Strong Seismic Motion Research Articles

Seismic Performance Evaluation of Asymmetric Reinforced Concrete Tunnel Form Buildings

Despite the excellent seismic resistance characteristics of reinforced concrete tunnel form (RCTF) buildings, their predominant torsional vibration modes, especially those related to asymmetric RCTF constructions, make them vulnerable to strong seismic ground motions. For this reason, design guidelines prohibit the construction of multi-story RCTF buildings with asymmetric plans. This lack of relevant code provisions in turn, forces the engineer to apply design methods relevant to typical reinforced concrete (RC) buildings despite the well-known differences in the seismic performance when compared to RCTF buildings. This issue becomes more challenging when one is interested in asymmetric RCTF buildings whose past seismic performance is generally unknown. The present study investigates the seismic performance of two-, five-, and fifteen-story asymmetric RCTF buildings with two distinct plans. A number of parameters such as the percentage of walls at each story level and the in-plan eccentricity, on the lateral capacity of the building subjected to strong ground motions are highlighted. The effect of coupling beams (spandrels) on performance of RCTF constructions is also examined. It is concluded that they do not generally contribute in strength and ductility of low height constructions and in taller ones; due to inducing more demands, these low strength shear-failure-type members fail prematurely. However, if these elements are designed based on building code requirements and implemented with adequate shear reinforcements, they may be used as the structural fuses for dissipating seismic energy. The multilevel performance-based response modification factor (R-factor) is considered in order to capture the seismic performance of the RCTF structures. Relevant demand/supply R-factors are determined for this particular case study involving all the effective parameters such as ductility, over-strength, redundancy, seismic hazard level, and performance level. As a general conclusion, the results of the research show an excellent seismic performance of this type of structures in spite of their inherent irregularities. The high lateral stiffness and strength of the RCTF building compensates for the relatively low torsional stiffness with respect to lateral stiffness; as a result of which, the building exhibits superior seismic performance in high seismic hazard regions.

Empirical Attenuation relationship for Peak Ground Horizontal Acceleration for North-East Himalaya

Empirical Attenuation relationship for Peak Ground Horizontal Acceleration for North-East Himalaya

Strong-Back System Coupled with Framed Structure to Control the Building Seismic Response

In the present paper, the coupled behavior of structural systems obtained by connecting a moment resisting frame structure with a vertical elastic truss, known in the literature as strong-back, which acts as a mast by imposing to the structure a given lateral deformed shape, is investigated. The rigid behavior of the strong-back, which is designed in order to remain in the elastic field under strong seismic ground motion, imposes a uniform inter storey drift along the frame height, thus avoiding undesired effects such as soft storey and weak storey mechanisms. Consequently, the whole structural system may be, at first approximation, modelled as an equivalent Single Degree of Freedom system thus allowing for an analytical description of its response. In particular, in the work the attention is paid to the mutual actions exchanged by the strong-back and the frame by solving the static equilibrium equations, assuming a shear type behavior for the frame. Finally, some numerical simulations of frame systems with strong-back systems as subjected to earthquake ground motions are developed, encompassing both shear type frames and frames with flexible beams.

Developing a smart structure using integrated DDA/ISMP and semi-active variable stiffness device

Recent studies integrating vibration control and structural health monitoring (SHM) use control devices and control algorithms to enable system identification and damage detection. In this study real-time SHM is used to enhance structural vibration control and reduce damage. A newly proposed control algorithm, including integrated real-time SHM and semi-active control strategy, is presented to mitigate both damage and seismic response of the main structure under strong seismic ground motion. The semi-active independently variable stiffness (SAIVS) device is used as semi-active control device in this investigation. The proper stiffness of SAIVS device is obtained using a new developed semi-active control algorithm based on real-time damage tracking of structure by damage detection algorithm based on identified system Markov parameters (DDA/ISMP) method. A three bay five story steel braced frame structure, which is equipped with one SAIVS device at each story, is employed to illustrate the efficiency of the proposed algorithm. The obtained results show that the proposed control algorithm could significantly decrease damage in most parts of the structure. Also, the dynamic response of the structure is effectively reduced by using the proposed control algorithm during four strong earthquakes. In comparison to passive on and off cases, the results demonstrate that the performance of the proposed control algorithm in decreasing both damage and dynamic responses of structure is significantly enhanced than the passive cases. Furthermore, from the energy consumption point of view the maximum and the cumulative control force in the proposed control algorithm is less than the passive-on case, considerably.

