Design of Seismic Confinement of RC Columns Using High Strength Materials
Date Issued
2011
Date
2011
Author(s)
Chen, Ying-Chang
Abstract
The use of high-strength concrete (HSC) and high-strength steel (HSS) in column elements of high-rise RC building has many benefits, such as increasing the axial load capacity and lateral stiffness, reducing the size of the component’s cross-section; enhancing interior space; and reducing the weight of the building as well as the seismic design force. However, HSC is essentially more brittle than the normal strength concrete (NSC), which limits its application in earthquake-resistant structures.
In fact, if the core of the column is provided with sufficient confinement, the ductility of HSC will be significantly improved, and this confining effect is greatly influenced by the amount of transverse stirrup and its configuration. Currently, the domestic building design code follows the American ACI Code. However, the amount of confinement stirrups required by these codes is clearly insufficient for the column elements subjected high axial load capacity under earthquake. Therefore, defining a suitable confinement design equation for HSC columns now becomes an urgent issues.
In this study, 8 column specimens with high-strength materials were designed and tested under axial load combining with cyclic loading on the MATS (Muti-Axial Testing System) in NCREE. The use of high-strength material includes the longitudinal reinforcement with yield strength of 685 MPa, the hoops with yield strength of 785MPa and concrete design compressive strength of 70 and 100 MPa. The specimens are divided into two groups based on the confinement type: the traditional tied columns and multiple spiral columns. The amount of axial force applied is refered to the Canadian Code (CSA A23.3-04) and Elwood et al’s design recommendation.
Test results showed that the columns with high-strength concrete have lower deformation capacity than the low-strength ones. In addition, 90 degree hooks have less confining effect than seismic hooks. It was also shown that the magnitude of the applied axial load indeed affects the demand of confinement.
Finally, this study proposes a new confinement design equation for both tied columns and spiral columns based on the test observations. Applicability of the proposed equations to the NSC columns is also checked with the available experimental data. Test results of these study show that the proposed equations can be reasonably applied to the columns with high-strength materials and columns under high axial load, and ensure them to have good deformability.
Subjects
column
confinement
high-strength concrete
high-strength reinforcement
high axial load
multiple spiral
design equation
SDGs
Type
thesis
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