Structural Design Post Mortem Building Structure (BLD 61003)
Tutor: Mr. Rizal Group Members: 1. Charlotte Chin Ya-Le 2. Ong Kar Chun 3. Lim Zhi Kang 4. Vivien Ng Su-Qi 5. Ho Yen Liang
0326940 0326487 0330914 0326476 0326660
Content 1.
Introduction / 3 1.1 Aims & Objectives / 4 1.2 Visitor Interpretive Centre / 5
2.
Appraisal of the existing structural design / 6 2.1 Foundation 2.1.1 Foundation selection and criterias / 7 2.1.2 Type of Foundation Used / 9 2.1.3 Type of Pile Construction / 10 2.1.4 Foundation Installation and Construction detail / 11 2.1.5 Pile Layout / 12 2.1.6 Considerations / 13 2.2 Column & Beam 2.2.1 Identification of Construction Type for Beam /18 2.2.2 Fixed Beam / 20 2.2.3 Identification of Material Used / 21 2.2.4 Identification of Column and Beam Sizes / 23 2.2.5 Fire Safety / 23 2.2.6 Pergola Structure / 24 2.2.7 Slanted Columns / 26 2.2.8 First Floor Slab / 28 2.2.9 Pitched Roof Support / 29 2.2.10 Overall Columns and Beams Modification / 31 2.3 Wall 2.3.1 Existing Types of Wall / 33 2.3.2 Load Bearing Wall / 35 2.3.3 Overall Load Bearing Wall Modification / 39 2.3.4 Curtain Wall / 40 2.3.5 Overall Curtain Wall Modification / 43 2.4 Roof 2.4.1 Existing Types of Roof / 45 2.4.2 Roof Structural System / 49 2.4.3 Overall Roof Structural Modification / 55 2.4.4 Roofing Material / 56 2.4.5 Integrated Mechanical System / 60
3.
Modification of The New Structural Design / 62 3.1 Modified Plans, Sections, Elevations / 63 3.2 Loads & Forces Diagram / 72
4.
Conclusion / 77
5.
Reference / 79
2
1.0 Introduction
3
1.1 Aims and Objectives
This project aims to appraise the existing structural design of a building proposed by students. Considerations of the following structural systems in terms of safety, feasibility, economy, optimization, integration, stability, strength and rigidity must be carried out and applied to the report. By coming out with the best solution we can imply to the existing structural systems, we were to modify the design and propose a new scheme with appropriate structural system. Significant changes in drawings to be shown as the conclusion of our discussion for this report. This project largely focuses on the discussion on solutions to improve the existing structural design as well as modification to fit a good structural system.
4
1.2 Visitor Interpretive Centre
When everyone is separated and struggled to find themselves, there will always be a place called home. Situated in Sungai Buloh, this Visitor Interpretive Center brings opportunities to dividing between the past and present, allowing visitors to experience the confinements, struggles and fear of death of the lepers of 1930s. The design approach is dividing it into two, contrasting the differences. Duality and Imbalance in materiality allows users to experience both old and new, by remaining memories of the past using old facade walls and incorporating present advancement of the new structural framings and construction.
5
Appraisal of The Existing Structural Design
2.1 Foundation
6
2.1 Foundation
No proposed foundation Figure 2.1.1.1 Section of building without modification showing no foundation
No pad footing/ pile cap
Figure 2.1.1.2 Ground floor plan of building without modification showing no pad footing/ pile cap under columns
2.1.1 Foundation Selection and Criteria There was no foundation proposed in building up the Visitor Interpretive Center. A suitable foundation is used based on the consideration of subsurface soil condition, structural materials, nature of loads, number of piles used and cost of construction. The type of foundation selected is a deep foundation which is Pile Foundation. This foundation are formed by columnar elements typically made from different materials such as steel or reinforced concrete, or timber. Pile foundation is used for a layer of weak soil at the surface building has very heavy, concentrated loads increasing the effective size of a foundation and resisting horizontal loads.
7
2.1 Foundation
Raft Foundation
Pile foundation
Shallow Foundation
Deep Foundation
Foundation that is placed near the surface of the earth that transfers load of structure to a shallow depth of the ground
Transfers load to deep strata and can withstand heavier loads to transfer to the ground
Depth of Foundation
about 3 meters or the depth of foundation is less than the footing with
Greater depth of 2.5 meters, which is not suitable than shallow foundation
Support structure
Used as both slab and foundation. Using reinforced concrete slab or T-beam slab
Piles are driven and located below columns. Use pile caps to tie a group of piles together to support and transmit column loads to the piles
Soil suitability
Useful for buildings with heavy columns and low bearing capacity
Useful for stiffer soil and less compressible
Load transfer
Distribute the building pressure over a large area and it is is constantly subjected to movement
Loads are transferred to the pile/pile cap to resist vertical, lateral and uplift load
Type of Foundation
Table 2.1.1.1: Comparison between Raft Foundation & Pile Foundation
8
2.1 Foundation
Table 2.1.2.1: Types of Foundation Flowchart
2.1.2 Type of Foundation Used Friction pile foundation Friction pile transfers the load from the structure to the soil by the frictional force between the surface of the pile and the soil surrounding the pile such as sandy soil.
Properties of Friction piling: â—? â—?
Can be developed for the entire length of the pile or a certain definite length of the pile, depending on the strata of the soil. The surface area of the pile multiplied by the safe friction force developed per unit area determines the capacity of the pile.
9
2.1 Foundation
Figure 2.1.3.1: Displacement Pile
Figure 2.1.3.2: Replacement Pile
2.1.3 Types of Pile Construction â—?
Piles can be classified into two parts â—‹ Displacement Pile â—‹ Non-Displacement Pile or Replacement Pile
Displacement pile are piles which causes the soil to be displaced vertically and radially when driven to the ground. As for Replacement piles, the ground is bored and soil is removed and then the resulting hole is either filled with concrete or a pre-cast concrete pile is inserted. As the foundation used in the Visitor Interpretive Center is using friction pile foundation the construction method used is displacement pile. These piles are solid or hollow sections with a closed end driven into soil. This pile construction method is used when no restrictions on lateral displacement and ground heaving of soil.
