Comparison between resistant load contours generated considering the parabolic-rectangular (DPR) and the rectangular (DR) stress-strain diagrams for rectangular sections under combined axial compression and biaxial bending

Abstract The aim of this study is to compare the load contour diagrams generated for rectangular RC cross-sections under combined axial compression and biaxial bending obtained by the two forms of analysis allowed by NBR 6118:2014 [1]: the first using the parabolic-rectangular stress-strain diagram (DPR) and the second using the rectangular (constant stress) diagram (DR). In order to compare the load contours generated, a reference cross-section was adopted for which the concrete strength class (from C20 to C90) and the deformation domains (4, 4a and 5) were varied for the study. It was studied whether the use of the different diagrams (DPR or DR) would provide greater (or smaller) resistant efforts for the same section. The results show that the use of the DR is only acceptable when the section is working up to the 4th domain. Above this domain, it was observed that the use of this diagram shows resistant efforts inferior to those calculated by the DPR. In addition, it was found that, for concretes with resistance class above C50, in oblique loading directions, the use of the DR presents higher resistant efforts than those calculated using the DPR.

摘要 本研究旨在对比依据NBR 6118:2014[1]允许的两种分析方法，得到轴压与双轴弯曲组合受力下矩形钢筋混凝土（RC）截面的荷载轮廓图：第一种方法采用抛物线-矩形应力应变图（DPR，即parabolic-rectangular stress-strain diagram），第二种方法采用矩形（常应力）应力应变图（DR，即rectangular constant stress stress-strain diagram）。为对比所生成的荷载轮廓，本研究选取一组基准截面，针对该截面，混凝土强度等级（C20至C90）与变形域（4、4a及5）均作为变量开展研究。本研究探讨了采用不同应力应变图（DPR或DR）时，同一截面的承载力是否会更大或更小。结果表明，仅当截面受力处于第4变形域时，采用DR的分析结果才具备可接受性；当受力超过该变形域时，采用DR得到的承载力低于DPR的计算结果。此外，研究发现，对于强度等级高于C50的混凝土，在斜向荷载作用方向下，采用DR得到的承载力高于DPR的计算结果。