Incremental Launching by Lag-Casting: İhsaniye Viaduct

Incremental Launching Method (ILM) is a bridge construction technique that has become an efficient alternative in Turkey in recent years. In the first phase of The Northern Marmara Motorway Project (KMO1), three viaducts were constructed using ILM. The KMO1 is followed by the second phase: KMO2. İhsaniye Viaduct is part of KMO2 on the European Side of Istanbul, located south of the Third Istanbul Airport (IGA), and constructed using the ILM. Several advantages are offered by the ILM technique, including quantity saving, enhancing the safety during construction and introducing innovative seismic design approach. This paper focuses on the deck and pier design of the İhsaniye Viaduct. The deck is constructed by lag casting of segments. First, only the bottom slab and the webs are cast. After reaching the launching strength, the U-section is pushed out-of-the formwork, where the top slab is cast simultaneously with the next segment’s U-section in the second step. This technique provided a fast launching track, optimizing the time required for strength and workforce. Detailed analysis of the construction staging, post-tensioning and rebar detailing are exhaustively studied. The pier design is governed by the seismic actions. Innovative double-wall pier shape was used to increase its flexibility in the transversal direction while providing energy dissipation through the creation of plastic hinges at double walls. Longitudinally, the deck is fixed on several piers and fluid viscous dampers are placed at the abutments to reduce the seismic displacement. The viaduct is two decks side by side, 21.5 m wide, 856 and 867 m in length with 66 m typical spans and an 80 m maximum span. The 80 m span is launched using a temporary steel pier.