Innovations in Earthquake Structural Design of Buildings and Construction

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1 Innovations in Earthquake Structural Design of Buildings and Construction Manish Shrikhande Department of Earthquake Engineering Indian Institute of Technology Roorkee October 06, 2015

2 Earthquake Effects of Buildings Earthquake ground motions induce vibrations Leading to additional forces due to the weight These forces act in horizontal (lateral) as well as vertical directions Resistance to vertical loads is generally not a problem The engineering challenge is to provide a safe load path for lateral forces to the foundations There can be several possibilities to design a structure to withstand earthquake effects The safety of foundations during earthquakes also needs consideration

3 Principles of Earthquake Resistant Design Earthquakes are random and rare phenomena It is not economical to design systems to withstand a very rare and very strong earthquakes without any damage The basic principle for earthquake resistant design is to ensure: Continued operation of facilities in moderate and relatively frequent earthquakes without or repairable damage No collapse during a rare and very severe earthquake The emphasis is on sustaining damages during a strong earthquake but in a preferred mode to prevent collapse The dissipation of energy during earthquake vibrations is an integral part of the earthquake resistant design strategy The choice of design strategy depends on the perceived level of seismic risk in a region represented by the seismic zoning map of India

4 Source: India Meteorology Department Seismic Zoning Map of India

5 Lateral Load Resisting Systems Lateral load resisting systems are important to ensure safe transfer to foundations Braced frames Shear walls Moment resisting frames Often these systems are used in combination The capacities of different members are decided to achieve a preferred sequence of damage which dissipates the earthquake energy by inelastic deformations without compromising the structural stability. This is akin to arm-wrestling with the earthquake trying to resist it by building stronger sections There can be another way to live with earthquakes peacefully vibration control.

6 Technologies for Earthquake Resistant Design-1 Base isolation Decouple the superstructure from the base by using a laterally flexible material (isolation bearings) Important to ensure the long-term stability of the mechanical properties of the material Needs a large clearance around the perimeter to accomodation the drift Suitable for constructions on hard rocks

7 Technologies for Earthquake Resistant Design-2 Energy Dissipation Devices Dissipation of energy can be achieved by several mechanisms The preferred mechanism is chosen by considering the target frequency and magnitudes

8 Technologies for Earthquake Resistant Design-3 Recent innovations

9 Technologies for Earthquake Resistant Design-3 Recent innovations Interlinked concrete block masonry to dissipate earthquake energy by sliding friction and yielding of link elements Pre-fabricated concrete blocks with grooves for connectors No other binder such as mortar between the blocks Very quick to assemble Performs exceedingly well during tests Friction based dissipation systems are interesting for low costs and effectiveness for all frequencies The Department of Earthquake Engineering, IIT Roorkee has long been working on the development of suitable friction based earthquake resistant design solutions and the work continues.