Generally, when structures are subjected to an earthquake, the response gets amplified from ground to higher floor levels. This is a function of ground motion frequency–amplitude characteristics, frequency and damping characteristics of structure.To make the response of structure independent of its frequency and damping, seismic base isolation techniques are adopted. It makes the structure isolated from ground motion and results in low seismic responses such accelerations and forces. However, there will be large displacement with respect to the ground. This concept will also help to reduce seismic demand on floor mounted equipment and piping systems and eventually helps the utility to standardize the seismic design of structure and floor mounted equipment and systems. In addition, the data generated will be useful for the designer to validate the design. Tests were performed on coupled structure, equipment (vessel) and piping systems. This paper presents details of experiments carried out, observations made on structure, vessel and piping responses.

Structures get distressed or health of the structures gets deteriorated with the time. Also demand on the structures may increase with the time. Good examples to mention are moving loads on the bridges, seismic loads on the structure etc. To take care of these aspects, structures have to be revisited frequently and assessed for its strength and serviceability status. If these requirements are not met, the structure needs to be rehabilitated to meet the initial design intent and retrofitted if the load demand increases. Conventionally after proper repair, steel jacketing, concrete jacketing, bracing etc. are adopted to rehabilitate and retrofit the structure. However, recently Fiber Reinforced Polymers (FRP) is taking the lead materials for rehabilitation and retrofitting of structures especially Reinforced Concrete structures. Along with fundamental procedure of FRP rehabilitation and retrofitting, details of testing as built and rehabilitated/ retrofitted structure are discussed in this paper. Importance of key parameters such as setting time, anchoring, workmanship etc. to achieve the target strength and ductility are also discussed. Brief explanation on modelling and analysis of tested as built and retrofitted structure is provided.

Bridge is the structure that is seen several dynamic loads unlike other structures. Ministry of Road Transport and Highways (MORTH) said that 10,876 people were killed due to potholes in the year 2015, which denotes the lack of proper maintenance of road pavements. When a vehicle moves along these surface irregularities, it not only causes uncomfortable to the passenger but also causes dynamic loads on the components like deck slab, bearings. Since the road surface irregularities like unevenness, potholes, etc., are unavoidable, we should understand the dynamic effect on the structure due to such undulations. IRC-6, standard to find the loads and load combinations on the road bridges, doesn’t talk about the dynamic load induced by surface irregularities with respect to the different classes of road profile as per ISO: 8608. On the other hand, IRC-6 only gives provisions of static analysis in the case of the vertical dynamic effect produced by moving vehicles. This study aims to generate road profiles having different degrees of unevenness as per ISO: 8608 and to propose a conservative method to find the vertical dynamic load on the bridge deck and its vertical response. A bridge deck is modeled as a Single Degree of Freedom system and the vertical dynamic responses of the bridge deck are found by Newmark’s Beta Linear Acceleration Method. It is found that the dynamic response, almost doubles when road profile quality changes from one class to the very next class.

In this study, soils from two locations namely Rudrapur and Khatima from Uttarakhand, India adjacent to Himalayan Frontal Thrust (HFT) have been considered for response analysis. The in-situ and dynamic soil properties determined from undisturbed and disturbed soil samples are taken for earthquake response analysis. Three moderate magnitude earthquakes of Himalayan origin have been used to study the variation of PGA, PGD, and excess pore water pressure of the thick alluvial soil deposits. Present study suggests that an earthquake of magnitude of Mw 4.7 to 6.5 will liquefy soils from Uttarakhand Plain in Himalayan region at a shallow depth.

The present work investigates the postbuckling, and postbuckled vibration behaviour of initially imperfect trapezoidal sandwich plates with functionally graded carbon nanotube reinforced composite (FG-CNTRC) face sheets and FG porous metal foam core under the influence of non-uniform edge compression. The plate's kinematic assumptions are based on a refined higher order theory and the strain-displacement relations include von Karman assumptions for geometrical nonlinearity. The weak form of governing equations derived using Hamilton's principle is transformed into a discretized form of algebraic equations using the element free Galerkin (EFG) method in conjunction with moving kriging (MK) interpolation functions. The pre-buckling stresses are determined using static analysis to evaluate accurate critical buckling loads. Modified Riks technique is used to trace nonlinear equilibrium paths. Parametric studies include the effect of CNT distribution in face sheets, porosity distribution in the core layer and edge loading conditions on the nonlinear stability and vibration behaviour of sandwich plates. New results on trapezoidal sandwich plates with initial imperfections, hitherto not found in the literature, are presented for the first time, which can be used as benchmark solutions for further research.

