Second‐Order Refined Plastic‐Hinge Analysis for Frame Design. Part I

TLDR

The paper examines simplified second‑order inelastic analysis for steel‑frame design, critiques the elastic‑plastic hinge method, introduces a refined plastic‑hinge approach, and evaluates both methods’ suitability for predicting ultimate strengths. The refined plastic‑hinge method models inelastic stiffness degradation using a column tangent‑modulus expression to represent effective stiffness under large axial loads. The study demonstrates that the elastic‑plastic hinge method inadequately represents inelastic behavior and lacks sufficient data for member ultimate strength assessment, while the refined plastic‑hinge method’s qualities and limitations are illustrated, with case studies and recommendations provided in a companion paper.

Abstract

This paper discusses the issues involved in using simplified second‐order inelastic analysis for design of steel‐frame structures. In particular the elastic‐plastic hinge method is examined and the assumptions inherent in its use are outlined. It is shown that this method does not always lead to an accurate representation of inelastic behavior, and that it does not furnish enough information for assessment of the ultimate strength of individual members. An alternative approach called the refined plastic‐hinge method is introduced, and its design implications are discussed. The refined plastic‐hinge approach accounts for inelastic stiffness degradation, and a column tangent‐modulus expression is utilized to represent the effective stiffness of the element when it is loaded with large axial loads. This paper highlights and illustrates the qualities and limitations of these two inelastic analysis methods with regard to their acceptability for use in predicting the ultimate strengths of steel frames and their members. Case studies and recommendations for use of inelastic analysis for direct frame design are presented in a companion paper.