Inelastic design of low-axially loaded high-strength reinforced concrete columns

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Plastic hinge length and ultimate curvature are the crucial parameters that enable inelastic deformability (deflection and rotation) of reinforced concrete columns to be evaluated. Prediction of deformability beyond the elastic range is important in the performance-based design of earthquake-resistant structures. Although large numbers of tests have been conducted in the past by numerous researchers on reinforced concrete columns subjected to simultaneous axial load and large inelastic displacement, available design tools that enable rapid evaluation of deformability of reinforced concrete columns are still limited. The situation is even worse for high-strength reinforced concrete columns. The objective of this paper is to investigate plastic hinge length and ultimate curvature for deformability evaluation of high-strength reinforced concrete columns. In connection with this, two equations are proposed in this paper for estimating the plastic hinge length and ultimate curvature of high-strength reinforced concrete columns leading to their deformability evaluation. The proposed equations are used to evaluate the theoretical deflection of other researchers' column test specimens, and it is proven that these theoretical deflections mostly underestimate slightly their respective measured deflections. Therefore, the proposed equations can be used for conservative estimation of high-strength reinforced concrete column deformability at an early design stage without performing the tedious load-deflection analysis. Notation IntroductionIt has been verified by theoretical analyses (Bai and Au, 2009;Kim et al., 2007;Lam et al., 2009;Pam and Ho, 2001) and experimental tests (Ahn and Shin, 2007;Bayrak and Sheikh, 1998;Ho and Pam, 2003a;2003b;Hong et al., 2006;Li et al., 1991;Sharma et al., 2007;Watson and Park, 1994;Xiao et al., 2008;Youssef and Rahman, 2007) that the flexural strength and ductility performance of reinforced concrete (RC) columns, including high-strength RC (HSRC) columns, can be improved significantly by installing a sufficient amount of transverse reinforcement to confine their concrete core. The transverse reinforcement not only averts brittle failure owing to shear, but also confines the core area to avoid premature concrete crushing and postpone inelastic buckling of longitudinal steel effectively. In the past, numerous researchers have conducted cyclic reversed loading tests on RC columns to assess their seismic performance by displacement ductility factor (Ahn and Shin, 2007;Baczkowski and Kuang, 2008;Xiao et al., 2008;Youm et al., 2007) or displacement as well as curvature ductility factor (Bayrak and Sheikh, 1998;Ho and Pam, 2003a;2003b;Li et al., 1991;Watson and Park, 1994) which is the ratio of the ultimate to the yield value of the respective parameter. Some theoretical analyses were also carried out to investigate the flexural ductility of RC beams and columns (Bai et al., 2007;Bai and Au, 2009;Ho et al., 2003;Kwan et al., 2002;Lam et al., 2009;Su et al., 2006;. In addition to ultimate curvat...

Section: Introductionmentioning

confidence: 93%

Section: Details Of Test Specimensmentioning

confidence: 99%

mentioning

confidence: 99%

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Deformability evaluation of high-strength reinforced concrete columns

Ho¹,

Pam²

2010

Self Cite

“…2; A g is the column cross-section area) (Ho and Pam, 2003a;Marefat et al, 2005;Mo and Wang, 2000;Tao and Yu, 2008;Watson and Park, 1994;Woods et al, 2007) (c) columns subjected to medium axial load level (0 . 2 , P/A g f 9 c < 0 .…”

Section: Derivation Of Equivalent Rectangular Concrete Stress Block Pmentioning

confidence: 99%

Equivalent stress block for normal-strength concrete incorporating strain gradient effect

Peng

Pam

et al. 2012

To account for the different behaviours of concrete under uniaxial compression and bending in the flexural strength design of reinforced concrete (RC) members, the stress-strain curve of concrete is normally scaled down so that the adopted maximum concrete stress in flexural members is less than the uniaxial strength. However, it was found from previous experimental research that the use of a smaller maximum concrete stress would underestimate the flexural strength of RC beams and columns. To investigate the effect of strain gradient on the maximum concrete stress developed in flexure, a total of 12 plain concrete and RC inverted T-shaped specimens were fabricated and tested under concentric and eccentric loads separately. The maximum concrete stress developed in the eccentric specimens was determined by modifying the concrete stress-strain curve obtained from the counterpart concentric specimens based on axial force and moment equilibriums. The test results revealed that the maximum concrete stress increases with strain gradient up to a certain maximum value. A formula was developed to correlate the maximum concrete stress to strain gradient. A pair of equivalent rectangular concrete stress block parameters that incorporate the effects of strain gradient was proposed for flexural strength design of RC members.

“…Traditionally in reinforced concrete structures, this is provided by installing closely spaced transverse steel (Ho and Pam, 2003;Mander et al, 1988). However, as the efficiency of transverse reinforcement dropped significantly with the increase in concrete strength (Ho et al, 2010), this form of confinement will result in serious steel congestion that adversely affects the concrete placing quality, and is not applicable to confine UHSC.…”

Section: Introductionmentioning

confidence: 99%

Curvature-relevant analysis of eccentrically loaded circular concrete-filled steel tube columns

Ouyang¹,

2014

The existence of curvature can reduce the effective confining pressure within concrete-filled steel tube (CFST) columns under eccentric compression. The existing analysis method ignores such an effect and still treats the confining pressure as constant across the whole section as if it is under axial compression. In this paper, the authors have made significant improvements on the existing model, so that the curvature effect can be taken into account to properly interpret the non-linear behaviour of eccentrically loaded CFST columns. Meanwhile, shortening between two hinges is an important data output in test programmes of this type, which has been completely neglected by the existing analysis method. This improved method also provides calculation steps to track the value of shortening for each load increment. Unknown parameters in this new method are determined on the basis of data fitting of 87 specimens from previous researchers' test programmes. The following parameters are incorporated in this study: effective tube length (660–4670 mm), diameter of tube (76–600 mm), tube thickness (1·52–8·81 mm), yield strength of tube (256·4–517·0 MPa), cylinder strength of concrete (26·42–112·70 MPa) and eccentricity (9·4–300 mm). The load–axial displacement, load–deflection and moment–curvature curves predicted by the new method agree well with their measured counterparts in the tests.