Soft Soil Sites Research Articles

Power Analysis of SDOF Structures With Tuned Inerter Dampers Subjected to Earthquake Ground Motions

Abstract Tuned inerter dampers (TID) have been demonstrated as efficient energy dissipation devices for seismic response control. However, its potential capability for energy harvesting remains largely unexplored. Here, we present a theoretical analysis of the power of a structure-TID system subjected to earthquake ground motions. The analytical solutions (ASs) of the average damping power of the system are derived for considering white noise base excitations and the Kanai-Tajimi earthquake model, respectively. Comparisons of the numerical results of a Monte Carlo simulation and the theoretical predictions verify the accuracy of the analytical solutions. Besides, we uncover the influence of the TID parameters on the average damping power and output power of the system. The optimal frequency ratio of the TID for maximizing its output power slightly differs from that for seismic response control, and the former varies with site conditions. In contrast, both the damping power and output power are not sensitive to the damping ratio of the TID. For short-period structures, a small inertance-to-mass ratio (μ) of the TID is beneficial to maximize its output power, while seismic response control requires a large μ. For long-period structures, the damping power and output power are not sensitive to the μ. Generally, a structure-TID system on a soft soil site absorbs more energy from a given earthquake and is capable of harvesting more energy than that on a hard soil site. This study may help develop new strategies for self-powered control and monitoring in civil structures.

Enhanced Seismic Structural Reliability on Reinforced Concrete Buildings by Using Buckling Restrained Braces

The control of vibrations and damage in traditional reinforced concrete (RC) buildings under earthquakes is a difficult task. It requires the use of innovative devices to enhance the seismic behavior of concrete buildings. In this paper, we design RC buildings with buckling restrained braces (BRBs) to achieve this objective. For this aim, three traditional RC framed structures with 3, 6, and 9 story levels are designed by using the well‐known technique nondominated sorting genetic algorithm (NSGA‐II) in order to reduce the cost and maximize the seismic performance. Then, equivalent RC buildings are designed but including buckling restrained braces. Both structural systems are subjected to several narrow‐band ground motions recorded at soft soil sites of Mexico City scaled at different levels of intensities in terms of the spectral acceleration at first mode of vibration of the structure Sa(T1). Then, incremental dynamic analysis, seismic fragility, and structural reliability in terms of the maximum interstory drift are computed for all the buildings. For the three selected structures and the equivalent models with BRBs, it is concluded that the annual rate of exceedance is considerably reduced when BRBs are incorporated. For this reason, the structural reliability of the RC buildings with BRBs has a better behavior in comparison with the traditional reinforced concrete buildings. The use of BRBs is a good option to improve strength and seismic behavior and hence the structural reliability of RC buildings subjected to strong earthquake ground motions.

Variations between foundation-level recordings and free-field earthquake ground motions: numerical study at soft-soil sites

It is typically assumed that accelerograms obtained from ground motion recording instruments adequately installed inside a building can be considered as representative of free-field conditions if the structure is less than 2-3 storeys high and does not feature a basement or a massive foundation system. In this work, such an assumption is verified through nonlinear soil-block finite element analyses, considering the induced seismicity Groningen gas field as a case-study and both types of structures. The capability of the numerical model in adequately reproducing nonlinear soil response and capturing interaction between soil and structure is first verified through a number of analyses and cross-checks. Considering soil profiles at the locations of different recording stations in the Groningen field, together with accelerograms from recent events in the region, the results obtained with the numerical model confirm that recordings from instruments located at the base of lightweight structures are not affected by Soil-Structure Interaction (SSI) effects, neither kinematic nor inertial. Heavy structures with a basement, however, do exhibit recordings with variations with respect to the free-field; these are identified and possible corrections to the recordings are analysed. Another set of analyses then demonstrates that soil consolidation prior to the construction of lightweight structures resting on shallow foundations may instead lead to foundation-level recordings that feature high-frequency ground motion amplitudes slightly lower than their free-field counterparts. Additional simplified analyses show the dependency of the recordings on inertial SSI effects due to deformability of the ground supporting the structure.

