Analysis & Design of a High Rise Thin Building - IJETMAS & Design of a High Rise Thin Building ... structural analysis and design software coupled ... low design stress limits in shear

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com March 2017, Volume 5 Issue 3, ISSN 2349-4476

268 Ajitha B & Nirupa N

Analysis & Design of a High Rise Thin Building

Ajitha B1 & Nirupa N

2

1Ajitha, Department of Civil Engineering

, JNTUA College Of Engineering(Autonomous), Ananthapuramu, Andhra

Pradesh, India. 2Nirupa,Department of Civil Engineering

, JNTUA College Of Engineering(Autonomous), Ananthapuramu, Andhra

Pradesh, India.

ABSTRACT

Earthquake load is becoming a great concern in our country as because not a single zone can be designated as

earthquake resistant zone. One of the most important aspects is to construct a building structure, which can resist the

seismic force efficiently. Study is made on the different structural arrangement to find out the most optimized solution to

produce an efficient safe earthquake resistant building.

In the present analysis, a thin building is analyzed with a height of 60m, width of the building is taken as 15m the

building is analyzed without bracings and with X bracings at optimum places and finding out the results of displacement,

shear, moment, in Zone-3 in loose soil for finding the results in both static & response spectrum analysis. A commercial

package of ETABS 2013 has been utilized for analyzing commercial building. The result has been compared using tables

& graph to find out the most optimized solution. Concluding remark has been made on the basis of this analysis.

Keywords: Bracings, Static analysis, Dynamic Analysis.

1. INTRODUCTION

Mankind has always had a fascination for height

and throughout our history we have constantly

sought to metaphorically reach for the stars. From

the ancient pyramids to today’s modern

skyscraper, a civilization’s power and wealth has

been repeatedly expressed through spectacular and

monumental structures. Today the symbol of

economic power and leadership is the skyscraper.

There has been a demonstrated competitiveness

that exists in mankind to proclaim to have the

tallest building in the world. This undying quest

for height has laid out incredible opportunities for

the building profession. From the early moment

frames to today’s ultra-efficient mega-braced

structures, the structural engineering profession

has come a long way. The recent development of

structural analysis and design software coupled

with advances in the finite element method has

allowed the creation of many structural and

architecturally innovative forms. However,

increased reliance on computer analysis is not the

solution to the challenges that lie ahead in the

profession. The basic understanding of structural

behaviour while leveraging on computing tools are

the elements that will change the way structures

are designed and built. The design of skyscrapers

is usually governed by the lateral loads imposed on

the structure. As buildings have taller and

narrower, the structural engineer has been

increasingly challenged to meet the imposed drift

requirements while minimizing the architectural

impact of the structure. In response to this

challenge, the profession has proposed a multitude

of lateral schemes that are now spoken in tall

buildings across the globe. This study seeks to

understand the evolution of the different lateral

systems that have emerged and its associated

structural behaviour, for each lateral scheme

examined, its advantages and disadvantages will

be looked at.

Effect of Soils:

The seismic motion that reaches a structure on the

surface of the earth is influenced by the local soil

conditions. The subsurface soil layers underlying

the building foundation may amplify the response

of the building to earthquake motions originating

in the bedrock. Although it is somewhat difficult

to visualize, it is possible that a number of

underlying soils can have a period similar to the

period of vibration of the structure. Greater

structural distress is likely to occur when the

period of the underlying soil is close to the

fundamental period of the structure. Tall buildings

tend to experience greater structural damage when

they are located on soils having a long period of

motion because of the resonance effect that

develops between the structure and the underlying

soils. If a building resonates in response to ground

motion, its acceleration is amplified.

It is possible that a number of underlying soils

layer s can have a period similar to period of




vibration of the structure. Low-to mid-rise

buildings typically have periods in the 0.10 to 1.0

sec range, whereas taller, more flexible buildings

have periods between 1 and 5 sec or greater.

Harder soils and bedrock will efficiently transmit

short-period vibrations(caused by near field

earthquakes)while filtering out longer-period

vibrations (caused by distant earthquakes),

whereas softer soils will transmit longer -period

vibrations. As a building vibrates due to ground

motion, its acceleration will be amplified if the

fundamental period of the building coincides with

the period of vibrations being transmitted through

the soil. Natural period of soil is in the range of 0.5

to 1.0 sec. Therefore, it is entirely possible for the

building and ground to have the same fundamental

period.

