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ISSN 2319-8885 Vol.05,Issue.11, May-2016, Pages:2145-2151 www.ijsetr.com Effect of Discontinuous Load Path on Seismic Performance of Building Using SAP2000 BUSHRA GASIM1, T. V. S. VARA LAKSHMI2 1 PG Scholar, Dept of Civil Engineering, University College of Engineering &Technology, A.N.U, Guntur, AP, India. Assistant Professor, Dept of Civil Engineering, University College of Engineering &Technology, A.N.U, Guntur, AP, India. 2 Abstract: During an earthquake, failure of structure starts at points of weakness, this weakness arises due to discontinuity in mass, stiffness and geometry of structure, and these may lead to discontinuity in load path, which plays a very important role in the performance of the structure when it is subjected to earthquake force. The stiffness behavior of the various structural components especially the columns which are the primary elements for taking up the loads tends to lose their stiffness as the height of the structure increases, which is mainly observed in tall buildings. The structures having this discontinuity in mass, stiffness and geometry are termed as irregular structures. In buildings discontinuity in load path mainly arises due to discontinuity in structural members as removal of shear wall in some floors due to parking or in commercial floors due to architectural requirement or by providing floating columns in buildings. Because of the discontinuity in load path the building is effected many unwanted moments and forces in structural members and heavy nodal displacements at the places of discontinuity in structure. Sometimes it makes highly complicate to make those members structurally stabile particularly when it is subjected to lateral forces. In this project the performance of the structural members at the point of discontinuity are studied by analyzing 15 storey building models under seismic zone III using SAP 2000. Keywords: Binarization, Thersholding Image Segmentation, Lloyds Clustering. I. INTRODUCTION A. Dynamic Characteristics Of Buildings Buildings oscillate during earthquake shaking. The oscillation causes inertia force to be induced in the building. The intensity and duration of oscillation, and the amount of inertia force induced in a building depend on features of buildings, called their dynamic characteristics, in addition to the characteristics of the earthquake shaking itself. The important dynamic characteristics of buildings are modes of oscillation and damping. A mode of oscillation of a building is defined by associated Natural Periodand Deformed Shapein which it oscillates. B. Natural Period Natural Period Tn of a building is the time taken by it to undergo one complete cycle of oscillation. It is an inherent property of a building controlled by its mass mand stiffness k. These three quantities are related by (1) C. Effect of Stiffness Increasing the column size increases both stiffness and mass of buildings. But, when the percentage increase in stiffness as a result of increase in column size is larger than the percentage increase in mass, the natural period reduces. Hence, the usual discussion that increase in column size reduces the natural period of buildings, does not consider the simultaneous increase in mass; in that context, buildings are said to have shorter natural periods with increase in column size. D. Effect of Mass Mass of a building that is effective in lateral oscillation during earthquake shaking is called the seismic mass of the building. It is the sum of its seismic masses at different floor levels. Seismic mass at each floor level is equal to full dead load plus appropriate fraction of live load. The fraction of live load depends on the intensity of the live load and how it is connected to the floor slab. Seismic design codes of each country/region provide fractions of live loads to be considered for design of buildings to be built in that country/region. E. Irregularities in Structural Systems Often structural systems are designed having various level irregularities in accordance with architectural requirements in order to produce aesthetic buildings. Irregular structures come into being due to discontinuity in mass, stiffness and strength in elevation and due to asymmetric geometrical configuration on plane. Generally, irregularities are classified as planar and vertical in the seismic codes. On the other hand, seismic codes discourage all type of discontinues, because seismic behavior of structural system and seismic demand on structural systems having irregular configuration or asymmetrical distribution of structural elements generally are Copyright @ 2016 IJSETR. All rights reserved. BUSHRA GASIM, T. V. S. VARA LAKSHMI larger than those of the regular ones. Furthermore, be ensured by following coherent architectural features that irregularities produce uncertainties in the analysis of the result in good structural behaviour. structural system, in the degrees of redundancy and on the load paths. Seismic codes state measures to compensate for Seismic Structural Configuration: Seismic structural uncertainties ranging from a simple requirement of use of configuration entails three main aspects, namely (a) modal superposition in case of torsional irregularity and use geometry, shape and size of the building, (b) location and size of a special load combination of gravity and seismic forces in of structural elements, and (c) location and size of significant case of out-of-plane offset irregularity. These measures can non-structural elements (Fig8). Influence of the geometry of a be recognized as penalties to discourage the irregular building on its earthquake performance is best understood structures. However, the imposing of the modal superposition from the basic geometries of convex and concave lenses from in the seismic design instead of the equivalent static load school-day physics class. The line joining any two points analysis cannot be recognized as a penalty in the widespread within area of the convex lens, lies