Stability of Dry-Stack Masonry
Date
2006-11-01T08:07:10Z
Authors
Ngowi, Joseph Vincent
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Abstract
This thesis presents the findings on empirical study of dry-stack masonry.
Dry-stack masonry refers to a method of building masonry walls, where most of
the masonry units are laid without mortar in the joints. Of late (since mid eighties)
in modern construction, dry-stacking or mortarless technology is increasingly
becoming popular because of its advantages. The construction industry is
acknowledging the need to accelerate the masonry construction process, as the
traditional method is labour intensive and hence slower due to the presence of a
large number of mortar joints. Early attempts were made to increase the size of
masonry units (block instead of brick), thereby reducing the number of mortar
joints, wherein the use of bedding mortar imposed constraints on the number of
courses to be constructed in a day. Elimination of bedding mortar accelerates
construction; thereby reducing cost, variation due to workmanship and generally
small pool of skilled labour is required in dry stacking. Dry-stack masonry is a
relatively new technology not yet regulated in the code of practice and therefore
very limited information on the structural behaviour of the masonry is available.
This project is based on the investigation of the HYDRAFORM dry-stack system,
which utilises compressed soil-cement interlocking, blocks. The system is now
widely used in Africa, Asia and South America. The main objective of the project
was to establish through physical testing the capacity of the system to resist lateral
load (e.g. wind load), vertical load and dynamic load such as earthquake loading.
In the first phase of the project investigations were conducted under static loading
where series of full-scale wall panels were constructed in the laboratory and tested
under lateral loading, and others were tested under vertical loading to establish the
mode of failure and load capacity of the system. Series of control tests were also
conducted by testing series of wallettes to establish failure mechanism of the units
and to establish the flexural strength of the system. Finally the test results were
used for modelling, where load prediction models for the system under vertical
loading and under lateral loading were developed. The theoretical load prediction
models were tested against the test results and show good agreement. After the load capacity was established the next step in the study was to further improve the
system for increased capacity particularly under dynamic loading. The normal
Hydraform system was modified by introducing a conduit, which allows
introduction of reinforcements. Series of dry-stack seismic systems were
constructed and initially tested under static lateral loading to establish the lateral
load capacity.
The second Phase of the project was to investigate the structural behaviour and
performance of the Hydraform system under seismic loading. A shaking table of
20 tonnes payload, (4m x 4m) in plan was designed and fabricated. A full-scale
plain dry-stack masonry house was constructed on the shaking table and subjected
to seismic base motions. The shaking table test was performed using sine wave
signals excitations starting from low to very severe intensity. A conventional
masonry test structure of similar parameters was also constructed on the table and
tested in a similar manner for comparison. The tests were conducted using a
frequency range of 1Hz to 12Hz and the specimens were monitored for peak
accelerations and displacements. For both specimens the initial base motion was
0.05g.
The study established the mode of failure of the system; the structural weak points
of unreinforced dry-stack masonry, the general structural response of the system
under seismic condition and the failure load. The plain dry-stack masonry failed at
0.3g and the conventional masonry failed at 0.6g. Finally recommendations for
further strengthening of system to improve its lateral capacity were proposed.
Description
Student Number : 0100677A -
PhD thesis -
School of Civil and Environmental Engineering -
Faculty of Engineering and the Built Environment
Keywords
dry-stack masonry, interlocking block, flexural strength, lateral loading, natural frequency