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2.1 Foundation
Figure 2.1.4.1: Axonometric of connection of floor slab, column to pile cap (Ching, 2014)
Figure 2.1.4.2: Section of friction pile connecting pile cap and column (Ching, 2014)
2.1.4 Foundation Installation and Construction detail Installation of Friction Pile â—?
Vibratory methods of pile driving
Piles are drilled into the ground with pile drivers or pile hammers. Vibratory methods can prove to be very effective in driving piles through noncohesive granular soils. The continuous vibration of the pile loosens the soil grains adjacent to the pile making the soil almost free flowing thus significantly reducing friction along the pile shaft. â—?
if the prominent load transfer is primarily by friction along the surface of the piles, then they are friction piles. Friction piles are generally used in low to medium dense sand and where hard strata is not available at reasonable depth.
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2.1 Foundation
Figure 2.1.5.1: Pile layout plan & column detail
Figure 2.1.5.2: Pile cap Recommended Dimensions ("Pile Cap Design Assumptions & Recommendations | | The Structural World", 2018)
2.1.5 Pile Layout Pile
Pile Layout shows the location of pile and pile caps below columns Pile cap provides a thick concrete mat that rests on piles and below column that have been driven into sandy soil ground to provide a stable foundation.
Pile cap
Figure 2.1.5.3: Varieties of pile cap sizes (Ching, 2014)
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2.1 Foundation
Placement of Pile
Drilling of Pile
Installation of Pile cap
Installation of Column
Figure 2.1.6.1: DIsplacement Columns Installation Sequence ("Displacement Columns - Keller Holding GmbH", 2018)
2.1.6 Considerations Economy ●
Cost ○
○
○
Pile foundation is more economical than raft foundation as it more widely used in the construction industry in Malaysia and can be found in most construction Pile foundation is usually used to reduce cost and when as per soil condition considerations, this foundation is more desirable to transmit loads to soil strata which are not capable as of shallow foundations Driven piles are the most cost effective deep foundation solution. The wide variety of materials and shapes available for driven piles can be easily fabricated or specified for high structural strength, allowing them to be driven by modern hammers to increased working loads thus requiring fewer piles per project, resulting in substantial savings in foundation costs.
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2.1 Foundation
Figure 2.1.6.2: Comparison of pile materials ("Pile Foundations | Types of Piles | Cassions", 2018)
Timber pile
Concrete pile
Steel H Pile
Strength
Low strength
High strength
High Strength
Resistant to corrosion
Yes
No
Yes, unless protected
Condition of pile
Precast or Cast in place
Precast
Precast
TIme efficiency
Slow
Fast
Fast
Table 2.1.6.1: Comparison of pile materials
●
Material Availability ○
○ ○ ○
Driven piles are installed to accommodate compression, tension or lateral loads. Piles can be selected to meet the specific needs of the structure, site conditions and budget. Steel or reinforced concrete, or sometimes timber. Concrete pile (cast-in-place or precast) Comparison of material are as above table
Driven Pile ○
○
Driven piles often gain capacity after installation. Shaft soil strength usually increases with time after pile installation is complete to provide additional load capacity. This phenomenon, called "setup", can result in substantial foundation cost savings when considered in the design and confirmed by testing. The incorporation of setup into the foundation design results in fewer piles and/or shorter piles driven with lighter equipment. Time, labor and materials can be reduced and provide substantial cost savings to the owner.
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2.1 Foundation
Safety ●
Factor of Safety (F.O.S) ○
○
○
Figure 2.1.6.3: Axonometric of connection from column to pile cap and pile (Ching, 2014)
●
The ultimate pile capacity must exceed the applied loads by a sufficient margin or else the foundation will have unacceptable settlements. The required pile capacity also depends on the test method for verification of the pile capacity and the frequency of testing. Pile capacity is easily verified by either static or dynamic pile testing. Capacity per pile or pile length can be easily optimized to provide exactly the required capacity (including safety factors) to minimize foundation costs. Testing also eliminates the uncertainty of bearing capacity estimates based on static analysis. There is no need to be overly conservative and thus wasteful to protect against failure.
Soil condition ○
○
The soil in the site, Sungai Buloh, Selangor, Malaysia consist of tropical Sandy soil (quartzipsamments soil) which is regarded as a very fragile soil. This is due to their very low nutrients and organic matter content. Properties of quartzipsamments soil: ■ Strong sandy texture with generally low to very low clay content and is very easily eroded ■ Not very fertile in content and not productive in agriculture even when fertilized.
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2.1 Foundation
Figure 2.1.6.4: Section of building showing load path from structural members to foundation
Stability: ●
Figures of loadings (load path) Driven piles have huge superior structural strength. Driven piles almost never fail structurally during static testing or static loading. They have high lateral and bending resistance for their entire length making them ideal to resist wind, berthing and seismic loading conditions. Driven piles can tolerate moderate eccentricity in the application of superstructure loads due to their full-length strength. ●
Piles can be driven either vertically or at various angles of inclination to increase support for lateral loads. In special cases, piles can even be driven horizontally.
Static loads are loads that are always constant applied without any build up of energy, and therefore is to remain motionless. Static load tests were required for test piles to confirm that the minimum specified allowable capacity was achieved and to better estimate or establish higher allowable design capacities. Dynamic load testing was required for test piles and for a portion of the production piles to: ● monitor driving-induced stresses in the piles ● evaluate hammer efficiency and performance ● estimate the soil-resistance distribution ● evaluate the pile capacity during initial installation driving and restrikes. A waiting period of 12 to 36 hours (h) was required after pile installation before restrike tests could be performed.
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2.2 Columns & Beams
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2.2 Columns and Beams
Figure 2.2.1.1 Section of the existing building
2.2.1 Identification of Construction Type for Beam The existing floor slab on the first floor have no actual structural members below to support it. Without a proper beam support the floor slab, it will certainly collapse and will be considered as structural failure. Beam member need to be featured into the building to function properly without causing any structural failure. However, the construction method of the beam and materials need to take into considerations. In addition to that, the selection of method and material also need to be thought through to achieve a safe, stable and economical structure.