Observations of Rayleigh waves in Mexico City Valley during the 19 September 2017 Puebla–Morelos, Mexico earthquake

This article discusses the principal features of Rayleigh surface waves generated by basin-edge effects in Mexico City during the Mw7.1 19 September 2017 Puebla–Morelos, Mexico earthquake. Rayleigh waves were extracted from ground motions recorded at 12 stations in Mexico City. We used a recently proposed method for extracting surface waves, where the earthquake record is filtered based on the normalized inner product of the Stockwell transform of the three-component earthquake recordings. Results of this study reveal that basin-edge effects produced strong Rayleigh waves, particularly at certain stations, with frequencies that are mainly between 0.2 and 0.9 Hz, which is consistent with previous frequency ranges reported in the literature. Evidence of higher-mode Rayleigh waves was found at all stations located on soft soil sites, even at stations that are more than 1 km away from the basin edges. It was also observed that peak acceleration spectral ordinates of the retrograde component of the extracted Rayleigh waves at two stations exceeded the design spectral ordinates of the 1976 and 2004 editions of the Mexico City Seismic Provisions.

2D nonlinear site response analysis of typical stiff and soft soil sites at shallow bedrock region with low to medium seismicity

In this study, an attempt has been made to estimate 2D nonlinear seismic site response of a small scale basin on typical stiff and soft soil sites in Peninsular India (PI). Six survey sites were selected from three shallow bedrock regions such as Kalpakkam, Bangalore and Vizag for which subsurface profiles are generated at these locations using Multichannel Analysis of Surface Wave -2D (MASW-2D) method. The subsurface profiles generated are classified as stiff and soft sites based on average 30 m shear wave velocity and further used for the 2D nonlinear site response analysis using the commercial program FLAC -2D. Thirteen intraplate ground motions from all around the world are selected for the site response analysis based on seismicity of the region. Results of the site response analysis were expressed in terms of short-period amplification factor (Fc) and long period amplification factor (Fs) for the intraplate shallow bedrock region. The results show that the Fc gives higher values than Fs in the case of stiff soil and it is showing a reverse trend in the case of soft soil. The trend of Fc is becoming more complex than that of the Fs especially in the case of stiff soil sites. Also, the 2D site response results were compared with conventional 1D nonlinear site response results using the program DEEPSOIL and aggravation factors were generated. Further, a parametric study has been carried out to quantitatively evaluate the effect of amplitude of ground motion on 2D site response analysis. Parametric study results show that subsurface heterogeneity is very sensitive to the low amplitude of input motion, especially in the case of stiff soil sites.

Experimental Study of Seismic Isolated Structures with Sliding Implant-Magnetic Bearings

ABSTRACT Sliding implant-magnetic bearing (IMB) is a new type of seismic isolators that benefits from its adaptive energy-dissipation behavior. In order to assess the performance of the sliding IMB for seismic protection, a complete shaking table test on the base-isolated structure is reported in the present paper. Tri-directional-recorded earthquake ground motions and mono-directional artificial earthquake ground motions pertaining to both site classes II and III are employed to drive structural vibration in the laboratory experiment, respectively. Seismic mitigation of the base-isolated structure with respect to dynamic characteristics, story accelerations, inter-story drifts, horizontal torsions, and local strains is addressed. Experimental study shows expected results that the base-isolated structure with sliding IMBs attains more profitable mitigations on story accelerations and inter-story drifts under earthquake ground motions pertaining to the stiff soil site than those pertaining to the soft soil site. Significant mitigations on horizontal torsion of the structure and on local strain at the column bottom are attained as well. In addition, seismic performance of sliding IMBs during the shaking table test is assessed. It is revealed that the isolators exhibit satisfactory energy-dissipation capacity and excellent frictional behavior, and maintain good working state during the entire experimental test.