The performances of a piled raft system in terms of serviceability and load-carrying capacity have been reviewed. The settlement behaviour of a square-piled raft in a layered soil is investigated using numerical analysis. The emphasis is given on quantifying the reduction of the average and the differential settlements of the raft in layered soil. A 3D finite element analysis using a commercial software called PLAXIS 3D (Version 2) is performed for various pile positions, pile numbers and pile lengths under the raft subjected to a uniform vertical loading. The settlement aspects for an efficient design of a piled raft subjected to vertical loadings have been addressed. It is found that the required piled group-raft area ratio (Bg/Br) for minimising the differential settlement of a raft in a layered soil should be within a range of 0.4 to 0.6.

In this paper, five storey RC (Reinforced Concrete) building is retrofitted using friction damper and steel bracing methods to achieve a target seismic performance level in terms of inter-storey drift and plastic hinge rotations. Firstly, a static pushover analysis is performed to get the required damping value for the target performance limit. Then a friction damper is designed for this required damping value. To study the effectiveness of friction damper, a time history analysis of building is performed using scaled time history compatible with IS 1893 response spectrum (zone V, soil type 1) in SAP2000 v20. To bring inter-storey drift to the permissible limit, steel bracing along with friction dampers are used. Further response spectrum analysis is carried out to compare the results of storey displacement, drift with that of time history results. So, the combination of friction damper and steel bracing is found to be effective in retrofitting five storey RC buildings.

Bridge is the structure that is expected several normal and postulated dynamic loads. Vehicle collision with the bridge pier is one of the postulated dynamic loads considered in the design provisions. The Indian code IRC-6 consider the vehicle collision load as equivalent static load, whereas European standards EN 1991-1-7 gives provisions for both static and dynamic analysis. However the both codes don’t give a simplified mathematical model for the dynamic analysis. The Finite element analysis (FEA) is the popular method used for analysis of pier subjected to the collision load. However, the finite element analysis requires a combination of vehicle and concrete structure modeling which is a tedious process. This analytical study includes calculation of dynamic load on the bridge pier as per Eurocode EN 1991-1-7 and its dynamic responses, due to the direct vehicle collision with pier. In this article a simplified model the pier is discussed. Since majority of mass located at the top of the pier and the collision load is acting at bottom part of the pier, pier is modelled as a Two Degrees of Freedom System and the Lumped mass approach is adopted. The dynamic responses of the pier are calculated by Newmark’s Beta Linear Acceleration Method. The dynamic analysis of vehicle collision load also gives the load transferred to the superstructure and its components like bearings. Comparison study of the effect of the impact of the vehicle having 30 tonnes mass and 300 kN/m stiffness with speed 130, 90, 70 and 50 km/h as per EN 1991-1-7: 2006, shows that there is no significant difference in response of the pier for hard impact when vehicle speed varies from 50 to 130 km/h. This may be due to the peak intensities of dynamic actions affect the structure over such a short time in which the structure cannot properly respond to them. However, acceleration response is significantly high when the velocity of impact increases. And vehicle impact load never fails to induce a considerable amount of base shear in the column which is more than the equivalent static loading suggested IRC-6.

The MACE telescope has recently been commissioned at Hanle, Ladakh, India. It had its first light in April 2021 with a successful detection of very high energy gamma-ray photons from the standard candle Crab Nebula. Equipped with a large light collector of 21 m diameter and situated at an alti-tude of similar to 4.3 km amsl, the MACE telescope is expected to explore the mysteries of the non-thermal Universe in the energy range above 20 GeV with very high sensitivity. It can also play an important role in carrying out multi-messenger astronomy in India.

For simulating any type of dynamic soil-structure interaction, a site response analysis is a necessary precursor. A 2-D equivalent linear model and a nonlinear model using hyperbolic tangent formulation are developed in-house for the purpose. Both the numerical models are validated by the experimental results on cohesionless soil conducted within a large-scale laminar box at Buffalo State University, New York and an open-source code DEEPSOIL. The non-linear soil behaviour of the laminar box is modelled by obtaining the normalised stiffness and damping ratio from torsional resonant column test. The validated program is used for prediction of the response behaviour at two sites in Mumbai. The ground response by equivalent linear and nonlinear method shows amplification factors of 2.95 for Site-1 and 3.55 for Site-2, 2.88 for Site-1 and 2.84 for Site-2, respectively. It is observed that the effects of the loading-unloading rules as well as the selection of the small strain damping values have a significant influence on the high-frequency content of the site-specific spectrum. The generated spectrum obtained from the nonlinear analysis may be used for any dynamic analysis at these locations with due regards to the values of small strain damping which is recommended to be around 1.0-1.5% for these sites.

