NATIONAL INSTITUTE OF CONSTRUCTION MANAGEMENT & RESEARCH, GOA CAMPUS NEW TECHNOLOGIES & MATERIALS Presentation on EARTHQUAKE RESISTANT STRUCTURES SUBMITTED BY: ROHAN MASKAY (GO6150)UNDER THE GUIDANCE OF SAINATH . S(G06167)PROFESSOR B.B. DAS NAGASHREE UPADHYAYA(G06178) 1 CHIRAG WAYKOLE (G06182)
CONTENTS• What is an earthquake?• Types of earthquakes?• Earthquake prone zones in India• Causes of an Earthquake• Seismic performance & design• Improving earthquake resistant of minor buildings• Roll of Shear Walls & advantages• Earthquake resisting structure techniques1) Base isolation Method2) Energy dissipation device3) Keeping building up thrust• Case study• Conclusion
What is an earthquake? An earthquake is the result of a sudden release of energy in the Earth’s crust that creates seismic waves. A sudden rapid shaking of the earth caused by breaking and shifting of rocks beneath the earth’s surface.
Focus and epicenter • FOCUS: • The point within Earth where faulting begins is the focus, or hypocenter. • EPICENTER: • The point directly above the focus on the surface is the epicenter • FOCAL DISTANCE: • Vertical distance from focus and epicenter
MAGNITUDERichter scale measurestotal amount of energyreleased by an earthquakeAmplitude of the largestwave produced by an eventis corrected for distanceand assigned a value on anopen-ended logarithmicscale
Seismic Waves• When the rock breaks, there is a sudden release of energy.• Shock waves spread out through and around the earth in all directions, starting from the focus of the earthquake. • At the earths surface the ground vibrates as the waves pass through it. • The way the waves spread is a bit like the ripples spreading on a pond when a stone is dropped into it.
Seismic Waves • Energy spreads out through the earth in three different wave types : P-wave•a longitudinal wave•travel through rock, liquid and the air•the fastest traveling seismic wave S-wave•a transverse wave•travel through rock, but not through liquid and the air•slower than a P-wave, but faster than a surface wave Surface wave:•the slowest traveling seismic waves•Their movement is greatest at the earths surface, and gets smaller deeper below the surface 8
Seismograph Vertical type Normal type seismograph Horizontal type Digitalize type seismograph
Tectonic Plates World map showing the tectonic plates with only the larger plates labeled The surface of the earth is made up of 21 tectonicplates, some large and some small, that are constantlymoving. As the plates are forced against each other, theydeform, and eventually they crush and fracture. The suddenfracture of the rock sends out a shock wave that causes theearths surface to shake. This is one way earthquakes can11
Causes of earthquake Earthquakes are casually related to compression and tensional stresses. Volcanic eruptions, rock fall, land slides and explosions can also cause earthquake.
Other Causes• Earthquakes can be caused by natural events or human activities. Here are some of the different causes of earthquakes.1. Tectonic Plate Movement- the most common cause2. Volcanic Activity3. Explosions4. Collapsed Mines5. Water Pressure in Reservoirs 14
Types of earthquake There are two types of earthquake • Inter plate earthquake • Intra plate earthquake Horizontal movement (strike slip) & vertical movement occurs(dip slip)
Earthquake Resistant BuildingsHow can engineers designbuilding that survives inearthquake?To explain how buildings: Vibrate during earthquakes, are strengthened to resist earthquakes, can be isolated from the shaking ground, use dampers to reduce vibrations from earthquakes. 17
Improving earthquake resistance ofminor buildings Size of the building Simpler the plan – better the building. Construction materials R.C.C preferable than P.C.C
Improving earthquake resistance ofminor buildings Strong column – weak beam Horizontal band necessary throughout the masonry Latur earthquake incident
Strengthening Buildings for Earthquakes• Horizontal structural systems (floors and roofs) Diaphragms Trussing• Vertical structural systems (columns, beams, walls and bracing) Braced frames Moment resisting frames Shear walls 21
Horizontal structural systems-Diaphragms• Horizontal diaphragms are usually floors and roofs. They are made up from a horizontal frame covered by a floor or roof deck.• When a diaphragm is stiff enough in its horizontal plane. it can share the sideways earthquake forces on a building between the vertical structural members, e.g. the columns and walls. 22
Horizontal structural systems- Trussing• Horizontal trussing is usually used in roofs where there is not enough deck to allow the roof to act as a stiff horizontal diaphragm.• The trussing transfers the sideways earthquake forces on a building to its vertical structural members e.g. the columns and walls. 23
Vertical structural systems-Braced Frames• Single Diagonals If a single diagonal, or brace, is used, it must be able to resist tension (stretching) and compression (squashing) Single diagonals in a 3-storey frame caused by sideways forces in both directions 24 on a frame.
