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This proposal is to develop an outline design for a proposed three storeys office development, connected to the existing building by an atrium with a basement car park. The client is seeking a value world class iconic architecture development of high quality and adventurous construction, and are awarded of the concept of while life costing. Environment concerns such as minimizing CO2 emissions from the building in both during construction and daily operation are taken into consideration. The main aim in this respect is to effectively minimize waste intake from all forms ranging from materials, time and energy in both construction and used.
This proposal focuses on a set of seven topics to be address with each providing recommendation and solutions, accompanied by detailed drawings and blueprint to establish the building design. Seven elements for the following areas:
General design for access and escape
Structural Frame proposals
Basement and Foundation design
Cladding and roofing proposals
2. PROJECT DESCRIPTION
Three storeys office development with basement car park, connected to existing Georgian building by an atrium at Edinburgh, Scotland.
Redevelopment of existing stone building at city centre location with an extension of new office accommodation, connected to the existing building by a cleared- cladded atrium and a basement car park below the new building.
The development is to seek high quality, adventurous construction and world class architecture. Environment concern such as minimize CO² emissions from the building construction and operation is addressed. Minimizing of waste in forms of materials and time to energy in both construction and operation would be the key aim in this respect.
2.3 Site design and Information
Located on a main road in a city centre occupied by a four storey Georgian building, with a site slopes flow from rear of existing building extend towards the rear access road. The site present no sign of unusual ground problems and partial excavation is expected for the basement car park which will formed as a partial basement storey within the building.
The main public entrance to the building will be located in the atrium between the south elevation of the existing building and the new extension. A three storeys new office accommodation linked to the existing building by an atrium to be erected, and design for flexible and adaptable for sub-division for separate tenants.
The mixture of materials for cladding system should only require minimum amount of maintenance and contribute significantly towards energy efficient to achieve sustainable building. Suitable access for personnel with mobility difficulties are provided throughout the building facilities that meet with building regulation and standards. Necessary emergency escape routes are also provided in the facilities in the event of fire emergency.
Key facilities provided within the extension are provided as follow:
Flexible office accommodation to permit numbers of different tenants over three storeys
Café area with associated seating and preparation/ sales areas
Facility Managers office
Staff kitchens with small kitchen and seating area in each office storey
Central Male and female staff changing area locker room equipped with WC facility
Male and female wc provision on each office storey
3 cleaners rooms with sinks and storage provision (one on each level)
Lifts/ stairs and access ramps as necessary
3. ACCESS AND ESCAPE
3.1 Building Accessibility
3.1.1 Key Master plan to Building Accessibility in Singapore
Accessibility in Singapore built environment has subsequently improved over the years, in expect of increasing numbers of people with mobility difficulties; and in response to the committee recommendation on handling ageing population issue. To prepare for those issues, the government is working closely with Building Construction Authority Singapore, towards successful key improvement in the built environment.
Three strategic thrust of the Master Plan are identified. Firstly is to improve the design of new building infrastructure so as to ensure seamlessly connection of accessible for users on wheelchair, other disabilities and elderly who suffer mobility difficulties in the build environment. The mandatory requirement in the Accessibility Code was introduced in the year 1990, in achieving barrier-free accessibility in both new buildings and existing building which undergoing major addition and alteration works. The Code was reviewed and enhanced to incorporate the principles of Universal Design (UD) which taken into consideration of physical, social and psychological needs of all personnel and user. BCA Singapore had worked closely with key stakeholders namely developers, architectures and relevant government agencies in considering the inclusion of those Universal Design features in the Accessibility Code.
The second strategic thrust focused on future challenges in improving accessibility of existing building built before 1990. Advisable upgrading of least basic accessibility for pre - 1990 buildings is on a voluntary basis as the mandatory requirement in the Accessibility Code do not apply retrospectively. To tackle the challenge, BCA introduced a 5 year 40 million incentive to defray the cost of upgrading, and also to encourage owners and existing private sector buildings to upgrade their building to enhance the accessibility and user-friendliness, which would eventually benefit users of these buildings and infrastructure.
