An innovative structural design in glued laminated timber for 115m

An Innovative Structural Design in Glued Laminated Timber for
115m Span Lisbon, Portugal Multi-Use Arena
Robert C. Sinn1
ABSTRACT
At up to 115 metres, the roof structure for the main hall of the Lisbon Multi-Use Arena represents the longest one-way
span of glued laminated timber in the world. There are two separate roof structures framed in exposed glued laminated
timber for the project: the main hall which is 200m long by 120m wide and is oval shaped in plan, and the auxiliary hall
which is 100m long by 50m wide. While glulam structures have been nearly non-existent in Portugal up to the present
due to the lack of suitable timber materials, glued laminated timber was chosen for the roof structures as the material best
suited to enhance the Lisbon 1998 world exposition environmental theme as well as being cost-effective in comparison to
alternative structural steel schemes. The structural design of the roof is also noteworthy from a structural engineering
standpoint as being one of the longest glued laminated timber roof spans in an active seismic zone. (See Figure 1.)
Figure 1. Model Section Through Main Hall
AESTHETIC AND PROGRAMMATIC CONSIDERATIONS
The design brief for the Lisbon arena competition called for a facility which would be a principal element of the 1998
World Expo as well as providing easy adaptation to accommodate a wide variety of indoor sporting, recreational, and
cultural events for the City of Lisbon in the longer term. The stadium would be located on the Expo’s 50 hectare
waterfront site along the Tagus river and would have a fixed seating capacity of 12,500 and a maximum capacity of
17,500. Portugal’s history is closely linked to the sea. (See Figure 2.) The building’s appearance and materials would
naturally complement the Expo’s environmentally friendly theme, “The Ocean: A Heritage for the Future.” The design
includes the capability to operate using natural ventilation and natural light for most of the daytime events. To promote a
long term commercial viability, the playing field meets Olympic standards with additional provision for adjacent warmup facilities in the auxiliary hall.
1
Associate Partner, Skidmore, Owings & Merrill LLP, 224 S. Michigan Ave., Suite 1000, Chicago, IL, USA 60604
Figure 2. Arena Site Along Tagus River.
The shape of the arena draws inspiration from the lines of the 16th century carabelas, the ocean-going sailing ships of
Vasgo da Gama’s day. (See Figure 3.) The same theme is further developed on the interior in the ribbed structure of the
glued laminated timber roof structure, manufactured from softwood, an environmentally conscious building material
produced from a sustainable source. More recent Portuguese history is reflected in the curvature of the front cantilevered
elevation which is based on the nose of a PANAM Clipper, the first transatlantic air-craft that disembarked passengers
near what is now the Expo site during the thirties and forties. The design is thus an “…example of the ongoing evolution
of large-span structures from regular geometric forms to more complex and intuitively shaped designs.” (Cohn, 1999)
Figure 3. Arena External Form
The choice of glulam for the roof structure was consistent with the architectural vision of the interior as suggesting a
ship’s hull. The primary engineering challenge was to structure the roof profile without the benefit of a pure parabolic or
circular arch meeting the ground. The architectural premise was to create a unique profile without exterior abutments or
piers while at the same time maintaining a tall entrance space ringing the grandstands on the interior. (See Figure 4.) The
portal arch form, while not as structurally efficient as a more geometrically pure arch or dome, served to create the
interior and exterior architectural vision with a reasonable amount of material expended.
Figure 4. Entrance Space Between Grandstand and Exterior
STRUCTURAL SYSTEM COMPONENTS
The main exhibition hall roof structure is framed parallel to the short direction by sixteen glued laminated timber twohinged, arched, portal truss frames spaced 9.0 metres on center with varying spans based on the oval plan up to a
maximum of 115 metres between bearings. To follow the unusual shape of the plan and roof surface, each portal truss is
geometrically set out with top and bottom chords along a unique circular arc meeting the haunch assembly which is in
turn configured based on an identical geometry for each truss line. Typical portal truss dimensions are indicated in Figure
5. The central trussed section of each portal frame is completed by glued laminated timber diagonal members in a Warren
truss configuration which are connected to the chords through a proprietary system developed by the specialty French
contractors Weisrock, who were responsible for the fabrication, erection, and final design calculations for the roof
structures. The trussed haunch assembly for the portals, which creates the transition from the circular central span down
to the support bearings, was conceived as a composite of structural steel and glulam members using the most favorable
characteristics of each material in their individual roles. The main hall roof structure is completed by longitudinal glulam
purlins, diagonal glulam braces and a plywood and subframe diaphragm in the roof surface to distribute lateral wind and
seismic loads.
