Geoscience Reference
In-Depth Information
the description of geological effects such as liquefaction, far-way effects, etc., are
important points where we can gain additional information. Several of these topics
were already addressed in detail. In this Section we will look into a few new topics
of great importance to understand incoming ground motion, namely looking at
The Aqueduct: “Aqueduto das Aguas Livres”;
-
-
The Corner Building: “Torreao do Terreiro do Pa¸o”;
-
The liquefaction distribution and the sinking of “Cais das Colunas”;
-
The return period associated to the event from paleoseismology related to the
tsunami.
Aguas Livres”
5.1 The “Aqueduto das
The “Aqueduto das Aguas Livres” in Lisbon, a magnificent masonry structure built
a few years before the earthquake, is a long structure crossing the Alcantara Val-
ley supported by tall pillars that transform into arches. It behaved quite well dur-
ing the earthquake suffering only stone block displacement in three airing towers
(“Torreoes”). The damaged towers were the ones positioned along the deck where
the heights in relation to the valley were larger.
Many analytical and experimental studies were performed to evaluate the seis-
mic input that generated the minor damage observed. Mathematic models were
developed after determination of the mechanical properties of the materials, and
were calibrated through the values of frequencies of vibration obtained with in-situ
measurements (Fig. 18), both with ambient noise vibration (Oliveira 1986) and from
records obtained during recent earthquakes (Oliveira 2005). Results indicate that
Peak Ground Accelerations (PGA) at the soil level that provoke the observed dam-
age should not have surpassed 100-150 cm/s 2 . Sincraian et al. (1998) developed
complex 2-D and 3-D non-linear models to obtain ultimate seismic loading causing
the collapse of the structure, and the PGA values obtained for the longitudinal direc-
tion are above 1 g. In the transverse direction, PGA values of 0.3-0.5 g are enough
to provoke the collapse of the structure.
5.2 The Corner Building: “Torreao do Terreiro do Pa¸o”
The “Torreao do Terreiro do Pa¸o” was a magnificent structure built just prior to the
1755 earthquake. As today, it is a massive good masonry structure (Fig. 19) founded
in a soft soil of a few tens of meters. The fundamental frequency of this structure
measured nowadays is on the order of 4-5 Hz. Assuming that the original structure
was similar to the present one, we can say that damage to the “Torreao” was not very
important. It seems that the vertical crack observed in Fig. 19 was essentially due
to settlement of the foundation soil, and the part at the lower section with diagonal
pattern denotes the N-S movement of incoming waves. In the adjacent cloister type
Search WWH ::




Custom Search