A Comparative Study on Analysis and Design of vertical irregular Buildings with Moment Resisting Frames and Dual Systems in High Seismic Zones

A Comparative Study on Analysis and Design of vertical irregular Buildings with Moment Resisting Frames and Dual Systems in High Seismic Zones

1 INTRODUCTIONThe basic objective of design of earthquake resistant structure is to resist from collapse during earthquakes by minimizing the risk of death or injury to people. The earthquake forces are generated by inertial forces exerted by earthquake waves as they dynamically respond to ground motion. The earthquake loads are different because of its dynamic nature and are different from other structural loads. The designer has to consider the earthquakes as strong ground motion and thus earthquake generated actions are able to solve. A good earthquake engineering design is one where designer as a control of the building by dictating how the building is respond after analysing. The earthquake motion records are the main input for designing the earthquake dynamic analysis as a main part of design of earthquake resistant structures.A multi-storey building is a vertically cantilevered structure from the ground surface subjected to lateral forces and gravity loading. It contains mainly frames, shear wall systems and slab structures, they distribute the lateral forces and axial loads imposed on building. The lateral forces generated due to inertial forces induced by seismic forces which results in developing shear and building. These forces can be resisted by use of dual system is one of the most efficient method of improving the stability of the multi-storey building.The buildings taller than 12 storeys, the frame action of beam and column is not adequate to give the required lateral stiffness. However it can be improved by placing shear walls as it very effective in maintaining stability of multi-storey building under earth quake loading. KeywordsOMRF, Dual System, Structural Irregularities, Stiffness irregularities, I.S 1893:2002(Part1) Provisions, Base Shear, Storey Drift

1.1 ObjectiveIn todays booming development of the world in construction technologies, several structural systems are introducing for resistance to gravity loads and lateral loads coming from the earthquake. The main objective of this project is to know the structural system which is efficient in resisting lateral force and providing safety to life of the structure. By comparing with OMRF and dual system for different patterns with same data, it is easy to conclude the best structural system.

1.2 MotivationIn previous days of building constructions in India, use of shear wall structural system is very rare because of scarcity of detailing shear wall in construction and execution. But later on developments experiments on shear wall system is carried. Through the experiments later on concluded that the moment resisting frame with shear wall system provides a sufficient resistance to the wind loads and lateral force. This provides us to find a comparison in our project on effectiveness of shear wall and OMRF in high seismic zones. In this dual system the different shear wall systems such as plain shear wall and coupled shear wall systems are also compared.1.3 MethodologyFor the design and analysis of the structural 2D and 3D models ETABS software is used. The 2D and 3D models are differentiated with different patterns for the analysis and they are listed below,2D Models:Type-1: Ordinary Moment Resistant Frame system [OMRF].Type-2: OMRF with plain shear wall.Type-3: OMRF with shear wall plus flat slab.Type-4: OMRF with coupled shear wall plus flat slab3D Models:Case-1: Ordinary Moment Resistant Frame system [OMRF].Case-2: OMRF with coupled shear wall [shear walls at opposite sides].Case-3: OMRF with coupled shear wall [shear walls at corners].Case-4: OMRF with coupled shear wall [shear wall as at channel sections].Case-5: OMRF with coupled shear wall [shear wall as core wall].After generating models the analysis is carried and graphs are generated for displacements, base shear and push over analysis for all the patterns shown above, particularly for the zone-5 with zone factor 0.36. The load combinations, static load cases, mass source and earthquake coefficients are derived in ETABS software.1.4 Scope of the study:The present work is focused on seismic response of the structure in high seismic zones. Seismic zone-5 is considered as the high seismic zone in India, which is having a zone factor of 0.36. In this zone we can expect a magnitude of the earth quake up to 8 and above. For this reason it is require to know the type of structural system, in which it is to be safe and results in good performance of its life. The ordinary moment resisting frames and dual systems are considered for the analysis. The different cases of the shear wall systems are analyzed for the displacements, base shear to determine the system which is safe. The push over analysis is also performed on the structure to know the seismic performance of the structure.The ETABS software is used for project work for the analysis and generation of graphs, the manual calculations are also made to compare with software results. 1.5 Definitions in Earth Quake Resistant Structures: [Earthquake Coefficients] Intensity of Earthquake: The intensity of an earthquake at a place is a measure of the strength of shaking during earthquake, and is indicated by a number according to the Modified Mercalli Scale or M.S.K Scale of Seismic Intensities.

