Geology topics

Mehmet Celebi

Publications and source records attributed to Mehmet Celebi.

At least 37 records · Page 2Linked to original sources

USGS2019

On the utilization of synthetic and measured earthquake ground motions for designing building monitoring systems in the near-field of major faults

Agencies and research groups engaged in studying measures for enhancing the resiliency of communities have recently placed emphasis on the need for extensive implementation of monitoring systems for rapid post-event assessment of structural integrity. Designing a monitoring system for a building requires a thorough knowledge of its potential nonlinear dynamic behavior with an associated localization of interstory drift. Extending this task across a regional scale becomes even more challenging because of the heterogeneity of the buildings inventory and the limited knowledge of the characteristics of the demand especially for sites located in the near-field of a major fault. The existing observational database of near-field ground motion records is in fact too limited to constitute a comprehensive basis for full understanding of the potential range of structural response variability at different locations near a major fault. In addition, current insight into monitoring system design typically relies on linear structural models and sensors deployed on a limited number of floors. In this context, this paper presents first results of a study that combines synthetic earthquake ground motions generated from a massively parallel regional-scale geophysics wave propagation model at frequencies of engineering interest (0-5 Hz) with nonlinear tall building models. The objective is to gain new insight into the potential impact of localization of nonlinearities in structures subjected to realistic near-field earthquakes and develop a methodology that optimizes the deployment of sensors at the building and site level. In addition to the large database of synthetic motions, available real records are also employed to compare and contrast with the trends observed using synthetic ground motions. Preliminary results confirm a tendency of the demand to localize in specific portions of the structure, especially when nonlinearities occur. The building analyses provide guidance for various sensor deployment configurations associated with different probability of error in measuring structural drifts.

Conference Paper↗

USGS2019

The behavior of the Salesforce Tower, the tallest building in San Francisco, California inferred from earthquake and ambient shaking

The newly constructed tallest building designed in conformance with performance-based design procedure in San Francisco, California is a 61-story building equipped with an accelerometric array that recorded the January 4, 2018 M4.4 Berkeley earthquake. The building is designed with concrete core shear walls and perimeter gravity steel columns. The earthquake records as well as on-demand recorded ambient responses of the building are studied to determine its dynamic characteristics and building-specific behavior. At the level of shaking of either the earthquake or ambient excitation, the frequencies and low modal damping ratios (<2%) are similar. The building exhibits torsional behavior most likely due to abrupt asymmetrical changes in the size of the core shear wall. The translational and torsional modes during the earthquake are closely coupled, which leads to a beating effect, the period of which is calculable. Due to the relatively low-amplitude shaking during the earthquake, the drift ratios were small and did not cause any damage. It is expected that during stronger shaking levels, these characteristics may change.

California↗

USGS2019

Responses of the odd couple Carquinez, CA, suspension bridge during the Mw6.0 south Napa earthquake of August 24, 2014

The behavior of the suspension bridge in Carquinez, CA, during the M w 6.0 24 August 2014 South Napa, CA earthquake is studied. Utilizing data from an extensive array of accelerometers that recorded the earthquake-excited motions, dynamic characteristics such as modes, corresponding frequencies and damping are identified and compared with previous studies that used ambient data of the deck only plus mathematical models. Data are systematically analyzed for vertical, transverse and torsional motions of the deck, and transverse, longitudinal and torsional motions of the towers. The transverse and vertical fundamental mode frequencies of the deck are the same (0.17 Hz) due to coupling. Higher frequencies for transverse and vertical coupled modes are also the same at 0.46 Hz and 0.98 Hz. Tower translational frequencies are 0.39 Hz in the transverse direction and 0.46 Hz in the longitudinal direction, and are also coupled with those of the deck. Coupling of torsional modes of the tower and deck is also identified. A beating effect is observed, particularly for torsional motions.

