Fatigue Experimental Analysis of Damaged Steel Beams Strengthened with Prestressed Unbonded CFRP Plates
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摘要: 老旧钢桥在长期运营过程中容易疲劳开裂，严重影响桥梁结构安全，为改善受损钢梁构件的疲劳性能，采用大比例疲劳模型试验对无粘结预应力碳纤维增强复合材料（CFRP）板加固受损钢梁进行研究，基于Paris公式提出疲劳强度-寿命（S-N）曲线的确定方法，并分析不同预应力水平对受损钢梁寿命影响. 对不同预应力水平CFRP板加固的双缺口受损钢梁在循环荷载下进行疲劳试验，结果表明：施加预应力可降低裂纹扩展速率和受损钢梁残余挠度超过40%，最少可延长受损钢梁的疲劳寿命3倍；最高预应力水平所加固的受损钢梁，其疲劳寿命最少提高了8倍，且预应力CFRP板加固后缺口钢梁疲劳强度等级由51 MPa提高到75 MPa. 理论预测结果与试验结果符合较好，可作为推荐方法.Abstract: Aged steel bridges are prone to fatigue cracking, which is a challenging problem for the safety of bridges during their service. An experimental and theoretical study was conducted to improve the fatigue performance of notched steel beams strengthened with prestressed unbounded carbon-fibre-reinforced polymer (CFRP) plates. The Paris law was used to obtain the S-N curve of the reinforced steel beam, and the effect of the prestress level on the fatigue life was presented. Double-edge-notched large-scale specimens were strengthened using an unbonded CFRP plate with different prestressing levels and were thereafter tested under cyclic loading. Experimental results show that prestress reduces both the crack growth rate and stiffness decay of the specimens by up to 40%, and thus, the fatigue life is extended by more than three times. The specimen with the highest prestress level exhibits the best performance, extending the fatigue life by more than eight times. Moreover, prestressed CFRP reinforcements upgrade the fatigue category of the notched beam from 51 MPa to 75 MPa. The theoretically predicted results are reasonably consistent with the experimental results, and the proposed method is recommended for lifetime evaluations of components.
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Key words:
- steel structure /
- reinforcement /
- unbounded CFRP /
- fatigue strength /
- prestress level /
- S-N curve
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图 9 疲劳S-N曲线与试验结果对比分析
Figure 9. Comparison between the experimental and S-N curve results
表 1 试件的几何和力学性能
Table 1. Properties of specimens
材料 长度/mm 宽度/mm 厚度/mm 力学性能 钢梁 3 000 175 11（底板）
& 7（腹板）Es = 200 Gpa
Sy = 235 MPaCFRP 1 650 100 2 Ec = 180 GPa
Sut = 2 000 MPa
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表 2 试件细节
Table 2. Details of specimens
试件 有效预
应力/MPa最大名义
应力σmax/MPa最小名义
应力σmin/MPa应力比R S0 114.6 14.3 0.13 S480 480 93.0 –7.3 – 0.10 S550 550 89.8 –10.5 – 0.10 S600 600 87.6 –12.7 – 0.15 S630 630 86.2 –14.1 – 0.15 S900 900 74.1 –26.2 – 0.35
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表 3 试件疲劳寿命
Table 3. Fatigue life of specimens
试件 有效预应力/MPa 疲劳寿命/万次 破坏模式 S0 — 27.2 完全断裂 S480 480 32.4 S550 550 67.8 S600 600 109.4 S630 630 87.3 S900 900 > 200.0 停止试验
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表 4 试件疲劳寿命计算值与实测值比较
Table 4. Comparison between the test and predicted results
试件 试验值 规范公式计算值 本文方法 中国规范 欧洲规范 B1 15.6 17.5 10.7 11.2 B5 82.0 39.2 24.0 25.2 B6 62.6 37.6 23.1 24.2 S0 27.2 40.7 24.9 26.1 S480 32.4 43.4 27.2 51.7 S550 67.8 44.5 28.1 53.5 S600 109.4 46.5 29.7 56.4 S630 87.3 46.6 29.8 56.6 S900 >200.0 52.1 34.8 116.6
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