Building Structures (BLD61003)
PROJECT 1: STRUCTURAL DESIGN POST MORTEM Tutor: Mr. Rizal
Chow Wei Qi Kirrthana Nanthini Ravindran Mazen Mahmoud Radi Rahma Nuru Hussein Kattanga Sarah Wasim Yap Shu Won
331447 328102 326610 332045 331249 331392
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Building Structures (BLD61003) PROJECT 1: STRUCTURAL DESIGN POST MORTEM Chow Wei Qi Kirrthana Nanthini Ravindran Mazen Mahmoud Radi Rahma Nuru Hussein Kattanga Sarah Wasim Yap Shu Won
331447 328102 326610 332045 331249 331392
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Introduction 1.1. Introduction to Design 1.2. Floor Plans 1.3. Sections + Elevations
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Foundation + Flooring system 2.1. Former Foundation system 2.2. Former Flooring System 2.3. Former Foundation + Flooring system analysis 2.4. Current Foundation System 2.5. Current Flooring System 2.6. Current Foundation + Flooring system analysis
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Wall System
3.1 Former wall system 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5
Structural Members of the former wall system Materiality of the former wall system Former Construction system Former Structural wall system analysis Structure modification proposal
3.2 Current wall system 3.2.1 3.2.2 3.2.3 3.2.4
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Structural Members of the current wall system Materiality of the current wall system Current Construction system Current Structural wall system analysis
ROOF SYSTEM
4.1 Former roof system 4.1.1 4.1.2 4.1.3 4.1.4 4.1.5
Structural Members of the former roof system Materiality of the former roof system Former Construction system Former Structural roof system analysis Structure modification proposal
4.2 Current roof system 4.2.1 4.2.2 4.2.3 4.2.4
Structural members of the current roof system Materiality of the current roof system Current Construction system Current Structural roof system analysis
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1
Introduction to VIC Design
This building is a part of a second year architectural studio project a “Visitor Interpretive Center” (VIC) aimed for the community around a famous Malaysian Landmark, the Batu caves. The objective of this VIC is to be a rendition or a depiction of the compassionate and humane journey that a visitor experiences at the Batu Caves. The building’s irregular form and design is a result of the complexity and intricacy of the original Batu caves hence the obscurity and hardship of the form is justified as it reflects the true nature of the temple.
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1.1
Floor Plans
Fig. 1.1.1 Original Design Ground Floor Plan
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1.1
Floor Plans
Fig. 1.1.2. Original Design First Floor Plan
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1.2
Elevations and Sections
Fig. 1.2.1. Original Design Section
Fig. 1.2.2. Original West Elevation Facade
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2.1. Former Shallow Foundation system 2.1..1. Strip footing System 2.1.2. Combined RC Footing 2.2. Former Flooring System 2.2.1. PreCast Reinforced Concrete Slab 2.2.2. Hollow Core RC Slab
Foundation and Flooring system
2.3. Former Foundation + Flooring system analysis ● Safety ● Feasibility ● Economy ● Optimization
2.4. Current Shallow Foundation System 2.4.1. Isolated/ Pad Footing System 2.4.2. Materiality of Isolated Footing 2.5. Current Flooring System 2.5.1. Materiality of the Flooring System 2.5.2 Steel Beam-Joists Connection 2.6. Current Foundation + Flooring system analysis ● Safety ● Feasibility ● Economy ● Optimization
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2.1
Former Shallow Foundation System
2.1.1. Shallow Strip Footing
Fig. 2.1.1. Former Foundation Plan Layout
The Foundation system for the Former structural design incorporated a Spread foundation system, specifically a combination of “Strip footing” and “Combined RC Footing” In order to realize the building’s external form a spread footing system was appropriate for the design’s configuration as well as to maintain the clustered and disproportionate location of the walls refer to Fig. 2.1.1. Wide strip foundation systems are typically made of “Reinforced Concrete” as it can readily be placed, spread and levelled if necessary in foundation trenches as they act as the base for the load-bearing Walls.
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Former Shallow Foundation System
2.1
2.1.1 Strip Footing Strip Footing system provides a continuous strip of support to the series of “Linear Placement” of the Load bearing Walls. As shown in Fig. 2.1.3 the sizes and positions of the strip is directly related to the overall width of the wall.
DETAIL 1 Load-Bearing Wall
DETAIL 1
A B A: 300mm B: 1000mm C: 400mm
Fig. 2.1.2. Foundation Plan Layout
Fig. 2.1.3 Strip footing + Foundation Wall
The Wall load in a Strip foundation system is transmitted from its base to the soil.The depth of a strip foundation is usually equal to the the overall width of the wall.The width of the Strip foundation must be higher than the width of the supported load bearing wall (400mm).
2.1.2 Combined RC Footing For the building’s previous structural design it was most appropriate in the case of having two columns on a single spread footing to use “Combined footing” system to support the Interior columns. Fig. 2.1.4. As shown in the floor plan, the interior columns of the intersecting walls are inordinately close to each other that may lead to their footings to overlap, and as a result the former foundation plan incorporated a combined footing system.
Fig. 2.1.4 Combined footing column placement
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2.2
Former Floor System
2.2.1. PreCast Reinforced Concrete Slabs Due to the Quick and ease of assembly, low self weight and long life span, Reinforced concrete slabs were a convenient and practical structural approach to manifest irregular configuration and form of the building.
RC FLOOR SLAB
RC STRIP FOOTING
Fig. 2.1.5. The Application of the RC slab to the strip footing
The Reinforced Concrete Floor slabs are prefabricated and sized correspondingly with the dimensions of the spread foundation. The Slabs are manufactured to occupy the form of the strip footing, filling the void within the boundaries of the foundation. Typically the slabs retain their thickness in accordance with the respective strip footing height.
2.2.2. Hollow Core RC Slabs
A
A: 200mm B: 120mm
B Fig. 2.1.6 Hollow Core slab section
The most common type of Prestressed concrete members is the Hollow core RC slabs, provided with voids that results in an overall low self-weight. During the final stage of applying this floor system, the pre-cast units are covered with a layer of “concrete toppings� connecting every adjacent concrete unit via reinforcing bars or steel fabric.
