Earthquakes and Structures

This paper describes the Dynamic Soil-Structure Interaction (SSI) effects on the underground structures. The finite element model for Nuclear Power Plant (NPP) and a tunnel was considered to analyze the effects of SSI. Dynamic analysis was carried out considering three transmitting boundary conditions. The effect of embedment for NPP founded on soft soil and seismic responses of a reinforced concrete building in proximity with an underground circular tunnel were studied. The lateral spacing of the circular tunnel from the center line of the building was varied while maintaining a constant depth below the ground level. The effect of embedment has been investigated and the result shows acceleration and displacement responses of the system are smaller with the infinite boundary as compared to viscous and kelvin boundary conditions. In tunnel analysis, the results shows maximum building response occurs when the tunnel is positioned directly below the centre line of the building.

Time–Frequency Analysis (TFA) techniques help to obtain the ideal time and frequency occurrence characteristics of earthquake motion confined in a seismic recorded signal. Time-histories from recording stations in Japan has been adopted in the present analysis, considering a large number of available data. The seismograms were transformed using Gabor transform, a Linear Joint TFA method, to assess their frequency content by generating their Gabor coefficients. Average Gabor coefficients were estimated for recorded seismograms within a magnitude range of 5.5–6.0 and hypocentral distances ranging from 0 to 50 km. The estimated average Gabor coefficients were used to synthesize a generalized acceleration-time history for the specific distance and magnitude ranges using Gabor Expansion, without compromising the frequency content of the waves. Additionally, it is demonstrated that the response spectra of the synthesized signal and the original signal match very well. These response spectra will be valuable for the nonlinear investigation of structures in this region.

As reported in literature number of buildings including five reinforced concrete and one steel framed buildings in the town of Onagawa and two buildings in the city of Miyako have failed by overturning during past 2011 Gear East Japan Tsunami. During Tsunami, exceedance of the instantaneous overturning moment due to buoyancy force and hydrodynamic force above the resisting moment due to self-weight of the building has been found to cause the overturning failure of building. In the present study, residual air space ratio (Cb), inundation depth (R) and height of the building (h) are identified as important parameters which influence the action of overturning. Residual air space ratio is defined in such a way that Cb equal to 1 means no water enters into building and Cb equal to 0 represents entire building is filled with water. The variation of overturning ratio of building w.r.t. the identified parameters are studied for four inundation depths, five heights of building and five air void ratios for the chosen 8mx8m plan of building. From the limited studies made, it is observed that when Cb is equal to 1 i.e. when no water enters the building, there is a maximum possibility for overturning. OR is found to increase linearly with Cb. Similarly, when the inundation depth is more, there is a maximum possibility of overturning of building, however the variation of OR with R is not linear. Based on the parametric study a model has been proposed for calculation of overturning ratio.

A semi-active control scheme for the vibration control of offshore steel jacket platforms is developed. Decentralized sliding mode control (SMC) algorithm is adopted for applying the control force to the structure with the help of Magneto-rheological (MR) damper for alleviating the earthquake-induced vibrations. SMC method is used due to its robustness against the parametric variations of the structures. The command voltage to the MR dampers is regulated through the clipped-optimal algorithm. A steel jacket platform, available in the literature, is modelled in MATLAB as an example to investigate the dynamic responses under the environmental loads. The earthquakes ground motions, scaled to 0.3 g PGA, considered in the present study are the El Centro (1940), Northridge (1994), San Fernando (1971) and Chichi (1999). Results indicate that sliding mode controller is able to reduce the responses of the offshore jacket platform significantly, subjected to different earthquake loads. It is observed that the positions and the number of MR dampers affect the performance of the controller to a great extend in the offshore jacket platforms. The control algorithm is stable against the variations and uncertainties in structural parameters.

