Adobe   Stone   Brick   Concrete Block             Earthquake resistant Stone masonry       Glossary, notations and useful knowledge       References       Glossary Notations Useful Knowledge Glossary Blocking: Solid wood block which provides lateral support as in bridging, and/or edge supporting for cladding Bond Beam: A continuous ring beam also known as :seismic band, tie-beam, collar beam, crown beam Buttress: A projecting tapered structure built agains a wall to support and/or reinforce it Cladding: The structural covering used directly over studs, rafters or trusses Diaphragm: A horizontal structure-such as floor or roof connected to walls able to transmit lateral loads to walls in respect of their stiffness Gable End Wall: The exteriour wall, with an upper vertical triangular-shaped portion, perpendicular to the roof ridge beam and parallel to roof rafters or trusses Grout: A mixture of cementitious material and aggregate to which water is added to provide up to 0.25m slump. Coarse grout consists of portland cement, sand, pea gravel and water. Fine grout consists of portland cement, sand and water Length: The dimension of exterior walls parallel to the roof ridge beam and perpendicular to the span of roof rafters or trusses Lintel: A beam used over wall openings to carry loads across the opening Load Bearing Wall: A wall that supports vertical load in addition to its own weight Pilaster: A rectangular support or pier projecting partially from a wall to support it laterally. In the past treated architecturally as a column with base, shaft and capital Plinth Course: A course built along the base of the wall in cut stone masonry or clay brick as a water tight layer and to ensure flood protection. Damp proof course can also be installed over plinth masonry and Width: The dimension of exterior walls perpendicular to the roof ridge beam and parallel to the span of roof rafters or trusses   Notations To beginning of document M: Magnitude of an earthquake; Also known as "Richter's magnitude ag: Peak ground acceleration I: Intensity of an earthquake MSK: A 12-grade Medvedev-Sponheuer-Karnik intensity scale MM: A 12-grade modified Mercalli intensity scale EMS: A 12-grade European macroseismic (intensity) scale   Useful Knowledge To beginning of document   1. Magnitude and intensity of an earthquake   The impact of an earthquake on built environment is closely related to the amount of energy released in the focus. The measure of released energy is the magnitude M, which was first defined by Richter in 1935, and is therefore called -Richter's magnitude. According to Richter, the magnitude of an earthquake M is given by a logarithm of the maximum displacement amplitude A (in mm), recorded by a standardised instrument, located at exactly 100 km from the epicentre: M=logA Hence the magnitude, M measures the absolute "size" of the earthquake, irrespective of location. The lightbulb analogy may be used: For a lightbulb, magnitude corresponds to the wattage, which indicates the absolute size in terms of the power it consumes. Intensity corresponds to the apparent brightness of the bulb to a viewer, which varies with location. The effects of earthquakes on the built environment are measured by means of various intensity scales. A 12-grade modified Mercalli (MM) scale and MSK-76 intensity scale are used predominantly in the US and Europe respectively. A new 12-grade European macroseismic scale (EMS), which is a modification of the MSK scale, has been recently developed.   2. European macroseismic scale (EMS)   The newly developed EMS scale is a modification of the MSK scale. In the EMS scale the definitions are based on Effects on humans...(a) Effects on objects and nature (excluding damage to buildings, effects on ground and ground failure)...(b) Damage to buildings...