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2.3 ●
Structural Analysis Safety Due to the provided bend in the building’s design, PreCast Load-bearing Walls are insufficient to uphold the load of the premise, and consequently, the application of Strip Footing system is inadequate, as strip footing can only be utilised in the case of using upright load-bearing Walls. Applying strip footing foundation, a system structurally inconvenient for buildings with irregular or unorganised forms, might lead to catastrophic failure upon the entire premise due to the weak and incompetent application of the wrong structural members.
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Feasibility The application of Prefabricated concrete floor slabs in an irregular building form is an impractical and unattainable structural approach due to the fact that precast concrete slabs are manufactured and sized in modular units and forms, therefore customising concrete panels for a design with many twists, edges and disproportionate overall shape is unachievable and unreliable.
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Economy If this structural design is to be applied it would be highly impractical and costly ambition to erect this premise with the provided structural components as they are considered incompetent and inadequate, therefore it will require plenty of additional reinforcement and treatment measures and trials that will lead to extremely high expenditure, while the possibility of successfully constructing this premise remains uncertain.
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Optimization Prefabricated structural members specifically concrete are one of the most effective, lightweight and practical means of construction, however, the implications of adopting such framework is fatal due to its inability to accommodate the architectural and organic requirements that is entitled in this building’s design.
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2.4
Current Shallow Foundation System
2.4.1. Pad Footing System
Fig. 2.2.1. Current Foundation Plan Layout
A more adequate structural approach to maintain the external form of the premise is to apply “frame” or “skeletal construction system”. Consequently, based on the new structural design, Pad footing was most applicable in a framing system due to its capability of supporting “Point Loads” such as columns or frames. The new structural design comprises of a series of “Isolated footings” and their placement is determined by the position of the to-be-built frame columns and vice versa.
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2.4
Current Shallow Foundation System
2.4.2. Materiality of Pad/ Isolated Footings Isolated footings are constructed out of concrete (usually reinforced), however it does not inform or dictate the materiality of the adjacent frame structure connected to it which in the case of this building, steel framing. DETAIL 2 C
A: 300mm B: 450mm C: 180mm
A DETAIL 2
B
Fig. 2.2.2. New structural design Section
Fig. 2.2.3 Pad footing + Steel Column
As shown in Fig. 2.2.3, the foundation system comprises of, Reinforced concrete footings placed at a depth of around 1.5m below ground level joined via “Steel Plates” to the “H-Section” steel column.
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2.5
Current Flooring System
2.5.1. Steel beam-Joists connection
DETAIL 3
DETAIL 3
Fig. 2.2.4 Steel Framing flooring System
Fig. 2.2.5 Steel Beam-Joists connection
The new flooring system comprises of shear connected H-Section Beams and joists, As shown in Fig 2.2.4 the end of the Steel beam is welded to the web of the girder and holes in the end plate are punched. The end plate is then bolted to the web of the girder. The final stage after positioning the beams and joists is installing the, Pre-cast concrete floor units.
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2.6 ●
Structural Analysis Safety In order to prevent the edifice from structural failure, Isolated pad footing joint to the building’s new skeletal frame system is a safe, durable, and efficient structural approach due to steel’s high tensile strength, beam-beam connections for the flooring system provides long-term stability for the overall premise.
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Economy Although steel structural members contain high tensile strength, they are considered to have low density and durable for construction. Although Precast concrete members are considerably expensive, they save up a great amount of time and labour.
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Feasibility Due to the skeletal framing systems wide range of application methods and construction techniques, its structural design types and possibilities seem endless and in most cases the available options are applicable, obtainable as well as efficient.
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Optimization Steel framing and post-beam system are considered as the most practical and pragmatic structural technique, due to its various joint methods and different strategies of application that makes this structural system specifically suitable for an irregular and asymmetrical design like this building.
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3 3.1 Former wall system 3.1.1 Structural Members of the former wall system ● Load bearing wall 3.1.2 Materiality of the former wall system ● Reinforced concrete 3.1.3 Former Construction system ● Load bearing wall construction (Precast）
Wall system
3.1.4 Former Structural wall system analysis ● Safety ● Feasibility ● Economy ● Optimization ● Stability ● Strength
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3.1.5 Structure modification proposal ● Steel framing proposal
3.2 Current wall system 3.2.1 Structural Members of the current wall system ● Steel columns ● Lightweight concrete panels 3.2.2 Materiality of the current wall system ● Lightweight concrete ● Steel 3.2.3 Current Construction system ● Rigid steel framing construction system 3.2.4 Current Structural wall system analysis ● Safety ● Feasibility ● Economy ● Strength ● Rigidity 17
3.1
Former Wall System
3.1.1 Structural members of the former wall system Load Bearing walls According to the design the wall system has only one structural member and that is the load bearing walls, these structural walls carry the weight of the whole roof and the first floor down to the foundation. The structure as a whole consists of 8 exterior load bearing walls and few more interior load bearing walls, the walls are prefabricated at dimensions of 5m height , 400mm thickness and with varying lengths of about 9m to 18m depending on the placement of the walls with reference to the design, then are later on assembled on site at a vertically slanting angle of 70° from the ground to fit the aesthetics purposes of the design.
Fig.3.1.1: A section of the structure showing the structural load bearing walls slanting at a 70° to the ground
3.1.2 Materials of the former wall system Reinforced concrete The walls system which is made of only load-bearing walls uses reinforced concrete, where the type of reinforcement used to precast the walls is a rebar, which is suitable for the design because it's versatile enough to allow it being bent into a shape desired. The reinforced concrete has a higher tensile strength due to the the presence of steel bars in the concrete which that made it suitable for the walls due to their load bearing function.
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3.1
Former Wall System
3.1.3 Former Construction System Solid Construction Overall the design is categorized as a solid structure it therefore uses the solid construction system, where the structural forms used in the construction are load-bearing walls that are precasted then later assembled onsite. The walls are divided into two parts in the structure, that is the exterior load bearing walls and the interior load bearing walls. This division later plays a role in the assembling of the structure on site since the method used is the cellular method where the exterior walls form the boundaries of the building and the interior walls divide the building to create separate spaces. This method allows the load to be distributed throughout the structure so as to attain stability.
