Strong Earthquake Shaking Research Articles

Seismic site characterization baseline data for microzonation and site response analysis of Otuasega Town, Bayelsa State, Niger Delta region of Nigeria

This study presents the findings of a comprehensive geotechnical and seismic site investigation conducted at Otuasega Town located in Bayelsa State within the Niger Delta region of Nigeria. Subsurface exploration involved advancing 10 boreholes to 30 m depth using hollow stem auger drilling. Continuous disturbed and undisturbed soil sampling was performed at 1.5 m intervals for detailed geotechnical testing. Laboratory tests on the recovered soil samples established the index properties, classification, densities and consistency limits of the stratified deposits. The subsurface profile comprised alternating layers of clay, silt and sand typical of deltaic sediments, with the clay fractions exhibiting medium to high plasticity. Shear wave velocity (Vs) profiling using Multichannel Analysis of Surface Waves (WASW) techniques categorised the site predominantly as Site Class C and D based on international standards. The Standard Penetration Test (SPT) N-values ranged from 5 to 10, indicating soft normally consolidated clay conditions typical of the Niger Delta region. Predictive empirical models developed from the field and lab data showed strong correlations for estimating key geotechnical parameters such as SPT blow count, Vs and liquefaction resistance. Ground response analyses using the Vs and SPT data indicated significant site amplification potential, with peak ground accelerations up to 1.5 times the bedrock motion. Liquefaction analysis based on the empirical SPT-based methods revealed a high potential for liquefaction in the sandy layers, especially under strong earthquake shaking. The study characterized the complex sedimentology and provided baseline information for seismic microzonation and site-specific ground response analyses to advance understanding of geohazards in this delta environment.

Preferred Seismic Performance Attainment in Important Buildings

In the aftermath of earthquakes, hospital buildings are expected to remain occupiable to treat the injured. For the purpose, firstly, an appropriate structural system that ensures no or limited structural damage should be provided in such buildings; wall-frames are the recommended structural systems in hospital buildings. Secondly, it is also essential to adequately design wall-frames to help meet the preferred Occupiability seismic performance. The work presented in this paper examines the contributing factors for failure of structural elements in hospital buildings and explores structural configuration and design strategies for mitigating these failures. Nonlinear analyses studies of a typical hospital building in high seismic region in India are carried out to help provide quantitative guidelines for: (a) Structural Plan Density (SPD) of structural walls, and (b) design parameters, for achieving the preferred performance. Displacement-based limit state of structural damage adopted from traditional displacement demand estimation rules is proposed. Lateral stiffness, strength, and ductility are evaluated of study buildings, and efficacy of results obtained from nonlinear static analyses confirmed by performing nonlinear time history analyses in commercial software PERFORM 3D. Results demonstrate inadequacy of moment frame structural system in hospital buildings under strong earthquake shaking, identifies optimum overall SPD of structural walls and relative column-to-beam strength ratio of frame members, required to achieve Occupiability. A minimum 3% SPD of structural walls in Wall – Special Moment Resisting Frame (WSMRF), 4% SPD in Wall – Ordinary moment resisting frame (WOMRF) hospital buildings, and a minimum column-to-beam strength ratio (CBSR) of 2 is required in hospital buildings to attain Occupiability performance.

Collapsing Response of a Nonlinear Shear-Beam Building Model Excited by Horizontal and Vertical Strong-Motion Pulses at Its Base

The sequence of collapsing stages of buildings during strong earthquake shaking is still a poorly understood phenomenon. This study aims to use numerical simulations to improve our understanding of the sequence of phenomena that accompany the collapse of buildings during damaging earthquakes. For that purpose, we use a nonlinear shear-beam model of a building that is excited by a sequence of large horizontal and vertical displacement pulses at its base. The propagation of the input pulses through the structure is simulated by a finite difference scheme. We select the properties of our model to be similar to those of a seven-story hotel in San Fernando Valley of the Los Angeles metropolitan area, which was damaged during the 1994 Northridge, California earthquake. We present results of one example of collapsing response of the model to hypothetical but plausible ground motion close to an earthquake fault. We illustrate the response only for a sequence of horizontal and vertical pulses. We show the differences in the nature of the collapsing sequence for vertical upward and downward pulses of ground motion. Rocking input motions will be added in our future work. Improved understanding of the stages of collapse of buildings will be useful for the development of design strategies to prevent it.

