case project

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A PROJECT REPORT ON

DYNAMIC ANALYSIS OF FOOD GRAIN

STORAGE HOUSE (WAREHOUSE)

SUBMITTED BY:

ASHISH LOYA 201211594

VIJAY PAVULURI 201211569

RISHIKESH KUMAR -201211520

EARTHQUAKE ENGINEERING RESEARCH CENTRE

IIIT, HYDERABAD.

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ACKNOWLEDGEMENT

We wish to express our deep and sincere feeling of gratitude to our project guide

P. Venkata Dilip Kumar, IIIT, Hyderabad for all the help and guidance he provided throughout

our project.

Our sincere thanks to CASE workshop teaching assistant, Mr. Swajit Singh Goud and

Ajay Kumar.S who have extended their timely help and eased our task.

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CONTENTS

ABSTRACT

CHAPTER DESCRIPTION

PAGE

NO

1 INTRODUCTION 6

1.1 Different types of warehouses 6

1.2 Food grain storage Warehouses in India 6

2 DETAILS OF THE STRUCTURE 10

2.1 Material Properties 10

2.2 Boundary Conditions 11

2.3 Components of Warehouse 11

2.3.1 Truss Configuration 11

2.3.2 Components of Truss 11

2.4 Design details of Truss 15

2.5 Loads acting on Industrial Building 15

2.6 Wind Pressures and Forces On Buildings/Structures 19

2.6.1 Wind Load Calculations 20

2.7 Siesmic Load 22

2.7.1 Base Shear Calculations 23

3 WORKING WITH STAAD.Pro 24

3.1 Input Generation 24

3.2 Types of Structures 24

3.3 Generation of the structure 25

3.4 Material Constants 26

3.5 Supports 26

3.6 Loads 26

3.7 General Comments 28

3.8 Post Processing Facilities 29

4

DYNAMIC ANALYSIS OF FOOD GRAIN STORAGE HOUSE

USING STAAD.Pro 30

4.1 Physical parameters of building 32

4.2 Generation of member property 33

4.3 Supports 33

4.4 Materials for the structure 33

4.5 Loading 34

5 DYNAMIC ANALYSIS 45

5.1 Time History Analysis 45

5.2 Response of the structure for different ground motions 45

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6 CONCLUSION 46

7 REFERENCE 47

List of figures:

Fig 1.1: Various types of Warehouses Designed in India

Fig 2.1: Components of Warehouse

Fig 2.2: A - Type Truss Configuration

Fig 3.1: STAAD input file

Fig 3.2: GUI

Fig 4.1: Plan of Warehouse

Fig 4.2: Elevation of Warehouse

Fig 4.3: 3-D Image of warehouse

Fig 4.4: Member property

Fig 4.5: Deformed shape

Fig 4.6: SF in X direction

Fig 4.7: SF in Z direction

Fig 4.8: Bending Moment

Fig 4.9: Mode shape 1




List of tables:

Table 2.1: Pitch of roof

Table 2.2: Interpolation of external pressure coefficient

Table 2.3: Wind load calculations

Table 2.4: Loads applied on truss nodes

Table 4.1:Wind load on truss roof

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ABSTRACT

The principle objective of this project is to analyze a Food grain storage Warehouses building for

time history and response spectrum using STAAD Pro. The analysis involves gravity and wind

load calculations manually and analyzing the whole structure by STAAD Pro. The design

methods used in STAAD-Pro analysis are Limit State Design conforming to Indian Standard

Code of Practice. STAAD.Pro features a state-of-the-art user interface, visualization tools,

powerful analysis and design engines with advanced finite element and dynamic analysis

capabilities. From model generation, analysis and design to visualization and result verification,

STAAD.Pro is the professionals choice. Initially we started with the calculation of various loads

coming on the structure manually and assigned it to the modeled structure in STAAD. Then the

structure was analyzed for all possible load combinations [dead, live, wind and seismic loads]

and time history and response spectrum plots are obtained.

We considered a one storey food grain storage warehouse frame with the dimensions of 10 bays

@5m in z-axis and 1bay @25m in x-axis. The eave height was 6.5m and A type truss

configuration is used as roof for the structure. The structure was subjected to self-weight, dead

load, live load, wind load and seismic loads under the load case details of STAAD.Pro. The wind

load values were generated by STAAD.Pro considering the given wind intensities at different

heights and strictly abiding by the specifications of IS 875. The materials were specified and

cross-sections of the truss members were assigned. The supports at the base of the structure were

also specified as fixed. The codes of practice to be followed were also specified for design

purpose with other important details. Then STAAD.Pro was used to analyze the structure. In the

post-processing mode we may check the deflection, shear force and bending moments of various

members under the given loading combinations.