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2.2 Columns and Beams The location of the missing beams in the building. There are no structural support below the floor slab
Figure 2.2.1.2 Selection of existing building without structural beam members
Issue : Beams are important structural member of a building. However, in the original design of this building, the beam members were not shown or put into the consideration during the design stage of this building. Therefore, the building will not be structural constructable at this state without the existence of the beam and high chances of it will lead to structural failure.
Figure 2.2.1.3 Selection of building with structural beam members added into it
Solution : Beam member need to be added into the structure to support the current floor slab. One of the stable and safe method to construct it will be the adding of fixed beam in this building without increasing the cost of construction drastically.
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2.2 Columns and Beams
Column
End of the beam is fixed to the column
Figure 2.2.2.1 Fixed Beam
Fixed beam
2.2.2 Fixed Beam The fixed beam construction method is where the beam has both ends built or constructed at the wall or column which restrict it from rotation. This type of beam construction will have the integrity formed together between beams and the columns. With this, the bending moment occured at the centre will be reduced due to the bending moment and load are be transferred from the beam to its support and that make the building more stable.
Fixed Beam
Column
PIllar
Transfer of load
Figure 2.2.2.2 Direction of load being transferred through the fixed beam
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2.2 Columns and Beams 2.2.3 Identification of Material Used There are also a few selections of material for fixed beam construction. Those materials with different properties are reinforced concrete, timber and steel.
Reinforced Concrete
Strength
●
●
Economy
●
Durability
●
●
Fire Resistance
Extremely strong when the process is done correctly
Low cost as it is easy to be produced.
Excellent in durability Resist to weathering, chemical attack and abrasion
High due to the nature of material is non-flammable
Timber
●
Strong in relation to its weight
●
Low cost as it is can be fabricated easily into shapes and sizes needed.
● ●
● ●
Less durable over the long haul Prone to termites
Low Require coating to improve resistance
Steel
● ●
Extremely strong Loses strength at fire
●
Lower cost due to faster and easier construction Maintenance cost for corrosion protection needed
●
● ●
Durable Corrosion protection needed
●
Medium as the nature of the material is non-flammable Loses strength at 500 degree celsius
●
Table 2.2.3.1 Comparison between materials for fixed beam
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2.2 Columns and Beams
2.2.3 Identification of Material Used
Column Reinforcement Column
Beam Reinforcement
Beam
Figure 2.2.4.1 Connection between the reinforced concrete column and reinforced concrete fixed beam
After the comparison of all the materials mentioned in the table, the most suitable material for fixed beam in this building will be reinforced concrete due to: ●
Relatively high in strength to support the floor slab due to concrete has high compressive strength and reinforced steel has high tension strength
●
It has the lowest production cost and maintenance cost in a long haul
●
Most durable compare to other materials due to its material properties
●
Extremely high in fire resistance without require to put any coating on fire protection and can act as fire shield
●
Slow rate of heat transfer
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2.2 Columns and Beams
2.2.4 Identification of Column and Beam Sizes (i) Column Size & Span Minimum Column Size : 225mm x 225mm Maximum Column Span for this Column Size : 4m The minimum column size and span requirement for double storey buildings. Hence to have a longer span between the columns, the size of the column we have chosen is 460mm x 475mm which is bigger and is the maximum span of 9m in this building.
(iI) Beam Size Beam Size : 200mm x 400mm (width x depth) A rectangular cross sectional beam is used for the entire building. With the deeper cross sectional depth a rectangular beam could provide, the structure will be stronger and beam could span larger as compared to square beam with the same width . Furthermore, rectangular beam is easy to construct and have good connection between beam-beam and also the beam-column junctions.
2.2.5 Fire Safety The purpose of fireproofing is to maintain structural stability and integrity of structural support for a defined period of time when fire occurs to allow the occupants have sufficient amount of time to escape to ensure safety. The material of the choice for this entire structure will be concrete and being reinforced by steel bars. Concrete that was made with Portland cement, has high fire resistance compared to steel whereas steel will lose its strength at around 500 degree celsius. However, concrete can withstand up to 1100 degree celsius during a fire breakout without cracking. Therefore, concrete will be our final choice of material as it is safer, more economical and easy to be constructed.
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2.2 Columns and Beams
Figure 2.2.6.1 Plan indicating position of pergola.
Pergola structure that is not evenly distributed and not being supported.
Figure 2.2.6.2 Section showing no columns and beam are supporting pergola.
2.2.6 Pergola (i) Stability & Economy Issue : Pergola structure is not attached to any support initially as if it is levitating. Hence, the arrangement of the wooden planks are not equally spread out which lead to stability issue due to unequal load distribution. In addition, the excessive tightly packed pergola joists at the area lead to unnecessary spending cost.
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2.2 Columns and Beams Steel Joist Hanger Existing wall
Main Timber Beam is secured onto existing wall by anchor bolt.
Timber joists are connected to timber beam by using steel joist hanger to hold it in place.
Figure 2.2.6.4 Plan showing distance between joists of pergola structure.
Figure 2.2.6.3 Showing construction of pergola joist and steel joist hanger. (retrieved from Fine Home Building, 2011).
Pergola Joist
Timber beam secured onto wall by anchor.
Figure 2.2.6.5 Section showing pergola joist with beam support.
2.2.6 Pergola (i) Stability & Economy Solution : Ensure the pergola structure attach to the two existing walls to make sure it is not a free-standing pergola. Two horizontal timber beams are anchored to both sides of the walls. The timber joists of pergola are connected to the wall-mounted beam by using joist steel hangers to keep it in place on the main beams with nails. After the modification, the load of the pergola structure will be transferred to the walls through the wooden beams and down to the columns. The equal distances between pergola joists (approximately 1.9m) will have a better distribution of loads to the main timber beams which make the structure stronger. As for those excessive wooden planks located at packed area will be removed in order to save cost. 25
2.2 Columns and Beams This part has no columns or beams originally. There is only a glass curtain wall as support. Distance between columns are not evenly distributed.
