Superstructure Frames Flashcards
In-situ
Built at an element’s final position, as opposed to being manufactured elsewhere.
Frame skeleton
A rectangular frame structure made of several elements joined together
Modern methods of construction (MMC)
Range of techniques involving off-site manufacture to minimise construction time on-site
Formwork
A temporary structure designed to contain fluid concrete
Beam
A structural element that supports the weight of floors, ceilings and roofs of a building and transfers the load to a vertical load bearing element
Lintel
A horizontal support used to span an opening in a wall or between two vertical supports
Column
A vertical structural member intended to transfer a compressive loadc
Composite construction
Construction involving multiple dissimilar materials - meant to increase stength, aesthetics, and environmental sustainability
Mass structure
Solid structures that rely on their own weight to resist loads (like dams)
Shell structures
Are assembled to make one piece. Mostly made from thin sheet material (making them light). Concrete architecture and cars are good examples of shell structures
Frame structures
Made from many small parts, joined together. EG stadiums, architectural designs etc
skeleton frames
Series of rectangular frames placed at right angles to each other -loads are transmitted from member to member until they are transferred to the foundations. Material type depends on site conditions, material availability, time, prefernece.
In-situ reinforced concrete frames
All the elements are constructed on-site using steel reinforcement bars and wet concrete
Why does concrete need to be reinforced with steel?
Concrete resists compressive stress but is weak in resisting tensile stress. Tensile stress is lengthening stress
Tension
Stretches or pulls apart
Compression
shortens or crushes
Shear
Pushes parts in opposite directions
Bending
Stretches and squashes at the same time
Torsion
twists
Formwork
AKA shuttering, temporary design to contain fluid concrete. Formed into required shape to support concrete until it cures and can be self-supporting. Most commonly timber
In-situ reinforced concrete frame advantages (3)
- Fire protection built into material, 2. Concrete can be moulded into any shape, 3. Cash flow advantages due to low initial costs
In-situ reinforced concrete frame disadvantages (3)
- Curing time required slows construction, 2. Potential for quality issues on-site, 3. Lots of temporary works required
When to use in-situ concrete frame?
Any framed building, but typically one-off projects and buildings with non-standard shapes
Precast reinforced concrete frames
Factory produced to EXACT specs. Erected using different methods for connecting the pieces.
Precast concrete frames advantages (4)
- Efficient use of reinforced concrete, 2. Curing periods can be accelerated in the factory, 3. Factory is a quality controlled environment 4. The system is unaffected by weather
Precast concrete frames disadvantages (3)
- Requires on site crane, 2. Maximum sizes limited by transport restrictions, 3. There could be issues with assembly in high winds
Where to use precast concrete frames?
Anywhere, but particularly suited to where there is much repetition.
Steel frames for multi-storey
one of the most common. Fabricated off-site and assembled/attached to pad foundations using bolted connections
How does expensive steel become economically competitive? (5)
- Material properties, 2. Optimum in reducing deadweight, 3. Prefabrication reduces time and labour costs, 4. High standard of dimensional accuracy, 5. Economically competitive used as a composite construction
Universal beams
Capital I shape (not that I) - thickness of web is critical to resist buckling, and depth of web important to resist bending. For columns, this is typically thicker to resist buckling
How do steel frames distribute load? (2)
- Joints rigid - allows bending forces to be transferred to the columns. 2. This reduces beam depth and saves on steel, although costs for joints increase because the joints have to be strong.
Bracing connection
Used in steel frames to join beams together. Essential that bracing is installed as the frame progresses, to avoid racking failure
Erection of structural steelwork safety points (4)
- prepping working area, and restricting access, 2.Mobile elevating work platforms (MEWPs) 3. PPE including fall arrest safety harness and lanyard, 4. Installing edge protection and fall arrest netting across entire area BEFORe construction
Steel frame - sequence of assembly (6)
- Erect 2 floor levels of steelwork, 2. Fit safety nets to underside of first-floor, 3. Install metal decking/precast concrete to first floor, 4. Fit safety nets to underside of second floor, 5. install metal decking to second floor, 6. repeat 2 to 6 until complete.
Steel frames advantages (5)
- Fast erection phase, 2. Off-site quality-controlled fabrication, 3. Standardised sections enable economies of scale for production, 4. Recycling, 5. Creates a strong structure
Steel frames disadvantages (4)
- Steel loses 50% strength in fires, 2. Need secondary fire protection finish, 3. Need to be treated to prevent corrosion from rust, 4. Repainting is required in external exposed locations EG bridges
When to use steel frames?
Almost universal in the UK.
Slim-floor construction
Fast, innovative, economical. Combines prefab slabs with built-in steel beams, integrating steel beams into the floor. Fire resistant and limited floor thickiness - an efficient use of materials combined with light elements
Composite construction
Multi storey building, takes a variety of forms and becoming more prevalent. Structural steel sections and reinforced concrete are combined. EG the steel frame is encased in concrete. EG the shard
Timber frame
Mostly used for domestic construction. Panel construction approach used, prefab offsite with light timber sections stiffened with a wood based board material. Also used in volumetric construction for temporary buildings
Timber frame advantages (4)
- Sustainable, 2. Cheap, 3. Structures can be occupied sooner as drying time is not required, 4. The lighter construction means savings on foundations
Timber frame disadvantages (4)
- Limited to six storeys, 2. Installation in high winds can be dangerous due to lighter weight and larger area of panels, 3. Timber decay with moisture can occur, 4. Design scepticism
When to use steel frames?
Repetitive modular buildings EG hotels/apartments
Portal frame
Type of steel frame, using sloping beams and columns, the rafters transfer roof loads to the stanchion, which can be bolted to the pad foundation. As there will be no internal columns, the ridge should be reinforced.
What to consider when deciding on a frame? (7)
- Site costs - financial return paramount so speed is key, 2. Steel or precast concrete - allow for maximum prefab offsite while foundation is constructed = more speed. 3. Client’s cash flow - slower forms of construction can reduce cash requirement, 4. Construction costs, 5. Pre cast or insitu? 6.Maintenance (Steel/in-situ low maintenance, precast is higher needing joint inspection) 7. Environmental concerns
