Effects of the adhesive layer and prestress on the flexural behavior of damaged steel beams strengthened with CFRP plates
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摘要: 为了对比粘结层和预应力对碳纤维增强聚合物复合材料(CFRP)板加固损伤钢梁抗弯性能的影响,进行了5根H型损伤钢梁的抗弯试验,分析了特征荷载、荷载-挠度曲线、CFRP板应变及其强度利用率的变化。试验结果表明:有粘结和无粘结CFRP板具有相近的加固效果,特征荷载差值小于2%;非预应力CFRP板在正常使用阶段的加固效果很小,而预应力CFRP板加固钢梁的特征荷载比非预应力CFRP板提高了近30%。平截面假定适用于有粘结CFRP板-钢梁复合截面,而不适用于无粘结CFRP板-钢梁复合截面。相比于非预应力CFRP板,对CFRP板施加预应力可以显著提高CFRP板的强度利用率。建立的有限元模型可以较好地预测试件的抗弯性能,增加CFRP板的预应力、厚度和弹性模量可以提高损伤钢梁的抗弯加固效果。Abstract: In order to investigate the effects of the adhesive layer and prestress on the flexural behavior of damaged steel beams strengthened with carbon fiber reinforced polymer (CFRP) plates, five damaged H-steel beams were tested under flexure. The characteristic load, load-deflection curve, CFRP plate strain and its strength utilization were analyzed. Test results show that the unbonded CFRP plate has a similar strengthening efficiency to the bonded CFRP plate, with a difference of less than 2% in the characteristic loads. The non-prestressed CFRP plate provides only a very small strengthening efficiency under the normal service state. However, the characteristic loads of steel beams strengthened with the prestressed CFRP plate can be significantly increased by about 30% compared with the non-prestressed CFRP plate. The plane section assumption is satisfied in the bonded CFRP plate-steel beam composite section while it is not satisfied in the unbonded CFRP plate-steel beam composite section. Compared with the non-prestressed CFRP plate, the strength utilization of the CFRP plate can be obviously increased when a prestress is applied in the CFRP plate. The developed finite element model can predict the flexural behavior of the specimens with good accuracy. The increase in the prestress, thickness and elastic modulus of the CFRP plate can increase the flexural strengthening efficiency of damaged steel beams.
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Key words:
- CFRP plate /
- bonded strengthening /
- unbonded strengthening /
- prestressing /
- steel beam /
- flexural behavior
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表 1 材料的主要力学性能
Table 1. Main mechanical properties of materials
Material type Elasticity modulus/GPa Yielding stress/MPa Tensile strength/MPa Elongation/% Q235 B steel 207.0 271 429.0 15.78 CFRP plate 163.0 - 2516.0 1.54 Adhesive 4.5 - 49.2 1.64 Note: CFRP—Carbon fiber reinforced polymer. 表 2 CFRP板加固损伤钢梁试件的加固参数
Table 2. Strengthening parameters of damaged steel beam strengthened with the CFRP plate specimens
Specimen Sectional area of CFRP plate/mm×mm Strengthening method Designed prestress/MPa B-0 - Unstrengthening - B-BR 50×2 Bonded strengthening 0 B-UR 50×2 Unbonded strengthening 0 B-PBR 50×2 Bonded strengthening 850 B-PUR 50×2 Unbonded strengthening 850 Notes: In the specimen, the first letter B represents the beam; The number 0 represents the unstrengthening, the letters BR, UR, PBR and PUR represent bonded CFRP plate strengthening, unbonded CFRP plate strengthening, prestressed bonded CFRP plate strengthening, and prestressed unbonded CFRP plate strengthening, respectively. 表 3 CFRP板加固损伤钢梁特征荷载比较
Table 3. Comparisons of characteristic loads of damaged steel beams strengthened with CFRP plates
Specimen P7.5/kN α7.5/% Py/kN αy/% B-0 102.5 - 105.8 - B-BR 104.6 2.0 124.6 17.8 B-UR 103.4 0.9 126.5 19.6 B-PBR 131.9 28.7 157.9 49.2 B-PUR 133.5 30.2 158.5 49.8 Notes: P7.5—Load when the mid-span deflection is 7.5 mm; Py—Yielding load; α7.5 and αy—Ratios between the P7.5 and Py of the strengthened beams and those of the unstrengthened beam, respectively. 表 4 CFRP板应变及强度利用率比较
Table 4. Comparisons of CFRP plate strain and strength utilization
Specimen ε0/10−6 εp7.5/10−6 εp7.5/εu/% εpy/10−6 εpy/εu/% B-BR 0 855 5.6 1287 8.4 B-UR 0 581 3.8 723 4.7 B-PBR 5605 6877 44.7 7276 47.2 B-PUR 5542 6300 40.9 6485 42.1 Notes: ε0—Initial tensioning strain of the CFRP plate; εp7.5—Strain of the CFRP plate at P7.5; εpy—Strain of the CFRP plate at Py; εu—Ultimate strain of the CFRP plate. 表 5 CFRP板加固损伤钢梁有限元与试验结果的对比
Table 5. Comparisons of finite element and test results of damaged steel beams strengthened with CFRP plates
Specimen P7.5 Py Test/kN Finite element/kN Ratio Test/kN Finite element/kN Ratio B-0 102.5 104.4 1.02 105.8 106.1 1.00 B-BR 104.6 107.4 1.03 124.6 131.1 1.05 B-UR 103.4 104.2 1.01 126.5 127.8 1.01 B-PBR 131.9 138.3 1.05 157.9 164.5 1.04 B-PUR 133.5 137.6 1.03 158.5 163.4 1.03 -
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