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Presentation on earthquake resistance  massonary structure

Presentation on earthquake resistance massonary structure






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    Presentation on earthquake resistance  massonary structure Presentation on earthquake resistance massonary structure Presentation Transcript

    • INTRODUCTION *What is earthquake resistance masonry structure *stresses in masonry walls during earthquake ground motions. *Applied element modeling of masonry. *Flow chart of AEM numerical analysis for masonry *wall behavior analysis *How buildings can be made more resistant to earthquakes *Earthquake Resistant Features in Buildings *Advantages of masonry building *conclusion
    • WHAT IS EARTHQUAKE RESISTANCE MASONRY STRUCTURE A structure which is constructed from the materials used by masons, such as stone, brick, tiles, or the like is called massonary structure. Masonry structures are very weak to resist the earthquake force as they have very less ductility.so to increase the ductility of the masonry structures containment reinforcement are provided. The structure made of the combination of the materials like bricks , stones etc and containment reinforcement to resist the earthquake forces is called earthquake resistance masonry structure.
    • STRESSES IN MASONRY WALLS DURING EARTHQUAKE GROUND MOTIONS The walls of a masonry building offer resistance against lateral dynamic loads by developing flexural and shear stresses, during earthquake ground motions. In an attempt to identify the regions in a masonry building where the flexural stresses and shear stresses are a maximum during an earthquake, a linear dynamic analysis has been carried out on a typical single storied masonry building of plan dimensions 6.0m x 3.0m, when subjected to earthquake ground motions. It is assumed that the earthquake ground motion is perpendicular to the cross walls of 6.0m length. Two openings were provided in the cross-walls and none in the shear-walls.
    • The areas of maximum stress in single storied building when subjected to the earthquake ground motions are given in the fig.below
    • The behavior of masonry buildings under lateral dynamic loads is rather complicated basically due to complexities of the walls such as orthotropy, presence of openings, continuity at junctions of cross-walls and shearwall etc. However, all these can be conveniently modeled using finite element technique.
    • EXAMPLES • Wall Failure • Shear Failure
    • APPLED ELEMENT MODELLING OF MASONRY In AEM, structure is assumed to be virtually divided into small square elements each of which is connected by pairs of normal and shear springs set at contact locations with adjacent elements. These springs bear the constitutive properties of the domain material in the respective area of representations (Fig.below). Global stiffness of structure is built up with all element stiffness contributed by that of springs around corresponding element.  Stress and strain are defined based on displacement of spring end points of element edges.
    •  As AEM so far has been used for homogeneous media like concrete and soil, to develop an application of it for multi-phase heterogeneous blocky material like masonry, it requires development of some technique that can address the particular features of masonry.  The flow as shown in chart 1 has been applied for the solution
    • WALL BEHAVIOR ANALYSIS Cracking Cracking in wall started from very early stage of loading initiating from loaded diagonal corners of opening. The cracks propagated towards the wall corner points. However, when cracking reached vicinity of corners where enough compression has been built, further propagation stopped and new small cracks appeared at opposite wall faces. After maximum resistance was attained, those major cracks had break through along the wall diagonal. Though the cracks lie mainly in mortar regions, there is also splitting of brick units near left bottom corners .
    •  The crack location and evolution obtained by analysis agrees well with reported observation. Crack pattern observed in test and obtained through analysis
    • Flow of Stress 1. Through numerical analysis, it is observed that with the increment of imposed displacement at top right corner, both compression and tension stress level increase. Compression occurs in two diagonal bands on either side of the opening and whereas tension takes place in opposite corner locations and middle diagonal band. Initial cracking takes place in those tension spots. As load increases by virtue of increased displacement, compression stress concentration takes place in four locations as marked in fig. below apparently forming hinges. 2. when cracks passed throughout diagonal crossing high compression zone, compression stress level does not increase and earlier high level of tension is reduced. This may be due to sliding of upper triangular part of wall over lower one through stepped cracks. In this state, energy is dissipated through sliding and wall behaves in ductile manner
    • Load-Displacement Relation Stiffness degradation starts when stress state lies on compression cap envelop where shear resistance is reduced with increment in compression. Sliding of upper part is represented by the flat plateau of load displacement curve. It is observed that load-displacement behavior in experiment is well captured by numerical analysis. From these observations, it is noted that though early response of masonry shear wall is mainly due to de-bonding and friction sliding, reduction in shear resistance in high compression governs the peak load and post peak behavior.