The third strategic thrust of the Master plan is to set out regulations in place to ensure that accessible facilities are maintained and still available for intended use and not removed or altered (e.g. the conversion of toilet for wheelchair users to storage and accessible car parking lot to normal parking lot)
3.1.2 Building Accessibility Objectives and Provisions.
The building designs are taken into consideration on the provision of accessibility ease for all user and personnel with mobility difficulties. BCA's Code of practice and Universal Design Guidelines (Commercial Building) are adopted in the design considerations which incorporate necessary building accessibility features for barrier-free passage. Some of the barrier free building features are described below in Table 3.1
Table 3.1 Provision of Barrier Free Building Features
Minimum of 3600mm moveable width provided for wheel chairs user and necessary ramps provided from carpark to building entrance and elevator lobby.
Car Parking Lot sign for wheelchair users are visible near to the entrance and clear directional signage are shown.
Automatic doors at elevator lobby. Minimum height requirement for cash card top up machines.
Main Entrance & Lobbies
Requirement dimensions for drop-off zone outside entrance with ramp up to floor level.
Automated glass doors with provision of non-slip floor finishes and Tactile Ground Indicator Surface (TGSI).
Warn of either a hazard or of a destination. Informing user that they are at the top or bottom of the staircases, lifts entrance, slop/ramps.
Direct user from one point to another along a safe path of travel. Provide assistance to locate target such as entrance to building, phone booth, directories and toilet.
Easy Signage and interactive directories at requirement height level for wheelchair users. Lift call button at requirement height for wheelchair users and floor buttons requirement height are provided in the lift car.
All Floor Level
Horizontal and Vertical circulation
Minimum corridor width of 1800mm and clear area with no obstacles.
Smooth wall surface finishes with tactile marking and directional for visual impaired user.
Minimum width of 1200mm for staircases and safety provisions of staircases treads and risers. Handrails constructed base of code of practice.
Provision of Wheelchair friendly toilet.
Requirement width, Visible signage and tactile finish provision for mobility difficulties users.
3.2 Fire Escape Provision
The proposed fire escape routes took references to the Fire Safety and Shelter Department (FSSD), Fire code 2007 (Singapore) and comply strictly with the requirement as stated in chapter 2 (Means of Escape). The code determines the safety means of escape for occupants from all building which includes subject on location, construction, design, arrangement and maintenance. Designated means of escape areas such as exit staircases, firefighting lobby, smoke stop lobby, exit passageway and corridors shall not be turned into other usage as mention in the Code.
3.2.2 FSSD Fire Code 2007 (Singapore)
The building escape design provision is complied with FSSD Fire Code 2007 (Singapore).The occupancy loads complies with the stipulated maximum number of persons per unit and the minimum requirement stated in Chapter 2 (Means of Escape) of FSSD code of practice under Table 2.2A. All other provisions in the building such as maximum travel distance on all stories and exit staircases conforming to the requirement of clauses 2.3.3 of FSSD Fire Code 2007. As the building do not contain shops on upper storeys and habitable height of not exceeding 15m. Provision of firefighting appliances access to the building is in compliance with the requirements in Chapter 4.
