RESEARCH ARTICLES CURRENT SCIENCE, VOL. 106, NO. 9, 10 MAY 2014 1280 *For correspondence. (e-mail: chalumuri.ravisekhar@gmail.com) On-site visualization monitoring for long span bridge on Delhi Metro Project Chitoshi Izumi 1 , Shinichi Akutagawa 2 , Ch. Ravi Sekhar 3, *, Rajan Kataria 4 , Reiko Abe 1 and Hirofumi Haga 5 1 Oriental Consultant Ltd, Tokyo, Japan 2 Department of Civil Engineering, Kobe University, Japan 3 Transportation Planning Division, CSIR-Central Road Research Institute, New Delhi 110 025, India 4 Design and Planning Department, Delhi Metro Rail Corporation Ltd, New Delhi 110 003, India 5 AKEBONO Brake Industry, Tokyo, Japan A new monitoring scheme, based on the concept of on- site visualization (OSV), was successfully applied for monitoring safety conditions during construction of a long span cantilever bridge in Delhi Metro Phase-II project in 2010. The bridge construction with chal- lenging features included a 100 m long span over the Northern Railways tracks passing below, the balanced cantilever construction methodology with a see-saw condition of the pin-connected girder during segment casting processes and a horizontal curvature of the girder with 300 m radius. The light-emitting sensors with dual functions, namely sensing and simultaneous visual output of measured results, were employed in this project and played crucial roles to capture unique behaviours of the bridge under construction and to ensure safety throughout the project. Keywords: Balanced cantilever construction, laser pointer, long span bridge, on-site visualization. AN accident during construction of long span bridges would often lead to catastrophic collapse and loss of properties and human lives. For example, in the accident of Can Tho Bridge (cable stay bridge with 550 m centre span), 100 km south of Ho Chi Minh City, Vietnam in 2007, the collapse of supporting temporary steel trestles and supporting steel beam together with fresh concrete girder resulted in a massive fatal accident with 2 years delay and huge additional cost 1 . Long span bridges, including suspension bridge, cable stayed bridge and box girder bridge become rigid and stable after completion of construction. However, these long bridges could be instable during construction stages (Figure 1) 2 . Any unbalanced loading caused by dead load, live load, structure deformation and ground settlement can lead to catastrophic failure of the total structure. In Vietnam, the requirement of loading test for bridge struc- ture and supporting structures is specified in Industrial Standard 3 and its application became more strict after the Can Tho Bridge accident. After the Great Hanshin Awaji Earthquake in 1995, Japanese safety standard for seismic design of bridges was dramatically improved in order to maintain lateral re- sistance of structure under large earthquake during opera- tion stage as well as construction stage 4 . In India, after encountering bridge accidents at construction stage as described below, Delhi Metro Rail Corporation Ltd (DMRC) improved the design procedure for elevated sec- tion from the Contractor’s design to DMRC’s direct design and appointed international consultant. In Singa- pore, after the Nicoll Highway Collapse during metro construction, the Land Transport Authority (LTA) strictly applied the ‘one strut failure’ rule into their temporary design, namely providing some redundancy into the de- sign such that failure of any one support would not lead to overloading and progressive failure of adjacent mem- bers or catastrophic failure during construction 5 . Long span bridge on Delhi Metro project Delhi Metro Phase II, urban mass rapid transit project implemented by DMRC, covering 120 km stretch from central Delhi to suburb regions funded by Japan Interna- tional Cooperation Agency (JICA) was completed in 2010 (ref. 6), just before the Commonwealth Games in Figure 1. Bridge collapse during construction stage 2 .