Backbone moment-rotation models for partial-strength steel endplate connections

Phenomenological rotational spring models are critical components of system-level numerical simulations that employ the concentrated plasticity approach. These models must accurately capture the nonlinear behavior and degradation mechanisms in structural members and connections. Robust models for partial strength/semi-rigid steel flush and extended endplate connections are currently missing. Using the large amount of experimental data in the literature for endplate connections, complemented with parametric continuum finite element simulation, robust nonlinear models are developed. The models characterize the nonlinear monotonic backbone moment-rotation response up to failure as well as the post-failure response. The models achieve high accuracy metrics with 75 % of the data being predicted with an error of less than ±10 %. Statistical metrics are also provided to quantify the model uncertainty. The regression-based models are consistent, in definition and format, with those found in existing modelling guidelines/standards such as ASCE 41. The proposed models support robust nonlinear analysis procedures, particularly as part of the performance-based evaluation, retrofit, and design framework.