Civil Engineering Reference
In-Depth Information
100 mm wide dense concrete blocks have the following
declared properties from the manufacturer:
Gross density 1450 kg/m
3
(High density)
Durability etc F0
Compressive Strength (fb) 7 N/mm
2
Masonry unit Category I
Voids <25% (solid block)
For the construction the following classes and mortar strengths
are to be used:
Construction class 1
Mortar strength (fm) M4
Blocks are to be constructed using collar jointed wall construc-
tion to clause 8.5.2.3. Therefore, K = 0.8K.
Based on the above information, the following values are derived
from BS EN1996-1 and the UK National Annex:
Masonry Group
A steel beam carrying 6 kN/m dead load and 5 kN/m imposed
load spans 5 m between masonry supports. The beam is sup-
ported on a 215 mm thick wall constructed in 10 N blockwork
in M6 mortar (see
Figure 20.9
) determine the bearing area
required.
Steel beam reaction (N
EDC
)
Loading factors of safety 1.35 Gk and 1.5 Qk
BS EN1990
N
EDC
= (1.35 Gk + 1.50 Qk) × span/2 = 39 kN
From the diagram, the load is located at an eccentricity of 50 mm
therefore is 0.23t which is less than t/4.
Masonry values:
Compressive Strength (fb) 10 N/mm
2
or more
Masonry unit Category I
Masonry Group Group 1 (<25% voids)
Construction class 1
Mortar strength (fm) M6
Therefore characteristic compressive strength is:
Group 1 (<25% voids)
Table 3.1
Equation Constants
Table 3.3 and
NA.4
k = 0.55,
a
= 0.70,
β
= 0.30
Material factors of
safety
Table NA.1
×=
×=
0.70
0.30
2
γ
m
= 2.30 for direct of
fl exural compression
γ
m
= 2.30 for fl exural
tension
a
f
k
f
a
f
0.55 10
6
4.72 N/mm
=×
f
=×
f k
b
f k ×=
f
f
×=
f
m
×=
m
×
10
×
=
f k
k
f kf
k
f k
f
=×
f k
=×
f
b
f
m
f
×=
f
m
f
m
f
m
Material factors of safety
γ
m = 2.30 for direct of fl exural
compression
Characteristic compressive strength:
Clause 3.6.1.2
×=
×=
0.70
4
0.30
f=
f
=
4.72
a
f
k
f
a
f
0.55 0.80 7
0.70
4
2
=×
f
=×
f k
b
f k ×=
f
f
×=
f
×=
m
××
0.8
××
0.80 7
×
f=
ff
f k
k
f kf
k
f k
f
=×
f k
=×
f
b
2.30
= 2.05 N/mm
f
m
f
×=
f
m
f
m
f
m
f=
γ
γ
m
2
Clause 3.6.1.2
Table NA.1
2.60 N/mm
m
=
f=
2.60
2
2.30
= 1.13 N/mm
f=
f=
The enhancement factor for concentrated loads (
β
) is given by:
Characteristic fl exural strength:
Table NA.6
Clause 3.6.3
f=0.25 N/mm f=
0.25
2
2
2.30
= 0.11 N/mm
1.5 1.1
A
A
β
=1+ 0.3
a
hc
xk
f=
xk
f=
xd
f=
xd
f=
1
b
f=
f=
f=
f=
=1
=1
=1
==1
==1
=1
=1
=1
=1
−
=1
=1
=1
ef
f =0.60 N/mm f =
0.60
2
2
2.30
= 0.26 N/mm
xk
f =
xk
f =
f =
f =
xd
f =
xd
f =
f =
f =
Equation 6.11
a
1
is the distance to the edge of the wall = 600 mm
hc is the height of the load = 2700 mm
A
b
bearing area of load = 20 000 mm
2
A
ef
this is the effective bearing area of the wall at mid-height
based on a 60° load spread and determines the effective
length of bearing at mid-height (see
Figure 20.10
).
Possible uses:
MX 1
Inner leaves of cavity walls, partitions, etc.
MX 2
Masonry in contact with moisture (e.g. plant
rooms, etc.) but not in aggressive soils.
20.5.2.6 Local loading (BS EN1996 clause 6.1.3)
Local loading checks are required where local high loads are
expected. This may be where steel or concrete beams are sup-
ported on beams or where precast planks land onto inner leaves
of masonry construction.
The effective bearing area = 339 485 mm
2
A
b
/ A
ef
ratio of bearing area and effective bearing area = 0.06,
limited to 0.45
