Figure 1: Changi Rise Development
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This $110 million condominium project consists of eleven 9-storey to 10-storey tower blocks linked by a common environmental deck with full recreational facilities (Figure 1). The deck also serves as the roof for an underground common car parking area. The contract was administered under and a design and build environment, and the structural work was completed within the first 16 months of the 28-month contract.
Critical Activities
Together with the client, SsangYong Engineering & Construction Ltd, we determined that a critical area was the construction time frame of the typical storey, including the floor, internal slab/ columns and the external facade with protruding bay windows at certain areas within a unit. The time cycle for each storey was eight days, including erection of all vertical structural members.
Structural Solution
The main feature of this project is the flat plate system our team adopted. A 175-mm (7-inch) -thick slab rested directly on the columns without any drop panels (Figure 2). This system offered higher ceilings and greater flexibility with the
Figure 2: Construction stage showing
the slab on columns . |
architectural layout in addition to great savings in formwork erection time and cost. Simple BRC1 mesh reinforcements facilitated very simple and fast installation. These features, combined with off-site precast bay window and facade units serving as edge beams that give lateral stability, resulted in substantial cost and time saving and the completion of the project on schedule.2
The wind loading resulting from the average 32m/s gust wind speed is resisted by the relatively stiff core wall system alone. This method has been proven to be effective for buildings less than 20 storeys high in Singapore.
The key features that contributed to the successful completion of this project were:
- The flat-plate structural system
- Proper planning on the delivery schedule of the pre-cast components
- Site formulation on crane utilization
- Proper sequencing of work.
The Changi Rise Development received the Singapore Buildable Design Award in 2005.
THE QUINTET DEVELOPMENT
Figure 3:
Structural design details
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The Quintet, a condominium project with 459 residential units, comprises six blocks of 19-storey to 22-storey buildings with two basements, a common environmental deck and full recreational facilities. As with the Changi project described above, this project was completed under a design and build environment with a 28-month completion period, of which only 16 months were allowed for the civil and structural work.
Innovations
The structural feature of interest in this project is the use of volumetric pre-cast structural elements. Unlike conventional pre-cast, which is usually limited to the non-structural facade and is done on a floor-to-floor basis, this system is a pre-cast two-storey-in-one go (Figure 3) and is inclusive of perimeter beams and part of the structural columns. These column parts are “stitched” to the remaining cast-in-situ columns by means of shear connection and proper interfacing details. This approach saves half of the hoisting and installation time as compared with the floor-by-floor system.
Figure 4: Elastic Analysis of Building
System (ETAB) wind lateral analysis
model:sher wall system
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Structural System
The structural system for the super-structure consists of a reinforced concrete frame with shear walls (Figure 4). Thus, it is a dual structural system of interacting reinforced concrete frames and walls to resist the lateral loads. The floor system is essentially a 175-mm (7-inch) -thick flat plate. There are no internal visible beams protruding in any units.
Conventional pre-cast driven piles were used for the foundation. At the time of writing, the basement construction had been completed and the first batch of the pre-cast units had been delivered to the site.
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