配筋率对RUHTCC梁弯曲性能的影响研究

Influence of reinforcement ratio on flexural behavior of RUHTCC beams

钢筋增强超高韧性水泥基复合材料(RUHTCC)梁的弯曲性能与配筋率、UHTCC拉压材料性能以及截面尺寸相关。以配筋率为研究的影响因素,理论给出RUHTCC梁3个特征配筋率即最小配筋率、最大弹性配筋率以及最大界限配筋率的计算式。以这3个特征配筋率为边界,理论分析破坏模式从受拉破坏到受压破坏不同情况下梁极限承载力、中性轴高度、曲率、开裂长度以及最外层边缘拉应变的变化规律。提出最优化配筋率的概念,并指出它的大小接近于最大弹性配筋率。进行4种不同配筋率RUHTCC梁和两组RC对比梁的弯曲试验,讨论配筋率对弯曲性能包括承载力、变形、延性以及裂缝开展情况的影响和配筋率对RUHTCC梁较RC梁弯曲性能提高程度的影响。结果表明,对不同配筋率的RUHTCC梁,配筋率越大,极限承载力增加,屈服变形增大,但极限变形减小,延性降低,裂缝宽度的变化不明显。同一配筋率下,RUHTCC可提高RC梁的承载力和延性,在屈服时刻裂缝宽度可控制在0.1mm以内,极大提高了结构的耐久性,但随配筋率的增大,提高程度降低。试验与理论预测进行对比,结果较为吻合。

The flexural behavior of steel reinforced beams composed of ultra-high toughness cementitious composite is related with the reinforcement ratio,tensile and compressive properties of UHTCC as well as the cross-section size. The influence of reinforcement ratio on the flexural response is studied. Three characteristic reinforcement ratios of RUHTCC beams are defined and the theoretical calculation formulae are provided. Taking the three characteristic reinforcement ratios as the boundary,theoretical prediction of the change of flexural behavior from tension failure to compression failure due to the difference in reinforcement ratios is conducted,and discussions on the flexural capacity,neutral axis depth,curvature or deformation,cracking zone length and tension strain at the most bottom fiber of the beam are presented. The concept of optimal reinforcement ratio is proposed and its magnitude is found to be close to the maximum elastic reinforcement ratio. Four-point bending tests are performed for four groups of RUHTCC beams with different reinforcement ratios and two groups of RC control beams,for the main purpose of investigating the influences of reinforcement ratio on the flexural response of RUHTCC and the significance on the improvement of RUHTCC beams. The results reveal that,for RUHTCC beams,the ultimate load capacity and yielding curvature increase with the reinforcement ratio,while the ultimate failure curvature and ductility decreases. The variation of crack width of RUHTCC beams with different reinforcement ratios is small. The comparison between RUHTCC and RC shows that RUHTCC not only could enhance the ultimate load capacity and ductility,but also could greatly restrain crack width at the moment of yielding to within 0.1mm,thus leading to significant improvement of the durability of structures. However,the degree of improvement reduces as the reinforcement ratio increases. The experimental results are in good agreement with the theoretical ones.