Flexure tests on steel-concrete composite beams strengthened with prestressed CFRP plates by string system
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摘要: 为研究张弦式预应力碳纤维增强树脂复合材料(CFRP)板加固方法的加固效果，进行了4根5.2 m长的钢-混凝土组合梁试件的四点弯曲试验。使用自主研发的顶升装置横向张拉CFRP板，配合可转动的端部锚具共同完成加固。试验结果表明：钢-混凝土组合梁均呈现出典型的弯曲破坏特征；加固梁的极限承载能力显著提高，分别提高31.5%、28.8%和47.9%，其中150CFRP(10)-S-C组由于锚具不当而导致CFRP板提前发生破坏；加固对梁的破坏时挠度影响很小，100CFRP(10)-S-C和150CFRP(15)-S-C梁的极限挠度仅降低了0.4%和1.6%；增大CFRP板截面面积对梁的抗弯刚度贡献较大，而提高初始预应力水平更有助于延缓钢梁屈服；加载全过程，CFRP板应力沿全长分布均匀，破坏时材料强度利用率达80%以上。为期约90 h的预应损失监测表明，张弦式加固方法的预应力损失不超过2.5%，且损失预应力补偿方便。但是，值得注意的是该方法对端部锚具的可靠性要求很高。
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关键词:
- 钢-混凝土组合梁 /
- 预应力碳纤维增强树脂复合材料(CFRP)板 /
- 张弦式 /
- 加固 /
- 抗弯试验
Abstract: The four-point flexure experiments of four steel-concrete composite beams including three beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates and one non-strengthened as reference were investigated. The CFRP plate was transverse stretched by independently designed string system equipment and fixed on bottom of steel beam by rotatable end-anchorage. Experimental results show that the failure modes of beams present typical bending failure characteristics. The ultimate load-bearing capacities of three beams strengthened with prestressed CFRP plates are significantly improved by 31.5%, 28.8% and 47.9%, respectively. Unfortunately, the failure of CFRP plate of 150CFRP(10)-S-C beam due to improper anchorage is premature. The ultimate deflections of 100CFRP(10)-S-C and 150CFRP(15)-S-C are little affected by the reinforcement method, reduced by 0.4% and 1.6%, respectively. The stress distribution of CFRP plate is almost uniform during the whole process, and the material strength utilization ratios of CFRP plates are more than 80% at failure. The prestress losses of CFRP plates after 90 h are not more than 2.5%, and its compensation is convenient. However, it should be noted that this method is highly dependent on the reliability of end anchorage. -
图 1 钢-混凝土组合梁尺寸与配筋示意图
$\phi $—Diameter
Figure 1. Schematic of steel-concrete composite beam size and reinforcement layout
图 3 张弦式预应力CFRP板加固组合梁
Figure 3. Composite beam strengthened with prestressed CFRP plates by string system
图 6 钢-混凝土组合梁跨中截面荷载-挠度曲线
Δ—Deflection of mid-span
Figure 6. Load-deflection curves at mid-span section of steel-concrete composite beams
图 8 混凝土板内纵筋的荷载-应变曲线
Figure 8. Load-strain curves of reinforcement bars in concrete slab
图 10 CFRP板荷载-应变曲线
M, L, R—Middle section, left section and right sectionof CFRP plate, respectively
Figure 10. Load-strain curves of CFRP plate
图 11 钢-混凝土组合梁跨中沿截面高度应变分布曲线
h—Height; P—Load
Figure 11. Strain distribution along section height in mid-span section of steel-concrete composite beams
图 12 加载过程钢-混凝土组合梁跨中截面中性轴位置变化曲线
Figure 12. Variation of the neutral axis in mid-span section of steel-concrete composite beams during loading
表 1 混凝土力学性能
Table 1. Mechanical properties of concrete
Grade Cube compressive strength/MPa Prism compressive strength/MPa Elastic modulus/GPa C50 54.7 49.1 30.2 
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表 2 钢筋力学性能
Table 2. Mechanical properties of steel reinforcement
Grade Diameter/mm Elastic modulus/GPa Nominal yield strength/MPa Tensile strength/MPa HRB335 6 200.3 541.8 645.3 8 199.6 488.8 603.1
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表 3 碳纤维增强复合材料(CFRP)板材料力学性能
Table 3. Mechanical properties of carbon fiber-reinforced polymer (CFRP) plate
Grade Tensile strength/MPa Elastic modulus/GPa Elongation ratio/% Interlaminar shear strength/MPa I 2521 195 1.7 51
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表 4 钢-混凝土组合梁抗弯试验参数
Table 4. Reinforcement parameters of steel-concrete composite beams
Sample Section size of CFRP plate Initial prestress level/% Specimens Thickness/mm Width/mm Area/mm2 U-S-C — — — — Reference beam 100CFRP(10)-S-C 2 50 100 10 Strengthened beam 150CFRP(10)-S-C 3 50 150 10 150CFRP(15)-S-C 3 50 150 15 Notes: U-S-C is un-strengthened steel-concrete composite beam as reference beam; The other three beams are strengthened by prestressed CFRP plates. Taking 100CFRP(10)-S-C as an example, this specimen is strengthened by CFRP plate with 100 mm2 of cross-sectional area and 10% of initial prestress level.
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表 5 钢-混凝土组合梁试验结果
Table 5. Test results of steel-concrete composite beams
Sample Py/kN Pu/kN PΔ=85 mm/kN Δi/mm Δy/mm Δu/mm Δu/Δy U-S-C 196 340 329 1.07 19.69 114.64 5.82 100CFRP(10)-S-C 224 447 427 0.17 22.56 114.16 5.06 150CFRP(10)-S-C 243 438 437 0.01 22.07 86.74 3.93 150CFRP(15)-S-C 274 503 462 −1.79 23.72 112.79 4.76 Notes: Py—Yielding load when the bottom flange of steel beam yields; Pu—Ultimate load when the composite beam failure; PΔ=85 mm—Load when the deflection of mid-span is 85 mm; Δi—Initial mid-span deflection after strengthening with prestressed CFRP plate; Δy, Δu—Mid-span deflections corresponding to Py and Pu, respectively; Δu/Δy—Ductility factor.
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表 6 CFRP板预应力损失统计
Table 6. Prestress loss of CFRP plate
Initial
prestress levelPosition Prestress
loss/MPaPrestress
loss ratio/%Average
value/%10% L 6.9 2.67 2.28 M 5.5 2.11 R 5.5 2.06 15% L 6.9 1.75 2.13 M 11.2 2.91 R 6.7 1.73
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