Early in the design process, an auxiliary hall with a capacity of 500 to 2000 users was added on the river side of the main
hall. Employed as a warm-up area for the athletes and for independent events (Cohn, 1999). The auxiliary hall roof is
also framed in glued laminated timber with nine 3.2 metre deep bowstring trusses spanning the 42 metres between
supports. Transverse bridging members spanning between the primary bowstring trusses serve to stabilize the truss
bottom chord under wind suction as well as reducing the span of the roof purlins. These braces take on a fan arrangement
along the span of the roof trusses lending visual interest to the structural composition. (See Figure 6.)
Figure 5. Arched Portal Truss Elevation
Figure 6. Auxiliary Hall Structure
SEISMIC DESIGN CONSIDERATIONS
Lisbon is in an area of moderate seismic activity. One of the largest earthquakes in continental Europe occurred in the
year 1755; nearly leveling Lisbon and taking some 60,000 lives. From an earthquake engineering standpoint, the roof
structure was completely analyzed in three dimensions through a modal response spectrum analysis in both the vertical
and horizontal directions. The seismic design is based upon the structure remaining essentially elastic in a seismic event
due to the lack of demonstrable ductility in the glulam construction.
The structural design of the glulaminated timber roof structures required an extensive utilization of the computer both in
geometrically setting out the form of the framework as well as analytically verifying the design with respect to the full
range of imposed loadings. The timber design is based on Eurocode 5. Glulam grades range from GL28 to GL36 for the
main hall truss chords. Fire engineering of the timber frame based on the required one-hour rating involved analyzing the
structure with reduced member cross-sections determined through the timber char rate formulation included in the EC5
code. Imposed wind suctions up to 1.7kN/m2 on areas of the roof surface typically govern the member sizes of the main
hall roof structure over seismic considerations. Suspended loads for concert and sporting events are accommodated over
certain predetermined areas of the roof footprint.
CONCLUSION
French glued laminated timber subcontractor Weisrock employed approximately 5000 cubic metres of timber for the
project. The trusses for the main hall roof are formed from Swedish spruce material. The time of construction was
approximately one year for the timber frame. (Perrin, 1998) The Lisbon Multi-use Arena thus marks a unique
application of glued laminated timber in a stadium application without a pure parabolic or circular arch form. The
structural engineering concept for the structure was a direct result of a dialogue between architects and engineers to form
a significant long-span framework which could respond to a particular set of architectural requirements. It is hoped that
the Arena will represent a lasting contribution for the people of Lisbon and for glued laminated timber around the world.
Figure 7. Arena Interior and Glued Laminated Timber Roof Trusses
CREDITS
Clients
Design Architect
Structural Engineer
Associate Architect
Associate Structural Engineer
Glued Laminated Timber Detailing / Fabrication / Erection
Parque Expo 98 SA, Atlantico – Pavilhao Multiusos
Skidmore, Owings & Merrill Inc., London
Skidmore, Owings & Merrill Inc., London
Regino Cruz – Architects and Consultants LDA, Lisbon
J. L. Cancio Martins, Lisbon
Weisrock, France
REFERENCES
Cohn, David, August, 1999. “Atlantico Pavilion Lisbon, Portugal”. Architectural Record. p.114-119.
Perrin, J.P., D. Quost, J.F. Bocquer, P. Racher, J.P. Biger, “Lisbon EXPO 98 Pavilhao Multiusos”, Proceedings, World
Conference on Timber Engineering, 1998.