Construction Technology and Environmental Services Flashcards
Which RIBA stage is on-site construction?
RIBA Stage 5 - Manufacturing and construction
What is buildability?
- The extent to which the design of a building facilitates ease of construction
- Early contractor involvement should be considered to benefit from their experience and expertise
- Other benefits include lower capital and life cycle costs, better quality, programming, sequencing and construction methods
Building works vs civil engineering works?
- Building works - all building types i.e. houses, offices, shops, hospitals
- Civil engineering works - drainage schemes, highways, bridges, retaining walls
What site surveys might be required for typical construction project?
- Topographic survey
- Site investigation
- Asbestos survey
- Drainage CCTV
- Utility searches
- Ecological
- Flood risk assessment
- Transport assessments
- UXO discovery
- CBR test
- Archaeological dig / excavation
- Existing condition survey
- Geotechnical survey
- Structural survey
- Condition survey (similar to struct, more on building fabric-materials)
Different types of survey?
- Desktop - looks at history of site and surrounding area to gain info
- Intrusive - site visit with investigation i.e. bore holes
Main site considerations?
- Access
- Storage and accommodation
- Temp services
- Plant
- Hoarding / fencing
- H&S
What is a CBR test?
California bearing ratio
- Tests load bearing capacity of ground, informs foundation design and construction details for other ground bearing elements (i.e. roads)
What are the objectives of a site investigation?
- Primary purpose to establish parameters for foundation and substructure design
- Assess properties and composition of soil and rock, potential ground contamination
Typical components of site investigations?
- Systematically collect and record data to help design / construction
- Adjacent site impacts
- Boundary hedges / fencing
- Existing trees, buildings
- Services location (gas, phone, elec, water, drainage)
- Ground water conditions
- Soil investigations
Tell me more about soil investigations
- Determine suitability of site for proposed works to determine adequate and economic fdn design (depends on building type too)
- Determine potential difficulties
How can location impact material choice?
Town centre not suitable for steel frame delivery
What would you do if land is contaminated?
- Contact local authority and environment agency
- Further testing required to see if soil is suitable and project can go ahead
- Hazardous material needs to be removed from site and disposed properly
Types of vegetation that can cause issues for construction project?
Invasive plants i.e. Japanese knotweed
What surveys were undertaken on your project to inform foundation choice?
i.e. Geotechnical technical survey
What are temporary works?
- Part of construction works not usually on drawings but are needed to enable permanent works to be built safely
- propping, scaffolding, formwork, excavation support
What are hoists?
Designed for vertical transportation of materials and/or people
What is shoring?
Form of temp support given to existing buildings and excavations. Prevent collapse / excessive movement
What is scaffold?
- Temp working platform erected around building/structure perimeter to provide safe working place at convenient height
- Usually required for 1.5m+ above ground
What is formwork?
Anything holding fresh in situ concrete in place until it hardens - plywood shutters, profiled decking, steel plan forms, fibreglass moulds
+ accessories i.e. wedges and clips for tightening joints and to make stripping easy
What is a tower crane and how do you erect one?
- Tall crane used to lift objects to high places. Has boom allowing longer reach and 360 deg access, longer boom = less payload capability
- Use smaller crane to erect
What would stop a tower crane from working?
Weather conditions, i.e. high strong winds
What is a borehole?
- Used for soil investigation / geothermal heating solutions
- Most suitable soil investigation method when foundations 3+m deep
- Geothermal boreholes permanent - use Earth’s natural heat to raise temp of circulated water. Closed system used to heat building above - sustainable tech
Main types of excavation?
- Open - battered excavation sides cut back to safe angle, eliminates need for temp support work, easily construct basement walls BUT extra excavation costs, needs a lot of space
- Perimeter trench - trench dug to form basement walls, supported as required. Basement walls constructed then inside excavated
- Complete excavation - firm subsoils, centre of basement excavated first, then basement slab cast while sides of excavation supported by struts
Different forms of excavation?
- Site clearance (remove vegetation and rubble)
- Strip topsoil
- Reduced level dig (reach formation level)
- Cut and fill
- Excavation for foundations
Key factors to consider when excavating?
- Soil type, moisture content
- Method
- Whether ground support systems required
- Proximity of existing buildings
- Depth required
- Underground services and drainage
What is landfill tax?