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CHAPTER 1

INTRODUCTION

Warehouses, defined here, are facilities that provide a proper environment for the purpose of

storing goods and materials that require protection from the elements. Warehouses must be

designed to accommodate the loads of the materials to be stored, the associated handling

equipment, the receiving and shipping operations and associated trucking, and the needs of the

operating personnel. The design of the warehouse space should be planned to best accommodate

business service requirements and the products to be stored/handled.

1.1 Different types of warehouses:

Heated and unheated general warehousesprovide space for bulk, rack, and bin

storage, aisle space, receiving and shipping space, packing and crating space, and office

and toilet space.

Refrigerated warehousespreserve the quality of perishable goods and general supply

materials that require refrigeration. Includes freeze and chill space, processing facilities,

and mechanical areas; and

Controlled humidity (CH) warehousessimilar to general warehouses except that they

are constructed with vapor barriers and contain humidity control equipment to maintain

humidity at desired levels.

Special-designed warehouses meeting strict requirements can also provide liquid storage (fuel

and non-propellants), flammable and combustible storage, radioactive material storage,

hazardous chemical storage, and ammunition storage. Warehouse spaces must also be flexible to

accommodate future operations and storage needs as well as mission changes.

Usage:

Warehousing and transportation forms the backbone supply chain of all industries.

Adequate storage capacity and strategic location of the warehouse enables efficient

functioning of supply and distribution.

Proper material handling, storage conditions and timely movement of goods to maintain

the quality of the stored product especially the perishables goods, biological drugs and

food stuffs.

Scientific storage of products to protect from the vagaries of weather, rodents, insects and

pests. They prevent quality and quantity losses.

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1.2 Food grain storage Warehouses in India:

India produces annually about 175 million tons of grain which is stored in various types of

structures of capacities 0.1 to 2500 tons. With increase in production the importance of scientific

storage is being felt. During the last three decades several developments have taken place in

design of structures both at the farmers as well as organizational levels. The warehouse designs

have been so modified that there is less requirement of steel and cement, and utilize maximum

floor space which has reduced the storage cost.

Several types of storage systems are followed in India depending on the length of storage and

product to be stored. Some of them are mentioned below:

Cover and Plinth Storage:

This is an Improvised arrangement of storing food grains in open, generally on a plinth, which is

damp and rat proof. The grain bags are stacked in a standard size on wooden dunnage. The

stacks are covered from all four sides and top with 250 micron LDPE sheets. Food grains in this

system are generally stored for 6-12 months.

Community Storage Structures:

Bulk storage structures of higher capacity are termed community storage. They are made from

reinforced bricks, corrugated galvanized Iron or aluminum sheets in capacities ranging from 25

to 75 t.

Godowns (Bag Storage Structures):

These are primarily meant for providing warehousing facilities to the farmers. The godowns, 100

t to 5000 t capacity, are owned by Govt. agencies.

Twin Span Warehouse with Structural Trusses:

This design was adopted in early Sixties and constructed with brick or stone masonry. Asbestos

or corrugated GI sheets supported by steel trusses are used for roofing. Due to provision of

valley gutters, there IS perennial problem of leakage resulting in damage of stored grain.

Flat RCC Roof Warehouse:

To overcome the disadvantage in earlier design, subsequently the RCC flat type roof structure

was developed to store about 5000 t of grain. The cost of construction of such structures is

excessively higher due to application of steel and cement and it takes a long time in construction.

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Warehouse with Wooden Trusses:

This type of design was found economical in hilly region where good quality wood is available

m plenty. The stored products are safe if the structures have been placed away from moisture.

Conventional Warehouse:

This design has been standardized for storing 5000 t of grain. The walls are made of brick/stone

or concrete masonry and roof of asbestos sheets is supported over RCC Columns.

Modified Conventional Warehouse:

The design of the conventional warehouse has been modified for saving of steel and cement. The

use of mild steel has been replaced by the cold twisted deformed steel. The numbers of

compartments are also reduced. The angle iron trusses are replaced with tubular trusses as they

are lighter in weight compared to steel trusses. The greatest advantage in this design is that no

Intermediate columns are provided to hold the structure as single span roof serves the purpose.

This gives maximum utilization of space without any obstruction.