Magnitude of the earthquake: The magnitude of earthquake is a number, which is a measure of energy released in an earthquake.

Seismic Weight (W): It is the total dead load plus appropriate amounts of specified imposed load.

Zone Factor (Z): It is a factor to obtain the design spectrum depending on the perceived maximum seismic risk characterized by Maximum Considered Earthquake (MCE) in the zone in which the structure is located. The basic zone factors included in this standard are reasonable estimate of effective peak ground acceleration.

Structural Response Factors ( Sa/g ): It is a factor denoting the acceleration response spectrum of the structure subjected to earthquake ground vibrations, and depends on natural period of vibration and damping of the structure.

Natural Period (T): Natural period of a structure is its time period of undamped free vibration.

Design horizontal acceleration coefficient (Ah): It is thehorizontal acceleration coefficient that shall be used for design of structures.

Response Reduction Factor (R): It is the factor by which the actual base shear force that would be generated if the structure were to remainelastic during its response to the Design Basis Earthquake (DBE) shaking, shall be reduced to obtain the design lateral force.

Ordinary Moment-Resisting Frame: It is a moment-resisting frame not meeting special detailing requirements for ductile behavior.

Dual System: Buildings with dual system consist of shear walls(or braced frames) and moment resisting frames such that: The two systems are designed to resist the total design lateral force in proportion to their lateral stiffness considering the interaction of the dual system at all floor levels; and The moment resisting frames are designed to independently resist at least 25 percent of the design base shear.

Storey Drift: It is the displacement of one level relative to the other level above or below.

2. LITERATURE SURVEY Shaikh Abdul Aijaj Abdul Rahman, Girish Deshmukh (2013) : Seismic Response of Vertically Irregular RC Frame with Stiffness Irregularity at Fourth Floor. Structural engineer's greatest challenge intodays scenario is constructing seismic resistant structure.Uncertainties involved and behavior studies are vital for all civil engineering structures. The presence of vertical irregular frame subject to devastating earthquake is matter of concern. The present paper attempts to investigate theproportional distribution of lateral forces evolved through seismic action in each storey level due to changes in stiffness of frame on vertically irregular frame. As per the Bureau of Indian Standard (BIS) 1893:2002(part1) provisions, a G+10 vertically irregular building is modeled as an simplified lump mass model for the analysis with stiffness irregularity at fourth floor. To response parameters like story drift, story deflection and story shear of structure under seismic force under the linear static & dynamic analysis is studied. This analysis shows focuses on the base shear carrying capacity of astructure and performance level of structure under severer zone of India. The result remarks the conclusion that, a building structure with stiffness irregularity provides instability and attracts huge storey shear. A proportionate amount of stiffness is advantageous to control over the storey and base shear. The soft computing tool and commercial software CSI-ETABS (version 9.7) is used for modeling and analysis.

Anantwad Shirish, Prof.M.R.Wakchaure ,Rohit Nikam : Effect of Plan Irregularity on High-rise Structures : This paper aims at studying description of different plan irregularities by analytical method during seismic events. In all the studied systems from which dual system is chosen for analysis and studying its effects on different irregularities in which analysis is based on the variation of displacements, with respect to structural systems. Analyses have been done to estimate the seismic performance of high rise buildings and the effects of structural irregularities in stiffness, strength, mass and combination of these factors are to be going to be considered. The work describes to the irregular plan geometric forms that are repeated more in the metro city areas such as Mumbai like T-section and Oval Shape plan geometry. These irregular plans were modelled in ETABS 9.7v considering 35 and 39 storied buildings, to determine the effect of the plan geometric form on the seismic behaviour of structures with elastic analyses. Also, effects of the gust factor are considering in T-shape and Oval Shape plans. Although these affects mainly on the architectural plan configuration, plan irregularity find better structural system solution such as dual system has been use for structural analysis. In structural configuration shear wall positions located are located in the form of core and columns are considered as gravity as well as lateral columns. Two types of models are going to be developed namely strength & serviceability models. In strength model all the lateral systems (i.e. shear walls and coupling beams) are to be analyzed.

