Construction Technology Flashcards
What are the typical components of site investigations?
Objective is to systematically collect and record data to help in design / construction
Should include anything on adjacent sites that may impact and:
Boundary hedges / fencing
Existing trees
Size, depth and location of services – gas, telephone, electricity, water, drains
Existing buildings
Ground water conditions
Soil investigations – trial pits etc
What are the main site considerations?
- Access considerations – approach roads etc
- Storage considerations
- Accommodation
- Temporary services
- Plant
- Fencing / hoarding
- Safety and health
What are the main types of excavation?
Open – use battered excavation sides cut back to a safe angle, eliminates the need for temporary support work, can easily construct basement walls and fall BUT extra excavation costs and need a lot of free site space.
Perimeter Trench Excavation – trench dug wide enough to form basement walls, this is supported as required – basement walls are constructed and then the inside of the basement is excavated.
Complete Excavation – used in firm subsoil’s. The Centre of the basement is excavated first, then the basement slab cast while the sides of the excavation are supported by struts.
Under what conditions would expect a raft foundation to be used for a substructure?
Lightly loaded buildings on poor soils
Where underground services i:e train lines dictate the use
Where it may be impractical to create individual strip or pad foundations for a large number of individual loads. In very general terms, if strip or pad foundations would cover 50% or more of the floor area, then a raft may be appropriate.
What are the different types of piling and when would you expect them to be used?
Sheet piles – a deep trench is excavated and concrete is poured in situ. The piles can be used to form basement walls or act as retaining walls.
Secant piles – interlocking piles (male and female, often different diameters and hardness) are bored to provide a combination of foundations and basement walls. They go some way in providing a waterproof structure. Secant piles are often seen when a top down construction method is used.
Bored Piles – an auger is used to excavate the soil and then concrete is poured in once complete. A variation to this is CFA (Continuous Flight Augured) where the piles are bored, Bentonite slurry is pumped in to stop the core collapsing and then concrete (which is denser than Bentonite) is poured in. Bentonite is environmentally harmful and is therefore not often used in the 21st century.
o Pre-cast piles – pre-cast piles are brought to site and hammered into the ground. Not often favoured due to the high noise levels associated with installation and the lack of flexibility in terms of depth required.
What is the difference between bored/pre-cast piles? What are the problems to the PQS regarding cost control with piling? Whose risk is the piling?
o Bored piles are defined when the process for removing the spoil to form the hole for the pile is carried out by a boring technique. They are used primarily in cohesive subsoil’s for the formation of friction piles and when forming pile foundations close to existing buildings where the allowable amount of noise and/or vibration is limited.
o Pre-cast Concrete piles are generally used where soft soil deposits overlie firmer strata. These piles are usually driven using a drop or single action hammer.
Explain how CFA piles work?
o Piling mat
o Rig is moved into position.
o Drill spins/drills to desired into the desired depth
o The concreting process is then commenced, whereby the auger is pulled out whilst the concrete is poured in.
o The reinforcement cage is then installed after the concrete has been poured – this is assisted by a hydraulic hammer to get it to the desired depth.
What is contiguous piling?
A line of non-interlinked piles in a sequence
What are grade 1 basements?
1- Some leakages and damp areas tolerable. Local drainage may be required. Used in Car parking
Plant rooms (excluding electrical equipment)
Workshops
What are grade 2 basements?
No water penetration but damp areas tolerable dependant on the intended use. Ventilation may be required to control condensation.
Used in Workshops and Plant rooms requiring drier environment than Grade 1 storage
What are grade 3 basements?
Dry environment. No water penetration. Additional ventilation, dehumidification or air conditioning appropriate to intended use. Ventilated residential and commercial areas including offices, restaurants, and leisure centres etc.
What are grade 4 basements?
Totally dry environment. Requires ventilation, dehumidification, or air conditioning appropriate to intended use. Used in Archives, Landmark buildings, and stores requiring a controlled environment
Can you tell me about what forms of modern methods of construction you are aware of.
Cross laminated timber
Modular construction
3D Printing
What is TM59 (CIBSE Guidance) 2017?
The most recent CIBSE TM59:2017 standardises the assessment method for dynamic thermal modelling of overheating at homes.
In order to comply with the CIBSE TM59 Overheating Methodology the following two criteria need to be passed for naturally ventilated rooms.
For Living Rooms, Kitchens and Bedrooms – The number of hours during which ΔT is greater than or equal to one degree (K) during the period May to September inclusive shall not be more than 3% of occupied hours.
For Bedrooms only – To guarantee comfort during the sleeping hours the operative temperature in the bedroom from 10pm to 7am shall not exceed 26°C for more than 1% of annual hours.
