An earthquake is a rapid shaking of the earth caused by sudden release of energy stored in the earth’s crust. The Indian subcontinent has experienced a number of devastating earthquakes in the last 3 decades, repeatedly reminding us about the high level of seismic hazard and risk prevailing in the country. Earthquakes leave behind a trail of destruction and hu-man misery. The devastating earthquakes of 2001 in Gujarat, 2008 in Jammu and Kashmir, 2011 in Japan, and 2015 in Nepal are grim reminders of the nature’s sudden fury and a warning that the next disaster will strike as soon as we have forgotten the last one.
The Earthquake Risk In Delhi / Ncr
The National Capital Region (NCR) of Delhi lies approximately 250 kilometers from the Himalayas where earthquakes originate. Several earthquakes of Magnitude 5.5 to 6.7 on the Richter scale are known to have occurred in or close to Delhi.
Experts warn that an earthquake measuring 6 on the Richter scale may result in the destruction of 70 percent of India.
Indian cities could go down like a pack of cards if hit by a powerful earthquake.
Over 344 towns fall in the high risk category of Zone 5.
Another 813 cities, including seven out of 24 metros fall under the Zone 4 category.
Delhi is among the most risk-prone because its population is presently touching almost 20 million. Delhi alone could have eight million dead when struck by such dreadful earthquake.
Base Isolation Technology – Worldwide
The earthquake base isolation technology for building originated in different forms since 1885. With the contemporary base isolation technology, the Pestalozzi School was built in Skopje in 1969; Prof. Robinson developed lead-rubber bearings in New Zealand in 1974, Dr. Zayas developed Sliding Pendulum Bearings in 1985; and Prof. Kelly developed high-damping rubber bearings in Berkley, USA in 1985. Since the beginning of use of this technology in 1985, today USA, Europe, Japan, New Zealand, France, Mexico, Chile, Italy, China have several thousands of base-isolated buildings constructed with excellent seismic performance.
In India, the first base-isolated building was built in 2003 in Gujarat for the Bhuj Hospital that was reduced to debris in the aftermath of the now infamous Bhuj earthquake disaster. Despite well-established and proven seismic effectiveness of the base isolation technology, India still has less than ten base-isolated building projects.
Recent calamities in the country demand steps for controlling the damage triggered by earthquakes. Amongst the various alternatives, the use of base isolation technique is the most cost-effective, having technical advantages and reliability.
Principle of Base Isolation
The main principle behind base isolation is to prevent earthquake from directly transmitting forces to a building by isolating it from the ground, to protect internal contents and occupants, besides the entire structure itself.
Buildings benefitting most would be hospitals, schools, disaster management centers, police and fire stations, government offices, apartments, IT and ITES, office buildings, industrial plants, nuclear power stations, museums, bridges etc. Existing buildings can also be retrofitted easily by using the base isolation technology.
Base-isolated Showcase Building Project
Founded in 1947, Resistoflex is renow-ned for Vibration and Shock control systems. Following success of Base Isolation Technology in defense projects, Resistoflex was motivated to bring it to the Civil Building domain at affordable prices.
The Base Isolated Showcase Building at NOIDA is a collaborative project with Indian Institute of Technology (IIT) Delhi. It is a landmark project, conceptualized to increase awareness and transfer the state-of-the-art technology to the Indian construction industry and thereby to our society. This base-isolated building is designed for continued functionality during and after severe earthquakes predicted for Delhi/ NCR in Zone 4 (approx. magnitude 7.5 on the Richter scale) by first time using double curvature sliding isolation systems for building in our country. This building will also showcase a technological advancement in the field of architecture of such project.
A special feature being added to this building will be to integrate sensors, to convey instantly to all stakeholders and occupants through mobile/ internet about the seismic effect in the building, to immediately demonstrate the efficiency of the advanced base isolation system. This would make it a truly Seismic Smart Building.
