Construction Technology and Environmental Services L1-3 Flashcards
WHAT IS SUBSTRUCTURE?
All works undertaken beneath the damp proof course, providing the basis for the superstructure.
WHAT IS EXTERNAL ENVELOPE?
Materials and components forming the external shell of a building.
These may be load bearing or non-load bearing.
WHAT ARE THE BUILDING REGULATIONS?
Statutory instruments which set the minimum performance standards for design and construction of buildings.
Supported by Approved Documents and other codes of practices, i.e. BRE Digests.
WHAT ARE THE APPROVED DOCUMENTS?
A. Structure
B. Fire Safety
C. Site Preparation and damp proofing
D. Toxic substances
E. Soundproofing
F. Ventilation
G. Hygiene
H. Drainage and waste disposal
I. Not in use
J. Heating appliances
K. Protection from falling, collision and impact
L. Conservation of fuel and power
M. Disabled access and facilities
O. Overheating
P. Electrical safety
Q. Security in dwellings
R. Infrastructure for electronic communications
S. Infrastructure for charging electric vehicles
7. Materials & workmanship
WHAT ARE BRITISH STANDARDS?
Publications issued by British Standards Institution prefixed BS.
Minimum standards for materials, components, design and construction of buildings.
WHAT ARE INTERNATIONAL STANDARDS?
Publications issued by the International Organisation for Standards prefixed ISO.
They are compatible with and complement the British Standards.
WHAT IS SUPERSTRUCTURE?
All internal and external elements above the damp proof course, made up of:
- External walls
- Stairs
- Roof
- Structural walls
- Suspended ceilings
- Raised floors
WHAT ARE THE TYPICAL COMPONENTS OF SITE INVESTIGATION?
To collect and record data to assist with the design and construction process. This should include matters that may impact the development, such as:
- Boundary hedges & fencing
- Existing trees
- Size, depth and location of services inc. gas, telephone, electricity, water and drainage.
- Existing buildings
- Ground water conditions
- Soil investigations
- Trial pit information
WHAT IS THE PURPOSE OF SOIL INVESTIGATIONS?
To determine the suitability of the site for the proposed works, determining adequate and economic foundation design.
To determine potential difficulties associated with the ground conditions, i.e. contaminated or easily eroded, to identify a suitable foundation solution.
WHAT ARE THE MAIN SITE CONSIDERATIONS?
- Access
- Storage
- Accommodation / welfare
- Temporary services
- Plant
- Fencing & hoarding
- Health & Safety risks
WHAT IS A RETAINED FACADE?
The facade of the building is retained whilst everything behind the front wall is demolished, often required as a result of listed building requirements.
Allowances for temporary support structure and cleaning and restoration works are required.
WHAT ARE TEMPORARY WORKS?
Temporary works do not usually appear on construction drawings but may be required dependent on method of construction being used.
May be required as a Health and Safety requirements, e.g. temporary propping.
WHAT IS A TOWER CRANE AND WHAT ARE SOME CONSIDERATIONS DURING ITS ERECTION AND OPERATION?
Tall crane used for lifting objects into high place, the boom allows longer reach with 360 degree access.
Longer boom reduces payload capacity.
Smaller cranes are used to erect tower cranes.
Weather conditions could prevent it from working, in particular high winds.
WHAT IS A SCAFFOLD?
Temporary working platform erected to the perimeter of a building, providing a safe working space at a convenient height.
Scaffold is usually required for works 1.5m above ground level.
WHAT IS SHORING?
Shoring is a form of temporary support given to existing building or structure when in danger of collapse during alterations / new build construction… think horizontal struts for large excavation.
This is a precaution against damage or injury due to collapse of the structure.
WHAT ARE THE MAIN COMPONENTS OF CONCRETE?
Cement
Aggregate (natural rock, crushed stone, gravel)
Water
WHAT IS A BOREHOLE?
Used for soil investigations or geothermal heating solutions.
Boreholes are the most suitable method of soil investigation beyond 3m depth.
