Ambient Vibrations Measurements and 1D Site Response Modelling as a Tool for Soil and Building Properties Investigation

Abstract

Abstract:The safety of historic buildings heritage is an important task that becomes more substantial when it is directed to educational purposes. The present study aims at evaluating the dynamic features of the Benedettini complex, a historic monastery located in downtown Catania, which is at present the headquarters of the humanistic studies department of the University of Catania. Both the building's complex response to a seismic input and the soil-structure interaction were investigated using ambient noise recordings. The results point out a multiple dynamic behaviour of the monastery structure that shows several oscillation modes, whereas the identification of a single natural frequency can be observed in some sites where the structure can more freely oscillate. This observation is also confirmed by the variability of computed damping values that appear linked to the different rigidity of the structure, as a function of the either the longitudinal or transversal orientation of the investigated structural elements. Moreover, the comparison between the building's fundamental period and spectral ratios frequencies, which were obtained from free field ambient noise measurements located outside the monastery, outline the presence of potential resonance effects between the site and structure during a seismic event. Numerical modelling of the local seismic response confirms the obtained experimental site frequencies, setting into evidence that higher amplification factors are reached in the same frequency range characterizing the building.

Assessment of the Seismic Site Amplification in the City of Ivanec (NW Part of Croatia) Using the Microtremor HVSR Method and Equivalent-Linear Site Response Analysis

“…Geosciences 2019, 9,312 19 of 25 response peak amplification in an area mostly dominated by coarse-grained clastic sediments (soil category B based on EC8) and which could possibly be prone to topographic site effects. Clearly, site response peak amplifications are correlate better with VS30 ( Figure 11) and input seismic ground motions (0.09 g and 0.19 g) than HVSR peak amplitudes, although similar distribution may be observed when the three maps are compared to each other [22,23]. Soft soil can play a very important role in the amplification (or de-amplification) of ground motion when propagated from bedrock to the surface (Figure 12d).…”

“…These maps clearly distinguish two major seismic microzones: the highest site response peak amplifications that occurs in the alluvial basin of Bednja River (also covering the central city area) where soft soils such as sands and gravels are dominant (designated as soil category C based on EC8 V S30 classification), and the zone exhibiting a smaller site response peak amplification in an area mostly dominated by coarse-grained clastic sediments (soil category B based on EC8) and which could possibly be prone to topographic site effects. Clearly, site response peak amplifications are correlate better with V S30 (Figure 11) and input seismic ground motions (0.09 g and 0.19 g) than HVSR peak amplitudes, although similar distribution may be observed when the three maps are compared to each other [22,23]. Soft soil can play a very important role in the amplification (or de-amplification) of ground motion when propagated from bedrock to the surface (Figure 12d).…”

“…Figure 12d shows the propagation of input ground motion from the bedrock level to the surface using a multi-layered soil column model. The main amplification effects are observed at the top soft surface soil layers [10,22,29,65]. The bedrock layer is defined as an elastic-half space with a unit weight of 24 kN/m 3 , 2% damping and V S = 800 m/s [41].…”

“…The seismic site amplification map for the city of Ivanec was derived from individual HVSR and site response analyses using a spatial interpolation method as applied for maps of fundamental frequencies ( Figure 6), sediment thickness ( Figure 9) and V S30 (Figure 11). Since the HVSR peak amplitude is only an indication of amplification in natural state and is related to impedance contrast between sediments and bedrock, the question remains as to the qualitative validity of HVSR peak amplitudes and differences between whole spectral HVSR amplitudes and seismic site response (amplification) for the local site when subjected to earthquake influence [21][22][23][24]. For these reasons, all three maps in Figure 13, i.e., the map of HVSR peak amplitude and maps of site response peak amplification for PGA ROCK = 0.09 g (95yrp) and 0.19 g (475yrp) are shown together to better perceive differences between HVSR peak amplitude and seismic site response (amplification).…”

“…The microtremor horizontal-to-vertical spectral ratio (HVSR) methodology expressed by the natural/fundamental soil frequency and HVSR spectral peak amplitude, introduced by Nogoshi and Igarashi [11] and extensively revised by Nakamura [12], has been used in numerous studies for estimating local seismic ground response, particularly in Slovenia, Italy, and Croatia [13][14][15][16][17][18][19][20]. The estimated HVSR site frequency and peak amplitude provides only an indication of the initial soil site frequency and amplification without earthquake activity [21][22][23][24]. One-dimensional (1-D) equivalent-linear (EQL) site response analysis estimates the effects of local soil conditions on ground shaking, based on one-dimensional wave propagation theory [5].…”