completely within the use of the computer software. On the other hand in some lens. But, the same is not true for the concave lens; a part of cases seismic codes provide empirical rules for dealing with the line may lie outside the area of the concave lens. additional seismic demands required due to structural Structures with convex geometries are preferred to those with irregularity. Generally these empirical rules require an concave geometries, as the former demonstrate superior increase in the structural capacity of the elements which earthquake performance. In the context of buildings, convex produces the irregularity and those of the structural elements shaped buildings have direct load paths for transferring in its neighborhood. Although the seismic codes define earthquake shaking induced inertia forces to their bases for irregularities in detail, there is often no definition for the any direction of ground shaking, while concave buildings degree of irregularity of the overall three-dimensional system. necessitate bending of load paths for shaking of the ground Often no attempt is made to define level of irregularity in along certain directions that result in stress concentrations at quantifiable manner, for example a parameter ranging from 0 all points where the load paths bend. to 1. Structural Stiffness, Strength and Ductility: The next three F. Discontinuities in Columns overall properties of a building, namely lateral stiffness, Irregularity in structural are defined in plan and in elevation. lateral strength and ductility, are illustrated, through the One of the irregularities in elevation is discontinuity in lateral load– lateral deformation curve of the building. Lateral columns and shear walls. Turkish Seismic Code does not stiffness refers to the initial stiffness of the building, even permit columns at any storey to be supported by a cantilever though stiffness of the building reduces with increasing beam. In this way an asymmetrical configuration and loading damage. Lateral strength refers to the maximum resistance are avoided at the outer edge of structural system. When the that the building offers during its entire history of resistance cantilever beam which supports the column has continuity to relative deformation. Ductility towards lateral deformation into the structural system, the negative effect of the column refers the ratio of the maximum deformation and the idealized discontinuity can be avoided partially. However, this is not yield deformation. The maximum deformation corresponds to permitted in the Turkish Seismic Code as well. the maximum deformation sustained by it, if the loadDiscontinuities in shear walls are not permitted due to large deformation curve does not drop, and to 85% of the ultimate bending moment and shear force to be transferred to the load on the dropping side of the load-deformation response lower stories by means of the supporting beam. On the other curve after the peak strength or the lateral strength is reached, hand shear walls supported by the columns are not permitted if the load-deformation curve does drop after reaching peak as well. Here, the continuity of the edge zones of the shear strength. walls can be established by the columns in vertical load. However, the shear walls produce a stiff story, whereas the Objectives: columns below it cause a soft story, which should be avoided To calculate the design lateral forces on regular and in the seismic loading. Furthermore, this type of structural irregular buildings using response spectrum analysis and configuration can produce weak and/or soft story which may to compare the results of different structures. cause the total collapse of the building. To study three irregularities in structures namely mass, stiffness and vertical geometry irregularities. G. Characteristics of Buildings To calculate the response of buildings subjected to There are four aspects of buildings that architects and design various types of ground motions equivalent static method engineers work with to create the earthquake-resistant design and response spectrum. of a building, namely seismic structural configuration, lateral To study the effect of discontinuous load path in seismic stiffness, lateral strength and ductility, in addition to other response of building. asepcts like form, aesthetics, functionality and comfort of building. Lateral stiffness, lateral strength and ductility of Scope of the Study: buildings can be ensured by strictly following most seismic Only RC buildings are considered. design codes. But, good seismic structural configuration can Only vertical irregularity was studied. International Journal of Scientific Engineering and Technology Research Volume.05, IssueNo.11, May-2016, Pages: 2145-2151 Effect of Discontinuous Load Path on Seismic Performance of Building Using SAP2000 provided that they do not have significant openings. Large Linear elastic analysis was done on the structures. openings or cut-outs in floors interrupt load paths and may Column was modeled as fixed to the base. prevent smooth, direct transfer of forces to vertical elements. The contribution of infill wall to the stiffness was not Openings in floors are necessary, e.g., to allow for elevator considered. Loading due to infill wall was taken into core or staircase to pass through. But, these should be as account. small as possible, and as few as possible. Their locations The effect of soil structure interaction is ignored. should be carefully considered; the ideal location for openings is close to center of floor slabs in plan. II. METHODOLOGY Review of existing literatures by different researchers. Selection of types of structures. Modeling of the selected structures. Performing dynamic analysis on selected building models and comparison of the analysis results. Ductility based design of the buildings as per the analysis results III. WHAT ARE LOAD PATHS? Mass is present all through in a building - from roof parapet to foundation. Earthquake ground shaking induces inertia forces in a