Geothermal boreholes are permanent, using Earth’s natural heat to raise the temperature of circulated water. This is a closed system, used to heat buildings above as a sustainable technology.
WHAT ARE PILES?
Columns inserted into the ground, transmitting the structure load to lower in the subsoil, providing stability.
Used where no suitable foundations conditions are present near ground level, or if the water table is high.
WHAT ARE THE DIFFERENT TYPES OF PILES?
Sheet piles:
- A deep trench is excavated and concrete is poured in situ, used to form basement walls or act as retaining walls.
Secant piles:
- Interlocking piles (male and female, different diameters and hardness) bored to provide a combination of foundations and basement walls.
- Provide a waterproof structure and are a top down construction method.
Bored piles:
- An auger (large drill) is used to excavate the soil and concrete is poured in once complete.
Pre-cast piles:
- Piles are hammered into the ground, not often favoured due to noise levels associated with installation and lack of flexibility in terms of depth required.
WHAT ARE THE DIFFERENT WAYS THE PILES TRANSFER THEIR LOAD TO THE SURROUNDING GROUND?
End bearing piles - Transfer load through low bearing capacity soil to a strong stratum, i.e. rock or very dense mud.
Friction piles - Bear on frictional resistance between their outer surface and the soil in contact.
Settlement reducing piles - Incorporated beneath the centre of raft foundations in order to reduce differential settlement to an acceptable level.
Tension piles - Resist uplifting forces causing movement such as hydrostatic pressure, seismic activity or overturning movement, by under-reaming (enlarging end of the pile), installing helical bearing plates or bonding the pile into the rock.
WHAT IS THE DIFFERENCE BETWEEN BORED VS. PRE-CAST PILES?
Bored piles:
- The process for removing the spoil to form the hole is carried out by a boring technique.
- Used primarily in cohesive soils to form friction piles and when forming pile foundations close to existing buildings as noise and vibration is limited.
Pre-cast piles:
- Used where soft soil deposits overlie firmer strata, driven using a drop or single action hammer.
- Issues can arise over noise levels associated with installation of pre-cast piles.
WHAT ARE THE PROBLEMS REGARDING COST CONTROL WITH PILING AND WHO OWNS THE RISK?
Pile depth is never certain and the procurement route used determines who takes the risk.
For example, under traditional or D&B procurement the Contractor would take risk, however under Management Contracting the risk remains with the Employer.
WHAT IS A RAFT FOUNDATION?
Raft foundations are the most popular type of raft, one solid, reinforced concrete slab.
Raft foundations spread the load of the superstructure over a large base, reducing load per m2 of the area.
Useful in low bearing capacity soil, e.g. silts / clay.
They can be solid raft slab or beam and slab raft such as a ground beam system and suspended PC concrete ground floor.
Beam and slab raft foundations have beams and thick edges, increasing strength (heavier loads of walls and columns).
WHAT IS A STRIP FOUNDATION?
Strip foundations are formed by creating a shallow continuous excavation to support the perimeter and internal walls.
They are referred to as strip footings and are suitable for most subsoils and a light structural design.
WHAT ARE PAD FOUNDATIONS?
Provide a base for reinforced concrete / steel columns.
Formed by making an isolated excavation in the shape of a square / rectangle.
Usually have reinforcement mesh installed within and spread the load to a layer of bearing soil or rock below.
UNDER WHAT CONDITIONS WOULD YOU EXPECT A RAFT FOUNDATION TO BE USED FOR A SUBSTRUCTURE?
Used for lightly loaded buildings on sites with poor soils.
Heavy loads have potential to cause movement sideways as a result of rafts not being very deep.
WHAT ARE RETAINING WALLS?
Act as an earth retaining structure for part or all of their height.
Used to support and retain soils laterally so it can be retained at two different levels on two sides.
WHAT ARE THE MAIN TYPES OF EXCAVATION FOR FORMING BASEMENTS?
Open excavations that use battered excavation sides which are cut back to a safe angle, eliminating the need for temporary earth work support. This requires additional excavation costs and significant working space when compared to other methods.
