Seismic Performance of Innovative Hollow-Core FRP-Concrete-Steel Bridge Columns

This paper presents the seismic behavior of hollow-core fiber-reinforced polymer-concrete-steel (HC-FCS) columns. The typical HC-FCS column consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The inner steel and outer FRP tubes provide continuous confinement for the concrete shell; hence, the concrete shell achieves significantly higher strain, strength, and ductility than unconfined concrete in conventional columns. Three large-scale HC-FCS columns were investigated in this study. Each column had an outer diameter of 610 mm (24 in.) and a height-to-diameter ratio of 4.0. The steel tube was embedded into a reinforced concrete footing with an embedded length of 1.6-1.8 times the steel tube diameter, whereas the FRP tube only confined the concrete wall thickness and truncated at the top of the footing level. In general, the columns exhibited high lateral drift, reaching to 11.6%, and failed gradually as a result of concrete crushing and local steel tube buckling. An equation to determine the steel tube development length of HC-FCS columns was introduced based on an extensive finite-element study. The finite-element analysis was validated with finite-element models. In addition, this paper introduces a quick-repair technique for HC-FCS columns. Guidelines for the preliminary design of HC-FCS columns under seismic loading are also presented to help implement this new technology