Collaborative Project with Indian Institute of Technology (IIT) Delhi for Resisto-flex Earthquake Base Isolated Showcase Building
Founded in 1947, Innovative engineering has made Resistoflex renowned for
- Vibration, Shock & Noise Control Systems
- Air Suspension systems
- Seismic Protection systems
We designed, Manufactured and supplied Base Isolation System for 8 buildings made by L&T for a Defence project in 2008. This prompted us to bring the technology to the civil domain at an affordable price.
Lead Rubber Bearings (LRB) were dev-eloped in collaboration with IIT Roorkee and a joint paper was presented to the 7th World Congress on Seismic Systems at Las Vegas in 2011.
Resistoflex is a very active industry partner for Govt. of India’s initiative for indigenous development of Base Isolation Systems for Earthquake mitigation and setting up of National Level test facilities at MNIT, Jaipur.
254 friction Pendulum Isolators were designed and tested as per EN 15129 and other agreed specification for an IT/ITES Project. The Isolators have been delivered to the project site. Installation will begin in January 2017.
A Collaborative project with Indian Institute of Technology (IIT) Delhi for a Seismic Base Isolated Showcase Building has been instituted. The clear objective for this Landmark project is to objectively demonstrate Base Isolation Technology and its Techno Economic advantages.
Soil testing and strengthening was carried out as recommended by Prof. Ghosh, NIDM.
The Building Architecture was desig-ned by GrupIsm Pvt. Ltd with the upper structure decoupled with Base Isolation at the stilt level.
A Complete Seismic Isolation System Consist Of :
- Building Isolation System using Sliding Pendulum Isolators
- Piping Isolation System using Gimbal & Universal Metal/Rubber Expansion Joints Lift Isolation System
- Stair Case Isolation System e) Flexible Conduiting System
- Smart Seismic Isolated Building Information System
The isolators have been designed by HIRUN using Friction Pendulum isolators with 22% damping and +212 mm maximum horizontal displacement.
To improve the general features of this project, two special pendulums were considered. These 2 units will be installed with a special fuse system in order to ensure that all the pendulums move in the same direction and avoid the pendulums exceeding their movement capacity. To optimize this technology, the number of this fuse pendulum are 2 and will be placed in the diagonal direction of the structure.
The Isolators have been tested for all the required characteristics.
The structural design of the building has been done by Mr. Aman Deep Garg (CCEPL) which has been analysed and vetted by IIT Delhi.
A special feature being added to this building will be to integrate sensors to instantly convey to all stakeholders and occupants through mobiles and internet about the incoming Seismic intensity and that actually transmitted to the building’s upper structure to demonstrate the efficiency of the Isolation System. This would make this a truly Seismic Smart Building.
Construction activity has got advan-ced significantly and Isolators already installed The building is slated to be ready by end of March 2018.
The perspectives of all the stakeholders is included in this document for a detailed understanding of the technology and the project.
The Indian Institute of Technology (IIT) Delhi has shown gladness for getting associated with this landmark project, in terms of the technological advancements transpiring in the construction industry, i.e. the Resistoflex Base-Isolated Showcase Building. In the opinion of IIT Delhi, The proposed building project will serve as an exhibit structure for increasing awareness and transferring the state-of-the-art technology to our society in India. This objective will be facilitated through direct access given to the visitors at the level of the innovative isolation devices, helping them to realise and appreciate the technology in a better manner. Furthermore, the planned continuous real-time monitoring of the Resistoflex Base-Isolated Showcase Building to assess its seismic performance will demonstrate effectiveness of this modern and matured technology adopted in this project. The base isolation is the most successful technology of seismic response control of structures used worldwide; however, in India, we have very few structures constructed using this technology in comparison with the base-isolated structures built worldwide. Hence, a demonstration of a fully functional multi storey base-isolated structure of this kind serves the purpose of confidence building in the stakeholders.
