Toulouse-Blagnac Airport: glass stiffeners more than 16 meters high

Unlike the façades of the boarding satellite made with breathing glass that integrates decorative solar filters made of crossed wood strips, the two large glazed walls in the entrance hall are designed to appear open to their environment.  The visual impact of the structural frames is restricted due to the use of glass stiffeners, in a spirit similar to what was predominant for the design of façades for the large passageway serving the satellite, in which all structural elements were shifted to the outside of the building.  The contractor (Eiffel) constructed these stiffeners that are unusual due to their large dimensions.  These stiffeners were suspended over a height of more than 16 meters from large 35-meter span trusses, to brace glass walls more than 30 meters long!

Jean-Marc Babet, engineer at Eiffel's special works division, explains that the trusses are independent of the rest of the roof in order to eliminate risks related to relative movements of the structure:  "The trusses do not resist any roof load.  They are fully dedicated to resisting façade loads, which has the advantage of eliminating deformation problems induced by parasite loads that depend on weather problems.  They resist only the self weight and wind loads of glass walls through turnbuckles from which the frame uprights are suspended."

Consistent assemblies

Apart from structural adaptations or adaptations to placement and manufacturing tolerances (the turnbuckles are used to adjust upright attachment lengths for this purpose), the biggest difficulty is in the construction of uniform facades.  How can these facades act "monolithically" as if they were composed of a single block?  How can the steel making up the glazing frame grid, and the HST hardened glass of the stiffeners, be made to function coherently?  " For example, a slight deformation of the structures under the effect of wind should not cause any relative slip between the stiffeners and the frame in the plane of the facade ", says Jean-Marc Babet.  Furthermore, the question of cohesion between the different construction components also arises for the 16 m high bracing because the length of manufactured glass elements is limited, making it necessary to place three glass parts end to end connected to each other by stainless steel splices.  How can these separate parts be assembled to create a uniform whole within which forces can be reliably transferred?

Bending tests on stiffeners

Jean-Louis Galéa, senior ATEx engineer for CSTB, reports that an intercalation was inserted between the splices and the glass to assemble the stiffeners.  An identical 2 mm thick intercalation characterised by an excellent coefficient of friction, was also placed between the uprights of the frame and these reconstituted stiffeners.   "The intercalations were sandwiched, and clamped by prestressed fasteners to compress them sufficiently to form an efficient bond between the glass and the steel."  Two tests validated the assembly systems before Eiffel completed the construction on site.  The first demonstrated that the 19 mm thick glass broke under a tension force before any slip occurred between the glass and the splices.  The second applied bending forces over the entire height of a stiffener:  jacks applied on a full scale model of a stiffener placed horizontally were used to simulate wind forces under extremely bad weather conditions.  In both cases, transmission of forces by bond of the intercalation assured the required "monolithic" function.  Physical coherence was achieved, while the apparent uniformity of the large transparent walls of the entrance hall was maintained.

Technical data sheet

  • Client:  TOULOUSE Airport- Project Manager:  CARDETE & HUET Group, architects (Agent);  Midi Pyrénées OTCE (Engineering Office)
  • Façades Engineering Office:  Terrell Maurette associés
  • Design and construction of 1172 m2 of facades with glass stiffeners:  EIFFEL
  • Inspection office:  VERITAS
  • Planned delivery:  commissioning in September 2009