Under Chapter 2 (Means of Escape) clause 2.6.1 for office/shop/factory/warehouse occupancy requirement stated that, at least two independent exit staircases or other exit shall be provided in compliance with the requirements of clause 2.2.11, except that one exit staircase is permitted to serve the upper storeys given that the building is of non-combustible construction and not exceeding four storeys. The building also complied with clause 2.10 for exit lighting and Directional Sign. (Refer to Appendix 1.1 for detail)
3.2.3 Determination of Occupancy Numbers and Load.
Under FSSD Fire Code for determination of occupancy load factor under purpose group IV, the following occupancy load requirements are shown below. (Refer to Appendix 1.2)
OCCUPANCY LOAD - SCHEDULE 4
PURPOSE GROUP IV - OFFICE
BUILDING TYPES - OFFICES, BANKS, PUBLISHERS, STOCK BROKERS
OCCUPANCY LOAD (m²/person)
Restaurant/Canteen/ Staff Canteen
3.2.4 Determination of Exit Requirements.
The development is categories into 3 different category and each to incorporate with the fire code 2007 Table 2.2A (Refer to Appendix 1.1)
Shops at Ground Level.
Offices at Ground, 1st, 2nd and 3rd floors.
Places of public & Carpark at building basement between the atrium and the purposed new building extension.
For the provision in clause 2.3.5 of the Fire Code 2007 (Basement Exit Staircase) which prohibits upper storeys exit staircases being continuous with basement staircases, unless allowed by the Relevant Authority. To complied with, naturally ventilated basement design is required with minimum 1-hour fire rated door to the basement staircase. Other consideration such as physical barrier in the form of a self-closing door or gate could be provided across the staircase landing at the ground level, to prevent occupants exiting continuously from upper storeys into the basement storey during an emergency. No Smoke stop lobby provision for entry into staircase at all storeys is required as the staircase do not serves more than 4 storeys, including basement.
Appropriate signage shall be provided inside the staircase enclosure to direct occupants out of the building at both ground and basement level stated in clause 2.3.5 of Fire code 2007 (Basement Exit Staircase). Other requirements such as numbers of exit staircases per storey, numbers of escape routes required, strategy adopted for evacuation and other necessary provisions will be provided accordingly to Fire Code 2007. (Refer to Appendix 1.1 and 1.2)
3.2.5 Firefighting Access
As stipulated in Chapter 4 (Site planning & External Fire Fighting Provision) of SCDF Fire code 2007, the primary objectives are as shown below.
Provision of space around building site to enable effective mounting of both rescue and external firefighting operations.
Provision of minimum width access way for accessibility of site to firefighting appliances, and necessary reliable water access for firefighting operations.
With reference to the clause 4.2 on provision of external access to building, the firefighting and accessibility on site are provided accordingly shown in the layout plan. (Refer to Appendix 1.3)
Structural loading of firefighting machinery onto access way is referred based on SCDF Fire Code 2007 under Appendix G. Minimum requirement width of access way shall be 6m wide and 15m in length.
All building features and basic minimum requirements are designed and construct to comply on all available Code of practices, which in term provide convenience for all users of the building and general public. All regulations and necessary of the building will be incorporated to meet the support of the Government's approach to plans and issues in the near future.
4. STRUCTURAL DESIGN
4.1 Background Introduction
The objective of this proposal is to propose a suitable solution for the various parts of building superstructure for the new propose office building. There are wide choices of structural frames selection appropriate to a buildings function and client need is a key decision with significant short and long term implications. Other obligation are taken into consideration such as working space, time frame, cost incur, buildability, and flexibility.
4.2 Structural Frame System
There are mainly two types of structural frame system, they are namely the Load bearing walls and skeletal frames method.
Load bearing walls systems are suitable for buildings of up to 15 storeys that bears a load resting upon it by conducting its weight to a foundation structure. Materials most often used in the construction of load bearing walls are concrete, block or brick, likewise damaging to a load bearing wall could cause collapse of entire sections of the building.
Skeletal frames building technique are suitable for low-rise buildings of up to 30 storeys. They are a series of angular frames placed at right angles to one another, so as to achieve transmitting of load from members to the foundations and to the subsoil. Lateral forces resisted by columns and diagonal braces or rigid frame.
Base on the flexibility aspect requirement of the office accommodation, skeletal frames would be the ideal choice that would utilize the proposed project.