For rooms that are predominately mechanical ventilated a fixed temperature test must be followed.
All occupied rooms should not exceed an operative temperature of 26°C for more than 3% of the annual occupied hours.
What is a green / brown / blue roof?
A green extensive roof is planted for ecological and aesthetic purposes. Normally does not require as deep substrate as intensive. Requires less maintenance.
A green intensive roof is where typically bigger plants are grown and there is paving or decked areas. This requires deeper substrate.
A brown roof is where the planting is based on the original site had the building not been there.
A blue roof is onethatstoreswater, can include openwatersurfaces,storagewithin or beneath a porous media or modular surface or below a raiseddeckingsurface or cover.
How was the basement on your scheme going to be constructed?
- Hoarding
- Excavation - open and battened back
- Secant wall piling installed (in fill piles are bored with the first set being a lower grade of concrete and these are not loadbearing and act as seals between the loadbearing piles.)
- Concrete capping will be installed
- Drained cavity and pump sump installed
What did you use instead of knauf?
Rockwool comfort board.
Why did you recommend a transfer slab/ changed column grid for One Woolwich?
This was because there was more uninterruptible space required on the ground floor and a transfer slab would require fewer columns.
In your documents you have highlighted the advantages/ disadvantages of Steel v Concrete. Could you talk me through some of these?
Steel Advantages: - Quicker to construct - Recyclable - Strong tensile strength Disadvantages - More volatile pricing - Low compression strength - Low sound/fire resistance
Concrete Advantages - High compression strength - Good noise resistance - Good fire protection - Can mould into complex geometry Disadvantages -Slower to construct - Need for reinforcement - High embodied carbon - Not as square and flat as steel
What are the types of piling?
Secant wall piling Contiguous wall piling Displacement Replacement Sheet piling
What are the types of curtain walling?
Stick system - assembled on site with each glazed element put together from either inside or outside, depending on accessibility.
Unitised - prefabricated in panels and delivered from off-site. Better quality due to factory quality control and quicker to assemble on site.
What are the 3 ways of waterproofing a basement under BS 8102?
Type A - Tanked protection,
Type B) - Structurally Integral Protection,
Type C) - Drained Cavity
What is basement tanking (Type A)- barrier protection?
A continuous waterproof barrier is applied to the inside or outside of the basement structure. The most common form is a bituminous ‘stick-on’ plastic sheet. Whilst this is relatively inexpensive, it can lose adhesion and is easily damaged during backfilling.
Alternatively, an external membrane can be painted or sprayed onto the external surface which can be covered by a drainage board to allow provide protection from the backfill.
What are Structurally Integral Protection basements (Type B)?
The structure itself is constructed as an integral water resistant shell. Invariably built of reinforced concrete, the basement structure must be designed within certain strict parameters to ensure it is water resistant.
What is a drained cavity basement (Type C)?
Cavities are formed between the internal and external wall and floor constructions to collect and drain away water entering the basement using a sump and pump. As well as the internal drain, a perimeter drain may also be included. This runs around the external perimeter of the building just below the level of the foundation, removing water from the building’s external face.
What are the risks with building basements?
Drainage difficulties and risks of flooding due to poor weather.
Poor ground conditions and natural ground heave or settlement.
Various obstructions, such as tunnels, existing services, mining works, archeological remains, and so on.
Boundary issues that may prove to be contentious, most commonly the foundations of nearby properties (see party wall act and right of support).
Loads from adjacent buildings and roads.
Failure of waterproofing, insurance and guarantees.
What level of noise protection did you need in your internal walls for imperial street?
The minimum level of airborne sound resistance for dividing walls or floors between homes is 45dB (decibels) in new builds and 43dB in conversion projects. This level should easily cut out normal levels of speech, TV and music playing.
What was the wall build up for a traditional handlaid brick wall in Clapham Park?
Brick, wall ties, cavity, insulation board, metal studs with mineral wool between, calcium silicate (sheathing board), 2 layers of plasterboard (1 vapour check and one fire resistant)
How are brick slip systems constructed? What is the typical cost?
Brick slips (aka brick veneers) can be laid as a form of cladding. Mortar (or a form of adhesive) is laid on the wall and bricks are spread in place, separated by spacers. Alternatively, they can be installed in free standing panels (normally prefabricated) including other components such as insulation. This can then be anchored back to the structural frame.
What are the pros and cons of brick slip systems?
Advantages to using brick veneers:
They are relatively easy and quick to install.
They are not as heavy as other forms of masonry, which reduces structural loading.
