CONTENT 5.1 SEISMIC BEHAVIOUR ... - CIB-W18
CONTENT 5.1 SEISMIC BEHAVIOUR ... - CIB-W18
CONTENT 5.1 SEISMIC BEHAVIOUR ... - CIB-W18
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Discussion<br />
Being the design ground acceleration PGAcode, equal to 0.35g, by applying<br />
the procedure given in 2.2, the q value is:<br />
q 1,20 / 0,35 3,4<br />
Of course the above value is valid only referring to the used Nocera Umbra<br />
ground motion record. A series of different quakes should be used with<br />
the same procedure. This is obviously impossible; therefore the importance<br />
of a good mathematical model that can simulate different quakes<br />
and cases is obvious.<br />
In any case, the above value has its own significance as an indicator.<br />
Moreover, it must be considered that the building has passed without any<br />
important reparation at least 14 "destructive" quakes in a row. It has kept<br />
its shape even with the last quake that has produced the near-collapse<br />
state. That means that this typology seems very promising when the design<br />
philosophy in seismic areas would convert to the NDD – no damage design<br />
– approach.<br />
39-15-3 A Heiduschke, B Kasal, P Haller<br />
Laminated timber frames under dynamic loadings<br />
Summary<br />
This paper discusses the results of time-history analyses of four-story moment-resisting<br />
timber frames subjected to various seismic loadings. The<br />
purpose of the case study was to document the difficulties, which arise due<br />
to large story drifts of the frames caused by the soft character of moment<br />
transmitting connections using dowel-type fasteners. Two frames were designed:<br />
one according strength and the second according stiffness requirements<br />
stipulated by the seismic code – EC8. From the design procedure<br />
it follows that, in general, the serviceability limit state design is the<br />
limiting criteria. Unacceptable lateral drifts made it necessary to increase<br />
the joint stiffness. Since connection stiffness increases significantly with<br />
the depth of the member, the member size inclusive the number of the fasteners<br />
was enlarged. This, in combination with densified and textile reinforced<br />
wood resulted in a frame design with an adequate lateral stiffness<br />
keeping the inter-story drift within the limit stipulated by the seismic code.<br />
The numerical model used to simulate the structural response of the<br />
frames utilized the hysteretic formulation of nonlinear connection behav-<br />
ior. The results of the dynamic pushover analysis were used to evaluate<br />
and verify the behavior factor q. In the seismic code, the elastic spectrum<br />
is modified with this factor to obtain an inelastic design response spectrum<br />
that is used to determine equivalent static forces.<br />
Conclusions<br />
From the design procedure it follows, that in general the SLS design will<br />
be the limiting criteria in the design process of moment-resisting frames.<br />
The inter-story drift of the frame designed in accordance to the strength<br />
and ductility criteria, exceeded the seismic code limitation at the SLS. The<br />
unacceptable deformations made it necessary to increase the joint stiffness.<br />
Since the stiffness increases significantly with the depth of the member<br />
size inclusive the number of the fasteners was enlarged. This, in combination<br />
with densified and textile reinforced wood, resulted in a frame design<br />
with an adequate lateral stiffness keeping the inter-story drift within the<br />
limit stipulated by the code. Over-sized members and a lateral strength<br />
larger then the design story shear characterize this frame-S, designed according<br />
to the stiffness requirements.<br />
From the modal analysis one can conclude that for the evaluation of the<br />
first fundamental period of the system, the connection behavior has to be<br />
taken into account. For the frame-C, long periods (T > 2s), were evaluated<br />
due to the low rotational stiffness of the connections. The structures were<br />
not within the period range of typical earthquakes and this result in small<br />
inertia forces. In order to get reasonable structural deformations, specific<br />
earthquakes, characterized by soft soil conditions were selected for the<br />
nonlinear time-history analysis.<br />
The frame-S had an adequate lateral stiffness to keep the inter-story<br />
drift at a reasonable level for strong ground motions up to 0.6g. In either<br />
simulation the frame performance improved with story drift reductions of<br />
25% to 160% when using densified wood.<br />
The cyclic test on connections have shown that textile reinforced joints<br />
have at least medium ductility, so that these frame types can be classified<br />
as structures having a medium capacity to dissipate energy. As a consequence,<br />
a q-factor of 2.5 can be assumed for the studied statically indetermined<br />
frames. The numerical time-history analysis showed that a q-factor<br />
of 2.5 is acceptable for the investigated frames.<br />
<strong>CIB</strong>-<strong>W18</strong> Timber Structures – A review of meeting 1-43 5 SPECIAL ACTIONS page 5.25