BUILDING STRUCTURES BLD61003
PROJECT 1 : STRUCTURAL DESIGN POST MORTEM
Lock Tian Jiun Wesley Wong Teck Won Ow Xun Cong Kelvin Douglas Cheong Tze Liem
0327636 0330496 0321997 0325939 0327955
INDEX
PAGE
1.0 Introduction of VIC
1
2.0 Foundation 2.1 Safety and Integration of Foundation 2.2 Strength and Stability of Foundation
2 4
3.0 Decking 3.1 Introduction of Decking 3.2 Safety of Decking 3.3 Solutions of Safety of Decking
6 7 8
4.0 Post & Beam 4.1 Introduction of Post & Beam 4.2 Safety of Post & Beam 4.3 Stability of Post & Beam 4.4 Strength & Rigidity of Post & Beam 4.5 Optimization of Post & Beam
9 10 12 14 16
5.0 Wall 5.1 Introduction of Walls 5.2 Safety and economy of Walls 5.3 Optimisation of Walls 5.4 Integration of Services of Walls 5.5 Stability of Concrete Structure
18 19 22 23 24
6.0 Staircase 6.1 Introduction of Staircases 6.2 Safety and stability of staircases 6.3 Solution of safety and stability of staircases 6.4 Solution of safety and strength of staircases
25 26 27 28
7.0 Roof 7.1 Introduction of Roof 7.2 Optimisation of Roof 7.3 Solutions of Optimisation of Roof 7.4 Safety and Strength of Roof 7.5 Solutions of Safety and Strength of Roof 7.6 Rigidity of Roof 7.7 Solutions of Rigidity of Roof 7.8 Feasibility and Economy of Roof 7.9 Solutions of Feasibility and Economy of Roof
29 31 32 33 35 37 38 39 41
8.0 Drawings 8.1 Original Floor Plans, Elevations and Sections with Modified Floor Plans, Elevations and Sections 9.0 Reference
1.0 Introduction of VIC
1.0 Introduction of VIC VIC before modification
The VIC responds contextually to its site, Sungai Buloh, Selangor. Sungai Buloh leprosy settlement is the world second largest leprosy settlement established by Dr. Travers in 1930. Based on garden city living concept, living environment is segregated from industrial and commercial area. Thus, this microsite is carefully proposed for my VIC building. After MDT was introduced in 1980, the incurable disease cured. Today, plants and flowers from the nursery are flourishing. Underlying this beauty is the bitter story of an isolated community that worked in unity. In the midst of discrimination & humiliation, little did we know their tearing smiles, smiling tears. Thus, this VIC instill in the users the DUALITY idea.
1
2.0 Foundation 2.1 Safety and Integration of Foundation 2.2 Strength and Stability of Foundation
2.1 Safety and Integration of Foundation Foundation is the lowest division of a building that helps to safely transfer the load of a building to the ground. As for the VIC’s foundation, it was not looked up initially when it was in the designing process. Without the foundation, the building structure will most likely fall apart or collapse in on itself. As the VIC has the concept of duality, the primary materials involved in the design are concrete and wood. For the concrete part of the building, the material is suitable for a foundation because the material is long lasting, durable, water and fire resistant and also termite resistant. Whereas wood are not allowed to have a direct contact to the ground due to its characteristics. Depending on the temperature and humidity in a tropical climate, wood is known to expand or contract. Besides that, termite attacks are also likely to be a difficult problem. As it is shown in the figure below, there are no proper integration of the walls and columns to the ground below. Without it, the building most likely would collapse when there is external loads act towards the building such as wind load and earthquake.
Figure 2.1 Sectional view of VIC
Figure 2.2 Absence of foundation in design
Figure 2.1 shows the sectional view of the VIC where the inappropriate integration between the columns and wall to the ground without foundation can be seen.
2
2.1.1 Solution of Safety and Integration of Foundation The suitable foundation that can be suggested for this VIC is Raft foundation. A raft foundation is a reinforced concrete slab under the whole of a building or extension, 'floating' on the ground as a raft floats on water. This type of foundation spreads the load of the building over a larger area than other foundations, lowering the pressure on the ground. In raft foundation, the weight of the building are equally extended over the entire land beneath the building. Although it has only two floors, the height of the VIC exceeds more than 6 meters which makes the building bigger and heavier in mass. Raft foundation are commonly used in commercial buildings where it is large and heavy which is why it is suitable and safe foundation for the VIC. Besides that, raft foundation are easier to construct, the materials are always available, less labor needed to construct it, and also cheaper compared to deep foundation. The material used to construct raft foundation is concrete because it has a better characteristics in strength and stability which makes it safe to use for this VIC. For the concrete walls and columns to be integrated with the column raft foundation is easy because both using the same material which is concrete. But for the wood columns and wall to be joint with the concrete raft foundation, it needs to have a steel member to join the wood column and wall to the concrete raft foundation. The joint that is suitable for this building is Timber Connector that include one two-pin pipe connectors because the joint is easy to install, has a good characteristics in strength and most importantly cost-effective.