4.3 Structural materials
There are three kinds of common structural frame systems for commercial buildings suitable for the proposed new extension. Below shows the comparison of those three structural materials and their rating in terms of key issues addressed below.
Structural Materials Key Rating
Safety and Fire Protection
Construction time frame
Quality and Maintenance
Finishes, Vertically and Horizontally
Constructability or Buildability
Time, Flexibility and Standard shape
Sustainability and Environmental performance
Green, recyclable, remit
Strength & Stability
Load, Span, Weight
âˆšâˆšâˆš - Great âˆšâˆš - Moderate âˆš - Low
The Structural frame of a building is the most important aspect a contractor consideration is essential before the beginning of construction.
In Situ Reinforcement Concrete
In situ reinforcement concrete structural frame consists of members such as the columns, beams, reinforced concrete floors and roof. Commonly used as a frame for both single and multi-storey buildings such as residential flats and commercial offices.
Flexible shape of structural and building design could be achieved to suit the occupant's requirement.
Repetitive floor plans could be formed based on engineer's design and calculation inside a skeleton frame of continues columns and floor according to design requirement.
Design can be proceed while structure is in the process of building.
Eliminate transportation problem as the entire structure construction activity can be carried out on site.
Shorten of Erection duration could be achievable due to uniformity design of formwork and column sections, result in building up economic structural frame.
Better structural rigidity and less leaking joints problem as compared to pre-fabrication method.
Design Adjustment and alternations can be made both before and during the construction
Solid and level surface are achievable when connecting directly to a solid concrete backing, columns, beams and floor slab where partitions and walls can be built.
Expensive and difficult to amend errors and mistake in setting of formwork or falsework once concrete has been casted.
Higher number of labour and plant are required on site
Slower and time consuming construction method
Difficult in alteration on change of use purpose of the structure.
Inconsistent quality affected by poor formwork construction and concrete quality delivered by different truck
Precast concrete structures are one of the common options used in both single and multi-storey structures. Structural elements are mass fabricated in a precast manufacturer by casting concrete in a re-usable mould or form, which is then cured under controlled conditions. Precast Concrete elements such as columns, beams, walls floor slabs and staircases are being delivered to site for erection and installation with other units.
High quality element finishes according to factory production. Result in shortening of construction duration.
High quality control of structural elements during fabrication process carried out in the factory
Labour and plant on site are reduced as no formwork and falsework are required on site during installation.
Pre-fabrication of components can proceed regardless of the weather condition.
Site storage space can be minimized as all structure elements are Pre-fabricated in factory, which benefits site with space restrain.
Difficult and impossible to do any amendment or adjustment to the structure during installation stage.
Finalized and completion of design need to be done with, before manufacturer commences casting.
Special attention needed when joining prefabricated sections to avoid failure such as leaks at joints.
Not suitable and flexible for future modification and alterations of structural.
Cost and time involved in handling, caring, transportation, protection and storage of precast elements on site.
Required careful handling of prefabricated component as damaging of component could result in delay of scheduled deadline.
Possibility of distortion on precast structure during curing period in the process of fabrication in the factory.
There would be installation schedule delayed if one of the structure elements on site is damaged.
Heavy duty cranes are required for precise transportation of prefabricated section members.
Possibility of uneven camber in different unit during installation such as pre-stressed floor panels or beams.
Structural steel is well known for its strength and able to achieve large opening spans in manufacturing areas. Steel sections are available in different varieties and dimensional ranges, which allot designers to have more options in their design criteria. In designing lightweight roofs, hollow steel sections are selected as it is not only strong, but light means of construction and widens the range of the scope of steel in designing lightweight roof.
Steel column can contribute more useable space as compared to concrete columns, and also reduce the visual obstructions.
Steel are more economically and easily accommodated when usage on structural such as floor openings, cantilevers, sloping surfaces, curved framing, clear spans and other special aesthetic features, which can contribute more flexibility with building layouts.
