Effects Of Local Site Conditions Research Articles

UAV-based thermography reveals spatial and temporal variability of evapotranspiration from a tropical rainforest

Evapotranspiration (ET) from tropical forests plays a significant role in regulating the climate system. Forests are diverse ecosystems, encompass heterogeneous site conditions and experience seasonal fluctuations of rainfall. Our objectives were to quantify ET from a tropical rainforest using high-resolution thermal images and a simple modeling framework. In lowland Sumatra, thermal infrared (TIR) images were taken from an uncrewed aerial vehicle (UAV) of upland and riparian sites during both dry and wet seasons. We predicted ET from land surface temperature data retrieved from the TIR images by applying the DATTUTDUT energy balance model. We further compared the ET estimates to ground-based sap flux measurements for selected trees and assessed the plot-level spatial and temporal variability of ET across sites and seasons. Average ET across sites and seasons was 0.48 mm h–1, which is comparable to ET from a nearby commercial oil palm plantation where this method has been validated against eddy covariance measurements. For given trees, a positive correlation was found between UAV-based ET and tree transpiration derived from ground-based sap flux measurements, thereby corroborating the observed spatial patterns. Evapotranspiration at upland sites was 11% higher than at riparian sites across all seasons. The heterogeneity of ET was lower at upland sites than at riparian sites, and increased from the dry season to the wet season. This seasonally enhanced ET variability can be an effect of local site conditions including partial flooding and diverse responses of tree species to moisture conditions. These results improve our understanding of forest-water interactions in tropical forests and can aid the further development of vegetation-atmosphere models. Further, we found that UAV-based thermography using a simple, energy balance modeling scheme is a promising method for ET assessments of natural (forest) ecosystems, notably in data scarce regions of the world.

A closer look at hazard-consistent ground motion record selection for building-specific risk assessment: Effect of soil characteristics and accelerograms’ scaling

Conditional spectrum (CS) record selection is a standard tool for the selection of ground motion recordings consistent with the hazard at a site of interest. For many important applications the seismic hazard is computed for reference rock conditions and the effects of local site conditions are investigated downstream via soil dynamics. Ideally, when selecting for rock conditions, the recordings should be real, recorded on rock sites, and strong enough to push the structure into its severe nonlinear range. However, rock-recorded ground motions are often scarce and the analyst is usually left with the suboptimal option of augmenting the set with scaled motions and motions recorded at soil stations. We investigated how this practice can affect the structural response estimates by means of nonlinear dynamic analyses of a comprehensive set of single-degree-of-freedom (SDOF) systems. We first performed site and structure-specific CS record selection using ground motion databases of only soil-recorded motions versus databases of only rock recorded ones. In addition, we performed the CS based on extreme cases of using ground motions scaled by either only small or only large factors. Our focus was on the statistical comparison of the common intensity measures (IMs) of the selected records and, more importantly, of the structural response estimates when these extreme opposite selection choices are made. We show no significant statistical differences in the distributions of the IMs and structural responses, while the fragility and response hazard remain almost identical, for all practical purposes. These results imply that, as long as hazard consistency is accurately enforced in the ground motion record selection, using CS, selecting soil-recorded motions or record scaled up to 10, will not bias the response estimates. Finally, repeating the above procedure for response prediction of one multiple degrees of freedom (MDOF) system suggests that our conclusions are applicable also to more complex structural systems.

Efficient simulation of stochastic seismic response of long-span bridges in river valleys using hybrid BEM-FEM