- Brought in by UK govt 1996
- Helps reduce amount of waste landfilled, promotes reuse, recycling and research into waste practices
- Applies to all waste disposed of at licensed landfill site, unless specifically exempt
- 2 rates, £3.15/tonne inert, £98.60 all other
Where would you dispose of asbestos?
Approved HSE area, fully bagged up, signage on truck etc
What is substructure?
- All structure below superstructure, i.e. below ground level inc GF bed
- Transmits building load to the ground
- Foundations, basements, retaining walls etc
What is ground heave?
- Associated with clay soil (swells when wet), causes ground to move upwards
- Soil can’t expand downwards / sideways -> exposed upper surface rises up
What are retaining walls?
- Earth retaining structure for whole / part of their height
- Purpose is to resist lateral pressure of soil with change in ground elevation
- Need to consider pressure of water and retained earth in design
Techniques available for ground improvement?
- Vibro compaction
- Vibro stone columns
- Vertical drains and vacuum consolidation
- Soil mixing
- Dynamic compaction
- Dynamic replacement
What is underpinning? Why might it be required?
- Method to repair and strengthen foundations
- Stabilises fdns undergoing settlement/movement/erosion/vibration damage
- Increase load capacity of existing fdn
- Accommodate new adjoining building, basement or deep sewer
Can you describe the substructure on one of your projects?
How have you been able to apply your knowledge?
- Producing estimates from early design stages, I have to apply my own knowledge to make reasonable assumptions of what would be most apt solution
- For example, I assumed xxx
- I undertook a cost analysis for different fdn solutions xxx
What is a foundation?
Function is to safely sustain and support superstructure, and transmit to ground the combined dead, imposed and wind loads of structure to avoid excessive settlement
Dead loads vs live loads on a structure?
- Dead - static forces, relatively constant for extended time (usually weight of materials)
- Live - dynamic forces from occupancy and intended use (inc people, furniture, appliances, moveable equipment)
Typical considerations when selecting type and size of foundations?
- Building load
- Nature and bearing capacity of ground
- Structure type
- Cost
- Construction constraints (proximity to nearby structures)
Different types of foundation?
- Strip
- Pad
- Raft
- Piled
Explain the suitability of different foundation solutions
- Strip - well-made ground with good load-bearing capacity, low load-bearing weight from structure
- Raft - poorly made ground with low load bearing capacity- spread load across entire building footprint
- Pad - well-made ground, for structures with high load-bearing points i.e. columns on steel frame
- Piled - High load-bearing, poor ground and tight sight conditions
Typical components in ext wall / foundation detail?
- Strip foundation
- Concrete block foundation wall
- Rebar reinforcement
- DPC
- Air bricks
- Suspended / GF slab
- Backfilling
- Drainage
Can you explain the foundation choice on xx project?
- i.e. built up area, soil quality, depth of potential bedrock, adjoining properties, structure type
What are pile foundations?
Pile = column (usually concrete) extending deep into ground
What are piles?
- Series of columns constructed / inserted into ground to transmit structure load to lower level of subsoil
- Used where no suitable fdn conditions near ground level / high water table, poor bearing capacity of soil
Main construction methods for piled foundations?
- Bored piles
- Driven piles
Different types of piles?
- Sheet - deep trench excavated and concrete poured insitu. Piles form basement walls / act as retaining walls
- Secant - Interlocking (male + female) piles of different diameter and hardness, solid barrier free of gaps- bored to provide combination of fdn and basement wall. Help provide waterproof structure. Used in top-down construction method / top form retaining walls
- Bored piles - auger used to excavate soil and concrete poured once complete. Variation is CFA (continuous flight augered) - piles are bored, bentonite slurry pumped in to stop core collapsing and concrete poured in. (Bentonite is environmentally harmful, not often used now)
- Pre-cast piles - brought to site and hammered into ground - high noise lvl and installation, lack of flexibility with depth
Different ways piles transfer load to the surrounding ground?