Flexibility in terms of delivering of steel structural members as smaller component can be fabricated in factory for site facing access constrain.
Reinforced of steel can be done easily for future additional loads added to the structure.
Flexibility of future alternation and adjustment of elements such as stairwells, elevators floor openings and architectural or mechanical requirements.
Steel framing allow fast track construction where steel elements can be rapidly purchased, fabricated and erected due to its case of design and construction is readily to leads.
Cost saving achievable where steel structure is used for smaller foundation which is normally lighter in weight.
Structural steel is commonly used in possibility earthquake zone as steel is considered a premier structural material for economically resisting earthquake. Recover cost could be minimized and maximizing life safety during seismic event.
Steel are consider green marked material as it is highly recyclable.
Erosion occur when steel are exposed freely to air and water. Thus protecting layer such as paint are painted thoroughly and periodically to prevent erosion-fatigue failures occur on steel members which would affect the strength of steel members.
Steel structural members are weak in fire. In the event of fire, steel member's strength is reduced tremendously at relatively low temperature. Therefore fire rated coating is needed to apply on steel members, resulted in incurring additional construction cost.
There may be difficulty in safe working conditions during steel erection until a profiled steel deck is in place.
Excellent heat conductor such as steel with non-fire coating may transmit enough heat from a burning section of a building to ignite the surrounding materials which are in contact in adjoining sections of the building.
Large number of tensile stress or tension could cause fatigue on steel which may reduce the strength.
Analysis and Recommendation of frame material
Steel frame is recommended because of client concern to environmental, time, energy used in construction and materials minimizing. Steel are highly recyclable which thus meet the key issue of sustainability. Steel uses less labour energy as compared to precast elements and uses lesser construction time as compared to two other materials. The proposed building consists of three storeys, therefore it is uneconomical to use pre-cast concrete frame as small quantities of structure elements are cater for different height as shown in table 4.4. As for other consent need to be taken into consideration of using steel frame is the fire protection coating as steel had the lowest resistance to fire tolerance as compared to two other materials.
Table 4.4 Heights of proposed new office building
Floor system for Steel Frame
ComFlor 210 is selected for the new proposed office building. ComFlor 210 (integrated beam) had become popular in the recent year as it provides minimum depth for steel-concrete floor construction. It is more efficient for longer span of larger between 5 to 10 m. The benefit of using ComFlor 210 construction is that the steel beams are embedded within the slab depth, therefore overall structural depth range between 280 to 320 mm. For detail see Appendix 2.1
5. BASEMENT AND FOUNCATION DESIGN
5.1 Background Introduction
The design of substructure such as basement is constructed to cater for the increasing demand of space in buildings located at densely populated areas. The key issues of the structural solutions in this proposal are to create as much usable space and to protect against moisture penetration, furthermore integrate with the superstructure, ensuring effective transferring of loading from building above to the foundation and finally to the subsoil. Consideration such as site survey, site layout, ground condition and building design would determine the method and choice of constructing basement. In addition, other issues such as uneven settlement throughout building lifespan and areas of uncertainty would be addressed in relation to this project cost plan design and to ensure this proposal is design and build for value.
5.2 Types of Basement Construction
When deciding on the method use for basement construction, design consideration should input issues such as site workable size and space on site, geotechnical condition, shape and typographical conditions of site and water table level in ground. Common employed basement construction method under various site conditions would be discussed as below.
Features of various basement construction methods
Size of site
Adaptable to most environment
Adaptable to most complex environment
Complex lateral support required
Limited shoring support
Temporary vertical support required
Staged platform or bucket
vertical shaft or bucket
Open- cut method is suitable for site with abandon of unobstructed working space. It is the simplest method where open excavation is carried out with sides being battered to angle suitable according to the surrounding soil condition. Temporary support such as steel sheet piles is usually used for open excavation. Backfilling would be done after construction.