Determining ground motions is essential for seismic analysis of long-span bridges located at complex sites. However, there is a lack of earthquake records for local site conditions. Thus, this study focused on the effect of local site conditions on the stochastic response of long-span high-pier rigid frame bridges crossing a valley with an overlying water layer. For this purpose, a hybrid boundary element and finite element method (BEM-FEM) is proposed to investigate the stochastic seismic response of long-span bridges at such a complex site. First, a simulation method for 3-D spatially varying ground motions ascribed to wave scattering from irregular surface topography, sedimentary soil, and water layers was established based on the BEM combined with the spectral representation method. Furthermore, the statistical properties of the bridge response were explored based on the FEM and Monte Carlo simulations. The advantage of this work is that it reveals how the seismic wave propagation in this particular valley topography and water layer affects the stochastic response of the bridge considered. Moreover, the results indicate that seismic wave scattering leads to a significant energy redistribution of the input waves in the tri-directions related to the surface location, and a decrease in the coherency loss functions at all frequencies. Owing to this change, the peak ground accelerations (PGAs), bridge response means, and response variability are doubled. The beneficial effect of the water layer on the PGAs is weakened, while the adverse effect of hydrodynamic pressure dominates. The parameter analysis results demonstrate that a 10-m-deep sedimentary soil layer produces a 47% increase in the internal force of the pier bottom. The solid-liquid dynamic coupling effect should be accurately quantified for bridges located at saturated sites. Considering the local site conditions, the coefficient of variation (COV) of the response of the pier top exceeded 0.3, indicating strong randomness.

Local site effect on seismic hazard of the relocated new Balakot town

This paper evaluates the effect of local site conditions on the seismic hazard of the relocated new Balakot town as a result of the complete destruction of old Balakot city due to the 2005 Muzaffarabad Earthquake. New Balakot town has been placed in a high seismic zone according to the Building Code of Pakistan because of its vicinity to active seismogenic faults. Representative sites from the new Balakot town have been selected to evaluate the local site effects. The acceleration time series was used as suite input motion in the ground response analysis selected from the worldwide earthquake catalog and matched to the target spectrum of Balakot. The site-specific equivalent linear (EL) and nonlinear (NL) analyses were conducted for which the ground model was developed based on the field and laboratory geotechnical test results. The mean surface ground response spectrum and also the mean Amplification Factor showed that the suite input motions were de-amplified and amplified respectively below and above the fundamental period of the site. The mean maximum amplification factor at 0.4 s shows that a four-story building may be subjected to resonant conditions. The transfer function that relates the amplitude of incident and transmitted motion at interface resulted in different mean peak ground acceleration. The higher surface peak ground acceleration value was obtained from that of suit base motions. The NL analysis was observed to yield more conservative maximum AF and PGA values in comparison to the EL analysis. This study is helpful to provide improved and site-specific values of ground acceleration based on local site effects of the new Balakot town, which is an important locality in the 2005 Muzaffarabad earthquake-affected region.

Effect of Local Site Conditions on Earthquake Ground Motions in Hanoi: Results from Numerical Simulations

This paper presents some numerical simulation results on the influence of local site conditions on earthquake ground motions in Hanoi. Numerical simulation method through DEEPSOIL program was used in the study. Geological data of 600 groundwater survey and engineering geology boreholes in Hanoi as well as the acceleration records of Imperial Valley earthquake in 1979 with magnitude M = 6.5, hypocenter of 26.5 km, and PGA of 0.169 g were chosen as input data for the research. By analyzing geological conditions, tectonics, seismic characteristics of different soil types in Hanoi, a geological cross-section cutting through different engineering geology in Hanoi areas have been constructed. Numerical simulations of site effect at typical locations along the cross-section show: (i) The geological conditions on the surface of Hanoi clearly influence the earthquake ground motion, this is confirmed by the increase in the amplitude of the horizontal component of ground acceleration and the change of the strong vibrations from short to longer period. These effects obey a general rule, they become stronger when moving on the cross-section from west to east, corresponding to an increase in the thickness of the weak sedimentary layers covering the hard rock; and (ii) However, at the place where the weak and soft soil layer appear (LK50 borehole), despite of the vibrations that are still converted from short to longer periods, the amplitude of the PGA is strongly attenuated at the surface layer.

