model has been verified using test specimens presented in previous research, and it has been found to provide a conservative estimate of the response of these columns.
Experimental testing of hollow circular and square columns with one layer of transverse reinforcement was performed to gain more understanding of the hollow columns' behavior, as well as to provide further validation of the proposed model. The test results found that hollow specimens with low axial load, low flexural demand, and sufficient wall thickness can produce a limited ductile response. Additionally, it was found that shear effects can be more significant in hollow columns than in equivalent solid columns.
The literature review and experimental program demonstrate that hollow columns can achieve a response very similar to that of a solid column with the same outer dimensions and reinforcement details, as long as the hollow column is designed appropriately. A recommended design procedure is proposed, which provides a simple estimate of the required wall thickness to achieve a ductile response for hollow columns with one layer of transverse reinforcement. The modified analysis method is incorporated into this design procedure, producing guidelines for the design and analysis of these hollow columns.