Earthquake resistant techniques

BY-Shreya Thusoo10403EN006IDD PART IV

SUPERVISED BY-Prof. RAJESH KUMARDept. of Civil EngineeringIIT(BHU), Varanasi

SEMINAR ON EARTHQUAKE RESISTANT

TECHNIQUES

INTRODUCTIONSome centuries back, landmark structures used to have:

heavy masonry cladding wall curtains strong bracings

As need for taller buildings grew, advanced innovative devices were introduced in structures.

The Todaiji Temple in Japan has log house constructionthat has resisted earthquakes thousands of years (most number any structure has survived).

EARTHQUAKE They are natural disasters of a generally unpredictable nature. It is the shaking of the earth due to the movement of earth’s

crust.

Terms:Fault planeHypocenterEpicentre

Interesting FACT

When such quakes happen, enormous amounts of energy is released, which is

FAR GREATER THAN BIG NUCLEAR BOMB.

IRANIAN CITY, BAM

MAGNITUDE : 6.6 RICHTER SCALE

KILLED : 40,000

LOMA PRIETA

MAGNITUDE : 7.1 RICHTER SCALE

KILLED : 62

CONVENTIONAL METHODSThe concept is to strengthen the building.Have stiffness and inelastic deformation

capacity.

CONVENTIONAL METHODSSome of the general design concepts:

Follow current earthquake standards and codes. Provide strong foundation. Use best quality materials. Avoid irregular shaped structures and framing system. Maintain integrity by providing seismic bands:

At the plinth level of the building. At the levels of lintels of doors and windows. Vertical reinforcing bars at all wall junctions.

Introduce shear walls to transfer seismic loads down to the bottom of foundation.

CONVENTIONAL METHODS

Remedial measured for soft storey buildings.

(a) bracings in columns of open ground storey, (b) Providing R.C. shear wall and (c) Providing brick infills between columns.

(a) (b) (c)

ADVANCED METHODS

Basic approach is to reduce the earthquake generated forces acting upon the building; rather than strengthening it.

Two main techniques:Base isolation Energy dissipation devices

BASE ISOLATION DEVICES

Spherical Sliding Isolation SystemsLead rubber bearings

Base Isolation Devices - separate building from building foundation by bearing pads.

BASE ISOLATION DEVICESSupported by a series of bearing pads which are placed between the building and the building's foundation.

In case of an earthquake:Fixed base building deform and are damaged.Base isolated building rocks back and forth like a boat.

Shaking is reduced by

as much as 5 times

ENERGY DISSIPATION DEVICES/ SEISMIC DAMPERS

•Viscous Dampers utilized the forced movement of fluids within the damper

Special devices introduced in building absorb the energy produced by seismic waves.

•Friction Dampers these utilize frictional forces to dissipate energy

•Metallic Dampers utilize the deformation of metal elements within the damper

CASE STUDIES -Torre Mayor

Intrinsic Bracing System

Large Viscous Dampers

252 Reinforced concrete piles on the foundation.46,916 m3 of concrete.21,200 tons. of structural and reinforcement steel.98 fluid viscous seismic dampers.

Calculated to exceed the seismic requirements of the Mexico city and California Construction Regulations, which are the strictest in the world.

CASE STUDIES –Transamerica Pyramid

Unique Truss System with X-Bracing above first floor to support vertical, horizontal and torsional forces.

Overhead horizontal X-Bracing to support torsional movement in vertical direction.

In the 1989 Loma Prieta, California earthquake, it swayed more than 1 foot but was not damaged at all.

CASE STUDIES –Taipei 101

CASE STUDIES –Taipei 101It uses a tuned mass damper, also known as a harmonic absorberSteel sphere 18 feet across and weighing 728 tonSuspended from the 92nd to the 87th floor

Device consists of:1. Massive steel ball that sways to

counteract the building’s movement2. Eight steel cables form a sling to

support the ball3. Eight viscous dampers act like shock

absorbers when the sphere shifts 4. Two additional tuned mass dampers for

additional protection

The ball can move 5 ft. in any direction and reduce sways by 40 percent

TECHNIQUES UNDER RESEARCHSHAPE MEMORY ALLOYS

Bounce back after experiencing large loads.Used in bearings, columns and beams and connecting

elements.Most common alloys used are copper-zinc-aluminum-

nickel, copper-aluminum-nickel or nickel-titanium.