At IIT Delhi, significant research contributions have been made on the base isolation technology, which are available in the standard literature in the form of patents, journal papers, and conference proceedings. Especially, the experimental tests conducted on variety of elastomeric bearings and sliding systems and shake-table table tests carried out on the new generation base-isolated structures have produced important database for the practitioners to develop assurance on the technology. The advantages of the base isolation technology in reducing inter-storey drift, seismic base shear, lower internal member forces, and protection of the contents within the base-isolated building have been demonstrated through series of tests aided with numerical investigations. The 3-dimensional (3D) finite element (FE)-based simulations on these systems and the structures equipped with them have duly been validated with the laboratory experiments. Therefore, IIT Delhi has been delightfully extending its expert technical guidance on the mathematical modelling, structural design, detailed drawings, and construction methodology for this unique and striking project.
Specifically, one of the highlights of this distinctive project has been the use of the double- concave (DC) friction pendulum system (FPS) with an articulated slider. This is advantageous in achieving desired variable effective stiffness as well as damping in the force- deformation hysteresis loop as a function of the amplitude of the bearing displacement. Such adaptable hysteretic behaviour provides the designed lower isolation stiffness at the design basis earthquake (DBE) and the necessary higher stiffness at the earthquake levels lower and higher than the DBE. This helps in achieving a trilinear force-displacement relation with improved restoring capabilities, while ensuring enhanced seismic energy dissipation within the controller, DCFP system. Further, the displacements across the isolation system are relatively lesser on account of the double-curvatures provided in this isolator; thereby, requiring smaller sizes of the DCFP system beneath the reinforced concrete (RC) columns. The added benefits of the DCFP system include: its friction force independent of the earthquake excitation frequency content, and nullifying or lowering the torsional coupling effects produced otherwise due to asymmetry. This is attributed to the facts that the centres of mass and resistance of the sliding support coincides, and the frictional force is developed at the base of the building proportional to the mass of the building. The following is an ideal hysteresis curve exhibited by the double-curvature friction pendulum system (DCFPS).
Therefore, selection of the DCFP
system in the Resistoflex Base Isolated Showcase Building has been a thoughtful decision.
The research team at IIT Delhi has extended their technical expertise in the development of the mathematical model and conducting non-linear seismic analysis of the Resistoflex Base- Isolated Showcase Building equipped with the double-concave friction pendulum (DCFP) system for the site-specific conditions. It is noteworthy to mention that the planning, modelling, analysis, design, structural detailing, and construction methodologies of the Resistoflex Base-Isolated Showcase Building are indigenously accomplished by the competent architect and structural designer in India. The IIT Delhi research team was glad to see the transfer of the sophisticated seismic base isolation technology from lab-to-land, while scientifically collaborating with these professionals from the construction industry.
Resistoflex Base-Isolated Showcase Building located at the prominent Udyog Marg in Sector 2 Noida is designed to be a landmark building in India. It is a seven storied building including two levels of car park in basement and stilts.
The building is designed to be an always operational building and will continue to remain functional even in case of severe earthquakes predicted for Zone 4.
Noida has stringent building bye laws for set backs, heights and coverage. The building complies with all norms con-firming to the latest National Building Code of India.
Architecturally the building is designed such that it can be occupied by a single corporate entity or multiple smaller tenants. It is designed for any arising future needs. It has a flexible layout that works in all situations. The entrance is through a modern lobby at the ground level and all individual floors then can be accessed by way of staircase and lifts. An additional staircase has been provided to work as a fire escape as well as for internal, floor to floor link.
The building has been designed for uninterrupted functioning. The services are designed to ensure that even in case of severe earthquake all functions and facilities remain operational without any down time and disruption. Special techniques have been used in the design which will ensure that water supply, sewerage, drainage, and firefighting lines do not get damaged and make the buildings uninhabitable, as it usually happens with ordinary buildings with damage to pipe lines. The vertical service lines as well as the vertical transport such as lifts and staircases have been designed to allow for seismic forces and flexibility using specially designed pipe joints, and space around these to allow for movement resulting from earthquake forces.
