Mechanical behavior of prestressed concrete T beam based on mixed shell element method
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摘要: 为了准确预测与评估预应力混凝土T梁的力学性能, 利用混合壳单元建立了T梁有限元计算模型, 对T梁从完好状态至破坏状态的力学行为进行了非线性分析。T梁中弯曲预应力钢筋采用组合壳单元模型, 应用虚功原理推导了其对组合壳单元刚度矩阵的贡献, 梁底平直预应力钢筋采用分层壳单元模型; 利用Owen双参数屈服准则和Hinton压碎准则描述混凝土材料非线性特性, 采用双折线本构模型模拟钢筋材料。分析结果表明: 混合壳单元法计算结果与试验结果吻合良好, 弹性阶段的T梁刚度折减不明显, 非线性阶段刚度发生明显折减, 跨中预应力钢筋应力增长幅度最大, 因此, 混合壳单元法对预应力混凝土T梁力学行为分析是有效的。Abstract: In order to accurately forecast and estimate the mechanical property of prestressed concrete T beam, its finite element model was set up by using mixed shell elements, and the nonlinear process of its mechanical behavior from wholeness to failure was studied. In T beam, curving prestressed steel was simulated with combined shell element model, its contribution to the stiffness matrix of combined shell element was deduced by using virtual principle, and straight prestressed steel was simulated with layered shell element model; the material nonlinear behavior of concrete was considered with Owen yield criterion and Hinton crushing criterion, and the behavior of steel was depicted with bilinear constitutive model. Analysis result indicates that the computational result of the model is close to experimental result, the stiffness degradation coefficient of T beam in nonlinearity phase is much larger than that in elasticity phase, and the most increase of steel stress is at the bottom of mid-span, so mixed shell element method is efficient and proper to analyze the mechanical behavior of prestressed concrete T beam.
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图 2 平直预应力钢筋的分层壳元模型
Figure 2. Layered shell element model of straight prestressed steel
图 3 弯曲预应力钢筋的组合壳元模型
Figure 3. Combined shell element model of curving prestressed steel
图 4 预应力混凝土T梁的构造及加载方式
Figure 4. Configuration of prestessed concrete T beam and positions of added loads
表 1 跨中的刚度折减
Table 1. Stiffness degradation in middle span
荷载步 荷载/kN 跨中挠度/mm 荷载比跨中挠度/(kN·mm-1) 刚度折减程度/% 注 1 0.00 0.00 弹性阶段 2 80.00 6.00 13.32 100.00 11 630.60 48.26 13.07 98.07 14 765.60 61.41 12.47 93.58 15 810.80 67.52 12.01 90.14 非线性阶段 17 900.80 86.48 10.42 78.18 20 1 035.80 199.11 5.20 39.05 22 1 130.00 551.65 2.05 15.38 
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表 2 跨中预应力钢筋的应力重分布
Table 2. Redistribution of stress in middle span
荷载步 荷载/kN 应力/MPa 荷载增量/kN 应力增量/MPa 应力增长率/(MPa·kN-1) 重分布系数 注 1 0.00 1 050.00 弹性阶段 2 80.00 1 076.96 80.00 26.96 0.34 1.00 11 630.60 1 310.38 45.00 33.89 0.75 2.23 14 765.60 1 451.43 45.00 22.71 0.50 1.50 15 810.80 1 471.05 45.20 19.62 0.43 1.29 非线性阶段 17 900.80 1 508.84 45.20 27.10 0.60 1.78 20 1 035.80 1 543.97 45.00 6.73 0.15 0.44 22 1 130.00 1 597.02 49.20 34.67 0.70 2.09
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