The paper presents the performance of a square footing with structural skirts resting on sand and subjected to a lateral load through a numerical study. Strip footings are subjected to lateral forces induced by earthquake movements, wind loads. The lateral forces acting on the footings may be predominant in certain structures such as waterfront structure, earth retaining structure and transmitting power towers. There has been a lack of information about the performance of skirted footings subjected to lateral loads. The results of this study revealed that skirted foundations exhibit lateral capacity values that are near, but not exact, to those of block foundations of the same width and depth. The enhancement in the lateral capacity of skirted foundation increases with increasing skirt depth and shearing resistance of sand.

The increasing demand for minerals and their subsequent mining causes tailings to be produced in large amounts. Hence, tailings dams have increased in number as well as height to accommodate more storage capacity. Failure of these structures is dangerous with respect to toxic exposure, landslides, liquefaction, etc. In this study, the possible failure mechanisms of the Las Palmas tailings dam, which failed following the 2010 Maule, Chile earthquake, have been examined. Numerical simulation of the dam is carried out using the GeoStudio package to assess the condition of the dam during this seismic event and a pseudo-static analysis is carried out. The strong ground motion of the 2010 Maule, Chile earthquake recorded at three of the stations near the dam site was used as input since there is no record available at the tailings dam site. Slope stability analysis is performed to understand the possible failure mechanism. The Mohr–Coulomb failure criterion is used to define the material properties. Furthermore, the simulation results are compared with the final dam failure scenario.

Ventilation Stack structure of a typical Nuclear Power Plant (NPP) is analysed and designed for a design basis wind velocity corresponding to 1000 years return period. Subsequent to the Fukushima Event, as a part of safety assessment of NPP structures, assessment of structural integrity of stack structures has been taken up against extreme natural events i.e., beyond design basis wind loading in both along and across wind direction using non-linear. In the present work, detailed Soil-Structure-Interaction (SSI) analysis of typical stack structure of NPP modeled as 3D finite element along with soil has been carried out in Abaqus software under sustained plus along and across wind load corresponding to extreme wind condition. Mohr–coulomb plasticity model is used for continuum soil medium. Elasto-plastic behaviour of the raft-soil interface is simulated using Coulomb friction model available in Abaqus. Steel reinforcements have been introduced at relevant layers/sections of the stack. Transverse shear deformation in element formulation and geometric non-linearity due to large deformation has been considered during the analysis. Non-linear analysis with detailed material characterization and failure models for both concrete and reinforcement has been carried out for a realistic estimation of post-cracking margins and to understand the non-linear behaviour of the stack at various load steps. This paper presents the analysis methodology for safety assessment of wind sensitive stack structures against beyond design basis wind with due consideration to SSI effects. The analysis procedures, material models adopted for the analysis, etc. and the analysis results under extreme wind have been discussed in this paper. Based on the results of the nonlinear analysis safety margin with respect to beyond design basis wind speed has been established.

One of the proposed site in Northern part of India for twin unit 700MWe Nuclear Power Plant (NPP) (based on Indian PHWR) is founded on alluvial soil. Considering the founding medium of alluvial soil, the effect of the deformation of foundation, both total and differential, is required to be accounted for in the analysis/design of the structural system. Since the deformation of such founding media has direct bearing on the structural response, detailed analysis and design considering soil structure interaction effects for safety related structures supported on raft foundation system shall be carried out. In the analysis of raft foundation, the most important parameter is determination of exact contact pressure distribution underneath the raft, which is a complex function of rigidity of the superstructure, raft itself and the supporting soil. In this paper, detailed soil structure interaction analysis of typical safety related structure of NPP, modeled as 3D finite elements along with soil has been carried out using Abaqus software [1] for both vertical sustained and lateral loads (seismic loads with pseudo-static approach) using site-specific geotechnical parameters. Elasto-plastic behavior of the raft-soil interface is simulated using three parameter model i.e. elastic slip, maximum shear strength and frictional coefficient. Mohr–coulomb plasticity model is used for modeling continuum soil medium. This paper presents the methodology for estimation of stiffness's of raft foundation system under static condition and compares the same with conventional formulations for static springs as per Vesic's approach using modulus of subgrade reaction.

