Types of Foundations, Building Frames and Partitions

TASK 1.1

Alternative sub-structure solutions:

In any building the superstructure, substructure (foundations) and the supporting soil acts in a coordinated way to give structural stability. Therefore the foundations act as connection between superstructure and the ground. Successful foundations should be:

• Foundations must be at minimum depth and size without exceeding the allowable bearing capacity of the soil.
• They must be strong enough to provide stability to the supporting structure.
• They must be able to withstand natural ground movements from corrosive chemicals, frost, moisture and heat.
• They must be economical and sustainable.

For our Englemere Village project we used Strip and Pad foundations.

Foundations can be classified as:

1. Shallow Foundations

1. Strip Foundations

• Traditional Strip Foundations
• Trench fill Foundations
• Combined- Stepped Foundations

2. Pad Foundations
3. Rafts
4. Pier and Beam Foundations

2. Deep Foundations

1. Piled Foundations

• Displacement Piles

• Replacement Piles

1. Shallow Foundations

The foundations which are placed beneath the lowest part of the structure and near to the ground level are shallow foundations.

1. Strip Foundations

Strip foundations are the most common foundations used in construction, it is a strip of concrete running under all load bearing walls. The depth and the width of the strip foundations depends on the nature of the soil and superstructure load, they can be 500-700 mm wide and as deep as per the nature of the soil/ground.

Strip foundations can be either traditional strip or trench fill and both can be stepped.

Traditional Strip Foundations

Strip foundations are used where soil has good bearing capacity. Load is transmitted at 45 degrees angle from the base of the wall. The width of strip foundation is three times the width of the wall. Thickness should be at least 150 mm, but 300 mm is most commonly used. Depth should be 450 mm minimum measured from finished ground level to protect from frost attack. See Appendix 1.

Trench fill Foundations

Trench fill is quicker and more cost effective than traditional strip. The thickness should not be less than 500 mm and should finish 150 mm below ground level. Trench should be dug to a depth where subsoil provides sufficient load bearing capacity, usually it is 1m deep. See Appendix 2.

Stepped Foundations

Stepped foundations are used on sloping sites. As top of foundation has to be level and on slopping sites foundations can end up too deep. Stepped foundations reduce the amount of excavating and cost. The step should not be bigger than the thickness of foundation and should work with heights of the bricks. Overlap should be at least twice the height of the step.

2. Raft foundations

Reinforced concrete raft is used when bearing capacity of soil is low. It spreads the load from structure over a large area. Reduces the amount of excavating. Concrete raft is usually at least 150 mm thick. Sometimes the raft is thickened under load bearing walls. See appendix 3.

3. Pad foundations

Pad foundations are used when isolated loads need to be supported, spreading the load to the ground below. They are used for columns or framed buildings. Pad foundations are constructed from reinforced concrete. See Appendix 4.

4. Pier and beam foundations

Pier and beam foundations are made from brick, block or timber piers on concrete pads. Beams sit on the piers and are usually raised above the ground to create a crawl space underneath. Pier and beam is a cost effective foundation for smaller buildings. See appendix 5.

2. Deep Foundations

The foundations that are constructed below ground level while using artificial arrangements such as piles can be termed as deep foundations.

Pile foundations

Pile foundations are used to transfer load of superstructure through weak soil onto strong soil or rock. Piles can be displacement or replacement. Pile caps or beams sit on top of the piles. See appendix 6.

Displacement piles are driven into the ground by pushing the soil out of the way. They are friction piles. This method is very noisy and vibrating. But there is no soil to be removed from site.

One of displacement methods is helical screw piling. A helical pile consists of a galvanised steel shaft onto which is welded a series of circular steel plates. They are power drilled in to the ground. Advantages are: fast installation, vibration and noise free, sustainability (can be removed and reused).

Replacement piles remove soil and replaces with reinforced concrete. They are end bearing piles. All soil needs to be removed from site but it is less vibrating and noisy than displacement pilling.

