Structural
This should be undertaken by a qualified structural engineer in
accordance with the relevant design codes and standards.
The recommendations for the Structural design of Masonry are
given in BS 5628 : Part 1 and 2. Additional guidance is also given
in BS 5628 Part 3 for walls subject to imposed lateral load only
and internal walls or partitions not designed for imposed loading.
Code of practice for masonry walls for housing or the appropriate
simple rules are in Approved Document A of the Building Regulations
2000 (England and Wales).
Buildings shall be designed and constructed so that the combined
dead imposed and wind loads are sustained and transmitted by it to
the ground.
The following factors, which affect stability should be taken
into consideration:
- Accommodation for movement
- Presence and position of opening
- Presence and position of abutting walls
- Chasing
- The likelihood of exceptional lateral loading arising from the
nature of the use of the building
- Wind load
- Fire resistance
SPECIAL CATEGORY
Fyfestone products are manufactured under special category of
manufacturing control.
The structural design of masonry walls, as described in BS 5628
Part 1 is based upon the principle of limit state design. This
philosophy ensures that an adequate margin of safety is employed
against reaching the ultimate limit state through the application
of partial safety factors on loads and materials. One such partial
safety factor m relates to the material strength and the
‘acceptance limit’ which can be expected. The degree of
manufacturing control is split into normal category and special
category.
Normal category should be assumed when the blocks are
manufactured to meet the requirements for compressive strength in
BS EN771-3 and 5, but in the case of Fyfestone, additional testing
is being carried out and an enhanced quality control scheme is
operated. Fyfestone blocks are thus contained within the definition
of special category where not more than 2.5% of the blocks supplied
are likely to fall below the acceptance limit.
The use of Fyfestone blocks in designing loadbearing masonry
allows the designer to use a lower partial safety factor which in
turn increases the effective loadbearing capabilities of the
product by over 10% when compared with normal category concrete
blocks.
The lower partial safety factor also permits greater panel sizes
to be designed, when allowing for lateral wind loads (see BS 5628
Part 3 and Fyfestone load bearing tables).
COMPRESSIVE STRENGTH OF BRICK AND BLOCK UNITS
Table A - Collar jointed walls COMPRESSIVE STRENGTH OF UNIT (N/mm2)
10.0 15.0 20.0 Mortar Group: Wall Thickness (mm): characteristic
compressive strength fk (N/mm2) (i) 215 5.7 7.7 9.5 (ii) 215 5.5
7.1 8.5 (iii) 215 5.3 6.4 7.5 Notes: The two leaves should be
adequately tied together Blocks have a face size of 440 x 215mm
Compressive strength of brick and block units
| Dimensions (mm) (L x W x H) |
Quantity (m2) |
Individual block weight(kg) |
| 440 x 100 x 215 |
9.88 |
14.00 |
| 440 x 140 x 215 |
9.88 |
18.30 |
| 440 x 190 x 215 |
9.88 |
37.80 |
REINFORCED MASONRY LINTELS
Fyfestone Architectural Masonry can offer reinforced masonry
lintels, designed in accordance with BS 5628 Part 2 `Code of
Practice for the use of Reinforced Masonry’. The particular
application of this form is to formation of lintels over span
openings. When the block pattern is to be maintained.
In order to achieve this, trough lintel or bond beam units (half
length trough lintels used where a fair faced soffit is required)
are laid on temporary formwork with an extra unit at each end to
form the bearing. The void achieved is then filled with the
necessary reinforcement and infill concrete to withstand the
applied load. The whole assemblage is allowed to cure before the
formwork is struck.
Sequence of construction
The sequence of trough lintel construction is as follows:
- build the blockwork to the soffit height of the lintel
- provide temporary propping to the lintel units
- lay the lintel units with a 10mm wide x 20mm deep temporary
spacer in each joint.
- Temporary joint spacers can be of any material which provides
adequate retention of the concrete infill and can be removed for
pointing (e.g. polystyrene)
- fit plastic spacers to the reinforcement to ensure correct
concrete cover place
- reinforcement as appropriate
- complete in-situ filling, tamping by hand
- after curing period strip propping, remove temporary joint
spacers and point joints carefully to match surrounding
blockwork
Bond Beams
Bond beams can be used as a structural element and as a means of
movement control.
Bond beams are constructed using specially shaped units, which
are filled with concrete and reinforced.
Other uses of bond beam courses are :
- below large panel openings
- at the top of walls to distribute vertical loads
- as horizontal beams to transfer lateral forces to columns or
piers
Description
Beam Lintels
Conventional reinforced beam lintels are traditionally cast in a
mould box using the semi-dry method. The concrete mixes used
Architectural Facing Masonry (dense weight) types. Because of the
manufacturing method, shear resistance limits maximum clear
spans.
Trough Lintel Blocks
Trough lintel blocks (full or half length) are cut from the same
blocks produced on the block-making machine, enabling a close
colour match. The open core is filled with reinforced concrete on
site. Trough lintels have increased performances compared with beam
lintels and longer spans are possible.
Standards
Lintels do not conform to a defined standard. Reinforcement
conforms to BS 4449 and tension bars are bent to BS 4466. Trough
lintel blocks conform to BS 6073: 1981. Quality is controlled at
every stage, with procedures assessed and certified to BS EN ISO
9002 standards.
RADIUS WALLS
Fyfestone masonry blocks may be laid in stretcher bond to create
curved or circular walls.
The length and thickness of the blockwork will determine the
width of the perpend on the outer face radius and the amount of
overhang between successive courses for a particular radius
wall.
For true radius plan walls, radius blocks are recommended.
Figure 1 gives information on curved walls based on the size of
the unit with a nominal 10mm perpend joint on the internal face. To
limit the size of the external perpend joint the joint on the
internal face can be reduced or the block cut on the splay.
| WALL WORK SIZE: 440 x 215mm |
RADIUS T=100 L=440mm |
RADIUS T=140 L=440mm |
OVERHANG PERPEND JOINT |
| 600 |
44 |
86 |
46 |
120 |
| 800 |
32 |
68 |
33 |
93 |
| 1000 |
25 |
56 |
26 |
76 |
| 1200 |
21 |
48 |
21 |
65 |
| 1400 |
18 |
43 |
18 |
57 |
| 1600 |
16 |
39 |
16 |
51 |
| 1800 |
14 |
36 |
14 |
46 |
| 2000 |
12 |
33 |
13 |
42 |
| 2500 |
10 |
28 |
10 |
36 |
| 3000 |
8 |
25 |
8 |
31 |
| 3500 |
7 |
23 |
7 |
28 |
| 4000 |
6 |
21 |
6 |
26 |
| 4500 |
5 |
20 |
5 |
24 |
| 5000 |
5 |
19 |
5 |
23 |
| 5500 |
4 |
18 |
4 |
22 |
| 6000 |
4 |
18 |
4 |
21 |