Slanted columns
Figure 2.2.7.1 Plan showing second floor slab and roof without support and location of slanted columns. Extra columns and beams are added here to support the floor slab and roof structure.
Two way slab is used for this second floor slab. Cross beams are added to support the floor slabs hence load are transferred in two directions.
Figure 2.2.7.2 Plan indicating position of proposed columns and beams.
2.2.7 Slanted Columns (i) Strength & Stability Issue : This part of the building is originally a row of structural slanted columns. These columns did not undergo any calculation to ensure its stability and strength. Furthermore, the distances between columns opposite each other are not evenly distributed or aligned at both sides. Solution : The introduction of vertical columns to replace those slanted columns as main structural columns will ease the construction process that include slanted columns. Columns on the both sides of the walls are also aligned which will lead to more evenly distribution of loads. Cross beams perpendicular to main beams are added to support the second floor slab.
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2.2 Columns and Beams
Figure 2.2.7.2 Plan indicating position of proposed columns and beams.
Figure 2.2.7.1 Precedent showing horizontal support from beam to support slanted columns.
Steel I-beam as horizontal support to slanted column. Non-structural Column Structural Column
Slanted
RC Column/ Beam Steel plate I-beam support
Vertical
Figure 2.2.7.3 Section of slanted columns.
Figure 2.2.7.3 Connection of steel I-beam support to concrete beam/column
2.2.7 Slanted Columns (ii) Economy & Optimization on Aesthetic Value and Quality Issue : The existing structural slanted columns are used mainly for aesthetic purposes (refer to Figure 2.2.7). Hence, the excessive use of structural slanted columns at this part is unnecessary which result in a higher spending cost due to complicated construction method. Solution : To complement the aesthetic features of the building the structural slanted columns have been converted into non-structural columns. With the steel I-beam attached to main concrete beam, steel plates are welded on the ends of I-beam then hex bolt & nuts are used to secure it in place. Slanted column end is cut to a certain angle in order to connect to the I-beam horizontal support as frame. Loads from slanted columns are being transferred down to the vertical columns through the added frame. This optimization construction method ensures the cost of complicated construction process of slanted columns are minimized without removing the aesthetic features hence still maintaining the quality of the building.
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2.2 Columns and Beams There is no support at all at this cantilevered second floor slab.
The only two columns at this part.
Figure 2.2.8.1 Plan second floor slab that has no support
2.2.8 First Floor Slab (i) Stability and Safety Issue : First floor slab was initially cantilevered for approximately 26m without any support from first floor. Thus, roof is relying on non-supported walls. This will lead to structural failure and bring risks to the occupants inside the building.
Loads transfer of first floor slab in two ways direction.
Figure 2.2.8.2 Plan indicating columns and beams showing load transfer direction.
Solution : Columns are added on the ground floor and extended to the roof. Fixed beams connecting the columns will act as a support for the first floor slab thus transferring the loads from first floor to the columns. This proposed solution will create a much stable and safer structure for the occupants. Column Size : 460mm x 475mm Column Span : 3.5m - 5m Beam Size : 200mm x 400mm (width x depth) 28
2.2 Columns and Beams The only columns to support first floor slab and pitched roof are in different sizes and spanning too far away. No column or beam is supporting.
Figure 2.2.9.1 Plan indicating position of pitched roof.
Pitched Roof
Glass Curtain Wall
Figure 2.2.9.2 Elevation showing curtain wall and pitched roof without support.
2.2.9 Pitched Roof Support (i) Strength & Stability Issue : There are only two columns in different sizes spanning across 13.5m (Refer to Figure 2.2.9.1 highlighted in yellow). The entire pitched roof structure and first floor slab are relying on these two columns and curtain wall which is technically impossible for this structure to stand. On the opposite side, the roof is attached to the glass curtain wall that is not strong enough to support the pitched roof on its own. Roof and first floor have high possibility to collapse if this issue is not addressed.
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2.2 Columns and Beams
Figure 2.2.9.3 Plan indicating new columns and beams added.
Figure 2.2.9.4 Section indicating new support for pitched roof structure and first floor slab.
2.2.9 Pitched Roof Support (i) Strength & Stability Solution : Columns and beams are added with equal sizes and column span in between to support the second floor slab and roof structure. Columns are aligned to its opposite columns so that beams are able to connect at both ends. Stability of the whole structure will be achieved in result when loads are distributed equally on every columns. Minimum column size : 225mm x 225mm Maximum column span : 4m With the minimum requirement for column size and span, we could determine that the longer column span, the bigger the column size needed in order to achieve a strong and stable structure. Proposed column size : 460mm x 475mm Propose column span : max. 9m
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2.2 Columns and Beams 2.2.10 Overall Columns & Beam Modification Before Columns were arranged in irregular form which may cause in structural failure when beams are connected in irregular way. Furthermore, beams were not taken into consideration at the beginning.
Figure 2.2.10.1 Plans showing columns before modifications.
After Columns are equally distributed and are in equal size. Columns are aligned so that beams can be connected and loads can be transferred down to ground more efficiently.
First Floor Slab Side beams supporting first floor slab and roof
Ground Floor Slab
Cross beams supporting first floor slab
Columns from ground floor to roof
Figure 2.2.10.2 Plan showing columns and beams after modification
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2.3 Wall
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2.3 Wall
Figure 2.3.1.1: Existing Load Bearing Walls & Curtain Wall (Plan)
2.3.1 Existing Types of Wall The existing types of wall used in the project are all load bearing walls, built with reinforced concrete. Some of the walls have no load bearing purposes, as they were built to partition the interior spaces. The major issues faced when utilizing load bearing walls are strength, rigidity, stability and economics. Regarding to those issues, non load bearing walls are introduced to replace the current load bearing walls. The comparison between these two types of wall can referred to Table 2.3.1. Curtain walls are used as an outer covering of a building in which the outer walls are non-structural. Strength and stability issue can be analyzed from the lack of roof support between the roof and the curtain wall system.
