EVALUATION OF A FORTY-YEAR OLD T. Y. LIN DESIGNED. ELLIPTICAL POST-TENSIONED CABLE-SUPPORTED ROOF
Randall W. Poston
Principal, WDP & Associates, Inc.
Austin, Texas, USA
E-mail: rposton@wdpa. com
A structural evaluation of the roof and post-tensioning system and an assessment of the current integrity of the roof of the Norick Arena located on the State Fair Grounds in Oklahoma City, Oklahoma was conducted.
The roof of the Norick Arena is an elliptical post-tensioned concrete roof system with a major axis of about 400 ft. and a minor axis of about 320 ft. The original design was performed by T. Y. Lin and Associates using three-dimensional load-balancing for full dead load and live load. Although elliptical in shape, the post-tensioning tendons form an inverted cable net in which precast concrete panels were suspended and subsequently made monolithic by casting thickened grout beams to form a structural roof that is a relatively thin, monolithic shell membrane.
The roof system is supported by a reinforced concrete compression ring, which in turn is supported by rectangular reinforced concrete columns. Stub tendons are cast into the ring beam and then coupled to the main suspended roof tendons. The post-tensioning is an unbonded, wire-based, button-headed system covered with mastic and placed in a waterproof paper, which essentially acts as a duct. The major axis tendon ducts are 2-1/4 in. in diameter, whereas the minor axis tendon ducts are 1-1/4 in. in diameter. Typical details of the post-tensioning system are shown in Figure 1.
Coated cable (cast in)
(wires coated with grease
and then wrapped with
Cold-formed – heads on – wires
Figure 1. Post-tensioning system details from literature.
M. Pandey et al. (eds), Advances in Engineering Structures, Mechanics & Construction, 343-354. © 2006 Springer. Printed in the Netherlands.
The arena was constructed in 1965 using a four-stage post-tensioning process with the monolithic concrete membrane stressed at the third stage. The post-tensioning was primarily staged to mitigate cracking in the compression ring. The fourth stage post-tensioning was applied to balance about 12 psf of live load (Lin and Burns, 1981). Figure 2 is an overall view of the arena from ground.
Figure 2. General view of arena exterior.
This paper will summarize the investigation of the post-tension roof of the Norick Arena roof. Results from field investigation procedures and from structural analyses are presented in the context of assessment of current integrity.