As per IS 1893 (Part I) – 2002, soils classification

can be taken as Type – I, Rock or Hard soil: Well

graded gravel and sand mixtures with or without

clay binder and clayey sands poorly graded or sand

clay mixtures, whose N (standard penetration

value) should be above 30. Type – II, Medium

soils: All soils wit h N between 10 and 30, and

poorly- graded sands or gravelly sands with little

or no fines. Type – III, Soft Soils: All soils other

than whose N is less than 10.

Objectives of the Study

To investigate the different ways in which the

tall structures can be stabilized against the effects

of strong horizontal wind loading and seismic

loading. Some other reasons why we use bracings

are tall structures can be constructed which

reduces the area used and we can accommodate a

large population in that particular area. Other

objective is to construct a cost effective structure

in less period of time. This study helps in the

investigation of behaviour of thin high rise

buildings.

The scope is to analyze the thin high rise building

with bracings & without bracings in Zone-3 Type

– III, loose Soils in Static and Dynamic analysis.

Firstly the model is implemented into known

computer software and then it is analyzed based on

the investigation of strength and stiffness.

2. LATERAL LOAD RESISTING SYSTEMS:

A multi-storey building with no lateral bracing is

shown in figure 2.1.When the beams and columns

shown are connected with simple beam

connections, the frame would have practically no

resistance to the lateral forces and become

geometrically unstable. The frame would be

laterally deflect as shown in the below figure even

under a small lateral load.

Loading on tall buildings is different from low-rise

buildings in many ways such as large accumulation

of gravity loads on the floors from top to bottom,

increased significance of wind loading and greater

importance of dynamic effects. Thus, multi-storied

structures need correct assessment of loads for safe

and economical design. Excepting dead loads, the

assessment of loads cannot be done accurately.

Live loads can be anticipated approximately from a

combination of experience and the previous field

observations. But, wind and earthquake loads are

random in nature. It is difficult to predict them

exactly. These are estimated based on probabilistic

approach. The following discussion describes the

influence of the most common kinds of loads on multi-

storied structures.

2.1 STRUCTURAL CONCEPTS: The key idea in conceptualizing the structural system

for a narrow tall building is to think of it as a beam

cantilevering from the earth (fig 2.2).

Figure 2.1.1:Structural concept of tall building The

laterally directed force generated, either due to wind

blowing against the building or due to the inertia forces

induced by ground shaking, tends both to snap it

(shear), and push it over (bending).

Figure 2.1 : multi- storey frame

without lateral bracing




Therefore, the building must have a system to

resist shear as well as bending. In resisting shear

forces, the building must not break by shearing off

and must not strain beyond the limit of elastic

recovery.

Figure 2.1.2: Building shear resistance;

(a) Building must not break

(b) Building must not deflect excessively in shear.

Figure 2.1.3: Bending resistance of building

(a)Building must not overturn

(b)Columns must not fail in tension or

compression

(c) Bending deflection must not be excessive.

In the structure’s resistance to-of bending-war

ensues that sets and the shear building in motion,

thus creating a third engineering problem; motion

perception or Vibration. If the building sways too

much, human comfort is sacrificed, or more

importantly, non-structural elements may break

resulting in expensive damage to the building

contents and causing danger to the pedestrians.

A perfect structural form to resist the effects of

bending, shear and excessive vibration is a system

possessing vertical continuity ideally located at the

farthest extremity from the geometric centre of the

building. A concrete chimney is perhaps an ideal,

if not an inspiring engineering model for a rational

super-tall structural form. The quest for the best

solution lies in translating the ideal form of the

chimney into a more practical skeletal structure.

2.2 LATERAL FORCE RESISTING

SYSTEMS: There are several systems that can be used

effectively for providing resistance to seismic

lateral forces. Some of the more common systems

are shown in figures below. All of the systems rely

on a complete, three–dimensional space frame; a

coordinated system of moment frames, shear

walls, or braced frames with horizontal

diaphragms; or a combination of the systems.

1. In buildings where a space frame resists the

earthquake forces, the columns and beams act in

bending. During a large earthquake, storey to

storey deflection may be accommodated within the

structural systems without causing failure of

columns or beams. However, the drift may be

sufficient damage elements that are rigidly tied to

the structural system such as brittle partitions,

stairways, plumbing, exterior walls, and other

elements that extend between floors. Therefore,

buildings can have substantial interior and exterior

non structural damage and still be structurally safe.

