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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
E. RIZZATTI | H. R. ROMAN
|
G. MOHAMAD | E.Y. NAKANISHI
block with hollow walls; (b) structural clay block with solid walls; (c)
structural clay block with solid walls but hollow internal walls; or
(d) drilled structural clay blocks as in Figure 05 [9]. The compres-
sion strength of blocks is the main factor that determines the com-
pressive strength of masonry. The British Standard 5628-1 [10]
can be used as reference because the existing Brazilian national
rules do not present results that correlate the strength of the ma-
sonry for different blocks and mortars, quoting only that strength
should be determined on experimental tests of prisms with three
blocks. BSI-5628-1 [10] presents graphs of the characteristic com-
pressive strength of brick or block masonry for different classes of
units and mortars, which is based on the design and the propor-
tions of cement, lime and sand by volume as follows:
i
(1:0.25:3),
ii
(1:0.5:4.5),
iii
(1:1:6) and
iv
(1:2:9). As shown in Figure 06, the ratio
of the compressive strength of the walls in relation to the compres-
sive strength of blocks tends to decrease with increasing compres-
sive strength of the block, and this ratio is higher for bricks than
for blocks. The BSI 5628-1 [10] considers only the relation of the
dimensions (height and width) of the block and does not taking
into account the geometry and the arrangement of the hollows.
For walls with relation between height (h) and width (w) of 0.6 to
2.0, the value of the compression strength of masonry should be
obtained from Figure 06.
3.2 The influence of block geometry on
the compressive strength of masonry
During the load application, the quantity and the arrangement of
hollows and shapes may lead to a concentration of stress on the
block that can decrease the potential strength of masonry, accord-
ing to work performed by GANESAN and RAMAMURTHY [11].
The authors stated that it is necessary to understand the geometry
effect of blocks to increase the efficiency of structural walls. The
authors carried out some analytical studies using finite element
methods to better understand the behaviour of concrete masonry
blocks, taking into account the influence of different geometries,
arrangements and properties of mortars. GANESAN and RAMA-
MURTHY [11] proposed the use of blocks with three types of ge-
ometry, including one with a double central web, that is, where the
thickness of the central web was twice the thickness of the face
shell that provides the alignment of the hollows. The geometries
were modelled with stack and running bond prisms with three
courses, using three different geometries of concrete block: blocks
with three hollows, blocks with two hollows and blocks with two hol-
lows and a double central web. Four types of mortar were used in
the masonry to compare the proportion between the elasticity mod-
ulus of blocks (
E
b
) to that of the mortar (
E
a
), where the proportions
were 1; 1.5; 2.0 and 2.8, while
E
b
was held constant. Establishing a
stiffness ratio of
E
b
/E
a
as a constant was found to affect the mortar
and the failure mode of the masonry. It was used a heterogeneous
elastic-linear behaviour in the model, by using a solid element of
eight (8) nodes for determining stress on the face shells and cross
Figure � � Types of the blocks studied by
GANESAN and RAMAMURTHY [11],
with the dimension in mm tested
at Building Technology Laboratory
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