The Singapore Engineer Aug 2014: National University Hospital

August 2014 MCI (P) 157/01/2014

The Magazine Of The Institution Of Engineers, Singapore

www.ies.org.sg

SINGAPORE ENGINEERSINGAPORE ENGINEER SINGAPORE ENGINEERSINGAPORE ENGINEERCOVER STORY:

CIVIL & STRUCTURAL ENGINEERINGNUH Medical Centre

FEATURES: Construction Technology • Health & Safety Engineering • Project Application

THESINGAPORE ENGINEER

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14 THE SINGAPORE ENGINEER August 2014

NUH Medical Centre is the latest, and one of three buildings serving hospital patients within the NUH campus. It houses 190 consultation rooms, more than 200 treatment and procedure rooms, 10 day surgery operating theatres, as well as dedicated space for teaching and clinical trials.

It is also home to the National University Cancer Institute, Singapore (Yong Siew Yoon Wing) which provides one-stop, comprehensive care for both adult and pediatric oncology patients. The NUH Medical Centre is fully integrated with infrastructure for support services, such as clinical laboratories;

facilities for dietetics services and imaging; pharmacy; and a health resource centre, designed to provide patients with holistic care.The 19-storey NUH Medical Centre was completed in 2013 and started serving patients in July the same year.

Generating a total GFA of 72,000 m2, the NUH Medical Centre was a fast-track project completed in 28 months. The consultant team was required to carry out thorough project planning, design coordination and review of construction methodology, to ensure engineering safety during project implementation as well as timely completion.

NUH Medical Centre The project won a BCA Design and Engineering Safety Excellence Award (Merit) under the Institutional & Industrial Category, at BCA AWARDS 2014. By adopting innovative engineering solutions to overcome the site and design challenges, the structural works were completed and delivered on time, despite tight schedules, to enable commencement of other trades.

NUH Medical Centre. Image by Penta Ocean Construction Co Ltd.

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15August 2014 THE SINGAPORE ENGINEER

As Structural Designer, T.Y. Lin International Pte Ltd (TYLI) collaborated with the NUH Medical Centre’s consultant team, drawing on TYLI Singapore’s expertise in engineering design for healthcare structures and complex buildings, to develop the optimum structural solution. The process encompassed the consideration of both design and construction methodologies for the structure. Er. Ng Swee Tong oversaw the project delivery as the Project Manager and Qualifi ed Person.

PROJECT HIGHLIGHTSA steel truss system was selected as the optimum structural system for the facility. This incorporated six sets of double steel transfer trusses located in between Levels 12 and 13. The transfer truss system is a key feature of this project, as this concept allowed the expansion of the Gross Floor Area (GFA) to 72,000 m², by supporting eight additional fl oors over the MRT station box.

There are six elevated radiation bunkers located on Level 8. Each has a 2.5 m thick concrete enclosure.

The stringent requirement for radiation shielding demanded effective temperature control of the large volume concrete casting, so as to eliminate micro-cracking of the bunker structures. The adequacy of the formwork system to support the massive wet concrete during construction of these bunkers was a key design consideration in locating the bunkers on Level 8, for the operational effi ciency of the cancer centre.

SITE CHALLENGESThe NUH Medical Centre is located directly above Kent Ridge MRT Station, within the fi rst reserve of the railway protection zone and adjacent to the NUH Kent Ridge Wing in operation. This presented a number of challenges that the team had to overcome, for timely completion of the project.

• The undulating site terrain, with the existing ground levels varying from 127.5 m to 141.95 m demanded careful design consideration and planning.

• Mitigating the potential traffi c impacts throughout the construction phase was crucial. The road network in the vicinity of the hospital experiences heavy traffi c movement especially during peak hours.

Development commencement and completion

The main contract commenced on 16 December 2010.

T.O.P. was obtained on 26 April 2013.

Figure 3: Elevated radiation bunkers

LINAC bunkers formwork

The site plan

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• Rigorous control processes were considered at the design stage and implemented stringently during construction, to safeguard the structural integrity of Kent Ridge MRT Station and the tunnels.

DESIGN CHALLENGESThe Kent Ridge Station structure was designed with provision for a future building, with 24 column stumps on top of the central zone of the station, that would house seven levels of medical units. A difference in levels of 14 m at two sides of the spiral ramp and the close proximity of the MRT tunnels posed challenges in construction.

The primary considerations in the selection of the structural system for the healthcare facility included:

• Structural stiffness to meet the operational requirements of various types of sensitive medical equipment.

• Building robustness to resist accidental loads.

• Ease of construction.

Special consideration was given to achieving high buildability scores, despite the above stringent requirements.

CONSTRUCTION CHALLENGESHeavy transfer structures are typically long-span and massive, and they pose challenges for quality control during fabrication and installation. As the site was in close proximity to the hospital wards, mitigation of noise and vibration generated during construction were essential, to avoid any inconvenience or disruption to the hospital operations.

SITE SOLUTIONSIn anticipating various weathering grades of undulating rock formation (from completely weathered to highly weathered sedimentary rocks), extensive soil investigation was conducted to map out the contours of rocks with SPT values greater than 100, for the entire site.