Although there are excellent theoretical and

economic reasons for resisting seismic forces by

frame

2. A shear wall (or braced frame) building is

normally more rigid than a framed structure. With

low design stress limits in shear walls, deflection

due to shear forces is relatively small. Shear wall

construction is an economical method of bracing

buildings to limit damage, and this type of

construction is normally economically feasible up

to about 15 stories. Notable exceptions to the

excellent performance of shear walls occurs when

the height-to-width ratio becomes great enough to

make overturning a problem and when there are

excessive openings in the shear walls. Also, if the

soil beneath its footings is relatively soft, the entire

shear wall may rotate, causing localized damage

around the wall.

3. The structural systems just mentioned may be

used singly or in combination with each other.

When frames and shear walls interact, the system

is called a dual system in the frame alone can resist

25% of the lateral load. Otherwise, it is referred to

as a combined system




Figure 2.2.1 : Lateral-force-resisting systems: (a)

steel moment-resisting frame; (b) reinforced

concrete moment-resisting frame; (c) braced steel

frame; (d) reinforced concrete shear walls; (e) steel

frame building with cast-in-place concrete shear

walls; (f) steel frame building with infilled walls of

non reinforced masonry.

3. BRACED FRAMES: Rigid frame systems are not efficient for

buildings taller than about 30-stories because the

shear racking component of deflection due to the

bending of columns are girders causes the drift to

be too large. A braced frame attempts to improve

upon the efficiency of a rigid frame by virtually

eliminating the bending of columns and girders.

This is achieved by adding web members such as

diagonals or chevron braces. The horizontal shear

is now primarily absorbed by the web and not by

the columns. The webs carry the lateral shear

predominantly by the horizontal component of

axial action allowing for nearly a pure cantilever

behaviour.

In simple terms, braced frames may be

considered as cantilevered vertical trusses resisting

lateral loads primarily through the axial stiffness

of columns and braces. The columns act as a chord

in resisting the overturning moment, with tension

in the windward column and compression in the

leeward column. The diagonals and girders work

as the web members in resisting the horizontal

shear, with diagonals in axial compression or

tension depending upon their direction of

inclination. The girders act axially, when the

system is a fully triangulated truss. They undergo

bending also when the braces are eccentrically

connected to them. Because the lateral load on the

building is reversible, braces are subjected in turn,

to both compression and tension; consequently,

they are most often designed for the more stringent

case of compression.

Figure 3.1 : Braced frame deformation

(a) flexural deformation

(b) shear deformation;

(c) Combined configuration

The effect of axial deformation of configuration of

the deflection with concavity downward and a

maximum slope at the top (Fig-a). The axial

deformations of the web members, on the other

hand, cause a “shear” configuration at the top (Fig-

b ). The resulting deflected shape of the frame

(Fig-c) is a combination of the effects of the

flexural and shear curves, with a resultant

configuration depending on their relative

magnitudes, as determined mainly by the type of

bracings. Nevertheless, it is the flexural deflection

that most often dominates the deflection

characteristics.

The role of web members in resisting shear can be

demonstrated by following the path of the

horizontal shear down the brace bent. Consider the

brace frames shown subjected to an external shear

force at the top level, the diagonal in each storey is

in compression, causing the beams to be in axial

tension; therefore, the shortening of the diagonal

and extension of the beams give rise to the shear

deformation of the bent. In the forces in the brace

connecting to each beam-end are in equilibrium

horizontally with the beam carrying insignificant

axial load, half of each beam is in compression

while the other half is in tension. the braces are

alternatively in compression and tension while the

beams remain basically unstressed. Finally, in




Fig3.6e, the end parts of the beam are in

compression and tension with the entire beam

subjected to double curvature bending. Observe

that with a reversal in the direction of horizontal

load, all actions and deformations in each member

will also be reversed.

4. MATERIALS & METHODS:

4.1 Plan Considered:

In this study an 35 storey building having same

plan in different type of zones (as per IS 1893

(Part I): 2002) and different type of soils is taken.

The tall building with X braces introduce in the

central location in two bays is consider to study

the effect of lateral deflection, bending moment,

shear force caused due to lateral load. i.e. due to

quake load (both static and dynamic).

4.2. Building Dimensions:

The building is 15m x 60m in plan with columns

spaced at 5m from centre to centre. A floor to floor

height of 3.0m is assumed. The location of the

building is assumed to be in Zone-3 and loose

soils.

