Fatigue Behavior under Rolling Load of a Full-Scale Bridge Deck with a Steel-Reinforced Section

Abstract

Fatigue tests were performed on a full-scale deck slab (15,240 × 3,890 × 210 mm) supported by steel girders spaced at 3.05 m using a rolling load simulator for up to 6 million equivalent cycles under two half axle moving loads of 90 kN each, spaced at 1.2 m. The loads were designed to produce the equivalent effect of the CL625 design truck of the Canadian Highway Bridge Design Code (CHBDC). The deck had several sections featuring three different reinforcement designs; namely, steel rebar, glass fiber–reinforced polymer (GFRP) rebar, and GFRP structural permanent form. The steel rebar was designed in accordance to the empirical method in Section 8 of the CHBDC. This paper focuses primarily on the performance of the 3,810 × 3,890 mm steel-reinforced section and compares it to the two adjacent GFRP-reinforced sections. It also introduces a method to define the loading cycle based on vertical deflection and recovery at the center of a section, which could differ from the vehicle travel cycles. As a result, it was shown that the middle steel-reinforced section experienced 6 million cycles, double that of the two end sections. It experienced a 71% reduction in stiffness and its live-load deflection increased by 2.36 times. The live-load strain of its bottom transverse reinforcement reduced from 384 to 264 με, while the strain of the top transverse reinforcement over the support increased from 20 to 301 με after 6 million cycles. The deflection limit of L/800 was satisfied up to 4.47 million cycles. A dense grid-pattern of cracks occurred at the bottom. Few transverse cracks occurred on top and longitudinal cracks developed above the girders. The empirical design methods in bridge codes provide a convenient way for engineers to design bridge decks with steel or glass fiber–reinforced polymer (GFRP) reinforcement. This paper verifies the fatigue performance of such deck designs under realistic rolling load that simulates the full life of a bridge. The study quantified changes in deflection, stiffness, and strains over time throughout the life of the bridge deck along with the development of cracking patterns. The study is also the first to compare the performance of a GFRP-reinforced deck to that of the traditional steel-reinforced deck under rolling load cycles. A method to quantify the number of cycles the deck experiences is also proposed.