Structural system. Images by Penta Ocean Construction Co Ltd.

MRT station structure

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A total of 14 bore holes were completed for the site. With the mapping of the rock contours, the pile design depths and socket lengths could be predicted more accurately.

The site investigation revealed some areas with possible existence of minor cavities in the limestone and these were demarcated. Cavity probing and provision for grouting were included in the piling contract, to detect the presence of fi ssures or cavities, prior to the installation of bored piles.

Substantial earthworks for site formation were necessary before commencement of the piling work and basement construction. The installation of foundation and contiguous bored piles began after the successful completion of two instrumented ultimate load tests.

A total of 270 foundation bored piles and 537 secant bored piles were installed. The bored piles range from 0.8 m to 2.2 m in diameter. The larger piles near the MRT station adit, with plunge-in steel columns, were designed to facilitate the top-down

method of basement construction. To socket the foundation piles into fresh rock stratum, in order to mobilise adequate skin friction and end-bearing, BG-35 and BG-40 boring machines were specifi ed in the contract.

Proper scheduling of construction works was done, with traffi c diversions deemed necessary, to ensure there was no disruption to the traffi c fl ow along Lower Kent Ridge Road.

To ensure no adverse effects on the structural integrity of the MRT station and tunnels, a number of measures were incorporated into the design and construction phase, including real-time monitoring within MRT tunnels. In addition to installing seven clusters of monitoring instruments, extensive ground settlement points were identifi ed and monitored on site by an independent specialist contractor during the construction.

In compliance with LTA’s requirements on railway protection during construction, the stress effects due to excavation and piling work carried out were assessed.

Boring machines

Stress changes

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Estimated movements. Images by Penta Ocean Construction Co Ltd.

• All movements within limits

• Justifi ed that 90% of bored piles within MRT reserves need not be de-bonded.

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The results indicated that the stresses induced were within the allowable limit of 15 kN/m², as per the LTA specifi cations. Real-time monitoring instruments were installed in the north- and south-bound tunnels. The MRT tunnels were found to be safe and the track alignment was not affected during piling and basement construction.

DESIGN SOLUTIONSSpecial consideration was given to the development of the structural systems to meet the robustness criteria for the building, in order to prevent disproportionate collapse under accidental loads.

The structural design options were determined by the performance requirements of the vital operational facilities of the hospital, including the delivery paths of medical equipment, the structural stiffness for stringent control of vibration of sensitive medical equipment and the need for radiation shielding.

The steel truss system was the optimum structural system in the design of the transfer structure. The design took consideration of effi ciency in fabrication and installation of the trusses, the QA/QC procedure and the reduction of the Concrete Usage Index (CUI), for sustainable construction.

The slab at Level 11 was checked for the construction loads of the temporary platform and construction equipment.

The transfer structure allowed a column-free space at Level 11 under the trusses for high fl exibility in layout confi guration.

CONSTRUCTION METHODOLOGYA difference in levels of 14 m at two sides of the spiral ramp and the close proximity of the MRT tunnels posed challenges in construction. The top-down construction method was adopted in the design, to eliminate extensive strutting or ground anchors. This provided better control of ground movement during excavation. The design provision with plunge-in steel columns was implemented by the piling contractor. The same method was also used for basement excavation next to the MRT adit structure.

Transfer structure. Images by Penta Ocean Construction Co Ltd.

Design of 11th storey slab Level 11 layout confi guration

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Top-down construction methodology

Spiral ramp

Top-down Construction

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The 2.5 m thick bunker slabs at Level 8 were cast in seven layers, using ice, water and cement replacements, for effective control of the peak and differential temperatures. Additional protective measures were taken, in case of adverse weather during the curing process.

CONCLUSIONThe adoption of an innovative approach and in-depth design with appropriate construction methodology, was essential to overcoming the site constraints and design challenges. The design considerations encompassed structural safety, buildability and sustainability.

An effi cient and cost-effective structural system and team effort during the construction stage, as well as a strong safety culture shared by all project team members, including the developer, contractor and consultants, contributed to the achievement of safety and excellence in engineering design and construction.

Construction work in progress

Casting sequence and thermal insulationLevel 8 radiation bunkers. Image by Penta Ocean Construction Co Ltd.

PROJECT CREDITSQualifi ed PersonEr. Ng Swee Tong

C&S ConsultantT.Y. Lin International Pte Ltd

BuilderPenta-Ocean Construction Co Ltd

DeveloperNational University Hospital (Singapore) Pte Ltd

Architectural ConsultantConsultants Incorporated Architects + Planners

CORRECTIONWith reference to the news article ‘Er. Dr Tan Guan receives Lifetime Achievement Award from ACES’, that appeared on Page 48 of the June 2014 Issue of ‘The Singapore Engineer’, T.Y. Lin International Pte Ltd wishes to clarify that whilst Er. Dr Tan was the Project Director for the project, Er. Ng Swee Tong was the QP and Project Manager.

All images by T.Y.Lin International Pte Ltd, unless otherwise stated.

Healthcare

The Singapore Engineer Aug 2014: National University Hospital