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Fig 1.Various types of Warehouses Designed in India

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CHAPTER 2

DETAILS OF THE STRUCTURE

Prior to the planning of a warehouse building, it is essential for the planner to consider the

following:

1. Size, shape and location of the plot

2. Specific usage of the warehouse

3. Fund resources available

4. Locally available materials for construction.

5. Meteorological conditions of the area

The plan considered in this project consists of a single storey warehouse with a steel roof truss

with asbestos sheeting on its roof. The structural details of the structure are as follows:

Type of Building: Food grain storage warehouse

Floor area of building: 50x25m

Eaves Height: 6.5m

Type of truss: A-Type truss

Capacity: As per Specifications of Grain godowns - NABARD

No of stacks:

6 Nos 7 x 6.75m

9 Nos 10 x 6.75m

Assuming each stack is approximately 3300 bags of 50 kg which sums up to 2500t.

Location: Hyderabad

2.1 MATERIAL PROPERTIES

Grade of Steel: Fe-415

Wall Cladding: Masonry (Unit weight: 19kN/m3)

Roof cladding: Galvanized corrugated iron sheets of 0.7mm thickness

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2.2 BOUNDARY CONDITIONS

Supports are specified as fixed at footing level. Fixed support has restraints against all directions

of movement.

2.3 COMPONENTS OF WAREHOUSE

For the purpose of structural analysis and design of warehouse the structural engineer has to

consider the following points:

1) Selection of roofing and wall material

2) Selection of bay width

3) Selection of structural framing system

4) Roof trusses

5) Purlins, girts and sag rods.

6) Bracing systems to resist lateral loads

Fig 2: Components of Warehouse

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2.3.1 Truss Configuration:

A roof truss is basically a framed structure formed by connecting various members at their ends

to form a system of triangles, arranged in pre-decided pattern depending upon the span, type of

loading and functional requirements. In industrial buildings and warehouses, steel trusses are

commonly used.

A-shaped truss: This is a type of truss that has a certain general shape resembling the letter A

and its configuration, which is compound of (a) Fink or fink fan, (b) N-truss, has-been used.

The steel truss has been designed as simply supported on columns. The analysis of A-type truss

has been done on the basis of relevant Indian Standards for the following different parameters:

Span length of A-type trusses (meters) = 25

Spacing between trusses (meters) = 5.0

Roof slope=1 in 3,

Column height = 6.5(meters)

Wind zone = Hyderabad

Permeability = Normal

Class of structure = B

Fig 3.A - Type Truss Configuration

*As per SP: 38 Handbook Of Typified Designs For Structures With Steel Roof Trusses A-Type

configuration provides the minimum weight when compared to (a) Fink or fink fan, (b) N-truss

(c) Combination of both i.e. A-Type truss, and at the same time may be easier to fabricate.

Hence, this truss configuration was used for the food grain storage structure.

2.3.2 Components of Truss:

Span

It is the horizontal distance between supports of the truss. When supported on wall

bearings, the distance centre to centre of bearings is the span. In case of trusses framed into

supporting steel columns, the clear distance between the column faces is the actual span.

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Rise

The vertical distance between the apex and the line joining the support is the rise of the

truss.

The roof pitch depends upon the rain or snow which falls on the roof and has to be drained

off. The pitches are steeper in areas of greater rainfall or where snowfall takes place. It also

depends upon the nature of roof cladding.

Slope

Slope of the roof is the angle which the inclined roof surface makes with the horizontal and

may be expressed in terms of degrees or as 1 vertical to x horizontal (1 V : x H). Thus,

value of slope is numerically twice that of pitch.

= 2()

Table 1: Pitch of roof

Pitch of Roof Covering Pitch of

Roof

Corrugated Iron Sheet 1/3 to 1/6

Corrugated Asbestos Cement Sheets 1/5 to 1/6

Tar and Gravel 0 to 1/124

Slate and Tile 1/3 to 1/4

Truss Spacing

The spacing of trusses is the distance (centre to centre) between adjacent trusses. This may

vary between 4 m to 10 m depending upon their size.

Normally they vary from 1/5 to 1/3 of the span.

Ridge Line

It is the line joining the vertices of the trusses.

Eaves Line

It is the line joining the lowest point of the roof trusses, on either side, where the drained

water is collected or lead to rainwater pipes.

Top Chord

The uppermost line of members extending from the eaves to the ridge is the top chord. It is

also called the principal rafter.

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Bottom Chord

The lowermost line of members extending from support to support is known as the bottom

chord. It is also known as main tie.

Ties

Members of the truss which are mainly under tension.

Struts

Those members of the truss which are principally under compression.