Figure 2.3 Construction process of columns along with raft foundation Figure 2.4 Sectional view of raft foundation
Column Post
Raft Foundation
Wire mesh, Reinforcement
Figure 2.5 Proper sectional view of raft foundation
Figure 2.6 Timberlinx connectors to connect wood column to concrete foundation
3
2.2 Strength and Stability of Foundation The strength and stability of a building depends on how strong and stable the foundation is and how good the physical properties of the materials used. In this VIC, there were no planned foundation as it has been mentioned earlier. Below figures show the transmittance of the building loads to the ground explained that there are no guarantee that the building would not collapse without the foundation. As you can see, the loads transferred from the structural member of the building goes straight to the ground which can cause the building to collapse. With a proper foundation, the loads of the building can be transferred easily and safely to the ground through foundation and thus the VIC can stand strong and stable. A stable and strong foundation keeps the building standing while the forces of nature wreak havoc. Well-built foundations keep the occupants of the building safe during calamities such as earthquake, floods or strong winds.
Figure 2.7 & 2.8 Load distribution of building to ground
4
2.2.1 Solution of Strength and Stability of Foundation For the safety of the VIC, a foundation is required because without the foundation, the VIC cannot stand on its own without collapsing. In the design of foundations for large buildings on deep deposit of cohesive soils it is generally seen that if raft foundation be chosen the foundation will have sufficient factor of safety against shear failure. Besides that, raft foundation is also a stable foundation because in raft, the entire basement floor slab acts as the foundation hence, the weight of the VIC is spread evenly over the entire footprint of the building and make the load transfer to the ground efficiently. The raft foundation is constructed using concrete material which has a high properties in strength where it cannot be weakened by moisture, mould or pests. Moreover, concrete has a high durability, fire-resistance and also affordable. Apart from the type and materials used for the strength and stability of the foundation, reinforcing of the foundation may be required because of the changes in functionality of the VIC. The act of strengthening a foundation is called underpinning. Near future when the VIC’s foundation being shaky and feeble increments with time; if development outperforms the farthest point of the balance plan, extra weight on the balance can make them split, twist and additionally pivot. Such anxieties will then exchange to the wall or floor slab above, prompting crack and breakage, in outrageous cases, may compromise the structural integrity of the VIC. To prevent all the damages to happen, underpinning is required for this VIC.
Figure 2.9 Load distribution of building to ground when foundation supports the building
Figure 2.10 Underpinning process of foundation
5
3.0 Decking 3.3
3.1 Introduction of Decking 3.2 Safety of Decking Solution of Safety of Decking
3.1 Introduction of Decking
Decking is the flat platform consisted of uprights,bearers,joists and flooring materials. It is capable to support force and load similar to a floor slab in the lateral load resistance mechanism.(live loads with horizontal force).Mainly designed for outdoor purpose, decking should be weather resistant (rain and sun),slip resistant, waterproof and fireproof. In our VIC, the timber decking is constructed with redwood. It is a pressure-treated(tanalised) and naturally durable option chosen. It is a attached deck instead of freestanding deck.Compared to metal decking, it is cheaper, easier to construct and easier to maintain. However, the floor joists are not secured on one end with any visible structural components, it can be said that they are cantilevering, this causes difficulties for usage as the flooring would not maintain stability when live loads in transferred upon it. In addition, the spacing between the timber decking at 100mm is slightly too large for user comfort, children will smaller feet might fall through when accessing this area of the building.
6
3.2 Safety of Decking The floor joists are cantilevering off the beams where it has only minimal securing. The span among individual planks are relatively wide apart, it poses danger issue for young children or people with smaller feet accessing the deck area.
Characteristics of redwood:
Insufficient securing between decking and beams
The span of timber decking is slightly loose which endangers users when accessing.
● ● ● ● ● ● ●
Virtually maintenance free Easy cleaning Weather resistant Insect resistant Environmental-friendly processing Easy workability Imported wood - not suited to local climate, and high price
7
3.3 Solution of Safety of Decking Decrease spans(to nearly zero air space) between individual planks to avoid risks of falling down. Drive in bolt through clearance hole on the main ledger beam so that it is fixed tightly to the wall. The joists are secured on both ends to newly placed beams to ensure the decking area is safe to access.
Add a 50 X 100 mm
rim joist at the edge.
Connection : Metal joist hanger, 40mm galvanised screw
Add floor joists and sill plate (500mm apart)beneath the decking. Supported by girders and load bearing walls They support structural planking.
8
4.0 Post & Beam 4.1 Introduction 4.2 Safety 4.3 Stability 4.4 Strength & Rigidity 4.5 Optimization
of of of of of
Post Post Post Post Post
& & & & &
Beam Beam Beam Beam Beam
4.1 Introduction of Post & Beam
Post and beam construction is a building method that relies on heavy timbers rather than dimensional lumber. With roots in early Asian architecture, the use of post and beam construction methods have long since spread across the globe. Several post and beam structures constructed during medieval times are still standing—a testament to their well crafted durability. In the aftermath of natural disasters like hurricanes and earthquakes, post and beam buildings are often the only structures that remain erect. Post and beam are important in constructing the VIC, they are main supporting member in the supporting system. Therefore, it is paramount on ensuring the post and beam are well-constructed.