    • HOW BUILDINGS CAN BE MADE MORE RESISTANT TO EARTHQUAKES  Flexibility • One of the most crucial physical features of earthquake resistant buildings and structures is flexibility. Buildings and their foundations need to be built to defy side to side movement • Taller buildings are naturally more flexible than low rise buildings and structures.  Reinforced Walls, Beams and Trusses Walls should also be strong enough to take the swaying load of an earthquake. The walls must sway and go equally in both directions. Reinforced beams and joints can also help prevent deformity and collapse of buildings and structures during and after an earthquake .
    •  Foundation Foundational plates and cushions can be layered to let the sliding movement and absorb the shock and movement during an earthquake. These specially designed foundation plates and cushions can help limit damage and help prevent collapse of buildings and structures.  The Future Progress in the field of structural engineering looks promising. Advances in the field of structural engineering and manufacturing of building materials are being done and new and more superior construction materials are emerging. Earthquakeproof buildings and structures may soon be a reality.
    • SHOCK TABLE TEST FACILITY Shock table test facility for evaluating seismic performance of buildings was designed and constructed. The table is of size 3.5m by 2.5m and is supported on 4 wheels with ability to move horizontally in one direction on rails. The table can be subjected to shocks through a swinging pendulum of 600kg mass with provision to increase the mass up to 1000kg. On the side of the table opposite to the pendulum, provision is made to generate a reverse shock through a reaction beam. The impulse force that can be given to the table can be varied by changing the swing angle of the pendulum, mass of the pendulum, the material to which the pendulum impacts. The reverse force to the table can also be varied by changing the gap between the table and the reaction beam before the start of the test. The photograph shows two brick masonry building models with different earthquake resistant features on the shock table with instrumentation to measure the table motion and the response of the building models.
    • Shock Table Test Facility for Evaluating Earthquake Resistant Features in Buildings Research & Development   Peak table acceleration 1.1g  Indigenous design and fabrication of test facility Novel earthquake resistant features for masonry buildings Simulating failure patterns same as those observed in buildings after an earthquake Pendulum (1.8m length & 600kg mass Max. swing 400) Masonry Building Models Rebound beam containment reinforcement with link Table acceleration response for a swing angle of 300 Table (payload 5000kg) Fund. Freq. 90Hz Data acquisition system Corner containment reinforcement with triangular link
    • Behavior of building models after 13 shocks Response after 5 shocks One fourth scale models Model 1 Response at top of cross wall Model 1 (ERF as per IS 4326:1993) Model 2 (ERF as per IS 4326:1993 plus additional R C band at Sill level and Containment reinforcement Model 2 Response at top of cross wall
    • CONCEPT OF CONTAINMENT REINFORCEMENT It is well known that most of the structures tend to undergo large deformations in the event of a strong earthquake. If the stresses caused due to lateral forces experienced by the structures exceed its strength, the structure yields, if it is ductile. If the structure is brittle, as in the case of un-reinforced masonry, it will suffer brittle failure. The pattern of failure of masonry buildings during an earthquake makes it clear that the prevention of sudden flexural failure of masonry wall is critical to ensure an earthquake resistant masonry structure. Again, since flexural tension can occur on both faces of the wall due to reversal of stresses during an earthquake, there is a need to provide ductile reinforcement on both faces. This can be accomplished by placing vertical reinforcement either on the surface or close to the surface and surrounding the wall, which is termed as “containment reinforcement”. Containment reinforcement is not primarily intended to increase the lateral strength of the wall, but to permit large ductile deformation and to avoid total collapse. In other words, containment reinforcement will act as main energy absorbing element of the wall which otherwise has poor energy absorption capacity.
    • Containment reinforcementent Link/tiese Masonry with containment reinforcement and links/ties connecting them through bed joints.
    • ADVANTAGE OF MASONRY BUILDING The use of materials such as brick and stone can increase the thermal mass of a building. Brick typically will not require painting and so can provide a structure with reduced life-cycle costs. Masonry is very heat resistant and thus provides good fire protection. Masonry walls are more resistant to projectiles, such as debris from hurricanes tornadoes. Masonry structures built in compression preferably with lime mortar can have a useful life of more than 500 years as compared to 30 to 100 for structures of steel or reinforced concrete.
    • Plate 4: Out-of plane failure of wall leading to collapse of lintel band (Bhuj)
    • Plate 3: Out-of-plane failure of sandstone in lime mortar masonry wall (Morbi)
    • Plate 6: Collapse of walls between openings (Khavda)
    • CONCLUSION we conclude that the un-reinforced masonry structures are more vulnerable to damage than the reinforced structure during an earthquake. The reinforced structure can withstand greater magnitudes of earthquakes and more earthquakes than the un-reinforced structures