A WiBS-PLS-RSM–Based Surrogate Model for Seismic Fragility Assessment of Ancient Masonry Pagodas

Due to material degradation and inherent structural weaknesses, pagodas often suffer severe damage in earthquakes. Conducting an accurate and efficient pre-earthquake fragility assessment of these pagodas is a key task within the performance-based seismic engineering framework. Therefore, this paper proposes a Width-tunable Basis Spline-Partial Least Squares-Response Surface Model (WiBS-PLS-RSM)–based framework for seismic fragility analysis of ancient masonry pagodas. In this framework, WiBS-PLS-RSM introduces the width parameter and jointly optimizes it with the number of segments to solve the overfitting or underfitting issues of traditional response surface model (RSM) in seismic fragility analysis under high nonlinearity, high dimensionality, and strong parameter correlations. The workflow is detailed and validated through a case study of the Guang Pagoda, including surrogate modeling of the means and standard deviations of damage indicators, derivation of fragility curves, and SHAP-based sensitivity analysis of collapse fragility. The results show that the prediction accuracy of the WiBS-PLS-RSM for the mean and standard deviation of the structural damage indicators is superior to that of the traditional RSM; determination coefficients R² increased by 3.8%-5.8% and 5.6%-6.4% respectively, thereby constructing an accurate seismic fragility curve. The proposed framework accurately resolves the magnitude and direction of parameter influences on collapse probability across different damage indicators.