9
4.2 Safety of Post & Beam In the construction of the VIC, the safety of structure is very important. In order to achieve the safety of the structure having a supporting structural system such as columns and beams are the main supporting members in maintaining the strength and stability of the building. However, there were a few structural flaws which could interfere the safety of the VIC.
Beams are not present
Column are not supported completely
The timber column used as screenwood facade are not fully supported. Timber column could not hang without incorporate with any support as the timber itself is heavy.
The building has no beam to support where the column are placed at, located on the ground lever supporting the first level floor slab and also the first level supporting the roof slab. Figure 4.1
Figure 4.2
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4.2 Safety of Post & Beam
Placing the beams in the grid composition so that the beam could act as a platform to transfer heavy load to the column then it is distributed to the foundation.
Concrete beam
Dimensions of the reinforced concrete beam used 300mm x 300mm in length and width
Timber beam
Dimensions of glulam beam used 150mm x 300mm In length and width
First floor
Battens Wooden column is connected to the batten using metal plate, bolt and nut.
Ground floor
Dimension of timber column used as facade 75mm x 200mm
Using timber column as a screened facade, it is still important to provide extra support as timber especially when it is overhanging. Besides, in terms of its materiality is generally heavy, so, a metal bar, battens should be incorporated to the timber column to provide support.
11
4.3 Stability of Post & Beam Another factor of existing structural system would be stability of the structure and their members. The stability of the structure depends strongly on the beams and columns as they are the main support in the supporting structure. Thus there are a few major issues that were need to resolve on in making the structure achieve stability.
Concrete column is rather small in diameter.
Timber column is rather small in diameter and it is not stable.
The dimension of the columns are rather small and are subject to failure by buckling where the columns begins to deflect laterally and cannot generate the internal forces necessary to restore its original linear condition.
As for the timber columns are long span and slender, they cannot withhold too much load and direct stress from the axial load of the building without a foundation to support.
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4.3 Stability of Post & Beam
Increase the dimension of the column to a required size, load distributed to the columns are able to transfer it to the foundation safely.
Concrete column
Timber framing
Timber frame were constructed to support the timber structure.
Dimension of the column used 300mm x 300mm Using a rectangular type of column as compared to the circular column which has a smaller cross section area (0.785 times the square column). Thus the rectangular column supports more to the structure.
Dimension of timber beam 150mm x 300mm Dimension of timber column 300mm x 300mm
Adding a raft foundation, a reinforced concrete slab under the whole of a building or extension. That would provide a spreading of load imposed by the columns or walls over the area of foundation. Reinforced concrete slabs uniform thickness typically 150 mm to 300 mm Raft foundation
13
4.4 Strength & Rigidity of Post & Beam In order of having a strong building, the strength and rigidity of the structure should be strong enough to withstand on its own. Having supporting members like beam and column, they are the main part of building a strong and rigid building. However, aside from the structure member being strong enough, the material should play their role in achieving strength and rigidity. Other than that the connection between the structural system should as well be strong.
Beam were absent in the structure. Some beam are not able to support itself
Some beam were absent to support weaker parts of the structure and the roof. Whereas column were not placed at a correct position to evenly distribute the loads
The timber supporting system has a lower capacity of undergoing stress than the concrete. The timber structure needs a frame to remain the rigidity.
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4.4 Strength & Rigidity of Post & Beam
Concrete column
Repositioning the concrete column to support the important part Maintaining the rigidity of the building.The columns are added using the grid composition to place the columns equally so that the load can be distributed evenly.
Connection of concrete beam and column
Prefabricated column with bearing pads on corbels as a connections for the beam
Connection of timber beam and column
Metal plate used as a connector between the timber column and timber beam.
Metal plate
Reinforced Concrete Beam: 300mm x 300mm in area Main steel 8 every 10mm distance Secondary steel 4 every 12mm distance Bearing Pad
Merbau wood and glulam use as timber column and beam respectively Dimension of timber beam 150mm x 300mm Dimension of timber column 300mm x 300mm
15
4.5 Optimization of Post & Beam In terms of the aesthetic view of the VIC, there are some factors like optimisation which plays a vital role in making sure that the architectural design has no issue in contrast to the engineering design. The discipline of adjusting a process to optimize some specified set of parameters without violating some constraint. Based on the structural optimization, there are a few structural needs to reconsidered. So that the design is structurally efficient and of course aesthetically pleasant.
Unnecessary function of the slanted columns Unnecessary column not really used as supporting member
Timber column were left overhanging without support
The slanted timber column was not really providing any support the roof slab. The column below as well does not provide much support either.