Fig. 3.1.2: The ground floor plan showing the position of the exterior and the interior beating walls using the cellular method arrangement
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3.1
Former Wall System
3.1.4 Former wall structural system analysis For a structural system to be efficient it needs to be analysed using the following criteria:
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Safety As explained earlier the only structural member of this structure are the precast concrete load-bearing walls which are positioned at a slanting angle.This generally makes the structure prone to collapsing because the weight of the whole structure is held by the walls, and because its kept in a slanting position this makes it have a low balance, hence not safe.
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Feasibility This structural system is not workable because firstly there are not enough structural members to hold the whole structure in place. The support of the whole structure is relied on only few load-bearing walls, which the ones on the exterior which are expected to have a higher capacity to transmit the load to the foundation are positioned on a slanting angle making them prone to collapsing. Thus this structural system is not feasible.
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Economy The use of very heavy load-bearing walls of 760 mm thickness, without incorporating any other structural support elements in the structure is a non-cost effective decision. This is because the cost of materials used to make these walls will be very high, as well as the transportation cost of such thick precast walls to the site will be very expensive due to their extensive weight. This will automatically increase the overall construction cost making the structural system not economic at all
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Optimization Structural optimization aims to find the best structure design that minimizes the weight, cost, and/or other selected criteria for a structure subjected to given loading, while satisfying the requirements of strength, stiffness, stability, functionality, and even aesthetics. For this particular structural system it does not reach most of the criteria listed, therefore the structural system used for the structure is not optimized.
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3.1 â—?
Former Wall System Strength and Stability The thick precast load bearing walls are very strong and rigid due to the presence of steel reinforcement in them increasing their tensile strength.However due to these walls being positioned at a slanting position this makes the structure prone to collapsing thus that makes it not stable.
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3.1
Former Wall System
3.1.5 Structure modification proposal As analysed in the section before, the structural system used is not efficient and can not be achieved, therefore from the issues identified there are modifications proposed in order to make the structure efficiently workable. Problems: 1. The load bearing walls will not be able to withstand the weight of the whole structure due to their slanting position. 2. The structure lacks enough vertical members to support the roof system above because the structural members which are the load bearing walls are only at the perimeter of the building, thus leaving the centre with no vertical support. 3. The weight of the walls is substantial due to its thickness and this increase the chances of the structure to collapse, and its also not an efficient Solutions: 1. Changing the construction system from a solid construction system to a rigid frame construction system 2. To reduce the weight of the overall structure, we introduce lightweight concrete panels as the filling of the steel frames 3. To increase the support of the structure to bear the weight of the roof system, the number of columns are increased in the structure.
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3.2
Current Wall System
3.2.1 Structural Members of the current wall system The current wall system is made up of a rigid steel frame structure with lightweight concrete panel claddings in replacement of the previous solid load bearing walls. Steel Columns The primary structure of the current wall system comprises of H section steel columns. These structural components are to evenly transmit the loads from the beam to floor loadings to the foundation under compression and tension. Therefore, steel is used due to its high tensile and compressive strength. The use of steel columns also reduces the cross section size, which provides more free space to reduce bending forces. The column to beam connections make up a rigid frame to resist rotation and flexibility. The building contain 8 columns which are each 180 mm thick and 3 m long. These columns make up the slanted walls which go up to 6 m high. The columns are also fixed vertically slanted at an angle of 70°
Concrete Panels The walls are filled in with precast concrete wall panels which are engineered for both structural integrity and architectural beauty. The panels are to work in conjunction with the columns. Each concrete wall panel is insulated, which gives it the thickness of 180 mm. .
- Exterior steel columns
Fig. 3.2.1: The ground floor plan showing the new position of the interior and exterior steel columns.
- Interior steel column supporting the weight of the first floor slab
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3.2
Current Wall System
3.2.2 Materiality of Current Wall System Lightweight Concrete Lightweight concrete is based on concrete panels composing of precast gray concrete tablets, 70mm thick, using recycled PET spheres to make them lighter. This type of concrete is manufactured from natural materials and industrial by-products. The type of lightweight concrete used on this building is Autoclaved Aerated Concrete (AAC). AAC benefits a building structure by contributing towards : ● ● ● ● ● ●
Reduction in dead loads by making savings in reinforcements and the foundation. Improved thermal properties. Improved fire resistance. Saving in transporting and handling precast units on site. Reduction in formwork and propping. Good insulation.
Fig. 3.2.2: Autoclaved Aerated Concrete Panels
Steel Structural steel, a category of steel mainly used in manufacturing construction members in variety of forms, which in this case, the H-section columns. This specific type of columns are very stiff to withstand excessive compressive loads and can prevent sagging in the long run. The steel members are covered 13 mm thick with intumescent paint which contains a series of chemicals in a binder. This adds to the existing thickness of the columns (180 mm) which then provides greater fire resistance as well as maintaining the aesthetics of the structure surface. The use of structural steel contributes to : ● ● ●
The tensile and compressive strength of columns Durability Increased lifespan of structural members
Fig. 3.2.3: Steel Rigid Framing connections
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3.2 Current Wall System 3.2.3 3.2.3 Current Construction System Rigid Steel Frame Structure The current structural system is a rigid steel frame structure it is characterized by it’s rigid connections between the steel H-section columns and beams. This system offers stability when under forces such as moment, torsion and shear due to the strong connections between the structural members. Steel has a high tensile strength which makes it able to withstand the load of the structure even at a slanting position, however, it’s still limited to a certain angle of 60° from the ground. The former wall had a 70° slanting angle from the ground, as shown in Figure 3.2.4, that allowed us to maintain the initial form of the design while still being in the safe limit of the standard requirements. The slanted columns will connect to the foundation using a base plate. The base plate is welded to the slanting columns and bolted to the foundation, forming a strong connection and bringing stability to the overall slanting structure.