California↗

USGS2019

Highlights of a cursory study of behavior of three instrumented buildings during the Mw7.1 Anchorage, Alaska, earthquake of November 30, 2018

This is a cursory study of the recorded responses of three buildings instrumented by the U.S. Geological Survey (USGS) in Anchorage, Alaska, during the M w "> M w Mw 7.1 earthquake of 30 November 2018. The earthquake caused the strongest shaking in Anchorage since the well‐known 1964 M w "> M w Mw 9.2 Great Alaska earthquake. Since the 1964 event, several structures (buildings and bridges) in Anchorage have been instrumented by the USGS, and their responses have been recorded during multiple events. For each of the three buildings (the 14‐story Frontier Building, the 20‐story Atwood Building, and the 22‐story Hilton Hotel) studied herein, essential dynamic characteristics and significant behavioral aspects such as beating and torsional motions are identified. Recorded peak accelerations and displacements are provided, and average drift ratios are computed using the peak displacements at the roof levels with respect to the ground level. These average drift ratios imply that the motions are at levels expected not to cause damage to the buildings. Visualization videos of both the 14‐story Frontier and the 20‐story Atwood Buildings have been developed to display overall shaking of the buildings during the earthquake.

Alaska↗

USGS2019

S2HM of buildings in USA

The evolution of seismic structural-health monitoring (S 2 HM) of buildings in the USA is described in this chapter, emphasizing real-time monitoring. Rapid and accurate assessment of post-earthquake building damage is of paramount importance to stakeholders (including owners, occupants, city officials, and rescue teams). Relying merely on rapid visual inspection could result in serious damage being missed because it is hidden by building finishes and fireproofing. Absent visible damage to a building’s frame, most steel or reinforced-concrete moment-frame buildings will be green-tagged based on limited visual indications of deformation, such as damage to partitions or glazing. Contrary, uncertainty in judging extent of structural damage may lead an inspector toward a relatively conservative tag, such as a red tag. In such cases, expensive, intrusive, and time-consuming inspections may be recommended to building owners (e.g., following the M w 6.7 1994 Northridge, Calif., earthquake, approximately 300 buildings were subjected to costly inspection of connections (FEMA 352)). Using real-time data-driven computation of drift ratios as the parametric indicator of structural deformation and damage to a structure could be of great value to minimize potential judgmental errors in such assessments. Recorded sensor data are an indication of performance, and performance-based design standards stipulate that the amplitude of relative displacement of a building’s roof (with respect to its base) indicates performance. Establishing sound criteria for performance is the most important issue for S 2 HM process, and since 2000 (in the USA), using real-time computed drift ratios and acceptable threshold criteria form the basis for almost all applications in S 2 HM.

Book chapter↗

USGS2019

Significant seismic behavior features of two tall buildings inferred from response records

In this paper, recent studies of recorded responses of behavior and performances of two instrumented tall buildings subjected to long-period motions from events that originate at far distances (e.g. 100-800km) are presented. Significant results indicate that (a) computed average drift ratios are substantial (~0.5%), and (b) there is permanent shift of fundamental frequencies for a tall building which was hundreds of km away from the epicenter of a large (M9.0) earthquake. In addition, (c) there are significant local site effects and basin effects, some causing resonance of buildings, (d) beating effect are observed particularly in elongated responses whereby elongated responses can contribute to low-cycle fatigue, and significantly, and (e) identified critical viscous damping percentages are low (<3%). This is consistent with recent recommendations of the Los Angeles Tall Buildings Design Council (LATBDC) 1 and the Tall Buildings Initiative (TBI) of Pacific Earthquake Engineering Center (PEER)2, and (f) beating effects are observed particularly in elongated responses whereby elongated responses can contribute to low-cycle fatigue. Analyses of one tall building from Japan affected during the 11 March 2011 M9.0 Tohoku earthquake, and one in Los Angeles, California during the 17 January 1994 M6.7 Northridge earthquake are presented. A variety of methods including spectral analyses, system identification, and time-frequency functions are used to extract dynamic response characteristics (modal frequencies and damping), drift ratios, and effect of site conditions including basin effects. In general, data-driven analyses show that, the two tall buildings (as well as many others not reported herein) exhibit (a) lower damping than those used in current design process analyses (<3%) and (b) a beating effect and significant basin effect. These are significant: (1) Additional damping generating elements can be considered during design processes to decrease the prolonged and amplified responses. (2) Basin effects are not considered during design, it is important to at least consider looking into such effects as these can result in resonance and amplified responses as shown in recent studies.

