Athens 2004 Olympic Stadium Roof Restyling
The Athens 2004 Olympic Stadium roof is an impressive cable-stayed steel roof structure designed by the renowned architect Santiago Calatrava and constructed by Cimolai Spa of Italy. The erection procedure resulted in a complex construction sequence where two separate halves were built and then transported to their final position above the Olympic Stadium. Given the significant slenderness of the two halves of the construction, important stability issues needed to be addressed during the erection phase of the roof. This project was a unique example of a race against time and harmonious collaboration between engineers, contractors and subcontractors.
The Crucial Part Played by Numerical Simulation in the Erection Phase
The stadium roof which was constructed as two sub structures has a length of 300 meters and varying in width from 60 to 100 meters. Each sub structure is a lens-shaped single span beam having tubular members as chords and cables connecting them in the vertical plane. Simulation played an important role in the structural verification process. This entailed the simulation of the main structural details of the cable stayed roof for ultimate, service and erection conditions. Our simulations allowed on site engineers to:
- experiment with onsite operation sequences in real time before actually carrying out the operations. This ensured that any last minute changes did not cause any costly structural problems which would have made it impossible to complete the project on time
- decide the sequence used to tighten the stays and bring the tension values as close to the theoretical values as possible in the shortest number of operations
As a result the design team was able to follow the complex erection procedure, step by step before the actual erection took place, to evaluate critical details and to appropriately implement cable tensioning sequences.
The Strand7 ad-hoc Customization
EnginSoft developed some automatic iterative procedures within Strand7 to provide a proper tensioning sequence such that cable axial forces could be adjusted with the minimum possible effort to match theoretical distributions. More complex versions were also implemented to match both the cable force distribution and target displacements on a number of points by increasing the multiplier of selected load cases.
A stress-prediction customized routine was also developed in order to:
- extract parallel and normal stresses for welds with complex geometries, such as the weld connecting arch and torsion tubes
- evaluate envelope stress values from all the ULS or SLS combinations
- run code checks to allow minimum weld throat estimates to be obtained
For sub-model analysis we wrote an automated procedure to extract the forces from the global model for all relevant load classed and applied to the detail such as the plate or brick element.For our code check procedures we use a custom written code check procedure for Strength and Stability of Steel Members that supports the following international standards: DIN18800, BS5950, EC3, NTC2008, ANSI/AISC 360-05, ISO19902 and Russian SNiP.