Novel Evaluation Method for Site Effect on Earthquake Ground Motion Based on Modified Horizontal to Vertical Spectral Ratio

The effect of local site conditions on the earthquake ground motion is a very important factor to be considered in engineering seismic fortification. Many methods, such as numerical simulation methods based on site analysis models and statistical empirical relation methods based on the earthquake ground motion observations and numerical simulation data, have been used to consider the site effects in actual engineering seismic fortification and earthquake disaster assessment. The statistical analysis to obtain characteristic parameters of site condition effect based on strong motion and microtremor records become an economical and practical method of determining the designed ground motion of engineering sites, especially for large survey areas and engineering sites where it is difficult to carry out a site survey. In this paper, a novel evaluation method for site effect on earthquake ground motion is proposed. The new method is based on the horizontal to vertical spectral ratio (HVSR) method, but the original HVSR is replaced by a modified HVSR considering the effect of the soil layer on the vertical ground motion. In order to build the model and determine the corresponding parameters of the modified HVSR, first, the ground motions in the bedrock below the soil layer are calculated using the one-dimensional equivalent linear method. These calculated records are independent of the influence of the downgoing wavefield, and the differences between the ground surface to bedrock spectral ratio (SBSR). The HVSR for the local sites of ground motion observation stations are analyzed using the strong ground motion records from the Kiban-Kyoshin network (KiK-net) in Japan. The statistical characteristics of the relationship between SBSR and HVSR are revealed, and then, a quantitative relationship between SBSR/HVSR and HVSR is established. The proposed evaluation method for the site effect has the advantage that the original HVSR method only requires ground motion records on the ground surface of the site, and it further considers the influence of the vertical seismic effect on the accuracy of the HVSR method. The proposed method can characterize the influence of the site conditions on ground motion more reasonably than the conventional method.

Topography modulates near-ground microclimate in the Mediterranean Fagus sylvatica treeline

Understanding processes controlling forest dynamics has become particularly important in the context of ongoing climate change, which is altering the ecological fitness and resilience of species worldwide. However, whether forest communities would be threatened by projected macroclimate change or unaffected due to the controlling effect of local site conditions is still a matter for debate. After all, forest canopy buffer climate extremes and promote microclimatic conditions, which matters for functional plant response, and act as refugia for understory species in a changing climate. Yet precisely how microclimatic conditions change in response to climate warming will depend on the extent to which vegetation structure and local topography shape air and soil temperature. In this study, we posited that forest microclimatic buffering is sensitive to local topographic conditions and canopy cover, and using meteorological stations equipped with data-loggers we measured this effect during 1 year across a climate gradient (considering aspect as a surrogate of local topography) in a Mediterranean beech treeline growing in contrasting aspects in southern Italy. During the growing season, the below-canopy near-ground temperatures were, on average, 2.4 and 1.0 °C cooler than open-field temperatures for south and north-west aspects, respectively. Overall, the temperature offset became more negative (that is, lower under-canopy temperatures at the treeline) as the open-field temperature increased, and more positive (that is, higher under-canopy temperatures at the treeline) as the open-field temperature decreased. The buffering effect was particularly evident for the treeline on the south-facing slope, where cooling of near-ground temperature was as high as 8.6 °C for the maximum temperature (in August the offset peaked at 10 °C) and as high as 2.5 °C for the average temperature. In addition, compared to the south-facing slope, the northern site exhibited less decoupling from free-air environment conditions and low variability in microclimate trends that closely track the free-air biophysical environment. Although such a decoupling effect cannot wholly isolate forest climatic conditions from macroclimate regional variability in the south-facing treeline, it has the potential to partly offset the regional macroclimatic warming experienced in the forest understory due to anthropogenic climate change.

Effects of short‐interval disturbances continue to accumulate, overwhelming variability in local resilience