Fig.3.2.5: Details of the column and foundation connection
Fig.3.2.4: A section of the structure showing the structural load bearing walls slanting at a 70° to the ground
The joint connections between the columns and the beams are adjusted on site using end plate splice connections bolted at their ends with the web or the flange. These connections are able to uphold the slanted angle under loading by forming a particular resisting moment. Beams are connected to the columns to support and transfer the load applied from the roof and the floor slab above. Once the framing system is erect, the concrete panels are secured to the primary structure using a bolted connection. End plates are welded to the columns and the beams which are then bolted to the concrete for a firm connection.
25 Fig.3.2.6: Connection of the concrete panel to the column
Fig.3.2.7: Connection between columns and beams
3.2 Current Wall System 3.2.4 Added columns Because the building span is too large for the concrete floor slab above ground to solely be supported by the primary framing system, columns were introduced within the building to support the dead load of the concrete slab as well as the live load. These internal columns are connected to the beams overhead allowing the load to be transferred down through the columns to the foundation. Concrete walls are then casted in between to form the necessary spaces within the building.
Fig.3.2.8: The diagram shows the plan with the additional columns to support the first floor slab.
Fig. 3.2.9:The right diagram is a section showing the positions of the newly added columns
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3.1 Current Wall System 3.2.4 3.2.4 Current Wall Structural System Analysis ●
Safety
One of the primary safety features in this building is the use of steel rigid framing. This form of a frame structure is made up of a series of steel beams and columns, connected to one another at their ends with joints that resist forces such as moment, torsion and shear, generated due to the dead and live load. It provides more stability and strength to the overall structure.The moment resisting connections are bolted end-plate beam-to-column connections. These rigid connections in the framing system specifically contribute to preventing the slanted walls from collapsing. The steel frame structure is is highly fire resistant as it has a lower vulnerability to a destructive flame. This gives the occupants extra time to evacuate the building in times of emergency. The use of the steel framing system gives the structure a longer lifespan. This gives a sort of an assurance to occupants on reliability on the structure’s wear and tear over time. Besides that, the usage of Autoclaved Aerated Concrete (AAC) in the concrete panels adds to the safety measures taken into this building by it’s improved thermal efficiency which reduces the heating and cooling load on this building. AAC comprises of a porous structure, that provides excellent fire resistance. AAC does not release harmful chemicals and provides excellent indoor quality. It’s semi porous structure acts as a natural barrier against airborne pollutants. This also includes protection against the outdoor temperature and maintains a constant cool indoor environment for the occupants.
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3.2 Current Wall System 3.2.4 â—?
Feasibility
The use of steel framing in a building eases the erection of the structure. Rigid framing which involves the use of H-section beams and columns, gives the steel a very low density, hence the structure is light. This type of beams and columns also offer a flat ended surface perpendicular to surface of connection, hence, simplifies the assembly of the beam-to-column connection. Connections are bolted easily onto the H-section columns as both the nut side and bolt head side are left exposed and accessible. This specific type of columns and beams also enable inspection to be carried out easier as the entire surface of the structural member is exposed. Besides that, the steel parts are pre-engineered separately and then shipped out to be erected on site which speeds up the construction. Pre-engineered steel manufactured separately at the plant also prevents human error from occurring, reducing the amount of time taken to assemble the structure. Another aspect on the feasibility of the use of a steel frame on this structure is on how it does not require much maintenance due to it having a long lifespan. The steel members are very durable where the wear and tear of the steel rigid frame does not involve any complications in the long run once constructed. The Autoclaved Aerated Concrete (AAC) is precast to quicken the assembly and and avoid human errors. This also eases the transportation methods of materials to site and reduces human labour on site by having the AAC panels readily made and fixed to position as wall fillings.
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3.2 Current Wall System 3.2.4 ●
Economy
Rigid steel framing is very energy efficient. The high quality connections between the prefabricated steel parts are so exact that they are airtight and comfortable ensuring the building is completely sealed. When two pieces of a puzzle are fixed in place, the building benefits in both durability and sustainability. The steel parts have a very economical material as it has a very high resale value. This also means that steel structural members are eco-friendly as they are easily recyclable. A lot of funds can be saved when it comes to waste management. The rate of recyclability of steel is very high due to it having a long lifespan. Over the time, steel production has raised and brought the prices of steel in construction to gradually decrease, which also saves up cost on construction. The steel framing enables a shorter construction period, which means fewer interest payments. This also saves up costs on labour on site when it comes to assembly and manufacturing. Due to steel being durable, it also saves up cost on maintenance fees, repairs and replacements. If so, only spent and kept to a minimal amount. Steel structures are known to have excellent resistance to movements and can withstand high winds, snow loads and ground seismic activities, combined with it’s resistance to pests and decaying. Therefore, insurance companies lower the premiums on policies for metal framed buildings. If so, only spent and kept to a minimal amount. As for the concrete, it can harvest heat from the sun and also from lighting fixtures throughout the building and contribute towards the building’s thermal mass if needed. This saves cost on additional enhancements and provides energy efficiency. Besides that, the long lifespan of concrete makes its way to the top as one of the most economical choice for a sustainable building. They reduce the urban “heat island” effect Used concrete is recyclable and can be made into aggregates for cement and concrete mixtures. The workability of the concrete panels are very wide, which minimises solid waste.
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3.2 Current Wall System 3.2.4 â—?
Strength
The steel rigid frame structure has a very high strength-to-weight ratio. This means that the steel structural members are very strong but do not exert a heavy weight onto the foundation. Hence, it is convenient to make up the slanted wall structures with these steel members as they have a good load carrying capacity. The extensions on the inside and the outside of the H-section columns strengthen the parts of the column that is most stressed when the column is bent parallel to the “web�, the part between the connections. Besides that, unlike other hollow columns, the H-section columns used are very highly resistant to buckling. The concrete used (AAC), is relatively strong but not as strong as regular concrete, therefore only used as a wall filling This is because it is made using a finer aggregate in the concrete mix. However, it gains strength over time. It is highly resistant against weather conditions, erosions, natural disasters and if needed, only requires minimal maintenance.
Fig.3.1.6: Load transferred from roof to foundation through steel columns.
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3.2 Current Wall System 3.2.4 â—?