Table 4.2.1: Size of Structural Members

4.3. Modeling :

To create a model firstly we have to form a grid.

Grid can be of uniform or non uniform. Uniform

refers to spacing which are in equal distances in

global x direction & equal distances in global Y

direction. It is not compulsory to make same

distances in both the global directions.

4.4.Defining Frame Sections and Slab sections:

After forming the grid we have to define frame

sections which includes beam & column. In this

software we can define a column with suitable

reinforcement which can be edited if the provided

reinforcement exceeds the limit. Beam defining &

Column defining is shown in below figures.

Figure 4.4.1 : Showing Defining of Beam

Figure 4.4.2 : Showing Defining of Column

Figure 4.4.3 :Showing reinforcement details for column

Figure 4.4.4 : Showing defining of slab

section 4.5 Loading: After the modeling is complete, ETABS generates

code-based loading conditions for gravity, seismic,

wind loads. We can specify an unlimited number

of load patterns and combinations. Load patterns in ETABS software:

Sr.

No. Contents Description

1 Size of column

From ground floor to

fifteenth floor: 1000

mm X 900 mm

From sixteenth floor to

thirty fifth floor: 900

mm X 600 mm

2 Size of beam 400 mm X 600 mm

3 Thickness of Slab

120 mm

4 Size of Brace

Members 230 mm X 230 mm

5 Materials

Concrete (M30) and

Reinforcement HYSD 500




Figure:4.5.1 Showing loads to be

applied on structure

Figure4.5.2: Showing of defining Load Combinations

And also model is analyzed in dynamic analysis by

response spectrum method.

4.6. Response Spectrum Method: Response spectrum method is simple when

compared to time history method, in this method

model is placed in particular zone & soil and we

see the behaviour of model or a building for that

particular earthquake zone & soil. Earth Quake

Data Is Referred from IS 1893-2002

Table 4.6.1 : Zone Factors in India

4.7. Analysis & Design:

Output and display formats are also practical and

intuitive. Moment, shear, and axial force diagrams,

presented in 2D and 3D views with corresponding

data sets, may be organized into customizable

reports. Also available are detailed section cuts

depicting various local response measures.

ETABS also features interoperability with related

software products, providing for the import of

architectural models from various technical

drawing software, or export to various platforms

and file formats. SAFE, the floor and foundation

slab design software with post-tensioning (PT)

capability, is one such option for

export. CSI coordinated SAFE to be used in

conjunction with ETABS such that engineers

could more thoroughly detail, analyze, and design

the individual levels of an ETABS model.

While ETABS features a variety of sophisticated

capabilities, the software is equally useful for

designing basic systems. ETABS is the practical

choice for all grid-like applications ranging from

simple 2D frames to the most complex high rises.

4.8.PLAN AND ELEVATION OF MODEL:

A simple plan of 150m X 60m is taken, with 5

bays of 8 m each as shown below.

Figure 4.8.1 : Building plan dimension(Common to

all floors, all models, units m‟).