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2.3 Wall
Figure 2.3.1.2: Load Bearing & Non Load Bearing Walls (Studopedia, 2014)
Load Bearing Wall Strength
●
●
Economic
●
●
Stability & Rigidity
●
●
Speed of Construction
Load is supported and transferred to the foundation through the masonry/concrete walls No structural elements, like columns or beams to support the load
Non Load Bearing Wall Column-beam structure has a combination of beams and columns to support and transfer the load
High cost spent due to the thicker wall used for supporting loads Walls must be strong enough for the purpose and are usually 9 inches or more in thickness
●
Lower stability & rigidity compared to non load bearing walls when openings are created on side walls Limited storeys construction
●
Time consuming due to erection of floor levels by levels
●
●
●
Cost reduction due to thinner walls used Perfect alignment and proper junction between the different materials required skilled work will add cost Sound and water seepage and hence need to be adequately water-proofed which adds to the cost Higher stability & rigidity of the walls due to support from columns & beams Able to add more floors to a building
Time saving due to ● Erection of columns and beams of the entire building ● Flexible interior layout and can be changed any time
Table 2.3.1: Comparison between Load Bearing Wall & Non Load Bearing Wall (CP, M., 2015)
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2.3 Wall
Load Bearing Wall Roof
Figure 2.3.2.1: Plan indicating Existing Load Bearing Wall
Figure 2.3.2.2: Roof Support by Existing Load Bearing Wall
2.3.2 Load Bearing Walls (i) Strength & Stability Issue: The load bearing wall has inadequate strength to support the load of the Butterfly roof due to the opening created on the wall. The rigidity of the wall with openings is low if there’s no other supporting columns and beams. The load bearing wall is not attached to the roof itself, therefore stability issue has been taken into account. Solution: Existing wall will be replaced with non load bearing walls with vertical columns on the side to support the roof weight. Thus, openings or voids on the wall can be created for natural ventilation to enter.
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2.3 Wall
Load Bearing Wall Roof
Figure 2.3.2.3: Plan indicating Existing Load Bearing Wall
Figure 2.3.2.4: Roof Support by Existing Load Bearing Wall with Glass
(i) Strength & Stability Issue: Insufficient strength from the load bearing wall and glass opening to support the roof weight. The opening created on top of the wall is covered by glass, this is to introduce natural lighting and also to shelter the indoor spaces. The glass opening is not properly framed to attach with the roof beams or roof trusses. Solution: Non load bearing wall will be used. Additional columns will be added on the sides and a non load bearing concrete wall can be built in between. The glass opening has to be framed with aluminium and constructed together with roof beams or a roof trusses. The comparison between aluminium windows and steel windows can referred to Table 2.3.2. Figure 2.3.2.3: Aluminium Window Frame Section (Ching, 2014)
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2.3 Wall
Figure 2.3.2.5: Aluminium Window and Steel Window Frame Section (Ching, 2014)
Aluminium Strength
● ●
Economic
● ●
Steel
Strong, but weaker in comparison with steel 3 times weaker than steel
●
Relatively low in cost and lightweight Life expectancy around 30 to 40 years excluding paint finish
●
●
●
Stronger in comparison with aluminium 3 times stronger than aluminium
Higher in cost spent as steel is a raw material Life expectancy around more than 60 years excluding paint finish
Thermal Performance
Efficient heat conductors, synthetic rubber or plastic thermal breaks required to interrupt the flow of heat from the warm to the cool side of the frame (Ching, 2014)
Lower coefficient of heat transfer, no thermal breaks needed (Ching, 2014)
Glazing
Can be Triple Glazed
Can be Single Glazed or Double Glazed
Rust Protection
Rust & Corrosion Resistant
Paint or Protective Coating required
Table 2.3.2: Comparison between Aluminium Window & Steel Window (Dardalis, N., & N., 2018)
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2.3 Wall
Load Bearing Wall Roof
Figure 2.3.2.6: Plan indicating Existing Load Bearing Wall
Figure 2.3.2.7: Roof Support by Existing Load Bearing Wall with Opening (Toilet)
(i) Strength & Stability Issue: The load of the roof is bear by load bearing walls on both sides and indoor partition walls, hence they are structurally weak to support the roof. The highlighted side wall above has no structural purpose to withstand the roof, its height is lower than the other walls to allow ventilation to pass through. Solution: Non load bearing walls will be used. Vertical columns will be added on the side to bear the load from the roof. Consequently, openings on the top part of the wall can be taken into considerations for natural ventilation purpose.
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2.3 Wall
Figure 2.3.3.1: Modification of the wall supporting the Butterfly roof
Figure 2.3.3.2: Modification of the wall supporting the pitch roof
Figure 2.3.3.3: Modification of the wall at the toilet spaces
2.3.3 Overall Load Bearing Wall Modification The major modification for load bearing walls is to replace it with non load bearing walls, as they are more economical and efficient to be constructed. The walls will be attached to the additional vertical columns on the sides. Hence, openings can be created on the wall without the concern of stability issue. The glass openings will be connecting with the steel roof truss and framed with aluminium.
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2.3 Wall
Curtain Wall
Figure 2.3.4.1: Plan indicating Existing Curtain Wall
Roof
Figure 2.3.4.2: Roof Support by Existing Curtain Wall
2.3.4 Curtain Wall (i) Stability Issue: Curtain wall is not structurally able to withstand the pitch roof, as it is an outer covering of a building in which the outer walls are non-structural. Solution: Additional vertical columns will be constructed together with the curtain walls to support the pitch roof. As a result, the curtain wall will now act as a non load bearing wall and an outer covering for the building.
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2.3 Wall
Floor Slab Curtain Wall
Figure 2.3.4.3: Reinforced Concrete Framing (Ching, 2014)
Figure 2.3.4.4: Lack of Curtain Wall Structural Framing
(ii) Strength Issue: Lack of curtain wall framing when applying the system onto the building. Therefore, the curtain wall panels have inadequate support by the structural frame.