The M6.9 Sikkim earthquake of September 18, 2011, caused widespread damage in the state of Sikkim and adjoining areas and it exposed the seismic vulnerability of the multi-storied construction. Damage that occurred in and around Gangtok was disproportionately high to the observed intensity of shaking, primarily due to poor compliance with seismic codes, inferior quality of raw materials and shoddy workmanship. The main objective of the survey was to observe the effects of the 18th September earthquake and aftershocks on the build environment in terms of seismological, geotechnical and structural damages. From this Earthquake, it can be clearly seen that there is a need for seismic vulnerability assessment of buildings in and around Gangtok town. This paper presents the study of seismic vulnerability of buildings by rapid visual screening method and detailed vulnerability assessment method.

Multistory structures are the type of structures which are often subjected to seismic and wind effects simultaneously. The actual strength in the plan of multistory building is the regularity in planning, the type of materials, construction techniques used during constructions. The structure is mostly constructed to have adequate horizontal solidness to oppose the lateral loads caused by the seismic action and to control the parallel float of the structures. The steel supporting framework in strengthened solid edges is suitable for preventing horizontal powers. In this paper we are preparing and analysing a G + 20 with 3 m spacing of each floors. In this structure we will distinguish exposed casing and edges having X-type bracings or knee bracings at the corners. A three dimensional structure is taken, and 20 stories is taken with story tallness of 3 m. The bars and segments are intended to withstand dead and live load only. Seismic tremor loads are taken by bracings. The bracings are given just on the fringe sections. Analysis and design has been carried out using ETABS software, and the results are discussed.

Determination of natural frequency of free spanning pipeline is essential as it governs the allowable length and also fatigue life of the pipeline. From the literature survey, it is seen that a considerable amount of works have been studied to determine the effect of seabed soil on natural frequency of free span by the previous researchers. However, researchers have assumed that soil of the supports of free span is homogeneous. Well-used code DNVGL-RP-F105 (for free span analysis of offshore pipeline) also considers soil as homogeneous. But, recently, researchers state that non-homogeneity of soil has significant effects on dynamic soil stiffness. The objective of this paper is to determine the effect of non-homogeneity of soil on the natural frequency of free spanning pipeline. In this paper, a frequency analysis of the free spanning pipeline on homogeneous soil is carried out by Det Norske Veritas (DNV) guidelines and finite element modelling. A free spanning pipeline is analysed considering it on a non-homogeneous soil using soil mesh finite element modelling. The non-homogeneous soil model is designed with different layered soil combinations. Finally, it has been observed that finite element analysis software can be incorporated for pipe-soil interaction effectively. For layered soil profile, if the topmost soil stratum is thin, it has been found out that there is a significant variation in both inline and cross-flow natural frequencies compared to those of homogeneous soil having same topmost soil. Whereas if the topmost soil stratum is thick, it will not significantly affect in-line natural frequency, but cross-flow natural frequency tends to be same as that of homogeneous soil.

The construction of buildings in hilly areas faces several challenges, such as slope stability, suitable building configuration, etc. The capacity of buildings on the sloping ground reduces as it has to accommodate different length columns in a single storey. These buildings possess both vertical and horizontal irregularities. The current study is an effort to comprehend the effect of seismic forces on the buildings in hilly regions and suitable protection systems. A comparative study of a fixed base, base-isolated, cabled-supported, and base-isolated building with cable support is carried out. The base isolator is designed according to the UBC-97 guidelines. Seismic analysis results show that the base isolator building outperformed other protection systems. Moreover, the base-isolated building with cable support also performed equally sound as base-isolated building. The reaction forces in the cables reduced the stiffness requirement of the isolator. On the other hand, the cabled building did not show any effect on the building.