Perimeter Trench Excavation requires earthwork support with the basement walls being constructed, then the inside of the basement excavated.
Complete Excavation - firm subsoils only. The basement is excavated from the centre first and basement slab cast while the sides of the excavation are supported by struts.
WHAT IS A BASEMENT?
A storey constructed below ground level.
WHAT ARE THE 3 DIFFERENT TYPES OF BASEMENT CONSTRUCTION?
(1) Retaining wall and raft consists of slab raft foundation serving as basement floor to distribute the load. The basement walls serve as retaining walls.
(2) Box and Cellular, similar to above, however internal structural walls are used to transfer and spread loads over the raft and divides the basement into cells.
(3) Piled solution where the main superstructure loads are carried to the basement floor by columns and transmitted to the ground via pile caps and bearing piles. In this example, the basement has numerous columns passing through it.
WHAT ARE BEARING PILES?
End bearing piles develop most of their load-bearing capacity at the toe of the pile, bearing on dense soil or a hard layer of rock.
The pile transmits through soft, compressible strata onto firm strata, alike superstructure columns continued.
WHAT ARE PILE CAPS?
A dense mat-like structure that rests on the pile, increasing the stability of the structure.
Used to cover the top of dock pilings to protect from water ingress and damage.
WHAT ARE THE 3 MAIN METHODS OF WATERPROOFING A BASEMENT?
(1) Dense Monolithic
(2) Tanking
(3) Drained Cavity
WHAT IS DENSE MONOLITHIC BASEMENT WATERPROOFING?
Dense Monolithic:
- Two piece rather than usual three piece construction - the floor and footings are poured simultaneously, then the walls built atop.
- Designed and built to form a watertight space using high quality reinforced concrete, requiring good workmanship and strict control.
- Success is dependent on the cement to water ratio and degree of compaction. Joints also need to be carefully designed.
WHAT IS THE DIFFERENCE BETWEEN COHESIVE AND NON-COHESIVE SOILS?
Cohesive soils will retain their shape and break into large pieces, i.e. clay and silt.
Non-cohesive soils will disintegrate into small particles, i.e. low amount of clay / silt, relying on friction and interlocking for strength & stability.
WHAT DOCUMENTS ARE AVAILABLE FOR REVIEW OF FOUNDATION STRUCTURE?
Building Regulations
Approved Documents
BRE Digest
WHAT IS SCABBLING?
Piston driven carbine tipped heads, impact surface at rapid rate to pulverise concrete surface.
Used where shot blasting is not effective.
Also removes level inconsistencies in concrete floors.
WHAT ARE TECHNICAL ADVANTAGES OF STEEL FRAMES?
Quicker to assemble in comparison to alternative methods.
Higher weight to strength ratio of any building material.
100% recyclable and inorganic, meaning no warping, splitting, cracking or creep.
Not vulnerable to termites, fungi or organism.
Dimensionally stable, not expanding or contracting with moisture or temperature changes.
Consistent quality due to controlled manufacturing conditions.
Steel is non-combustible, not contribute to the spread of fire.
Steel frames are light in comparison to concrete, therefore, benefit from a cheaper foundation solution.
WHAT ARE THE TECHNICAL DISADVANTAGES OF STEEL FRAMES?
Steel frames require fire protection to be retrospectively installed.
Fixing components require replacement over time.
Steel prices fluctuate, lack of cost certainty.
Experienced builders required at additional cost.
Resources can be difficult to require dependent on market conditions.
WHAT ARE THE TECHNICAL ADVATANGES OF CONCRETE FRAMES?
Fire protection is provided inherently as part of the structure.
Slower form of construction, likely result in reduced cashflow early in the development.
Relatively low maintenance required.
Provides good sound and heat insulation properties in comparison to steel frame construction.
WHAT ARE THE TECHNICAL DISADVANTAGES OF CONCRETE FRAMES?
More time consuming to construct, compared to steel frame.
May also be complications during installation due to colder or inclement weather.