2.1 Characteristics of Earthquakes:Earthquakes are caused by the slippage of adjacent plates of the earths crust and the subsequent release of energy in the form of ground waves. Seismology is based on the science of plate tectonics, which proposes that the earth is composed of several very large plates of hard crust many miles thick, riding on a layer of molten rock closer to the earths core. These plates are slowly moving relative to one another, and over time tremendous stress is built up by friction. Occasionally the two plates slip, releasing the energy which is known as earthquakes. One of the most well known boundaries between two plates occurs between the Pacific plate and the North American plate along the coast of California. Earthquakes also occur in mid plates, but the exact mechanism, other than fault slippage, is not fully understood. The plates slip where the stress is maximum, usually several miles below the surface of the earth. Where this occurs is called the hypocenter of the earthquake. The term heard more often is the epicenter, which is the point on the earths surface directly above the hypocenter.When an earthquake occurs, complex actions are set up. One result is the development of waves that ultimately produce the shaking experienced in a building. There are three types of waves: P or pressure waves, S or shear waves, and surface waves. Pressure waves cause a relatively small movement in the direction of wave travel. Shear waves produce a sideways or up-and-down motion that shakes the ground in three directions. These are the waves that cause the most damage to buildings. Surface waves travel at or near the surface and can cause both vertical and horizontal earth movement.The ground movement can be measured in three ways: by acceleration, velocity, and displacement. All three occur over time, with most earthquakes lasting only a few seconds. It is the acceleration of the ground that induces forces on a structure.The interaction of the various waves and ground movement is complex. Not only does the earth move in three directions, but each direction has a different, random acceleration and amplitude. In addition, the movement reverses, creating a vibrating action. Even though there is vertical movement which is to be neglected under certain types of seismic design. The weight of a structure is usually enough to resist vertical forces. It is the side-to-side movement that causes the most damage.[4]

2.2 Measurement of Earthquakes:Earthquake strength is commonly measured in two ways: with the Richter Scaleand with the Modified Mercalli Intensity Scale. The Richter Scale measures magnitude as an indirect measure of released energy based on instrument recordings according to certain defined procedures. The scale runs from zero at the low end and is open at the upper end, although the largest earthquake ever recorded had a Richter magnitude of nine.The Modified Mercalli Intensity Scale is a measure of an earthquakes intensity. It is an entirely subjective rating based on the observed damage to structures and other physical effects. The scale ranges from I to XII, with the upper rating being the most severe. Each scale includes a verbal description of the effects and damage of an earthquake. The records obtained by these instruments provide valuable data for research and design of similar buildings in the same geographical area. The acceleration they measure is usually expressed as a fraction of the acceleration of gravity, g, which is 32 feet per second. Thus, an earthquake may be recorded as having an acceleration of 0.55g.[4]

2.3 The Effect of Earthquakes on Buildings:When an earthquake occurs, the first response of a building is not to move at all due to the inertia of the structures mass. Almost instantaneously, however, the acceleration of the ground causes the building to move sideways at the base causing a lateral load on the building and a shear force at the base, as though forces were being applied in the opposite direction. See Figure below. As the direction of the acceleration changes, the building begins to vibrate back and forth.

Fig 2.1: (a) Response of a Building to Earthquake (b) Period of a Building

Theoretically, the force on the building can be found by using Newtons law, which states that force equals mass times acceleration. Since the acceleration is established by the given earthquake, the greater the mass of the building, the greater the force acting on it. However, the acceleration of the building depends on another property of the structure by its natural period.If a building is deflected by a lateral force such as the wind or an earthquake, it moves from side to side. The period is the time in seconds it takes for a building to complete one full side-to-side oscillation. See Fig 2.2 (b). The period is dependent on the mass and the stiffness of the building.In a theoretical, completely stiff building, there is no movement, and the natural period is zero. The acceleration of such an infinitely rigid building is the same as the ground. As the building becomes more flexible, its period increases and the corresponding acceleration decrease. As mentioned above, as the acceleration decreases, so does the force on the building. Therefore, flexible, long-period buildings have less lateral force induced, and stiff, short-period buildings have more lateral force induced.As the building moves, the forces applied to it are either transmitted through the structure to the foundation, absorbed by the building components, or released in other ways such as collapse of structural elements. The goal of seismic design is to build a structure that can safely transfer the loads to the foundation and back to the ground and absorb some of the energy present rather than suffering damage. The ability of a structure to absorb some of the energy is known as ductility, which occurs when the building deflects in the inelastic range without failing or collapsing. The elastic limit is the limit beyond which the structure sustains permanent deformation. The greater the ductility of a building, the greater is its capacity to absorb energy. Ductility varies with the material. Steel is a very ductile material because of its ability to deform under a load above the elastic limit without collapsing. Concrete and masonry, on the other hand, are brittle materials. When they are stressed beyond the elastic limit, they break suddenly and without warning. Concrete can be made more ductile with reinforcement, but at a higher cost.[4]