Tunnels are generally constructed in urban areas and metro cities to fulfill the rising need of space and passage due to urbanization. These infrastructure may get damaged because of earthquakes occurring in that particular area where tunnels are constructed. While designing tunnels in seismic prone zones, it is ensured that tunnels must withstand under both seismic and static loading. Recently occurred large magnitude earthquakes caused significant damages of the tunnels including the 1995 Kobe earthquake in Japan, the 1999 Chi-Chi earthquake in Taiwan and the 2008 Wenchuan earthquake in China. During damage evaluation, tunnel damages are broadly categorized into five classes based on damage index including no damage, minor damage, moderate damage, major damage and collapse. This paper gathers the materials of tunnels affected by the 1995 Kobe earthquake in Japan and the 1999 Chi-Chi earthquake in Taiwan, and the grades of damage are calculated based on seismic performance. Earthquake intensity, distance from fault, rock classification, tunnel length and overburden depth are considered as the tunnel damage factors while doing analysis. Considering these parameters, the formula for seismic damage evaluation for tunnel is deducted using the least square method. Further, this formula is modified after taking into account additional factors like construction time, seismic fortification strength and portal stability.

This work studies seismic vulnerability of an irregular block of Jorhat Engineering College old building, constructed in 1960 with predated code situated in Seismic Zone-V. Non-linear Static Pushover Analysis performed in SAP 2000® using modal load pattern with infill walls modelled as strut as per IS IS1893 (Part-I):2016. Sub-soil exploration is conducted and stiffness of the spring for the spring base structure is calculated as per ATC-40 guidelines. Detail plan of the structure showing different beams and column dimension is made using Autodesk AutoCAD®. The structure is simulated in SAP2000. Infill walls are designed as per IS1893 (Part-I):2016. Modeling of infill is done as Equivalent Strut, pin-jointed to the RC frame. Plastic hinges are assigned to the members as per FEMA-356, to identify the critical members which have exceeded their capacities. Non-linear analyses are performed for both the fixed and flexible base conditions. Inter-storey drift ratios and plastic hinge locations were selected as response parameters. From the analysis, it is observed that the pushover curves at the calculated target displacements are linear for both the cases, which indicate that the deformation of the structure is in elastic range.

In the present study, a base isolation system has been designed for an eight-story framed building. Non-linear time history analysis has been performed to compare the non-linear response of the base-isolated building and conventionally designed building. The computer program SAP 2000 has been used for modelling and analysis. The comparative response of the fixed base building and the base-isolated building has been studied in terms of base shear, roof displacement, and roof acceleration. In addition to this, a cost-effective approach for designing a base-isolated building has been proposed. In this approach, the total number of base isolators to be used in the building have been gradually decreased to optimize the cost. The base isolators have been redesigned for each case, and linear and non-linear performances have been checked to ensure that the performance of the building has not been compromised.

Vibrations in four buildings located at different positions along the Delhi Metro Rail Corporation (DMRC) network have been measured and reported. Vibrations developed due to the passage of metro trains through tunnels located at a depth up to 30 m from the ground level were measured on the considered buildings at different floor levels. To interpret the effect of vibrations on buildings, different vibration parameters, viz. Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV) and frequency content are obtained from the recorded vibrations. These parameters change with the location, depending on the dynamic characteristics of the soil profile at the site of measurement and the building. It is observed that the maximum amplitude of vibrations measured during this study is more than the threshold provided by standards of different countries and can cause vibration of rigid building components, annoying physical sensations in the human body, interference with activities such as sleep and conversation, rattling of window panes and loose objects and fear of damage to the building and its contents.

Ancient structures were constructed by considering only vertical static loads. The seismic response of ancient masonry structures depends on their material properties, the geometry of the structure, the types of connections between various structural components, the stiffness of the floors and the strength of the non-structural elements. The rich and diverse architectural traditions across India provide evidence of the structural efficiency and technological skill of Indian craftsmen and builders. Studying the structural behaviour of Indian heritage buildings has national importance. In this study, the seismic vulnerability of the Amritesvara temple was evaluated. Built in 1196 and is located 260.8 km from Bengaluru, India. This study involved a shake table test of the temple. Experiments were conducted at the Earthquake and Vibration Research Centre, Bengaluru. According to the size and payload capacity of the shaking table, a 1:3 scale model was adopted. The model was subjected to various peak ground accelerations from 0.05 to 0.1 g. The dynamic properties of the model were evaluated through the experiments. The experimental results were used for validating the numerical model, which was used to conduct further investigations on the prototype.

