Experimental Study on Steel Tub Girders with Modified Cross-Section Details

Steel box girder systems, consisting of steel tub girders with a cast in-place concrete deck, are a popular alternative for straight and horizontally curved bridges due to their high torsional stiffness and aesthetics. However, steel tub girders possess relatively low torsional stiffness during transport, erection and construction because of the thin-walled open section. Thus, they require extensive bracing during construction, such as top flange lateral bracing and internal K-frames. This paper highlights results from a study related to improving the structural efficiency and economy of steel tub girders, and highlights results of experiments of tub girders with modified cross-sectional details. The experimental program consisted on testing three tub girders with different cross-section details subjected to bending, as well as combined bending and torsion. The first specimen was fabricated following current design practice, while the second and third girders were built with top flanges offset towards inside the tub and with flatter webs (1H:2.6V), respectively. The impact of modified cross-section details was assessed by conducting multiple elastic-buckling tests on the specimens with several configurations of top lateral bracing and K-frames. Finally, a concrete deck was poured on top of the specimens with enough shear studs to guarantee full composite action. The impact of the modified cross-section details in the ultimate flexural strength of composite tub girders was assessed by testing the girders up-to failure under positive and negative moment. The final goal of this study is to improve steel tub girders efficiency by providing better detailing without undermining their structural performance.

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