Study of a Flat Slab Building with a Shear Wall at Core and X-Bracing

Construction with flat slabs is quite dangerous when there is strong earthquake shaking. Two different forms of flat slab buildings—flat slab with shear wall at core and flat slab with x-bracing—are considered in the study. These flat slab constructions’ structural rigidity is increased by this lateral force-resisting mechanism. It has been found that adding a shear wall considerably boosts the flat slab structure’s ability to withstand lateral forces.

Influence of Structural Parameters on the Buckling of Longitudinal Steel Bar in RC Structural Wall

Reinforced Concrete (RC) structural wall is widely used in multistoried RC frame buildings to enhance lateral stiffness and lateral strength for earthquake resistance. One of the possible failure modes, observed during strong earthquake shaking, is the buckling of longitudinal steel reinforcement in the boundary elements of the wall. This also assumes importance in establishing damage states for seismic fragility analysis of RC wall. Although a few past studies have focussed on longitudinal bar buckling in RC members, detailed parametric study is absent particularly for such instability of bars in the boundary elements of the wall. In the present study, displacement-controlled nonlinear static analysis of several wall specimens is carried out using fibre-discretization of cross-section and distributed plasticity modelling in OpenSEES. Here, 27 different models of the isolated slender wall are created considering variations in six structural parameters, namely (a) length ratio of the boundary element to the wall, (b) axial force ratio, ratios of (c) longitudinal steel in web, and (d) transverse steel and (e) longitudinal steel in the boundary elements. The effect of wall thickness is accounted for through variation in axial force ratio. Using the analytical results from the nonlinear analysis of the wall models, the trends in drift ratio at the onset of longitudinal bar buckling damage states as functions of various key structural wall properties, has been investigated.

Seismic vulnerability of jacket supported large offshore wind turbine considering multidirectional ground motions

Large numbers of offshore wind turbines in earthquake prone areas increase the scientific interest in analysing their seismic vulnerability. This study investigates the deformation and collapses susceptibility of a 10 MW jacket supported offshore wind turbine (OWT) considering different geometry of pile and jacket. A three-dimensional finite element model of the soil-pile-jacket-tower is developed in ABAQUS. A performance-based analysis is conducted to quantify the engineering demand parameters by choosing first mode spectral acceleration as the intensity measure for different pile length-to-diameter ratios and the base width of the jacket. The significance of considering higher modes and the vertical component of the earthquake motion on the dynamic response of offshore wind turbines is also discussed. Considerable amplification of acceleration is observed at the nacelle due to vertical excitation. In low to moderate earthquake shaking, jacket base width shows a marginal influence on the responses, while a significant impact is observed for strong earthquake shaking. Mudline rotation and acceleration response at the nacelle are the most critical parameters that govern the design under the serviceability limit state. Moreover, it is observed that initiation of the rocking mode of vibration for jacket-supported OWTs resting on a pile foundation is significantly less until its embedment length reduces considerably (3 to 5 m).

