Gable metal frames are popular, cost-efficient structural systems for commercial and industrial buildings. The use of relatively thin web material typically leads to buckling of the panel zone in the beam-to-column connections when the frame is subjected to lateral loads. However, the panel zones may still be capable of developing post-buckling resistance by means of tension field action (TFA). Previous experimental research has shown that the exterior corner of a panel zone in gable frame knee joints may not be stiff enough to fully develop TFA. Although these test results have demonstrated the development of post-buckling strength, the amount of TFA and the design parameters that affect such action are not well understood. This paper presents a theoretical model for TFA in knee joints based on plastic analysis, and an accompanying equation for predicting the post-buckling panel zone strength for positive bending (wherein the tension field is oriented from the interior to the exterior corners). The TFA was found to primarily depend on three design parameters, namely, flange flexural strength, panel aspect ratio, and panel slenderness. To calibrate the proposed equation, a parametric analytical study was conducted using the finite element method. The modeling scheme accounted for material and geometric nonlinearity and was validated with experimental test data. The study involved 98 prototype gable frame configurations and allowed the investigation of the impact of the aforementioned three design parameters on the TFA. The proposed equation was found to predict the panel zone shear strength for the prototype frames with an average error of 1 % and an error standard deviation of 5%. Therefore, the equation can be used to calculate the post-buckling shear strength of panel zones for the range of design parameters considered in the parametric study.
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