Influence of Strong Seismic Motions of the 1977 Earthquake on Specific Building Type

This paper presents the dynamic investigations on the response of an important building from Craiova, Romania, the building housing the Faculty of Electrical Engineering affected by the major seismic motion from March 1977. Dynamic experimental/instrumental investigations of the technical condition of the structural components of the building were mainly focused on technical expertise of the current technical condition of the building resistance structure. The processing of the data obtained through this investigation gave important conclusions about the influence of the major seismic ground motions on a specific type of structure. The final findings and conclusions contributed to elucidate the building behavior (including bearing capacity) during intensive seismic ground motions and the completion of solutions for the building rehabilitation that were to be made. This research paper work is the result of documentary studies evidenced by theoretical and experimental research conducted by the author in order to achieve the objective and aimed at bringing their contributions to the seismic assessment of Craiova City for buildings made by reinforce concrete with P+8 height regime. As a result of the dynamic investigations the quantified level of the seismic performance was determined for this building. All these investigations, in conjunction with specific seismicity characterization of the site, gave specific decisions for intervention on structural and nonstructural components of the building.

Results of Post-Field Survey on the Mw 8.3 Illapel Earthquake Tsunami in 2015

On 16 September 2015, a Mw 8.3 earthquake occurred off the coast of Illapel, Central Chile, generating a tsunami that caused moderate damage along the coast of Central Chile. To investigate tsunami damage and evacuation responses, we conducted a post-tsunami field survey between La Serena and Concón. The average tsunami inundation height in the survey area was 3–4 m; however, in the innermost corner of Coquimbo Bay, which was shielded from the tsunami source by the Coquimbo Peninsula, the tsunami inundation height was 6.0–6.2 m, decreasing gradually along the coast away from the corner. This phenomenon was also confirmed around Tongoy Bay, which is geographically similar to Coquimbo Bay. Based on our results, we hypothesize that the tsunami was diffracted and refracted by the peninsula, and then converged on the innermost corner of the bay, located behind the peninsula. Interviews with local residents confirmed that most people evacuated immediately after feeling strong seismic motion, but before the tsunami warning and evacuation orders were issued. However, several people did not evacuate, either because they believed that they were located in a safe place, or because they wanted to protect their property.

On-site structure-specific real-time risk assessment: perspectives from the REAKT project

The availability of computationally powerful and energy-efficient wireless sensing units or WSUs (one or more arranged in the form of a network in the vicinity and/or within a structure of interest) has led to new developments in the field of building and seismic strong motion monitoring. These WSUs can serve several functions. Those of largest earthquake engineering and engineering seismology interest are the recording of ground shaking the building is subjected to, as well as its response, and the capability of running rapid seismic risk analyses on the basis of vulnerability models of the structure, possibly coupled with recorded data. The REAKT project has shed light on a number of prospective applications of the last generation of monitoring devices for seismic risk management of critical structures. These applications refer to real-time and near-real-time risk assessment, that is: earthquake early warning, immediate post-event response evaluations based on recorded shaking, and short-term aftershock risk management for automated building tagging. This paper summarizes these perspectives that, despite still presenting some challenges that may limit readiness to date, have potential for scientific innovation in the field.

Submerged Floating Tunnels under Seismic Motion: Vibration Mitigation and Seaquake effects

In this work the activity of the research group active at Politecnico di Milano in the field of the dynamic behavior of Submerged Floating Tunnels (SFTs) is reviewed, with emphasis on the possibility to mitigate the dynamic response through structural control solutions and the modeling of seaquake effects.A SFT model, equipped with suitable passive control devices, is accounted as a case study to assess the vibration mitigation under strong seismic motions. Elastic-plastic axial springs restrain the tunnel at the shores, and bars made of inelastic material anchor the tunnel to the seabed.Earthquake and seaquake motions are introduced accounting for spatial variability of the seabed motion during an earthquake.Some conclusions are drawn from a comparison between the response of the case study SFT due to earthquake and earthquake plus seaquake, which point out as seaquake forces can be an important source of excitation for SFTs. The paucity of studies on this topic, as well as the extent of the effects induced, call for further researches and developments.