Design of a fuse link beam-to-column connection for earthquake resistant moment frames

This paper presents details of numerical investigations on exterior beam-column joint sub-assemblages with a novel fuse link beam-to-column connection. The connection is designed to protect the connected beams and columns of moment frame buildings during strong earthquake shaking by confining the inelasticity within the connection elements. The connection consists of two fuse links and one standard shear tab. Detailed numerical analyses are performed to study the behaviour of the connection including the level of plastic strain distribution around the connection region. First, the results of numerical analyses are validated using experimental results of full-scale experimental investigations on exterior beam-column joint sub-assemblages, which demonstrated the good performance and replaceability of the connection. Then, parametric studies are carried out to identify and investigate the effect of major parameters on the connection behaviour - the key parameters being the geometric parameters of fuse link and the beam depth. Finally, it is shown that the results of the numerical study are in good agreement with those of an analytical model that can be used for proportioning of the fuse link connection at the design stage. Also, the results of the analytical model can be used in global analysis of moment frames using the developed fuse link connection.

Seismic Analysis of 3D Framed Building

Generally RC framed structures are designed without regards to structural action of masonry infill walls present. Masonry infill walls are widely used as partitions. These buildings are generally designed as framed structures without regard to structural action of masonry infill walls. They are considered as non- structural elements. RC frame building with open first storey is known as soft storey, which performs poorly during strong earthquake shaking. Past earthquakes are evident that collapses due to soft storeys are most often in RC buildings. In the soft storey, columns are severely stressed and unable to provide adequate shear resistance during the earthquake. Hence a combination of two structural system components i.e. Rigid frames and RC shear walls or Rigid frames and Bracings leads to a highly efficient system in which shear wall and bracings resist the majority of the lateral loads and the frame supports majority of the gravity loads.

Seismic design and evaluation of controlled outriggered rocking wall (CORW) using equivalent energy design procedure (EEDP)

Next-generation earthquake engineering design seeks to develop robust structural systems to limit structural and non-structural damage after strong earthquake shaking. In this study, an innovative high-performance tall building, named Controlled outriggered rocking wall (CORW) system is proposed. The CORW system improves the conventional reinforced concrete (RC) core wall by adding a damped outrigger system and a damped controlled rocking base. The CORW is designed using the novel Equivalent energy design procedure (EEDP) to meet different performance objectives for different shaking intensities. Detailed EEDP for the CORW system is presented in this paper. Three prototype buildings (with 25, 35, and 45 stories) located in Vancouver Canada were designed using the proposed procedure. Robust finite element models of the CORW systems were developed in OpenSees and subjected to a series of nonlinear time history analysis. The results of the nonlinear time history analysis indicate that the CORW system designed using EEDP performs well under different levels of earthquake intensities, where it can be used reliably as an effective seismic force resisting system for high-rise application.

Performance evaluation of self-centering rocking shear walls: Part 1 — Quantification of structural damages

Self-centering rocking shear wall (SCRSW) is an innovative structural system which is designed to achieve low damage after strong earthquake shaking. In this paper, an effective damage quantification method is developed to quantify the damages of SCRSWs. The procedure is applied in the performance evaluation and damage quantification for 24 SCRSWs. An equation of the critical parameter β in the damage model is proposed. The results show that increasing stirrup reinforcement ratio, self-centering parameter and concrete strength can reduce the damage developed in SCRSWs effectively, while higher prestress in post-tensioned (PT) tendons tends to increase the damage. An empirical equation between the critical parameter β and structural features is proposed. The critical parameter is then used to quantify the damage index (DI) of SCRSW. The result shows that the proposed β can be used to evaluate and quantify the damages developed in SCRSWs efficiently and accurately.

A drift-based design procedure for RC buildings considering the effect of shear wall-floor slabs junction

Reinforced Concrete (RC) structural wall is widely used in the lateral force resisting system for multistoried RC frame buildings located in earthquake-prone regions. In such buildings, the wall is connected to the RC slab at every floor level. The junction region of shear wall and floor slab constitutes an important link in the load path from slab to wall during earthquake shaking, thereby influencing the pattern of lateral load distribution in the shear wall. In case of multistoried building, the maximum elastic drift is estimated by carrying out linear static analysis for different load combinations as recommended by the Indian Earthquake Code IS 1893 (Part 1): 2016. However, during strong earthquake shaking, the inelastic lateral drift needs to be monitored to avoid undesirable levels of damage in structural members. The inelastic drift level of an isolated slender shear wall considering the behaviour of wall-slab junction has not been studied in the past. The present study aims to investigate the possible lateral drift limit of RC wall frame building considering the effect of floor slabs.

