Seismic Requalification Research Articles

Integrated Underground Analyses as a Key for Seasonal Heat Storage and Smart Urban Areas

The design and performance of a shallow geothermal system is influenced by the geological and hydrogeological context, environmental conditions and thermal demand loads. In order to preserve the natural thermal resource, it is crucial to have a balance between the supply and the demand for the renewable energy. In this context, this article presents a case study where an innovative system is created for the storage of seasonal solar thermal energy underground, exploiting geotechnical micropiles technology. The new geoprobes system (energy micropile; EmP) consists of the installation of coaxial geothermal probes within existing micropiles realized for the seismic requalification of buildings. The underground geothermal system has been realized, starting from the basement of an existing holiday home Condominium, and was installed in dry subsoil, 20 m-deep below the parking floor. The building consists of 140 apartments, with a total area of 5553 m2, and is located at an altitude of about 1490 m above sea level. Within the framework of a circular economy, energy saving and the use of renewable sources, the design of the geothermal system was based on geological, hydrogeological and thermophysical analytical studies, in situ measurements (e.g., Lefranc and Lugeon test during drilling; Rock Quality Designation index; thermal response tests; acquisition of temperature data along the borehole), numerical modelling and long-term simulations. Due to the strong energy imbalance of the demand from the building (heating only), and in order to optimize the underground annual balance, both solar thermal storage and geothermal heat extraction/injection to/from a field of 380 EmPs, with a relative distance varying from 1 to 2 m, were adopted. The integrated solution, resulting from this investigation, allowed us to overcome the standard barriers of similar geological settings, such as the lack of groundwater for shallow geothermal energy exploitation, the lack of space for borehole heat exchanger drilling, the waste of solar heat during the warm season, etc., and it can pave the way for similar renewable and low carbon emission hybrid applications as well as contribute to the creation of smart buildings/urban areas.

Response of Piping System with Semi-active Magnetorheological Damper under Tri-directional Seismic Excitation

ABSTRACT Seismic loads on piping system due to earthquakes can cause excessive vibrations, which can lead to serious instability resulting in damage or complete failure of piping system. Vibrations in the piping system can be reduced using passive control, active control, semiactive control and hybrid control. In this paper, semi-active magnetorheological (MR) dampers have been studied to mitigate seismic response and vibration control in piping system used in the process industries, fossil and fissile fuel power plant. The performance of MR dampers using various control algorithms is explored. A study is also conducted on the performance of control due to variation in the command voltage of MR dampers. The effectiveness of the MR dampers in terms of the reduction in responses, namely, displacements, accelerations and base shear of the piping system are compared with uncontrolled and passive controlled responses. This study is carried out under four artificial earthquake motions with increasing amplitudes in all the three directions of motion. The analytical results demonstrate that the MR dampers under particular optimum parameters are very effective and practically implementable for the seismic response mitigation, vibration control and seismic requalification of piping system.

Scenario based seismic re-qualification of caisson supported major bridges – A case study of Saraighat Bridge

Many major river bridges were constructed in highly active seismic areas of India much before the seismic code development. Bridges are lifelines infrastructure and as a result, it is necessary to requalify/reasses these structures in the light of the new and improved understanding of seismic resistant design philosophies. The aim of the paper is to develop a simplified methodology to carry out scenario based seismic requalification of major river bridges supported on caisson foundations (also known as Well Foundation). An example problem of Saraighat Bridge located in highly active Himalayan seismic zone is considered to demonstrate the application of the methodology. Field investigation and advanced laboratory tests on soil samples from the bridge site were carried out. The test results reveal that the soil is susceptible to liquefaction and as a result, soil structure interaction analyses are carried out. It is shown that good performance of these type of bridges depend on the displacement response of the pier head so as not to cause unseating of the decks. It is concluded, owing to the large stiffness of the foundations, bridges supported on caisson foundations may not be adversely affected by liquefaction induced effects.

Comparative performance of passive devices for piping system under seismic excitation

Among several passive control devices, X-plate damper, viscous damper, visco-elastic damper, tuned mass damper and multiple tuned mass dampers are popular and used to mitigate the seismic response in the 3-D piping system. In the present paper detailed studies are made to see the effectiveness of the dampers when used in 3-D piping system subjected to artificial earthquake with increasing amplitudes. The analytical results obtained using Wen's model are compared with the corresponding experimental results available which indicated a good match with the proposed analytical procedure for the X-plate dampers. It is observed that there is significant reduction in the seismic response of interest like relative displacement, acceleration and the support reaction of the piping system with passive devices. In general, the passive devices under particular optimum parameters such as stiffness and damping are very effective and practically implementable for the seismic response mitigation, vibration control and seismic requalification of piping system.