Causes of Foundation Failure

Failure in transferring the load between superstructure and soil can lead to building movement and cracking, but failure of foundations cannot be held alone responsible for cracking there can be other reasons for these kind of damages. Seasonal movements, chemical attack, building alterations, trees, soil creep and variable ground conditions are few causes of foundation failures.

Alternative systems for structures, envelope and roof coverings

Constructed structures start with architectural and engineering plans, however all structures follow basic design steps as follows;

• Preparing the site
• Installing foundations
• Building the framework
• Enclosing the structure
• Finishing the exterior and interior
• Completing the site

Building the Framework

The framework depends on the foundations as foundations provide base for building the framework. Floors, interior and exterior walls, ceilings and roof are included in the building process of framework. Therefore framework provides a rigid shape and structure to the buildings.

Brick and block is a traditional method of building. Brick and block houses use a cavity wall construction with a gap filled with insulation. These walls are load bearing, they support floor joist and roof.

In MMC (modern method of construction) systems for structures framing process is mostly done offsite and are only erected on site. MMC system provides much quicker way of building. There are different types of frames as listed below are used in MMC systems for structures.

• Steel frame
• Timber frame
• Portal frame
• Concrete frame
• Structural Insulated Panels (SIPs)
• Insulated Concrete Framework (ICF)

Steel frame

Steel frame construction is a quick way of building as all the parts are manufactured offsite. It is a lightweight structure compared to traditional masonry or block work. Steel frame can be used from domestic housing to really tall skyscrapers and it is a sustainable way of building as steel can be recycled many times. The skeleton is formed from vertical steel columns and horizontal I beams. All the loads are transferred to foundation through columns.

Timber frame

Timber frame panelling system is another fast construction method used in domestic housing. All panels and roof trusses are made offsite and erected on site in a number of days. It has 30% shorter building times than brick and block. This means the house is water tight more quickly and other trades can start work sooner. Timber frame has higher insulation properties than brick and block.

Portal frame

Portal frames are used for a single storey construction which requires a large floor space for example: warehouse, factories or supermarkets. It has no intermediate columns that mean large open space areas can be created within the structure. It is manufactured offsite – fast construction.

Concrete frame

RC (reinforced concrete) frame is a very common type of building. The skeleton is made out of vertical columns, horizontal beams and slab in between. Concrete is cast into formwork.

SIP (structural insulated panels)

SIPS have very good insulation value and structural strength. SIPS panels can be used in walls, floors and roofs for domestic, industrial and other constructions. SIPS are made from Polystyrene (EPS) sandwiched between two Oriented Strand Boards (OSB) making them lightweight and quick to erect by interlocking them together.

ICF (Insulated Concrete Framework)

ICF involves building a site with laying a series of hollow blocks, made up of expanded polystyrene (EPS) and then are pumped with ready-mixed concrete. EPS provides a high insulation wrapping around the concrete once the structure is finished. This framing system not only provides speedy construction but also it gives a protection against sudden climatic changes. Although adopting ICF will cost higher than an average timber frame build but it can provide reduced construction times and lower energy bills.

Thin Joint

Thin joint provides improved thermal performance and building accuracy over conventional brick and block construction. The structures are made with large aircrete block and quick drying mortar. 75% less mortar is used. This thin joint framing can be erected in no time, furthermore it provides a stability to the overall structure and an adaptation to extend the building at later date.

The MMC building systems are used in order to save construction time and the cost of the construction but they must be used after reviewing the local construction laws and other weather conditions.

Building Envelope

The building envelope acts as a physical separator between an exterior and interior environment, therefore it can be termed as the building enclosure. It provides a shell to maintain an indoor environment of any building, it also helps in facilitating the climate control.

Building envelope is exterior skin of the building that separates interior from exterior. It protects building from rain, wind and sun. Envelope includes external walls and roofs.

