Research report submitted to the Faculty of Engineering and the Built Environment, University of
Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of
Science in Engineering
Johannesburg 2017 / This report investigates the seismic response of catenary vaults. Through a series of
tests, the inherent seismic resilience of catenary vaults was assessed and a number
of reinforcement strategies were investigated to improve this.
An analytical model, based on the virtual work method, was developed by
Ochsendorf (2002) for the assessment of circular voussoir arches. This model was
adapted for catenary vaults. This model is used to calculate the minimum lateral
acceleration required to cause the collapse of a catenary vault (λmin) for any catenary
profile.
The model indicates that there is a linear relationship between cross sectional depth
of the arch and λmin until the depth to ratio passes approximately 0.3, where the
change in λmin becomes exponential. Using the model, it is also predicted that λmin
decreases exponentially with an increase in the height to width ratio up to a value of
approximately 1.6. After this point λmin linearly decreases with increased height to
width ratios and approaches zero.
The first series of tests involved subjecting unreinforced catenary vaults to seismic
loading. In these tests the frequency of vibration was varied and the stroke was kept
constant. From the results of the tests, it was found that there was no frequency at
which the vaults underwent excessive vibration due to resonance. It was observed
that during seismic loading, hinges form at locations where pre-existing cracks occur
despite the higher computed λmin values for these positions. The tests also indicate
that the vaults’ behaviour changes drastically with each hinge that forms.
In the next series of tests the frequency was set and the stroke was increased. The
vaults were subjected to seismic loading at 2 Hz and 6 Hz, representative of low and
high frequencies respectively. The tests indicated that the collapse acceleration of
arches subjected to vibration at 2 Hz was lower than that of the vaults subjected to
vibrations at 6 Hz. Despite this, the stroke, representing ground movement, required
to cause collapse at 2 Hz was substantially higher than that of the 6 Hz tests. This
indicates that the duration of load cycles has an effect on the collapse acceleration.
In comparing the computed collapse acceleration, λmin, with the actual collapse
accelerations, it was found that the computed values are highly conservative. Yet
this is expected as the model is based on an infinite duration of lateral loading. It was
found that the analytical model was more accurate for low frequency tests as
compared to high frequency tests in terms of the predicted hinge locations.
Finally, three reinforcement strategies were investigated using basalt fibre geogrid.
This was found to be an economical and viable reinforcement material. The first
strategy consisted of laying the geogrid over the arch and securing it at the arch
base. The second was the same as the first with the addition of anchors which held
the geogrid down. The final strategy involved prestressing the arch using the
geogrid. The latter 2 methods were found to be the most effective, with observed
collapse accelerations being over 60% higher than that of the same unreinforced
arch. The anchorage solution was found to be the most viable due to the
substantially higher technical input required for the prestressing solution. / MT2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/22992 |
| Date | January 2017 |
| Creators | Surat, Daniel |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (163 leaves), application/pdf |
Page generated in 0.0021 seconds