building where mass is present. These inertia forces are transferred downwards through horizontally and vertically aligned structural elements to foundations, which, in turn, transmit these forces to the soil underneath. The paths along which these inertia forces are transferred through building are Load Paths (Figure 1a). Buildings may have multiple load paths running between locations of mass and foundations. Load paths are as much a concern for transmitting vertical loads (e.g., self weight, occupancy load, and snow; Figure 1b) as for horizontal loads (e.g., earthquake and wind; Figure 1c). Structural elements in buildings that constitute load paths include: Horizontal diaphragm elements laid in horizontal plane, i.e., roof slabs, floor slabs or trussed roofs and bracings; Vertical elements spanning in vertical plane along height of building, i.e., planar frames (beams and columns interconnected at different levels), walls (usually made of RC or masonry), & planar trusses; Foundations and Soils, i.e., isolated and combined footings, mats, piles, wells, soil layers and rock; and Connections between the above elements. A. Horizontal Diaphragms Floor and roof slabs are thin, wide structural elements laid in a horizontal plane at different levels. They transfer inertia forces induced by their own masses, to vertical elements on which they rest. During earthquake shaking, horizontal diaphragms act like beams in their own horizontal plane and transmit inertia forces to vertical elements, such as structural walls or planar frames. Slabs that are long in plan (i.e., flexible in their own plane), bend and undergo undesirable stretching along one edge and shortening along the other (Figure 2); they perform best when relative deformations are minimal and in-plane stiffness and strength sufficiently large. In general, slabs should be rectangular with plan length/plan width ratio less than 3 Horizontal floors can effectively resist and transfer earthquake forces through direct load paths, B. Vertical Elements Typical structural elements (present in vertical planes) of buildings are columns, braces and structural walls or a combination of these (Fig3). They collect gravity and (horizontal and vertical) earthquake inertia forces from floor diaphragms at different levels, and bring them down to the foundations below. It is possible to design and construct earthquake resistant buildings with various structural systems, including Moment Resisting Frames (MRFs), Frames with Brace Members (called Braced Frames (BFs)), Structural Walls(SWs; also called Shear Walls), or a combination of these. Some of these systems require more advanced knowledge of design and higher quality control during construction than others, as reflected by their relative performance during earthquakes. For instance, buildings with SWs are easy to design and construct, and generally perform better during earthquakes, than buildings with MRFs alone. C. Load Path Buildings are generally composed of vertical and horizontal structural elements. The vertical elements commonly used to transfer lateral forces to the ground are: 1) shear walls; 2) braced frames; and 3) moment-resisting frames. The horizontal elements that distribute lateral forces to the vertical elements are: 1) diaphragms, such as floor and roof slabs; and 2) horizontal bracing that transfers large shears from discontinuous walls or braces. The seismic forces that are proportional to the mass of the building elements are considered to act at their centers of mass. All of the inertia forces originating from the masses on and off the structure must be transmitted to the lateral force-resisting elements, and then to the base of the structure and into the ground. A complete load path is a basic requirement for all buildings. There must be a complete lateral-force-resisting system that forms a continuous load path between the foundation, all diaphragm levels, and all portions of the building for proper seismic performance. The general load path is as follows. Seismic forces originating throughout the building, mostly in the heavier mass elements such as diaphragms, are delivered through connections to horizontal diaphragms the diaphragms distribute these forces to vertical force-resisting elements such as shear walls and frames; the vertical elements transfer the forces into the foundation; and the foundation transfers the forces into the supporting soil. If there is a discontinuity in the load path, the building is unable to resist seismic forces regardless of the strength of the elements. Interconnecting the elements needed to complete the load path is necessary to achieve good seismic performance. Examples of gaps in the load path would include a shear wall that does not extend to International Journal of Scientific Engineering and Technology Research Volume.05, IssueNo.11, May-2016, Pages: 2145-2151 BUSHRA GASIM, T. V. S. VARA LAKSHMI the foundation, a missing shear transfer connection between a IV. MODEL DSESCRIPTION diaphragm and vertical elements, a discontinuous chord at a Selected three buildings type same area with 15-story diaphragm‟s notch, or a reentrant corner, or a missing concrete framed building with six bays along X and six in Y collector. A good way to remember this important design direction , molding according the following table detail. The strategy is to ask yourself the question, “How does the inertia molding by sap 2000 of building with continuous load path of load get from here (meaning the point at which it is each column towards the earth will done as Table 1. generated) to there (meaning the shear base of the structure, typically the foundations)?”. V. RESULT AND COMPARSION Results of this paper is as shown in bellow Figs.1 to 11. 