Short structures when they are designed using base isolation, dynamic wind effects may be more, and it may govern the design. This issue is taken care to some extent using Lead plug bearings. This puts the limits on effective seismic performance only for design basis or beyond. At lower seismic excitation levels, it may not be that effective. In view of this a suitable passive control system using the knowledge of isolators and absorbers is developed and analysed. Five storey shear building models with fixed base, base isolated separately supported on laminated rubber bearing (LRB), lead plug bearing (LPB) and isolated with LRB and install with tuned mass damper (TMD) are developed. These structures are numerically analysed considering six Indian earthquakes and dynamic wind load. TMD used in LRB supported building is provided in LPB supported building and responses of building models also observed under wind load which is more than design basis. Results of all cases are compared. Combined passive isolation along with absorber found suitable for multi-hazards like earthquakes where peak displacement increases by 0.76 times to 38 times, peak acceleration decreases by 73% to 99%, maximum inter-storey drift decreases by 71% to 99% when comparing with fixed base structure and for wind, values of peak displacement, peak acceleration, maximum inter-storey drift decreases by 45%, 46%, 44% when comparing with LRB provided structure.

The present paper discusses the study of longitudinal vibrations in turbomachines coupled with skewed slotted bar cage induction motors and which are of the typical configurations in refinery industries. Based on vibration data, the severe longitudinal vibrations in tilting pad thrust bearing assembly and its failure mechanism during start up transient and steady-state operations has been observed. The excitation sources for these longitudinal vibrations originates from asymmetric air gaps in cage induction motors. Hereby, the study of longitudinal vibrations in turbomachines with thrust bearing is found to be necessary. A simplified Single degree freedom (SDOF) analytical model is proposed to estimate the peak response based on tuned variable stiffness method. Uniform air gap with rotor skew causes fixed thrust and is proportion to square of the load current. Static eccentricity across the rotor motor air gap causes variations in gap length and intern creates the torque fluctuations. This value is proportional to variance in square of the load current. In the proposed model evaluates the cascade effect of preloaded thrust due to rotor motor skewness and followed by compressor thrust due to differential pressure across the impeller in the form of the variable stiffness. This model has advantage in analysing the coupled motor and turbomachinery system response in longitudinal direction in a simple manner. The longitudinal vibrations estimate at thrust bearing and compared with experimental vibration data obtained from the field machinery. There is a good convergence between results of the analytical model and experimental field vibration data.

Experimental investigations on soil samples collected from the sites of Baraut, Noida and Mandi in North India have been performed to study the static and cyclic behavior of soil. Liquefaction potential of the sites near Himalayan range is also carried out. The SPT and downhole seismic tests have been performed for the estimation of static and dynamic properties of soil. Strain-controlled cyclic triaxial tests are also carried out on soil samples collected from the borehole at various depths up to 30 m for the evaluation of dynamic soil properties. The study examined the effects of parameters such as cyclic shear strain, loading frequency and overburden pressure on the cyclic behavior of the soil. One- and two-dimensional dynamic response analysis has been performed on three sites. The initiation of initial liquefaction ranged from 202 to 752 cycles for the Baraut site, 212 to 722 cycles for the Noida site, and 121 to 617 cycles for the Mandi sites. The final design response spectra of the sites are obtained from 1D ground response analysis. The results from the response analysis have been compared with the reported results. The soils from the present study areas are prone to liquefaction at 10 m to 15 m from the ground surface.

In the present paper, the site-specific response spectra at bedrock level are generated by deterministic seismic hazard analysis and soil amplification study for Kolkata (India) is performed. The site-specific bedrock spectra are obtained by enveloping 10 response spectra corresponding to 10 attenuation relationships with pga 0.104 g. Eighteen seismic downhole test data upto 50 m depth are collected from various sites in Kolkata, along with the SPT-N value profile. An empirical relationship between shear wave velocity and SPT-N value is proposed considering nonlinear power law for soft soil. The results of this study can be used for site response study of Kolkata. The average of Kolkata soil varies from 146 to 295 m/sec. As per NEHRP classification, the sites are classified as Class D and E. Nonlinear soil amplification study is conducted in all borehole locations and uncertainty of soil parameters, like shear wave velocity with plasticity of soil, are considered. A total of 1170 soil profiles are analyzed, and site-specific response spectrum is proposed. A maximum surface PGA of 0.18 g is obtained corresponding to 3.8 times amplification in peak spectrum. The proposed acceleration time history and the response spectra may be used for design and safety evaluation of infrastructures in Kolkata.