Seismic response of the outer shell of a liquefied natural gas storage tank using a semi-analytical dynamic substructuring technique

This paper deals with the seismic response of the outer shell of a liquefied natural gas storage tank. The concrete shell is considered as three inhomogeneous subsystems, namely; a circular plate of varying thickness on an elastic foundation, a cylindrical wall and a spherical dome. The linear dynamic response of the complete system, subjected to a strong seismic ground motion, is derived in the frequency domain using a semi-analytical approach. The concept of frequency- and wavenumber-dependent dynamic spring stiffness is introduced for the exact satisfaction of the displacement continuity and force equilibrium at the interfaces between the three subsystems. The ground motion is described kinematically in the form of a Rayleigh wave propagating along the free surface of the soil. The influence of the Rayleigh wave speed and of the interference of the structural responses to the horizontal and the vertical seismic ground motion are examined for a particular case.

Settlement of piled raft subjected to strong seismic motion

Settlement of piled raft subjected to strong seismic motion

On the Torsional–Translational Response of Wind Turbine Structures

In the present paper, the torsional–translational response of a prototype wind turbine tower considered as an irregular structure is studied. As a matter of fact, a plethora of wind turbine towers has collapsed during the last decades due to torsional dynamic actions. An effective numerical model of the prototype irregular wind turbine tower is herein developed which has been verified by the application of the continuous model method considering both a fully fixed and a partially fixed foundation. As known, the higher eigenmodes of the tower strongly affect the structural response and may become critical in the case that the tower is subjected to strong dynamic loading, as is, e.g., wind loading, when simultaneously excited by a strong seismic motion. In order to estimate the role of the fundamental torsional modes of the above-mentioned structure in its overall structural response, three pairs of appropriately selected artificial seismic accelerograms having response acceleration spectra (for equivalent viscous damping ratio 0.03) equivalent to the Eurocode elastic acceleration spectra are used and then, applying a type of backwards analysis, an equivalent dynamic or static torsion loading is defined.

Expected seismic performance of irregular medium-span simply supported bridges on soft and hard soils

This paper presents the parametric study of irregular RC bridge structures subjected to strong seismic records. We determine the expected damages and the concentration demands on short piers of bridges with columns of unequal height located on soft and rigid soil sites. Medium length span bridges are analyzed using the most common structural configurations built in many countries with several height pier configurations. The structures were subjected to strong seismic ground motions recorded on soft and hard soils of earthquakes generated at subduction seismic sources. The parameters of interest in the study are the strength and stiffness characteristics of the substructure and the influence of the dynamic characteristics of the seismic records. The parameter combinations produced more than three hundred 3D non-linear time history analyses conducted with the Perform-3D software. Based on the evaluation of damages indexes, we determine the pier expected damages and the importance of the soil type, on the behavior of irregular pier bridge substructures. It is also quantified the impact of the pier configuration in the global behavior of the bridges and the influence of the shortest pier in the expected damages of the other piers. In most of the cases, the piers adjacent to the tallest piers of the bridge were the elements more affected by the irregularity.

Concept and methodology for evaluating core damage frequency considering failure correlation at multi units and sites and its application

The Tohoku earthquake (Mw9.0) occurred on March 11, 2011 and caused a large tsunami. The Fukushima Daiichi Nuclear Power Plant with six units were overwhelmed by the tsunami and core damage occurred. Authors proposed the concept and method for evaluating core damage frequency (CDF) considering failure correlation at the multi units and sites. Based on the above method, one of authors developed the procedure for evaluating the failure correlation coefficient and response correlation coefficient between the multi components under the strong seismic motion. These method and failure correlation coefficients were applied to two different BWR units and their CDF was evaluated by seismic probabilistic risk assessment technology. Through this quantitative evaluation, the validity of the method and failure correlation coefficient was confirmed.

Amalgamation in landslide maps: effects and automatic detection

Abstract. Inventories of individually delineated landslides are a key to understanding landslide physics and mitigating their impact. They permit assessment of area–frequency distributions and landslide volumes, and testing of statistical correlations between landslides and physical parameters such as topographic gradient or seismic strong motion. Amalgamation, i.e. the mapping of several adjacent landslides as a single polygon, can lead to potentially severe distortion of the statistics of these inventories. This problem can be especially severe in data sets produced by automated mapping. We present five inventories of earthquake-induced landslides mapped with different materials and techniques and affected by varying degrees of amalgamation. Errors on the total landslide volume and power-law exponent of the area–frequency distribution, resulting from amalgamation, may be up to 200 and 50%, respectively. We present an algorithm based on image and digital elevation model (DEM) analysis, for automatic identification of amalgamated polygons. On a set of about 2000 polygons larger than 1000 m2, tracing landslides triggered by the 1994 Northridge earthquake, the algorithm performs well, with only 2.7–3.6% incorrectly amalgamated landslides missed and 3.9–4.8% correct polygons incorrectly identified as amalgams. This algorithm can be used broadly to check landslide inventories and allow faster correction by automating the identification of amalgamation.