(c) In this scale, damage to masonry buildings is classified according Table 2. To account for seismic resistant design, however, the buildings at risk are classified according to their expected seismic vulnerability (Table 1). Definitions of quantity are also specified : fw=10%; many=20-50%; most=60-100% There is 10% overlapping between the categories. Type of Masonry Vulnerability class A B C D E F Rubble stone ; field stone O           Adobe (earth brick) O --]         Simple stone [-- O         Massive stone   [-- O --]     Unreinforced brick /concrete block [-- O --]       Unreinforced brick with RC floors   [-- O       Reinforced brick (confined masonry)     [-- O -- --] Table 1- EMS scale -differentiation of masonry structures into vulnerability classes   Classification of damage to masonry buildings Grade 1 Negligible to slight damage (no structural damage).Hairline cracks in very few walls; fall of small pieces of plaster only. Fall of loose stones from upper parts of buildings in very few cases only. Grade 2 Moderate damage (slight structural damage, moderate non-structural damage) Cracks in many walls; fall of fairly large pieces of plaster; parts of chimney fall down. Grade 3 Substantial to heavy damage (moderate structural damage, heavy non-structural damage) Large and extensive cracks in most walls ; pantiles or slates slip off. Chimneys are broken at the roof line; failure of individual non-structural elements. Grade 4 Very heavy damage (heavy structural damage, very heavy non-structural damage) Serious failure of walls; partial structural failure. Grade 5 Destruction (very heavy structural damage) Total or near total collapse. Table 2- EMS scale -classification of damage to masonry buildings   The following classification of earthquake intensities is proposed in the new EMS scale: EMS value Summary of damage Full Description I Not felt (a) (b) (c) Not felt even the most favourable circumstances No effect No damage II Scarcely felt (a)       (b) (c) The tremor is felt only by very few(less than 1%)individuals at rest and in a specially receptive position indoors. No effect No damage III Weak (a)   (b) (c) The earthquake is felt indoors by a few people at rest feel a swaying or light trembling Hanging objects swing slightly No damage IV Largely observed (a)                 (b)       (c) The earthquake is felt indoors by many and outdoors only by very few people. A few people are awakened. The level of vibration is not frightening. The vibration is moderate. Observers feel a slight trembling or swaying of the buildings, room or bed, chair, etc China, glasses, windows and doors rattle. Hanging objects swing. Light furniture shakes visibly in a few cases. Woodworks creak in a few cases No damage V Strong (a)               (b)                       (c) The earthquake is felt indoors by most, outdoors by few people. A few people are frightened and run outdoors. Many sleeping people are awakened. Observers feel a strong shaking or rocking of the whole building, room or furniture Hanging objects swing considerably. China and glasses clatter together. Small, top-heavy and/or precariously supported objects may be shifted or fall down. Doors and windows swing open and shut. In a few cases windows panes break. Liquids oscillate and may spill from well filled containers. Animals indoors may become uneasy. Damage of grade 1 to a few buildings VI Slightly damaging (a)         (b)           (c) Felt by most people indoors and by many outdoors. A few people lose their balance. Many people are frightened and run outdoors Small objects of ordinary stability may fall and furniture may be shifted. In few instances dishes or glassware may break. Farm animals (even outdoors) may be frightened. Damage of grade 1 is sustained in many buildings; a few suffer from grade 2 damages VII Damaging (a)         (b)       (c) Most people are frightened and try to run outdoors. Many find it difficult to stand especially on the upper floors Furniture is shifted and top-heavy furniture may be overturned. Objects fall from shelves in large numbers. Water splashes from containers, tanks and pools Many buildings of vulnerability class B and a few of class C suffer damage of grade 2; many buildings of class A and a few of class B suffer damage of grade 3; a few buildings of class A suffer damage of grade 4. Damage is particularly noticeable in the upper parts of buildings. VIII Heavily damaging (a) (b)             (c) Many people find it difficult to stand even outdoors. Furniture may be overturned. Objects like TV sets, typewriters fall to the floor. Tombstones may occasionally be displaced, twisted or overturned. Waves may be seen on very soft ground Many buildings of vulnerability class C suffer damage of class 2; many buildings of class B and a few of class C suffer damage of grade 3; many buildings of class A and a few of class B suffer damage of grade 4;a few buildings of class A suffer damage of grade 5; a few buildings of