Adnoc HQ Tower - Abu Dhabi, United Arab Emirates
The project is located at the Abu Dhabi Corniche and consists of a 75-storey office tower and two levels of basements. The overall building height is 343 m with a gross office area of 160.000 m2 and a helipad on the roof.
BESIX Engineering - Dubai presented an alternative design which resulted in significant savings. Upon award of the project, the redesign had to proceed at a fast rate to enable the commencement of the construction activities within three months. With this difficult design, the choice of software became all the more important and BIM was applied for an effective verification of the alternative design.
The design is extremely complex due to the fact that the building is highly asymmetrical. The centre of mass is offset by 3 m due to the fact that the south core walls are only counterbalanced by six slender composite columns. Elastic shortening and long term creep causes the building to twist around its vertical axis and to lean forward towards the column line.
The original design relied heavily on structural steel inserts in the walls to provide adequate stiffness. In the alternative design all inserts were removed and additional stiffness was achieved by specifying high strength concrete with enhanced Young’s modulus (E = 48GPa for grade 65/80 concrete instead of 40GPa as per EC). The original columns were square composite with internal steel made-up sections and called for very elaborate fabrication and erection procedures. The BESIX design comprises 1.5 m diameter tubes (tmax = 90 mm) filled with high strength concrete and 20% of original steel. PT beam/steel column connections are fully fixed for increased stiffness. The original design was as per ACI and IBC codes and the modelling was carried out using ETABS. BESIX applied the Eurocode suite and 3D modelling with Scia Engineer and Revit Structures.
The site is generally characterized by 8 m of sandy material overlaid by bedrock. The foundation system consists of a 3.5 m raft supported on a total of 364 bored piles 20 m long and diameter 1.0 m, 1.2 m and 1.5 m.
Seismic and wind loads
A site specific study indicated that the project is located in an area of low seismicity, equivalent to Zone 1 UBC 1997 (Z = 0.075). However, to comply with Abu Dhabi Municipality regulations, seismic zone 2a was adopted (Z = 0.15).
The wind loading was based on tunnel testing, carried out by BMT. The reference wind speed for 50 year return was 38 m/s (thunderstorm).
Structural 3D Modelling - BIM
From the very beginning of the tender BESIX opted to use BIM. As a first approach a Revit model was prepared and was then imported directly into Scia Engineer. The model interface works well both ways between the two software and any subsequent changes done in Scia Engineer were exported directly into Revit:
Revit - Detailed 3D model of all structural elements used in quantity take-off for concrete, reinforcement, and structural steel and for preparation of 2D drawings exported to Acad.
Scia Engineer - 3D model was imported from Revit and loads were introduced including wind and seismic. Scia Engineer was used to analyse the structural behaviour both in terms of global effects (sway and inter-storey drift) and detailed member design.
The effective interface between Scia Engineer - Revit - Acad allowed BESIX to optimize both the geometry and the final quantities of the building to achieve an overall 20% saving. It also allowed a more comfortable construction schedule through simplified detailing. At the detailed design stage the same interface allows BESIX to maximize the production speed of drawings by using the 3D environment for the coordination between 3D models and 2D drawings.
The construction of the ADNOC HQ Tower is currently into its ninth month. The first concrete for the raft was poured in September 2010 and the core walls are at Level 3 above ground level. The erection of the helipad roof is foreseen for May 2012. Once the building is completed it is earmarked to be one of the major landmarks along Abu Dhabi’s Corniche.