Rigidity
To maintain the rigidity of the steel columns, column splices are applied at specified distances to reduce the torsion forces applied onto the columns and increase the stiffness. In general, the rigid steel frame allows lower bending moments, where movements from foundations are not excessive and do not affect the wall structure. The column to beam connections are connected in a linear manner to resist rotations. The H section columns and beams are used because the H shape of the member provides more area available to where the stresses are more. The lightweight AAC panels attached to the moment resisting steel frame provides resistance against shear forces. The resulting tendency of the panel to rotate is resisted by the connections to the supporting beam. Cladding the frame with AAC panels is essential to increase the racking stiffness of the frame structure.
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4.1 Former roof system 4.1.1 Structural Members of the former roof system ● Load bearing roof 4.1.2 Materiality of the former roof system ● Reinforced Concrete ● Tempered Glass ● Aluminium 4.1.3 Former Construction system ● Solid construction system ● Glass skylight glazing system
2 2
Roof system
4.1.4 Former Structural roof system analysis ● Safety ● Feasibility ● Economy ● Optimization ● Integration ● Stability ● Strength ● Rigidity 4.1.5 Structure modification proposal ● Steel framing proposal
4.2 Current roof system 4.2.1 Structural members of the current roof system ● Steel rafter ● Steel Purlin ● Lightweight concrete tiles 4.2.2 Materiality of the current roof system ● Steel ● Lightweight Concrete Tiles ● Laminated Glass 4.2.3 Current Construction system ● Steel framing construction system 4.2.4 Current Structural wall system analysis ● Safety ● Feasibility ● Economy ● Optimization ● Integration ● Stability ● Strength 32 ● Rigidity
4.1
Former Roof System
4.1.1 Structural Members of the former roof system The former roof system is made up of load bearing roof structure with precast concrete and having skylights embedded with concrete roof.
Load Bearing Roof The former structure did not have a roof as the design intention of the visitor interpretive centre was to form a habitable first floor with slanted load bearing panels. The load from the panels are rested and the load is transferred to the slanted load bearing wall. The roof consists of 8 load bearing panels, slanting inwards ranging from an angle of 30° to 45°. These panels are prefabricated customly at different dimension of 100 mm thickness with 9.5mm diameter of rebar.
Load bearing concrete roof Skylight
Fig 4.1.1: Axonometric of former building
Skylight The roof structure also consists of fixed skylight on the concrete panels, while the pyramid skylight at the top of the roof structure, allowing the light to penetrate into the building as well as for aesthetic purposes. The skylight is made out of 10mm thickness of tempered glass and 50mm for the thickness of framing. The skylights are installed on the roof panels following the slanting angle of the roof panels which vary from 30° to 45° angles.
Fig 4.1.2 Section showing load bearing planes and fixed skylight slanted at an angle of 45° and 35°.
:
Dimensions: plan 33
4.1
Former Roof System
4.1.2 Materiality of the former roof system
Load bearing concrete roof
Fig 4.1.3: A diagram indicating the reinforced concrete part of the roof.
Reinforced Concrete The former roof was constructed using precast reinforced concrete. Reinforced concrete is embedded with steel (rebar) as the reinforcement in such a manner that the two materials act together in resisting forces. The reinforced steel absorbs the tensile, shear, and sometimes the compressive stresses in a concrete structure. Plain concrete does not easily withstand tensile and shear stresses caused by wind, earthquakes, vibrations, and other external forces and therefore plain concrete is unsuitable in most structural applications. In reinforced concrete, the tensile strength of steel and the compressive strength of concrete work together to allow the member to sustain these stresses over considerable spans. Reinforced concrete are resistant to fire, termites, fungi and water damage. It has high tensile strength and costs lesser than traditional wooden framing roof as it requires less skilled labours. It has a high tensile strength due to the presence of the steel reinforcement. However in this design, reinforced concrete roof are too heavy to be supported by the walls, causing it to be structurally unstable and prone to collapse, especially when it is subject to additional stresses.
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V
4.1
Former Roof System
Skylight
Fig 4.1.4: Skylight for former roof
Tempered Glass Tempered glass is used for the skylight of the building as it is considered as a safety glass. Tempered glass is difficult to break and even in the event of a breakage, it disintegrates into small relatively harmless globules. ● Tempered glass has higher thermal strength, and it can withstand high temperature changes of up to 250°C. ● The glass surface after heat treatment has the same resistance to surface damage as annealed glass. ● Tempered glass cannot be cut or altered. ● Weather resistant as it can withstand the effect of rain, wind and sun. It can absorb, reflect and refract light as it enables us to control and manipulate natural light into our building. ● Low thermal expansion value ● High compressive strength ● High tensile strength One problem that can also exist with tempered glass is spontaneous breakage, where the glass can break for no apparent reason. Spontaneous breakage occurs when nickel sulfide stones increase in size due to repeated heating and cooling. Aluminium Fixed skylights are used in this design which come in different shapes. Aluminium is used for the framing of glass skylight. ● Less expensive than other materials, ● Easy to maintain, available in anodized or baked-on finishes, so repainting is not needed. ● Aluminum window frames are lightweight and can be customized to fit specific configurations. ● Warp-resistant corners are mechanically joined to maintain their shape for many years However, metal is a very poor insulating material and leads to low efficiency in building. ● It has a high U-value because it conduct heat and loses cold easily. Therefore, aluminum is the least energy efficient of all the materials. ● Susceptible to corrosion if exposed to salt water and salt air. This can lead to problems with operation and overall performance.
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4.1
Former Roof System
4.1.3 Former Construction system
Fig 4.1.6: Rebars are installed before casting the concrete into desired sizes and shapes. Fig 4.1.5: Section of building showing the load bearing system
Load Bearing Roof Construction The former roof is constructed using load bearing structure. 300mm thickness of concrete panels are precasted and transported to site. Rebars are installed before casting the concrete into a desired shapes. 12mm thickness of steel bars are embedded into the concrete to increase the strength of concrete to withstand external force. A formwork is built for the intended roof which serves as a temporary support for the roof panels during installation to mimic the correct shape and then it’s later on removed from the structure. The Concrete panels are connected using loose plates, washers and bolts. However, there are gaps between the concrete planes and it if not treated well. It leads to leakage of water when raining. This problem is taken into consideration before applying new structural system.