Inelastic displacement ratio for high damping SDOF systems built on soft soil sites

The main purpose of this study is to estimate the inelastic displacement ratio, C1, of highly damped systems built on soft soil sites. For this purpose, results of linear and nonlinear time history analysis of 79 single-degree-of-freedom (SDOF) systems with damping ratios of 0.05, 0.1, 0.2, 0.3 and post-yield stiffness ratios of -0.01, 0, 0.05 and 0.1 under a large number of ground motion records obtained at soft soil deposits, were used. Oscillators exhibited ductility levels as high as 6. Based on the results, a new simplified equation as a function of the period of vibration normalized by the predominant period of ground motion records, the level of inelastic deformation, post-yield stiffness ratio and damping ratio for structures built on soft soil, has been proposed using nonlinear regression analysis.

Seismic soil–structure interaction analysis of structure with shallow foundation using response spectrum method

Seismic soil–structure interaction (SSI) of structure with shallow foundation is studied using response spectrum method (RSM). A SSI model is first constructed with the consideration of the coupling of horizontal and rocking motions of structural foundation. In this model, the structure is modelled by finite elements and the soil by the accurate lumped parameter model (LPM) based on rational approximation. The SSI model is a non-classically damped system due to introducing damping of LPM. Complex mode superposition RSM is subsequently applied to solve the non-classically damped SSI system under design response spectrum. Seismic responses of 3-story and 6-story shear structures on two types of sites are finally calculated using the SSI model and RSM. The numerical experiments indicate that RSM can be an effective tool to analyze seismic SSI of structure with shallow foundation, and some conclusions are drawn: (1) the coupling of horizontal and rocking motions of foundation should be considered for relatively high structure on soft soil site, (2) the rational-approximation-based LPM is more accurate than the simple one, (3) the over-damped case can be neglected in the complex mode superposition process although it arises at fundamental frequency, and (4) the quasi spectrum transform relationship can be used to obtain the relative displacement and relative velocity response spectra from the given absolute acceleration design response spectrum.

A new method of seismic site classification using HVSR curves: A case study of the 12 November 2017 Mw 7.3 Ezgeleh earthquake in Iran

On the 12th of November 2017, a strong earthquake with a moment magnitude of 7.3 struck the west of Iran, causing massive damage in SarpoleZahab and surrounding areas. In this study, the Horizontal to Vertical Spectral Ratio (HVSR or H/V technique) of strong ground motion recorded at 60 stations is used for identifying of site response and subsequent site classification. Very clear amplification is observed at stiff and soft soil sites. Empirical equations from the literature relating frequency of HVSR peak to average shear wave velocity in the upper 30m(VS30), commonly used as a proxy for site classification, were found to be unreliable, making site classification difficult. To overcome this problem, a soft computing method based on the Generalized Regression Neural Networks (GRNN) algorithm is used. This algorithm relies on HVSR curves at the recording stations and uses pattern recognition against a set of pre-defined curves for different site types. In this approach, site characterization is based on the overall features of the HVSR curves rather than just the peak frequency. The stations are classified into four different site classes, and the results are consistent with local geotechnical information, where available. Rather than relying on VS30, which has been found deficient in many studies, and is known to have difficulty in reliably estimating when geotechnical data is lacking, site classification proposed in this study uses the overall characteristics of HVSR curves of response spectra of recorded strong motion data. This method is proposed as a more reliable and direct method for site characterization in seismically hazardous regions.

The effect of stone column area replacement ratio on seismic behaviour of foundation

Tall buildings require additional foundation solutions in order to resist the applied actions on soft soil sites. Nowadays the piled foundations are often altered by stone column solutions, as a cheap alternative. Structures built on soft soil or stiff soil, generally results in different behavior under earthquakes. However, the earthquake behavior of the stone column solution on different types of soil is still unclear. This paper aims to investigate the influence of different characteristics of soil structure interaction on the seismic response of stone column matt foundation. A reinforced concrete matt foundation was simulated with parametric soil stiffness and area replacement ratio of stone column. An analytical method was used to model the soil profile and appropriate ground motion data were incorporated for the analyses. The comparative results were presented and highlighted in terms of soil amplification and seismic response.