class D suffer damage of grade 2. IX Destructive (a)   (b)   (c) General panic. People may be forcibly thrown to the ground. Many monuments and columns fall or are twisted. Waves are seen on soft ground Many buildings of vulnerability class C suffer damages grade 3; many buildings of class B and a few of class C suffer damage of grade 4; many buildings of class A and a few of class B suffer damage to grade 5; many buildings of class D suffer damage of grade2 ;a few suffer grade 3 damages. A few buildings of class E suffer damage of grade 2. X Very destructive (c) Many buildings of vulnerability class C suffer damage of grade 4; Many buildings of class B and a few of class C suffer damage of grade 5, as do most buildings of class A. Many buildings of class D suffer damage of grade 3; a few suffer grade 4 damages. Many buildings of class E suffer damage of grade 2 ; a few suffer grade 3 damages. A few buildings of class F suffer damage of grade 2. XI Devastating (c) Most buildings of vulnerability class C suffer damage of grade 4. Most buildings of class B and many of class C suffer damage of grade 5. Many buildings of class D suffer damage of grade 4; a few suffer grade 5 damages. Many buildings of class E suffer damage of grade 3; a few suffer grade 4 damages. Many buildings of class F suffer damage of grade 2; a few suffer grade 3 damages XII Completely devastating (c) Practically all structures above and bellow ground are destroyed. Table 3 -Classification of earthquake intensities according to EMS scale   3. Earthquake ground motion and effects on buildings   Observed intensity reflects the effects of earthquakes on buildings. However, as a measure of earthquakes, it can only be used to assess the damage to similar type of buildings when subject to earthquakes of similar intensity. For design purposes the intensity of an earthquake can only be useful if correlated with physical quantities such as accelerations , forces etc. To determine the intensity of a particular earthquake the peak ground acceleration ag is often considered. A formula that correlates the values of peak ground acceleration ag and intensity I has been developed for the MM scale: Log ag = 0.25 *I+ 0.25 Table 4 displays average values of the peak ground acceleration (in % of gravity , g=9.81ms-2) in dependence on intensity.   Intensity scale Grade VII Grade VIII Grade IX MSK-76,78 10 20 40 MM 10 18 32 Table 4- Average values of peak ground acceleration in % of gravity in dependence on intensity   4. Seismic zones in India   Zone A: Risk of Widespread Collapse and Destruction (MSK IX or greater) Zone B: Risk of Collapse and Heavy Damage (MSK VIII likely) Zone C: Risk of Damage (MSK VII likely) Zone D: Risk of Minor Damage (MSK VI maximum) Categories of Buildings for Strengthening Purposes: For categorising the buildings in order to achieve efficient design, three parameters are considered: Seismic Intensity Zone for building location Importance of building Foundation soil properties   Category Combination of Conditions for the Category I Important Building on Soft Soil in Zone A II Important Building on Firm Soil in Zone A Important Building on Soft Soil in Zone B Ordinary Building on Soft Soil in Zone A III Important Building on Firm Soil in Zone B Important Building on Soft Soil in Zone C Ordinary Building on Firm Soil in Zone A Ordinary Building on Soft Soil in Zone B IV Important Building on Firm Soil in Zone C Ordinary Building on Firm Soil in Zone B Ordinary Building on Firm Soil in Zone C Ordinary Building on Soft Soil in Zone C Notes: 1. Seismic Zones A, B and C and type of buildings ie. ordinary/important are defined bellow 2. Firm soil refers to those having safe bearing value more than 1 kg/cm2 and soft those less than 1 kg/cm2 Table 5 -Categories of Buildings for Strengthening Purposes   IMPORTANT -Hospitals, clinics, communication buildings, fire and police stations, water supply facilities, cinemas, theatres and meeting halls, schools, dormitories, cultural treasures such as museums, monuments and temples, etc. ORDINARY -Housings, hostels, offices, warehouses, factories, etc. To beginning of document For information about this web site, click here. Purpose of this web site and disclaimer, click here. To find out How to use this web site, click here. The layout of this web site has been tested using Internet Explorer 6.0, Navigator 7.0 and Firefox 0.9.