Damage Detection and Localization on Real Structures Subjected to Strong Motion Earthquakes Using the Curvature Evolution Method: The Navelli (Italy) Case Study

In recent years, structural health monitoring (SHM) has received increasing interest from both research and professional engineering communities. This is due to the limitations related to the use of traditional methods based on visual inspection for a rapid and effective assessment of structures and infrastructures when compared with the great potential offered by newly developed automatic systems. Most of these kinds of systems allow the continuous estimation of structural modal properties that are strictly correlated to the mechanical characteristics of the monitored structure. These can change as a result of material deterioration and structural damage related to earthquake shaking. Furthermore, a suitable configuration of a dense sensor network in a real-time monitoring system can allow to detect and localize structural and non-structural damage by comparing the initial and a final state of the structure after a critical event, such as a relevant earthquake. In this paper, the modal curvature evaluation method, used for damage detection and localization on framed structures, considering the mode curvature variation due to strong earthquake shaking, is further developed. The modified approach is validated by numerical and experimental case studies. The extended procedure, named “Curvature Evolution Method” (CEM), reduces the required computing time and the uncertainties in the results. Furthermore, in this work, an empirical relationship between curvature variation and damage index has been defined for both bare and infilled frames.

Bayesian Detection of Streamflow Response to Earthquakes

AbstractDetecting whether and how river discharge responds to strong earthquake shaking can be time‐consuming and prone to operator bias when checking hydrographs from hundreds of gauging stations. We use Bayesian piecewise regression models to show that up to a fifth of all gauging stations across Chile had their largest change in daily streamflow trend on the day of the Mw 8.8 Maule earthquake in 2010. These stations cluster distinctly in the near field though the number of detected streamflow changes varies with model complexity and length of time window considered. Credible seismic streamflow changes at several stations were the highest detectable in eight months, with an increased variance of discharge surpassing the variance of discharge following rainstorms. We conclude that Bayesian piecewise regression sheds new and unbiased insights on the duration, trend, and variance of streamflow response to strong earthquakes, and on how this response compares to that following rainstorms.

Characterization of Six-Degree-of-Freedom Sensors for Building Health Monitoring.

Six-degree-of-freedom (6DoF) sensors measure translation along three axes and rotation around three axes. These collocated measurements make it possible to fully describe building motion without the need for an external reference point. This is an advantage for building health monitoring, which uses interstory drift and building eigenfrequencies to monitor stability. In this paper, IMU50 6DoF sensors are characterized to determine their suitability for building health monitoring. The sensors are calibrated using step table methods and by comparison with earth’s rotation and gravity. These methods are found to be comparable. The sensor’s self-noise is examined through the power spectral density and the Allan deviation of data recorded in a quiet environment. The effect of temperature variation is tested between 14 and 50 C. It appears that the self-noise of the rotation components increases while the self-noise of the acceleration components decreases with temperature. The comparison of the sensor self-noise with ambient building signal and higher amplitude shaking shows that these sensors are in general not sensitive enough for ambient signal building health monitoring in the frequency domain, but could be useful for monitoring interstory drift and building motion during, for example, strong earthquake shaking in buildings similar to those examined here.

Seismic performance of a two-span steel girder bridge with ABC connections

This paper presents the discussion and results from the first shake table test of a steel girder bridge system constructed using accelerated bridge construction (ABC) techniques. The bridge model was tested at the multi-shake table testing facility at the University of Nevada, Reno. The objective of this study was to evaluate the seismic performance of a bridge system incorporating six types of ABC connections under strong bidirectional earthquake shaking. The test model was a 0.35-scale, two-span steel plate-girder bridge with seat type abutments. The model was subjected to eight earthquake motions adopted from the 1994 Northridge-Sylmar ground motion applied with increasing amplitudes. The paper presents the global and local response of the bridge model with focus on ABC connections. Moreover, the paper provides a first hand demonstration of a full ABC bridge system seismic performance, which was found to be satisfactory and adequate to adopt the utilized ABC connections for future projects.