RC buildings constructed on hill slopes pose complex structural behaviour as compared to conventional buildings resting on a plain ground. The hill buildings come under the category of irregular buildings, which are asymmetric in elevation as well as plan at different floor levels, due to which the centre of gravity and stiffness at subsequent floor levels always vary and cause additional torsional moments in the buildings. Further, the length of the columns in hill buildings also varies pertaining to steep slopes, resulting in variation of lateral stiffness in all columns. Moreover, the base isolation systems have shown a profound effect to reduce the seismic vibrations in the buildings. Thus, in this study, the influence of a commonly used base isolation system, i.e. Laminated Lead Rubber Bearing (LLRB) on the seismic performance of two hill building configurations, viz. stepback and setback-stepback, was investigated. All the configurations have been modelled using a finite element software, and examined by Response Spectrum analysis and Non-linear Static Pushover analysis. The dynamic parameters obtained from the numerical study were discussed as variations in storey shear, base shear, time period, drift, maximum top storey displacement values and plastic hinge development pattern in the building structure. finally, the vulnerability and suitability of the different configurations against seismic excitations were compared.

To mitigate ever-growing traffic congestion in Dhaka city, the Government of Bangladesh is implementing the Mass Rapid Transit (MRT) project. The MRT Project consists of several metro rail routes in the city, some of these routes are elevated rail, while some are planned to be partly elevated and partly underground. Construction of MRT Line 6 consisting of elevated rail is in progress, while the second route (MRT Line 1) being planned for construction consists of some underground portions. Bangladesh, located near the plate boundaries of the Indian Plate colliding with the Eurasian Plate, possesses significant seismic hazard. According to the latest updated version of the Bangladesh National Building Code (BNBC-2020), Dhaka city has a seismic zone coefficient of 0.20 (maximum considered earthquake) for rock sites. For local soil conditions, ground motions may exceed 0.25 g. This paper considers a site near Kamalapur Railway station, the Railway Hub in Dhaka city, where MRT Line 1 will end. The seismic response of a typical cross-section of subway tunnel is analyzed using the finite element software PLAXIS 2D. Time history analysis under 2D plane strain conditions is conducted for various intensity levels of earthquake motion incorporating site effects.

A structure in high seismic regions must perform under large forces without failing; hence, in this scenario, inelastic energy dissipation plays an important role in resisting large forces mainly caused by an earthquake. A ductile structure can deform and dissipate energy during an earthquake because it keeps deforming without reaching ultimate failure or collapse. In this study, the ductility of mid-rise RC buildings was compared under high seismic zones for different aspect ratios. Investigations were performed by following the Indian standard code with respect to plan aspect ratios. Reinforced concrete buildings with 10, 20 and 30 stories were modelled using five different plan aspect ratios of 1:1, 1:2, 1:3, 1:4, 1:5 and 1:6 under two categories, viz., category 1 with different plan aspect ratio and category 2 with the same plan area. The buildings were analysed by employing response spectrum and non-linear static analysis to obtain the results using Etabs software.

Liquid storage tanks are the predominant structures and they have to be designed to withstand major earthquake loads. In the present study, an elevated intze water tank of capacity 700 m3 was considered and analyzed for seismic effects. Finite element modeling of the tank was made in ANSYS. A series of transient analyses was carried out for El Centro and Kobe earthquakes which are applied in the horizontal direction. The fluid inside the tank accelerates and causes additional hydrodynamic pressures on the tank. Past studies reveal that the convective hydrodynamic pressure is more than the impulsive hydrodynamic pressure. Time history plots were made to describe the sloshing phenomenon in the tank for various levels of the liquid. The sloshing displacements for the one-third level of the liquid were found to be maximum. The sloshing displacements in the horizontal direction are more than in the vertical direction.

