1 Introduction
2 Experimental Investigation
Specimen | f’c [MPa] | \(\frac{{\text{P}}}{{{\text{f}}_{{\text{c}}}^{^{\prime}} {\text{A}}_{{\text{g}}} }}\) | Longitudinal Reinforcements | Lateral ties | HCWM | ||||
---|---|---|---|---|---|---|---|---|---|
Bars | \({\text{f}}_{y}\) [MPa] | ρ [%] | Bars | fyt [MPa] | S [mm] | Mesh size [mm] | |||
ODN | 82 | 0.178 | 8ϕ14 | 510 | 3.08 | 2ϕ8 | 505 | 150 | – |
OD2 | 82 | 0.188 | 8ϕ14 | 510 | 3.08 | 2ϕ8 | 505 | 150 | 25 |
OD4 | 82 | 0.178 | 8ϕ14 | 510 | 3.08 | 2ϕ8 | 505 | 150 | 40 |
IDN | 81 | 0.189 | 8ϕ14 | 510 | 3.08 | 2ϕ8 | 505 | 100 | – |
ID2 | 81 | 0.186 | 8ϕ14 | 510 | 3.08 | 2ϕ8 | 505 | 100 | 25 |
ID4 | 81 | 0.179 | 8ϕ14 | 510 | 3.08 | 2ϕ8 | 505 | 100 | 40 |
SDN | 75 | 0.180 | 8ϕ14 | 510 | 3.08 | 3ϕ8 | 505 | 50 | – |
SD4 | 75 | 0.182 | 8ϕ14 | 510 | 3.08 | 3ϕ8 | 505 | 50 | 40 |
2.1 Material
No. | Cement [g] | W/C | Superplasticizer (% of cement) | Sand [g] | Gravel [g] | Fly ash [g] | slump flow [cm] | Compression strength [MPa] |
---|---|---|---|---|---|---|---|---|
A | 520 | 0.347 | 0.921 | 900 | 500 | 200 | 51.30 | 78.80 |
B | 520 | 0.435 | 0.512 | 900 | 500 | 200 | 82.30 | 47.80 |
C | 520 | 0.395 | 0.854 | 1000 | 470 | 220 | 68.50 | 64.20 |
D | 520 | 0.410 | 0.675 | 1000 | 470 | 220 | 79.50 | 54.50 |
Slump flow | J-Ring | L-Box | ||||||
---|---|---|---|---|---|---|---|---|
Slump flow [mm] | T50 (sec) | Slump flow [mm] | T50 (s) | Concrete average height [mm] | Difference of slump flow in J-Ring test and slump test [mm] | H1 [mm] | H2 [mm] | (H2/H1) |
685 | 3.21 | 655 | 3.88 | 9.2 | 30 | 94.33 | 76.44 | 0.813 |
2.2 Test Setup
2.3 Lateral Loading
3 Observed Behavior and Test Results
3.1 Envelope Curve of Hysteresis Loading and Bilinear Envelope Curve
3.2 Strength and Deformation
3.3 Ductility
3.4 Energy Dissipation
3.5 Failure Modes of Specimens
3.5.1 OD Specimens
3.5.2 ID Specimens
3.5.3 SD Specimens
4 Conclusions
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- Implementation of HCWM enhances the ductility and energy absorption of the columns in all specimens by enhancing the number of loading cycles and preventing the abrupt failure of columns and buckling of longitudinal rebars in the final steps of loading. More cracks developed along with the specimens in the damaged region in the specimens which HCWM was wrapped around the transverse rebars, although the depths of the cracks were diminished. The OD4 demonstrates more increase in ductility among the other specimens. In ODs specimens, HCWM confinement provides three times more energy dissipation compared to the controlling specimen. Ductility was observed to increase as much as 65% in ODs specimens compared to the specimen confined only by transverse rebars.
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- The ultimate deformations of OD4 and ID4 specimens are increased by 21% and 8.3% compared to their control specimens (ODN and IDN, respectively). Confining of SD members by HCWM has a neglecting effect on the ultimate strain. Moreover, the ultimate strength of ODs and IDs specimens were increased 15% and 22% compared to ODN and IDN specimens, respectively, while ultimate strength did not change for SD4 compared to the specimen without HCWM.
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- HCWM prevents sudden failure of the specimens by enclosing the longitudinal bars and damaged core concrete. So the specimens could endure more deformation and this can be considered as a merit of using HCWM in improving the performance level of buildings.
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- With regard to the construction costs, HCWM only increases 2% of the cost of the construction in comparison to the specimens without HCWM. Therefore, HCWM can be proposed as an economically feasible option for retrofitting of the exciting RC columns.
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-Finally, it could be concluded that the use of HCWM improves the performance of the structure at the collapse prevention level, leading to a reduction in human and economic losses in earthquake events.