Fig 4.1.7: Fixed skylight
Fig 4.1.8: Custom shaped pyramid skylight
Glass skylight Glazing The glass skylight is assembled to shape off site and then later installed on the site after the concrete roof is installed. All the skylights are custom made as they all come in different sizes and shapes. The skylights are directly installed into the holes cut when precasting the concrete panels using bolt and nuts. There is no waterproofing installation as this factor is not taken into consideration during design. Therefore, there will be a leakage of water when raining.
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4.1
Former Roof System
4.1.4 Former Structural roof system analysis
Fig 4.1.8: Figure shows load distribution from roof to wall
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Safety
The roof is safe in terms of materials for as concrete has fire resistance properties and will not lose its strength in high temperature. But the concrete panels are precasted in different shape, therefore the load distribution is uneven for different concrete panels. The weight of the concrete panels and skylight glass are exerted on the wall system below then to the foundation. But due to the substantial weight of former roof design is not structurally stable as the slanted load bearing wall could not support the overloading concrete planes and skylight glass. Not only that, the load of the roof are not transfer evenly into the ground but also the overall weight of the roof itself is a problem. Therefore this will result in a distorted appearance of the whole structure that will threaten the safety of the structure.
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Feasibility
The whole roof system is not feasible as in it can not work structurally this is because the overall weight the roof is too enormous and due to the wall system being placed at a slanting angle It will be hard to support the roofs weight. The other problem is that the roof structure does not have enough vertical members to support it and this can result in its to collapse thus it is not feasible
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4.1 ●
Former Roof System Economy
Structural designs are usually not taken into consideration thus this leads to poor choice of structural system. For this design only the aesthetics were put into consideration resulting in the use of really thick and expensive materials which is reinforced concrete with the thickness of 300mm. This added cost to precasting the reinforced concrete and the transportation costs to the site. Thus, this is not an economy approach.
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Optimization
The former roof structure was constructed using raw concrete. However, rather than taking a more feasible approach to apply this material to the structure, the overall roof dimensions were kept thick resulting in minimum optimization of the materials resource. Glass Glazing -Both the glass attachment and weather seal became easier to produce and offered better performance
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Integration
The integration of services in building are not taking into consideration in this design. The service runs are left exposed in the building.
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Stability
The roof’s geometry is unstable even though it has sufficient strength and rigidity. The geometry of the roof will not remain when the load is applied. The structure will eventually fall when the roof’s element are put together.
Fig 4.1.9: Diagram shows the structure may fail when the compression force acts on the roof.
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4.1 â—?
Former Roof System Strength and Rigidity
Concrete has high tensile strength and shear strength. It can withstand axial stress, shear stress, bending and torsion. But due to the geometry of roof, despite concrete being an efficient material to apply, it will still lead to structural failures. In this former roof structure design, there are no proper connections and supports applied. The roof structure will bend under compression force applied. Concrete roof as a rigid body are not connected properly while skylight glass are directly installed into the concrete roof which added additional load on the roof structure. Therefore, this may lead to collapsing of the structure.
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4.1
Former Roof System
4.1.5 Structure modification proposal The former roof has many structural failures including load bearing roof, materials selection, skylight installation. Therefore, there are some solution to overcome the problems. Problem : 1. The former roof is structurally unstable as it is not able to withstand the loads supported although materials used are high in tensile strength and high in compression strength. 2.
The roof is overloading the structure, therefore unable to be beared by the walls when external force is applied on the structure.
3.
Lack of safety consideration and unsuitable materials used for skylight.
4.
No proper connection to connect all the structure which leads to an non-rigid structure.
Solution: 1. Load bearing concrete roof changed to steel framing roof with concrete tiles finishes. 2.
Skylight glass are improved by changing tempered glass into laminated glass to increase the efficiency of the building.
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4.2
Current Roof System
The current roof system is made up of a rigid steel frame structure with concrete tiles and skylight glass in replacement of the previous solid load bearing roof.
4.2.1 Structural Members of the current roof system Steel Rafter The stell rafter is a vertical structural member that connects to the collar beam and ceiling joists. Rafters acts as load transmitting members of the roof, they transmit live load, dead load, wind load as well as other loads acting on them which eventually transfer these loads to the load bearing steel column in the new wall system then to the foundation. A series of steel rafters of dimension 305mm x 102mm x 25mm are used for the roof structure, sloping at varying angles ranging from 35° to 45°.
Fig 4.2.1.1 : Placement of rafters as the main structural members for the roof framing.
Batten Steel battens of dimension 50mm x 25mm x 2mm and 1200mm long are installed on the rafters horizontally, set at centre 600mm apart with the ability to span 3 rafters. Its is used to support and fastened the concrete tiles to prevent them from lifting.
Fig 4.2.1.2: Placement of battens above rafters.
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Steel Collar Beam Ceiling Joists
Fig 4.2.1.3 : Placement of steel collar beam and ceiling joists.
Steel Collar Beam This is a horizontal member between 2 rafters. Collar beams are designed to work in compression to keep the rafters from sagging
Ceiling Joists It is a horizontal structural member integrated in steel framing to span an open space between rafters that subsequently transfer loads to vertical members which are the load bearing columns. Ceiling joists is installed around the steel roof framing, connecting the lower point of two rafters. This framing provides a stronger stability to the structure when an external load or pressure exerted on the roof.
Concrete Roof Tiles Concrete tiles of dimension 420mm x 330mm with a top surface rise of 12mm are used as the finishes for the roof. Concrete roof tiles are provided with a double protective layer which protects them against UV-rays, damp, cold and atmospheric pollution. This protective layer mostly consists of transparent synthetic acrylate. The layer does not only offer protection, it also changes the look of the roof tile into a glossy appearance. Concrete tiles are screwed directly on the batten and is supported by the rafters.
330mm
12mm
420mm
Fig 4.2.1.4 : Dimension of concrete roof tiles
Skylight Frame The skylight itself is not a structural member but the framing is a structural part of the design where as its made of aluminium framing that is connected in different ways to make the varied shapes of the skylights.