2.4 The Basic Principles of Earthquake Resistant Design:Earthquake forces are generated by the dynamic response of the building to earthquake induced ground motion. This makes earthquake actions fundamentally different from any other imposed loads. Thus the earthquake forces imposed are directly influenced by the dynamic inelastic characteristics of the structure itself. While this is a complication, it provides an opportunity for the designer to heavily influence the earthquake forces imposed on the building. Through the careful selection of appropriate, well distributed lateral load resisting systems, and by ensuring the building is reasonably regular in both plan and elevation, the influence of many second order effects, such as torsion effects, can be minimized and significant simplifications can be made to model the dynamic building response. Most buildings can be reasonably considered as behaving as a laterally loaded vertical cantilever. The inertia generated earthquake forces are generally considered to act as lumped masses at each floor (or level). The magnitudes of these earthquake forces are usually assessed as being the product of seismic mass (dead load plus long-term live load) present at each level and the seismic acceleration generated at that level. The design process involves ensuring that the resistance provided at each level is sufficient to reliably sustain the sum of the lateral shear forces generated above that level.[5]

2.5 Structural Systems to Resist Lateral Loads:

2.5.1 Bearing wall system:A bearing wall system is a structural system without a complete vertical load carrying space frame, in which the lateral loads are resisted by shear walls orbraced frames. Bearing walls or bracing systems provide support for all or most gravity loads. Remember that a space frame is defined as a three-dimensional structural system, without bearing walls that is comprised of members interconnected such that it functions as a complete, self-contained unit.

2.5.2 Building Frame Systems:A building frame system is one with an essentially complete space frame that provides support for gravity loads in which the lateral loads are resisted by shear walls or braced frames. A braced frame is a truss system of the concentric or eccentric type in which the lateral forces are resisted through axial stresses in the members. Just as with a truss, the braced frame depends on diagonal members to provide a load path for lateral forces from each building element to the foundation. Fig 2.2(a), shows a simple one-story braced frame. At one end of the building two bays are braced and at the other end only one bay is braced. As with Fig 2.2 (b), this building is only braced in one direction and uses compression braces because the diagonal member may be either in tension or compression, depending on which way the force is applied. Fig 2.2(b) shows two methods of bracing multi-storey building. A single diagonal compression member in one bay can be used to brace against lateral loads coming from either direction. Alternately, tension diagonals can be used to accomplish the same result, but they must be run both ways to account for the load coming from either direction.

Fig 2.2: (a) Single Story Braced Frame (b) Multi Story Braced FrameBraced framing can be placed on the exterior or interior of a building, and may be placed in one structural bay or several. In a trussed tube building, the diagonals span between several floors of the building. Obviously, a braced frame can present design problems for windows and doorways, but it is a very efficient and rigid lateral Force resisting system. [4]