Seismic Requalification of Geotechnical Structures

The most recent major earthquakes demonstrated the need for seismic requalification of important structures built earlier (such as nuclear power plants, hospitals, important buildings and bridges), in the light of new, revised and better understanding of seismic effects on the built environment. The extent of earthquake damage to structures depends not only on the details of the structure but also on the quality of the ground on which the structure is built. It is well recognized that geotechnical aspects of the ground can be a major contributor to seismic damages and as a result good and solid understanding of seismic soil–structure interaction is very important. “Geotechnical Structures” covers a wide range of topics and it is difficult to do justice to all the topics in one journal issue. This issue therefore focuses on pile foundations and earth retaining structures as they are invariably used for supporting many structures and are very common in any major infrastructural development. This article discusses about seismic requalification and its various stages. The special issue contains nine papers covering various aspects of seismic requalification: Hazard Assessment (three papers), Methods of Analysis (four papers) and Methods of Strengthening and Retrofitting (two papers). A brief example of seismic requalification for pile-foundation is also presented.

Seismic Requalification of Pile Foundations in Liquefiable Soils

Pile-supported structures founded on liquefiable soils continue to collapse during earthquakes despite being designed with required factors of safety against bending due to lateral loads and axial capacity (shaft resistance and end-bearing). Recent research identified a few weaknesses in the conventional design approach: (a) when soil liquefies it loses much of its stiffness and strength, so the piles now act as long slender columns, and can simply buckle (buckling instability) under the combined action of axial load and inevitable imperfections (e.g. out-of-line straightness, lateral perturbation loads due to inertia and/or soil flow). In contrast, most codes recommend that piles be designed as laterally loaded beams; (b) Natural frequency of pile supported structures may decrease considerably owing to the loss of lateral support offered by the soil to the pile and the damping ratio of structure may increase to values in excess of 20 %. These changes in dynamic properties can have important design consequences. The immediate need is not only to rewrite the design code to incorporate these effects, particularly buckling instability but also to requalify and, if necessary, strengthen the existing important piled foundations in liquefiable soils. This paper aims to provide a methodology for carrying out requalification studies. A practical example is taken to show the application of the methodology.

Health Assessment of Existing Nuclear Fuel Cycle Facility: A Case Study

Abstract Before taking up seismic re-qualification and retrofitting of an existing concrete structure, if required, assessment of the current strength of structure is an important aspect. Health assessment ascertains variation in properties of concrete, particularly strength, attained over the initial development phase when subjected to service exposure for a long time. It further tries to assess the deterioration of the reinforcing steel and degradation of the concrete through the various mechanisms over time. Health assessment of a reinforced concrete (RC) Nuclear Fuel Cycle Facility was taken up through Non-destructive (NDT) and Partially-destructive testing (PDT) in the recent past. The RCC framed-cum-shear wall structure was of dimensions 98 m by 84 m and had been constructed around 15 years back. From the results the various material properties of concrete like compressive strength and density were determined. The health of the concrete was found to be in satisfactory condition with chloride and sulphate content within permissible limits specified by International standards. The paper provides an overview of the different tests performed for health assessment and further provides a brief account of the results and inferences therefrom.

Response of piping system with semi-active variable stiffness damper under tri-directional seismic excitation

Seismic loads on piping system due to earthquakes can cause excessive vibrations, which can lead to serious instability resulting in damage or complete failure. In this paper, semi-active variable stiffness dampers (SAVSDs) have been studied to mitigate seismic response and vibration control of piping system used in the process industries, fossil and fissile fuel power plant. The SAVSD changes its stiffness depending upon the piping response and accordingly adds the control forces in the piping system. A study is conducted on the performance of SAVSD due to variation in device stiffness ratios in the switching control law and modified switching control law, which plays an important role in the present control algorithm of the damper. The effectiveness of the SAVSD in terms of reduction in the responses, namely, displacements, accelerations and base shear of the piping system is investigated by comparing uncontrolled responses under four different artificial earthquake motions with increasing amplitudes. The analytical results demonstrate that the SAVSDs under particular optimum parameters are very effective and practically implementable for the seismic response mitigation, vibration control and seismic requalification of piping systems.

Seismic Requalification of an Underground RCC Duct

The present paper deals with the reevaluation of design stresses and assessment of safety margins available for an underground reinforced cement concrete (RCC) duct. For stress analysis, a two-dimensional mathematical model has been adopted to appropriately represent the structure. The structure has been analyzed for both static and seismic loads. The seismic analysis has been carried out for site-specific response spectra. The design checks have been performed using available international standards and, accordingly, the safety margins have been evaluated. The structure has been found to possess sufficient safety margins under all the postulated design loadings. The seismic reassessment methodology conforms to the available international standards.