Seismic Response Mitigation of Base-Isolated Buildings

Earthquake response mitigation of a base-isolated (BI) building equipped with (i) a single tuned mass damper at the top of the building, (ii) multiple tuned mass dampers (MTMDs) at the top of the building, and (iii) MTMDs distributed on different floors of the building (d-MTMDs) is studied. The shear-type buildings are modeled by considering only one lateral degree of freedom (DOF) at the floor level. Numerical approach of Newmark\u27s integration is adopted for solving the coupled, governing differential equations of motion of 5- and 10-story BI buildings with and without TMD schemes. A set of 40 earthquake ground motions, scaled 80 times to get 3200 ground motions, is used to develop simplified fragility curves in terms of the isolator maximum displacement. Incremental dynamic analysis (IDA) is used to develop simplified fragility curves for the maximum target isolator displacement. It is found that TMDs are efficient in reducing the bearing displacement, top floor acceleration, and base shear of the BI buildings. In addition, it was noticed that TMDs are efficient in reducing the probability of failure of BI building. Further, it is found that the MTMDs placed at the top floor and d-MTMDs on different floors of BI buildings are more efficient in decreasing the probability of failure of the BI building when compared with STMD

Analysis of a Benchmark Building Installed with Tuned Mass Dampers under Wind and Earthquake Loads

Publisher's version (útgefin grein)This study presents analysis of a benchmark building installed with tuned mass dampers (TMDs) while subjected to wind and earthquake loads. Different TMD schemes are applied to reduce dynamic responses of the building under wind and earthquakes. The coupled equations of motion are formulated and solved using numerical methods. The uncontrolled building (NC) and the controlled building are subjected to a set of 100 earthquake ground motions and wind forces. The effectiveness of using different multiple TMD (MTMD) schemes as opposed to single TMD (STMD) is presented. Optimal TMD parameters and their location are investigated. For a tall structure like the one studied here, TMDs are found to be more effective in controlling acceleration response than displacement, when subjected to wind forces. It is observed that MTMDs with equal stiffness in each of the TMDs (usually considered for wind response control), when optimized for a given structure, are effective in controlling acceleration response under both wind and earthquake forces. However, if the device is designed with equal mass in every floor, it is less effective in controlling wind-induced floor acceleration. Therefore, when it comes to multihazard response control, distributed TMDs with equal stiffnesses should be preferred over those with equal masses.The authors acknowledge the support from the University of Iceland Research Fund.Peer Reviewe

Tuned Mass Dampers for Response Reduction of a Reinforced Concrete Chimney Under Near-Fault Pulse-Like Ground Motions

Publisher's version (útgefin grein)The article investigates response mitigation of a reinforced concrete (RC) chimney subjected to pulse-like near-fault ground motions using tuned mass damper (TMD) schemes. The total height of the chimney is 265 m with a mass of 11,109 ton. Three TMD schemes are used: single tuned mass damper (STMD), multiple TMDs having equal stiffness (w-MTMDs) and multiple TMDs having equal masses (e-MTMDs). The STMD is tuned to the fundamental frequency of the chimney while both w-MTMDs and e-MTMDs have three TMDs for controlling each of the first and second modes (total of six TMDs) of vibration. Response of the uncontrolled and controlled structures is calculated for 69 recorded ground motions containing a dominant velocity pulse. Displacement and acceleration at top node of the RC chimney are the response of interest for performance assessment. It is found that e-MTMDs are more effective and robust than other schemes. It is also found that the pulse period of ground motion plays a very important role in how effective the control schemes are. There is a large variability in the reduction of response across these ground motions, and optimization methods independent of ground motion are not robust. There is a need for more advanced optimization methods incorporating information about local seismic sources.We acknowledge support from University of Iceland Research Fund.Peer Reviewe

Shared Tuned Mass Dampers for Mitigation of Seismic Pounding

Publisher's version (útgefin grein)This study explores the effectiveness of shared tuned mass damper (STMD) in reducing seismic pounding of adjacent buildings. The dynamics of STMDs is explored through numerical simulations of buildings idealized as single and multiple degree of freedom oscillators. An optimization method proposed in the literature is revisited. It is shown that the optimization results in two different solutions. The first one corresponds to the device being tuned to one of the buildings it is attached to. The second solution corresponds to a very stiff system where the TMD mass hardly moves. This solution, which has been described as an STMD in the literature, is shown to be impractical due to its high stiffness and use of a heavy stationary mass that plays no role in response mitigation but adds unnecessary load to the structure. Furthermore, it is shown that the second solution is equivalent to a viscous coupling of the two buildings. As for the properly tuned solution, i.e., the first solution, sharing the device with an adjacent building was found to provide no added benefits compared to when it is placed on one of the buildings. Based on results from a large set of real earthquake ground motions, it is shown that sharing a TMD mass with an adjacent building, in contrary to what is reported in the literature, is not an effective strategy.This research was funded by University of Iceland Research Fund.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

