Influence of earthquake spatial variability on differential soil displacements and SDF system response

Abstract

SUMMARYThe aim of this study is to develop design criteria, which account for the e ects of earthquakes spatial variability. The two simplest forms of this problem are dealt with: di erential ground displacements and di erential structural displacements, for points and structures separated in space. The structures considered are linear elastic single degree of freedom oscillators. These problems may seem trivial, but some of the codes considered appear improvable on this aspect.First, the mathematical model is set up using basic random vibration theory and the code provisions critically examined. Then, the sensitivity of the ground and structural di erential response is assessed. The di erential displacements can be mathematically expressed in a straightforward fashion, both for the ground and the structures. These expressions are simple enough to be used as design rules.Comparison with the European and Italian Civil Protection codes shows that these can be improved on this aspect; and, for this reason, the Italian draft code for bridges has been mainly drafted following the results of this study.

Surface Generation of Asynchronous Seismic Signals for the Seismic Response Analysis of Bridges

“…The EW accelerometric components, recorded at AQA and AQV strong motion stations during the main-shock of L'Aquila seismic event happened on 04-06-2009, were used as inputs to generate arrays of asynchronous earthquake signals at the ground surface in correspondence of three points in a line with a span of 50 meters, possible foundation points of a bridge, through the software GAS 2.0 [6,7,9,10,[26][27][28][29].…”

“…These positions were chosen to consider accelerometric signals at the bridge foundations which have differences due to: (i) the distance among the generation points and (ii) the local site effects due to the soil characteristics below each generation point. The software GAS 2.0 -Generation of Asynchronous Signals-was used to obtain the asynchronous accelerometric signals at surface on the base of the generation procedure described in [6,7,28 Figure 1) placed on the soil U-AQA or on the soil U-AQV; (iv) the characteristics of the input signal (power spectrum) recorded at AQA to include the local site effect (wave-soil interaction) in U-AQA for the generation points 1-4; (vi) the characteristics of the signal (power spectrum) recorded at AQV to include the local site effect (wave-soil interaction) in U-AQV for the generation points 5-9.…”

“…However, synchronous actions are usually considered during the design and this practice can be unsafe in case of long structures [1][2][3][4][5][6][7][8][9][10][11][12]. There are a few international design codes [13][14] which consider the effect of asynchronous seismic actions applying relative displacements among the foundation points.…”

“…This procedure considers the signal frequencies content variation and the different arrival time of the wave from point to point. The numerical asynchronous signals generation procedure described in [6,7] was improved [28,29] and implemented in MATLAB [30] as a framework of functions named GAS 2.0 -Generation of Asynchronous Signals -.The signal frequency content at each point is calculated by assuming a normal distribution of the signal amplitudes. The mean and variance of this normal distribution are obtained from point to point considering the amplitudes of the signals generated at previous points by means of the joint conditioned probability theory and the covariance matrix of the propagation problem.…”

Seismic Behaviour of Isolated Rc Bridges Subjected to Asynchronous Seismic Input

“…Designers of long structures should take in account these differences to define with attention the asynchronous design actions which can be more detrimental than the synchronous ones [1][2][3][4][5][6][7][8][9][10][11][12].…”