We began our designs based on steel frame structure. However, being a showcase building we changed it to RC as that is the prevalent construction system in India. The Base Isolation system however is equally suitable for either of the technologies.
We are confident that our building will showcase a technological advancement in Architectural field which is not only ideally suited to critical and essential buildings like school, hospitals and police stations but also for IT/ITES, office buildings and apartments.
Structural Engineer’s – Perspective
The structural system of the Showcase Building has a RCC Column-Beam frame arrangement with RCC slabs Base-Isolators at Stilt Floor roof base to support the building. The Isolators rest on the Rigid Column-Beam frame of the lower part of the building and supports the super- structure which would be isolated or separated from getting jerks of Earthquake.
The total design force resists in proportion to their lateral stiffness considering the interaction at each floor level. As the building above Isolator level would have negligible earthquake force, the same has been analyzed as Reinforced Concrete Ordinary Moment Resisting Frame as per IS: 1893 (Part1) – 2002. (Seismic Forces are negligible owing to use of isolator). However, the building below Isolator level is analyzed as RC Special Mo-ment Resisting Frame as per IS: 1893 (Partl) and detailed as per IS 13920 due to earthquake forces of applicable earthquake zone.
Applicable Seismic Forces
The Resistoflex Proposed Showcase Building has the following factors for designs as per IS:1893 (Partl)
- Seismic Zone: IV
- Zone factor: 0.24 (As per Fig.1 & Table 2 -IS: 1893)
Response reduction Factor: 3 (OMR Frame for building above isolator) 5 (SMR Frame for building below isolator)
The term base isolation means that the structure (building or equipment) is separated from its foundation. The original terminology of base isolation is more commonly replaced with seismic isolation, reflecting that the separation is somewhere above the base.
We all know that earthquakes of various intensities do happen and cannot be controlled. Therefore, to have an earthquake resistant building design, we have to accept the demand and make sure that the capacity of the structural members/ connections exceeds it. The earthquake causes inertia forces proportional to the building mass and the earthquake ground accelerations. As the ground accelerations increases, the strength of the building, the capacity, must be increased to avoid structural damage.
It is not practical to continue to increase the strength of the building indefinitely. In high seismic zones the accelerations causing forces in the building may be significantly high. Designing for this level of strength is not cheap. Therefore, technical documents and Standards/ Codes of practice allow the structural designers/Engineers to use ductility to achieve the capacity (R=5 for ductile design as per IS 1893). Ductility is a concept of allowing the structural elements to deform beyond their elastic limit in a controlled manner. Beyond this limit, the structural elements soften and the displacements increase with only a small increase in force. Therefore, Seismic Base Isolators can play an important role for the structural design development for building being designed in high seismic zones, for life line buildings (which need very high level of earthquake safety) or for the bui1dings/ structures where high level of performance is required/ deflection or sway control required such as Hospitals.
Procedures For Analysis
The building can be analyzed using a number of procedures, in increasing order of complexity:
- Equivalent static loads.
- Linear response spectrum analysis.
- Linear Time History Analysis.
- Nonlinear Time History Analysis.
Nonlinear time history has been used in this project owing to the accuracy of equivalent stiffness analysis results. Time history analysis should always be used.
The isolators are installed on the columns between the stilt floor roof. The connection design must ensure that the maximum forces are safely transferred from the building above isolator to the substructure and foundation through the bearing. Connections are designed for two conditions, (1) maximum vertical load and (2) minimum vertical load, each of % which is concurrent with the maximum earthquake displacement and shear force. The bearing is bolted to the structure top and bottom and so acts as a fixed end column for obtaining design moments.
The isolation system design and evaluation procedures produce the maximum base shears, displacements and structural forces for each level of earthquake, usually the DBE and MCE. These represent the maximum elastic earthquake forces that will be transmitted through the isolation system to the structure above. This project has been designed elastically to the MCE level of loading. The vertical load- carrying elements of the isolation system are required to be stable for the MCE displacements. The MCE displacements also define the minimum separations between the building and surrounding retaining walls or other fixed obstructions.
