Ambient noise H/V spectral ratio in site effects estimation in Fateh jang area, Pakistan

Local geology or local site effect is a crucial component while conducting seismic risk assessment studies. Investigations made by utilization of ambient noise are an effective tool for local site estimation. The present study is conducted to perform site response analysis at 13 different sites within urban settlements of Fateh jang area （Pakistan）. The aim of this study was achieved by utilizing Nakamura method or H/V spectral ratio method. Some important local site parameters, e.g., the fundamental fre- quencies f0 of soft sediments, amplitudes A0 of corre- sponding H/V spectral ratios, and alluvium thicknesses over 13 sites within the study area, were measured and analyzed. The results show that the study area reflects low fundamental frequency fo. The fundamental frequencies of the sediments are highly variable and lie in a range of 0.6-13.0 Hz. Similarly, amplification factors at these sites are in the range of 2.0-4.0.

The role of soil in structure response of a building damaged by the 26 December 2018 earthquake in Italy

Local soil conditions can significantly modify the seismic motion expected on the soil surface.In most cases,the indications concerning the influence of the underlying soil provided by the in-force European and Italian Building Codes underestimate the real seismic amplification effects.For this reason,numerical analyses of the local seismic response(LSR)have been encouraged to estimate the soil filtering effects.These analyses are generally performed in free-field conditions,ignoring the presence of superstructures and,therefore,the effects of dynamic soil-structure interaction(DSSI).Moreover,many studies on DSSI are characterised by a sophisticated modelling of the structure and an approximate modelling of the soil(using springs and dashpots at the foundation level);while others are characterised by a sophisticated modelling of the soil and an approximate modelling of the structure(considered as a simple linear elastic structure or a single degree of freedom system).This paper presents a set of finite element method(FEM)analyses on a fully-coupled soil-structure system for a reinforced concrete building located in Fleri(Catania,Italy).The building,designed for gravity loads only,was severely damaged during the 26 December 2018 earthquake.The soil was modelled considering an equivalent visco-elastic behaviour,while the structure was modelled assuming both the visco-elastic and visco-inelastic behaviours.The comparison made between the results of the FEM analyses and the observed damage is valuable.

Simplified seismic scenario analysis of existing masonry buildings accounting for local site effects

This study discusses the effects of local sites and hazard amplification on the seismic vulnerability assessment of existing masonry buildings.In this context,a rapid seismic evaluation procedure was implemented on an old masonry building stock in the historical center Galata,located inİstanbul,to determine the seismic risk priority of the built heritage.Damage scenarios were generated for all soil classes,different moment magnitudes,and source-to-site distances to obtain more accurate results for the seismic vulnerability assessment of the studied building stock.Consequently,damage distributions estimated under nine different scenarios with/without site effects were compared and illustrated in maps to discuss changes in vulnerability owing to amplification effects.In this study,by re-examining the rapid seismic evaluation procedure by including geo-hazard-based assessment,the importance of site effects on the vulnerability and risk assessment of built heritage was underlined.The proposed framework integrating field data and local site effects is believed to advance the current applications for vulnerability assessment of masonry buildings and provide an improvement in the application of rapid seismic assessment procedures with more reliable results.

Influence of earthquake ground motion incoherency on multi-support structures

A linear response history analysis method is used to determine the influence of three factors:geometric incoherency,wave-passage,and local site characteristics on the response of lnulti-support structures subjected to differential ground motions.A one-span frame and a reduced model of a 24-span bridge,located in Las Vegas,Nevada are studied,in which the influence of each of the three factors and their combinations are analyzed.It is revealed that the incoherency of earthquake ground motion can have a dramatic influence on structural response by modifying the dynamics response to uniform excitation and inducing pseudo-static response,which does not exist in structures subjected to uniform excitation.The total response when all three sources of ground motion incoherency are included is generally larger than that of uniform excitation.

Development and Prospect of Study on Soil Nonlinear Dynamic Characteristics under Strong-Motion

Ground motions are significantly influenced by dynamic characteristics of overburden soil layers near ground surface,as thick and soft soil layers would obviously amplify the ground motion strength. The conventional research method on soil nonlinear dynamic characteristics under strong motions is based on experiments in laboratories for the deficiency of observation data,but it is difficult to reliably simulate the complex factors of soils in actual earthquake durations,including loading paths,boundary conditions,and drainage conditions. The incremental data of the vertical downhole observation array,which is comprised of at least one observation point on ground surface and one observation point in a downhole rock base, makes it possible to study soil nonlinear dynamics according to in situ observation data,and provides new basic data and development opportunities to soil nonlinear dynamics studies.

Response of a transmission tower-line system at a canyon site to spatially varying ground motions

Collapses of transmission towers were often observed in previous large earthquakes such as the Chi-Chi earthquake in Taiwan and Wenchuan earthquake in Sichuan,China. These collapses were partially caused by the pulling forces from the transmission lines generated from out-of-phase responses of the adjacent towers owing to spatially varying earthquake ground motions. In this paper,a 3D finite element model of the transmission tower-line system is established considering the geometric nonlinearity of transmission lines. The nonlinear responses of the structural system at a canyon site are analyzed subjected to spatially varying ground motions. The spatial variations of ground motion associated with the wave passage,coherency loss,and local site effects are given. The spatially varying ground motions are simulated stochastically based on an empirical coherency loss function and a filtered Tajimi-Kanai power spectral density function. The site effect is considered by a transfer function derived from 1D wave propagation theory. Compared with structural responses calculated using the uniform ground motion and delayed excitations,numerical results indicate that seismic responses of transmission towers and power lines are amplified when considering spatially varying ground motions including site effects. Each factor of ground motion spatial variations has a significant effect on the seismic response of the structure,especially for the local site effect. Therefore,neglecting the earthquake ground motion spatial variations may lead to a substantial underestimation of the response of transmission tower-line system during strong earthquakes. Each effect of ground motion spatial variations should be incorporated in seismic analysis of the structural system.