GNGTS 2021 - Atti del 39° Convegno Nazionale

297 GNGTS 2021 S essione 2.2 PRELIMINARY STATISTICAL ANALYSIS ON 2D AGGRAVATION FACTOR FOR SEISMIC GROUND RESPONSE OF SHALLOW SEDIMENTARY BASINS C. Madiai, G. Ciardi, J. Facciorusso, M. Uzielli Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Firenze, Florence, Italy Introduction Current seismic building codes require that design spectra be obtained through site- specific ground response analysis or, for certain specified geometric and stratigraphic conditions, by means of code-based simplified approaches. Most building codes allow simplified procedures to account for 1D stratigraphic effects. In addition, some of them (e.g., Eurocode 8 (CEN 2004); Italian building code (MIT 2008)), provide a basic approach to account for topographic effects despite the complexity of these predictions, while site effects due to subsurface geometry are totally neglected. Moreover, in current routine engineering practice, amplification effects are mostly evaluated on 1D models, neglecting multidimensional effects, possibly leading to non-conservative estimate of ground motion at sites in sedimentary basin. For these reasons, many researchers have recently tried to develop a simplified approach to account for the additional effect of 2D/3D basin response on the 1D response by means of a suitable “aggravation factor” (Makra et al. 2005; Paolucci & Morstabilini 2006; Riga et al., 2016; Madiai et al. 2017; Zhu et al. 2020). Because highly populated areas are often located on shallow sedimentary basins, a basic way to predict seismic response in such geological and geomorphological settings starting from the results of 1D ground response analysis is of prime interest to geotechnical engineers and engineering seismologists. This study investigates the 2D aggravation effects in symmetric basins overlain by two-layered deposits. To this aim, a large number of numerical two-dimensional (2D) and one-dimensional (1D) local seismic response analyzes are conducted on simplified schemes approximating realistic sedimentary basins. An aggravation factor, defined as the ratio between 2D and 1D response spectrum amplitude for a given period at the same location on the basin ground surface, is used to quantify the 2D effects. A non-parametric statistical correlation test is applied to assess the existence and strength of statistical dependency between the aggravation factor and a broad set of dimensionless parameters related to basin geometry, stratigraphic layering, dynamic geotechnical soil properties, and seismic input motion. The relationship between peak spectral aggravation values and normalized spectral periods (i.e., ratio of the period corresponding to peak aggravation to the fundamental period of the 1D soil profile at the center of the basin) is also investigated. Calculation approach and modelling The aggravation factor defined by García & Faccioli (2000) was assumed to quantify the 2D basin effects. It is given by: 2D AGGRAVATION FACTOR FOR SEISMIC GROUND RESPONSE OF SHA SEDIMENTARY BASINS C. Madiai, G. Ciardi, J. Facciorusso, M. Uzielli Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Firenze, Florence, Italy Introduction. Current seismic building codes require that design spectra be obtained throu specific ground response analysis or, for certain specified geome ric and stratigraphic conditi means of code-based simplified approaches. Most building codes allow simplified proced account for 1D stratigraphic effects. In addition, some of them (e.g., Eurocode 8 (CEN Italian building code (MIT 2008)), provide a basic approach to account for topographic despite the complexity of these predictions, while site effects due to subsurface geometry are neglected. Moreover, in current routine engine ring practice, amplification effects are evaluat d on 1D models, neglecting multidimensional effects, possibly leading to non-conse estimate of ground motion at sites in sedime tary basin. For these reasons, any researche recently tried to develop a simplified approach to account for the additional effect of 2D/3 response on the 1D response by means of a suitable “aggravation factor” (Makra et al. Paolucci & Morstabilini 2006; Riga et al., 2016; Madiai et al. 2017; Zhu et al. 2020). highly populated areas are often located on shallow sedimentary basins, a basic way to seis i res onse in such geological and geomorphological settings starting from the results ground response an lysi is of prim in erest to geotechnical engineers and engi seis ol ists. This study investigates the 2D aggravation effects in symmetric basins overlain by two-l deposits. To this aim, a large number of numerical two-dimensional (2D) and one-dimension local seismic response analyzes are conducted on simplified schemes approximating r sedimentary basins. An aggravation factor, defined as the ratio between 2D and 1D re spectrum amplitude for a given period at the s me location on the basin ground surface, is quantify the 2D effect . A non- arametric statistical correlation est is applied to ass existence and strength of statistical dependency between the aggravation factor and a broa dimensionless parameters related to basin geometry, stratigraphic layering, dynamic geote soil properties, and seismic input motion. The relationship between peak spectral aggravation and normalized spectral periods (i.e., ratio of the period corresponding to peak aggravation fundamental period of the 1D soil profile at the center of the basin) is also investigated. Calculation approach and modelling. The aggravation factor defined by García & Faccioli was assumed to quantify the 2D basin effects. It is given by: AGF ( T , x ) = S a, 2 D ( T , x ) S a, 1 D ( T , x ) where S a, 2 D ( T , x ) is the elastic pseudo-acceleration response spectrum at 5% damping rat given control point located at a distance x from the center of the basin surface as obtained fr analysis, and S a, 1 D ( T , x ) is the response spectrum at the same control point from 1D analysis. A total of 192 2D models of symmetric two-layered basins were analyzed, with soil 1 overlyi 2. An elastic seismic bedrock was assumed, whose geometry can be fully described by the B Bouchon (1980) semi-sine-shaped formulation: (1) wher D AGGRAVATION FACTOR FOR SEISMIC GROUND RESPONSE OF SHALLOW EDIMENTARY BASINS . Madiai, G. Ciardi, J. Facciorusso, M. Uzielli ipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Firenze, Florence, Italy ntroduction. Current seismic building codes require that design spectra be obtained through site- pecific ground response analysis r, for certain specified geometric n stratigraphic conditions, by eans of code-based simplified appro ches. Most building codes allow simplified procedures to ccount for 1D stratigraphic effects. In addition, some of them (e.g., Eurocode 8 (CEN 2004); talian building code (MIT 2008)), provide a basic approach to account for topographic effects espite the complexity of these predictions, while site effects due to subsurface geometry are totally eglected. Moreover, in current routine engineering practice, amplification effects are mostly valuate on 1D models, neglecting multidimensional effects, possibly leading to non-conservative stimate of ground motion at site in sedimentary basin. For these reasons, many resear hers have ecently tried to develop a simplified approach to account for th additional effect of 2D/3D basin esponse on the 1D response by means of a suitable “aggravation factor” (Makra et al. 2005; aolucci & Morstabilini 2006; Riga et al., 2016; Madiai et al. 2017; Zhu et al. 2020). Because ighly populated areas are often located on shallow sedimentary basins, a basic way to predict eismic response in such geological and geomorphological settings starting from the results of 1D round response analysis is of prime interest to geotechnical engine rs a d engineering eismologists. his study investigates the 2D aggravation effects in symmetric basins overlain by two-layered eposits. To this aim, a large number of numerical two-dimensional (2D) and one-dimensional (1D) ocal seismic response analyzes are conducted on simplified schemes approximating realistic edimentary basins. An aggravation factor, defined as the ratio between 2D and 1D response pectrum amplitude for a given period at the same location on the basin ground surface, is used to uantify the 2D effects. A non-param tric statistical correlation t st is applied to assess the xistence nd strength of statistical dependency between the aggravation factor and a broad set of imensionless parameters related to basin geometry, stratigraphic layering, dynamic geotechnical oil properties, and seismic input motion. The relationship between peak spectral aggravation values nd normalized spect al periods (i.e., ratio of the period corresponding to peak aggravation to the undamental period of the 1D soil profile at the center of the basin) is also investigated. alculation approach and modelling. The aggravation factor defined by García & Faccioli (2000) as assumed to quantify the 2D basin effects. It is given by: AGF ( T , x ) = a, 2 ( T , x ) S a, 1 D ( T , x ) (1) here S a, 2 D ( T , x ) is the elastic pseudo-acceleration response spectrum at 5% damping ratio at a iven control point located at a distance x from the center of the basin surface as obtained from 2D nalysis, and S a, 1 D ( T , x ) is the response spectrum at the same control point from 1D analysis. i the elastic pseudo-acceleration response spectrum at 5% damping ratio at a give control point located at i tance 2D AGGRAVATION FACTOR FOR SEISMIC GROUND RESPO SEDIMENTARY BASINS C. Madiai, G. Ciardi J. Facc orusso, M. Uzielli Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Firenze, Introduction. Current seismic building codes require that desig spectra b speci ic ground response analysis or, for c rt in specified g ometric and stra means o ode-base simplified approaches. Most building codes allow s account for 1D stratigraphi