Figure 2.3.4.5: Plan indicating Existing Non Load Bearing Wall
Solution: Reinforced concrete framing is applied as concrete floor slabs were utilized in the building. L-brackets act as anchors to secure the curtain wall to the structural frame of the building. They are cast onto the edge of the concrete floor slabs and also the surface of the columns.
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2.3 Wall
Non Load Bearing Wall Curtain Wall
Figure 2.3.4.6: Plan indicating Existing Non Load Bearing Wall
Figure 2.3.4.7: Section of the existing wall between both sides of curtain walls
(iii) Stability of the Wall // Strength & Rigidity of Curtain Wall Issue: A non load bearing wall is constructed in between curtain walls on both sides. This will affect the strength and rigidity of the curtain wall as they are non-structural members. The stability of the wall is low as it is structurally unable to be built if there’s lack of support on the sides. Solution: The additional vertical columns introduced in between the curtain walls, could be the solution to this issue. The non load bearing wall should be attached to the columns, instead of the curtain walls.
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2.3 Wall
Figure 2.3.5.1: Vertical Columns introduced together with Curtain Wall system
Mullion L-bracket
Figure 2.3.5.2: Modified non load bearing wall attaching with vertical columns
2.3.5 Overall Curtain Wall Modification The load of the pitch roof is unbearable by the strength of curtain wall itself, thus columns and beams are used to withstand the load from above. Curtain wall panels will be secured by the reinforced concrete framing. Regarding the stability issue of the non load bearing wall, it will be solved by attaching the wall to the columns on the both sides of the curtain wall system. Consequently, the load of the wall will not affect the rigidity of the curtain wall.
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2.4 Roof
44
2.4 Roof
Figure 2.4.0.1: 3D View of Overall Structure
Figure 2.4.0.2: East Elevation of Existing Structure
The existing roof consists no structural components to support at all. This leads to high possibility of roof failure without proper load transmission from top to bottom. The three different types of roofs tend to have different length of roof eaves, continually expanding out in an unconventional length further enhances the chance of it collapsing without proper support from other structural components. High consideration of materials has to be taken as well to optimize its practicality, functionality, economically and aesthetically. To make the roof structure a complete one, gutter system plays significant role to deal with the rain and protect the roof structure.
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2.4. Roof
Figure 2.4.1.1: Location of Gable Roof
2.4.1 Existing Types of Roof Gable
Roof
Figure 2.4.1.1 showcases gable roof chosen as one of the roof type in the project. Gable roof can be built in a lower cost, allows water to run off easily, well ventilated and can be used as a space for attic. However, consideration of large wind exerting an uplift force onto the bottom part of the roof must be taken.
Figure 2.4.1.2: Location of Butterfly Roof
Butterfly Roof The butterfly roof in Figure 2.4.1.2 is beneficial in collecting rainwater for other uses. It can resist wind damage due to its extremely aerodynamic configuration which helps in lowering the maintenance cost.Unfortunately, installation of the butterfly roof is much complex comparing to the other roof types inflicting higher construction cost. Also water pooling on top may be undetected due to its difficulty in observing the rooftop situation from ground level causing unwanted weight dealing onto the roof.
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2.4 Roof
Figure 2.4.1.3: Location of Flat Roof
Flat Roof Flat
roof
Usage of flat roof maybe cheap and quick to install but it has tendency of leaving water puddle on top damaging the roof materials. Additional of mechanisms for proper drainage and frequent maintenance is economically unsustainable. (i) Economy / Safety / Optimization Issue: Tendency of accumulation of water puddle on rooftop especially in tropical country with frequent rainfall is an extra load for the roof to withstand. Leakage may occur to damage roof structure leading to unstable supporting. Solution: Modification of the flat roof into a monopitch low slope roof to direct water into the gutter and downpipe. By heightening the columns on one side, it creates an angle for the roof to be placed.
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2.4 Roof
Figure 2.4.1.4: Sectional Details of Monopitch Roof (williammoseleyfan, 2015)
Figure 2.4.1.5: Sectional Details of Flat Roof (Jordan B, 2018)
Monopitch Roof
Safety
● ●
Higher stability due to better load distribution Resist resultant force more efficiently
Flat Roof
● ● ●
Economic
● ●
●
Higher construction cost Less maintenance needed thus compensate the extra cost for construction Less prone to water damage, more affordable in long term
● ●
Tendency of water puddle accumulation Water leakage to damage roof structure Lower stability
Significantly cheaper in construction cost Cost more for frequent maintenance, not suitable in tropical climate with high rain frequency
Lifespan
●
Longer lifespan over 100 years if covered in high quality natural slate
● ●
Shorter lifespan Frequent inspection needed to extend its lifespan
Thermal Insulation
●
More compact thus reduces surface exposed to exterior Mostly have eaves for shading
●
Less compact compared to monopitch roof
●
Table 2.4.1: Comparison between Monopitch Roof and Flat Roof
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2.4 Roof
Figure 2.4.2.1: Gable Roof
W-shaped beam acts as purlins to support upper roof sheath and provides ventilation space on top
Steel bearing plate resting on top of structural concrete column support
Webs provide support at points to prevent secondary shear and bending stress
Figure 2.4.2.2: Steel Belgian truss
2.4.2
Roof
Structural
Lateral bracing to withstand lateral forces such as wind
System
Gable Roof (i) Strength & Stability Issue: The roof is lump without roof supportive structure causing it to break and collapse anytime. The whole surface is rested on curtain wall without proper framing and connections to the roof structures. Solution: Installation of steel belgian truss largely enhances the strength and stability of the overall roof structure since it provides lateral support, prevents shear and bending stress. With proper roof structure to transmit load down to the columns, the roof is much firmer than the initial ones. The steel truss is also able to withstand heavy superior spanning capacities ratings, suitable for large overhangs.
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2.4 Roof
Figure 2.4.2.3: Butterfly Roof
Lateral bracing to withstand lateral forces such as wind
Figure 2.4.2.4: Steel Monopitch Truss for Butterfly Roof
Webs provide support at points to prevent secondary shear and bending stress
Butterfly Roof (i) Strength & Stability Issue: Similar problem with gable roof, there are no roof structures to support the roof. Roof eaves are not supported properly, hanging in the air, which is not practical in real life. Solution: Addition of steel monopitch roof truss which is connected to the structural concrete column using steel bearing plate. Purlins are bolted to the steel roof truss while the metal roof sheath is drilled to the purlins.