<b>Development of Autonomous Negative Stiffness Damper for Reducing Absolute Responses</b>

In this paper, a new vibration control device realizing negative stiffness in a passive manner is proposed in order to reduce the absolute response of structures under strong seismic motions. The developed device consists of a sliding plate with a PTFE portion, and they are vertically pressurized by coil springs. The shape of the sliding plate is convex, by which the control force is negatively proportional to the deformation. The prototype of the proposed device was assembled, and its performance was investigated through both sinusoidal and hybrid loading tests. It was confirmed that the proposed device reduced the maximum acceleration of the structure significantly without any significant increase in absolute displacement.

北野天満宮の石灯籠建立時系列に記録された京都市街の歴史地震動

Kyoto City has experienced a number of large seismic ground motions since it was established approximately 1200 years ago. Descriptions of these shakings are recorded in written documents which have been used to investigate historic earthquake hazards. In those documents often appears that stone lanterns at major temples and shrines collapsed and suffered damages, and descriptions of such damages are used to determine that the shaking at that site was at least as severe as 5 in JMA Intensity Scale. When stone lanterns are heavily damaged during earthquakes, some of them would be removed from the site and replaced by new ones afterward, which implies that the age distribution of stone lanterns which we observe today is affected by the history of strong ground motions. We examine ages of stone lanterns at Kitano-Tenmangu Shrine, Kyoto and investigate whether the correlation between the ages of stone lanterns and historic earthquakes is evident at this site. Severe damages of stone lanterns caused by strong ground motions in 1830 and 1854 at this site are documented in the historic documents, and we are able to identify that high numbers of stone lanterns that were newly build within a few years of these earthquakes currently remain at this site. We statistically argue that ages of existing stone lanterns at Kitano-Tenmangu Shrine are affected by historical strong seismic ground motions in Kyoto, and that these stone lanterns as a group record occurrence of historic earthquakes in Kyoto.

A novel horizontal to vertical spectral ratio approach in a wired structural health monitoring system

Abstract. This work studies the effect ambient seismic noise can have on building constructions, in comparison with the traditional study of strong seismic motion in buildings, for the purpose of structural health monitoring. Traditionally, engineers have observed the effect of earthquakes on buildings by usage of seismometers at various levels. A new approach is proposed in which acceleration recordings of ambient seismic noise are used and horizontal to vertical spectra ratio (HVSR) process is applied, in order to determine the resonance frequency of movement due to excitation of the building from a strong seismic event. The HVSR technique is widely used by geophysicists to study the resonance frequency of sediments over bedrock, while its usage inside buildings is limited. This study applies the recordings inside two university buildings attached to each other, but with different construction materials and different years of construction. Also there is HVSR application in another much older building, with visible cracks in its structure. Sensors have been installed on every floor of the two university buildings, and recordings have been acquired both of ambient seismic noise and earthquakes. Resonance frequencies for every floor of every building are calculated, from both noise and earthquake records, using the HVSR technique for the ambient noise data and the receiver function (RF) for the earthquake data. Differential acceleration drift for every building is also calculated, and there is correlation with the vulnerability of the buildings. Results indicate that HVSR process on acceleration data proves to be an easy, fast, economical method for estimation of fundamental frequency of structures as well as an assessment method for building vulnerability estimation. Comparison between HVSR and RF technique shows an agreement at the change of resonance frequency as we move to higher floors.

