Effects of Digital Filtering in Data Processing of Seismic Acceleration Records

The paper presents an application of digital filtering in data processing of acceleration records from earthquakes. Butterworth, Chebyshev, and Bessel filters with different orders are considered to eliminate the frequency noise. A dataset under investigation includes accelerograms from three stations, located in Turkey (Dinar, Izmit, Kusadasi), all working with an analogue type of seismograph SMA-1. Records from near-source stations to the earthquakes (i.e., with a distance to the epicenter less than 20 km) with different moment magnitudes Mw = 3.8, 6.4, and 7.4 have been examined. We have evaluated the influence of the type of digital filter on time series (acceleration, velocity, displacement), on some strong motion parameters (PGA, PGV, PGD, etc.), and on the FAS (Fourier amplitude spectrum) of acceleration. Several 5%-damped displacement response spectra applying examined filtering techniques with different filter orders have been shown. SeismoSignal software tool has been used during the examples

Dynamic properties of colloidal silica soils using centrifuge model tests and a full-scale field test

Traditional ground improvement methods to mitigate the effects associated with liquefaction damage are often not feasible in developed areas. Commonly used soil improvement methods can have adverse affects on the surrounding infrastructure and less invasive methods are therefore required. Passive site stabilization is a non-invasive grouting technique where a stabilizing material can be injected at the edge of a site and delivered to target locations through the groundwater. As the stabilizer flows through the subsurface, it displaces the pore water and subsequently forms a permanent gel that binds to soil particles, resulting in a stronger soil formation.Based on its unique characteristics, colloidal silica has been selected as an ideal material for passive site stabilization. For purposes of liquefaction mitigation, the dynamic behavior ofcolloidal silica soils was studied through centrifuge model tests and a complementary, full-scale field test. The centrifuge tests provided comparisons of the response for untreated sands and sands treated with 4%, 5%, and 9% colloidal silica concentrations (by weight) subjected to a sequence of dynamic shaking events. To complement the model tests, a full-scale field test was conducted to compare the response of a liquefiable soil formation to a soil grouted with colloidal silica. Permeation grouting techniques and field procedures were developed in order to treat an approximately 1.5 m (5 ft) thick liquefiable soil layer.The centrifuge model tests and field test both show that colloidal silica soils reduce settlement, lateral spreading, and shear strains induced when subjected to large dynamic loads.For purposes of developing soil models, shear modulus degradation curves were developed and relationships that govern unloading-reloading behavior were identified in centrifuge model tests. Amplification in the acceleration response and increases in excess pore pressure ratios were determined to be direct indications of treatment levels. Large transient changes observed in pore pressure response were shown to describe the behavior of stress transmittal between the soil and gel during cyclic loading. Additionally, the hysteretic response of colloidal silica soils exhibited greater hysteretic damping and cyclic mobility consistent with dense sands. The response also revealed a lower degree of cyclic degradation for higher concentrations of colloidal silica.Ph.D., Civil Engineering -- Drexel University, 201

SPEKTRI POTRESNOG ODZIVA PLITKO TEMELJENIH KONSTRUKCIJA NA MEKIM TLIMA

Rad obrađuje potresni odziv plitko temeljenih konstrukcija na mekim tlima. Istraživanje u okviru rada je pokrenuto uz glavnu pretpostavku da europski normirani spektri odziva za meka tla nisu dobro definirani te da ne uključuju učinke međudjelovanja tla i konstrukcije. S ciljem definiranja poboljšanog spektra odziva kao osnovnog alata za proračun sigurnih i potresno otpornih konstrukcija, izrađene su i funkcije impedancije i prijenosne funkcije koje omogućuju uključivanje učinaka međudjelovanja tla i konstrukcija u proračunima primjenom metode spektara odziva. Oslonac studiji daju rezultati eksperimentalnih istraživanja provedenih na potresnom stolu na Sveučilištu u Bristolu te u geotehničkoj centrifugi na institutu IFSTTAR. Numerički modeli korišteni za provedbu parametarske studije su uspješno kalibrirani s obzirom na rezultate spomenutih eksperimentalnih istraživanja. U radu je dan prijedlog primjene funkcija impedancije, nastalih u okviru ovog rada, u klasičnim računalnim programima koji primjenu nalaze u znanosti i praksi. Osim toga, dan je prijedlog za primjenu funkcija impedancije u okviru N2 metode.This thesis deals with seismic response of shallow founded structures on soft soils. Research within the thesis is initiated with the main assumption that the European code-based response spectra for soft soils are ill-defined and that they do not include soil-structure interaction effects. With the aim to provide improved response spectrum, as a key engineering tool for design of earthquake resistant structures, both impedance and transfer functions were developed. Those functions enable incorporation of both soil compliance and its capability that dissipates earthquake energy. Parametric study was conducted using numerical models calibrated with regards to experimental results obtained both from testing performed in enhanced gravitational field using geotechnical centrifuge at the IFSTTAR institute and on shaking table of the University of Bristol at 1g. Numerical modelling, and thus parametric study, was governed using equivalent linear method. The last chapter of the work provides proposed methodology for including the developed functions into classical program packages mostly used by engineering practice and academia for structural analysis and design. Also, proposal for application of impedance functions within the framweork of N2 method is provided