1 Introduction
2 Research Significance
3 Experimental Program
3.1 Details of the Tested Beams
3.2 Materials Properties
3.2.1 Properties of the Concrete
3.2.2 Properties of the Steel Reinforcement
Diameter (mm) | Type of steel | \(f_{y}^{{}}\) (MPa) | \(f_{u}\) (MPa) | E (GPa) | Usage |
---|---|---|---|---|---|
Ø 6 | Mild | 360 | 522 | 204 | Stirrups |
Ø 8 | Mild | 326 | 485 | 200 | Stirrups |
Ф 10 | High tensile | 509 | 665 | 196 | Compression steel |
Ф 16 | High tensile | 542 | 638 | 203 | Tension steel |
3.2.3 Properties of the FRP Strengthening Materials
Type | Diameter (mm) | Modulus of elasticity (GPa) | Tensile strength (MPa) | Rupture strain (%) |
---|---|---|---|---|
BFRP-14 | 14 | 59.7 | 772 | 1.29 |
Types of fibers | Fiber aerial weight (g/m2) | Thickness (mm) | Modulus of elasticity (GPa) | Tensile strength (MPa) | Rupture strain (%) |
---|---|---|---|---|---|
Basalt (BUF7-300) | 300 | 0.17 | 91.0 | 2100 | 2.6 |
3.2.4 Properties of the Epoxy
Epoxy type | Mechanical properties | Values |
---|---|---|
Epoxy (sikadur® 30 [33] | Ultimate strength (MPa) | 24–27 (15 °C); 26–31(35 °C) |
Shear strength (MPa) | 14–17 (15 °C); 16–19(35 °C) | |
Elastic modulus (GPa) | 11.2 (23 °C) | |
Epoxy (sikadur® 330 [34] | Ultimate strength (MPa) | 30 (23 °C) |
Tensile adhesion strength (MPa) | Concrete fracture (> 4 N/mm2) on sandblasted substrate | |
Elastic modulus (GPa) | 4.5 (23 °C) |
3.3 External Strengthening with NSM deformed BFRP stirrups
3.3.1 Manual Made U-shaped BFRP Stirrups
3.3.2 Manually Manufactured Closed BFRP Stirrups
3.3.3 Strengthening Procedure and Instrumentation
Beam specimen | Fcu28 (MPa) | Fcu (MPa) At test day | Type of strength. | Spacing “S” (mm) |
---|---|---|---|---|
TBC | 25.1 | 27.8 | – | |
TBS200-ii | 25.5 | 28.9 | Bars | 200 |
TBS200-[] | 26.2 | 28.4 | Closed stirrups | 200 |
TBS100-ii | 31 | 34 | Bars | 100 |
TBS100-U | 27.1 | 32.7 | U-stirrups | 100 |
TBS100-[] | 30.5 | 36.5 | Closed stirrups | 100 |
4 Experimental Results and Discussion
4.1 Overall Response
Beam | Cracking | Ultimate | Ultimate | Deflection | Increase over reference beam (%) | Increase in shear force (%) due to | Max. BFRP | Failure | ||
---|---|---|---|---|---|---|---|---|---|---|
Specimen | Load kN | Load (Pu) kN | Shear kN | At Pu (mm) | Ultimate load | Deflection (at Pu) | Anchorage kN | Spacing | Strain (με) | Modea |
TBC | 80 | 227 | 150.7 | 3.37 | – | – | – | – | – | SF |
TBS200-ii | 72 | 246 | 163.3 | 4.4 | 8.3 | 30.6 | – | – | 4470 | DE |
TBS200-[] | 77 | 317 | 210.5 | 5.9 | 39.6 | 75.1 | 29 | – | 4519 | SF |
TBS100-ii | 110 | 332 | 220.5 | 5.08 | 46.3 | 50.74 | – | 35 | 3450 | CCS |
TBS100-U | 90 | 412 | 273.6 | 9.5 | 82 | 181.9 | 24 | 30 | 7612 | FF |
TBS100-[] | 94 | 342 | 227.1 | 6.01 | 50.7 | 78.3 | 3 | 8 | 6308 | SF& CCZ |
4.2 Influence of the Spacing Between the BFRP-NSM Bars
4.3 Load–Deflection Curve
4.4 Crack Pattern and Failure Modes
4.5 Load and Steel Stirrup Strain Relationship
4.6 Load–BFRP Strain Relationship
4.7 Shear Crack Width
5 Conclusions
-
The test results showed that the NSM method using BFRP bars enhanced the shear capacity of RC T-beams, and the BFRP bars could be used as a shear-strengthening material for RC beams.
-
The test results emphasized that the use of the proposed anchorage enhanced the shear capacity of RC beams. The increase in the shear capacity, based on the reference beam, ranged between 8.3 and 46% for beams strengthened with NSM-BFRP bars without anchorage, and the increase ranged between 39.6 and 81.6% for beams strengthened with NSM-BFRP bars with the proposed anchor.
-
The test results assured that the use of the proposed anchorage enhances the shear contribution of the NSM bars. The maximum strains of the BFRP bars ranged from 27 to 35% from their ultimate strain for strengthened beams without anchorage. However, these values ranged from 35 to 59% for beams strengthened with the proposed anchorage.
-
Beams strengthened without anchorage failed due to the debonding of the NSM-BFRP bars before the internal steel stirrups yielded in contrast to the beams strengthened with NSM-BFRP bars using the proposed anchorage. Thus, internal steel stirrups may have contributed less than what was predicted by existing shear strength models.
-
The test results showed that ETS end anchorage for U-shaped BFRP stirrups through the flange of the RC T-beams was sufficient and there was no need for the closed BFRP stirrup technique.