Analysis And Design Of Shear Wall

• For a structural engineer a tall building can be defined as one whose structural system must be modified to make it sufficiently economical to resist lateral forces due to wind or earthquakes within the prescribed criteria for strength, drift and comfort of the occupants. • High land prices, limitations of its availability, transport problems and in-creasing availability of energy, advance in technology and communications among other between them, are moving the society to grow vertical. • Between 1940 and 1950 shear walls were introduced as an economical efficient bracing system for multistoried buildings.

• Traditionally, the primary concern of the structural engineer designing a building has been the provision of a structurally safe and adequate system to support vertical loads. • The effect of lateral loads like wind loads, earthquake force and blast force etc., are attaining increasing importance and almost every designer is faced with the problem of providing adequate strength and stability against lateral loads.

• The buildings are subjected to both vertical and horizontal loads. • Ideally an efficient system should not require an increase in the sizes of members when the effect of lateral loads is also incorporated('Premium free design’ ). • Horizontal loads can be divided into the following three categories: (I) Wind loads (ii) Earthquake loads, and (iii) Blast loads.

The structural requirements are: (a) Strength (b) Stiffness (c) Stability The functional requirements are: To prevent non-structural damage in frequent minor ground shaking  To prevent structural damage and minimize non-structural damage in occasional moderate ground shaking  To avoid collapse or serious damage in rare major ground shaking

• Reinforced concrete (RC) buildings often have vertical plate-like RC walls called Shear Walls. • Shear walls are vertical elements of the horizontal force resisting system or Shear walls are vertical walls that are designed to receive lateral forces from diaphragms and transmit them to the ground. • The forces in these walls are predominantly shear forces in which the fibers within the wall try to slide past one another

• Shear walls provide large strength and stiffness to buildings in the direction of their orientation. • shear walls carry large horizontal earthquake forces, the overturning effects on them are large. • Shear walls should be provided along preferably both length and width. • Door or window openings can be provided in shear walls, but their size must be small to ensure least interruption to force flow through walls. • Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in buildings.

• Simple rectangular types and flanged walls(bar bell type) • Coupled shear walls • Rigid frame shear walls • Framed walls with in filled frames • Column supported shear walls • Core type shear walls

• Shear walls, in particular, must be strong in themselves and also strongly connected to each other and to the horizontal diaphragms. • In a simple building with shear walls at each end, ground motion enters the building and creates inertial forces that move the floor diaphragms. • This movement is resisted by the shear walls and the forces are transmitted back down to the foundation. • While designing the walls a balance must be found in the ratio of vertical load and ductility. • The possibility of any of the modes of failure occurring can be minimized by increasing the vertical load on the wall.

As shear walls act primarily as cantilevers they have three basic failure modes.

• The stiffness of the shear wall, just like its strength, depends on the combined stiffness of its components. • Shear walls provide stiffness in large part by the ratio of their height to width. • Long short walls are stiffer than tall narrow ones. • For a wall of constant height, the stiffness will grow exponentially as the wall length increases.

• Properly designed and detailed buildings with shear walls have shown very good performance in past earthquakes. • In past earthquakes, even buildings with sufficient amount of walls that were not specially detailed for seismic performance (but had enough well-distributed reinforcement) were saved from collapse. • Shear walls are easy to construct, because reinforcement detailing of walls is relatively straightforward and therefore easily implemented at site.

Japanese concrete shear-wall apartment buildings after the 1964 M 7.2 Niigata earthquake. Despite the fact that the foundations of the buildings failed due to liquefaction, the building structures were undamaged and the buildings were later jacked back to an upright position and they were reoccupied.

Shear core used in multi-storey structure (NZ).

Millikan Library, a 9 story building in Pasadena, CA, USA

El Castillo Building in Mayaguez, Puerto Rico. 19story, 2 basement concrete shear wall structure

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• Murthy, C.V.R. (2004), Earthquake tip 23, IITK-bmtpc Earthquake tips, IIT Kanpur, India. • IS 1893(Part 1) : 2002, Criteria for Earthquake Resistant Design of Structures, BIS, New Delhi • IS 13920: 1993 code of practice for Ductile detailing of reinforced concrete structures subjected to seismic forces. • P.C.Varghese, “Advanced Reinforced Concrete Design”, PrenticeHall of India Private Limited, New Delhi, 2001 . • Paulay,T. and Priestley, M.J.N (1992) , Seismic design of reinforced concrete and masonry buildings. • Farzad Naeim, “The seismic design handbook”, Chapman and Hall, New York-1999. • J. N. Bandyopadhyay, “Earthquake Resistant Design and Detailing of RCC structures as per codal provisions”, chapter 17-SE 106 NPCBEERM, MHA (DM).