External walls used in an envelope can be classified as follows

• Cavity Walls
• Stone cladding
• Load bearing stone masonry walls
• Glazed concrete blocks
• Wood cladding

External walls in making an envelope must provide the bearing, insulation and shape to the building. To give more insulation to the external walls they must have insulating fillings, separate insulating layer and air insulating layer.

Roof coverings

Roof covering must bear the following functions;

• Protection of the building against rainfall, snowfall etc and other weather conditions.
• Protection against cold, heat, overheating, wind and noise.
• Protection against fire.

To cover all these protections roof covering must have the following items in its architectural design

• Water proofing insulation
• Thermal insulation
• Wind stability
• Sound insulation

Roofs are divided into Flat and Pitched.

Flat roofs could be: Ash felt, felt, EDPM, Fibre glass, glass.

Pitched roofs could be: lean to, couple, purlin, mansard, trussed, hipped, trussed rafter, attic truss.

MMC alternatives for partition walls

Partitions are the vertical walls or panels that are used to divide portions of the building and they can be classified as load bearing or non-load bearing. Traditionally timber was used as partitions but with the advancement in construction methods and the use of light weight partitioning and light weight insulation block, its use as a partition is decreasing significantly.

Partitions can be constructed using various materials, but the most common types of partitions are:

1. Timber Stud Partitions.
2. Metal Stud or Dry wall Partitions.
3. Glass Partitions.
4. Sliding Partitions
5. Room dividers
6. Re-locatable office Partitions

1. Timber Stud Partition

Timber stud partitions are non-load bearing and light weight partitions. Timber stud partitions consist of wooden framework between horizontal head and sole pieces at the top and bottom of the framework and a series of uprights called studs holding the whole framework. The noggings are intermediate stiffening material placed between the studs to ensure the overall stability of the framework. Timber frame partitions are formed with butt joints or framing anchors to significantly facilitate the low labour cost and speed of erection. Plasterboard is usually used as a covering material for timber partitions.

2. Metal Stud or Dry wall Partitions

Metal stud partitions are non-load bearing partitions consisting of a metal studding framework. This metal studding makes the partitions light weight but comparatively strong and stable than timber stud partitions. They can be covered with ordinary plasterboards or special fire resistant sheets, which on final sealing can make these partitions sound proof as well as fire resistant. Metal stud partitions are quick and easy to erect, they are cost effective, sustainable for all types of buildings and they are available in variety of finishes. Due to these strong characteristics metal stud partitions are mostly used in public buildings and hospitals. The metal studs are manufactured from galvanised steel sheet folded into various shaped sections which slot into each other. The sections are produced in various lengths ranging from 2.4 m to 6 m in length and widths ranging from 50 mm to 146 mm.

3. Glass partitions

Glass fulfils an important role in creating divisions between indoors and out as well as between individual interior spaces.

The technical advances in the material mean that it is suitable for a wider range of applications than ever before.

• Double & single glazed options • Excellent acoustic performance up to 47db (Rw) • Attractive and Stylish • Full range of manifestation options • Wide range of profile colours • 10mm and 12mm glazing • Option of standard height or full height doors

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Single glazing can be used where clean lines and an aesthetically pleasing design are essential. The partitioning is designed with the minimum amount of framework to give a frameless appearance. To maintain the open feel of the office environment frameless doors or framed glass doors are fitted within the system using floor pivots and patch fittings or floor springs if required.

Where desired or in order to comply with building regulations, fully glazed panels have manifestation film applied to them. These can be used to simply highlight the presence of the partitions, create individual designs or incorporate company logos using either 10/12mm toughened glass depending on the height of the partition, glazing is achieved with the use of clear glazing gaskets that remove the need for silicone around the perimeter of the system.

Vertical silicone joints maintain the visual simplicity of the product or clear plastic jointing sections to provide dry joints between glass panels.

Appendix 1

Traditional strip foundations

Appendix 2

Trench fill foundations

Appendix 3

Raft foundations

Appendix 4

Pad foundations

Appendix 5

Pier and beam foundations

Appendix 6

Pile foundations