Seismic performance of controlled-rocking concentrically braced frames designed by the equivalent energy procedure

Recent earthquakes in New Zealand and Japan showed that structures designed according to modern building codes might suffer significant damages with hefty financial and social losses. The primary reason lies in the seismic design approach, where most seismic force resisting systems (SFRS) were designed to prevent structures from collapse during strong earthquake shaking, without considering the damage and the usability of the structure after an earthquake. In this paper, a controlled rocking-concentrically braced frame (CR-CBF) is proposed. CR-CBF is a fused structural system that uses a combination of post-tensioned tendons (PTs) and energy dissipation devices (EDs) to create a controlled-rocking mechanism to minimize structural repair costs and down time after a strong earthquake. PTs are placed in the structure to provide the restoring forces and to minimize any residual deformation in the structure, while EDs are placed at the base of a structure to dissipate the earthquake energy. To ensure the CR-CBF can achieve high performance, two (CR-CBF) prototypes with different heights are designed using the novel equivalent energy design procedure (EEDP). The EEDP procedure allows designers to select different performance objectives at different shaking intensities. The results of nonlinear dynamic analyses of the CR-CBFs show that CR-CBFs have superior seismic performances as intended and can be efficiently designed using EEDP. Finally, the seismic performance of CR-CBF against collapse is assessed using incremental dynamic analysis (IDA) outlined in the FEMA-P695 methodology. The results show that the CR-CBFs designed by EEDP have sufficient safety against collapse, hence it can be used as an efficient seismic force resisting system.

Numerical Studies of Three-Dimensional Isolated Structures with Vertical Quasi-Zero Stiffness Property

ABSTRACT A novel three-dimensional (3D) seismic isolator combining the quasi-zero stiffness (QZS) system in the vertical direction with the friction pendulum system in the horizontal direction is presented and applied to a moderately tall building model. The isolation system dynamic properties are first assessed in vertical and rotational directions separately using a simplified 3D model based on an equivalent analytical method with the frequency-amplitude functions and displacement transmissibility curves. The effectiveness of the 3D isolation system is then verified through numerical time history analysis of a tower building with a bottom podium modeled in OpenSees including a new numerical element representative of the 3D isolators implemented in the software. A comparison of the dynamic response is made between a fixed-base model, a 2D isolated model with friction pendulum bearings in the horizontal direction only, and the novel 3D isolated model. The input excitations consist of strong earthquake shaking and low-amplitude field recorded metro vibration. Results demonstrate that the 3D isolator can effectively reduce the seismic actions in three directions compared with the fixed based model and the 2D isolated model. The overturning movement can be controlled within safe limits under maximum considered earthquakes. In addition, the 3D isolators can significantly decrease human discomfort from high frequency environment vibration.

Geomechanical characterisation and dynamic numerical modelling of two anthropogenic fill slopes