Structures which resist the normal as well as accidental loads due to natural hazards or manmade hazards have major role on risk. Risk may be synonym of loss of life or economy. In this script, qualitatively, it is referred as low risk and high risk and is a function of hazard levels and structural vulnerability and exposure time. In this paper, structures are referred to civil engineering buildings, equipment and piping systems. Every structural system will contribute to the risk. The risk levels are function of type of structural systems such as residential structures, office buildings, Industrial structures and lifeline structures. The risk level in industrial structures handling poisonous gases and liquids is high. Lifelines such as transport related structures, hospitals, water supply piping systems, evacuation centers including schools have to be treated exclusively/specially since these will contribute to the risk during and also after hazards especially natural one. For brevity, qualitative description is made on hazards and risk reduction targeting clear vision.

Spent fuels from the nuclear power reactors (NPRs) are stored in water pools, which are provided with thick RCC walls, lined with SS plates. Seismic behavior of these submerged freestanding spent fuel trays in spent fuel storage water pool (SFSWP) is highly nonlinear due to sliding, impact of trays stack and hydrodynamic effect of sloshing water. Earlier, only uncoupled or simplified methods were implemented to consider the hydrodynamic effect of water on submerged trays stack system. Hence, numerical model accounting gap, contact, friction and sliding between trays and bottom surface accounting coupled with hydrodynamic effect on the trays is developed and validated with shake table test results. The water mass is simulated using Navier–Stokes equation. The numerical model of the two systems, that is freestanding trays stack and contained water mass are solved simultaneously using coupled Arbitrary Lagrangian–Eulerian (ALE) method to resolve high mesh deformation issues which can lead to non-convergence in the solution. Safe Shutdown Earthquake (SSE) level of site-specific design seismic ground response spectra (DGRS) of 0.2 g Peak Ground Acceleration (PGA) with compatible time history is generated and considered for the analysis. Response parameters such as convective and impulsive frequency, mode shape and slosh displacements of the system obtained from the coupled numerical analysis are compared with the shake table experiment results and are found in very close agreement. The convective frequency of sloshing water is around 0.53 Hz. No out-phase motion of freestanding trays stack system is observed in the shake table experiment and analysis.

Numerical optimization techniques are used widely for different engineering fields. But there are limited applications of this method in geotechnical engineering. However in this study, topology optimization of pile foundation for different site conditions and loading conditions is obtained through a finite element (FE) analysis study. The suitable topology of piles in foundation system offering minimum internal energy, i.e. maximum stiffness for a given fraction of material is studied. The study is also enhanced to the piles which are located in the soils prone to liquefaction. In the present study, the design methodology for cost optimization of construction of a pile group with a raft foundation is also presented through a case study. In the optimization algorithm, the raft dimensions, no of piles, pile diameter, pile length are taken as the design variables.

Pile foundation is considered as a suitable and best foundation system at the site with the top stratum of soils possessing comparatively lower bearing capacity with respect to intended loads. It is also recommended at the site where soils possess susceptibly liquefaction potential (liquefaction prone site). In the present paper, it is studied various challenges encountered during the design and construction of pile foundations in non-liquefiable and liquefiable soils. It is also presented various suitable, appropriate, feasible and technically acceptable solutions adopted to overcome the same. In the present work, it is also investigated various suitable methodologies adopted for the construction of pile foundations considering site condition and size of projects. It is also briefed the engineering measures adopted at liquefaction prone site for pile foundation, ground improvements and liquefaction mitigation techniques. Various codes and their guidelines for construction, testing of pile foundation also briefed. It is observed, evaluation of various soil properties from the geotechnical investigation, evaluation of liquefaction potential of soil is very essential before selecting the appropriate pile foundation system and design the same in non-liquefiable and liquefiable soil. Suitable construction methodology also very essential to accomplish the execution of pile foundation safely, meeting desired quality and within the required time frame.

The present work describes the application of a numerical technique to predict fatigue-ratcheting failure level for a typical six-inch carbon steel piping system. The failure prediction is done by choosing limits on ratcheting and fatigue usage factor. Strain accumulation in the system is predicted using the numerical method. In this method, ratcheting in the piping loop is evaluated by carrying out response spectrum analysis at system level using the envelope characteristics at component level. Fatigue usage factors are evaluated using alternating stress along with Miner’s rule. These estimated levels are compared with excitation levels for static collapse evaluated from closed-form equations from literature.