Los Angeles, Osaka↗

USGS2018

The 19 September 2017 M 7.1 Puebla‐Morelos earthquake: Spectral ratios confirm Mexico City zoning

One important element of understanding basin response to strong shaking is the analysis of spectral ratios, which may provide information about the dominant frequency of ground motion at specific locations. Spectral ratios computed from accelerations recorded by strong‐motion stations in Mexico City during the mainshock of the 19 September 2017 M "> M M 7.1 Puebla‐Morelos earthquake reveal predominate periods consistent with those mapped in the 2004 Mexican seismic design code. Furthermore, the predominant periods thus computed validate those studies using mainshock and aftershock recordings of the handful strong‐motion stations that recorded the 19 September 1985 M "> M M 8.1 Michoacán earthquake. Even though the number of stations in each of the zones (zones I, II, IIIa, b, c, and d) is not the same, they still allow confirmation of site frequencies (periods) attributable to the specific zones (particularly those in zones IIIa, b, c, and d). Spectral ratios are computed with two different methods: (1) horizontal to horizontal (H/H) ratio of smoothed amplitude spectrum of a horizontal channel in direction X of a station with respect to the smoothed amplitude spectrum of the horizontal channel in the same X direction of a reference stiff soil (or rock) station and (2) horizontal to vertical (H/V) ratio (or also known as the Nakamura method) of both horizontal (H) and vertical (V) channels of the same station. We show a comparison of the identified frequencies (periods) derived by both methods and find they are very similar and in good agreement with those indicated in the zoning maps of Mexico City in the 2004 seismic design code.

Mexico City↗

USGS2018

Quantifying the effect of beating inferred from recorded responses of tall buildings

The beating phenomenon observed in recorded earthquake responses of a tall building in Japan and of two others buildings in the U.S. are examined in this paper. The objective of the paper is to discuss the significance of beating and to estimate what percentage of total shaking energy impacting a building is contributed by beating when it occurs. Beating is prominent in the prolonged resonant responses of lightly damped structures and is a periodic vibrational behavior caused by distinctive coupling between translational and torsional modes that typically have close frequencies. Resonances from site effects may also enhance beating. Spectral analyses and system identification techniques are used herein to quantify the periods and amplitudes of the beating from strong-motion recordings of the three buildings. Quantification of beating is a first step towards determining remedial actions to improve building resilience to this phenomenon. It is shown by the analysis presented in this paper that the ratio of additional vibrational energy of a building exhibiting beating with respect to a postulated zero beating status can be as much as 105% depending on the building and the strong shaking record. Hence, beating should be considered during design and analyses process. Alternatively, remedies maybe implemented for existing buildings.

Conference Paper↗

USGS2017

U.S. Geological Survey National Strong-Motion Project strategic plan, 2017–22

The mission of the National Strong-Motion Project is to provide measurements of how the ground and built environment behave during earthquake shaking to the earthquake engineering community, the scientific community, emergency managers, public agencies, industry, media, and other users for the following purposes: Improving engineering evaluations and design methods for facilities and systems; Providing timely information for earthquake early warning, damage assessment, and emergency response action; and Contributing to a greater understanding of the mechanics of earthquake rupture, groundmotion characteristics, and earthquake effects.

Open-File Report↗

USGS2017

Before and after retrofit behavior and performance of a 55-story tall building inferred from distant earthquake and ambient vibration data

A sparsely instrumented 55-story building in Osaka, Japan had recorded unprecedented, severe and long-duration long-period resonating responses during the March 11, 2011 M9.0 Tohoku earthquake that occurred at 767 km distance. Thereafter, studies of the records resulted in implementation of a significant retrofit design, comprising dampers and buckling restrained braces (BRBs). The responses of the retrofitted building were also recorded during the April 24, 2016 M7.3 Kumamoto earthquake that occurred at 478 km. The earthquake and on-demand acquired ambient response data are analyzed in this study to assess the impact of this rare, retrofitted and instrumented tall building subjected to long period strong shaking from events originating at far distances. As expected, the fundamental frequency and critical damping ratio of the building increased, albeit small, after the retrofit as compared to before the retrofit. Increase of damping percentage is a positive finding and indicates that even larger percentages may be attained under shaking stronger than the 2016 event. The records indicate that the building still experiences significant resonance, torsion, as well as a beating effect.

