Halving joint connection for link bridge beams between Metro Station and Viaduct

HALVING JOINT CONNECTION FOR LINK-BRIDGE BEAMS BETWEEN METRO STATION AND VIADUCT 1) Ranjil P Ramath -Project Manager; 2) B. Deepak Kumar-Design Engineer; 3) Raja Prabu-Design Engineer; 4) Sankaralingam Anandha Kumar- CAD Technician

Synopsis The metro station box was proposed to be in integral connection to the adjacent viaduct, as part of the typical platform access. In this concept, for the advancement of the viaduct construction the designs were made and dowels were left for the beam connection to station. Later, new station box was introduced in connection and has caused altogether and increases in the stress resultants in the integral, monolithic beam. Provided dowel reinforcement was found to be insufficient. A solution was worked out, by providing a halving joint in the beam and converting the fixed end to simple bearing support.

Problem Statement In one of the over ground elevated stations in a Metro Rail Project, the station box was proposed to be in integral connection to the adjacent viaduct, as part of the typical platform access. In this concept, for the advancement of the viaduct construction the designs were made based on the preliminary layout and dowels were left for the beam connection to station. Later, during the detailed design development of the architectural layout, new station box was introduced in connection to the existing station box and beam and has caused altogether and increases in the stress resultants in the integral, monolithic beam. (Pier and viaduct substructure were found to be satisfactory, with existing cross section and reinforcement). Provided dowel reinforcement in the viaduct was found to be insufficient and also modifying beam depth was not possible because of the clearance to flyover below. It was required to go for an option to satisfy the as-built dowels to transfer the loads, and without altering the approved GADs.

Fig-1 Station aerial view showing connecting bridge

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Fig-2 Station entrance showing connecting bridge

Fig-3 Dowels proposed for bridge

Fig-3 As-built pier with couplers inside

Fig-4 Preliminary layout of the station

Fig-5 Layout with new station box

Solution offered A solution was worked out, by providing a halving joint in the beam and converting the fixed end bearing support to a simple bearing support. This considerably reduced the hogging moment at viaduct pier junction and made the section to qualify for the load transfer with existing dowels from viaduct. To take care of the seismic loads, steel alloy bars are also proposed along with seismic stopper. This proposal was accepted by the employer and is detailed for construction now.

Seismic analysis (Dynamic) has been also carried, with the actual boundary condition to establish the safe and satisfactory performance of the system during earthquake event.

This solution using problem solving skills has saved substantial construction time for contractor, to absorb the new change without affecting the freezed structural system of station box.

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Fig-6 Halving joint beam concept

Fig-7 Cross section of the beam connection with station box

Fig-8 Station area view from bottom-1

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Fig-9 Station area view from bottom-2