OPAC Consulting Engineers

Arroyo Cangrejillo Bridge

Andalgala, Catamarca, Argentina


Minera Alumbrera Limited
L.N. Alem 619 , 2 Piso 1001
Buenos Aires, Argentina
Leo Flannigon
Tel. 54-1-3345541


Construction completed 1998
Design completed 1997

Scope of work:

Design and Construction Supervision

Construction cost (incl. rock stabilization):

US $5 million

Services Performed:

  • Conceptual design and type selection
  • Final design
  • Wind section model test and dynamic analysis
  • Engineering support during construction


  • Innovative bridge design
  • Design for a difficult site
  • Complex construction staging

OPAC is the Prime Designer responsible for structural type selection, design documents, construction engineering, and field supervision for this 1200 ft (337m) span bridge. It is the longest single span in South America, and won the Bridge Design & Engineering 2002 International Foot Bridge Award, presented in Paris, in the long span technology category.

The construction program developed by OPAC consisted of casing mass concrete anchorages on the cliffs, securing these anchorages to the rock with post tensioned rock anchors, and then making the first aerial connection across the arroyo with a steel pilot cable. After installing and adjusting the final cables to their prescribed force and drape, the deck was erected using a crane and a movable platform suspended from the main cables. Framing components were delivered to the movable platform by a rail guided cart. Up to 9 segments were completed per day.

OPAC performed a complete stage-by-stage erection sequence analysis using SFRAME/S3D to support this construction method. It included the nonlinear cable geometry as segments were added, and provided initial installation geometry for the inclined cables so that the bridge would be completed at the final geometry required for safety and for proper functioning of the mining slurry pipeline. OPAC provided supervising engineers on site during the entire erection period.

The Arroyo Cangrejillo Bridge was featured on the cover of the February 1999 issue of Structural Engineering International, the Journal of the IABSE.