Design and Construction of Pre-Tensioned Sutlej Bridge in Punjab

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2. Construction aspect
(a) Provision of track-line for gantries as proper
embankment in the river bed;
(b) Provision of temporary Service Bridge across the river;
(c) Mechanisation of concreting for pretensioned beam.
(d) Use of large panel formwork for piers and beams;
(e) Bearing configuration, fixing of bearings and
stabilisation of beams after the erection till the casting
of diaphragms and deck slab;
Many of the above design and construction aspects
warrant in depth knowledge and meticulous micro planning to
suit the adoption of particular type of technology.
3. Proposal for codal guidelines for pretensioning
On the basis of designing and executing long span
pretensioned bridge spans, the authors propose the following:
(a) The minimum dimensions of the cross section shall
be
(i) Thickness of top flange: 100 mm
(ii) Thickness of bottom flange: 150 mm
(iii) Thickness of web: 150 mm
HEGGADE, MEHTA & PRAKASH ON
DESIGN AND CONSTRUCTION OF PRE-TENSIONED SUTLEJ BRIDGE IN PUNJAB
(b) The span to depth and depth to width ratios for
optimum beam cross section from lateral stability
considerations shall satisfy following Factor Of
Safeties
(i) FOS with out casting imperfections > 2
(ii) FOS with initial imperfections > 1.5
(iii) FOS with Actual angle of tilt > 1.1
(c) Provided adequate un-tensioned reinforcements are
designed for pre cast girder, the tension shall be
permitted at the top fibre of the girder which may be
restricted to 0.36(Fck) 0.5 .
(d) The losses due to seating and friction are not
applicable to pre tensioning. The elastic shortening
loss shall be considered for a condition that all strands
are stressed at the same time and pre stress transfer to
concrete is simultaneous. In case of pre tensioned
girders relaxation losses start as soon as pretensioning
is carried out, but the effect of which is transferred to
concrete at the time of pre stress transfer due to which
relaxation losses calculated as per IRC:18 shall be
divided by 2 for assessment of actually available pre
stressing force at transfer. It is not necessary to
consider 20 per cent additional time dependent losses
for pre-tensioned girders.
(e) Transmission length due to ‘Hoyer’s effect’ shall be
considered to be 30 times the diameter of tendon.
(f) Pre tensioning bench for long line casting shall be
designed for 20 per cent additional capacity to
overcome ‘Long Line Bench Effect’.
ACKNOWLEDGEMENTS
The authors would like to place on record the sincere thanks
to honourable Managing Director, Joint Managing Director,
Chief Engineer and his colleagues of Punjab Infrastructure
Development Board (PIDB) without whose cooperation,
guidance and encouragement, the successful completion of
this bridge would not have been possible. The authors would
also like to thank all the engineers at H.O. and site of Gammon
India Limited for their monumental efforts to construct such a
large bridge within a very short period.