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4.2
Current Roof System
4.2.2 Materiality of the current roof system The current roof is made out of steel and lightweight concrete tiles. The skylight glass are pre assembled and installed on site. Steel Structural steel are commonly used in most of the construction nowadays due to its composition, strength, and other physical and chemical properties. I-beams are used for constructing the roof. The rafters are bolted to the steel beam. Steel is sustainable, durable, low maintenance, versatile, and low in cost. Not only that, usage of steel framing roof required less time, lightweight and easy to construct than traditional timber construction. However, steel are weak in resisting high temperature. Therefore, intumescent coating are applied directly to increase the fire resistance of the steel. Photo 4.2.2.1: I beam used for rafters
Concrete Tiles Concrete tiles are the most economical and durable roofing material on the market. Concrete tiles are made of mixture of sand, cement and water, which are molded under heat and high pressure. The exposed surface of a tile may be finished with a paint like material. One of the biggest advantages for concrete roofing tiles is that it is incredibly strong.
Photo 4.2.2.2: Flat concrete tiles
Unlike many asphalt, clay and metal sheet roofs, concrete can withstand intense wind and rainstorms that would tear up other types of roofing materials. Just like concrete bridges and the structural elements of buildings, concrete tiles get stronger with age as they continue to harden being baked in the sun. Concrete tiles truly embrace the harsh elements. They also have additional water locks, or interlocking ribs on the edges that prevent water infiltration. They are resistant to hail, wind, and fire, making them a very safe roofing material when properly installed. Additionally, they are not as susceptible to wind uplift, unlike other types of roofs. This strength contributes to their long lifespan. Besides, less maintenance is needed and it can last as long as 50 years. Finally, concrete is relatively cheap, given its durability, especially if it is being compared to tile or slate roofing.
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4.2
Current Roof System
Fig 4.2.3: Custom Pyramid Skylight
Fig 4.2.4: Fixed skylight
Laminated glass Glass is used for the skylight of the building. Glass is a hard material that has greater impact resistance against applied load, but at the same time, it is a brittle materials as it breaks immediately when subjected to load. To address this problem, Laminated glass is used in current skylight.. Laminated panel separate two or more sheets of glass, typically annealed or heat strengthened glass, using an interlayer. The interlayer is essentially a film or an extra sheet of material which, by catching falling shards of glass, can prevent injuries to those below a shattering skylight. With sufficient thickness, size and material selection, the interlayer can also provide load-bearing capability to prevent other objects from falling through or collapse when load is applied. Laminated glass is weather resistant as it can withstand the effect of rain, wind and sun. It can absorb, reflect and refract light as it enables us to control and manipulate natural light into our building. Not only that, glass has low thermal expansion value, its an excellent insulator, high compressive strength and high tensile strength.
Aluminium framing This is used for the laminated glass and polyamide thermal break is applied on the aluminum framing. Although aluminium is very strong, light, and almost maintenance free, aluminum window frames conduct heat very rapidly, which makes metal a very poor insulating material. Therefore, thickness of 5mm of thermal breaks is applied to reduce heat flow and the U-factor. Thermal break or thermal barrier is a material of low thermal conductivity placed in an assembly to reduce or prevent the flow of thermal energy between conductive materials. When it comes to aluminium windows it is essentially to have a break in a conductive material, aluminium, with a material of low thermal conductivity stopping the conduction of temperature across the system.The polyamide sections are designed to be fitted straight into the aluminium extrusion and rolled together to ensure a strong and durable structure whilst keeping the internal section of the aluminium framework separate from the external part.
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4.2
Current Roof System
4.2.3 Current Construction system Steel Framing The current structure is a steel frame structure, consisting steel rafter, batten, collar beam and ceiling joists . These components form the skeletal steel framing for the roof. Collar beam is connected to the higher end of the rafters while ceiling joists is connected to the lower end of the rafters. The steel batten is screwed above the rafters, supporting the concrete tiles and to keep it in place. The rafters are placed with 600mm spacing in between while the battens are placed with 350mm spacing in between.
Fig 4.2.3.1: The steel framing roof structure with skylights
Fig 4.2.3.2: The connection between rafter and rectangular hollow section (rhs)
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4.2
Current Roof System
Fig 4.2.3.3: The diagram shows interlocking concrete tiles arranged in a broken bond pattern
Interlocking Concrete Tiles Flat concrete tiles are interlocked in a broken bond pattern as shown in the figure below, with the interlocks staggered. A 76mm overlap is maintained for all tiles. This aids the performance of the tiles as the broken bond configuration allows water draining into the interlock on one tile to disperse safely onto the flat surface of a tile below. Underlayment is also installed to prevent wind-driven rain and water that migrates through the joints between each concrete tiles through capillary action. Hip batten support blocks are screwed to the hip rafter between the tiling battens at the edge of downwards slope, ‘V’ type hip tiles are then installed above with screws and tile clip while leaving 5mm ventilation gap in between. Steel battens are nailed to the roof rafters to provide support for the concrete tiles at the correct set out and to prevent slippage of tiles. The correct batten spacing is necessary because it corresponds to the gauge and head lap of the roof covering being installed. The correct gauge and head lap has a direct influence on a tiles resistance to withstand the ingress of rainwater through capillary, ensuring that the roof remains watertight. It is also important aesthetically, so that the tiles on the finished roof are equally spaced.
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4.2
Current Roof System
4.2.3 Current Construction system
Fig 4.2.3.1: Fixed skylight in installed and the surrounding is sealed
Skylight In current construction for skylight, few factors including waterproofing are taken into consideration before installing. Fixed skylight is installed and attach to structure to permit sufficient adjustment to accommodate construction tolerances and other irregularities. The skylight to the roof using bolt and nuts with metal brackets. Thermal isolation and skylight underlayment is applied around the perimeter of the skylight. Pre-manufactured flashing kit is interlaced with the shingles to provide a lifetime, leak free installation, the drywall finisher is added at the corner bead around the opening and taped.
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4.2
Current Roof System
4.2.4 Current Structural roof system analysis ●
Safety
Steel framing is safer as compared to a concrete roof. It is lighter than concrete. To improve the fire resistance properties of the steel it is sprayed on fireproofing thus that includes their safety measures ,thus it can sustain greater temperatures in case of fire outbreak and, therefore, provide additional safety. Concrete does not burn when exposed to fire and it can withstand a variety of severe wind and weather conditions. The weight of the whole roof is a lot less now that makes its weight bearable and safer for as the structure won't collapse like in the initial structural system.