Figure 4.8.2: Showing elevation view of high rise

building

ZONES ZONE

FACTOR

ZONE-II 0.10

ZONE-III 0.16

ZONE-IV 0.24

ZONE-V 0.36

https://wiki.csiamerica.com/display/safe/Home

https://wiki.csiamerica.com/display/kb/Tendon

http://www.csiberkeley.com/




5.RESULTS: Table-1: Comparative values of Displacement in

Zone-3 loose soil in Static Analysis

Graph 1 : Displacement variationin Zone-3 loose soil

in Static Analysis

Table-2: Comparative values of Displacement in

Zone-3 loose soil in Dynamic Analysis

Graph 2 : Showing Displacement variation

in Zone-3 loose soil in Dynamic Analysis

Storey

Without

Bracings

With

Bracings

Storey35 26.4 22.8

Storey34 26.1 22.4

Storey33 26 22.2

Storey32 25.9 22

Storey31 25.7 21.8

Storey30 25.5 21.5

Storey29 25.1 21.2

Storey28 24.7 20.8

Storey27 24.2 20.3

Storey26 23.6 19.8

Storey25 23 19.3

Storey24 22.3 18.7

Storey23 21.6 18.1

Storey22 20.8 17.4

Storey21 20 16.7

Storey20 19.1 15.9

Storey19 18.1 15.1

Storey18 17.2 14.3

Storey17 16.2 13.5

Storey16 15.3 12.7

Storey15 14.3 11.9

Storey14 13.3 11.1

Storey13 12.3 10.3

Storey12 11.2 9.4

Storey11 10.2 8.6

Storey10 9.2 7.8

Storey9 8.2 7

Storey8 7.2 6.2

Storey7 6.1 5.4

Storey6 5.1 4.6

Storey5 4.1 3.8

Storey4 3.1 3.1

Storey3 2.1 2.3

storey2 1.2 1.5

Storey1 0.4 0.7

Base 0 0

Storey

Without

Bracings

With

Bracings

Storey35 45 38.2

Storey34 44.5 37.7

Storey33 44.3 37.3

Storey32 44 36.9

Storey31 43.6 36.4

Storey30 43 35.8

Storey29 42.3 35.2

Storey28 41.5 34.4

Storey27 40.5 33.6

Storey26 39.5 32.7

Storey25 38.4 31.8

Storey24 37.2 30.7

Storey23 35.9 29.6

Storey22 34.5 28.5

Storey21 33 27.3

Storey20 31.5 26.1

Storey19 30 24.8

Storey18 28.4 23.5

Storey17 26.9 22.2

Storey16 25.3 20.8

Storey15 23.6 19.5

Storey14 22 18.1

Storey13 20.3 16.8

Storey12 18.7 15.4

Storey11 17 14.1

Storey10 15.3 12.7

Storey9 13.6 11.4

Storey8 11.9 10

Storey7 10.2 8.7

Storey6 8.5 7.4

Storey5 6.8 6.1

Storey4 5.2 4.9

Storey3 3.5 3.6

storey2 2 2.3

Storey1 0.7 1

Base 0 0




Table-3: Comparative values of Shear in


Graph 3 : Showing Shear variation

in Zone-3 loose soil in Static Analysis

Table-4:Comparative values of Shear in Zone-

3 loose soil in Dynamic Analysis

Graph 4 : Showing Shear variation

in Zone-3 loose soil in Dynamic Analysis

Storey

Without

Bracings

With

Bracings

Storey35 79.5 30.76

Storey34 58.7 21.84

Storey33 61.1 22.9

Storey32 60.4 22.8

Storey31 60.06 22.9

Storey30 59.5 23.16

Storey29 58.86 23.38

Storey28 58.12 23.62

Storey27 57.2 23.87

Storey26 56.3 24.11

Storey25 55.2 24.33

Storey24 54.1 24.56

Storey23 52.6 24.67

Storey22 41.5 25.4

Storey21 59.4 21.11

Storey20 57.6 35.46

Storey19 57.4 28.59

Storey18 55.1 29.9

Storey17 53.3 29.88

Storey16 51.8 29.96

Storey15 50.2 29.98

Storey14 48.5 29.97

Storey13 46.7 29.94

Storey12 44.8 29.85

Storey11 42.7 29.92

Storey10 40.6 29.53

Storey9 38.3 29.3

Storey8 35.9 28.9

Storey7 33.4 28.42

Storey6 30.7 27.01

Storey5 27.7 25.99

Storey4 26.9 25.01

Storey3 22.4 19.72

storey2 19.6 25.97

Storey1 18.5 12.3

Base 14.5 11.4

Storey

Without

Bracings

With

Bracings

Storey35 8.3 30.76

Storey34 58.7 21.84

Storey33 61.1 22.9

Storey32 60.4 22.8

Storey31 60.06 22.9

Storey30 59.5 23.16

Storey29 58.86 23.38

Storey28 58.12 23.62

Storey27 57.2 23.87

Storey26 56.3 24.11

Storey25 55.2 24.33

Storey24 54.1 24.56

Storey23 52.6 24.67

Storey22 41.5 25.4

Storey21 59.4 21.11

Storey20 57.6 35.46

Storey19 57.4 28.59

Storey18 55.1 29.9

Storey17 53.3 29.88

Storey16 51.8 29.96

Storey15 50.2 29.98

Storey14 48.5 29.97

Storey13 46.7 29.94

Storey12 44.8 29.85

Storey11 42.7 29.92