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2.4 Roof
Figure 2.4.2.5: Flat Roof
Figure 2.4.2.6: Steel Monopitch truss for Monopitch Roof
Monopitch Roof (modified flat roof mentioned in Figure 2.4.1.3) (i) Strength & Stability Issue: Modified monopitch roof requires structural support as well Solution: Addition of steel monopitch roof truss for structural support
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2.4 Roof
Overly extended roof eave with no structural support
Figure 2.4.2.7: Non-supported Extended Roof Eaves
Figure 2.4.2.8: Butterfly Roof Diagonal Bracing
Figure 2.4.2.9: Gable Roof Diagonal Bracing
Gable Roof & Butterfly Roof (ii) Safety Issue: Large extension of protruded roof overhangs with no support has possibilities of collapsing and being blown up by uplift force of large winds. The roof eaves exceeded 2 feet, which is an unstable structural integrity. Solution: Insertion of haunch or diagonal bracing, connected from columns or beams to the overhangs. This can help in withstanding lateral forces of wind, acts as a safety measurement to fix the trusses to the overall structure that counters uplift wind force and at the same time to transmit loads from the overhang to the overall structure.
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2.4 Roof
Roof Truss
Roof Truss Roof Rafter
Roof Rafter
Figure 2.4.2.10: Comparison between Quantity of Roof Truss and Rafter Framing Needed
(iii) Economy Issue: Usage of conventional rafter framing requires higher quantity of structural components. This results in higher construction cost and is less environmental friendly. Solution: Usage of steel roof truss as structural components lowers the quantity needed to support the roof due its high strength and rigidity characteristics inherent from triangular shape. Installation of steel roof truss cuts down construction cost and time since there are fewer quantity needed to be installed.
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2.4 Roof Roof Truss
Strength & Stability
●
●
● ●
Economic
●
●
●
Rafter Framing
Series of triangles inside help distributing weight load of roof Reduces needs for interior load bearing walls, to allow for a more open floor plan High strength-to-weight ratio Able to withstand superior spanning capacities ratings which is suitable for large overhangs
●
Able to support roof with lower amount of quantity needed Material saving, utilizing smaller amount of components producing less waste Less installation time thus less construction cost
●
●
●
●
Cannot span as much as a roof truss does, lower strength compared to roof truss Larger sizes needed to achieve similar strength of a truss
Requires large numbers of rafters, costs more Non environmental friendly, utilizing large amount of lumber producing certain amount of waste Longer installation time which eats up significant construction cost
Installation Speed
●
Prefabricated at factory and assemble on-site, less installation time needed
● ●
Lead time However longer installation time needed since it has to be cut into sizes before installing
Disadvantages
●
Requires some amount of time to prepare since it requires engineering and drawings.
●
Flexible to change any single components but definitely weaker in terms of stability compared to truss provided with no diagonal bracing to withstand lateral force
Table 2.4.2: Comparison between Roof Truss and Rafter Framing
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2.4 Roof
Figure 2.4.3.1: Modification of Gable Roof and Flat roof
Figure 2.4.3.2: Modification of Butterfly Roof
2.4.3
Overall
Roof
Structural
Modification
The addition of the 2 types of roof trusses namely belgian truss and monopitch truss into three different types of roof is to provide practical structural support that holds the roof in place, to withstand lateral and uplift forces from wind. The selection of trusses helps in achieving highest stability for the roof with the most economical cost, at the same time to contemplate safety issues. Not to forget, insertion of diagonal bracing for the overly extended roof eaves are important in making the overall roof structure a more stable one, since considerations of occupants safety is the priority for every structures built.
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2.4 Roof
Figure 2.4.4.1: Overall Roof in Elevation and Roof Plan
Webs provide support at points to prevent secondary shear and bending stress
Figure 2.4.4.2: Installation of Galvanized Metal Sheet on Roof Trusses
2.4.4
Roofing
Material
Economy Issue: Concrete roofing is a heavy material with porous properties, without proper maintenance of the roof, water seeping will occur, damaging the entire roof structure which is very not economic. Solution: Replacing concrete roofing with galvanized metal roof sheets. Galvanized metal sheets are light in weight and can be installed in any sloped roof with ease. Also the galvanized metal sheets are fire-resistant and resistant to pest which is safe to be used in the most economical way since it is one of the cheapest roof materials found in the market. It is ease to be installed thus cutting down the construction cost while having a long life span with low maintenance required.
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2.4 Roof
Figure 2.4.4.3: Galvanized Metal Roof Sheet (Clipartxtras, 2006)
Figure 2.4.4.4: Concrete roofing with metal decking (Ganesh, 2006)
Galvanized Metal Roof
Strength & Stability
●
●
Economic
● ●
●
Concrete Roof
Not as strong as concrete but manageable in all types of weather resistant. Strong and ductile
●
Strong in compressive strength but lack in tensile strength thus must be reinforced by steel rebar
Cheaper and lighter Can be installed in any sloped roof with ease thus less construction cost Recycled material which is cheap and universal
●
Heavy concrete requires high maintenance Higher installation cost since it is very time consuming during on-site pouring of concrete Extra cost for steel rebar
●
● Safety
● ● ●
Fire resistant, non combustible Resistant to pest Light thus low possibility of collapsing
● ● ●
Fire resistant, non combustible Susceptible to pest Heavy thus high possibility of causing injuries when collapse
Sustainability
● ●
Recyclable Can be adapted many times with no structural integrity
●
Concrete’s compounds are natural, environmental friendly
Weakness
●
Prone to expansion or contraction. Oil canning leading to a roof without air-tight seal
●
Porous properties of concrete, when exposed to rainwater will cause water seeping into the roof structures
●
Table 2.4.4.1: Comparison between Galvanized Metal Roof and Concrete Roof
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2.4 Roof
Figure 2.4.4.5: Position of Roof Trusses
Optimization Issue: Selection of materials for the proposed roof trusses needed to be considered. Types of material will greatly affect the life-span, cost, construction speed and strength of the roof structures. Solution: With consideration of all aspects, we concluded the selection of steel as the roof trusses material is the most suitable among the other choices. The selection criteria for the material is to balance the quality, cost needed, level of blending in with the building, strength and sustainability. Table 2.4.4.2 will summarize the reasons of selecting steel over timber as the material for the roof trusses.