Uncertainty Analysis in Prediction of Settlements for Spatial Prefabricated Vertical Drains Improved Soft Soil Sites

This paper presents the quantification of uncertainties in the prediction of settlements of embankments built on prefabricated vertical drains (PVDs) improved soft soil deposits based on data collected from two well-documented projects, located in Karakore, Ethiopia, and Ballina, Australia. For this purpose, settlement prediction biases and settlement distributions were statistically computed based on analyses conducted on two Class A and Class C numerical predictions made using PLAXIS 2D finite element modelling. From the results of prediction bias, Class C predictions agreed well with the field measured settlements at both sites. In Class C predictions, the computed settlements were biased to the measured values. For Class A predictions, the calculated settlement values were in the range of mean and mean minus 3SD (standard deviations) for Karakore clay, and they were within mean and mean minus 2SD limit for the Ballina soil. The contributing factors to the settlement uncertainties of the Karakore site may include variability within the soil profile of the alluvial deposit, particularly the presence of interbedded granular layer within the soft layers, and the high embankment fills, and the limited number of samples available for laboratory testing. At the Ballina test embankment site, the uncertainties may have been associated with the presence of transitional layers at the bottom of estuarine clay and sensitivity of soft soil to sample disturbances and limitations in representing all the site conditions.

Vertical and Lateral Bearing Capacity of FRP Composite Sheet Piles in Soft Soil

Fiber‐reinforced polymer (FRP) composite sheet piles are usually favored for slope and river‐retaining structures due to their construction and environmental efficiency. Their applications, however, have been hindered by the lack of understanding of the bearing capacity. This paper studies the vertical and lateral bearing capacity of FRP composite sheet piles through three full‐scale tests conducted in Haiyan, a soft soil site in the Yangtze River Delta of China. In the three tests, we measured the vertical bearing capacity of the FRP composite sheet piles, the bearing capacity of the composite foundation, and the lateral capacity of the FRP composite sheet piles, respectively. The test results show that the Q‐S (load on the top of the pile versus settlement) curve of the FRP composite sheet piles exhibits a steep fall while that of the composite foundation is relatively flat. Moreover, the ultimate bearing capacity of the FRP composite sheet piles is measured to reach 23.8 kN while that of the composite foundation increases by 47.1 %, reaching 35.0 kN. It shows that the FRP composite sheet piles under the composite foundation have a favorable bearing performance. Finally, the final horizontal displacement of the FRP composite sheet pile in the reinforced area with anchoring the sheet pile is smaller than the final horizontal displacement in the nonreinforced area, indicating that the horizontal bearing capacity can be significantly improved by anchoring the sheet pile.

Surabaya earthquake hazard soil assessment

The vulnerability of land in an area to earthquake ground motions is one of the factors causing damage caused by the earthquakes. The city of Surabaya, which is crossed by two active fault segments, needs an assessment to reduce the risk of being affected by an earthquake that might occur. The aims of this study are (1) to find out the distribution of Seismic Site Classes, (20 to know the distribution of the value of Seismic Amplification, and (3) to know the potential of liquefaction in the city of Surabaya. Surabaya city, which is geologically dominated by alluvium deposits, consists of soft soil (SE) and medium (SD) sites based on N-SPT30 and Vs30 data. The level of soil amplification against earthquakes ranging from 1 to 4. This occurs because the physical properties of the Surabaya City soil layer are dominated by alluvium deposits. Regions with more than 2 amplification values are located around the coastline on the North and East coasts of Surabaya City. Based on the potential liquefaction index value, Surabaya City is included in the region with a high potential for liquefaction with a potential liquefaction index value of more than 5.