Osaka↗

USGS2017

Responses of a 64-story unique San Francisco, CA. building to four earthquakes and ambient motions

We analyze the ambient and earthquake responses of a 64-story, instrumented, concrete core shear wall building in San Francisco, Calif. equipped with tuned sloshing liquid dampers (TSDs) and buckling restraining braces (BRBs). In an earlier paper [1], only ambient data were used to identify dynamic characteristics. Recently, the 72-channel instrumental array of the building recorded the 24 August 2014 Mw6.0 South Napa and three other earthquakes – allowing comparison of the dynamic characteristics using ambient and earthquake data. Peak accelerations of ambient and the larger South Napa EQ responses at the basement are 0.12 and 5.2 cm/s/s, respectively – a factor of ~ 42 and, at the 61st level, are 0.30 and 16.8 cm/s/s, respectively –a factor of ~56. Fundamental frequencies determined from spectral ratios for the NS (~0.3Hz), EW (0.27Hz) and torsional accelerations for the earthquake response vary within an insignificant frequency band of ~ 0.02-0.03 Hz as compared to those determined from ambient data. At the level of shaking, BRBs or TSDs are not effective enough to alter dynamic characteristics (frequency or damping). Under future stronger (e.g. design level) shaking of the building, the nonlinearities caused by actions of TSDs and BRBs can substantially shift the dynamic characteristics of the building.

California↗

USGS2016

Learning from the recent Taiwan Meinong Earthquake

This paper highlights the lessons learned following a reconnaissance trip to Tainan, Taiwan two weeks after the February 2016 earthquake. The reconnaissance was conducted by Gilsanz, Murray Steficek engineers (GMS) and an earthquake engineer from the United States Geological Survey (USGS), in collaboration with the Earthquake Engineering Research Institute (EERI), the Applied Technical Council (ATC) and the National Center for Research in Earthquake Engineering (NCREE) of Taiwan. Observations were made of damages, success of base-isolated high-rise and retrofitted school buildings, site effects and ground failures as well as the response of both city agencies and building owners to the earthquake. The motivation for engineers and the public for such a mission is to learn from the observations to be better prepared for the next earthquake.

Meinong↗

USGS2016

Evaluation of performance of Taiwan housing stock and schools during the Mw6.4 Kaohsiung/Meinong Earthquake of February 6, 2016

The recent Kaohsiung Meinong Earthquake which occurred on February 6, 2016 affected several categories of building stock for which risk identification programs were previously developed by NCREE. A typical building type in the city of Tainan is a mixed-use three-to-five-story structure. The ground floor of this typical structure is an open-front commercial or manufacturing space, which is laterally a soft story. The upper floors are residential and extend over a covered sidewalk, with column supports at the front of the building. NCREE has an established “street house” program which provides criteria for homeowners to evaluate and retrofit these structures. This program is discussed below, as well as damage and structural deficiencies related to this type of structure that were observed during a field reconnaissance trip following the Meinong Earthquake. An active evaluation and retrofit program is in place for school buildings in Taiwan. This program identifies buildings with seismic deficiencies and determines whether or not a retrofit is warranted. The program and retrofit strategies are discussed, as well as the performance of schools with and without retrofit during the Meinong Earthquake.

Conference Paper↗

USGS2013

Ambient response of a unique performance-based design tall building with dynamic response modification features

A 64-story, performance-based design building with reinforced concrete core shear walls and unique dynamic response modification features (tuned liquid sloshing dampers and buckling-restrained braces) has been instrumented with a monitoring array of 72 channels of accelerometers. The responses of the building to ambient motions from ground or wind were recorded and analyzed to identify modes and associated frequencies and damping. Not unexpectedly, the low-amplitude dynamic characteristics are considerably different than those computed from design analyses. Nonetheless, these computed values serve as a baseline against which to compare future strong shaking responses. Such studies help to improve our understanding of the effectiveness of the response modification features at various levels of shaking, to evaluate the predictive capabilities of the design analysis tools and to improve similar designs in the future.