Storey10 40.6 29.53

Storey9 38.3 29.3

Storey8 35.9 28.9

Storey7 33.4 28.42

Storey6 30.7 27.01

Storey5 27.7 25.99

Storey4 26.9 25.01

Storey3 22.4 19.72

storey2 19.6 25.97

Storey1 18.5 12.3

Base 14.5 11.4




Table-5: Comparative values of Moment in


Graph 5 : Showing Moment variation in Zone-3 loose

soil in Analysis

Table-6:Comparative values of Moment in

Zone-3 loose soil in Dynamic Analysis

Graph 6 : Showing Moment variation in Zone-3 loose

soil in Dynamic Analysis

Storey

Without

Bracings

With

Bracings

Storey35 97 37

Storey34 93.4 47.6

Storey33 64.5 25.9

Storey32 61.3 24.5

Storey31 57.5 22.27

Storey30 54.5 20.67

Storey29 51.5 19.2

Storey28 48.6 17.9

Storey27 45.7 16.7

Storey26 42.8 15.6

Storey25 39.9 14.6

Storey24 37 13.6

Storey23 34.1 12.6

Storey22 31.3 11.7

Storey21 27.8 10.9

Storey20 24.2 11.3

Storey19 48.2 14.7

Storey18 18.7 1.4

Storey17 1 8.6 4.8

Storey16 18.1 5.3

Storey15 16.4 5.3

Storey14 14.6 5.2

Storey13 12.7 5.1

Storey12 10.8 4.9

Storey11 0.7 4.6

Storey10 6.6 4.3

Storey9 4.3 3.9

Storey8 1.9 3.4

Storey7 4.5 2.8

Storey6 10.4 4.9

Storey5 16.9 7.93

Storey4 24.9 11.56

Storey3 36.8 16.4

storey2 59.9 24.9

Storey1 114.221 58.2

Base 265.97 293.5

Storey

Without

Bracings

With

Bracings

Storey35 90 35.45

Storey34 65.14 32.4

Storey33 62.8 36.32

Storey32 59.92 33.23

Storey31 57.74 30.01

Storey30 55.53 28.43

Storey29 53.31 29.43

Storey28 51.06 25.3

Storey27 48.79 22.32

Storey26 46.48 21.2

Storey25 44.12 20.33

Storey24 41.71 20.12

Storey23 39.26 19.85

Storey22 36.37 19.23

Storey21 34.09 19.55

Storey20 56.46 18.44

Storey19 32.3 17.43

Storey18 31 16.7

Storey17 30.21 18.5

Storey16 28.7 17.44

Storey15 27.07 16.88

Storey14 25.35 18.76

Storey13 23.55 19.33

Storey12 21.65 16.32

Storey11 19.65 15.6

Storey10 17.54 13.22

Storey9 15.3 12.1

Storey8 12.944 10.2

Storey7 10.5 8.6

Storey6 8.09 6.5

Storey5 6.07 4.32

Storey4 4 3.22

Storey3 4.09 3.221

storey2 3.65 2.1

Storey1 3.6 3.2

Base 3 2.1




(a)

(b)

Figure 6.1 : The variation of (a)Shear (b)Moment

in 3D View

4. CONCLUSIONS:

Based on the analysis:

In static analysisThe structural

performance is analyzed in two different

models i.e. Without bracings, With X

Bracing, the displacement of 40% is

reduced when lateral systems are

provided.

Shear is also analyzed for both the models,

Shear of 30% is reduced when the lateral

systems i.e., X bracings are provided.

Moment is also compared for both the

models, moment of 60% is reduced when

x bracings are provided.

By providing the bracings the stiffness of

the structure is increased and storey shear

is decreased with increase in height of

structure.

Dynamic Analysis i.e.. Response

Spectrum analysis is performed for all the

models i.e. without bracings & with

bracings. The displacement of 40% is

reduced when X bracings are provided


Spectrum analysis is carried out for all the


bracings. A shear of 30% is reduced when

X bracings are provided.


Spectrum analysis is carried out for all the


bracings. A moment of 40% is reduced

when X bracings are provided.

By providing lateral systems in the framed

structures the reduction in the

displacement, shear, moment thereby

increasing the stiffness of the structure for

resisting lateral loads due to earth quakes

REFERENCES

1. Mahmoud R. Maheri, R. Akbari (2003) “Seismic

behaviour factor, R, for steel X-braced and knee-braced

RC buildings” Engineering Structures, Vol.25, 14 May

2003, pp 1505-1513.

2. J.C.D. Hoenderkamp and M.C.M. Bakker (2003)

“Analysis of High-Rise Braced Frames with

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