Hollow-core slab solutions for fast-track, sustainable developments

by Darren
Hollow core slab solutions

Hollow-core concrete slabs, structural steel frames and raft foundations were used for the fast-track construction of a new office development in Boksburg.


Local property developer, Krisp Properties, is busy building a new office development at Clearwater Estate in Boksburg. Structural steel frames, raft foundations and hollow-core concrete slabs are being used for the fast-track construction of this development. The developers already had a lease agreement with tenants before the first sod had been turned, which meant the project team only had seven months to erect the building.

The office development will be built in two phases, the first phase compromising of a gross lettable area (GLA) of ±3 100m² and the second phase 3 700m² GLA.

The first phase of the development was completed in November 2013 and comprises two double-storey buildings, each measuring 1 550m² (GLA), which are linked by a central entrance atrium.

The architects chose to embrace new energy-efficient legislation and incorporated a variety of sustainable design methods during the planning stages of the project.

“The design uses overhangs above all the windows and doors to minimise the impact of the sun and to reduce the escape of heat from the buildings,” said Francois Marais of Francois Marais Architects.

Jordan Mann, executive director of Krisp Properties, said the Echo Prestress hollow-core slabs that were used were specified by PDS Civil and Structural Engineers. These slabs were chosen for a number of reasons.

“We deployed hollow-core slabs for the first floors as well as the roofs, and this assisted us in reducing the construction time by several weeks. Hollow-core slabs were used for the roofing, which would allow the necessary support for the installation of photovoltaic power generation units in the future. Moreover, the roofs have created ideal catchment areas for harvesting rainwater, which will be stored in subterranean tanks,” said Mann.

A total of ±3 100m² were used for phase one and the second phase will make use of ±3 750m² of Echo slabs. Slabs of between 5-7m were installed on the roof, both the first floor and roof panels were topped with steel reinforced screeds, and a bitumen coating was used to waterproof the roofs. H-shaped universal steel columns of 9m were also supplied by Echo in order to provide slab support for the internal cantilevering.

Spiros Sdralis of PDS Civil and Structural Engineers said they appreciated Echo’s involvement in the project.

“We provided Echo with a set of drawings and they then prepared a layout which took all the servicing requirements into account. Echo’s engineer, Daniel Petrov, was involved from the outset and he was always on site when we needed him, particularly in solving specific on-site challenges,” said Sdralis.

Some of the slabs had to be modified so that the upper section of steel skeleton could be anchored to the first floor on a solid platform. This meant that the hollow-core end sections of some slabs had to be packed with concrete to provide the solid base. The structural engineers were able to drill out holes for the bolt anchor sleeves in the same way they had done on the ground floor, thanks to Echo being able to fill in the voids with concrete.

“The builders were able to begin the assembly of the upper level steel frame as soon as the slabs had been installed and this was the prime advantage of using hollow-core slabs. If in-situ flooring had been used, it would have delayed the completion dates on both buildings by several weeks,” concluded Sdralis.

Echo Prestress
Website: www.echo.co.za

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