Uniaxial and lateral strain behavior of ribbed reinforcement bars inspected with digital image correlation

Publisher's version (útgefin grein)Knowledge about the plastic behavior of reinforcement steel bars in reinforced concrete (RC) structures is important, especially for seismic design. This paper presents the results of experimental tests where the main aim was to map the plastic deformations of long ribbed reinforcement bars, both in the axial and lateral directions, in order to provide useful information about the behavior of reinforcement bars inside concrete. The study showed that the digital image correlation (DIC) technique is very suitable for this kind of tests. The uniaxial stress–strain curves for side‐by‐side and different gauge lengths (1d, 3d, 5d, 10d) were identical all the way to the max stress, but after that the segment including the neck dominated the strain development. The Poisson's ratio increased rapidly during the yielding phase to 0.44–0.49 and was constant all the way to rupture. The location of the neck could be predicted at the end of the yielding phase.This work was supported by a doctoral grant from the Eimskip University Fund of the University of Iceland, by the University of Iceland Research Fund, and by the Ludvigs Storr Trust Fund.Peer Reviewe

Statistical modelling of seismic vulnerability of RC, timber and masonry buildings from complete empirical loss data

Publisher's version (útgefin grein)In June 2000 two shallow, strike slip, Mw6.5 earthquakes occurred in the middle of the largest agricultural region in Iceland. The epicentres were close to small towns and villages and almost 5000 residential buildings were affected. A great deal of damage occurred but no residential buildings collapsed and there was no loss of life. Insurance against natural disasters is compulsory for all buildings in Iceland and they are all registered in a comprehensive official property database. Therefore, to fulfil insurance claims, a field survey was carried out after the two earthquakes where repair cost was estimated for every damaged building. By combing the loss data with the property database it was possible to establish a complete loss database, where all residential buildings in the affected area were included, both buildings with loss as well as buildings with no-loss. The main aim of the study was to fit a statistical vulnerability model to the data. Due to the high proportion of no-loss buildings in the database (~84%) a new and novel vulnerability model was used based on a zero-inflated beta regression model. The model was fitted to the three main building typologies in the affected region, i.e. low-rise structural wall RC, timber, and masonry buildings. The proposed model can be used to predict the mean and desired prediction limits of the losses for a given intensity level as well as to create fragility functions. All the typologies showed outstanding performance in the two destructive earthquakes, which is important to report, model and learn from.The authors thank the Natural Catastrophe Insurance of Iceland for placing the earthquake damage database and other relevant information at their disposal, and the University of Iceland Research Fund for financial support (Grant no. RSJ-2017 ).Peer Reviewe

Open-Source MASW Inversion Tool Aimed at Shear Wave Velocity Profiling for Soil Site Explorations

Publisher's version (útgefin grein)The shear wave velocity profile is of primary interest for geological characterization of soil sites and elucidation of near-surface structures. Multichannel Analysis of Surface Waves (MASW) is a seismic exploration method for determination of near-surface shear wave velocity profiles by analyzing Rayleigh wave propagation over a wide range of wavelengths. The inverse problem faced during the application of MASW involves finding one or more layered soil models whose theoretical dispersion curves match the observed dispersion characteristics. A set of open-source MATLAB-based tools for acquiring and analyzing MASW field data, MASWaves, has been under development in recent years. In this paper, a new tool, using an efficient Monte Carlo search technique, is introduced to conduct the inversion analysis in order to provide the shear wave velocity profile. The performance and applicability of the inversion scheme is demonstrated with synthetic datasets and field data acquired at a well-characterized geotechnical research site.This research was funded by the Icelandic Research Fund, grant number 206793-051, the University of Iceland Research Fund, grant number 73077, the Icelandic Road and Coastal Administration, grant number 1800-373, and the Energy Research Fund of the National Power Company of Iceland, grant number NYR-18-2017.Peer Reviewe

Combination of dispersion curves from MASW measurements

Publisher's version (útgefin grein)Multichannel analysis of surface waves (MASW) is a seismic exploration method for determination of near-surface shear wave velocity profiles based on analysis of horizontally travelling Rayleigh waves. This paper aims to propose a methodology and recommendations for combining dispersion data from several multichannel records. The dispersion curves are added up within logarithmically spaced wavelength intervals and the uncertainty of the mean phase velocity estimates is evaluated by using classical statistics and the bootstrap. The results indicate that combining multiple dispersion curves, which have been gathered by receiver spreads of different lengths (but with the same midpoint), can increase the investigation depth of the survey, improve its resolution at shallow depth and overall improve the reliability of the results as compared to the use of a single record. Moreover, the uncertainty of the combined mean dispersion curve can be determined and further used to present the shear wave velocity profile with upper and lower boundaries.This work was supported by the University of Iceland Research Fund [Grant no. 73077]; the Icelandic Road and Coastal Administration [Grant no. 1800-373]; and the Energy Research Fund of the National Power Company of Iceland [Grant no. NYR-18-2017].Peer Reviewe

