2. SUPER-STRUCTURAL ELEMENTS
WALLS AND PIERS
• After the foundations are completed the external walls are set
out and construction commences.
• Walls are the vertical elements of a building which enclose the
space within it and which may also divide that space.
• Together with the roof they form the ‘environmental envelope’.
1
3. TYPES OF WALLS
• Walls may be divided into two types:
Load bearing –supports loads from floors above and roof in
addition to their own weight and resist side pressure from
wind and, sometimes from stored material or objects within
the building.
Non load-bearing- carry no floor or roof loads.
2
4. • Each type may be further divided into external, or enclosing
walls and internal dividing walls.
• The virtue of the load bearing wall is that:
it is capable of fulfilling at one and the same time the dual
functions of loadbearing and of space enclosure and division.
• It however suffers certain inherent disadvantages:
As a load bearing element it can become thick and heavy at
the base of a very tall building.
3
5. • The external non-load bearing wall, related to a framed
structure, is termed
a panel wall if of masonry construction
An infilling panel if of lighter construction or
A cladding when applied to the face of the frame.
• The term PARTITION is applied to walls, either loadbearing or
non-loadbearing , dividing the space within a building into
rooms
4
6. • SEPARATION WALLS AND DIVISION WALLS are internal
walls which separate different occupancies within the same
building or divide the building into compartments for purposes
of fire protection.
• RETAINING WALLS support and resist the thrust of soil and,
perhaps, subsoil water on one side.
The most important functional requirement of this type of wall
is strength and stability.
5
7. FUNCTIONAL REQUIREMENTS OF WALLS
• The primary function of the wall is to enclose or divide space,
but in addition, may have to provide support.
• In order to fulfill these functions efficiently there are certain
requirements which it must satisfy. These include:
Strength and stability;
Weather resistance;
Fire resistance;
Thermal insulation;
Sound insulation6
8. DEFINITION OF TERMS
• In studying the functional requirements of walls it is necessary
to have regard for the forms of construction which may be
employed. These are described by the terms below:
MASONRY WALLS- The wall is built of individual blocks of
materials , such as bricks, clay or concrete blocks or stone,
usually in horizontal courses, cemented together with some
form of mortar.
7
9. DEFINITION OF TERMS CONT’D
MONOLITHIC WALL- The wall is built of a material requiring
some form of support or shuttering in the initial stages. The
traditional earth wall and modern concrete wall are examples.
Monolithic concrete walls may be either of plain concrete or of
reinforced concrete.
8
10. FRAME WALL- The wall is constructed as a frame of
relatively small members, usually of timber, at close intervals
which together with facing or sheathing on each side form a
load bearing system. This is a wall construction and should
not be confused with structural frame of a building.
MEMBRANE WALL-The wall is constructed as a sandwich of
two thin skins or sheets of reinforced plastic, metal, asbestos-
cement or other suitable material bonded to a core of foamed
plastic to produce a thin wall cement of high strength and low
weight.
DEFINITION OF TERMS CONT’D
9
12. Strength and stability
• The strength of a wall is measured in terms of its resistance to
the stresses set up in it by:
Its own weight;
Superimposed loads and lateral pressure such as wind;
• The strength of the wall is determined by its thickness and
also the compressive strength of the materials used in its
construction.
11
13. • The wall thickness needs to be sufficient to keep the stresses
imposed by the applied loads within the safe compressive
strength of the construction materials.
• The mortar used to bond the materials together should be
slightly weaker than the brick or block
so that if movement in the wall occurs due to settlement, the
break will be concentrated within the mortar and not the
brick/block.
• This allows repair to be undertaken more easily.
12
14. • Bonding of bricks and blocks, both along the length of the wall
and also through its thickness, assists the distribution of
the applied load so that
Over-stressing of materials at specific points is avoided.
• The wall should also be stable enough to resist
overturning due to the application of lateral forces; or
buckling due to excessive slenderness of the wall.
13
16. Weather resistance
• External walls of buildings, whatever their form are required to
provide adequate resistance to rain and wind penetration.
• The actual degree of resistance required in any particular wall
will depend largely on:
Its height; and
The locality and exposure
15
17. Weather resistance cont’d
• The problem of wind penetration rarely presents difficulties in
solid wall construction.
• Tests by the Building Research Station on solid and cavity
walls have shown that provided these are plastered internally,
there is a negligible penetration of wind.
16
18. • Dampness may penetrate through external walls into the
house in three main ways:
Rain penetrating horizontally through the fabric of the wall;
The capillary rise of ground water; and
Rain penetrating vertically down from the head of the wall.
17
20. • Rain penetration through walls can be resisted in three ways:
By ensuring a limited penetration only into the wall thickness;
By preventing any penetration whatsoever through the outer
surfaces; and
By interrupting the capillary paths through the wall.
19
21. Fire resistance
• A degree of fire resistance adequate for the particular
circumstances is an essential requirement in respect of walls,
which like upper floors, are often required to act as highly
resistant fire barriers.
• They are used to compartmentalize a building so that a fire is
confined to a given area:
To separate specific fire risks within a building;
To form safe escape routes for the occupants; and
To prevent the spread of fire between buildings.
20
22. • The term fire resistance is a relative term applied to elements
of structures and not a material.
• It is not to be confused with non-combustibility.
• An element may incorporate a combustible material and still
exhibit a degree of fire resistance which will vary with the way
in which the material is incorporated in the element.
21
23. Thermal insulation
• The external walls of a building together with the roof must provide a
barrier to the passage of heat to the external air in order to:
Maintain satisfactory internal conditions without a wasteful use of the
heating system.
• They should also serve to prevent the interior heating up excessively
during hot weather.
• Adequate thermal insulation is attained in a variety of ways.