AbstractIncreasing rates of short‐interval disturbances have the potential to rapidly transform ecosystems via shifts in post‐disturbance regeneration. While research has explored compound events in multiple biomes, we know little regarding how local site conditions interact with short‐interval disturbances to influence post‐disturbance regeneration. Furthermore, questions remain regarding the consequences of continued high frequency events: What happens when emerging new communities are themselves subject to short‐interval disturbances? To investigate effects of ongoing short‐interval fires on regeneration, we examined post‐fire forest regeneration in two locations in interior Alaska. We established 50 plots across a mosaic of fire histories (one, two, or three fires in <70 yr) in an upland and lowland site in interior Alaska. To investigate how shifts in community driven by short‐interval fires differ according to local site conditions, we quantified abundance, proportion, and density of conifer and deciduous regeneration in a drier upland site and a wetter lowland site. Both sites were dominated by black spruce prior to burning. In the drier upland site, black spruce (Picea mariana) presence declined sharply after two fires, while paper birch (Betula neoalaskana) became increasingly abundant with each additional fire. In the wetter lowland site, less organic soil was consumed by fire and presence of black spruce persisted through an initial single reburn (two fires), indicating local topography may temporarily buffer reburning impacts. However, after three burns, conifers were effectively eliminated in both upland and lowland stands. Deciduous regeneration differed with site: Birch dominated in upland plots, while willow (Salix spp.) and aspen (Populus tremuloides) dominated in lowlands. These results offer strong empirical evidence of the divergence of boreal successional trajectories from previous historic norms. Furthermore, results from this study demonstrate shifts in post‐fire succession in forested ecosystems continue to accumulate with additional short‐interval disturbance events, overwhelming the interactive effects of local site conditions.

Influence of the variability of soil profile properties on weak and strong seismic response

Characterizing the potential effect of local site conditions on the amplification of ground motions is a critical aspect of seismic hazard and risk assessment. The aim of this study is to investigate the reliability and the limit of using the average shear wave velocity in the upper 30m of the soil profile vs,30, as single proxy, to characterize seismic site effects for weak and strong events.To this regard, a dataset of 300 one-dimensional soil profiles with a given vs,30 are generated through a Monte Carlo approach. Their seismic responses are computed for a set of 40 real accelerograms, with different seismic features. The vertical propagation from the bottom of the generated columns is modeled using a finite element spatial discretization, accounting for both linear and nonlinear soil behavior.The site dominant frequency f0 and the shear wave velocity gradient in the profile B30 are proposed as proxies to characterize seismic site effects and the variability of the response spectra for the numerical signals, at the free surface of the set of columns, is discussed. Correlations between site-specific amplification factors deduced using the numerical response spectra and the proposed site proxies are analyzed for different sub-ranges of periods. The obtained amplification factors are then compared to those proposed by different international and national design codes. The results, obtained under assumption of linear and nonlinear behavior of soil, emphasize the need to introduce complementary site parameters proxies, in addition to vs,30, to characterize the expected site effects in design response spectra.

The Effect of Soil Type and Different In-situ Test Results on Soil Amplification Analysis

The effect of local soil conditions is taken into consideration in the evaluation of ground motion properties in seismic design of structures. One of the most important effects on the ground surface due to strong ground motion is soil amplification resulted in the structural damage. Soil amplification can be determined both by dynamic analyses performed according to analytical methods based on local site conditions and obtained with investigations based on the results of in-situ testing methods. Therefore, the effects of local site conditions are considered to evaluate the properties of ground motion for seismic design of structure. In this study, soil properties of İnönü district are evaluated based on Standard Penetration Test (SPT) and Multi-Channel Analysis of Surface Wave (MASW) method which is one of the geophysical methods. İnönü is located at the west of Eskişehir surrounded with numerous active fault systems and subjected to very intensive tectonic activities in geological history. The studies related to seismic activity have been made on the basis of probabilistic seismic hazard analyses. Soil amplification analyses are performed with Shake2000 software comparatively by taking into considerations data from in-situ testing methods.

Forest understory vegetation is more related to soil than to climate towards the cold distribution margin of European beech

AbstractQuestionIt is debated whether forest understory communities will be sensitive to projected climate change or inert due to the regulating effect of local site conditions and soil parameters. A distinction between the relative importance of climate or soil is often hardly possible because both factors usually change at different spatial scales in forests. Here, we compare the relative influence of climate and soil on the forest understory vegetation in lowland beech forest ecosystems (Fagus sylvatica), which were selected for their ecological homogeneity.LocationNine sites along a strong temperature gradient (ΔT = 4 K from east to west in winter, south to north in summer) between Rostock (Germany) and Gdańsk (Poland) in a Baltic Quaternary ground moraine landscape.MethodsWe conducted a vegetation survey in 55 vegetation plots (80 m2 each) across nine forest sites mono‐dominated by European beech and analysed how much variation in understory plant composition is explained by climate and soil parameters.ResultsSoil explained 32% of the compositional variation of understory vegetation across sites, climate 22%, and their interaction 14%. Topsoil pH, subsoil organic matter content, and subsoil C/N ratio were the most important soil variables; growing season temperature and annual water availability were the most important climatic variables.ConclusionThe strong dependence on soil properties could moderate the response of the forest understory vegetation to projected climate change. Forest soil properties, however, also depend on the dominant tree species and the macroclimate. To predict climate change impacts on forest understory vegetation, climate change assessments should consider indirect climate change effects as well as interactions between climate and soil.

