The Ethiopia Railway Viaducts: Steel Girder Launching and Permanent Bearing Design

Abstract

The Awash-Kambolcha-Hara Gebaya (AKH) Railway project is 389 km long single railway line over 54 bridges constructed in Ethiopia. The 5 m wide precast concrete composite deck rests on two built-up steel box girders side by side, supported on steel piers. The typical span is 46.4 m, formed by four 11.6 m segments using friction bolts. The construction of shallow pier and short bridges is performed using lifting cranes. For the construction of tall pier and long bridges, where the crane capacity is exceeded, incremental launching method (ILM) is used. Eight out of 51-bridges, ranging from 200 to 615 m continuous in length, are launched to provide construction ease and speed. The 11.6 m long steel box pieces are bolted at the assembly yard and launched over temporary bearings with an 18 m steel front nose. The longest bridge (B24) has 14 spans with 800 m horizontal radius, 2.42% slope and 45 m pier height. All launching equipment: back nose, pulling stick, guiding devices, temporary bearings and jack supports, are designed and manufactured locally in Turkey. The bridge design did not consider ILM method initially, so the authors worked with the already drilled existing web/flange splice bolt holes to connect the launching devices. In addition to the launching equipment, the permanent elastomeric bearings of all bridges are designed and manufactured in Turkey. The deck is supported on sliding elastomeric bearings longitudinally, to minimize seismic forces on the piers. Prestressed damping systems (PDS) are used in longitudinal direction to create a fixed point at one abutment in service state, while providing additional rigidity and damping during earthquake. The deck is fixed transversally using steel shear keys between the girders and the piers. The paper presents details about launching and bearing design of AKH railway bridges.