- End bearing - transfer load through low-bearing capacity soil to strong stratum (rock/dense sand)
- Friction - frictional resistance between outer surface and soil in contact
- Settlement reducing - beneath central part of raft foundation to reduce differential settlement to acceptable level
- Tension (tall chimneys, transmission towers, jetties) - resist uplifting forces that may otherwise cause structure to be extracted from hydrostatic pressure, seismic activity or overturning movement
- Laterally loaded piles - bridge piers, tall chimneys, retaining walls
How do end bearing piles transfer the load of the building?
- Bottom of the pile rests on layer of strong soil / rock
- Building load transferred through pile to strong layer
How do friction piles transfer the load of the building?
- Pile-bearing capacity by shear stresses along side of pile
- Surface of the pile works to transfer the forces to the soil
When would you use a bored pile? What’s the process involved?
- Build up areas with cohesive soils (i.e. clay) with requirement to go down 15m+
- Used where load requirement greater than CFA capabilities - larger diameter, greater depths
- Heavy duty crane with Kelly bar, concrete mixer truck and bentonite storage. Soil excavated, bentonite and casing inserted to stabilise, concrete pour with mixing truck and reinforcement cage, casing removed on completion
Bored pile vs CFA pile
- Bored piles have excavation and concrete pour done separately, crane + more substantial piling rig, larger diameter and greater depths, casing required
- CFA - concrete pour done as auger pulled out
Bored vs pre-cast (/ driven) piles
- Bored - removing spoil to form hole is carried out by boring technique. Cohesive soils for friction piles and when forming fdn close to existing buildings is limited
- Pre-cast - soft soil deposits overlie firmer stata - usually driven using drop / single action hammer
Advantages and disadvantages of driven / precast piles?
Advantages
- Can be precast to required spec
- Any size, length and shape can be made in advance
- Driven into granular soil compacts adjacent soil mass -> bearing capacity can increase as a result
- Fast, neat and clean installation
Disadvantages
- Requires heavy equipment to handle and deliver
- Increased noise and vibrations
- Costly if piles are too short
Advantages and disadvantages of bored piles?
Advantages
- Any size / shape can be formed on site
- No risk of damage during delivery and handling
- Less vibrations and noise
Disadvantages
- Significant spoils generated - need to be handled
- Reliance and coordination on multiple trades (reinforcement, piling and concrete crews/suppliers
- Don’t improve bearing capacity of ground
QS problems regarding cost control with piling?
End depth never a certainty
Whose risk is piling?
- D&B and traditional - main contractor
- Management - employer
Where would piled foundations be the best solution?
- Heavy structure, weak underlying soil
- Settlement issues common in area
- High sub-soil water table
- Load distribution of structure not uniform
- Horizontal forces present
What is a raft foundation?
- Continuous slab extending over entire footprint of building
- Spread load of superstructure over large base, reduce load per sqm of area
- Useful in load bearing capacity soils and heavy individual column loads
- Solid raft slab / beam and slab raft - ground beam system and suspended PC concrete GF
What conditions are required where you’d expect a raft foundation?
- Lightly loaded buildings, poor soils
- Heavy loads can cause raft to move sideways (as it’s not very deep)
What is a strip foundation?
- Formation in strip of linear structure, spreading weight across total ground area (supports masonry)
- Suitable for most subsoils and light structural design
- Usually reinforced
What are pad foundations?
Provide a base for reinforced concrete / steel columns. Usually constructed from reinforced concrete, square / rectangular on plan
What is a basement?
Storey below ground storey
3 types of basement construction?
- Retaining wall and raft (monolithic) - slab raft foundation, basement walls are retaining walls
- Box and cellular raft - similar to above, internal structure walls transmit and spread loads over raft, divides basement into cells
- Piled - main superstructure loads carried to basement floor by columns, transmitted to ground via pile caps, bearing piles (lots of columns going through basement)
3 methods of waterproofing a basement?
- Dense monolithic - designed and built to form watertight space using high quality reinforced concrete, needs strict control and good workmanship
- Tanking (i.e. polythene sheeting, bitumen, epoxy resin), applied internally/externally to provide continuous membrane to base slabs and walls. External better as this protects structure too
- Drained cavity - can be used for new / refurb work. Accepts small water seepage levels, collects and drains away. Inner non-load bearing wall to form cavity, floor laid to falls, moisture drains to sump, discharged direct
-> waterproofing solution often influenced by basement final use
Different grades for waterproofing basement?