2.5.3 Dual Systems:A dual system is a structural system in which an essentially complete frame provides support for gravity loads, and resistance to lateral loads is provided by a specially detailed moment-resisting frame and shear walls or braced frames. The moment-resisting frame must be capable of resisting at least 25 percent of the base shear, and the two systems must be designed to resist the total lateral load in proportion to their relative rigidities.Horizontal Elements :I n all lateral force-resisting systems, there must be a way to transmit lateral forces to the vertical resisting elements. This is done with several types of structures, but the most common way used is the diaphragm. A diaphragm acts as a horizontal beam resisting forces with shear and bending action. Other types of horizontal elements include horizontal trussed frames and horizontal moment-resisting frames. There are two types of diaphragms: flexible and rigid. Although no horizontal element is completely flexible or rigid, distinction is made between the two types because the type affects the way in which lateral forces are distributed. A flexible diaphragm is one that has a maximum lateral deformation more than two times the average story drift of that story. This deformation can be determined by comparing the midpoint in-plane deflection of the diaphragm with the story drift of the adjoining vertical resisting elements under equivalent tributary load. The lateral load is distributed according to tributary areas. With a rigid diaphragm, the shear forces transmitted from the diaphragm to the vertical elements will be in proportion to the relative stiffness of the vertical elements (assuming there is no torsion). If the end walls in the diagram are twice as stiff as the interior walls, then one-third of the load is distributed to each end wall and one-third to the two interior walls which is equally divided between these two. The illustration shows symmetrically placed shear walls, so the distribution is equal. However, if the vertical resisting elements are asymmetric, the shearing forces are unequal. Concrete floors are considered rigid diaphragms, as are steel and concrete composite deck construction. Steel decks may be either flexible or rigid, depending on the details of their construction. Wood decks are considered flexible diaphragms.[4]

2.5.4 Moment Resisting Frames:Moment resisting frames typically comprise floor diaphragms supported on beams which link to continuous columns. The joints between beam and columns are usually considered to be Rigid. The frames are expected to carry the gravity loads through the flexural action of the beams and the propping action of the columns. Lateral loads, imposed within the plane of the frame, are resisted through the development of bending moments in the beams and columns. Framed buildings often employ moment resistant frames in two orthogonal directions, in which case the column elements are common to both frames. Moment resisting frames are well suited to accommodate high levels of inelastic deformation. When a capacity design approach is employed, it is usual to assign the end zones of the flexural beams to accept the post-elastic deformation expected, and to design the column members such that their dependable strength is in excess of the over-strength capacity of the beam hinges, thereby ensuring they remain within their elastic response range regardless of the intensity of ground shaking. Moment resisting frames are, however, often quite flexible. When they are designed to be fully ductile, special provisions are often needed to prevent the premature onset of damage to non-structural components. [5]2.5.5 Braced Frames:Frames which employ diagonal braces as the means of transmitting lateral load are common in low-rise and industrial buildings. The bracing elements are typically inclined axially loaded members which traverse diagonally between floors and column lines. They are very efficient in direct tension and may also be detailed to accept axial compression although suppression of compression buckling requires careful assessment of element slenderness. Two major shortcomings of braced systems are that their inclined diagonal orientation often conflicts with conventional occupancy use patterns (either internally or across windows or external fabric penetrations); and secondly they often require careful detailing to avoid large local torsion eccentricities being introduced at the connections with the diagonal brace being offset from the frame node. A variation on this form of lateral resisting system is the eccentrically braced frame. This system employs a horizontal K form of bracing with the central zone of the K acting in flexure as the tension/compression legs of the brace drive the beam element into direct flexure.[5]

2.5.6 Shear wall systems:A shear wall is a vertical structural element that resists lateral forces in the plane of the wall through shear and bending. Such a wall acts as a beam cantilevered out of the ground or foundation, and, just as with a beam, part of its strength derives from its depth. Figure shows two examples of a shear wall, one in a simple one story building and another in a multi-storey building.