RC frame structures resting on a hill slope exhibit diverse seismic responses in comparison with conventional buildings built on plain ground. Due to asymmetric structural configuration at different floor levels, the hill buildings attract additional lateral shear force and torsional moments in the structural members. Further, unreinforced masonry infills play a critical role in the energy dissipation during seismic excitements and are often neglected in the seismic analysis of buildings. Moreover, base isolation systems have also been shown to reduce the seismic vibrations in the buildings. Thus, in the present study, the effect of unreinforced masonry infill panels as well as a commonly used base isolation system, i.e. Laminated Lead Rubber Bearing (LLRB) on the seismic performance of two hill building configurations, viz. stepback and setback-stepback, was studied. All the configurations have been modelled using finite element software, and analysed by Response Spectrum and Non-linear Static Pushover method. The seismic parameters obtained from the numerical study were discussed in terms of base shear, fundamental time period, maximum top storey displacement and plastic hinge formation pattern in the building structure. Finally, the vulnerability and suitability of the different configurations against earthquake were compared in along and across slope directions.

Mass Rapid Transit (MRT) Line 1 is planned for the eastern part of Dhaka city connecting the capital’s International Airport Terminal at Kurmitola with the Main Train Station Terminal at Kamalapur. This line also has a second branch from Future Park to Purbachal. While a significant portion of the proposed MRT Line 1 will be above ground, three significant portions will be underground: (i) Khilkhet to Bhatara (ii) Bhatara to Bashundhara (iii) Mailbag to Kamalapur. Subway tunnel construction for metro rail involves many unique geotechnical design considerations such as the effects of fast-moving trains in an underground tunnel on adjacent property. The resulting vibrations can be the subject of legal complaints by owners of buildings in the immediate vicinity. The primary objective of this paper is to perform a numerical study to have an impression of the ground vibrations generated in the surrounding soils due to moving loads in an underground tunnel near the Kamalapur Railway Station. A numerical model is created using the finite element software PLAXIS 3D for moving load on rails in an embedded tunnel in an idealized soil profile. Numerical analysis is performed for a two-wagon train running on an underground tunnel at various depths.

The process of soil response influencing the motion of the structure and vice versa is termed as soil-structure interaction. Conventionally, SSI has been considered to pose beneficial effects on the seismic response of a structure because of causing the structure to be more flexible resulting in an increased natural period and enhanced effective damping ratio. These modifications suggest a reduction in base shear demand for a structure as compared to its fixed-base counterpart. This study presents analyses of four-storeyed ordinary RC framed structures assuming the base of the column as fixed and supported on stiff, medium and soft soil springs. The study also includes isolated rectangular concrete footing fixed at the base and supported on the same springs as used in the structure. The results are somewhat different than the assumption of fixed-base analyses being always conservative. The study also suggests appropriate modeling to capture maximum response in structural members.

The process of soil response influencing the motion of the structure and vice versa is termed as soil-structure interaction. Conventionally, SSI has been considered to pose beneficial effects on the seismic response of a structure because of causing the structure to be more flexible resulting in the increased natural period and enhanced effective damping ratio. These modifications suggest a reduction in base shear demand for a structure as compared to its fixed-base counterpart. This study presents the analyses of a four-storeyed load-bearing brick masonry building. It has been analyzed with the base of the walls as fixed and supported on stiff, medium and soft soil springs. The structure has also been analyzed considering stepped brick masonry strip footing fixed at the base and supported on the same springs as used in the structure. The results are somewhat different than the assumption of fixed-base analyses being always conservative. The study also suggests appropriate modeling to capture maximum response in structural members.

The process of soil response influencing the motion of the structure and vice-versa is termed as soil-structure interaction. Conventionally, SSI has been considered to pose beneficial effects on the seismic response of a structure because of causing the structure more flexible resulting in the increased natural period and enhanced effective damping ratio. These modifications suggest a reduction in base shear demand for a structure as compared to its fixed-base counterpart. This study presents analyses of a four-storeyed load-bearing structural walled building. It has been analyzed with the base of the walls as fixed and supported on stiff, medium and soft soil springs. The structure has also been analyzed considering stepped brick masonry strip footing fixed at base and supported on same springs as used in the structure. The results are somewhat different than the assumption of fixed-base analyses being always conservative. The study also suggests appropriate modeling to capture maximum response in structural members.