The overhanging timber column could not hold on without a proper support
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4.5 Optimization of Post & Beam
Slanted are removed as they do not provide any support, it is turn into a open verandah.
Battens
Wooden column is connected to the batten using metal plate, bolt and nut.
The timber column that was used as a screen facade, should be connect to the battens at least from the top and the bottom to secure the column to prevent from falling or losing its support.
17
5.0 Wall 5.1 Introduction of Walls 5.2 Safety and economy of Walls 5.3 Optimisation of Walls 5.4 Integration of Services of Walls 5.5 Stability of Concrete Structure
5.1 Introduction of Wall
The walls of the design adheres to the concept of DUALITY, which comprises of two construction methods significantly differing from each other - concrete construction for one side and timber construction for the other. Timber walls composed of large, heavy sawn timber of one whole length conjoining into post-and-beams of smaller size than required for support. Concrete walls expands the whole length of the structure relying solely on the strength of the wall-to-slab connection and the geometry of the arrangement.
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5.2 Safety and Economy of Walls Safety of Timber Walls In timber construction, the safety of the structure is gauged on the stability and strength of the timber frame, and its approach towards fire precaution. In terms of fire safety, large timber components have slow burning properties, where an insulating charred-layer protects the unburnt side, retaining substantial strength of the structure. However, its untreated quality means that gradual wear over time results in the timber losing its original density, the splinters from damage may catch fire easily because of high combustible area. Moreover, as structures are not thoroughly focused on beforehand and is improperly laid into design, our building is erected on an unconventional framing system, where beams sit on thick, load-bearing solid timber walls, which is structurally unsafe, as the weight of the walls exceeds the carrying capacity of beams, as well as resulting in a system which uses a greater amount of timber components than required to uphold the structure, causing a wastage of resources and money.
Large timber components has slow burning properties, which allows evacuation before structural failure
The walls are too thick and heavy in mass to be successfully supported by relatively thin beams over time
Figure 5.2.1 : An unconventional timber framing system where over-long horizontal members of 150x150mm bears its weight onto solid walls of same width as well as on decorative studs
Safety of Concrete Walls The concrete wall structures of the visitor interpretation centre functions with load bearing properties and mainly relies on geometry and wall-slab connection to stay upright, however the load bearing walls does not anchor into the ground or have any foundations for support. Moreover, our walls are of insufficient thickness to successfully bear loads of upper levels. In addition, these thin concrete walls span an entire elevation of the building, without reinforcement these walls are prone to collapse when met with external forces or crack from exceeding carrying capacity.
These load-bearing walls have insufficient thickness to successfully carry imposed loads Supports itself and loads from above as it does not have a structural frame
Second floor walls connects to a very thin slab for anchorage
Figure 5.2.2 : The walls in the concrete part of the VIC act as main structural support but has insufficient thickness and improper connections to successfully carry out so.
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Problems Timber Structure The problems in timber walls of the VIC are mainly that it is erected as a main horizontal load transfer member, but has incorrect connections with other structural members. The entire wall structure composing of untreated timber makes its splinters susceptible to quick spread of fire
Extravagance to use heavy timber walls, which hikes up price of project and requires stronger post and beam supports
The wall is only secured to another wall and not supported by timber framing, will collapse easily
Rot/water resistant wood of such sizes are even costlier
The weight of solid timber wall of 150mm exceeds the carrying capacity of 150x200mm timber post and beam Figure 5.2.3 : Problems in Timber Structure
Concrete Structure
Entire second level supported by flimsy walls of 150mm thickness.
Elevation-wide expanse 150mm wall structure that bears loads of upper levels supported solely by wall-to-slab connection.
Figure 5.2.4 : Problems in Concrete Structure
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Solutions Timber Structure
Timber Framing Timber post and beam frame is used to replace the load bearing full-length walls.This increases the safety of structure as the weight of compression and tension members are essentially same sizes and will not overwhelm one another. They are secured together with timber connections, these structures are adequate to carry their own weight in addition to imposed loads. 6000mm
Column spacing is determined by size and proportion of the bays
6000mm
3000mm
• The species and grade of lumber used - Merbau hardwood. Superior performance in withstanding harsh environmental conditions, making it optimal for outdoor construction Characteristics: High tensile strength, good strength to weight ratio, weather resistant, minimal maintenance
Wooden cladding 25mm wood fibre board Adhesive or mechanical Vapour barrier Treated fire-retardant plywood Timber frame
Fire-Resistive Wall Assemblies Fire prevention in the modified structure can be carried out through fire resistant assemblies, where the in place of heavy timber components, the walls are composed of light frame which is insulated in within with fire retardant layers.
Concrete Structure Reinforced concrete columns 305mm
Concrete Frame, Non-structural walls A concrete frame of columns casted together with beams and slabs are used to support the walls. The walls will be relegated to act with non load bearing properties, and perform merely as non-structural panels. The walls will retain its 150mm size as it is still required to withstand horizontal loads, such as wind and seismic forces.