Displacement-based seismic design with damage control of asymmetric buildings

Abstract This paper presents a procedure for the displacement-based seismic design of in-plan asymmetric buildings with earthquake-induced damage control. Damage is defined on the structural elements in the in-plan and elevation layout of the structure. The proposed method is based on the concepts of the performance-based seismic design philosophy and the application of basic equations of structural dynamics that are regularly used for the current design of buildings. In its application, the simultaneous bidirectional seismic demand is characterized by smooth design spectrum as proposed by most current regulations. To illustrate the steps required in the application of the design method proposed, the paper presents the design process of a 15- and 12-story buildings with in-plan asymmetric distribution of stiffnesses and subjected to a design demand given by the spectrum a real seismic event representative of soft soil sites such as those of the bed-lake of Mexico City. The results obtained are compared with the corresponding results of the nonlinear dynamic step-by-step analyses under the same seismic demand. Based on the results obtained, the relevance of this procedure in the displacement-based seismic design of asymmetric buildings and the implications for its consideration in future regulations are discussed. Graphical Abstract

Determination of The Site Amplification on Deep Soil Layer Using 1-D Site Response Analysis (Case study: Jakarta City, Indonesia)

The dynamic response of deep soil layers is used in the development of microzonation maps. The empirical correlation between standard penetratation blow count numbers and S-wave velocity was derived for practical purposes in site characterization based on local data in a case study in Jakarta, Indonesia. For estimating the intensity of potential earthquake shaking at the ground surface as a function of depth to the bedrock surface layer, 1-D site response analysis was carried out in 5745 simulations. The site amplification values were then evaluated by dividing the spectral acceleration (SA) at ground surface by the SA at rock outcrop. Plots of the SA amplification values at interested depth intervals of the bedrock surface layer were assigned. The results showed that the site amplification values estimated by considering the local depth of the bedrock surface layer were generally smaller than the SA amplification values from the Indonesian seismic building code SNI-1726-2012. Also, there appears to exist a tendency of lower levels of mean regression of amplification, in particular for the soft soil site class.

Nonlinear dynamic analysis of Qom Monorail Bridge considering Soil-Pile-Bridge-Train Interaction

Railway tracks experience has shown that considering the effects of Soil-Structure Interaction (SSI) especially for soft soil sites is necessary. These effects can also be important for monorail bridges on soft soil beds. The main aim of this study is to investigate the effects of Soil-Pile-Bridge-Train Interaction (SPBTI) on the Qom Monorail Bridge (QMB) responses. In spite of many studies on the effects of monorail train-bridge (fixed-base structure) interaction, very little information is available in the literature on the effects of monorail trains on SPB systems. In this paper, an advanced three-dimensional (3D) continuum finite element analysis of QMB subjected to train moving loads was developed. The SPBT models have been validated using three case studies (two bridge-monorail train studies and a soil-pile-structure study) available in the literature. The maximum displacements of the guideway beam at the different train speeds were obtained for various SPBT system conditions. The effects of the stiffness and thickness of the soil, the bridge span length, and the amplitude, length, and geometry of the train loading on the critical speed of the SPBT system are discussed in detail. Finally, the results have been synthesized into simple design charts to select the appropriate straddle-type monorail train and determine its critical speed for a particular soil-bridge condition. In addition, a new simple method for simulating the behavior of the finger-bands (as one of the excitation source of vertical bridge vibrations) in commercial software was presented. The results show that the position of a monorail train bogies plays an important role in determining critical speed so that with uniformity the spacing between the bogies decreases the critical speed in the vertical direction.