With the advancement in technology, urban transportation systems have been modernized with the construction of underground structures due to restricted movements and inadequate space. Many cities already have or plan to construct underground box structures for metros and subways. These structures may undergo severe damages caused by excessive deformation due to seismic shaking. Hence, it is necessary to have an accurate estimation of deformation and bending moment caused by the movement of the surrounding soil under seismic conditions. In the present investigation, an attempt has been made to carry out a parametric study for a typical box structure 9.6 m wide × 5.8 m high with varying soil parameters from loose to medium, medium to dense and very dense in different seismic zones. The results of the study reveal that about 16–26% of the variation in distortion and 8–12% of the variation in bending moment occur with different subsoil conditions (loose to medium, medium to dense and very dense) under the same seismic conditions. Once seismic conditions change from lower to higher seismic zone (zone-III to zone-IV), the deformation becomes almost double even for the same soil condition (loose to medium or medium to dense or very dense). The findings of the present study may be useful in the design of underground subways and metro box structures for practicing engineers.

Liquid storage tanks are usually located in nearshore or coastal regions with soil profiles containing thick layers of compressible soils. These storage tanks are usually of large diameter up to 90 m and carry high loads, and the tanks are often placed on heavy foundations such as piles. Piles supporting such tanks are to be designed for high lateral loads due to wind and earthquake, and any damage to storage tanks with highly inflammable liquids leads to disastrous conditions (Niigata and Alaska, 1964; 2011 Tohoku), etc. Performance of piles in liquefying ground under earthquake loading has been extensively studied; however, seismic behavior of piles in very soft clays has received relatively less attention, especially on their lateral capacity. The design of laterally loaded piles due to soil movement relies on several theoretical and numerical approaches. The subgrade reaction method (IS 2911 Part-1/Sect. 2: 2010) is most widely used for the design of laterally loaded piles in India and using this method, estimation of the magnitude of soil movement with reasonable confidence and accuracy is difficult. This paper discusses the analysis of lateral load on piles supporting storage tanks using the subgrade reaction method and load-deflection curves (p–y). The scope of this paper is limited to analysis using these methods. The results of the study indicate that the maximum bending moment in the piles that occurred during the earthquake using 3D FEM analysis is comparable to their moment capacities.

This study is intended to check the performance of linear and nonlinear theories to determine the dynamic characteristics of the pile supported machine foundations. Forced vibration tests are performed in the field on a 3-pile group having pile length of 3 m and outer diameter of 0.114 m subjected to axial harmonic loading. The dynamic tests are performed for four different eccentric moments under a static load of 12 kN. The frequency-amplitude responses are measured for each eccentric moment. Theoretical study is also performed using both the linear and nonlinear solutions which are based on continuum approach method. The theoretically predicted frequency-amplitude responses are compared with the dynamic field test results for all the eccentric moments. It is found that the predicted responses of the linear solution indicate lower values of the resonant amplitude and much higher values of the resonant frequency as compared to the test results. In the case of nonlinear solution, the predicted dynamic response curves are reasonably well matched with the tests results. Such agreement with the nonlinear analysis results are achieved by considering precise values of boundary zone parameters and soil-pile separation lengths.

Pile foundations are the most vulnerable components of the entire structure and are prone to failure due to earthquake loading. Thus it is mandatory for proper seismic analyses to be conducted with the incorporation of all the necessary influencing factors to ensure no failure occurs to the pile foundation. Even though dynamic analysis has been the conventional seismic analysis method, a new nonlinear static analysis known as pushover analysis is seen to realistically predict earthquake response of the pile. This calls for proper research to be conducted to check if static pushover analysis can be used as an alternative to dynamic analysis for seismic analysis of structures to save time and ease on the complexity of dynamic analysis. In this research work, single piles of different diameter have been taken into consideration which has been embedded in stratified soil containing layers of different soil types. Dynamic analysis and static pushover analysis have been conducted for each case to compare the results of both the analyses. The Finite Element modeling as well as the analyses has been conducted in the user friendly interface of OpenSees known as OpenSees PL. From the results obtained, it is seen that pushover analysis can estimate the maximum bending moment witnessed by the pile while taking into account the effects of surrounding soil condition on it due to earthquake loading. Similar results of maximum bending moment have been obtained for both the analyses.s