STATUS of project as on date
The Showcase Building design has been guided by IITD to ensure the desired performance. The critical design aspects have been taken care with proper detailing and isolation of the upper structure with the lower structure. The staircase has been structurally separated at stilt floor whereas the Lift Well has been detailed with hanging walls/ pit upto the basement level, supported at upper level i.e. above stilt floor or isolation bearing. Efforts being done to get best performing building which ultimately results in fulfilling the functional requirements, giving not only safety but should be economical also. The Design and Details have been finalized fully and Construction activities have reached upto 4th Floor.
The Indian subcontinent has experienced a number of devastating earthquakes in the last 3 decades, repeatedly reminding us about the high level of seismic hazard and risk prevailing in the country. Therefore, Indian earthquake agencies, academia and building construction industries have to come forward with live and showcase projects.
There is an urgent need for the testing and evaluation of earthquake impact on buildings and application of base isolation technologies. In this regard, the country was on the back foot when Bhuj (2001) earthquake shook us and we had to buy all base Isolators for the new Bhuj District Hospital from abroad at a high cost. Our country’s R&D in association with indigenous Industries, are striving to come forward to find economical solutions specially for housing projects for the masses.
We also need to focus on the existing building stocks and their poor resilience against impending earthquakes encompassing 60% of India’s land mass. Most retrofitting initiatives in the country have been in post-earthquake scenarios. Currently, few efforts have been directed to assess the vulnerability of lifeline buildings and transportation structures, monuments and heritage structures. Some retrofitting initiatives in the country have taken place in areas damaged by earthquakes such as Latur (1993), Jabalpur (1997), Bhuj (2001), Kashmir (2005), Sikkim (2011) and Imphal (2016) earthquakes. Nationally, we are in need of effective interventions for retrofitting to the construction fraternity. Base Isolators can convert several existing seismically deficient buildings into formidable earthquake tolerant buildings. For this, a nationwide awareness campaign is the need of the hour. The current initiative, i.e., Showcase Base Isolated building can be very useful for this purpose.
Earthquake-Resistant Design Conception considers that the seismic behavior of the structures improves when the following conditions are observed:
- Symmetry, for mass distribution and stiffness as well
- Minimum weight, especially for higher levels
- Adequate selection and use of construction materials
- Adequate resistance
- Continuity in the structure, in plan and elevation
- Limited deformation
- Inclusion of successive resistance lines
- Consideration of ground local conditions
- Good construction practice and strict structural inspection
Having stated as above and in addition to the recent revision of National Building Code (2016) and IS:1893-2016, where we are still divided in the acceptance/limitation of “performance” criteria in the earthquake resistant building design in the country, the Showcase Base Isolated structure can serve as a good alternative. This building can be a live example for the building industry, common people and government policy makers.
It is a well known fact that, buildings if constructed following codes and expert guidance, are able to resist earthquake threat at the desired level of safety. There are some established methodologies to assess the weakness, if any, in buildings but adopting strengthening/retrofitting measures as per expert guidance, usually benefit those buildings that are having working spaces at all sides. Though, the country has been taking few such challenges, especially after Bhuj (2001) earthquake, there is paucity in proper documentation and more so, efficacy of those measures later by another earthquake has yet to be proven/tested. In the current Showcase project, it is planned to document the entire construction process, design, testing and process of functioning of the Base Isolators as a model example. It is hoped that the current Showcase Building initiative will be helpful in achieving the country’s pledge towards earthquake resilient nation.
The following measures have been taken for the Resistoflex Base Isolated Showcase project:
Soil investigation for routine and seismic parameters that helped to determine the safe bearing pressure of the soil below basement.
Ground improvement measures, which have been done by simple densification of sandy-silty sub-soil, additional depth of 1 to 1.sin would compact. In doing so the raft foundation shall be ensured with uniform subgrade reaction during earthquake shaking.