Figure 5.3.2 Cable support on concrete walls
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5.3 Optimization of Walls In this design, the concrete wall is of a single storey level and does not connect to the upper level, the slanting slab is instead supported by a network of steel trusses which directs the forces travelling back to the walls. This decision is less optimized as additional considerations in terms of technicality, ecomicality need to be considered, and special connections and workmanship need to be employed. The cavity opening does not provide any significantly different than full length wall with casted openings, thus the weighing of importance lies on choosing the most economical way around.
Problems
Weight of the concrete roof slab is quite immense Steel trusses require different connections with concrete walls
Force travelling diagonally down is suddenly travelling directly downwards, the stresses are not properly addressed by the structure Figure 5.3.1 Pre-optimized concrete wall
Solutions
Concrete walls rise up to upper floor slab supported by concrete frame to establish a same language in structure Ventilation is preserved by creating opening on the newly connected wall
Figure 5.3.2 Optimized concrete wall
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5.4 Integration of Services of Walls Services were not considered in the original design of the building, wiring connections were simply left as is in the previous design. Modifications were made in both the timber and concrete walls to pay attention to the integration and importance of services in our building.
Problems Services were not previously considered in the design.
Solutions Timber - Cable support inside walls Electrical wires will fit through the openings created at the timber studs of the wall planes. The wires will be stapled to the studs every 5 feet to prevent shortages or failures resulting from unruliness from interfering with building service operations.
Staples every 5 feet
Cables not required when it runs through holes of studs
Figure 5.4.1 Cable support inside walls
Staples where cables change direction
Protective metal stud is used when wire is within 1.25 inch of stud face 1.25 inch clearance required Figure 5.4.2 Detail of cable connection through timber studs
Concrete - Cable support on walls As the wall now does not need to carry vertical loads of the structure, recesses and holes can be made upon the concrete wall to accommodate for the wirings which will be located at the surface of the wall. The wires are made on the surface of wall to preserve the structural integrity of wall as well as preventing cost incrementation from extra work needed to install these wires inside the casted concrete.
Recesses in wall allows accommodation for M & E service wirings, provide slight protection from external damage Wirings run on surface to prevent additional labour required when casting to hide service components Figure 5.4.3 Cable support on concrete walls
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5.5 Stability of Concrete Structure Although concrete structures have inherent strength from its material property that keeps it upright, the structures still relies heavily on other factors considered such as the structural geometry and the arrangement of the framework to establish a successful building structure considered safe to use. Our VIC’s geometry is slightly precarious but support appears to be provided at points required, but at close inspection it is noticed that the structural components are not set out correctly to be able to provide strength to maintain stability of the concrete structure, therefore some amendments had to be made.
Problems Improper connections in an precarious geometry resulting in structural instability. Unusual geometry of which nearly ½ of the 2nd level is cantilevered The cantilever beam ends at this point, and is not anchored by any vertical member The columns are too thin to successfully carry the load of the upper level
Solutions Introduction of a proper concrete formwork which can successfully pin down the weight of the cantilevered structure. Addition of concrete framework system which the load of the upper level will be transported through the beams onto columns and onto ground, the cantilever beam will be pinned down onto columns Exterior columns are removed as its unnecessary after modification 300mm
225mm
300mm
The rebars will need to have the required anchorage value on boths sides, the end of the cantilever shall not be lesser than ⅔ of the thickness of concrete slab
300mm
Column thickness
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6.0 Staircase 6.1 Introduction 6.2 Safety and stability 6.3 Solution of safety and stability 6.4 Solution of safety and strength
of of of of
Staircases staircases staircases staircases
6.1 Introduction of Staircases
Straight staircases are the most basic type of staircase spanning two points in a straight line. Some of these use landings to break up long staircases. One variation of the straight stairs is the L shaped staircase, also called a quarter-turn staircase. This involves two spans of straight stairs jointed at a right angle with a landing between them. Another variation is the U shaped staircase, also called a half-turn or switchback staircase. For these, the two spans of straight stairs are placed parallel to each other so that people on the landing turn completely around to walk up or down the next set. Timber staircase is constructed as the VIC is only two-storey high (not higher than three storey).
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6.2 Safety and Stability of Staircase This VIC uses timber staircases and concrete staircases. There are three staircases located as shown in the ground floor plan below:
Concrete staircase Timber staircase
Figure 6.1 Ground floor plan
Open-riser without full stringer weakens its geometrical stability as the treads experience only little structural support.