Need for steel reinforcement can lead to price fluctuations, therefore, cost uncertainty.
Concrete frames are heavier and require larger foundations.
DESCRIBE A TYPICAL COLD FLAT ROOF CONSTRUCTION
The void is insulated from heat loss from below, therefore the void is colder than the room below during colder weather.
Insulation is installed just above ceiling level between the roof joists with a void being maintained to allow for cross ventilation.
Ceiling joists form the main horizontal members and are fixed to wall plates.
Risk of condensation forming within the roof void, therefore good cross ventilation is essential.
Plywood decking is secured on the roof joists and finished with respective roof covering.
DESCRIBE A TYPICAL WARM FLAT ROOF CONSTRUCTION
Insulation is placed on top of the roof deck and joists but beneath the waterproof membrane.
The vapour control layer is usually placed beneath the insulation, reducing the risk of condensation as the ceiling / roof void is a similar temperature to the roof.
DESCRIBE A TYPICAL INVERTED FLAT ROOF CONSTRUCTION
Insulation is placed above the waterproof membrane, with no vapour control needed.
The roof void and deck are maintained at a similar temperature to the room below.
The insulation protects the membrane from damage but must be anchored down.
Often used where ballast / supported slabs are installed.
DESCRIBE A TYPICAL PARAPET WALL - ROOF ABUTMENT DETAIL
The parapet is built along the perimeter edge of the roof, the height extending above the roof level.
At the wall to roof junction, flashing or waterproofing detail is required with counter flashing installed above the flashing, and a DPC placed at the head of the wall under the coping detail.
DESCRIBE A PITCHED ROOF DETAIL
Pitched roofs are made up of rafters, spanning from the roof apex to the top of the external wall, fixed to a wall plate.
Ridge tiles at the apex of the roof are supported by the ridge board.
The roof covering, concrete/slate tiles, are typically fixed to roof battens.
Supporting the rafters and roof coverings are the struts, purlins and roof beams.
A soffit and eaves board may be fixed to the end of the protruding rafters, along with guttering.
Vent tiles used to provide ventilation for the roof void.
DESCRIBE A CLADDING STICK DETAIL
In the stick system, the curtain wall frame (mullions) and glazing panels are installed and connected together piece by piece.
Stick curtain wall systems allow for integration of other systems, i.e. sliding doors / windows.
Less specialised and can be built by all types of fabricators as they are not dependent on having a large factory.
However, require multiple steps to erect and seal the wall, therefore more time spent on site - approx. 70% work on site, 30% in the factory, incurring additional labour time costs.
DESCRIBE A PANELLISED SYSTEM
Alike Unitised systems, panellised curtain walling is pre-assembled to improve quality control and speed of erection.
The systems comprise large pre-fabricated panels of bay width and storey height, connected to the primary structural columns / floor slab.
Panels may be precast concrete or structural steel framework, often clad with stone, metal and masonry cladding materials.
Advantage - Improved adherence to specification due to factory pre-fab, improved quality control and rapid installation with minimum number of site sealed joints.
Disadvantage - Panellised systems are less common and more expensive than unitised construction.
DESCRIBE A CLADDING RAINSCREEN DETAIL
Rainscreen cladding provides a screening function shielding the wall (masonry, metal studwork or glazing), rather than an enclosure in its own right.
Usually a rainscreen is designed to permit controlled leakage with the main resistance to air and water being provided by the shielded wall behind.
Cladding > insulation > metal bracket including thermal break pad > aluminium clip angle > air/moisture vapor barrier > concrete/masonry wall with fixing points.
DESCRIBE A UNITISED CLADDING SYSTEM
Unitised system comprise narrow, storey-height aluminium framed units containing glazing or opaque insulation panels.
Entire system is pre-assembled in factory conditions - improved quality control and speed of installation.
Panels craned into position, with pre-positioned brackets attached to the floor slab / structural frame, increasing the speed of installation and often minimise the requirement for scaffolding.
Higher direct costs despite the reduced labour during install.
