DEFLECTION PRESTRESSING BEATS M11 PROBLEM

This brief article is concerned with a novel prestressing system used to build beams for six viaducts on the M11 motorway at Redbridge, London. Problems with the project were lack of a suitably sized existing yard and constrained access. The beams were 29M long, weighed 27t each, and 417 were required. The innovation involved stressing along the tendons' deflected path rather than stressing before deflection. After lodging the method with the patents office the contractors (W. & C. French) built a 100 M long concrete bed shaped as an inverted beam to carry four lines of three beams. Three were stressed simultaneously, the seven pairs of strands in each being threaded at 50 mm vertical centres through the rings of a high-tensile steel ladder at each of the deflection points. 300mm diameter pulleys prevented kinking. A vertical macalloy bar was used to anchor tendons to the concrete bed. A petrol driven J38 strand saver jack was used for the stressing when the concrete was poured into the moulds, vibrated and steam-cured. Stress transfer took place after about 3 days (40n/mm2 strength). It was necessary to release the longitudinal stress first to avoid cracking. A production rate of nine beams a week was achieved. /TRRL/

Media Info

  • Features: Figures; Photos;
  • Pagination: p. 28
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00149032
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Report/Paper Numbers: Analytic
  • Files: ITRD, TRIS
  • Created Date: Jun 17 1977 12:00AM