Figure 6.4 Open riser timber staircases
Besides, multiple gaps caused by potentially cause the users to fall.
the
empty
risers
Unlike a normal ramp that does not usually need railings,all the VIC staircases without railing poses risk and danger for the users.Without some supporting structural members like soffit, carriage, stringers, ledgers and kick plate,the overall timber staircase system is deemed to be moderately weak. Figure 6.2Concrete staircases
Figure 6.3 Weak timber staircases system
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6.3 Solution of Safety and Stability of Staircase Alter the open riser timber staircases into closed riser timber staircases.(Figure 6.6 and Figure 6.7) Integrate carriages,also known rough stringers and the the principal inclined beams to support the treads and risers of a flight stairs. Add the sloping finish member,stringers to run alongside a staircase,against which the risers and treads terminate. Add kick plate to anchor and absorb the thrust of an inclined stair carriage to increase the individual member`s stability. Figure 6.5 Timber staircases
carriages stringers
Figure 6.6 Open riser staircases run rise
fireblocking soffit
Dovetail balusters into treads,giving extra support to timber staircase
Spacer
Figure 6.7 Open riser staircases
Figure 6.8 Closed riser staircases with housed stringer
Integrate and route housed stringer to receive ends of treads and risers in a series of housings.Use wedges to assure a tight fit
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6.4 Solution of Safety and Strength of Staircase
Headroom at 2000 mm
between 50 mm to 65 mm
Minimum requirements proposed: handrail
1) 50 X 50 balusters turned or fluted
2) 3)
230 mm minimum 1 X shoe rail for balusters
4) 100 mm maximum
Baluster spacing maximum Clearance above minimum Landing length & stair width Landing railing above landing
(clear) 100 mm nosing
200
mm
width equal to 95
to
110
mm
5) Nosing 30 mm 6) Riser 200 mm maximum 7) Stair railing 750 to 850 mm above nosing 8) Tread 23 minimum 9) Width of stair 92 mm minimum 10) Maximum pitch 42 degree
nosing of thread
30 mm part.bd.bullnose treads Provide minimum 920 mm clear width at stairways
25 mm plywood risers 50 X 300 stringers
Figure 6.9 Section of detail
Figure 6.10 Newly proposed structural system
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7.0 Roof 7.1 7.2 7.3 Solutions of 7.4 Safety 7.5 Solutions of Safety
Introduction Optimisation Optimisation and Strength and Strength 7.6 Rigidity 7.7 Solutions of Rigidity 7.8 Feasibility and Economy 7.9 Solutions of Feasibility and Economy
of of of of of of of of of
Roof Roof Roof Roof Roof Roof Roof Roof Roof
7.1 Introduction of Roof
Based on the conceptual design of the roof of VIC, the roof stands out as a grandeur, dominance essence to the site. Both roof, timber and concrete roofing are to show the triumph of nature always defeat modernism. In the existing building, the roofs consist some structural components to support them. Yet, those structural supports has some serious flaws for them to do their part. There is a high chance of roof failure if the roof structures did not undergo any reinforcement or modifications. There are two types of roofing: sloped roofing and flat roofing, each of them has their own distinctive issues which could affect the whole load bearing structure in the VIC.
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7.1 Introduction of Roof Based on the conceptual design of the roof of VIC, the roof stands out as a grandeur, dominance essence to the site. Both roof, timber and concrete roofing are to show the triumph of nature always defeat modernism. In the existing building, the roofs consist some structural components to support them. Yet, those structural supports has some serious flaws for them to do their part. There is a high chance of roof failure if the roof structures did not undergo any reinforcement or modifications. There are two types of roofing: sloped roofing and flat roofing, each of them has their own distinctive issues which could affect the whole load bearing structure in the VIC. Some notable modification of roofing in terms of optimisation, safety and economy has to be improved. The selection of both materials need to be highly resistant towards the climate as well as from safety and maintenance issues. Overall, there will be a big makeover towards the roof design and structural parts but in the same time, the aesthetic value of the roof shall be remained.
Figure 7.2 Long roof trusses
Figure 7.1 Roof plan
Figure 7.3 Large roof cavity with curved and long span of roof slab
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7.2 Optimisation of Roof From the view of aesthetic of this VIC, it is an intriguing kind of a building. Yet, the aesthetic value of VIC roof does not respond well with the whole roof structural part. Both concrete and timber building in this VIC has a fairly large roof cavity respectively, which is a non-used area, leading to spatial wastage and imposing extra loads and stresses to the structures. As a result, more columns are erected just to handle the forces and loads from the roof cavity itself. Some design modification has to be executed to achieve the optimization of the aesthetic look yet did not lose the structure aspects.
Overwhelming forces from the roof cavity towards the columns
Large roof cavity resulting imposing of unnecessary load
Overly cantilevered roof
Unnecessary columns to support roof cavity’s load
Figure 7.4 Load distribution of Roof Cavity
A staggering 3.9 meter high roof cavity, which is similar to a one-storey height, resulting overloaded of unnecessary loads and forces to the building and structures.
Figure 7.5 Unused Space in Roof Cavity
The roofs are cantilevered out from the building. With its large and heavy volume of cantilever, the roof had to impose additional structure to it, which leads to use more columns to support the extruded part of the roof.
