再生混凝土梁开裂弯矩与抗弯刚度计算方法

Methods for Calculating Cracking Moment and Flexural Stiffness of Recycled Concrete Beams

为研究再生混凝土梁的抗弯性能,验证公路桥梁规范中开裂弯矩与抗弯刚度的计算方法对再生混凝土梁的适用性,设计1根普通混凝土梁和2根再生骨料取代率分别为50%、100%的再生混凝土梁进行抗弯性能试验,并将试验值与规范计算值进行对比。结果表明:与普通混凝土梁相比,再生混凝土梁的开裂弯矩、屈服弯矩及极限弯矩均偏小,分别约为普通混凝土梁的66.0%、85.4%及88.3%,其中再生混凝土梁的开裂弯矩降低幅度最大;再生混凝土梁的跨中挠度随着再生骨料取代率的增加而增大,且大于普通混凝土梁的跨中挠度;按照公路桥梁规范的计算方法,再生混凝土梁的开裂弯矩计算值较试验值大25%左右,而跨中挠度计算值较试验值小10%左右,即公路桥梁规范的抗弯刚度计算值大于试验值;公路桥梁规范关于开裂弯矩和抗弯刚度的计算方法不直接适用于再生混凝土梁。利用国内外既有典型试验数据,分别对公路桥梁规范中开裂弯矩和抗弯刚度的计算方法进行修正,并对修正后的方法进行验证。修正后方法的计算值与试验值吻合较好,预测精度较高,可分别用于计算再生混凝土梁的开裂弯矩和抗弯刚度。

In this study, tests were conducted to investigate the flexural performance of recycled concrete beams and to validate the applicability of formulas for calculating the cracking moment and flexural stiffness of recycled concrete beams as provided by the China Highway Bridge Code(CHBC). Flexural performance tests of a reinforced concrete beam and two recycled concrete beams with 50% and 100% replacement proportion of recycled aggregate were performed. Experimental results were compared with the computed results from the CHBC. Results show that the cracking, yield bending, and ultimate bending moments of recycled concrete beams are nearly 66.0%, 85.4 %, and 88.3% less than those of reinforced concrete beam, respectively. The reduction in the magnitude of the cracking moment of recycled concrete beams is the largest. Their mid-span deflection is also greater than that of the reinforced concrete beam, and it increases with an increase in the replacement proportion of the recycled aggregate. However, for recycled concrete beams, the computed results of the cracking moment and mid-span deflection according to the CHBC are approximately 25% higher and 10% lower than the experimental data, respectively. This suggests that the computed flexural stiffness of recycled concrete beams in accordance with the CHBC is larger than the experimental data. Therefore, the formulas for calculating the cracking moment and flexural stiffness as suggested by the CHBC are not suitable for recycled concrete beams and require revision. These formulas were modified based on the experimental data collected from the flexural performance tests conducted by domestic and overseas researchers. Subsequently, the modified formulas were validated by the experimental data obtained from this study. The modified formulas of the cracking moment and flexural stiffness have a high prediction accuracy, which can provide guidance for the calculation of the cracking moment and flexural stiffness of recycled concrete beams.