Cumulative Structural Damage Due to Low Cycle Fatigue: An Energy-Based Approximation

ABSTRACT The seismic response of structures to strong ground motions is a complex problem that has been studied for decades. However, current seismic regulations do not assess the potential level of damage that a structure may undergo during a given seismic event. This will happen in spite that the design objectives for any structural system are formulated in terms of acceptable levels of damage. This paper develops simple expressions to estimate plastic energy demands for soft soil sites (particularly, those located in Mexico City) capable of generating long duration narrow-banded ground motions. To overcome the limited scope of previous studies, about 35,000 seismic simulations were performed using two scaling methodologies: linear and seismological. A new simplified relation between plastic hysteretic energy and maximum ductility demands is presented, and also, a discussion offered on how this relation can be used to allow for an energy-based design aimed at controlling structural damage under the explicit consideration of low cycle fatigue.

Residual displacement estimation for soft soils: Application to Mexico city lake-bed

Current seismic regulations do not assess the seismic performance of structures during a given seismic event, and therefore do not require an estimation of their residual displacement or level of structural damage. Nevertheless, this information is relevant after intense ground motions to assess the possibility of re-occupying a building. This paper develops simple expressions to estimate the maximum displacement demand from the residual displacement of single-degree-of-freedom systems subjected to long-duration narrow-banded ground motions generated in soft soil sites (particularly, those located in Mexico City). To overcome the limited scope of previous studies, more than 35,000 seismic simulations were performed. The influence of the lateral strength of the single-degree-of-freedom systems is considered. A simplified relation between the residual and maximum displacement demands is established.

Determination of Ground Profile and Peak Surface Acceleration (PSA) using single station microtremor Inversion method for earthquake hazard zonation of Lombok Island

There were two fairly destructive earthquake phenomena in 2018 of M 6.4 and M 7 at East Lombok District. However, severe damage occurred in the West Lombok District, Mataram City, and North Lombok District where the three locations were far from the earthquake epicenter. This proves that the potential for infrastructure damage does not only depend on the magnitude and the earthquake source distance, but rather the presence of local site effects. This study aims to determine the dynamic characteristics of the soil and the distribution of Peak Surface Acceleration (PSA). The method used are HVSR analysis (Horizontal to Vertical Spectral Ratio) and inversion of Rayleigh wave ellipticity curve from single station microtremor measurements. The results showed that West Lombok Regency, Mataram City, and the western part of North Lombok Regency were dominated by sedimentary layers which were softly and included in the SD (stiff soil / soft soil) site category. These regions are soil deformation vulnerable due to the earthquake. Based on PSA distribution, the southern part of Lombok Island and Mataram City have a relatively high PSA value. The high value of PSA has the potential to cause ground shaking hazard that are strong enough when an earthquake occurs. This research is expected to be a reference for the design of spectra response to minimize damage of building infrastructure at various levels due to earthquake events.

Stochastic Finite-Fault Method Based on Dynamic Corner Frequency to Simulate the Mw6.2 Tottori earthquake in Japan

Stochastic finite-fault method is the main method to simulate near field strong earthquakes in current seismic engineering. For specific ground motion, the accuracy of parameter selection is important, such as field effect, because the number of rock sites is scarce in many areas of China, the calculation of crustal amplification and site amplification of a specific soft soil site can not only eliminate the limitation of station selection, but also improve the accuracy of simulation results. In this paper, a stochastic finite-fault method based on dynamic corner frequency is used to simulate the Mw6.2 Tottori earthquake on October 21, 2016 in Japan. The comparison with the actual records shows that the simulation results are in good agreement with the short period and have great feasibility. This paper discusses the differences between the simulated response spectra (PSA) of stations with various azimuths and the observed one. Meanwhile, it also demonstrates the dissimilarities in simulation results between the stations located on the hanging wall and those located on the flat wall of the fault plane. The results show that for soft soil sites, crustal amplification and site amplification, as well as the geometrical position relationship between stations and faults have a certain impact on the simulation results. Based on the calculation of specific crustal amplification and site amplification in a specific region, the location relationship between stations and faults is included in the analysis, so that the future earthquake can be predicted more accurately, and an important reference can be provided for the disaster assessment in this region and the site selection of major projects.