Corrosion effects of longitudinal reinforcement on shear behavior of concrete beams without web reinforcement
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摘要: 以鋼筋混凝土梁為研究對象，考慮鋼筋非均勻銹蝕膨脹效應，建立三維鋼筋混凝土梁剪切破壞分析的數值分析模型。通過多階段分析方法(鋼筋銹蝕階段，構件性能退化階段)探索銹蝕對結構力學行為的影響。鋼筋的非均勻銹蝕膨脹以施加非均勻徑向位移的方式模擬，獲得保護層的破壞狀態，并以此“最終狀態”作為之后混凝土梁靜載試驗的“初始條件”輸入，進而模擬構件的力學行為。在驗證了多階段數值模型合理性的基礎上，分析了縱筋銹蝕、剪跨比對無腹筋混凝土梁抗剪性能的影響規律。結果表明，縱筋銹蝕使混凝土梁產生明顯的縱向裂縫。縱筋銹蝕率增大，保護層開裂區域增加，梁的抗剪承載力下降嚴重。另外，剪跨比對梁的抗剪承載力產生影響，剪跨比對未銹蝕梁的影響明顯大于對銹蝕梁的影響程度。最后，基于模擬結果對相關設計規范中的抗剪承載力計算公式進行了討論，發展建立了考慮銹蝕影響的無腹筋混凝土梁抗剪承載力計算方法。Abstract: Rebar corrosion is the principal factor affecting the service performance of reinforced concrete (RC) structures. Corrosion reduces the effective area of rebars as well as performance, and weakens the pin bolt effect of rebar on concrete. In addition, when the rebar is severely rusted, the concrete cover breaks, and the bond behavior between reinforcement and concrete deteriorates, affecting the mechanical properties of RC structures. In this study, a three-dimensional numerical model for shear analysis incorporating the nonuniform corrosion of reinforcement was established using an RC beam as the research object. The effects of corrosion on the mechanical behavior of the RC beam were explored via a multistage analysis method (namely, corrosion-induced expansion stage and structural deterioration stage). To model and simulate the expansion of the corrosion products, nonuniform radial displacement was applied to the concrete surrounding the rebar. The cracking process and the damage patterns of concrete resulting from corrosion were obtained. Then, taking the corrosion state as the initial condition, the static load was applied to analyze the mechanical behavior of the RC beam. After verifying the rationality of the multistage numerical model, the effect of the corrosion of tensile reinforcement and the shear-span ratio on the shear behavior of concrete beams without web reinforcement was analyzed. The modeling analysis results show that the corrosion of longitudinal reinforcement causes obvious longitudinal corrosion fractures in the concrete beam. Moreover, with the development of corrosion, the cracking area of the protective layer increases, reducing the shear capacity of the beam significantly. Furthermore, the shear-span ratio has a larger effect on the shear capacity of noncorroded beams than that of corroded beams. Finally, based on the simulation results, the calculation formulas of shear capacity in relevant design codes were discussed, and a methodology for predicting the shear capacity of RC beams without web reinforcement was proposed.
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Key words:
- RC beam /
- longitudinal reinforcement /
- corrosion /
- mesoscale numerical simulation /
- shear behavior
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圖 1 多階段銹蝕數值模擬方法
Figure 1. Framework of the numerical approach: multistage analysis strategy
圖 6 模擬與試驗結果梁破壞模式對比
Figure 6. Comparison of the distribution of typical cracks in experimental and simulated failure modes
圖 7 構件荷載位移曲線對比
Figure 7. Comparison between the simulated and experimental midspan deflection
圖 8 縱筋銹蝕4.35%下混凝土保護層破壞過程
Figure 8. Cracking process of concrete dcover under the corrosion level of 4.35%
圖 9 縱筋銹蝕4.35%下混凝土梁破壞過程
Figure 9. Cracking process of RC beam with the corrosion level of 4.35%
圖 10 不同銹蝕率下保護層破壞模式
Figure 10. Failure patterns of the cross-section of RC beams with various corrosion levels
圖 11 不同銹蝕率下保護層銹脹壓力分布
Figure 11. Distribution of the rust pressures of concrete cover with various corrosion levels
圖 12 不同銹蝕率下梁的破壞模式
Figure 12. Failure patterns of the RC beams with various corrosion levels
圖 13 不同銹蝕率下梁的荷載位移曲線
Figure 13. Load–deflection curves of the RC beams with various corrosion levels
圖 14 不同剪跨比梁的荷載位移曲線
Figure 14. Load?deflection curves of the RC beams with various shear–span ratios
圖 15 混凝土截面內銹蝕損傷分布
Figure 15. Distribution of the damage concrete on the cross-section of RC beams
圖 16 模擬與規范歸一化名義抗剪強度對比
Figure 16. Comparison of nominal shear capacity between the simulated and theoretical data
表 1 混凝土細觀組分力學參數
Table 1. Mechanical parameters of the mesocomponents of concrete
Components Compressive strength, σc/MPa Tensile strength, σt/MPa Elastic modulus, E/GPa Poisson ratio, ν Aggregate 70 0.2 Mortar *39 *3.5 *32 0.2 Interfacial transition zone ^31 ^2.8 ^26 0.2 Note：data with “*” are measured in the tests[20]; the data with “^” are measured by repeated trial. 
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表 2 黏結-滑移本構參數
Table 2. Parameters used in the bond-slip model of steel and concrete
Key point Bond stress, τ/MPa Slip, s/mm Crack (cr) τcr = 2.5ft scr =0.025d Peak value (v) τv = 3.0 ft sv = 0.04d Remnant (r) τr = ft sr = 0.55d Note: d means the diameter of steel; ft means the tensile strength of concrete.
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表 3 模擬值與理論值對比
Table 3. Comparison of shear capacity between the simulated and theoretical data
Spec. ID Vsiml/kN Vpred/kN β = 1 β = 1/2 β = 1/3 β = 1/4 NS-0 62.4 37.4 37.4 37.4 37.4 NS-4.35 43.9 20.1 23.8 25.1 25.7 NS-8 31.4 11.6 15.3 16.5 17.1 NS-12 20.1 6.8 9.7 10.7 11.2
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