Fig 2.3: (a) End Shear Wall and Interior Shear Wall (b) Interior Shear Wall for Bracing in Two DirectionsIn Fig 2.3 (a), the shear walls are oriented in on direction, so only lateral forces in this direction can be resisted. The roof serves as the horizontal diaphragm and must also be designed to resist the lateral loads and transfer them to the shear walls. This is also shows an important aspect of shear walls in particular and vertical elements in general. This is the aspect of symmetry that has a bearing on whether torsional effects will be produced. The shear walls in Fig 2.3(a) show the shear walls symmetrical in the plane of loading. Fig 2.3(b) Illustrates a common use of shear walls at the interior of a multi-storey building. Because walls enclosing stairways, elevator shafts, and mechanical chases are mostly solid and run the entire height of the building, they are often used for shear walls. Although not as efficient from a strictly structural point of view interior shear walls do leave the exterior of the building open for windows.Notice that in Fig 2.3(b) the shear walls in both directions, which is a more realistic situation because both wind and earthquake forces need to be resisted in both directions. In this diagram, the two shear walls are symmetrical in one direction, but the single shear wall produces a non-symmetric condition in the other since it is off center. Shear walls do not need to be symmetrical in a building, but symmetry is preferred to avoid torsional effects. Shear walls can be constructed from a variety of materials, but the most common are plywood on wood framing for residential and small commercial buildings, and concrete for larger buildings. Reinforced masonry walls can also be used. Shear walls may have openings in them, but the calculations are more difficult and their ability to resist lateral loads is reduced depending on the percentage of open area. The primary function of shear walls is to resist lateral loads although they are often used in conjunction with gravity frames and carry a proportion of gravity loads. Shear walls fulfill their lateral load resisting function by vertical cantilever action. It can be seen that both the shear force and bending moment generated by the earthquake actions increase down the height of the building. Since shear walls are generally both stiff and can be inherently robust, it is practical to design them to remain nominally elastic under design intensity loadings, particularly in regions of low or moderate seismicity. Under increased loading intensities, post-elastic deformations will develop within the lower portion of the wall (generally considered to extend over a height of twice the wall length above the foundation support system). This can result in difficulties in the provision of adequate foundation system tie-down to prevent uplift. The design of rocking foundations is common with shear walls, although care is required to ensure permanent rotational offsets are avoided following an earthquake. A good post-elastic response can be readily achieved within this region of reinforced concrete or masonry shear walls through the provision of adequate confinement of the principal reinforcing steel and the prohibition of lap splices of reinforcing bars. Shear wall structures are generally quite stiff and, as such inter-storey drift problems are rare and generally easily contained. The shear wall tends to act as a rigid body rotating about a plastic hinge which forms at the base of the wall. Overall structural deformation is thus a function of the wall rotation. Inter-storey drift problems which do occur are limited to the lower few floors. A major shortcoming with shear walls within buildings is that their size provides internal (or external) access barriers which may contravene the architectural requirements. This problem can be alleviated by coupling adjacent more slender shear walls. The coupling beams then become shear links between the two walls and with careful detailing can provide a very effective, ductile control mechanism.[4]Reinforced concrete buildings often have vertical plate like RC walls called Shear Walls in addition to slabs, beams and columns. These walls generally start at foundation level and are continuous throughout the building height. Their thickness can be as low as 150mm, or as high as 400mm in high rise buildings. Shear walls are usually provided along both length and width of buildings. Shear walls are like vertically-oriented wide beams that carry earthquake loads downwards to the foundation.[2]Shear walls have been the most lateral force resisting elements for tall building besides frame systems. It is an efficient method of ensuring the lateral stability of tall buildings and also efficient against torsion effects when combined together with frame structures. Their stiffness is such that sway movement under wind load can be minimized. The structural forms of shear walls are commonly used in buildings with 10 to 30 story. Monolithic shear wall can be classified as short, squat or cantilever as in according to their height/depth ratio. The shear walls may be planner, flanged or core in shape. [1]

2.5.7 Coupled shear walls:Coupled shear wall is a continuous wall with vertical rows of opening created by windows and doors, coupled by connecting beams. When two or more shear walls are interconnected by a system of beams and slabs, the total stiffness of the system exceeds the summation of the individual wall stiffness because the connecting slab or beam restraints the individual cantilever action by forcing the system to work as composite unit. Such an interacting shear wall system can be used economically to resist lateral loads in buildings up to about 40 stories. Shear walls may come in many forms and there are various types of opening shape due to architectural and planning requirement as shown fig below. However, due to ease of analysis, design and construction, regular shapes with openings throughout thed height are preferred by the engineers.[1]

Staggered bandSingle bandSingle band

Wide baseThree bandsTwo bandsAsymmetric

Fig 2.4:Typical Arrangement of Elevation

Fig 2.5: Plan Shapes of Shear Wall Structures2.5.8 Advantages of Shear Walls in RC Buildings:Properly designed and detailed buildings with shear walls have shown very good performance in past earthquakes. The overwhelming success of buildings with shear walls in resisting strong earthquakes is summarized in the quote:We cannot afford to build concrete buildings meant to resist severe earthquakes without shear walls.Shear walls in high seismic regions require special detailing. However, 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 wall buildings are a popular choice in many earthquake prone countries, like Chile, New Zealand and USA. Shear walls are easy to construct, because reinforcement detailing of walls is relatively straight-forward and therefore easily implemented at site. Shear walls are efficient, both in terms of construction cost and effectiveness in minimizing earthquake damage in structural and non-structural non-structural elements (like glass windows and building contents).