Piles should possess the structural integrity to carry the design load and transfer to the soil/rock below. As per Indian standard IS 14893:2001, in general following defects are observed in the pile, which may lead to catastrophic failure. (a) Pile shaft necking, (b) Discontinuity of concrete, (c) Intrusion of foreign matter, (d) Improper toe formation due to contamination of concrete at the base with soil particles, (e) Washing of concrete due to high water current, and (f) Poor quality control with improper construction methods. NDT-based low strain pile integrity testing can be effectively used for evaluation of quality and acceptance of pile foundations. Low strain pile integrity test is based on pulse echo method. Pile integrity tester gives the velocity plot versus time. The plot is observed for the reflections, which indicate the change in the property of wave passing medium. The reflections may be due to soil resistance (stiffness) effects, cross-sectional changes, and soil property changes. In this study, bored cast-in-situ piles are evaluated for its integrity.

Caisson foundations are widely used as the foundation system of bridges, transmission towers, and scour vulnerable structures for transmitting high structural load to the soil beneath. In seismically active regions having potentially liquefiable soils, one important consideration is the effect of liquefaction induced lateral spreading on deep foundations. During this phenomenon, caissons are subjected to seismic forces and simultaneously it loses the lateral support of surrounding soil due to liquefaction and an extra kinematic loading acts because of the flow of the liquefied soil. In this present study, a caisson embedded in liquefiable soil in gentle sloppy ground has been modeled in finite element-based software package PLAXIS 3D for capturing the response of the caisson in laterally spreading ground. The proposed numerical model has been found to compare well with the available centrifuge test results. Further parametric study has also been performed for lateral response of the caissons in liquefying soil for different ground slopes, embedment depth to caisson width ratio, frequency and amplitude of the dynamic motion. Behavior of the rigid caisson foundations subjected to liquefaction induced kinematic loading have been thoroughly discussed in the present study to assist the seismic design of caissons embedded in potentially liquefiable soil.

Dealing with soft and loose soils is always a challenge to the practicing Civil Engineers. Foundations to support heavy loads on weak deposits in high seismic zones attracts more attention in design of foundations of structures. Seismic wave propagation and its impact on foundation elements induces additional bending moments and shear forces. This paper deals with analysis and design of foundations adopted for a 41 m diameter storage tank executed in the East Coast of India. The efficacy of lateral pile capacity has been assessed using PLAXIS 3D dynamic module. The performance of foundation system under earthquake loading was extensively studied and covered in this paper. A full geotechnical seismic site response analysis was conducted with a full mesh of soil layers and piles. Appropriate site-specific seismic acceleration history with time was imposed on the bedrock. Sloshing forces for both full and empty tank conditions were considered in the analysis. The 3D FEM seismic analysis of the pile movement and forces during and after earthquake were checked for structural adequacy of the piles against the M–N envelope.

Mechanically Stabilized Earth (MSE) or Reinforced Soil structures are composite structures consisting of alternating layers of compacted backfill and soil reinforcement elements that are fixed to a facing. The stability of MSE structures is derived from the interaction between the backfill and soil reinforcements, involving friction and tension. The facing is relatively thin and is intended to perform the primary function of preventing erosion of the structural backfill. The significant relative cost saving that can be realized when this system is used compared to traditional RCC retaining structures, combined with ease of construction has resulted in widespread adoption of this technology in India and around the world. MSE structures have been found to perform satisfactorily when subjected to seismic loading conditions provided that recommended practices are adopted during their construction. This paper presents case studies of superior performance of MSE structures when subjected to seismic loading both during and after completion of construction including a case study on the behaviour of MSE structures founded on soft silt deposit in seismically active hilly terrain in the stretch from Quazigund to Baramulla where an earthquake measuring 5.4 on the Richter scale occurred during construction of the structure.