Cavities behind external brick veneers can aid insulation.
They are durable and fire-resistant.
They can achieve a wide range of decorative functions
They require little maintenance.
Disadvantages include:
They are more susceptible to damage as they are thinner than conventional brick walls.
They do not contribute to structural integrity.
They can be susceptible to water damage.
Over time, the veneer will require re-pointing with new mortar.
How did UCL (part of CPD reading) achieve BREEAM outstanding using concrete frame?
Cornish Concrete could source china clay waste locally inthe Duchy and achieve 100% recycledaggregate in the structural precast. “The 50% GGBS content coupled with 100% secondary content aggregates meant each cubic metre of precast was 90% secondary sourced material,” says Moses.
What is build ability?
Buildability is a pre-construction exercise that assesses designs from the perspective of those that will manufacture, install components and carry out the construction works. This is in relation to:
- Achieving the desired final quality;
- Meeting the programme requirements;
- De-risking perceived problems, and
- Achieving optimum value for money.
What were the transfer slab grids used on One Woolwich before and after the change?
5 x 5 before which increased to 8 x 8.
Why was it more cost effective to use steel frame on the top floors?
Market tested rates were coming back slightly less than concrete (around £230/m2 compared to £270/m2), however the other benefits of steel including reduced foundations and quicker programme (reducing preliminaries) meant it was a more cost effective option.
Would using a steel frame on the top two floors affect buildability?
There would need to be more trades on site, however the sizes and spans on the top floors are very different to the below floors and if these were concrete, they would need to be constructed differently anyway.
What is a rain-screen cladding system?
A rainscreen (sometimes referred to as a ‘drained and ventilated’ or ‘pressure-equalised’ façade) is part of a double-wall construction that can be used to form the exterior walls of buildings. Typically rainscreens are formed of relatively thin, pre-fabricated panels. The rainscreen itself simply prevents significant amounts of water from penetrating into the wall construction. Thermal insulation, airtightness and structural stability are provided by the second, inner part of the wall construction.
What materials are used for rainscreen cladding?
Rainscreen cladding can be fabricated from metal sheeting such as aluminium, stainless steel, zinc, copper and so on, or can be a formed from metal composite materials (MCM) which consist of two skins of metal (such as aluminium, or ACM) bonded to either side of a lightweight core such as polyethylene (PE) or polyurethane (PUR), a profiled metal core or a mineral core. Other materials, such as terracotta, brick slips, stone, timber and so on are also used.
How did the Grenfell tower’s facade contribute to the spread of the fire in 2017?
The ACM (aluminium composite material) rainscreen cladding fitted retrospectively to the original concrete facade had a gap between which allowed a chimney effect for the fire to spread. The celotex insulation and cladding were both found to be flammable.
What is the Hackitt review?
An independent review of the building regulations related to fire safety. Dame Judith Hackitt was the CEO of the HSE.
The review looked at:
-The regulatory system around design, construction and on-going management in relation to fire safety.
-Compliance and enforcement issues.
-International regulation and experience in this area.
What did the Hackitt review find?
- the roles and responsibilities of those procuring, designing, constructing and maintaining buildings are unclear;
- the package of regulations and guidance can be ambiguous and inconsistent;
- the processes that drive compliance with building safety requirements are weak and complex with poor record keeping and change control in too many cases;
- competence across the system is patchy;
- the product testing, labelling and marketing regime is opaque and insufficient; and
- the voices of residents often goes unheard, even when safety issues are identified.
What did the Hackitt review recommend?
- a new Joint Competent Authority (JCA) comprising Local Authority Building Standards, fire and rescue authorities and the Health and Safety Executive to oversee better management of safety risks of high rise residential buildings;
- a set of rigorous and demanding roles and responsibilities for “duty holders” (i.e. building owners) to ensure a stronger focus on building safety;
- a single, more streamlined, regulatory route to oversee building standards to ensure that enforcement can and does take place where necessary;
- clearer rights and obligations for residents to maintain the fire safety, working in partnership with the duty holder;
- a package of regulations that is simpler to navigate but genuinely reflects the level of complexity of building work; and
- continuous improvement and best practice learning through membership of an international body.
How is composite metal cladding fixed to a steel frame?
Bolted
Riveted
Welded.
What is screed?
A thin top layer of material (sand and cement) laid on to a floor surface to level it out.
What are the types of screed?
- Bonded - laid to ready prepared rough, cleaned concrete base.
- Unbonded - laid to sound, clean bitumen DPM.
- Floating - laid with steel or fibre reinforcements to the insulating board which can be laid on to a suitable DPM.