Wasted or unused space is created for the sake of its aesthetic value without considering the extra materials used
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7.3 Solutions of Optimisation of Roof Based on the stated issues from the VIC, the roof cavity shall be removed. For the concrete construction, the roof cavity will changed into an usable accommodation space for the visitors, whereas for timber construction, the whole roof cavity is being deconstructed to use as a balcony, which is also transformed into a usable space. In other issue, the cantilevered part of the roof should be taken away. As a result, those unnecessary load bearing columns can be removed for saving cost and decrease the usage of space of the VIC
The removal of the cantilevered roof has resulting in eliminating the load bearing columns
Figure 7.6 Removal of unnecessary columns and cantilevered roof
Deconstruction of the roof cavity to use as a workable space maximises the usage of space without any spatial wastage
Figure 7.7 Transformation of space in roof cavity
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7.4 Safety and Strength of Roof The aesthetic value of the VIC is incorporated with the load bearing structure, which is now seen as a problematic issue where the load bearing structures are not acting its role as it should be. The slanted aesthetic columns from the roof facade are not meant to be load bearing. For sloped roofs, they are initially contains no roof beam to support them but solely supported by overly spanned roof trusses, whereas the flat roof is basically supported solely by the surrounding walls. The absence of roof beams and in this case, a proper roof facade, causing insufficient load transfer from top to bottom which eventually became one of the major issues to the roof as it would cause collapsing of the roof.
Load distribution dependant only on the surrounding walls
Roof slab supported solely by overly spanned roof trusses
The trusses are fully occupied with the stresses from the roof slab
High risk of collapsing in absence of load bearing structure Figure 7.9 Overloading loads on roof trusses
Although the roof trusses had provided a fairly amount of support to the roof, it is still insufficient as it is only a one-sided support which could cause instability of roof and eventually collapse. Non-load bearing wall is the only structural support to the flat roof
Aesthetic slanted columns attached to the roof slab, yet did not provide any structural support due to the slanted angle of the column Figure 7.8 Dependency of roof support
The implication of roof slab towards its supporting structure is lacking in such way that roof beams are missing in this VIC. The distribution of loads are imbalance as the only support dependency of the roof is directly to the wall as the aesthetic slanted column does not provide any load bearing benefits to the roof.
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7.4 Safety and Strength of Roof Originally, the timber building is a lightweight timber construction, using normal plywood as their material. In terms on fire issues, the timber building is highly prone to fire as lightweight timber has little inherent fire resistance properties due to their small sizes of timber members. If fire happens, the fire would rapidly engulf the whole building in no time as its material properties are rather weaker and vulnerable than most of the hardwood. Speaking of its material properties, plywood consists of layers or plies of thin solid wood that are glued together to form a panel. The glue shear strength inside the plywood are relatively weak in terms of sustaining loads, causing the individual plies come apart.
Relatively low fire resistance properties Leads to high vulnerability towards fire
Characteristics of plywood: ● ● ●
Weak physical properties resulting unable to resist bend and shear strength
● ● ● ● ● ●
Consists layers of wood Made up of both hardwood and softwood Uses special adhesive glue Relatively weak in terms of shear strength Easy flammable Cheap Low dense Tends to have splinters Often used in lightweight framework construction
1 2 3 4 5
Section cut of plywood: Figure 7.10 Material issues from its physical attributes
The usage of plywood in lightweight timber construction for such large scale of roof volume, its physical attributes weakened the structural of the roof.
1. 2. 3. 4. 5.
Face veneer Cross band Cross veneer Cross band Back veneer
Figure 7.11 Plywood
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7.5 Solutions of Safety and Strength of Roof For the sake to prevent the roof from collapsing, the aesthetic slanted columns will no longer be used. Instead, it will be replaced by a load bearing wall which could hold on the loads from the roof slab. Moreover, the wall will not be slanted inwards like the slanted columns but instead it will be held upright to give maximise support for the roof. Roof beams are then added to sloped and flat roofs respectively for improving the load bearing structures of the roof and the load distribution will be more even.
Aesthetic columns are removed to reduce the burden load to the roof
Wall is used to replace the roof facade for further structural support Figure 7.12 Modification of roof facade in relation to the roof structure
200mm
Characteristics of I beam: ● ● ●
Implication of I beam to the roof structure
● 100mm
Made from steel High rigidity Can withstand abundant of load Comes in different sizes
Figure 7.14 Section and dimension of I beam
Figure 7.13 Adding beams into the roof structure
The size of the I beam is taken with the consideration of the roof size
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7.5 Solutions of Safety and Strength of Roof Overall, timber construction of the roof, the timber roof slab and the roof structures should consider using heavy timber construction (solid hardwood) , which could potentially reduce the risk of catching fire as all timbers in the construction are thick and dense from its properties. Moreover, the strong and durable properties of hardwood could withstand shear and bend forces produced by the roof loads. For further fire protection, implication of fire resistant coating onto the roof slabs as well for the roof structures.
