1. INTRODUCTION A total of 93 recorded earthquakes (magnitude 2.0~5.0) were reported in the Korean peninsula during 2013. The most recent earthquake (magnitude 5.1) hit the western part of Korea in April 2014. Although some evidence has pointed to increased seismic activity, many civil structures were constructed before the design code incorporated seismic load. This is a latent security issue for the Korean population. According to studies performed in the aftermath of earthquakes in Loma Prieta (1989) and Northridge (1994) in the United States and Kobe (1995) in Japan, bridge failures were generally caused by inadequate lateral reinforcements and insufficient lap splices of reinforcing bars. Considerable research has focused on seismic retrofit techniques for substandard RC columns. The application of fiber-reinforced polymer (FRP) as a jacket for columns vulnerable to seismic loads provides several benefits: high installation speed, low maintenance costs, and a high strength-to-weight ratio. However, the FRP jacketing system involves potential delamination issues because epoxy is used to paste the FRP sheets on RC columns. To overcome this disadvantage, Susantha et al. (1990) introduced a pre-compression method for concrete in a circular steel tube and improved its performance. Xiao and Wu (2000) used partially stiffened steel jackets to retrofit RC columns, to enhance strength and improve the ductility of concrete. Mortazavi et al. (2005) used pre-tension FRPs to strengthen RC columns. Choi and Rhee (2008) used epoxy- glued vertical steel-reinforced FRP strips to improve the lateral resistance of plain gravity bridge columns; these steel-reinforced FRP strips can be mounted automatically by a winding machine. Choi et al. (2009) introduced a new steel jacketing method to retrofit RC columns without grouting and assessed its performance using compressive tests for concrete cylinders. The present study involved using external mechanical pressure on steel plates around RC columns to attach the steel plates onto the concrete surface. is experimental investigation involved two stages. During the first stage, 45 concrete cylinders ( φ 150 mm × 300 mm) were fabricated with varying design concrete strengths (21, 27, and 35 MPa). Two split steel jackets and two vertical strip bands were used to confine each cylinder, as shown in Figure 1(a). The steel jackets had thicknesses of 1.0 and 1.5 mm, and dimensions of 230 mm × 290 mm (B × H). Failure occurred at the welding line between the strips and jackets, but this jacketing method did not induce full plastic deformation of the steel jackets, so the failure strains were relatively small. During the second stage, 12 concrete cylinders were constructed in an attempt to improve the performance of the proposed jacketing method. In this test, a whole jacket of stainless steel and lateral strip bands [shown in Figure 1(b)] was used to confine cylinders, instead of using two Constitutive Model for a Confined Concrete Cylinder with an Unbonded External Steel Jacket Young-Sook Roh Department of Architectural Engineering, Seoul National University of Science and Technology, Seoul, Korea http://dx.doi.org/10.5659/AIKAR.2015.17.1.41 Abstract Early investigations focused mainly on manipulating the confinement effect to develop a reinforced concrete column with lateral hoops. Based on this legacy model, Li’s model incorporated the additional confinement effect of a steel jacket. However, recent experiments on plain concrete cylinders with steel jackets revealed relatively large discrepancies in the estimates of strength enhancement and the post- peak behavior. Here, we describe a modified constitutive law for confined concrete with an unbonded external steel jacket in terms of three regions for the loading stage. We used a two-phase heterogeneous concrete model to simulate the uniaxial compression test of a 150 mm × 300 mm concrete cylinder with three thicknesses of steel jackets: 1.0 mm, 1.5 mm, and 2.0 mm. e proposed constitutive model was verified by a series of finite element analyses using a finite element program. e damaged plasticity model and extended Drucker-Prager model were applied and compared in terms of the level of pressure sensitivity for confinement in 3D. e proposed model yielded results that were in close agreement with the experimental results Keywords: Confined concrete, Heterogeneity, Steel Jacketing Method ARCHITECTURAL RESEARCH, Vol. 17, No. 1(March 2015). pp. 41-48 pISSN 1229-6163 eISSN 2383-5575 Corresponding Author: Young-Sook Roh Department of Architectural Engineering, Seoul National University of Science and Technology, Seoul, Korea Tel: +82-2-970-6554 e-mail: [email protected] is study was partially supported by the Research Program funded by the Seoul national University of Science and Technology. ©Copyright 2015 Architectural Institute of Korea. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons. org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Constitutive Model for a Confined Concrete Cylinder with an Unbonded External Steel Jacket
May 10, 2023
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