Gulf Construction Online - Complex job no sweat for UPC

Higher Colleges of Technology

Complex job no sweat for UPC

01 November 2003

In precasting terms, the new Higher College of Technology for Men is considered to be one of the largest and most complex projects in Dubai.

The development comprises 11 precast buildings interconnected by corridors, with a built-up area of 44,000 sq m. Originally designed by Dar Al-Handasah to be an in-situ construction, the client later decided to adopt the precast concrete option. The construction of these structures - including redesign and foundations - was completed in a total of nine months.

United Precast Concrete Dubai (UPC) supplied and installed all units as complete building systems, comprising hollowcore slabs, prestressed beams, reinforced beams, columns, internal walls, stairs, external 400 mm-thick insulated sandwich panels, parapets and a boundary wall.
The biggest challenge of the project was to provide the architectural finish required for the external facades and meet the structural specifications set for the seismic load requirements of the buildings, says Jens Fussing, design manager with UPC.

Architecture
All the architectural aspects including the geometric and aesthetic features of the project originally designed for in-situ construction were converted into precast elements - which in effect meant that all the outer surfaces are exposed or sandblasted.

'This meant that, especially in the corridors and other open areas, the panels and columns were to be surface-treated on all four sides, requiring meticulous attention to the production and handling of the precast components,' he says.

'Furthermore, to ensure the finished product matched the designs originally drawn up for the project, special moulds had to be built for the corner panels in the stairwells. These panels, which are up to 13 m high, were produced as a single unit, connected to the roof and the ground, to support the horizontal loads acting on the stairwells since the precast stair flights do not contribute to the lateral stability. Panels in the corridors are 600 mm thick while the 6 m by 6 m panels at main entrance are 800 mm thick.'

In general, the project required a lot of large panels where the 'normal' production limits have been extended, he adds.
'The colour difference between the white sandblasted surface and peach-coloured exposed surface was obtained in the treatment alone since the concrete mix was the same,' Fussing points out. 'Omani aggregate was used in the white concrete mix and exposed where required.'

Structural issues
UPC carried out the complete redesign of the precast concrete structures as well as the foundations.
He continues: 'Since the lateral loads were approximately five times larger than the normal, more structural components were required, such as moment frames, to ensure building stability. Due to the earthquake design criteria and the magnitude of the lateral forces, a layer of structural screed was added on all floors to provide the diaphragm action. Stability-wise, all building sections have either been manually or computer analysed three-dimensionally because of the vertical and horizontal irregularities of the buildings due to the location of the expansion joint, among other aspects.

'In the early design phase, shear walls were in-situ structures but through co-operation and a close teamwork with the consultant a more precast-friendly solution was developed, so that three-storeyed buildings are now purely precast structures.

'Experience in precast earthquake design gained from New Zealand and the US were available through PCI (Precast Concrete Institute), which also provided a lot of supporting design literature. In particular, moment stiff connections between columns and beams as well as wall-to-wall connection were adopted through the PCI research material.

Erection
'The 11 buildings stretch over an area of 320 by 220 m and, to reach target completion dates, a thorough planning of the erection sequence was essential. The planning of the access roads and turning spaces on the site was particularly critical. While the completed buildings had to be handed over to the subcontractors, one had to be careful not to block the access paths to other buildings. This dilemma was solved by simultaneously erecting the two largest buildings furthest apart from each other. Following their completion, the rest of the buildings in between them were erected.

'Because of the large sizes of some of the panels, especially at the main entrance, special low-bed trailers were fabricated to transport them - and their transportation was only possible as there were no bridges over the roads along their route to the site.
'The foundation works and erection of the precast concrete structures was successfully accomplished, thanks to the precise planning and daily coordination with the main contractor.'

Commenting on the precast concrete industry in the UAE and the challenges it faces, he says: 'The Higher College of Technology for Men marks a major step forward for precast building systems in the UAE. As precast building systems become more widely accepted among contractors and consultants, even higher quality and faster performance can be expected in the near future.

'One of our biggest challenges right now is to guide and ensure that the consultants in the preliminary design phase approaches the precast design in the proper manner - for example by defining all shaft areas and MEP routing -to speed up the entire completion period.

'In many ways, precast structures in the UAE are only at the threshold of what has been accomplished and developed around the world. By reaching a broader acceptance among designers and decision-makers here in the UAE, we believe that there are many future challenges to accomplish. For example, building systems for 10 to 15-storey towers, using floor diaphragm action in slabs without introducing structural screed, vertical post-tensioning of wall systems for the lateral stability, car parks and bridges.'

Finally, the behaviour and building physics of, for example, insulated panels goes hand in hand with the latest regulations from Dubai Municipality towards saving the environment, decreasing cooling costs and bringing better comfort inside buildings, he adds.