Nemetschek Engineering User Contest 2009 • Category 2: CAE Housing & Buildings 33 2 The Tornado, Qipco Office Tower • Perimeter Diagrid – Diagonal Steel columns and peripheral steel beams • Floor slabs – Composite radial steel beams + 180 mm thick concrete slab on metal deck. The building fundamental period was T1 = 4.2 sec Design Software The structural design of the basements and tower was by Meinhardt (Singapore) using ETABS. The BESIX Engineering Department in Dubai was appointed to carry out a third party independent check. BESIX used ESA-Prima Win for full 3D modelling. CICO, the client’s engineer and architect, carried out a separate check by modelling the building in STAAD PRO. Foundations The geology of the Qatar peninsula consists mainly of extensive carbonate sediments overlying basement rocks up to 10 km in thickness. The tower is founded on Simsima Limestone. The foundation system consists of a 2.7 m central raft and perimeter pile caps interconnected by a series of radial ground beams 2500 W x 750 H. The raft itself is supported on bored RC piles as follows: • 1200 mm DIA – 14 m long – 129 Nos • 900 mm DIA – 8 m long – 20 Nos Seismic loads Seismic design was based on Uniform Building Code 1997 and seismic Zone 1 (Z = 0.075). Earthquake base shear was calculated as 8555 kN, less than 1% of the tower gravity loads. Wind loads Theoretical wind loads were calculated using CP3 and with Vb = 41.67 m and were verified by wind tunnel testing. The loads calculated from the wind tunnel results were 5% lower than the theoretical values: • Wind Base Shear = 14,846 kN • Base Bending Moment = 1,628,212 kN.m Structural 3D Modelling BESIX developed two separate 3D models of the tower for the purposes of checking the design. Model A – Core walls modeled as FE plates and beams and columns using member properties. Slabs were introduced as dead weight to the beams. Model B – Same as model A but slabs were modeled as FE plates. Floor beams where given vertical eccentricity to replicate the actual situation on site The geometry of the diagrid was exported from the architectural AutoCAD files in ESA in DXF format. This saved considerable time in creating the non-linear geometry of the external diagrid system. The load distribution between central core and diagrid is 75% to 25% respectively. Total gravity load is 999,000 kN. Designing with ESA-Prima Win Model A was used to check and verify the overall stability of the building and to confirm its natural frequency. The time required to solve the model was generally less than 10 min and this afforded the designer the possibility to test different layout arrangements in order to obtain the most optimal in terms of economy. Model B was used to investigate the effects of radial in-plane forces transferred from the diagrid nodes to the core walls through the slab plates. The running time of the full dynamic model was approximately 2 hrs and was therefore used in final detailed design. The following points are considered to represent the main advantages afforded by ESA-Prima Win to BESIX designers: 1. Relatively short time required to run the basic models when compared to other commonly used software in the Gulf. 2. Use of the dynamic module for obtaining the lowest significant Eigen frequencies of the structure 3. Ability to run quickly and effectively sensitivity studies including the influence of elastic shortening of the central core under different values of Young’s Modulus, in order to determine the effect of load transfer between core walls and diagrid columns 4. Use of concrete design module to verify RC quantities 5. Use of structural steel module to verify the diagrid columns and beams Conclusion The Tornado has been successfully completed and has become a major landmark in the Doha Corniche. With its unique shape and character it has changed the City’s skyline ones and for all.
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