CONTENT 5.1 SEISMIC BEHAVIOUR ... - CIB-W18

of loading tests in structures after assembly, proposing an agile dynamic
variant to them.
General
Dynamic tests on structures (free vibrations)
In the field of structures already assembled, be they in steel, reinforced
concrete or maonry, dynamic test methods have already started making
themselves known.
Just to give a broad outline, these methods consist of exciting the structure's
free vibrations, detecting the relative frequencies by means of accelerometers
or other instruments capable of detecting vibrations more generically,
and comparing results to those predicted according to a mathematic
model previously prepared.
Application field
These tests are not only applicable to structures which have to support dynamic
actions during their life span, but also to every type of structure as
they enable one 0n one hand to obtain experimental indications useful in
finding a more precise theoretical model of the structure, and on the other
in finding principal "elastic" parameters of the material. All this is done
through general information, that is not limited to a few sections and
which is obtained through tests that are not expensive owing to loading
means and times even if, on the contrary, they require sophisticated experimental
survey equipment.
The case of wooden structures
The present paper's writers think it is not unsuitable to start experimenting
this testing methodology on wooden structures, especially if one considers
that this method requires excitations lasting' only for few seconds; it enables
one to derive indications that are not affected by time as in the case of
static loading.
Moreover, the static loading due to their own nature, in the case of assembled
structures of a certain dimension and structural complexity, can't
be easily codified and lead to results that are anyway affected by creep
phenomena in the wood, which are not negligible right from the tests beginning
unlike other building materials such as steel and concrete, for example.
Other dynamic tests
Other dynamic methods like the resonance or ultrasonic tests which have
already come into use and which can be used for the stress-grading of
sawn pieces of wood are unsuitable for large structures already being assembled
whether due to the very-nature of the test (in the case of the resonance
test, it can be carried out easily in a laboratory on specimens of reduced
dimensions but it can become very problematic on assembled structures
or due to the power of the necessary equipment which in the case of
ultrasounds should be much higher than that used at present for stressgrading.
The sonic method is easier to use but it enables one to obtain useful indications
of single structural elements but not of the whole structure taken
as a whole.
Subject of the present paper
The present work illustrates an example of application of the proposed
methodology just at it was used during testing carried out on a structure in
glued-laminated timber with a span of 40 m.
Conclusions
Also for timber structures, the dynamic testing methods with the excitation
of free oscillations, already applied successfully to structures in otter materials,
seem worthy of being refined through further theoreticalexperimental
studies, due to their positive contribution when checking
structures already assembled in terms of results validity and in terms of reduction
of test.
19-15-1 A Ceccotti, A Vignoli
Connections deformability in timber structures: a theoretical evaluation
of its influence on seismic effects
Object and scope
Timber construction plays an important role in many areas throughout the
world, and finds a wide application in low-cost residential dwellings and
public buildings.
Many of the areas where wooden structures proved to be very feasible are
highly seismic regions; indeed, as earthquake experiences have taught,
they provide a very good response to seismic waves.
CIB-W18 Timber Structures – A review of meeting 1-43 5 SPECIAL ACTIONS page 5.6