In the last 22 years, four large (between approximately 1000 and 5000 m3) flowslides in anthropogenic fill materials have occurred in residential areas of the greater Wellington region, New Zealand. Such failures are relatively rare, given that there are over 1600 mapped fill bodies, formed between the early 1900s and present day within the region. Nonetheless, their performance under strong earthquake shaking has yet to be tested, given no strong ground motions (>0.15 g) have shaken the region since their construction. In this study, we used remote sensing techniques, borehole investigations, geotechnical testing and numerical modelling to investigate two fill bodies that are characteristic of those constructed across the Wellington region. This paper presents the results from the dynamic analysis of these two sites under strong earthquake shaking.The maximum anthropogenic fill thicknesses at both sites ranged between 20 m and 30 m. The fills tested varied from sandy gravel with some silt to clayey gravelly silt sand (D50 from 0.02 mm to 10 mm and D90 from 5 mm to 50 mm). Based on the field mapping, site investigation and laboratory results, two-dimensional geotechnical cross-sections of the sites were generated and used as the basis for the numerical simulations. Accelerograms recorded from eleven local and overseas earthquakes were used as inputs for the modelling. These were selected and scaled to simulate the amplitude and frequency content of the different types of earthquake shaking that could affect the sites up to 2.5 g, which represents a peak ground acceleration with an approximate annual exceedance probability of 0.00005. The results indicate simulated permanent ground displacements, due to sliding of the fill in the range of 0.01 m to >10 m, with the amount of displacement increasing with increasing Peak Ground Acceleration (PGA). Although at small displacements it is unlikely the fill slopes would fail catastrophically to form flowslides, the simulated permanent displacements are large enough for an earthquake with a free field PGA of >0.6 g (annual exceedance probability (AEP) of 0.002) to potentially disrupt buried elastic pipe utilities (especially the water pipes). Such deformation could lead to the leakage of water from broken pipes, and an increase in pore-water pressure within the fills, which could in turn lead to the development of post-earthquake flowslides. After a major earthquake, such cascading hazards may pose a major problem for recovery activities.

Integration of 3D large‐scale earthquake simulations into the assessment of the seismic risk of Bogota, Colombia

AbstractBogotá, the capital city of Colombia, is mostly located on a lacustrine soil deposit surrounded by hills in a central plateau of the eastern cordillera of the Colombian Andes. This highly populated urban area is exposed to a significant seismic hazard from local and regional fault systems. In addition, the potential ground motion amplification during earthquakes due to the presence of soft soil deposits, along with the effects of the surface and subsurface topography, can strongly influence the seismic hazard and consequently the seismic risk to the city. This study aims to develop a physics‐based framework to generate synthetic ground records that can help better understand the seismic response of the basin and other amplification effects during strong earthquake shaking in the region, and to incorporate these effects into the estimation of seismic risk. To this end, a set of simulations were first conducted on Hercules, the wave propagation octree‐based finite element simulator developed by the Quake Group at Carnegie Mellon University, to identify the impacts of hypothetical strong earthquakes scenarios. Then, the results from these simulations were integrated with the exposure and vulnerability information previously developed for the main building constructions in the city to assess the seismic risk in the region under different conditions of analysis. Results from this more detailed model are compared with previously published results from simplified models. Sensitivity analyses help identify critical aspects that should be considered in the future to improve the seismic risk assessment of infrastructure.

Postdisaster image‐based damage detection and repair cost estimation of reinforced concrete buildings using dual convolutional neural networks

AbstractReinforced concrete (RC) buildings are commonly used around the world. With recent earthquakes worldwide, rapid structural damage inspection and repair cost evaluation are crucial for building owners and policy makers to make informed risk management decisions. To improve the efficiency of such inspection, advanced computer vision techniques based on convolutional neural networks have been adopted in recent research to rapidly quantify the damage state (DS) of structures. In this article, an advanced object detection neural network, named YOLOv2, is implemented, which achieves 98.2% and 84.5% average precision in training and testing, respectively. The proposed YOLOv2 is used in combination with the classification neural network, which improves the identification accuracy for critical DS of RC structures by 7.5%. The improved classification procedures allow engineers to rapidly and more accurately quantify the DSs of the structure, and also localize the critical damage features. The identified DS can then be integrated with the state‐of‐the‐art performance evaluation framework to quantify the financial losses of critical RC buildings. The results can be used by the building owners and decision makers to make informed risk management decisions immediately after the strong earthquake shaking. Hence, resources can be allocated rapidly to improve the resiliency of the community.