Vertical structural systems-Braced Frames• Cross Bracing • If two diagonals are used, in the form of cross-bracing, they only need to resist tension. • This is because one brace is in tension for the sideways force in one direction on the frame, while the other brace is in tension when the force is reversed. • Steel cables can be used for cross-bracing, as they can be stretched, but not squashed. Cross-bracing in a 3-storey frame 25
Vertical structural systems-Braced Frames Miscellaneous Methods – Steel bracings Inverted V Bracing Knee Bracing K Bracing V Bracing 26
Vertical structural systems-MomentResisting Frames • In moment resisting frames, the joints, or connections, between columns and beams are designed to be rigid. This causes the columns and beams to bend during earthquakes. So these structural members are designed to be strong in bending. • Moment resisting frames simply means frames that resist forces by bending. 27
Shear wall & its advantages Vertically oriented wide beams. It carries seismic loads down to the bottom of foundation Provides large strengths and stiffness to buildings Thickness generally varies from 150mm to 400 mm in high rise buildings
Shear wall & its advantages Should be symmetrical in plan along both the axis The opening provided in the shear wall should be symmetrical Shear wall is effective when located along the exterior perimeter of the building
Shear wall & its advantages Efficient in terms of • Cost • Effectiveness • Construction • Helps in minimizing the effect on non-structural elements. It is said that : “We cannot afford to build concrete buildings meant to resist severe earthquakes without shear walls.”
ClassificationSimple rectangular type Coupled Rigid frame Framed Core type Column supported shear wall
Types of shear walls Based on what strength we want and the soil strata following types of shear walls can be constructed: • R.C shear wall • Plywood shear wall • Mid ply shear wall • Steel shear wall
Earthquake resisting structurestechniques • Base isolation method • Energy dissipation device - seismic dampers • Keeping building up thrust
Base isolation method • Introduces flexibility to the structure. • Building is rested on flexible pad. • When earthquake strikes building does not move • It is suitable for hard soil only
Types of Base isolator LEAD RUBBER BEARING Frequently used to base isolation Made from layers of rubber sandwiched together with layers of steel Very stiff and strong in the vertical direction Flexible in horizontal direction
Base isolation in India In India base isolation technique was first demonstrated after 1993 Killari earthquake. Two single storey buildings were built with rubber base isolators resting on the ground The four storey Bhuj hospital was built with base isolation technique after 2001 bhuj earthquake
Energy dissipation device –Seismic Dampers • These re used in place of structural elements such as diagonal braces. • Acts like a hydraulic shock absorbers • When seismic energy is transmitted through them, dampers absorb part of it, and thus damp the motion of the building
Types of seismic dampers Viscous dampers – Energy is absorbed by silicone-based fluid passing between piston cylinder and arrangement Friction Dampers – Energy is absorbed by surfaces with friction between them rubbing against each other. Yielding dampers – Energy is absorbed by metallic components that yield. Viscoelastic Dampers – Energy is absorbed by utilizing the controlled shearing of solids
Keeping building upright CONCEPT: • When the earthquake strikes the system dissipates energy in the building cores and exteriors • The frames are free to rock up and down within fittings fixed at their bases • It has been recently discovered in Japan • It has found to be survived in extreme earthquakes
Case study – Taipei 101• Formerly known as Taipei world Financial centre – 101 floors• Taipei 101 is designed to withstand earthquake tremors common in its area.• Most designs achieve the strength by structural elements such as bracing.• The design achieves both strength and flexibility for the tower through the use of high-performance steel construction.• Thirty-six columns support Taipei 101, including eight "mega-columns" packed with 10,000 psi (69 MPa) concrete.• The foundation is reinforced by 380 piles driven 80 m (262 ft) into the ground
Case study – Taipei 101• These features combine with the solidity of its foundation to make Taipei 101 one of the most stable buildings ever constructed.• The stability of the design became evident during construction when, on March 31, 2002, a 6.8-magnitude earthquake rocked Taipei.• The tremor was strong enough to topple two construction cranes from the 56th floor.• Five people died in the accident, but an inspection showed no structural damage to the building, and construction soon resumed.
Conclusion• While earthquakes are inevitable, each earthquake need not turn in to a disaster• Earthquake don’t kill, but improperly designed structures do.• Though the structures may get damaged, but by applying certain measures we can save human lives.