2.5.9 Overall Geometry of Shear Walls:Shear walls are oblong in cross-section, i.e., one dimension of the cross-section is much larger than the other. While rectangular cross-section is common, L- and U-shaped sections are also used as shown in fig below. Thin-walled hollow RC shafts around the elevator core of buildings also act as shear walls, and should be taken advantage of to resist earthquake forces.

Fig 2.6: Different Geometries of Shear Wall

2.6 Aspects of shear walls:Most of the RC buildings with shear walls also have columns; these columns primarily carry gravity loads (i.e., those due to self-weight and contents of building). Shear walls provide large strength and stiffness to buildings in the direction of their orientation, which significantly reduces lateral sway of the building and thereby reduces damage to structure and its contents. Since shear walls carry large horizontal earthquake forces, the overturning effects on them are large. Thus, design of their foundations requires special attention. Shear walls should be provided along preferably both length and width. However, if they are provided along only one direction, a proper grid of beams and columns in the vertical plane (called a moment-resistantframe) must be provided along the other direction to resist strong earthquake effects. Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in buildings. They could be placed symmetrically along one or both directions in plan. Shear walls are more effective when located along exterior perimeter of the building such a layout increases resistance of the building to twisting.

2.7 Seismic Zones of India:The varying geology at different locations in the country implies that the likelihood of damaging earthquakes taking place at different locations is different. Thus, a seismic zone map is required to identify these regions. Based on the levels of intensities sustained during damaging past earthquakes, the 1970version of the zone map subdivided India into five zones I, II, III, IV and V. The maximum Modified Mercalli (MM) intensity of seismic shaking expected in these zones were V or less, VI, VII, VIII,and IX and higher, respectively. Parts of Himalayan boundary in the north and northeast, and the Kachharea in the west were classified as zone V.The seismic zone maps are revised from time to time as more understanding is gained on the geology, the seismo-tectonics and the seismic activity in the country. The Indian Standards provided the first seismic zone map in 1962, which was later revised in 1967 and again in 1970. The map has been revised again in 2002, and it now has only four seismic zones II, III, IV and V. The areas falling in seismic zone I in the 1970 version of the map are merged with those of seismic zone II. Also, the seismic zone map in the peninsular region has been modified. Madras now comes in seismic zone III as against in zone II in the 1970 version of the map. This 2002seismic zone map is not the final word on the seismic hazard of the country, and hence there can be no sense of complacency in this regard.The national Seismic Zone Map presents a large-scale view of the seismic zones in the country. Local variations in soil type and geology cannot be represented at that scale. Therefore, for important projects, such as a major dam or a nuclear power plant , t he seismic hazard is evaluated specifically for that site. Also, for the purposes of urban planning, metropolitan areas are micro zoned. Seismic microzonation accounts for local variations in geology, local soil profile.The current generation of earthquake loading standards uses a single seismic zonation map with iso-seismal contours to represent the relative seismicity between locations. The product of the zone factor, Z, and the lateral acceleration coefficient derived from the design spectrum is used for design. 2.8 PROJECT DESIGN

Fig 3.1: Flow chart of system designA dual system is important in high rise buildings to resist the lateral forces coming from earthquakes. So that the dual systems are effective in high seismic zones. A thorough detail on dual systems is collected in literature survey to study and implication for the project. Modeling is carried on the 2D and 3D models through ETABS software with different structural systems such as OMRF and dual system. In the modeling of these structural systems the data regarding the frame properties (columns and beams), material properties are assumed according to the building requirements and earth quake co-efficients are considered from the IS code books.The analysis is carried through the ETABS software and by generating the graphs for displacement, base shear and seismic weights. By comparison of all the graphs we can analyse the structure which can resist the lateral forces. The software and manual calculations are carried for the equivalent static force method to compare on design seismic base shear at the base.