effects. In addition, some of them (e.g., Eu Italian building code (MIT 2008)), provide a basic appr ach to acc unt despite the complexity of these predictions, while site eff cts due to subsurf neglected. Moreover, in current routine engin ering practice, amplificat evaluated on 1D models, neglecting multidimensional effects, possibly lead estimate of ground motion at sites in sedimentary basin. For these reasons, recently tried to develop a simplified ppr ach to account for the additiona response on the 1D response by means of a suitable “aggravation factor Paolucci & Morstabilini 2006; Riga et al., 2016; Madiai et l. 2017; Zh i hly popul ted areas are often located on shallow sedim ntary basins, seismic response in such geol gical and geomorphological settings starti grou d respons a alysis is of prime interest to geotechnical engi seismologists. This st dy investigates the 2D aggravation effects in sym tric b sins o deposits. To this aim, a large number of numerical two-dimensio al (2D) an local seismic response a alyzes are conducted on simplified scheme sedim tary basins. An aggravation factor, defined as the ratio betwee pectrum mplitude for given period t the same l cation o the basin gr quantify the 2D ffe ts. A no -pa ametric statistical correlation test is existence and stre gth of statistic l de endency betwee the a gravation f dime sionless paramet rs related to basi g ometry, str ti phic layering soil properties, nd seismic input m tion. The relationship between peak sp and normalized spectral periods (i. ., ratio of the period corresponding to fundamental period of the 1D soil profile at the center of the basin) is also in Calculation approach and modelling. The aggravation factor defined by G was assumed to quantify the 2D basin effects. It is given by: AGF ( T , x ) = S a, 2 D ( T , x ) S a, 1 D ( T , x ) where S a, 2 D ( T , x ) is the elastic pseudo-acceleration response spectru at given control point located at a distance x from the center of the basin surfa from the c nt r of the basin surface as obtained from 2D analysis, and 2D AGGRAVATION FACTOR FOR SEISMIC GROUND RESPONSE OF SEDIMENTARY BASINS C. Madiai, G. Ciardi, J. Facciorusso, M. Uzielli Dipartimento di I ge eria Civile e Ambientale, Università degli Stu i di Firenze, Florence, It Intr duction. Current s ismic building c des require t at desi n spectra b obtained specific round response analysis r, for certa n s ecified geometric and stratigraphic c means of code-based sim lified approach . Most building codes allow simplified p account for 1D stratig aphic effects. In addition, some of them (e.g., Euro ode 8 ( I alia building code (MIT 2008)), provide basic ap r ach to ccount for topogr d spite the co plexity of these predictions, while sit effects due t ubsurfac geom t neglected. More ver, in current routine engineering practice, amp ification effect evaluated on 1D m dels, neglecti g multidimensional effects, possibly leading to non- estimate f ground motion at sit s in sedimentary basin. For these reasons, many rese recently tried to dev lop a simplified approach to accou t for the additional effect f response on the 1D response by m ans f a suitable “ag ravatio factor” (Makra Paolucci & Morstab lini 2006; Riga et al., 2016; Madiai t al. 2017; Zhu et al. 20 highly populated areas are often located on shallow sedimentary basins, a basic w eism c r pons in such geological and g omorphological setting starting from the ground response analysis is of prime interest to geotechnic l engineers and s ologi ts. This study investigates the 2D aggravation ffects in symmetric basins overlain by deposits. To this aim, a larg number of numeri l two-dim nsional (2D) and one-dime local seismic respon e alyzes are conducted on simplified schemes appr xima sedimenta y basins. An aggravation factor, defi ed as the rati between 2D and pectrum amplitude for a given period at the same location on the basin ground surfa quan fy the 2D effects. A n -param tric stat stical correlation test is applied t existence and strength f statistic l dependency between the ag ravation f ctor and a dimensionless parameters related to basin geometry, stratigraphic lay rin , dynamic soil properties, and seismic input motion. The relationship between peak spectral aggra and ormalized spectral periods (i.e., ratio of the peri d corresponding to peak aggra fundamental period of the 1D soil profile at the center of the basin) is also investigated. Calculation approach and modelling. The aggravation factor defined by García & Fa was assumed to quantify the 2D basin effects. It is given by: AGF ( , x ) = S a, 2 D ( T , x ) S a, 1 D ( T , x ) where S a, 2 D ( T , x ) is the elastic pseudo-acceleration response spectrum at 5% dampi given control point located at a distance x from the center of the basin surface as obtai analysis, and S a, 1 D ( T , x ) is the response spectrum at the same control point from 1D an is the response spectrum at the same control point from 1D analysis.