Joints

The point where more than one member meet; they are usually connected to a gusset plate

by means of welds or rivets; and are known as welded or riveted joints.

Panel

It is the distance between two adjacent joints in the same line in a member.

Purlin

The purlins are horizontal members spanning across top chord of trusses and support the

roof cladding. In case of tiles and slates these are supported on secondary members called

rafters which are laid over purlins. The purlins are normally placed at the adjacent panel

points of the top chord (or principal rafter); hence the distance between these points is also

the spacing of the purlins.

Sag Tie

A sag tie is a vertical member joining the apex of the truss to the mid-point of the bottom

chord. It is provided to reduce the deflection of the bottom chord member.

Sag Rods

These are round bar threaded at their ends (parallel to the roof slope) and secured to the

purlin webs with nuts (often at their mid-points or one-third points of their span). This is

used to reduce the stresses caused by biaxial bending of the purlins.

Wind Bracing

In case of roof trusses supported on steel columns, lateral bracing has to be provided

against horizontal forces due to wind or earthquake. These are known as wind bracings.

The following bracings can be applied in the three mutually perpendicular planes:

Bracings in vertical plane in the end bays in the longitudinal direction

Bracings in horizontal plane at bottom chord level of roof truss

Bracings in the plane of upper chords of roof truss

Bracings in vertical plane in the end cross sections usually at the gable ends.

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The function of bracing is to transfer horizontal loads from the frames (such as those due to wind

or earthquake or horizontal surge due to acceleration and breaking of traveling cranes) to the

foundation. The longitudinal bracing on each longitudinal ends provide stability in the

longitudinal direction. The gable bracings provide stability in the lateral direction. The tie

bracings at the bottom chord level transfer lateral loads (due to wind or earthquake) of trusses to

the end gable bracings.

2.4Design details of Truss:

a) Roof Slope: It is the slope of the roof material with respect to the span length.

In general, use of 1 in 3 slopes is recommended as this may not pose any fabrication problem

as mentioned in SP: 38, Clause 1.1.

b) Pitch of roof: The pitch of a symmetrical truss is defined as the ratio of rise to the full

span.

Based on the slope of the roof the pitch of truss is determined by using similar triangles

approach, which is 4.2m (1/3 rd. of half of span of truss)

c) Spacing of the Purlin: A structural member fixed perpendicular to the top chord of a truss to support roofing.

The distance between nodes in the rafters is restricted to be less than or equal to 1.4 m such

that the purlins may be located directly at the nodes and thus avoid panel bending of rafters

which has led to lower truss weight. (As per SP: 38, Clause 1.2.1.)

d) Economical spacing of trusses and no of trusses: The economical spacing of trusses is

defined as the spacing which makes the cost of trusses, purlins, columns, roof covering

etc., and minimum.

Spacing between trusses is taken as 5meters. (As per SP: 38, Clause 1.1.). And based on

spacing, the no of trusses along longitudinal direction for roofing can be determined. As

uniform spacing is taken, based on the length of warehouse overall 11 trusses of same

configuration have to be installed.

e) Roof coverings: Roof covering materials include corrugated asbestos sheets or galvanized corrugated (see IS 277) sheets, steel sheets or corrugated aluminum sheets or black

corrugated sheet, not thinner than 0.56 mm. (As per Code of Practice for Construction of

Food grains Storage Structures, Annexure 1).

Galvanized corrugated iron sheets of thickness 0.7mm are used as roof covering.

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2.5Loads acting on Industrial Building

The industrial buildings are subjected to the following loads:

Dead loads:

Dead load on the roof trusses in single storey industrial buildings consists of dead load of

claddings and dead load of purlins, self-weight of the trusses in addition to the weight of

bracings etc. Further, additional special dead loads such as truss supported hoist dead loads,

special ducting and ventilator weight etc. could contribute to roof truss dead loads. The dead load

loads may be calculated from the dimensions of various members and their unit weights.

a) Weight of sheeted steel trusses including rivets can be determined theoretically by

using below empirical formula:

= 4.88 + 0.075

100

where A=plan area in m2

Total dead weight of the roof truss = 0.142kN/m2

Self-weight of truss= 0.142x25x5 = 17.81kN

However, in STAAD the weight of the modeled structure is assigned by default.

