Bridge Type Classification: Supervised Learning on a Modified NBI Data Set

Abstract

A key phase in the bridge design process is the selection of the structural system. Due to budget and time constraints, engineers typically rely on engineering judgment and prior experience when selecting a structural system, often considering a limited range of design alternatives. The objective of this study was to explore the suitability of supervised machine learning as a preliminary design aid that provides guidance to engineers with regards to the statistically optimal bridge type to choose, ultimately improving the likelihood of optimized design, design standardization, and reduced maintenance costs. In order to devise this supervised learning system, data for more than 600,000 bridges from the National Bridge Inventory (NBI) database were analyzed. Key attributes for determining the bridge structure type were identified through three feature selection techniques. Potentially useful attributes like seismic intensity and historic data on the cost of materials (steel and concrete) were then added. Decision tree, Bayes network, and support vector machines were used for predicting the bridge design type. Due to state-to-state variations in material availability, material costs, and design codes, supervised learning models based on the complete data set did not yield favorable results. Supervised learning models were then trained and tested using 10-fold cross validation on data for each state. Inclusion of seismic data improved the model performance noticeably. The data were then resampled to reduce the bias of the models toward more common design types, and the supervised learning models thus constructed showed further improvements in performance. The average recall and precision for the state models were 88.6 and 88.0% using decision trees, 84.0 and 83.7% using Bayesian networks, and 80.8 and 75.6% using SVM.