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2.4 Roof
Figure 2.4.4.6: Steel Roof Truss and Timber Roof Truss (Ching, 2014)
Steel Roof Truss
Strength
● ●
Economic
● ● ●
Safety
●
● ● ●
Timber Roof Truss
Light-weight but can span larger than timber roof truss Higher strength-to-weight ratio
●
Could not span as much as steel roof truss
Either cost 10% higher or lower than timber roof truss Last longer Lower maintenance cost compensating its construction cost
● ●
Cheaper Does not required skilled labour Shorter life span Higher maintenance cost
Non-combustible but structural failure may occur at certain fire temperature Resistant to pest Weather resistant Affected by temperature fluctuation
●
● ●
● ● ●
Sustainability
● ● ●
Conclusion
Recyclable Can be adapted many times with no structural integrity Lower energy efficiency, lower thermal mass
More suitable as it blends in well with the steel columns, higher strength, economically friendly in a long run, safe and long-lasting.
● ●
Burns slowly during fire, have different layers to protect and insulate wood layers below Susceptible to pest and rot causing structural failure More likely to be damaged by weather Warp and bow over time causing structural damage
Non-environmental friendly Higher energy efficiency due to it having good thermal properties with high thermal mass
Although possesses several beneficial characteristics, steel roof truss can be more suitable in terms of long-run usage and the building’s function.
Table 2.4.4.1: Comparison between Galvanized Metal Roof and Concrete Roof
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2.4 Roof
Figure 2.4.5.1: Existing roof plan without gutter system
2.4.5 Integrated Mechanical System A good design will integrate the building function in the structural of the building. To protect the roof structure from the rain, the integration of roof gutter and downspout system will be added into the building.
Issue : In this existing building, the roof does not have a gutter and downspout system that will channel down the rain water to the storm sewer system or dry well effectively. Solution : Roof gutter system also known as roof drainage system need to be included in the existing roof structure as rainfall intensity in Malaysia is fairly high. To prevent rainwater accumulate or flowing down causes ground erosion, gutter system acts as a passage to channel the water down to the dry well or storm sewer system through downspouts.
Figure 2.4.5.2: Location of gutter proposed on roof plan
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2.4 Roof
Gutter will be placed at the lowest point of the roof
Galvanized Metal Roof
Insulation
Purlin Plywood Deck Gutter Steel Roof Truss
Gutter Downspout
Figure 2.4.5.3: Call out Sectional Details of Roof to Show Gutter
Mechanical services such as piping, conduit, and ductwork may pass through the web spaces
Downspout is connected to the gutter and will act as a channel to direct the collected rainwater from the gutter into storm sewer system. The typical shape of the downspouts are rectangular and will be the same material as the gutter to prevent destructive galvanic actions.
Figure 2.4.5.4: Mechanical Systems integrated to Roof Truss
Figure 2.4.5.5: Precedent Study of Ductwork System on Roof Truss
Besides integrating the gutter system into the roof structure, there are also different components can be integrated into the web spaces of the roof. For example, ductwork, piping and also conduit.
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3.0 Modification
62
3.2 Loads and Forces Diagram
Figure 3.2.1 Loads and Forces Diagram of Overall Structure
Overall forces of load distributed throughout the structure. The modified structure mainly consists of non-load bearing structure in which the load from the roof is transferred to the columns and beams. Columns transfer load from the beams and slabs down to the ground where upthrust reaction from the foundation cancels off each other to attain stability and prevents settling.
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3.2 Loads and Forces Diagram
Horizontal Steel I-Beam to hold slanted columns.
Slanted Column
Vertical Structural Column
Figure showing load path at slanted columns area. Vertical columns are used as structural columns therefore, no force or load is transferred at slanted column. Weight or load that acts on slanted columns are transferred to the horizontal i-beam then down to columns and foundation.The horizontal i-beam acts as a framing that not only holds slanted column in place but also helps to transfer its loads.
Figure 3.2.2 Loads and Forces Diagram of Slanted Columns Part.
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3.2 Loads and Forces Diagram
Figure 3.2.3 Loads and Forces Diagram of Columns within Curtain Wall
Figure above shows how the load is transferred from roof to the foundation. Curtain wall does not act as a structural support. Loads from roof and first floor slab are transferred to the beams instead of curtain wall framing , down to the columns and down to the pile foundations.
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3.2 Loads and Forces Diagram
Figure 3.2.4 Loads and Forces Diagram of Non- Load bearing Wall
Figure above shows that the structure is supported by columns and beams where walls are not load bearing. More openings are able to be created within the walls. Loads from the roof are transferred to the truss horizontally then to the beam and vertically down to the column, foundation and ground.
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3.2 Loads and Forces Diagram
Figure 3.2.5 Loads and Forces Diagram of Steel Roof Truss
Every member of a truss is a 2 force member, where the members are organized so that the assemblage as a whole behaves as a single object. The truss is strong in both compressive strength and tensile strength. The forces can be seen evenly distributed from the truss to beam, the shear from the compression can be transferred to the tension flanges. The end of every members are connected to the nodes which every external forces and reactions act on it reverting the forces into only tensile or compressive.
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4.0 Conclusion
77
4.0 Conclusion
From this project, we have learnt how to apply structural theory in designing structural elements, appraise the technical standards as well as structural design codes and loading codes to be applied to building design. Through research and analysis on appropriate structural members and materials used, we learnt to incorporate precise construction methods and terminologies used in the construction industry. We gained knowledge on finding the suitable construction joints and connections in building up the structural members.
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5.0 Reference
79
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