Seismic parameter design assessment for the Kribi deep seaport in Cameroon

In the Kribi region (south-western Cameroon), a new industrial harbour has been built. This area is marked as a low-seismicity zone, according to the global seismic hazard map. This estimate is based, however, on a poorly documented data set. Industrial harbours are critical facilities and, consequently, appropriate cautions have to be taken in the seismic design. This paper illustrates the methodology adopted to compute the expected ground motion for the seismic design of the new harbour, starting from the available information. The standard probabilistic seismic hazard assessment is based on a logic tree approach considering areal and fault sources with two earthquake rate models (characteristic earthquake and Gutenberg–Richter), and two ground motion prediction equations. As expected, the obtained ground motion at the bedrock for a return period of 475 years is not very large [0.07 g, in terms of horizontal peak ground acceleration (PGA)] with a well marked peak between 0.1 and 0.2 s. This result is in agreement with that of the Global Seismic Hazard Assessment Project, where a general PGA between 0.04 and 0.08 g is associated with south-western Cameroon. The effects of local site conditions are evaluated through geophysical methods (single station and array surveys) and 1D linear-equivalent numerical modelling. Considering the two geotechnical models identified in the study region, by a specific geophysical survey executed during this study, local amplifications of 1.9 and 2.2 have been calculated for the two sectors, respectively. Furthermore, the results obtained, in terms of uniform hazard response spectra, have been used as guidelines to determine the design ground motions for the maritime and land infrastructures planned in the Kribi harbour area. This study represents a summary of the present knowledge on the seismicity of this part of Africa as well as the first regional and local seismic hazard assessment for the Kribi area.

Can a buried gas pipeline experience local buckling during earthquake ground shaking?

The damage potential of spatially variable seismic ground motion on buried pipelines has long been confirmed by field evidence, but it is still debatable whether transient seismic loads can be truly detrimental to the pipeline integrity. In the absence of systematic scrutiny of the effects of local site conditions on the seismic behaviour of such structures, this study presents a staged approach to numerically investigate the elastic-plastic buckling response of buried steel natural gas pipelines subject to transient differential ground motions arising from strong lateral site inhomogeneities. The first stage involves the study of 2D linear viscoelastic and equivalent-linear site response for the case of two sites and the resulting seismic demand in terms of longitudinal strains for input motions of various intensities and frequency content. The influence of key problem parameters is examined, and the most unfavourable relative ground deformation cases are identified. In the second stage of analysis, the critical in-plane ground displacement field is imposed monotonically on a near-field trench-like 3D continuum soil model encasing a long cylindrical shell model of the pipeline. Next, the performance of the buried pipeline is assessed under axial compression. The impedance contrast between the laterally inhomogeneous soil profiles is shown to govern the amplitude of induced elastic strains, which are maximized for low-frequency excitations. It is also demonstrated that peak axial strains along the pipeline considering equivalent-linear soil behaviour under strong earthquake motion can be as much as two orders of magnitude larger than their linear counterparts, as a result of the severe, spatially variable moduli degradation. It is finally shown that the seismic vibrations of certain inhomogeneous sites can produce appreciable axial stress concentration in the critically affected pipeline segment near the material discontinuity, enough to trigger coupled buckling modes in the plastic range. This behaviour is found to be controlled by pronounced axial force-bending moment interaction and is not accounted for in code-prescribed limit states.