California↗

USGS2012

Response of a tall building far from the epicenter of the 11 March 2011 M 9.0 Great East Japan earthquake and aftershocks

The 11 March 2011 M 9.0 Great East Japan earthquake generated significant long-duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of a tall building at 770 km from the epicenter of the mainshock and other related or unrelated events show how structures sensitive to long-period motions can be affected by distant sources. Even when the largest peak input motions to the building is about 3% g , the strong-shaking duration was about 140 s. The 300- to 1000-s prolonged responses of the building are primarily due to a combination of site resonance (e.g. structural fundamental frequency ~0.15 Hz and site frequency ~0.13–0.17 Hz) and low damping (~1–2%) of the structure. Response modification technologies can improve the response of the building during future earthquakes. The need-to-consider risks to such built environments from distant sources are emphasized.

Honshu↗

USGS2012

Beating effect identified from seismic responses of instrumented buildings

Beating effects observed in the recorded responses of buildings are examined in this paper. Beating is a periodic, resonating and prolonged vibrational behavior caused by distinctive close coupling of translational and torsional modes of a lightly damped structure. Repetitively stored potential energy during the coupled translational and torsional deformations turns into repetitive vibrational energy causing the ensuing prolonged motions. Beating, if a dominant response characteristic, may impact the instantaneous and long-term shaking performances of the buildings during earthquakes. In many cases, it is noted that resonance caused by site effects also contributes to accentuating the beating effect. Records from the buildings exhibit structural responses with beating effects. Spectral analyses and system identification techniques are used to quantify dynamic characteristics used in computing beating periods. The beat frequency generally known in acoustical physics is denoted by the absolute value of the differences in frequencies that cause the phenomenon. Engineering implications of the beating may be summarized as (a) prolonged cyclic shaking due to beating effect may take its toll on the structural system, (b) repetitive shaking can accentuate fatigue and low-cycle fatigue, and (c) resonating beating cycles can and do cause discomfort to occupants. Identification of beating effects is the key to find remedial action in modification of dynamic characteristics in order to attenuate or eliminate such effects.

Conference Paper↗

USGS2012

Structural engineering research at the U.S. Geological Survey

The U.S. Geological Survey (USGS) is the lead federal agency of the National Earthquake Hazards Research Program (NEHRP) to conduct research related to earth sciences. Therefore, whether it is research on structures or other civil engineering disciplines, the subject matter of such research at USGS must meet NEHRP objectives. The most recent charges for USGS are outlined in the Draft of the NEHRP Strategic Plan (August 2000) which details several research issues on the effects of ground motions on built environment.

Conference Paper↗

USGS2011

Method for detecting moment connection fracture using high-frequency transients in recorded accelerations

The 1994 Northridge earthquake caused brittle fractures in steel moment frame building connections, despite causing little visible building damage in most cases. Future strong earthquakes are likely to cause similar damage to the many un-retrofitted pre-Northridge buildings in the western US and elsewhere. Without obvious permanent building deformation, costly intrusive inspections are currently the only way to determine if major fracture damage that compromises building safety has occurred. Building instrumentation has the potential to provide engineers and owners with timely information on fracture occurrence. Structural dynamics theory predicts and scale model experiments have demonstrated that sudden, large changes in structure properties caused by moment connection fractures will cause transient dynamic response. A method is proposed for detecting the building-wide level of connection fracture damage, based on observing high-frequency, fracture-induced transient dynamic responses in strong motion accelerograms. High-frequency transients are short (<1 s), sudden-onset waveforms with frequency content above 25 Hz that are visually apparent in recorded accelerations. Strong motion data and damage information from intrusive inspections collected from 24 sparsely instrumented buildings following the 1994 Northridge earthquake are used to evaluate the proposed method. The method’s overall success rate for this data set is 67%, but this rate varies significantly with damage level. The method performs reasonably well in detecting significant fracture damage and in identifying cases with no damage, but fails in cases with few fractures. Combining the method with other damage indicators and removing records with excessive noise improves the ability to detect the level of damage.

Journal of Constructional Steel Research↗