- Grade 1 - some water seepage and damp is tolerable (i.e. car parks)
- Grade 2 - No water penetration acceptable
- Grade 3 - No dampness / water penetration acceptable (i.e. ventilated resi and commercial areas - homes, offices, shops)
What is superstructure?
- All internal and external structure above substructure / DPC
- Primary elements - ext walls, stairs, roof, struct walls
- Secondary elements - suspended ceilings, raised floors, balustrades, doors
- Finishes - tiles, paint, stair nosings
Describe external wall build up on one of your projects?
i.e. SFS, vapour control layer, cement particle board, 80mm insulation, aluminium facing bracket
What is the external envelope?
- Materials and components forming external shell / enclosure of a building - boundary between interior and exterior
- May be load or non-load bearing
- Typically consists of brickwork, cladding, curtain walls
What is a retained facade?
- Facade retained whilst everything behind front wall demolished
- Allowance needed for temp support and cleaning/restoration works
- Often for listed buildings
Key considerations designing external walls?
- Weather protection
- Fire resistance
- Acoustic, thermal and structural performance
- Aesthetic / appearance
- Lifespan
- Future maintenance
What is a curtain walling system?
- Typically, lightweight aluminium frame, with glazed / opaque infill panels fixed to it
Different cladding options?
Timber, aluminium, brick, slip, PCC, glazed, stone
What is a movement joint? Why are they used?
- Safely absorb expansion and contraction of construction materials
- Allow for movement associated with ground settlement, seismic activity
In brick/block cavity wall, how are window openings dealt with?
- Prevent water penetration - cavity tray (DPC crossing cavity, forming gutter leading to weephole in outer leaf) and DPC (same width as wall to stop moisture rising from the ground up external leaf of wall
- Structurally - Lintel, small beam over window / door head usually carries wall load only
What is rain-screen cladding?
- Cladding manages flow of rainwater on building
- Not necessarily waterproof itself
- Serves as screen and protection against rain for rest of building
What is rainscreen cladding used for?
- Exterior surface to break force of sideways, wind-driven water movement
- Most water bounces off/runs down, any that gets through loses momentum
- 2 key system types: drained & ventilated, pressure-equalised
How is composite metal cladding fixed to a steel frame?
Bolted, riveted, welded
What is a cladding stick system?
- Curtain wall frame (mullions) and glass/opaque panels installed and connected piece by piece
- Versatile, allows integration of other systems (sliding doors, windows)
- Less specialised, can be build by all types of fabricators
- Multiple steps to erect and seal wall, more time spent on site (70% on site vs 30% in factory), additional labour time
What is a unitised cladding system?
- Narrow width, storey-height aluminium framework units containing glazed/opaque insulated panels
- Entire system pre-assembled under factory controlled conditions
- Unitised panels craned into position- pre-positioned brackets attached to floor slab / structural frame
- Modern techniques increase speed of erection and minimise scaffolding requirement
- Unitised systems have higher direct costs (despite lower labour)
Stick vs unitised cladding system
- Stick - constructed onsite, transoms and mullions (vert and horiz respectively) made from aluminium, connected together on-site to floor slabs
- Unitised - Component parts constructed off-site - pre-fab units delivered to site and fixed straight to building
Benefits and limitations of stick and unitised
cladding systems?
Stick
- Lower cost, flexibility due to on site construction
- Longer to erect on site, requires more labour, less quality control
Unitised
- Erected on-site in 1/3 of time, better quality control, achieve more complex design
- Higher cost, risk of mistakes during fabrication affect installation on site
What are panelised systems?
- Constructed in factory (better quality control and speed of erection
- Large prefabricated panels of bay width and storey height, connected to primary structural columns / floor slabs
- Panels may be precast concrete / have structural steel framework clad with stone, metal and masonry materials
- Improved adherence to spec, quality control, rabid insulation, min. no. site sealed joints
- Less common, more expensive than unitised
What other elements are affected by the type of cladding systems used?
Frame, roof, M&E
Types of curtain walling?
- Stick - panels / glazing in between transoms
- Unitised - narrow storey height units, preassembled in factory
- Panelised - large preassembled panels connecting back to structural columns
- Structural glazing
When have you advised on the frame option?
Would be subject to structural engineer, however on similar projects I used xxx
Frame construction methods?
