Earthquake resistant building
- 1. Subject name : Building And Town Planning Subject code : 2140607 Guided by : Prof. Mehul gamit Prof. Pinank Patel
- 2. Topic: Earthquake Resistant Building Name Enrolment no. Bhavik Deshmukh 151103106002 Yogesh Gain 151103106004 Jayveer kotila 151103106008 Aditya Mistry 151103106009 Dhrumil Pandya 151103106010
- 3. Outline What are Earthquake? Precautions while planning Non engineered masonary structure Failure mechanisms of masonary building Box action in masonary Suggestions for construction of new masonary building in earthquake sensitive area Water tank
- 4. What are Earthquake? A sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth's crust or volcanic action.
- 5. Precautions while planning Lightness Symmetry Regularity Simplicity Continuity Size of building
- 6. 1. Lightness: Since the earthquake force is a function of mass, the building shall be as light as possible. Heavier structure means large inertia force and collapse these structures results in heavier damage and loss of lives. Thus, roofs and upper storey of buildings, in particular, should be designed as light as possible.
- 7. 2. Symmetry The building as a whole or its various blocks should be kept symmetrical about both the axes. The asymmetrical buildings are subjected to twist or torsion during earthquakes. Twist in buildings causes different portions at the same floor level to move horizontally by different amounts. Irregularities of mass, strength and stiffness in a building can result in significant torsional response. Torsion arises from eccentricity In the building layout.
- 8. 3. Regularity: The building should have a simple rectangular plan. It is seen that simple shapes behave better during earthquake than complex shapes like L,T,E,H,U and C etc. It is seen that during earthquakes the building with re-entrant corners have suffered great damage. Torsional effects of ground motion are pronounced in long, narrow rectangular blocks. Separation of a large building into several blocks may be required so as to obtain symmetry and regularity of each block.
- 9. 4. Simplicity: Ornamentation involving large cornices, vertical or horizontal cantilever projections, facia stones and the like are dangerous and undesirable from a seismic viewpoint. Simplicity is the best approach. Where ornamentation is insisted upon, it must be reinforced with steel which should be properly embedded or tied into the main structure of the building.
- 10. 5.Continuity: The earthquake forces developed at different floor levels in a building need to be brought down along the height to the ground by the shortest path. Any deviation or discontinuity in this load transfer path results in poor performance of the building. Building with vertical setback (like the hotel building with a few storeys wider than the rest) cause a sudden jump in earthquake forces at the level of discontinuity. Some building have reinforced concrete walls to carry the earthquake loads to the foundations.
- 11. 6. Size of building Buildings of great length or plan area may not respond to earthquakes in the way calculated. Buildings that are two long in plan may be subjected to different earthquake movements simultaneously at the two ends, leading to disastrous results. As an alternate such building can be broken into a number of separate square buildings. In a building with large plan area like warehouse , the horizontal seismic forces can be excessive to be carried by column and walls.
- 12. Non-engineered masonry structure The advantage of masonry construction are as follows: Use of locally available materials. Need of less skilled labour. Easy and cheap repair. Good insulation against heat and sound. Less formwork. Possibility of easy alteration after construction.
- 13. The poor performance of masonry building in earthquake is because of the following reasons: The material is brittle and its strength degrade due to repetitive loadings. Masonry has very low tensile strength and low shear strength specially with poor mortars. Masonry has great weight weight because of thick walls. Consequently the inertia force are large. Large stiffness of the material, which leads to large response to earthquake waves of short natural period. The wall to wall connection and roof to wall connection is generally weak. In masonry construction, stress concentration occurs at corners of doors and windows. Poor construction quality because of use of locally available materials and unskilled labours.
- 14. Failure Mechanisms of Masonry Buildings: A masonry building may fail in various ways under the action of earthquake forces. Some of the common modes of failure are: Out of plane failure In plane failure Connection failure Diaphragm failure Failure due to opening in walls Non-structural components failure
- 15. 1. Out of plane failure The force acting on the mass of the wall tends to overturn it. The seismic resistance of the wall is by virtue of its weight and tensile strength of mortar and it is very small. This wall will collapse by overturning under the ground motion. The wall has very less resistance in this direction due to small depth. The bending of the wall results in development of tensile stress. The masonry is very weak in tension and hence it cracks. The cracking can lead to full or partial collapse of the wall. This type of failure is called out of plane failure.
- 17. In plane failure: The free standing wall fixed on the ground is subjected to ground motion on its own plane. The damage modes if an unreinforced shear wall depend on the length to width ration of the wall. A wall with small length to width ratio will generally develop a horizontal crack due to bending tension and then slide due to shearing. A wall with moderate length-to-width ratio and bounding frame diagonally cracks due to shearing. A wall with large length-to-width ratio, may develop diagonal tension at both sides and horizontal cracks at the middle.