The effect of structural variability and local site conditions on building fragility functions

In this study, the effect of local site conditions (site class and site amplifications) and structural variability are investigated on fragility functions of typical building structures. The study area is chosen as Eastern Turkey. The fragility functions are developed using site-specific uniform hazard spectrum (UHS). The site-specific UHS is obtained based on simulated ground motions. The implementation of ground motion simulation into seismic hazard assessment has the advantage of investigating detailed local site effects. The typical residential buildings in Erzincan are represented by equivalent single degree of freedom systems (ESDOFs). Predictive equations are accomplished for structural seismic demands of ESDOFs to derive fragility functions in a straightforward manner. To study the sensitivity of fragility curves to site class, two sites on soft and stiff soil are taken into account. Two alternative site amplification functions known as generic and theoretical site amplifications are examined for these two sites. The reinforced concrete frames located on soft soil display larger fragilities than those on stiff soil. Theoretical site amplification mostly leads to larger fragilities than generic site amplification more evidently for reinforced concrete buildings. Additionally, structural variability of ESDOFs is generally observed to increase the fragility especially for rigid structural models.

Autecology and growth of Aleppo pine ( Pinus halepensis Mill.): A comprehensive study in France

Abstract Aleppo pine (Pinus halepensis Mill.) is one of the dominant conifer species in the Mediterranean area. Many studies have investigated the role of climate variables (precipitations, temperature) in its occurrence and growth, but few have taken the effect of local site conditions into account, nor their interaction with climate. This study aimed at thoroughly assessing forest sites potential for Aleppo pine in France, and designing a practical tool to help forest managers implementing these results. The study is based on a network of 512 plots laid out in the French Mediterranean area, where 2158 trees were measured. A site index was computed using a height growth model calibrated on these plots. Using neural networks and partial least square regression models (PLS), we disentangled the effects of climatic factors and local site conditions in Aleppo pine presence and growth. Local water balance (assessed through topography, soil, geology and legacies of past human activities) was the main factor driving Aleppo pine productivity in the study area. Climate played a significant role as a whole but more important at the species distribution margins, frost and snow limiting Aleppo pine range northwards and in elevation. Based on these results, a practical tool was designed for two different types of mother rocks to help assessing forest site potential for Aleppo pine. As the span of climate conditions in south-eastern France includes most of those found in Aleppo pine distribution area, except the driest and hottest ones found in its southernmost locations, this study could easily be used or adapted in most other concerned countries. Because of the ongoing climate change and increasing drought in the Mediterranean area, the balance between local and climate factors may change in time and space. Our results show that without an accurate knowledge of local conditions, the impact of climate change cannot be predicted.

Inelastic Displacement Ratios for Evaluation of Degrading Peak – Oriented SDOF Systems

Estimation of the inelastic displacement demand (IDD) is an important part of the performance-based design. Coefficient method is one of the methods for the estimation of IDD and in this method, IDD is determined by multiplying elastic displacement demand with inelastic displacement ratio (CR ). Previous researches showed that structures deteriorate and also exhibit dynamic instability under severe earthquakes and these behaviors should be considered in the estimation of CR to estimate a reliable IDD. In this study, CR of the non-degrading bilinear hysteretic model and the degrading peak-oriented hysteretic model with collapse potential were determined and effects of degradation on IDD were investigated. Nonlinear time history analysis of SDOF systems were performed using considered hysteretic models. Furthermore a new equation is proposed for the mean CR of degrading SDOF systems. Also, effect of local site conditions and post-yield stiffness on the mean CR of degrading SDOF systems were investigated.

An empirical model for the mean period (Tm) of ground motions using the NGA-West2 database

Frequency content is an important characteristic of earthquake shakings. The mean period (Tm) of a ground motion has been regarded as the preferred frequency content parameter. In this paper, a new predictive model for Tm is developed based on the horizontal components of ground motions selected from the expanded NGA-West2 database. The new model includes a piece-wise linear moment magnitude (Mw) term with a breaking Mw value as 5 and a cutoff value as 7.3, which is adopted based on the distribution of empirical data as well as physical considerations. A trilinear rupture distance term with breaking points at 100 km and 200 km is also adopted in the model. The average shear wave velocity at top 30 meters (Vs30) and a basin depth parameter (Z1) are used to represent the effect of local site conditions on Tm. A forward directivity term that takes effect at rupture distances within 40 km is included in the functional form. Besides, we derive a magnitude-dependent aleatory variability model to capture the varying within-event standard deviations versus Mw. The proposed model can be used to estimate Tm for earthquake scenarios with magnitudes in the range of 3–7.9 and rupture distance up to 300 km.