Some fluidized landslides triggered by the 2011 Tohoku Earthquake (Mw 9.0), Japan

The 2011 Tohoku Earthquake off the Pacific coast of Japan generated a large tsunami and many landslides, resulting in a great number of casualties. Although almost all casualties resulted from the tsunami, some long-travel, fluidized small-scale landslides also killed 13 people. After the earthquake, we surveyed seven of these catastrophic landslides triggered by the earthquake. We found that most of them have nearly identical geological features, with slopes consisting of pyroclastic deposits formed at different times, and with a palaeosol layer that outcropped in most cases after the landslide. Above the palaeosol there are layers of pumice and scoria. The palaeosol had a natural moisture content of ~160%, and the pumice and scoria had a moisture content of ~145%. From field observations we concluded that the sliding surface originated in the very upper part of palaeosol, and liquefaction occurred in both layers, resulting in the fluidization of displaced landslides. To examine the trigger and movement mechanism of these landslides, we monitored the ground motion of one landslide area during the many aftershocks, and compared the results with records obtained by a national seismic station nearby. We inferred that strong seismic motion occurred in the landslide area during the main shock. We sampled the palaeosol and pyroclastic deposits, and performed undrained static/cyclic shear tests on the materials both in a saturated state and at natural moisture content. The results indicate that high pore-water pressure was generated, resulting in decreased shear strength even in samples with the natural moisture content. The shear strength of the palaeosol lowered to a very small value with continuous increase of shear rate, enabling the high mobility of the displaced landslide materials.

Special Issue on Strong Ground Motion Prediction and Seismic Hazard Assessment

We have been conducting seismic hazard assessment for Japan under the guidance of the Headquarters for Earthquake Research Promotion of Japan since the 1995 Hyogo-ken Nanbu Earthquake, and have made National Seismic Hazard Maps for Japan for use in estimating strong ground motion caused by future earthquakes. This special issue reviews the results of these efforts. Such work includes the development of seismic hazard assessment methodology for Japan, highly accurate prediction techniques for strong seismic ground motion and modeling underground structures for evaluating strong ground motion. Related research on utilization initiatives and risk assessment based on hazard information has also been conducted. An open Web system – the Japan Seismic Hazard Information Station (J-SHIS) – has even been developed to provide information interactively. The 2011 Mw9.0 Great East Japan Earthquake was the largest such event recorded in the history of Japan. This megathrust earthquake was not considered in National Seismic Hazard Maps for Japan. But efforts toward revising seismic hazard assessment in Japan are progressing based on lessons learned from this earthquake. Hazard assessment is currently being reviewed in relation to the large earthquakes anticipated to occur in the near future based in the Sagami Trough and the Nankai Trough in the waters of offshore Japan. This assessment, which considers earthquakes larger than those assumed to have occurred in the past, is being reviewed as of this writing. In light of these pressing circumstances, studies are now being implemented to evaluate the long-period ground motion accompanying these large earthquakes. The knowledge that has been cultivated in Japan in terms of seismic hazard assessment has reached a high level, and it is important to expand such knowledge both internationally and domestically. This is just one of the reasons that efforts here in Japan are being made to help improve the level of seismic hazard assessment in the Asian region and throughout the entire world. It is expected that this special issue will help contribute to the further development of strong ground motion prediction and seismic hazard assessment now and in the future. Finally, I extend our sincere thanks to all of the contributors and reviewers involved with these articles.

Strong Ground Motion in the 2011 Tohoku Earthquake: A One-Directional Three-Component Modeling

Local wave amplification due to strong seismic motions in surficial multilayered soil is influenced by several parameters such as the wavefield polarization and the dynamic properties and impedance contrast between soil layers. The present research aims at investigating seismic motion amplification in the 2011 Tohoku earthquake through a one-directional three-component (1D-3C) wave propagation model. A 3D nonlinear constitutive relation for dry soils under cyclic loading is implemented in a quadratic line finite element model. The soil rheology is modeled by mean of a multi-surface cyclic plasticity model of the Masing-Prandtl-Ishlinskii-Iwan (MPII) type. Its major advantage is that the rheology is characterized by few commonly measured parameters. Ground motions are computed at the surface of soil profiles in the Tohoku area (Japan) by propagating 3C signals recorded at rock outcrops, during the 2011 Tohoku earthquake. Computed surface ground motions are compared to the Tohoku earthquake records at alluvial sites and the reliability of the 1D-3C model is corroborated. The 1D-3C approach is compared with the combination of three separate one-directional analyses of one motion component propagated independently (1D-1C approach). The 3D loading path due to the 3C-polarization leads to multiaxial stress interaction that reduces soil strength and increases nonlinear effects. Time histories and spectral amplitudes, for the Tohoku earthquake, are numerically reproduced. The 1D-3C approach allows the evaluation of various parameters of the 3C motion and 3D stress and strain evolution all over the soil profile.