- 19. Connection Failure The ground shakes simultaneously in the vertical and two horizontal directions during earthquakes . However, the horizontal vibrations are the most damaging to normal masonry buildings. To ensure good seismic performance, all wall must be jointed properly to the adjacent walls. In this way, walls loaded in their weak direction can take advantage of good lateral resistance offered by walls loaded in their strong directions. Further, walls also need to be tied to the roof and foundation to preserve their overall integrity.
- 21. Diaphragm Failure Consider a complete wall with enclosure with a roof on the top subjected to earthquake force acting along with x-axis as shown in fig. The roof/slabs will transfer the earthquake force to the walls, causing shearing and bending them. To transfer the forces the roof must have enough strength in bending in the horizontal plane. This action is called diaphragm action. The roofs and floors which are rigid and flat are bonded to the walls properly, do not show any sign of diaphragm failure.
- 23. Failure due to opening in walls: Openings are necessary in a building but the location and size of the opening in walls affect the performance of masonry buildings during earthquake, During earthquake shaking, inertia forces act n the strong direction of some walls and in weak direction of others. Walls shaken in weak direction seek support from other walls. Walls B1 and B2 seek support from walls A1 and A2 for shaking in the direction shown in fig. Thus, walls transfer loads to each other at their junctions. Hence, the masonry courses from the walls meeting at corners must have good interlocking. For this reason, opening near the wall corners are detrimental to good seismic performance.
- 24. Non-structural components failure The non-structural damage is that due to which the strength and stability of the building is not affected. Such damage occurs very frequently even under moderate intensities of earthquakes. Some non-structural damages are: Cracking and overturning of masonry parapets, roof chimney, large cantilever balconies and cornices. Falling of plaster from walls and ceiling. Cracking and overturning of partition walls. Cracking of glass panels. Falling of loosely placed objects, overturning of cupboards.
- 25. Box action in masonry buildings Brick masonry building have large mass and hence attract large horizontal forces during earthquake shaking. They develop numerous cracks under both compressive and tensile forces caused by earthquake shaking. The focus of earthquake resistant masonry building construction is to ensure that these effects are sustained without major damage or collapse. Appropriate choice of structural configuration can help achieve this. The structural configuration of masonry buildings include aspects like Overall shape and size of the building. Distribution of mass and lateral load resisting elements across like building.
- 26. Suggestions for construction of new masonry building in earthquake sensitive are: Site investigation must be carried out. Bearing capacity of soils should be more than required safe bearing capacity. Construction work should be carried out by qualified civil engineer. Plan of building should be square or rectangular. Flat concrete roof is preferred. The thickness of wall should not be less than 230 mm. All the construction material like cement, steel, sand, aggregates, bricks, stone, timber, tiles etc. Should be of good quality conforming to IS specification. The proportion of cement: sand mortar should not be weaker than 1:4. First class bricks should be used. Minimum compressive strength of bricks should not be less than 35 kg/cm^2. Number of stories should not be more than four.
- 27. The total height of building should not exceed 15 m. Opening in wall should be minimum and centrally located. Total length of opening in wall should not exceed 33% of the length of the wall. Vertical reinforcement must be provided at corners of walls and t door jambs. Proper R.C.C bands should be provided at plinth level, lintel level, caves level, etc. At window sill level, U-shaped, 8 f bars should be provided t every sixth layer. Masonry work should be carried out in proper bond so that vertical joints are broken. Horizontal dowel bars should provided t all T and L-junctions. Dowels are placed in every fourth course or at 50 cm intervals. 8 mm dia bars used as dowel bars. At T and L-junctions, toothed joints should be provided in masonry.
- 28. Water tank Elevated water tank contain huge mass t height supported on column or circular RCC shft. It is an example of single degree of freedom. As large mss is supported at height, centroid of mss will be higher. During earthquakes inertia force produced due to mass will be higher. During earthquke inertia force produced due to mass of water and earthquake acceleration my cause overturning of the tank. Inertia force= Mass * acceleration Higher the mass, more will be the inertia force acting on the water tank, i.e. mass of water. The columns or RCC shaft acts as stiffening member, providing stiffness resistance during earthquake.
- 29. The location of the water tank on roof slab should be carefully decided. It should be centrally located on the building. Water tank on edge or corner of a building may cause imbalance of mass, resulting in overturning of tank. For small residential buildings, light weight PVC tanks are preferred to reduce mass of the building.