Empirical vulnerability curves for Icelandic low-rise buildings based on zero-inflated beta regression model

In June 2000, two earthquakes of ~Mw6.5 struck in South Iceland, and in May 2008 the same region was hit again further west, with Mw6.3 event. Almost 5000 residential buildings were affected in each of these two seismic events. To fulfil insurance claims, detailed, and complete loss data were collected in each case, and the 2000 dataset and 2008 dataset were established. Having access to two high quality loss datasets from different size earthquakes, affecting the same building typologies in the same region, is rare to find in the literature. An advanced empirical vulnerability model based on zero-inflated beta regression was fitted to five building typologies, classified according to the GEM taxonomy system, independently for the 2000 dataset and the 2008 dataset. Status of seismic codes was considered when defining the building typologies. PGA was used as intensity measure. For all the five building typologies, the calibrated vulnerability functions and the fragility curves are substantially different from these two datasets. This indicates that PGA is not alone an adequate intensity measure to predict losses. The results also show that status of seismic code affects the performance of the buildings as one would like to see.The authors thank the Natural Catastrophe Insurance of Iceland for placing the earthquake damage database and other relevant information at their disposal. This work was partly financed by the SERICE project funded by a Grant of Excellence from the Icelandic Centre for Research (RANNIS), Grant Number: 218149-051. We also acknowledge support from the University of Iceland Research Fund

High spatial-resolution loss estimation using dense array strong-motion near-fault records. Case study for Hveragerði and the Mw 6.3 Ölfus earthquake, South Iceland

The most recent and costliest damaging earthquake in Iceland is the w6.3 29-May-2008 Ölfus earthquake to date. In particular, Hveragerði town located in the extreme near-fault region, suffered intense horizontal peak ground accelerations (PGA) of ∼40–90%g and large amplitude and long-period near-fault pulses, recorded on a dense urban strong-motion array in the town. In this study we collated a high-spatial resolution exposure database (building-by-building) complete with actual reported losses and classified the buildings by building materials and construction year according to the code design requirements in place at the time. We took advantage of the array data and evaluated a set of well-known ground motion intensity measures (IM), including PGA, pseudo-acceleration response spectra at short-to-long periods, Arias Intensity and Cumulative Absolute Velocity. We applied empirical Bayesian kriging geostatistical analyses to generate high-resolution shakemaps and provide IM estimates for each building. The shakemaps showed significant and systematic variation of the IMs across the small study area, with the lowest ground motions observed centrally and highest values in the outskirts. Furthermore, correlation analysis was carried out for the damage ratio and the exposure data IMs, but only low-to-moderate correlations were observed. A key reason is the incurred losses were primarily due to damage to non-structural components, to which the code design requirements do not apply. We carried out a seismic loss assessment in Hveragerði for the earthquake scenario of the Ölfus earthquake both on building-by-building, and municipality levels of spatial resolution. We applied both local and global fragility models for associated with detail building typologies identified based on the SERA taxonomy scheme. The results show that the global fragility functions severely underestimate the seismic performance of the building stock, except for one-story reinforced concrete buildings, while overall the masonry buildings were associated with the most predicted and observed losses. On the other hand, the local models predicted losses that conformed well with the observed damages to timber and concrete buildings. The high-spatial resolution predictions of losses gave results that better correlated with the observed losses in most typologies.This study was funded by the TURNkey H2020 European project (Towards more Earthquake-Resilient Urban Societies through a Multi-Sensor-Based Information System enabling Earthquake Forecasting, Early Warning and Rapid Response Actions) [www.earthquake-turnkey.eu] under grant agreement No 821046. This work was facilitated by an Erasmus+ staff mobility grant No. IS-TS2020-87850 for the lead author to the University of Alicante, Spain. This work was also partly supported by a Postdoctoral fellowship (No. 218255-051), grant of excellence (No. 218149-051) from the Icelandic Research Fund of the Icelandic Centre for Research, and the University of Iceland Research Fund

Strong ground motion in the epicentral area of the 2020-2021 earthquake swarm in the Reykjanes Peninsula, Iceland

