The objective of this study is to analyze the behavior and failure mode of the brackets that support middle slabs in the double-deck tunnels by conducting laboratory experiments. In the double-deck tunnels, the middle slabs are supported by the brackets connecting to the tunnel lining. The brackets are subjected to the loads due to the weight of middle slabs and traffic moving on the middle slabs. Since the damages of brackets are directly associated with the safety problems such as falling down of middle slabs, the appropriate design of brackets is one of the most important factors when designing double-deck tunnels. In this study, the reinforcement design of concrete bracket was performed based on the concrete structure design guide, and the load capacity was evaluated by conducting laboratory loading tests. A small scale concrete bracket specimen was fabricated using the scale factor of 0.5. The reaction wall is normally needed to simulate the tunnel lining in this kind of test; however, two brackets were attached symmetrically to a column, which was assumed to be tunnel lining, to be able to conduct the tests without using the reaction wall. When the bracket specimen was fabricated, the lining part was fabricated first and after curing of the lining part, two brackets were fabricated at the same time at both sides of the lining part. In the tests, the loads were applied to both brackets simultaneously using a loading frame and the displacements were measured at different locations. The main behaviors of the bracket systems such as the vertical displacements of brackets and the displacements at the interfaces between the brackets and lining were measured and the horizontal displacements of the specimen were also measured at the bottom of the lining part to confirm if there was any slip or rotation of the specimen during the tests. The experimental analysis results showed that the initial damage of the specimen was observed at the interface between the bracket and lining with appearing the gap and the failure of the specimen was reached with cracking in the brackets. The load capacity (safety factor) of the bracket specimen to the initial damage based on the design load was 2.5 and to the failure was 3.3.

• Beom Keun Park(Kyung Hee University, Yongin, Korea)
• Young Kyo Cho(Kyung Hee University, Yongin, Korea)
• Seong-Min Kim(Kyung Hee University, Yongin, Korea)