Shake table tests of steel towers supporting extremely long-span electricity transmission lines under spatially correlated ground motions

Transmission lines from electricity transmission systems crossing wide rivers or canyons can have much longer spans (e.g. longer than 1000m) compared with components from conventional civil structures. Steel towers supporting such extremely long-span transmission lines are unavoidably subjected to spatially correlated ground motions together with the coupling action between supporting towers and transmission lines. However, the influence of spatial variation of ground motions is not considered in current seismic design of the towers supporting extremely long-span transmission lines. This research was focused on an electricity transmission system crossing the 2nd longest river in China (which is also the 5th longest river in the world) to address the influence of spatial variation of ground motions on seismic response of the towers supporting extremely long-span transmission lines. A reduced-scale experimental model of the prototype was tested using shake tables. Spatially correlated ground motions generated taking into account the wave passage effect, the effect of coherency loss and the effect of local site conditions were used as inputs of the shake table tests. It was found that the spatially correlated ground motions can significantly amplify tower responses and such an effect should not be neglected in seismic analysis and design. Based on the test database, an empirical model was proposed to modify the acceleration response, member stress response and top displacement responses of the towers supporting extremely long-span transmission lines from uniform ground motions as conservative estimates of responses of the system under spatially correlated ground motions with the same magnitude.

Seismic Site Response Analysis Leading to Revised Design Response Spectra for Australia

This study explores the effects of local site conditions on seismic site response and investigates the validity of the site classification system and the response spectra in codes, with a focus on the Australian earthquake loading standard. The results show that the averaging process used to derive the design spectra in existing codes has led, in general, to an underestimation of the site response. A new systematic method is proposed for obtaining the displacement response spectra based on the correlations between the initial and degraded fundamental natural site period and amplification factors. Modifications to the site classification system are also recommended.

Evidence of complex site effects and soil non-linearity numerically estimated by 2D vs 1D seismic response analyses in the city of Xanthi

This study discusses the effects of local site conditions on earthquake ground motion for city of Xanthi, North-Eastern Greece, focusing on the influence of complex site effects and soil non-linearity. Although city of Xanthi is characterized as a low seismicity area, documented strong earthquake events of past centuries indicate the necessity of an appropriate estimation of ground surface motion of the region. Therefore, a typical 2D cross-section along the city following an E-W direction is constructed, based on the synthesis of available geological, geotechnical and geophysical data of the broader area. 1D and 2D numerical models are generated utilizing the Finite Difference Method and site response is investigated for different seismic scenarios. Wave amplification is captured as a result of 1D resonance phenomena integrated with potential 2D complex wave effects, due to lateral propagation of the locally generated at the discontinuities surface waves. The additional, relatively to 1D, 2D amplification or de-amplification of ground shaking, in terms of its amplitude and its spectral content is quantified. The impact of soil deposits non-linearity on amplification level, as well as, on generated 2D wave fields is considered by implementing both equivalent-linear and non-linear approaches. The results reveal that, across the city, spatial variation of ground surface motion is obvious, attributed primarily to the variation of subsurface soil profiles. 2D wave effects have been generated signifying that, at particular site locations, ground motion is additionally amplified or de-amplified with respect to 1D response. However, 2D versus 1D differentiation has been calculated of ±20% in terms of PGA and spectral accelerations up to 1.0s, in the majority of the examined sites, implying that site response even though, influenced by 2D resonance phenomena, could be sufficiently captured by an 1D approach. Moreover, it is shown that if soil non-linearity is properly accounted for, it may play an important role on the estimated ground response, since non-linear approach seems to produce lower amplification levels with regard to 1D and 2D equivalent-linear approaches. As a general trend across the investigated site, for the entity of the various scenarios, the numerically calculated response spectra exceed EC8 seismic code provisions.