Bottom-up method refers to order in which the subfloors are constructed from the deepest level of the car park basement, and construct that bottom level with primary foundation. Follow by other layers are then build up one follow another, by the necessary supports for the next floor are lay by the contractors. Bottom-up method is suitable for basement of small to medium size.
Top-down method is suitable for basement of very large size with complex environment. This advanced method employed to substructure construction where basement concrete slabs act as lateral bracing for the perimeter wall system (diaphragm wall). The ground level and first basement slabs are poured, with access opening left to permits excavation equipment to commence construction at first storey basement slab. As each subsequent subgrade level is completed, the slab would acts as lateral bracing in the form of a permanent structure wall system. These processes are repeated until the last basement slab is completed.
5.3 Types of Excavation lateral support system
Sheet Pile: Permanent
Interlocking prefabricated steel piles driven into ground forming a wall that is continuous and permanent
Light weight, water tight, safe,
tensile stresses, suitable for deep excavation, suit all soil type
not economical for big one off project, cost,
water acting as a
Interlocking prefabricated steel piles driven into ground forming temporary wall
Can be reused,
to allow a
piers and houses
that have a high
Bored Pile: continuous
Soldier piles that are
repeated to create a wall
Stiff walls, good
in confined site
be used as
Soldier piles are
used mainly as
they are cheap
and don't disturb
as much as other
Bored Pile: tangent
Continuous bore piles that
meet at their tangential
Bored Pile: interlocking
Continuous bore piles that
have in their gap
secondary piles that are
unreinforced weak concrete mix
Bored Pile: secant
Continuous bore piles
where the primary piles
are the unreinforced piles
and the secondary piles
A trench that is filled with
slurry to prevent a
collapse when reaching its
depth reinforcement is
lowered and the concrete
displaces the slurry
can be used as
work, lack of
joints, can be
used as footings
Good for water
areas, top down
used in very
Summary of Excavation Lateral support systems:
Sheel pile: permanent
Bored Pile: continuous
Bored Pile: tangent
Bored Pile: interlocking
Bored Pile: secant
Permanent structural concrete wall formed in one
Ability to deal
than 1:200 with
left in wall to
Vertical loads can
5.4 Evaluation Summary of Proposed Basement Construction Method
From the preliminary soil investigation, the bore holes laboratory report indicates that groundwater was recorded at depth of 2.85m, and the minimal bearing stresses of 25Kn/m² is located at depth 0.40m below ground level. A basement car park located beneath the atrium and the new office accommodation is only partial, and accompanied by side slope located at the east and west side, offering 7.5 meter width offset away from the proposal building boundary.
Based on the above site information, the suitable proposed basement design and construction sequence is to install underpinning by jet-grouting at south elevation of existing building prior to commencement of basement construction. Such method could provide support to the existing building and stabilize the soil. (Refer to Appendix 3.1 for jet-grouting detail)
Installations of diaphragm wall along north elevation of proposed new office building, for it serve as permanent support for basement excavation and basement wall at north elevation, as the same time provide support of loading from both the basement slab and the atrium above. To overcome the high water table coinciding with the founding level of basement slab at around 3.5m below ground, temporary sump pits are excavated for the installation of mechanical pumps, to temporary lower the water table level for basement excavation so as to be able to construct on dry surface.
Due to the use of diaphragm wall along the north elevation of proposed new office building, vertical cut excavation method is more suitable for the site as the site isn't very big, and the single basement of the new proposed office building is only partially underground. Thus vertical cut method would be a simpler and more economical method to adopt as it is more adaptable to most environments compared to two other methods. The site is surrounded by one existing building and two side slope where open-cut method is only applicable to unobstructed environment and top-down method would be too complex for the proposed project.
Secant pile wall would be constructed on both east and west side of the basement wall. external tanking method for water exclusion system would be adopt for the secant pile wall while the wall would provide interlocking required to deter the passage of water. Likewise exposed surface of the secant pile wall will be treated to required architectural finishes.