TECHNIQUES UNDER RESEARCH

MUSSEL FIBERS Elastomeric fibers combine stiffness and flexibility which helps

mussel to attach to hard surfaces. Construction materials made of a similar blend of firm and

flexible parts could help buildings withstand high-stress forces during an earthquake.

Ratio of stiff-to-flexible fibers = 80:20.

TECHNIQUES UNDER RESEARCH

VISCO-ELASTIC DAMPERS CST30Two layer of high damping rubber sandwiched between

steel plates.Absorb energy produce from vibrations.

TECHNIQUES UNDER RESEARCH

VISCO-ELASTIC DAMPERS CST30 Advantages over traditional damping system.

Effective utilization of interior space. Improvement in the degree of freedom of design. Accepts different vibration types. High performance and high quality. Environmental friendliness. Maintenance free.

TECHNIQUES UNDER RESEARCH

RUBBER CLOAKING DEVICE

Rubber 'cloaking device' could make buildings immune to earthquakes.

Waves can be made to bend their path by various techniques. Seismic waves can also be redirected. This is called

‘cloaking’.

TECHNIQUES UNDER RESEARCH

RUBBER CLOAKING DEVICE• INSTALLATION: Concrete-and-plastic plate of concentric rings encircles

the foundation.• DETOUR: During earthquake, bending force deflects waves from their

path toward a stiffer ring away from the building.• EXIT: About halfway around plate, bending force weakens; waves'

forward momentum propels them on their original path.

WORK ON EARTHQUAKE RESISTANCE IN INDIA

In India, base isolation technique was first demonstrated after 1993 Killari earthquake. Two single storey building were built with rubber base isolators resting on hard ground.

The four storey bhuj hospital building was built with base isolation technique after 2001 bhuj earthquake.

IS CODES FOR EARTHQUAKE RESISTANT DESIGN

IS 1893 (Part 1), 2002, Indian Standard Criteria For Earthquake Resistant Design of Structures (5th revision).

IS 4326, 1993, Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Buildings (2nd revision).

IS 13827, 1993, Indian Standard Guidelines for Improving Earthquake Resistant of Earthen Buildings.

IS 13828, 1993, Indian Standard Guidelines for Improving Earthquake Resistant of Low Strength Masonry Buildings.

IS 13920, 1993, Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces.

SEISMIC ZONES IN INDIA

REFERENCES[1]. Morris, Neil; Earthquakes; Crabtree Publishing Company; 1998.[2]. Mazza and Vulcano; Base-isolation techniques for the seismic protection of RC

framed structures subjected to near-fault ground motions; Paper No. 2935; 13th World Conference on Earthquake Engineering at Vancouver, B.C., Canada; August 1-6, 2004.

[3]. Kelly, Skinner and Heine; Mechanisms of energy absorption in special devices for use in earthquake resistant structures; Bulletin of N.Z. Society for Earthquake Engineering, Vol. 5 No. 3, September 1997.

[4]. Seismic Protection with Fluid Viscous Dampers for the Torre Mayor, a 57-Story Office Tower in Mexico City, Mexico; Publisher: Taylor Devices, Inc.;Date: 2011-02-18.

[5]. Kourakis, Ioannis; Structural systems and tuned mass dampers of super-tall buildings: case study of Taipei 101; Publisher: Massachusetts Institute of Technology; 2007.

[6]. Farhat, Guenneau and Enoch, Flexural waves on a thin elastic plate are smoothly bent around an obstacle ("E") surrounded by a metamaterial cloak, Volume 103, Issue 2, DOI 10 July 2009.