22
24. Sound insulation
• It occurs through the vibration of the structure by direct
contact, i.e. footsteps, hammering that creates noise in
adjoining rooms.
• Air borne sound is caused by vibration through conversation,
radio, aircrafts, etc.
23
25. Sound insulation cont’d
• Only in exceptional circumstances are the sound insulation
qualities of an external wall a significant factor in its design
since the other functional requirements which must be fulfilled
usually necessitates a wall which excludes noise sufficiently
well in most circumstances.
• Windows provide weak points in this respect and in some
circumstances these may have to be treated as double
windows.
24
26. KINDS OF WALLS
• SOLID WALLS- usually of masonry construction in sandcrete
blocks, bricks, clay and concrete blocks solid in nature.
• HOLLOW WALLS- constructed with hollow masonry
materials
• MONOLITHIC WALLS- in-situ wall usually of concrete and
requires shuttering during construction.
25
27. KINDS OF WALLS CONT’D
• CAVITY WALL- formed of two separate leafs of masonry
materials but with a cavity or air-space of 50mm in-between
the leafs
• COMPOSITE WALLS-Sandwich construction of two or more
different materials.
26
28. • Composite walls often include:
Panel or in-fill walls- used as enclosing or dividing elements in
framed structural elements.
Retaining walls-masonry/concrete construction that resists
earth and liquid pressures.
COMPOSITE WALLS
27
29. Claddings-external facing to masonry structures or concrete
or steel framed backgrounds in thin stone, brick and pre-cast
concrete slabs.
Curtain walling- a system of cladding fixed to the face of a
structure usually at each floor level, and on in-filling of panels,
glazed or solid, required to perform both the functions of
window and wall.
COMPOSITE WALLS CONT’D
28
35. Parapets and copings- a parapet is the upper part of an
external wall carried above the level of a roof gutter or a roof
plane.
Party wall- partition wall separating two separate adjoining
properties.
Pier- constructed of masonry materials and constitutes a
structural part of a wall of which it is a part.
34
37. Retaining walls
• Retaining walls resist the lateral thrust of a mass of earth on
one side or the pressure of sub-soil water.
• Its basic function is to retain soil at a slope which is greater
than it would naturally assume, usually at a vertical or near
vertical position.
36
38. Retaining walls cont’d
• A retaining wall should be designed so that:
It does not over-turn;
It does not slide forwardly;
The materials used are suitable and not over stressed; and
The soil on which it rests (subsoil) is not overstressed.
37
39. FACTORS TO CONSIDER IN
DESIGNING RETAINING WALLS
• Nature and characteristics of the subsoil
• Height of water table- The presence of water can create:
Hydrostatic pressure, which can affect the bearing capacity of
the subsoil
Reduce frictional resistance between the underside of the
foundation.
38
40. FACTORS TO CONSIDER IN DESIGNING
RETAINING WALLS CONT’D
• Type of wall
• Materials to be used in
the construction
39
41. • The pressure on the back of the wall is called ACTIVE PRESSURE and it
tends to overturn the wall and push it forward.
• The force exerted by the earth on the front of the wall is resisting movement
of the wall under active pressure and it is called PASSIVE EARTH
RESISTANCE.
40
42. • Active water pressure can be avoided by the provision of
DRAINAGE behind the retaining wall.
41
43. • By reducing the quantity of water the wall has to retain, the
active pressure will also be reduced. An impermeable
covering may help.
• The tendency of the wall to slide is resisted by friction on the
underside of the base and by the passive earth resistance at
the front of the wall.
• When the frictional resistance is insufficient, the passive earth
resistance must be used to increase total resistance to sliding
and this necessitates the provision of RIBS on the base of the
wall.
42
44. • In basement retaining walls, sliding or rotation can be
overcome by;
Making the active pressures on each side of the basement
counteract each other through the floors.
• The weight of the structure over often assists the weight of the
wall in resisting overturning.
43
45. FAILURE OF RETAINING WALLS
Failure of retaining wall (dam) due to water pressure
44
46. TYPES OF RETAINING WALLS
The gravity or mass retaining wall
• Constructed in brickwork/masonry/or mass concrete, mainly used for
heights up to between 1.8-2m and depend on mass for their strength
and stability.
• It relies on its own mass together with the friction on the underside of the
base to overcome the tendency to slide or overturn.
• Can be constructed of semi-engineering quality bricks bedded in 1:3
cement mortar or mass concrete.
45
50. Cantilever retaining wall
• Constructed of reinforced concrete.
• Reinforced concrete cantilever retaining walls are more slender than mass
concrete types.
• They are suitable for heights between 4m to 6m, above this height
counterforts should be introduced to give additional restraint.
• As the resultant of the lateral pressure and weight of wall falls outside the
thickness of the wall, high tensile stresses are induced, hence, it is
necessary to use reinforcement so that the stem can act as a vertical
cantilever.
49
51. These walls come more economical in use of materials, occupy less space and
weigh less than gravity walls.
50
52. Basic forms of cantilever retaining walls
• A base with a large heel
• Cantilever T
• Cantilever with a large toe
• Cantilever L
51
55. Counterfort retaining walls
• Can be constructed of reinforced or prestressed concrete.
• Suitable for over 4.5 m.
• Triangular beams placed at suitable centres behind the stem
and above the base to enable the stem and base to act as
slab spanning horizontally over or under the counterforts.
54
56. Precast concrete retaining wall
• Manufactured from high grade precast concrete on the
cantilever principle.
• Can be erected on a foundation as a permanent retaining wall
or be free standing to act as dividing wall between heaped
materials which it can increase three times the storage
volume of any material.
55
57. • Among its advantages are:
Reduction in time by eliminating curing period;
Cost of formwork;
Time to erect and dismantle the temporary forms.
56
