Foundation Construction - Strip Foundations

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6/30/2014

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Foundation Construction - Strip foundations.
Saturday, December 4, 2010

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▼ 2010 (60)

Strip foundations consist of a continuous strip, usually of concrete, formed centrally under load
bearing walls. This continuous strip serves as a level base on which the wall is built and is of such
a width as is necessary to spread the load on the foundations to an area of subsoil capable of
supporting the load without undue compaction. Concrete is the material principally used today for
foundations as it can readily be placed, spread and levelled in foundation trenches, to provide a
base for walls, and it develops adequate compressive strength as it hardens to support the load on
foundations. Before Portland cement was manufactured, strip foundations of brick were common,
the brick foundation being built directly off firm subsoil or built on a bed of natural stones.
The width of a concrete strip foundation depends on the bearing capacity of the subsoil and the
load on the foundations. The greater the bearing capacity of the subsoil the less the width of the
foundation for the same load.
A table in Approved Document A to the Building Regulations sets out the recommended minimum
width of concrete strip foundations related to six specified categories of subsoil and calculated total
loads on foundations as a form of ready reckoner. The widths vary from 250 mm for a load of not
more than 20 kN/linear metre of wall on compact gravel or sand through 450 mm for loads of 40
kN/linear metre on firm clay, to 850 mm for loads not exceeding 30 kN/linear metre on soft silt, clay
or sandy clay.
The dimensions given are indicative of what might be acceptable in the conditions specified rather
than absolutes to be accepted regardless of the conditions prevailing on individual sites.
The strip foundation for a cavity external wall and a solid internal, load bearing wall illustrated in Fig.
6 would be similar to the width recommended in the Advisory Document for a firm clay subsoil
when the load on the foundations is no more than 50 kN/linear metre. In practice the linear load on
the foundation of a house would be appreciably less than 50 kN/linear metre and the foundation
may well be made wider than the minimum requirement for the convenience of filling a wider trench
with concrete for the convenience of laying brick below ground.

▼ December (60)
Damp-proof courses above
ground.
Damp-proof courses.
Materials for underfloor insulation.
Resistance to the Passage of
Heat.
Mastic asphalt or pitch mastic.
Bitumen sheet.
Bitumen solution, bitumen/ rubber
emulsion or tar/...
Hot pitch or bitumen.
Polythene and polyethylene sheet.
Materials for damp-proof
membrane.
Damp-proof membrane below a
floor screed.
Surface damp-proof membrane.
Damp-proof membrane below site
concrete.
Damp-Proof Membrane Concrete.
Made up ground - Soils.
Metamorphic Rocks.
Oversite Concrete (Concrete
Oversite).
Soluble sulphates, Portland blastfurnace cement, ...
Ready-mixed concrete.
Concrete mixes.
Proportioning materials.
Water-cement ratio.
Cement.
Fine aggregate and coarse
aggregate.
All-in aggregate Ballast.
Aggregate.
Concrete.
Blinding.
Brick of tile rubble, Concrete
rubble, Gravel and ...
Hardcore - Name given to the infill
of materials.

Fig. 6 Strip foundation.

Oversite concrete - Portland
Cement.

The least thickness of a concrete strip foundation is determined in part by the size of the aggregate
used in the concrete, the need for a minimum thickness of concrete so that it does not dry too
quickly and lose strength and to avoid failure of the concrete by shear.

Laying Drains.

If the thickness of a concrete strip foundation were appreciably less than its projection each side of
a wall the concrete might fail through the development of shear cracks by the weight of the wall
causing a 45° crack as illustrated in Fig. 7. If this occurred the bearing surface of the foundation on
the ground would be reduced to less than that necessary for stability.

Subsoil drains.

Shear is caused by the two opposing forces of the wall and the ground acting on and tearing or
shearing the concrete as scissors or shears cut or shear materials apart.

Site preparation - Building.

Drains - Natural system, Herring
bone system, Grid...

Site drainage.
Resistance to ground moisture.

Foundations on sloping sites.
Raft foundation on sloping site.
Raft foundation.
Pad foundations.
Short bored pile foundation.
Narrow strip (trench fill) foundation.
Wide strip foundation.

http://civilconstructiontips.blogspot.com/2011/06/foundation-construction-strip.html

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6/30/2014

Foundation Construction - Strip foundations. | Civil Construction Tips
Foundation Construction - Strip
foundations.
Functional Requirement - Strenght
and stability – ...
Trial Pits - make an examination of
the subsoil on...
Site visit - Soils.
Site Investigation - Select a
foundation from tabl...
Unstable ground - Soils.
Frost Heave - Soils.
Fig. 7 Shear failure.

Volume Change - Soils.
Fine Grained Cohesive Soils.

Related Posts by Category:

Sand.
Soils: Top Soil, Subsoil, Coarse
grained non-cohes...

Construction
Foundation
Support for Foundation trenches.

Sedimentary Rocks.
Rocks - Groups.

Foundations on sloping sites.
Raft foundation on sloping site.

Igneous Rocks.

Raft foundation.

Foundation of a Building.

Pad foundations.

Foundations and Oversite
Concrete History.

Short bored pile foundation.
Narrow strip (trench fill) foundation.
Wide strip foundation.
Functional Requirement - Strenght and stability – Foundation.
Trial Pits - make an examination of the subsoil on a building site.
Site Investigation - Select a foundation from tables, or to design a foundation.
Foundation of a Building.
Foundations and Oversite Concrete History.

Posted by Edd at 4:46 PM
Labels: Construction, Foundation

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Aggregate (7)
Asphalt (2)
Bitumen (4)
Bricks (10)
Building Tips (16)
Buildings (6)
Cement (6)
Concrete (18)
Construction (1)
Drains (2)
Dwellings (2)
Floor (2)
Foundation (14)
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Foundation Construction - Strip foundations. | Civil Construction Tips

Polythene (2)
Roads (1)
Rocks (4)
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Soils (12)
Steel (2)
Stones (11)
Walls (64)
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