In reality, masonry is loaded under a triaxial stress-situation.
By taking cores from the masonry, it is liberated from this three-dimensional stress state. Further compressive tests on these cores cannot simulate the original three-dimensional stresses. The confining stress from the surrounding masonry units in-situ is lost. For the research of masonry under triaxial stresses, a triaxial cell will be installed at the Reyntjens Laboratory (end of September 1997). The technical characteristics are outlined in table 1.
| Triaxial cell | |
| dimensions of the cores | F = 150 mm, h = 300 mm |
| maximum confining stress (sIII) | p = 15 MPa |
| piston | F = 150 mm, range = 50 mm |
| data acquisition: | LVDT : 4 vertical (50mm), 4 horizontal, (25mm) |
| vertical force | DARTEC compressive press |
Research will focus on the influence of the
confining stress on the compressive strength of the masonry. Therefor as
well horizontal (a = 0°) as vertical ( a = 90°) taken cores will be
tested.
The target is also to become information about the strength relation
between horizontal and vertical taken cores, as in reality often cores are
taken horizontally for practical reasons. As the slenderness of the
masonry cores has a great influence on the compressive strength, the test
program will include cores with a height of 190 mm (thickness of 1 stone
masonry) and cores with a height of 300 mm (slenderness l = 2). In-situ it
will not always be possible to take cores of relatively great height
because of the weak mortar in the bed joints. Then having the disposal of
a correction factor to correct for the obtained slenderness is useful.
Following data will be measured:
f'm : the compressive strength of the masonry,
s - e , E , n : the stress-strain relationship, modulus of elasticity and
coefficient of Poisson, graphical interpretation of the occurring failure
mode.
The next aim is to become the material
properties required to define theCoulomb type limit state function:
- (mode I) shear failure of bed joints: gL1 : c + msy
- tyz = 0.
The parameters c en m will be looked for using masonry cores taken at
different angles: a = 0°, 30°, 45°, 60° en 90°. The objective is to
find out the influence of a preferential failure plane, which is presumed
to follow the bed joints, figure 1.
By means of the confining stress sIII it is possible to reach different failure points (si ,ti) on the limit state surface gL1, from which the parameters of the probability distribution function for the stochastic variables c and m can be estimated.
The evolution of the main stresses sI en sIII as a function of time is outlined in figure 1. The stress-levels that need to be applied in the test will be looked for in a preliminary research program. The software needed for the joined real-time interaction of the triaxial cell and the compressive stress (Dartec compressive press) to become the load-path as outlined in figure 1 ore others, is part of the research.
To eliminate the influence of scale effects on the shear characteristics c en m, future research foresees comparative shear-tests on masonry panels. Further filling in of the test setup depends on the results obtained from the shear-tests on cores in the triaxial-cell.
These tests must give the information necessary to obtain the parameters characterizing the failure envelop of the masonry.
Copyright 1996, Katholieke Universiteit Leuven
Information provider: Katholieke Universiteit Leuven
Responsible for the contents: L.
Schueremans
Page Lay-out: Danny Uten
URL: http://www.bwk.kuleuven.ac.be/bwk/materials/ls02.htm