- Steel
- Concrete
- Timber
- Hybrid (i.e. CLT)
- Load bearing masonry
Key factors to consider when selecting structural frame type?
- Programme
- Fire protection
- Acoustic and thermal properties
- Market conditions, supply costs
- Site constraints/logistics
- End user requirements (i.e. column free space)
- Sustainability objectives
- M&E strategy
- Future expansion requirements
Components of steel frame construction?
- Beams, columns
- Purlins
- Rafters
- Eaves, eaves haunch
- Base plate
- Apex haunch
- Cladding rails
- Fixings
Steel frame advantages?
- 100% recyclable, won’t warp, crack, split, nor be vulnerable to termites / organisms
- Highest strength:weight ratio
- Dimensionally stable - won’t expand / contract depending on weather conditions
- Consistent material quality, strictly produced in accordance with national standards, no regional variations
- Non-combustible- won’t contribute to spread of fire
- Lighter- in poor soil conditions steel is preferred to concrete
- Faster to install than concrete
- Can span over long distances
- Manufactured on-site - quality benefits
- Voids within floor can run services
- Suitable for irregular shaped buildings
Steel frame disadvantages?
- May need fire protection
- Although they don’t burn, they fail (collapse) before wood component in fire
- Parts may need replacing
- Variable cost
- Experienced builders required (+ cost)
- Lower load bearing capacity vs concrete
- Don’t have same acoustic / thermal properties of concrete frame
- Prone to corrosion in coastal areas
- High embodied carbon (often procured from abroad)
- Long lead-in times - Letter of intent / materials off site may be required
Different parts of steel beam?
Flange - top and bottom of vertical steel
Web - vertical steel part of I
Root - where flange and web join
What is a steel table?
Table providing std info on steel sections in tabulated form - serial size and universal beam number
Weight of steel?
10mm3 = 0.0078kg
What is powder coating?
- Durable factory applied organic coating on metals, i.e. polyester, acrylic, epoxy, sprayed on, followed by heat curing to give film thickness 50-100microns
- Any holes/cutting to be done before coating applied
What is RHS / SHS?
Rectangular / Square Hollow Section
What is intumescent paint?
- Fire-resistant paint, passive fire protection system
- Rapidly expands in extreme temps to protect surface it’s applied to
- Prevents/minimises/delays structural fire damage
How do you apply intumescent paint?
Sprayed on in factory, touched up by hand on site
Steel connections and percentage?
Plates, bolts, welding
5% by weight
What is a portal frame? What type of buildings are they suitable for?
- Beam / rafter supported at either end by columns
- Columns typically connected to rafters (haunch/eaves connections)
- Long clear spans - large areas of open space
- Commonly used for warehouses, factories
Concrete frame advantages?
- Concrete framed buildings marginally less than steel framed buildings
- Fire protection is part of structure
- Slower - reduces cashflow early on
- Low maintenance
- Cladding easily fixed to concrete and replaced
- Good sound and heat insulation
- Insitu allows alteration at late stage of construction
- Complex geometrical shapes easier dealth with than steel
- High compressive strength
- Lower embodied carbon - can be made with by-product of coal and iron industry
Concrete frame disadvantages?
- Slower to construct, inc long curing time
- Requires formwork
- Edges may not be as square / surfaces not as flat as steel
- Steel reinforcement leads to cost issues associated with steel
- Heavier -> larger foundations
- Bulkier structure
- Doesn’t span as well as steel
- Low tensile strength
- Higher floor height required to accommodate services
- In-situ quality dependant on skill of operatives
What is formwork (in relation to concrete frames)?
- Usually temp structure to contain poured concrete and mould to required dimensions
- Stripped away after hardened and can support itself
Timber frame advantages?
- Faster construction on-site vs in situ concrete
- Relatively lightweight structure
- Aesthetically pleasing
- Sustainability benefits (assuming timber harvested responsibly)
Timber frame disadvantages?
- Skilled workmanship required for high-quality finish
- Potential for wet/dry rot, woodworm
- May require fire protection
Elements of a pitched roof?
- Rafters, battens, eaves, fascia, soffit, gutter, joist, ridge, ridge board, hanger, membrane, tiles
- Vent tiles may be used to provide natural ventilation to roof space