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Vol.05,Issue.11,
May-2016,
Pages:2145-2151
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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
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