Numerical analysis of experimentally tested frame corners with opening moments using the Compatible Stress Field Method (CSFM)

The critical parts of structures are typically discontinuity regions, where abrupt changes in geometry occur or large concentrated loads are applied. In engineering practice the verification of the ultimate limit stage of such discontinuity regions employs strut-and-tie models or stress fields based on the lower bound theorem of plasticity theory. These models are mechanically consistent but they can be prohibitively time consuming and are not directly applicable for serviceability limit state analysis as they do not consider strain compatibility. To overcome these limitations the Compatible Stress Field Method (CSFM) was developed for the design and assessment of discontinuity regions in concrete structures. The CSFM consists of a simplified nonlinear finite element-based stress field analysis procedure.Considering compatibility and equilibrium conditions at stressfree cracks, uniaxial constitutive laws as provided in concrete standards are used. While the concrete tensile strength neglected in terms of strength, the CSFM accounts for tension stiffening to obtain realistic predictions of deflections and crack widths, and cover the deformation capacity aspects. The effective compressive strength of concrete is automatically evaluated based on the transverse strain state. The present work validates the ability of the CSFM to reproduce the observed behaviour of experimentally tested frame corners with an opening moment. A quantitative comparison between the outcomes from the numerical analyses and reported experimental results proves the CSFM to be a reliable tool for assessing the structural behaviour of discontinuity regions. In addition, a numerical study is conducted to investigate the sensitivity of the CSFM to several input and model parameters.