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Feasibility
Quality is enhanced because of off-site fabrication, and that the productivity opportunities that exist in construction can be best addressed in off-site fabrication with a reduction of actual on-site time and on-site construction. The concrete roof tiles are lighter will also speed up the installation process as less time is taken on moving materials around on site.While the weight of the tile is known to reduce installation time, the fact that several concrete roof tiles can be installed at once rather than one at a time will also ensure a erection of roofing is completed quicker, while sacrificing nothing on durability, aesthetics or performance.
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Economy
The roof steel framing is very economical compared to the concrete roof used previously due to the economic use of the steel to the structure rather than the precasted thick load bearing roof. This cuts down the production cost as well as the transportation cost. Since there is a wide range of readily made steel structural sections available so there is no need of customizing the elements Concrete tiles are comparatively light.and cheaper they also require less cost in its installation as well as its production
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Optimization
The new roof structure uses the resources effectively, initially the whole structure was made of just thick concrete making its weight unbearable and un functional, the steel framing combination with the concrete tiles are efficient use of the resources available because they still maintain the aesthetics even though the they are of lower cost and safer option
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4.2 â—?
Current Roof System Stability
The analysis tasks for the steel frame design include (1) linearly elastic frame analysis to determine resultant forces and deformation of frame members, (2) elastic stability analysis of the frame under vertical loads, (3) nonlinear frame analysis to determine the load-bearing capacity, and (4) elastic and elasto-plastic seismic frame analysis Steel is lightweight and strong and will not rot or be affected by termites. Steel Battens and tiles are far more fire resistant than timber. Steel battens, being straight edged, eliminate the warping or curvature often associated with other battens.
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Strength
Steel framing does very well under high [wind] loads because it is ductile, which means it has the ability to bend without breaking and can absorb that kind of energy Steel has the highest strength-to-weight ratio of any construction material Steel can accomplish extremely long spans in structures [and] very open-bay footprints without intermediate columns. It’s a very flexible material in terms of different ways to address design requirements
5
Conclusion
Therefore, with the improvement made to the overall structure, the new structural system is proved to be more efficient because it qualifies in all the criterias that were listed, thus its safe, feasible, economic, optimal, strong and stable .
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List of references Construction of Steel Structure Foundations, Columns, Beams, Floors. Retrieved from https://theconstructor.org/structures/construction-steel-structure-foundations-columns-beams-flo ors/18648/ 6 Reasons Why Steel Frame Structures are Safer. Retrieved from https://gensteel.com/resources/expert-insights/6-reasons-steel-buildings-are-safer Team, W. (2017). What is a Rigid Frame Building?. Retrieved from https://www.whirlwindsteel.com/blog/bid/378452/what-is-a-rigid-frame-building Precast Concrete Construction in Buildings. Retrieved from http://www.understandconstruction.com/precast-concrete-construction.html Construction of Steel Structure Foundations, Columns, Beams, Floors. Retrieved from https://theconstructor.org/structures/construction-steel-structure-foundations-columns-beams-flo ors/18648/ 6 Reasons Why Steel Frame Structures are Safer. Retrieved from https://gensteel.com/resources/expert-insights/6-reasons-steel-buildings-are-safer Team, W. What is a Rigid Frame Building?. Retrieved from https://www.whirlwindsteel.com/blog/bid/378452/what-is-a-rigid-frame-building Precast Concrete Construction in Buildings. Retrieved from http://www.understandconstruction.com/precast-concrete-construction.html What is reinforced concrete? - Quora. Retrieved from https://www.quora.com/What-is-reinforced-concrete Windows, G., Lanterns, E., Skylights?, W., managed, T., guide, A., & rooflights, M. et al. (2018). Specifiers’ Guide to Glass Skylights | Sunsquare. Retrieved from https://www.sunsquare.co.uk/blog/specifiers-guide-to-glass-skylights/ Windows, G., Lanterns, E., Skylights?, W., managed, T., guide, A., & rooflights, M. et al. (2017). Thermally Broken – The BIG Question | Sunsquare Skylights. Retrieved from https://www.sunsquare.co.uk/blog/thermally-broken-the-big-question/ Equal, R. Window Materials 101: Advantages & Disadvantages. Retrieved from https://www.ecolinewindows.ca/window-materials-advantages-disadvantages/ How To Choose Between Laminated vs. Tempered Glass | Glass.com. Retrieved from https://info.glass.com/laminated-vs-tempered-glass/ Team, W. (2017). Building Services Integration in Steel Construction. Retrieved from https://www.whirlwindsteel.com/blog/building-services-integration-in-steel-construction 50
List of references Commercial Sky Lighting for Architects | Metal Framed Structural Systems. Retrieved from https://www.wascoskylights.com/product-category/for-architects-and-builders/skylight-systems/ structural-systems/ Systems, M., Protection, T., Intumescent Paint, a., <!-- ATB3 removed the linked titles in articles --> Intumescent Paint, a., Architect Credential Info State: CEU, R., & Exam, H. et al. Intumescent Paint, Fireproofing, and Firestopping - archtoolbox.com. Retrieved from https://www.archtoolbox.com/materials-systems/thermal-moisture-protection/intumescent-paintfireproofing-and-firestopping.html Team, W. (2015). 7 Advantages of Structural Steel Frame Construction. Retrieved from https://www.whirlwindsteel.com/blog/bid/407580/7-advantages-of-structural-steel-frame-constr uction Steel Frame Structures | Steel Framing | Steel Structures. Retrieved from http://www.understandconstruction.com/steel-frame-structures.html beSteel. Retrieved from https://be-steel.eu/en/articles/technology/steel-construction-advantages Structural Steel Framing. Retrieved from https://www.buildusingsteel.org/build-using-steel/structural-steel-framing What is Structural Steel?. Retrieved from https://www.brighthubengineering.com/structural-engineering/48671-structural-steel-construction -material/ Chudley, R., & Greeno, R. Building construction handbook eleventh edition. Ching, F., & Mulville, M. European building construction illustrated.
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