The Geldingadalur eruption in the Reykjanes Peninsula on 19 March 2021 was preceded by several earthquakes of volcano-tectonic origin throughout 2020 and 2021. Seven earthquakes with magnitude M≥5 took place during the swarm, all of them recorded by the Icelandic Strong Motion Network operated by the Earthquake Engineering Research Centre of the University of Iceland. In this paper we present salient features of strong ground motion in the epicentral area caused by the swarm. Interestingly, earthquakes as small as M5.0 caused peak ground acceleration (PGA) larger than the 475-year return period PGA at a town near the epicentral area. At two recording stations, unusually high energy content at vibration periods <0.3s was detected, with spectral accelerations exceeding the design values. The largest recorded horizontal PGA was ~0.4g at Krýsuvík, station, which is the strongest PGA recorded in Iceland since the MW6.3 2008 Ölfus Earthquake. For this station we present horizontal-to-vertical spectral ratios indicating likely site-effects. We also compare the attenuation of PGA of the largest event of the sequence with two groundmotion prediction equations (GMPEs). The recorded PGA attenuation is well captured by a local GMPE.This work was partly financed by the SERICE project funded by a Grant of Excellence from the Icelandic Centre for Research (RANNIS), Grant number: 218149-051. The authors also acknowledge support from the University of Iceland Research Fund. The authors wish to thank the Icelandic Meteorological Office for access to the earthquake catalogue.Peer Reviewe

Liquefaction Assessment of a Loose Silty Sand Site in the 2008 Mw 6.3 Ölfus Earthquake

Seismicity in Iceland is related to the Mid-Atlantic plate boundary and primarily consolidated in two complex fracture zones. Liquefaction was observed after the Mw 6.3 Ölfus earthquake in 2008 at the site Arnarbaeli. The site consists of a thick silty sand stratum on the banks of the estuary of the river Ölfusa, and it is located less than 10 km from the earthquake epicentre. Based on nearby time history registrations, the estimated acceleration at the site was 0.6 - 0.7g. Using a simplified method, the safety factor against liquefaction based on the equivalent linear (EL) approach has been estimated. The analysis is built on in-situ field test data (i.e., MASW, and SPT). The analysis reveals the liquefaction depth, 4.4 m. It is shown that not only the current procedure is capable of predicting the occurrence of liquefaction, but also the safety factor which is in good agreement with the observed surface evidence of liquefaction at the site.This work was supported by the Icelandic Research Fund (Rannis), Grants number: 206793-052 and 218149-051.Peer Reviewe

Non-Structural Risk Evaluation: Experiences From Pilot Areas Of The Knowrisk Project

This paper presents a multidisciplinary approach to quantify seismic hazard and ground motion intensity parameters for non-structural seismic risk evaluation. In the framework of the European KnowRISK Project, three pilot areas were selected for testing different methodological approaches aimed at evaluating elements and measures to reduce seismic risk coming along with the failure of non-structural elements. At Mt. Etna, Italy, instrumental and historical macroseismic data are used to generate ground motion time series for different scenario events. Risk maps for non-structural damage are generated by using building vulnerability from census data and a damage model based on fragility curves; interstory drift spectra have been also calculated for a representative test site. In South Iceland, scenarios are defined basing on the June 2000 seismic sequence, which provided strong-motion data at several locations. The recorded data and other parameters of the source are used to perform finite-fault simulations of ground motion at different locations in the area and then to calculate interstory drift spectra. In Portugal a scenario referring to the Lower Tagus Valley was selected and finite-fault simulations for the nearby city of Lisbon were performed.PublishedThessaloniki, Greece5T. Sismologia, geofisica e geologia per l'ingegneria sismic

Non-Structural Earthquake Risk Management for Residential Buildings

As buildings become more resilient against structural damage the cost of non-structural damage and their consequences becomes proportionally higher, giving non-structural damage greater importance in earthquake risk reduction. Providing residents with detailed guidance on how to evaluate their risk regarding non-structural earthquake damage, and what mitigation and preparedness options they have, can increase both home and societal earthquake resiliency. Earthquake damage data from destructive earthquakes in south Iceland in 2000 and 2008 were used to develop simple but detailed twelve-step risk-management guidelines for residents. The guidelines are based on a set of disaster-related objectives. A standard loss estimation study was used to develop guidelines for the fixed non-structural elements and photographs from inside homes that had sustained significant non-structural damage were used to develop guidelines for loose items. Virtually every item in the studied homes was considered to understand its importance and its relevance to the function of a home. Information in terms of financial, functional and emotional value were used in the guidelines to help residents decide which mitigation options to take. The photos provided valuable information by placing each item in context with its surroundings, for example, to understand the possibility of motion and consequences to other items. The proposed approach, although based on observations from residential buildings, is useful for facilities that have sensitive operations, such as offices, industrial facilities, hospitals and government services. As societies become more complex and reliant on non-structural elements, systematic and thorough studies such as the one outlined herein become an increasingly critical part of sound earthquake risk management