Ian Hume has good news
on the likely effects of traffic vibration
old buildings


ROAD TRAFFIC VIBRATION
ON HISTORIC BUILDINGS
VIBRATIONS & BUILDINGS
The effects of vibration on buildings and
their occupants is a very technical and
complex subject. Vibrations can be
caused by passing road traffic, by rail-
ways, both surface and underground, by
users of the building and by numerous
other sources including blasting and build-
ing works, particularly piling. When heavy
goods vehicles pass, windows vibrate,
ornaments rattle and vibrations may be
felt by the occupants. As well as being
technically complex it is a very emotive
subject.
The response to vibrations by the
inhabitants of the buildings may range
from mild annoyance, through to grave
alarm, probably via sleepless nights, but
it must be remembered that the human
body is a very sensitive instrurnent and it
will ‘register’ the most minute sensations.
Unlike sophisticated scientific
equipment, the human body sometimes
has difficulty in sorting out the effects of
vibration from those caused merely by
noise. The human mind and body are
affected by. thoughts and opinions
whereas scientific equipment. takes
measurements without such
psychological distractions.

VIBRATIONS FROM ROAD TRAFFIC
A passing lorry generating a lot of noise
will draw attention to itself and the ob-
server may therefore be more suscepti-
ble to a level of vibration which, without
the accompanying sound, might pass
unnoticed.
The condition of the road surface near
the building has a very significant effect
on the levels of vibration; vehicles on a
smooth road surface create much lower
levels of vibration than do similar vehicles
travelling at similar speeds: on an uneven
surface. Poor road surfaces with badly
filled potholes or service trenches will
generate vibrations, particularly if the
traffic is fast moving and/or heavy.
However, BRE Digest 353 of July 1990
Damage to structures from ground-borne
vibration states “Although vibrations
induced in buildings by ground-borne
excitation are often noticeable, there is
little evidence that they produce even
cosmetic damage (ie small cracks in plaster)”.
Between 1986 and 1988 members of
the Conservation Engineering Branch of
English Heritage collaborated with the
Transport and Road Research Laboratory
(TRLL) in the production of two reports:
namely TRILL Research Reports 156 and
207. These both relate to the effects of
vibration on historic buildings and were
produced as a result of a number of
investigations on historic buildings in
varying conditions.
At all sites, ground-borne road traffic
vibration was the most significant source
of building vibration; however, when the
road surface is even, airborne vibrations
dominated. Peak vibration levels were, as
might be expected, greater on the upper
floors and walls at the front of the building
rather than at foundation level. Despite
the relatively high vibration levels, crack
movements measured on existing cracks
were small, being much lower than those
observed for normal variations in
temperature and humidity.
Window pane vibrations were found
to be relatively high but at one site (a
church with only a narrow footpath
between the wall face and the kerb)
where stained glass windows exposed to
high levels of airborne road traffic
vibration were compared with similar
windows at much greater distances from
the road, no differences in their condition
were found which could be attributed to
traffic vibration.
The English Heritage Conservation
Engineering Branch input to the
investigations which resulted in the
publication of the these reports was to
inspect the buildings, to report on the
cracking and other signs of distress and to
assess the possible causes. Some fractures
in the buildings were clearly attributable
to settlement, some to thermal and
climatic movements and others due to
decay or overload. Most were patently
nothing to do with the effects of passing
road traffic. One village corner shop had,
suffered major damage when a large van
suddenly appeared in the sales area, but
this had little to do with vibration which
it caused!
Cosmetic damage, cracking of plaster
for example, might be attributable to
traffic vibrations but even this is a very
difficult question to resolve.
To draw ‘scientific’ and quantitative
conclusions from the work done in
collaboration with TRILL was difficult,
but it was our opinion that vibrations
from road traffic did not cause any’
problems to the structure of a fairly robust
historic building, but that they might
possibly cause problems to’ fragile
buildings, probably exacerbating existing
cosmetic damage. However, it was also
our view that these fragile buildings were
in such a poor condition that they
demanded repair even without the effects
of road traffic vibration being taken into
account.
In our opinion, the traffic vibration on
a building would become intolerable to
the occupants long before structural
damage was caused.
Clearly road traffic vibrations cause
major problems to those people who
have the misfortune to live in properties;
affected by large volumes of heavy traffic.
It would be interesting to hear of any
cases where road traffic vibration is
thought to be causing problems to the
structure of buildings rather than just
being tiresome for the occupants.
Other sources of vibration such as
nearby piling or blasting may well create
vibrations of a much more serious level’
will have a greater potential for damage
and therefore must be treated accordingly.
The object of this article is to generate
some discussion rather than to be an
authoritative statement on the subject;
feedback will be most welcome. Please
respond to: 429 Oxford Street, London,
W1R2HD.
Ian Hume DIG DiplConsAA CEng MlStructE, is
the Chief Engineer (Conservation Engineering
Branch) atEnglish Heritage
EFFECTS OF
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