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

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

Multi-Hazard Risk Assessment of Kathmandu Valley, Nepal

Natural hazards are complex phenomena that can occur independently, simultaneously, or in a series as cascading events. For any particular region, numerous single hazard maps may not necessarily provide all information regarding impending hazards to the stakeholders for preparedness and planning. A multi-hazard map furnishes composite illustration of the natural hazards of varying magnitude, frequency, and spatial distribution. Thus, multi-hazard risk assessment is performed to depict the holistic natural hazards scenario of any particular region. To the best of the authors’ knowledge, multi-hazard risk assessments are rarely conducted in Nepal although multiple natural hazards strike the country almost every year. In this study, floods, landslides, earthquakes, and urban fire hazards are used to assess multi-hazard risk in Kathmandu Valley, Nepal, using the Analytical Hierarchy Process (AHP), which is then integrated with the Geographical Information System (GIS). First, flood, landslide, earthquake, and urban fire hazard assessments are performed individually and then superimposed to obtain multi-hazard risk. Multi-hazard risk assessment of Kathmandu Valley is performed by pair-wise comparison of the four natural hazards. The sum of observations concludes that densely populated areas, old settlements, and the central valley have high to very high level of multi-hazard risk

Using non-structural mitigation measures to maintain business continuity : A multi-stakeholder engagement strategy

Funding Information: Acknowledgments. This work was carried out in the framework of the KnowRISK project (Know your city, Reduce seISmic risK through non-structural elements), co-financed by the European Commission’s Humanitarian Aid and Civil Protection (Grant agreement ECHO/SUB/2015/718655/PREV28), with partial support from Instituto Superior Técnico (IST) and Laboratório Nacional de Engenharia Civil (LNEC) from Portugal; Istituto Nazionale di Geofisica e Vulcanologia (Italy) and the Earthquake Engineering Research Centre (EERC) from University of Iceland. The KnowRISK project gratefully acknowledges the assistance of the following public and private entities for their outstanding contribution of time and expertise, namely CP Comboios de Portugal, CTT Correios de Portugal, EDP - Energias de Portugal, EPAL - Grupo Águas de Portugal, IKEA Portugal, Infraestruturas de Portugal, Jerónimo Martins, Metropolitano de Lisboa, NOS communications and entertainment group, PT-Altice, Siemens, SONAE MC and the collaboration of the Laboratorio di Storia e Comunicazione della Scienza (DOS) of the Ferrara University. The earthquake field missions which took place during the course of KnowRISK, were also helpful and essential to the authors for the study of the causes of non-structural damage. Funding Information: This work was carried out in the framework of the KnowRISK project (Know your city, Reduce seISmic risK through non-structural elements), co-financed by the European Commission?s Humanitarian Aid and Civil Protection (Grant agreement ECHO/SUB/2015/718655/PREV28), with partial support from Instituto Superior T?cnico (IST) and Laborat?rio Nacional de Engenharia Civil (LNEC) from Portugal; Istituto Nazionale di Geofisica e Vulcanologia (Italy) and the Earthquake Engineering Research Centre (EERC) from University of Iceland. The KnowRISK project gratefully acknowledges the assistance of the following public and private entities for their outstanding contribution of time and expertise, namely CP Comboios de Portugal, CTT Correios de Portugal, EDP-Energias de Portugal, EPAL-Grupo ?guas de Portugal, IKEA Portugal, Infraestruturas de Portugal, Jer?nimo Martins, Metropolitano de Lisboa, NOS communications and entertainment group, PT-Altice, Siemens, SONAE MC and the collaboration of the Laboratorio di Storia e Comunicazione della Scienza (DOS) of the Ferrara University. The earthquake field missions which took place during the course of KnowRISK, were also helpful and essential to the authors for the study of the causes of non-structural damage. Publisher Copyright: © 2021 the Author(s). All rights reserved.Encouraging property owners and individuals to adopt mitigation measures to improve the resilience of their buildings and equipments to seismic hazard has been a major challenge in many earthquake-prone countries. Few business leaders are aware of the fragility of their supply chains or other critical systems due to earthquake hazard. Bridging the gap between research production and research use is another crucial challenge for the earthquake risk research process. The KnowRISK project outcome is aimed at encouraging the proactive engagement of multi-stakeholders (community at large, schools, business community and local govern-ment groups) undertaking non-structural mitigation measures that will minimize earthquake losses to individuals and communities. Engaging stakeholders, taking into account their needs and inputs to maintain critical and urgent business activities, can contribute to the research findings and ensure that our data collection is thorough and complete. Engagement with stakeholders, during the whole process can lead to improved outcomes and for the development of viable solutions, for business and society, because of stakeholder’s role and influence within the organizations.Peer reviewe