1. A. Building Displacement D. Continuous Load Path A continuous load path, or preferably more than one path, with adequate strength and stiffness should be provided from the origin of the load to the final lateral-load-resisting elements. The general path for load transfer is in reverse to the direction in which seismic loads are delivered to the structural elements. Thus, the path for load transfer is as follows: Inertia forces generated in an element, such as a segment of exterior curtain wall, are delivered through structural connections to a horizontal diphragm (i.e., floor slab or roof); the diaphragms distribute these forces to vertical components such as moment frames, braces, and shear walls; and finally, the vertical elements transfer the forces into the foundations. While providing a continuous load path is an obvious requirement, examples of common flaws in load paths are: a missing collector, or a Fig.1. Displacement For the building with continuous discontinuous chord because of an opening in the floor load path. diaphragm, or a connection that is inadequate to deliver diaphragm shear to a frame or shear wall. E. Seismic analysis Is a major tool in earthquake engineering which is used to understand the response of buildings due to seismic excitations in a simpler manner. In the past the buildings were designed just for gravity loads and seismic analysis is a recent development. It is a part of structural analysis and a part of structural design where earthquake is prevalent. There are different types of earthquake analysis methods. Some of them used in the project are Equivalent Static Analysis Response Spectrum Analysis TABLE I: The Molding by SAP2000 of Building with Continuous Load Path of Each Column Fig.2.Displacement building with corner and outer discontinuous load path. Fig.3. Displacement for the building with corner, outer and central discontinuous load path. International Journal of Scientific Engineering and Technology Research Volume.05, IssueNo.11, May-2016, Pages: 2145-2151 Effect of Discontinuous Load Path on Seismic Performance of Building Using SAP2000 Fig.4. Comparison between three building in displacement. Fig.7. Time Periods, frequency. B. Inter Story Drift Fig.5. Comparison between three building in inter story drift. Fig.8. Comparison Between Mode of Building. D. Bending Moment, Shear Force , Torsion ,Axial Force C. Base Reaction, Base Shear, Base Moment Fig.6. Fig.9. compassion-in axial forces. International Journal of Scientific Engineering and Technology Research Volume.05, IssueNo.11, May-2016, Pages: 2145-2151 BUSHRA GASIM, T. V. S. VARA LAKSHMI It can be observed that that reduce in load path increase the displacement of building under seismic load and this increment also increase as the discontinuous load path increase, so the relation can be consider as (direct proportion) between discontinuous load path and displacement The percentage of increment about (20%) Axial load on column from dynamic load increase as decrease the number of load path. The problem of increase axial load is consider have much effect on bottom column . Shear force of building with continuous load path have steady performance while the building with discontinuous load path have variable performance that effect can consider in first and second story. „ Bending moment of building with continuous load path have steady performance while the building with discontinuous load path have variable performance that effect can consider in first and second story Fig.10. compassion-in shear forces. As the discontinuous load increase the percentage of failure in column increase near the position of discontinues in column Design codes classify irregularity and require increases of in all internal forces. However, due to column discontinuity the load path changes in the structural system considerably and the empirical requirements given in the codes are expected to deal with the additional seismic demands do not seem to be satisfactory. Furthermore, the effect of the discontinuity is more much pronounce, when the frame has only two spans, as it is the case in the present analysis. Column discontinuity produces the soft story in the frame, when the number of the column is small in a specific story. There are large numbers of parameters which affect the behavior of the frame subjected to vertical and lateral loads. The variation of the load path depends on the stiffness distribution in the columns and beams neighboring the column discontinuity. Especially, the decrease in the stiffness of the beam which supports the discontinuous column affects significantly the load path Fig.11. compassion-in moment forces. to the support of the structural system. Remembering that the cracking of the concrete section decreases the VI. CONCLUSION bending stiffness up to %30, the significance of the A. General variation can be understood. This study presents both theoretical investigation and modeling for building subjected to earthquake-induced load C. Recommendations by sap2000 using response spectrum method for analysis of Study the effect of both discontinuously load path in building . The objective of this work is to study effect of vertical and horizontal direction. discontinuous load path in structure subjected to seismic Study the effect of change the type of resistant moment ground motion. The following sections summarize the frame system have discontinuous load path in the conclusions resulting from this research work as well as response of building. recommendations for future research. Study the effect of building weight with discontinuous load path on building response to seismic action . B. Conclusions An investigation study on effect of material type on Based on the theoretical and modeling findings, the discontinuous load path. following conclusions can be drawn: Establishing an guidance for design building with The displacement of building increase as the discontinuous load path. discontinuous load path increase. International Journal of Scientific Engineering and Technology Research Volume.05, IssueNo.11, May-2016, Pages: 2145-2151 Effect of Discontinuous Load Path on Seismic Performance of Building Using SAP2000 ISSN 2090-4304 Journal of Basic and Applied Scientific VII. REFREANCE [1].John A. 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