GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 2.3 GNGTS 2024 During outreach events for the secondary school, we show models displaying some aspects of seismic site efects (Fig. 2a). Two seismometers installed into sand and gravel flled buckets are used to show lithostratgrafc seismic amplifcaton. A jump by students simulates earthquake shaking and waveforms from the seismometer installed on sof soil (sand) are visually compared with those recorded on hard soil (gravel). Soil liquefacton is shown with a model of buildings at a small scale placed on top of water- saturated sand. A small engine shakes the sand untl the typical shear strength is drastcally reduced by the increasing pore pressures. The phenomenon can be observed by the appearance of water that overturns scaled models of buildings. Buildings response to ground shaking: the Shake-It! Laboratory The general public ofen asks questons such as “why do buildings collapse?”. To explore in depth the concept of vulnerability to seismic ground shaking, a laboratory about buildings’ resonance has been implemented. The dynamic characteristcs of buildings play an important role in predictng their seismic behaviour and therefore their vulnerability. This parameter is highly important during an earthquake, since, if an earthquake carries signifcant energy near the natural period of the structure, or if the foundaton’s sof soil has its predominant period near the structure’s period, the physical phenomena of resonance could happen (Mucciarelli et al., 2002). In the “Shake it!” laboratory key aspects of this concept have been addressed highlightng that the largest oscillatons occur when earthquake frequency matches the building’s natural frequency. A metal structure building-model placed on a unidirectonal small-scale educatonal shaking table was used to visualize the downscale phenomenon of earthquake building resistance. A wi-f accelerometer placed on top of the building, and a second one on the platorm, that Is at the base of the building-model, were used to measure the ground-shaking displayed on a monitor. A real earthquake and a synthetc sinusoidal signal, in a 2Hz to 10Hz frequency range, were used as input for the shaking table. While the real signal was used to highlight the diference between the shaking at the ground and that on top of the building, the synthetc sinusoidal allowed to visualize the phenomenon of the resonance (Fig. 2b). Afer watching the shake table experiment the class was asked to make its own experiment. The building-model had to be done using spaghet and marshmallows and the shake table was made by a cardboard platorm on top of a small electrical engine. The challenge was to build the frame structure as tall and stable as possible. To have a more stable structure it was suggested to add braces. The building-models were placed on the shake-box to verify its seismic performance (Fig. 2c). Key-issues on community preventon and preparedness: Videogaming actvity Risk communicaton must enhance both preventon and preparedness to a seismic event. These concepts could be summarized by two key questons: