CALCULATION METHOD AND EXPERIMENTAL STUDY ON BENDING DEFLECTION OF PRESTRESSED STEEL-BAMBOO COMPOSITE BEAMS
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摘要: 为分析预应力钢-竹组合梁的受弯挠度,以加载方式、张弦位置、预应力度为变量,对12根组合梁试件进行了设计与试验研究。在此基础上,假定梁变形分布符合正弦半波曲线,并考虑梁加载过程中几何关系变化与预应力反拱的影响,采用弹性理论建立了组合梁中预应力筋应力增量的计算方法,推导得出一点或两点加载、一点或两点张弦时,组合梁受弯挠度计算的统一公式。试验与理论计算结果的对比表明:该文提出的挠度计算方法可较好的预测组合梁在正常使用阶段的挠度;随着预应力度的增加,组合梁的等效抗弯刚度不断提高,且两点张弦时可获得更高的等效抗弯刚度。此外,对于初始预应力为零的试件,需采用可靠预紧措施,以保证体外预应力筋能够有效发挥作用。Abstract: To investigate the bending deflection of prestressed steel-bamboo composite beams, twelve composite beams were designed and tested with loading mode, prestressing position and prestressing level as variables. Based on the assumed half-wave sine curve for the deformation distribution and taking the consideration of the influence of geometric change and prestressing camber of the beam in the loading process, a method for calculating the stress increment of prestressed strands in composite beams is established using the elastic theory. A unified formula for calculating the bending deflection of composite beams under one-point or two-point loading (prestressing) schemes is also developed. The comparison between the experimental and theoretical results indicates that: the proposed method can provide suitable estimations for the deflection of composite beams in the serviceability limit state. With the increase of the prestressing level, the equivalent bending stiffness of composite beams increases continuously, and higher equivalent bending stiffness can be obtained when two-point prestressing scheme is applied. Moreover, For the specimens with zero initial prestress, reliable pre-tightening measures should be adopted to ensure that the external prestressing strands can play an effective role.
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表 1 试件设计参数
Table 1 Design parameters of specimens
编号 加载
方式加载点至
梁端距离/mm张弦方式 张弦点至
梁端距离/mm预应
力筋初始
预加力/kNL-1 1 1900 — — — — L-2 2 1350 — — — — L-3 1 1900 1 1900 2ΦS15.2 40 L-4 1 1900 1 1900 2ΦS15.2 60 L-5 2 1350 1 1900 2ΦS15.2 40 L-6 2 1350 1 1900 2ΦS15.2 60 L-7 1 1900 2 1350 2ΦS15.2 40 L-8 1 1900 2 1350 2ΦS15.2 60 L-9 2 1350 2 1350 2ΦS15.2 40 L-10 2 1350 2 1350 2ΦS15.2 60 L-11 2 1350 2 1350 2ΦS15.2 80 L-12 2 1350 2 1350 2ΦS15.2 0 注:加载方式1和2分别表示跨中单点加载和两点对称加载;张弦方式1和2分别表示跨中一点张弦和两点对称张弦。 表 2 材料的力学性能指标
Table 2 Mechanical properties of materials
材料 规格尺寸 强度指标/MPa 弹性模量/MPa 重组竹 −140×20.0(翼缘)
−160×20.0(腹板)155.2(静曲强度)
93.47(抗压强度)
124.04(抗拉强度)15673 薄壁钢板 [160×60×2.0 284(屈服强度)
378(极限强度)2.0×105 钢绞线 1×7Φs15.2 1860(极限强度) 1.95×105 表 3 试件的等效弯曲刚度
Table 3 Equivalent bending stiffness of specimens
编号 加载方式 张弦方式 初始预拉力值T0/N 竖向荷载F/N 跨中截面相对挠度f0/mm 等效弯曲刚度E′I′/(N·mm2) L-1 1 — 0 25 000 14.286 1.563×1012 L-2 2 — 0 30 000 15.180 1.531×1012 L-3 1 1 40 000 35 000 13.993 1.729×1012 L-4 1 1 60 000 40 000 13.613 1.738×1012 L-5 2 1 40 000 40 000 14.280 1.705×1012 L-6 2 1 60 000 50 000 15.167 1.841×1012 L-7 1 2 40 000 40 000 14.773 1.818×1012 L-8 1 2 60 000 45 000 14.880 1.833×1012 L-9 2 2 40 000 45 000 14.647 1.796×1012 L-10 2 2 60 000 55 000 14.981 1.890×1012 L-11 2 2 80 000 60 000 14.168 1.961×1012 L-12 2 2 0 30 000 14.264 1.629×1012 -
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