3D MODELLING DATACASE 1 ordinary moment resisting frame(OMRF)Number of floors15+1 terrace roofTypical storey height 3.0 mPlinth level 1.5 m from top of the foundationTotal height of the building 46.5 mBase dimention of the building 50mx40mDiaphragm are 1400 m2 at 1 floor levelGrade of concrete M25Grade of steel fe 415Beam 300x450 mmColumn-300X900 mmSlab 200thk(two way slab)Live load 3 kn/m2Live load reduction considered for the design of vertical structural elementsSUPER Dead load 0.75 kn/m2Terrace live load 1.5 kn/m2

EARTH QUAKE CO-EFFICIENTS: Response reduction factor-3 Importance factor-1 Zone factor-Z=0.10 for zone 2(Low) Z = 0.16 for zone 3(Moderate) Z = 0.24 for zone 4(Severe) Z = 0.36 for zone 5(Very severe)Time period, Ta = 0.075 h^0.75 = 0.075*46.5^0.75 sec

fig3.2: 2D plan and 3D view of OMRF

fig3.3: 2D and 3D view of irregular building with OMRF

Fig: 3.4 2D plan and 3D view of vertical irregular building with OMRF and shear wall

Fig: 3.5 2D and 3D view of vertical irregular building with OMRF and shear wall

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STORY 155.93771.2408

STORY 160.93040.195

Table: 1 storey v/s base shear for model 1 and model 2

STORYMODEL 1MODEL 2

STORY 1118.373272.638

STORY 2114.641567.3259

STORY 3109.72461.8136

STORY 4103.523856.01

STORY 596.126149.9944

STORY 687.859343.9615

STORY 779.134638.1181

STORY 869.748332.2371

STORY 960.094626.5345

STORY 1050.624921.2841

STORY 1140.895616.2273

STORY 1231.309711.6214

STORY 1322.37997.7686

STORY 1413.69524.4296

STORY 156.03951.8271

STORY 160.91870.2842

Table2: story v/s base shear of OMRF and dual system

REFFERENCE[1] NorlizanBinti Wahid, Frame Analysis of Concrete Shear Walls With Openings, Faculty of Civil Engg, University Of Teknologi, Malaysia.[2] C.V.R Murthy, Learning Earth Quake Design and Construction, Indian Institute of Technology, Kanpur.[3] P. S. Kumbhare, A. C. Saoji (2012), Effectiveness of Reinforced Concrete Shear Wall for Multi-Storeyed Building. International Journal of Engineering Research and Technology (IJERT).Vol 1 Issue 4. June 2012.[4] Lateral Forces-Earthquakes, Professional Publications.[5] Andrew king, Structural Engg Section Leader, Earthquake Loads And Earthquake Resistant Design Of Buildings, Building Research Association Of Newzealand.[6] S.H.Song, Y.K.Wen, M.ASCE Redundancy of Dual Systems under Earthquake Loads. University of Illinois, Urbana.

[7] J.Fu, J.I. Shibuya and T.Saito. 3-D Inelastic Earthquake Response of RC Frames With Shear Walls Tohoku University. Japan.

[8] J. P. Moehle and S. A. Mahin. Observations on The Behavior of Reinforced Concrete Buildings During Earthquakes. University of California.Berkely.

[9] BassamBlal. Concept of Structural Design and Evaluation of Multi-storey Building under Wind and Seismic Loads Technical University of Civil Engineering. Bucharest.

[10] V. Kapur, Ashok K. Jain. Seismic Response of Shear Wall Frames Versus Braced Concrete Frames. University of Roorkee. April 1983.

[11] IS 1893 (PART-1) : 2002, Indian Standard Criteria for earthquake resistant design of structures Bureau Of Indian Standards, New Delhi.

[12] IS 456: 2000. Indian Standard Plain and Reinforced Concrete Bureau of Indian Standards, New Delhi.

[13] A. Kadidand A. Boumrkik, Pushover Analysis Of Reinforced Concrete FrameStructures, Asian Journal Of Civil Engineering (Building And Housing) VOL. 9, NO. 1 (2008)

[14] PankajAgarwal and Manish ShrikhandeEarth Quake Resistant Design of Structures

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