Characteristics of Merbau wood: ● ● ● ● ● ● ● ● ● ●
A type of hardwood Dark in colour Consists in a whole Highly durable High dense Weak flammable compared to plywood Expensive Low dense Do not have splinters when cut Often used in heavy timber framework construction
Figure 7.16 Section cut of Merbau wood Figure 7.15 Implication of Merbau wood into roof structure
The usage of Merbau wood has significantly enhances VIC’s structural strength due to its unique and strong properties and to be more fire resistant than plywood. Figure 7.17 Merbau wood
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7.6 Rigidity of Roof Every building needs to have a strong support framework in order to withstand overwhelming forces and loads that produced by its own. For instance, the strength of the roof trusses are yet to be strengthened as the motif of the roof structure did not provide sufficient uplift support to the roof, and the bracing of roof trusses are wide apart, causing loads to be distributed unevenly. Overly spanned roof truss bracings resulting in uneven load distribution
The span of each bracing is 2.6m, which causes the nodes to bear a tons of loads Inappropriate roof truss motif design towards the roof load
Figure 7.19 Overly extended roof truss
Insufficient bracing in the roof trusses creates overly load stressed nodes, which is caused by imbalance of shifting the loads Figure 7.18 Unsuitable roof truss motif
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7.7 Solutions of Rigidity of Roof For the modification of the roof structure, the span of the bracing should be reduced to 1 meter per node. This will enhance the rigidity of the trusses from encountering the uplift forces. Also, the roof trusses motif should be more rigid wise as in increasing of bracing and nodes for supporting the loads. With the implication of gusset plate, the trusses can be locked stationarily and provides more rigidity to the structure.
Vertical and slanted bracing gives more durability to the roof as its span is shortened
Figure 7.5 Gusset plate
Figure 7.20 Modification of roof trusses
Rigidity of the roof structure is enhanced by the modification of the motif and the implication of the gusset plate.
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7.8 Feasibility and Economy of Roof Suitability of construction method is very crucial to a building design as well as the structural part. Like in this VIC, the roof slabs are curved in shape, which technically hard to produce and it would be costly if do so. Curved roof slab usually has a higher tendency to crack as the load is mainly imposed at the centre of the curve part, which again requires more maintenance for the roof. Moreover, the curved shape has indirectly alter the shape of the roof trusses, which is also costly to manufacture and basically no reason to do so either. The installation and labour cost would be much higher as curve structure requires professionalist for handling the construction job.
Curved roof requires high cost manufacturing process
The curve flow of the roof slab and the roof trusses
Curved roof trusses are forced to produce
Figure 7.22 Curved-shape roof trusses Figure 7.21 Curved-shape roof slab
The roof slab is curved in shape. The manufacturing cost is relatively higher than normal slab as it requires extra skills no matter what type of construction used.
From the result of the curved roof slab, the roof trusses need to suit with the roof slab, Hence, curved roof trusses are required to produce for the sake of getting it to be attached together without any problem.
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7.8 Feasibility and Economy of Roof The usage of materials that consists only the roof of the VIC is way too excessive and it is unnecessary to use in such way. Like the roof cavity of both timber and concrete construction, it is far too big and did not serves any purpose other than aesthetic, causing unnecessary expenses to just show the beauty. Apart from that, those unnecessary loads will eventually transfer down to the ground, resulting of having unnecessary beams and columns which cost for another fortune for that. As for maintenance wise, concrete roofing does not have any waterproofing membrane to prevent moisture from penetrating into it. This would causes the concrete roofing to be cracked. If so, it would be costing too much money for repairing the concrete surface. In addition, the water feature right on top of the roof makes unnecessary use as it could contain water on a concrete surface, which elevates the speed of penetration of water.
Highly permeable towards moisture Resources wastage due to oversized construction
Unnecessary water feature for the concrete surface
Placement of water feature on top of roof could damage the concrete surface
Overwhelmingly usage of materials causes wastage of materials and space
Porous holes in concrete
Figure 7.23 Issues of roof structures in terms of maintenance
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7.9 Solutions of Feasibility and Economy of Roof The curved roof slabs are converted into a single plane sloped roof, which would ease the construction method and reduction of cost. In the same time, the roof trusses are transformed into a triangular shaped trusses, which also saves some money from manufacturing it. Overall, labour and construction cost would be reduced and the aesthetics are still be remained. As for maintenance, waterproofing membrane is added to the concrete roof slab and the water feature will be removed. This would save the maintenance cost of the concrete roof. Meanwhile, the whole construction of the roof has scaled down and remove the unnecessary components from the construction.
Figure 7.24 Removal of unnecessary construction from roof
Figure 7.25 Conversion of curved roof into proper sloped roof and triangular trusses
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8.0 Drawings 8.1 Original Floor Plans, Elevations and Sections 8.2 Modified Floor Plans, Elevations and Sections
9.0 Reference
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Roof truss remodified
Curved roof flattened to slanting roof
Timber frame introduced to support wooden structure
VIC after structural modifications
Decking optimised to hold itself and be user friendly
Concrete framing introduced to remove load from walls
Raft foundation as ground support
Concrete framing now supports the cantilever level instead of walls