Table 3. Representative load increase due to strengthening methods for timber arch elements
| Specimen | Retrofitted method | Major parameter | Loading system | Failure mode |
| Ultimate load (kN) | Load increased (%) | Ductility index |
| R | | - | 14.0 | - | 1.1 | Interface |
| RF | CFRP strip only | CFRP | 23.8 | +70.0 | 3.1 | Debonding |
| 3F | CFRP layer | CFRP | 20.8 | +48.6 | 4.5 | Interlayer opening |
| 5F | CFRP layer | CFRP | 14.0 | 0.0 | 4.9 | Local crushed |
| 7F | CFRP layer | CFRP | 22.2 | +58.6 | 3.6 | Longitudinal cracks |
| 3FF | CFRP strip and layer | CFRP | 32.0 | +128.6 | 3.1 | FRP cracking failure |
| 5FF | CFRP strip and layer | CFRP | 29.8 | +112.9 | 4.6 | Bending cracks |
| 7FF | CFRP strip and layer | CFRP | 28.2 | +101.4 | 4.8 | Thin cracks |
CFRP: carbon-fiber-reinforced polymer.