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 – These are interlocking sheets (normally steel) that are driven into the ground and are 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 retaining walls. They can be used to provide a waterproof structure.
- Rotary Bored Piles (Replacement) – an auger is used to excavate the soil and then concrete is poured in once complete. The reinforced steel is then inserted. CFA (Continuous Flight Augured) is where the boring and pouring takes place simultaneously. Support casing can also be used.
- Pre-cast piles (Displacement) – 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.
- Contiguous piles - A row of successive cast-in-situ concrete piles constructed with unconnected small gaps formed using CFA or rotary bored piles. Quick and easy method for retaining walls.
What is the difference between Bored and Pre-cast piles?
Pre-cast piles are hammered into the ground. Advantages:
• Piles of any size, length and shape can be made in advance and used at the site. As a result, the progress of the work will be rapid.
• A pile driven into granular soil compacts the adjacent soil mass and as a result the bearing capacity of the pile is increased.
Bored uses a rotary auger to remove the soil and then replace it with concrete pour in-situ followed by steel reinforcement. Advantages:
• Low noise/impact when working near other buildings
• CFA version is quickest version
What are the typical components of site investigations?
Objective is to systematically collect and record data to help in design / construction. Should include:
• 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 grade 1 basements?
Some leakages and damp areas tolerable. Local drainage may be required. Used in Car parking Plant rooms (excluding electrical equipment)
What are grade 2 basements?
No water penetration but damp areas tolerable dependent 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
What are British Standards?
- Publications issued by the British Standards Institution – (prefixed with ‘BS’)
- They give recommended min standards for materials, components, design and construction practices
- Manufacturers have to pay to have their products and manufacturing processes tested in order to receive BSI Kitemark
What are international standards?
- Prepared by the International Organisation for Standardisation – (prefixed ‘ISO’ or ‘EN’ or both)
- Compatible with and complement BS’s using noted with ‘EN’
- In June 2018, it was announced that the UK would apply to stay in the European Standards system for industry products and services after Brexit.
Name some forms of modern construction methods?
- Cross Laminated Timber (CLT) – Pre-fabricated boards made of dried timber glued at 90 degrees to the previous layer which reduces movement.
o High strength to weight ratio
o Acoustic performance and airtightness performance - Modular construction – Prefabricated units
o Speed of supply and installation
o Reduced cost (labour, waste, economies of scale)
o Quality control
o Improved safety
o Reduced storage requirements - 3D Printing – Computer-controlled sequential layering of materials to create complex three-dimensional shapes
What are the main site considerations?
- Access – approach roads etc
- Storage
- Accommodation
- Temporary services
- Plant
- Site security
- Safety and health
What is TM59 (CIBSE Guidance) 2017?
• Standardised assessment method for dynamic thermal modelling of overheating in homes.
To comply with the CIBSE TM59 Overheating Methodology there are criteria thresholds for mechanically and naturally ventilated homes.
• Not compulsory but widely adopted
What is a green roof?
Green roofs are roofs that are purposely fitted or cultivated with vegetation. They are also be known as living roofs or eco-roofs.
Extensive – low maintenance
Intensive – More intensive like a garden. May required additional loading capacity
- Decreased surface water runoff
- Decreased heating and cooling demands for the building
- Increased local biodiversity
- Improved local air quality
- Disadvantage - Higher capital cost
What is a blue roof?
A blue roof is a roof designed for the retention of rainwater above the waterproofing element of the roof. This is as opposed to more conventional roofs which allow for rainwater to drain from the roof.
• Can be used to reduced water runoff and therefore flooding
• Can be used for rainwater harvesting which can be used to supplement the mains water supply, WC flushing or irrigation of a green roof.
What are the advantages and disadvantages of steel frames?
Advantages • Quicker to construct • Recyclable • Strong tensile strength Disadvantages • More volatile pricing • Low compression strength • Low sound/fire resistance (needs treating)
What are the advantages and disadvantages of concrete frames?
Advantages • High compression strength • Good noise resistance • Good fire protection • Can mould into complex geometry Disadvantages • Slower to construct • Low tensile strength (improved with steel reinforcement) • High embodied carbon • Not as square and flat as steel • Heavy so large buildings require increase foundation cost
What are the risks with building basements?
- Risks of flooding due to poor weather
- Poor ground conditions and natural ground heave or settlement.
- Buried structures
- Contaminated soil
- Loads from adjacent buildings and roads
- Failure of waterproofing, insurance and guarantees
What is build-ability?
This assesses the design from the perspective of those that will manufacture, install components and carry out the construction works
How did the Grenfell tower’s façade 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 by Dame Judith Hackitt who was the CEO of the HSE
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 go 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.
What actions have been taken since the Hackitt review?
- A snap ban was introduced for combustible cladding on all buildings over 18m. This is likely to change to 11m.
- There is also a proposal to introduce sprinklers to all buildings over 11m. The previous law was over 30m.
