Behaviour of GFRP strengthened masonry wall panels under base shock vibrations
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Masonry structures are prone to extensive damage followed by
failure and collapse when subjected to loads resulting from wind, earthquake
and other natural or man-made events. Recent earthquakes and terrorist acts
have clearly demonstrated the need for the development of effective and
affordable strategies for the strengthening of masonry. As a response to these
challenges, fiber reinforced polymer (FRP) composites are found to offer
technically and economically viable solutions. In the context of research
undertaken worldwide, this thesis presents an overview of the studies and
field applications of masonry strengthening with FRP composites as
conducted in the last few decades.
In particular, the thesis covers basic materials and installation
techniques, namely: externally bonded laminates, experimental test programs
dealing with the out-of-plane behaviour of walls with discussion of failure
modes and applications including historical structures. Without providing full
details, an effort has been made to address issues related to design so that
practicing engineers can immediately appreciate the potential of this
technology and understand the key parameters affecting performance and the
areas that need further experimentation. The objective of the research is to
study the failure pattern of simple masonry elements with and without GFRP
wrapping subjected to base shock vibrations for out-of-plane loadings, the
behaviour of GFRP wrapped masonry elements were compared with
conventional masonry elements in terms of first crack load, energy
absorption, velocity of impact, cumulative energy, Peak Base Acceleration
(PBA), and Peak Response Acceleration (PRA).
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Further, to critically analyze the effectiveness of different GFRP
layouts subjected to base shock excitation and to observe the response of the
wall by changing different impact actions. Also, to assess the accuracy and
performance of available analytical formulations from masonry standards of
masonry walls and to compare the experimental results with the values
obtained from numerical and analytical study was made to understand the
failure modes. This thesis starts with a brief review of the existing
rehabilitation methods available and explains that the use of FRP is a possible
alternative. Results of material tests performed on the masonry and fiber
materials are then presented.
The overall results show that externally applied FRP greatly
increases the strength and energy absorption capacity of un-reinforced
masonry walls. This thesis reports on finite element models which are
developed to predict the response of masonry walls in the case of out-of-plane
loading. The wall panels made of clay bricks were investigated and the
effectiveness of different types of FRP elements used for strengthening is
analysed. The behaviour of FRP strengthened masonry walls subject to out-
of-plane loading is examined and then both experimental and numerical
results compared and found to be in close agreement.
In this investigation, an un-plastered and plastered masonry panel
of size 1 m x 1 m x 0.15 m was installed on a specially developed shock table
for this occasion and tested. Under the base impact, using pendulum of
varying masses and height of fall, collection of details of time history of
vibration, acceleration, energy absorption, and failure pattern of panels is
possible. The panels were repaired using three different types of GFRP
wrappings, namely, vertical, diagonal and inner diagonal patterns.
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They were later tested in the same manner and corresponding
quantities were collected. The frequency of unrepaired panel was 10 Hz and
that of repaired panel was 17.5 Hz.
The energy absorption of the plastered wall panel was greater than
that of unplastered one by 2.75 times. In the case of unplastered and
strengthened panel with GFRP, the energy absorption was 65 times higher
than that of un-strengthened and un-plastered panel. In the case of plastered
and strengthened panel, energy absorption was 34.45 times higher than that of
plastered panel without GFRP wrapping.
Among the GFRP strengthened and plastered wall panels, those
provided with diagonal inner wrappings behaved well and sustained a greater
number of impacts and absorbed more energy.
The conclusion drawn from this experimental and numerical
investigation is that panel strengthend with GFRP behaved monolithically by
preserving its integrity, enhancing higher energy absorption and sustaining
more numbers of impacts over virgin panel.
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