b) From IS : 875 (Part 1) 1987- Code of practice for design loads: Dead Loads,

Table1, 39 no, the unit weight of Galvanized corrugated sheeting is 6.5kg/m2

Weight of roofing material = 6.5 x Length of roofing slope x spacing between trusses

x No of sheets per bay

= 6.5 x 13.18 x 5 x 6nos

= 2570.1kg (25.7kN)

c) Miscellaneous loads = 3.5kg/m2 = 3.5 x 25 x 5= 437.5kg

Total Dead load = 25.7+4.37 = 30kN

Dead Load on each intermediate panel = 30

= 30/10 = 3kN

Dead Load on end panel = 3/2 = 1.5kN

Dead load due to RCC wall of 230mm thickness in KN/m = 0.2x6.5x19 = 24.7kN/m

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Imposed loads:

The live load on roof trusses consist of the gravitational load due to erection and servicing as

well as dust load etc. and the intensity is taken as per IS:875-1987. Additional special live loads

such as snow loads in very cold climates, crane live loads in trusses supporting monorails may

have to be considered.

From IS : 875 (Part 1) 1987- Code of practice for design loads: Imposed Loads, clause 6,

Table 2: Sloping roof with slope greater than 10 degrees: For roof membrane sheets or purlins-

0.75 KN/m2 less 0.02 KN/m2 or every degree increase in slope over 10 degrees.

Imposed Loads= 0.75 - (8 x 0.02)=0.59KN/m2

Imposed Load on each intermediate panel = 0.59 x spacing b/t trusses x Length of panel in base

of truss

= 0.59 x 5 x 1.4 cos (1826)

= 3.89kN

Imposed Load on end panel = 3.89/2 = 1.94kN

Wind load:

Wind is air in motion relative to the surface of the earth. The primary cause of wind is traced to

earths rotation and differences in terrestrial radiation. The radiation effects are primarily

responsible for convection either upwards or downwards. The wind generally blows horizontal to

the ground at high wind speeds. Since vertical components of atmospheric motion are relatively

small, the term wind denotes almost exclusively the horizontal wind, vertical winds are always

identified as such. The wind speeds are assessed with the aid of anemometers or anemographs

which are installed at meteorological observatories at heights generally varying from 10 to 30

meters above ground.

Design Wind Speed ():

It is the wind speed for which the structure is to be designed. The basic wind speed (V,) for any

site shall be obtained from and shall be modified to include the following effects to get design

wind velocity at any height (V,) for the chosen structure:

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a) Risk level;

b) Terrain roughness, height and size of structure; and

c) Local topography.

It can be mathematically expressed as follows:

Where:

=

= design wind speed at any height z in m/s;

= probability factor (risk coefficient)

= terrain, height and structure size factor and

= topography factor

Risk Coefficient (1 Factor):

It gives basic wind speeds for terrain Category 2 as applicable at 10 m above ground level based

on 50 years mean return period. In the design of all buildings and structures, a regional basic

wind speed having a mean return period of 50 years shall be used.

Terrain, Height and Structure Size Factor (2 Factor):

Terrain - Selection of terrain categories shall be made with due regard to the effect of

obstructions which constitute the ground surface roughness. The terrain category used in the

design of a structure may vary depending on the direction of wind under consideration.

Wherever sufficient meteorological information is available about the nature of wind direction,

the orientation of any building or structure may be suitably planned.

Topography (3 Factor):

The basic wind speed Vb takes account of the general level of site above sea level. This does not

allow for local topographic features such as hills, valleys, cliffs, escarpments, or ridges which

can significantly affect wind speed in their vicinity. The effect of topography is to accelerate

wind near the summits of hills or crests of cliffs, escarpments or ridges and decelerate the wind

in valleys or near the foot of cliff, steep escarpments, or ridges.

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2.6 Wind Pressures And Forces On Buildings/Structures:

Design Wind Pressure (PZ)

It depends upon the basic wind velocity (Vb), the height of the structure (z) above ground level,

the terrain category, the local topography, the aspect ratio (i.e. ratio of the length and breadth of

the building or structure), the slope of the structure and the solidity ratio or openings in the

structures. This is obtained by the following formula

= .() /

where Vz is the design wind speed in m/sec at height z. For determination of Vs. and, therefore,

Pz, you are referred to consult IS: 875 (Part III: Wind Loads).

The effect of wind on steel roof structures is also to create either suction (negative pressure) or

pressure (positive) depending on the angle of inclination or slope of the roof, and the direction of

prevailing winds.

Pressure Coefficients - The pressure coefficients are always given for a particular surface or

part of the surface of a building. The wind load acting normal to a surface is obtained by

multiplying the area of that surface or its appropriate portion by the pressure coefficient (C,) and

the design wind pressure at the height of the surface from the ground. The average values of

these pressure coefficients for some building shapes Average values of pressure coefficients are

given for critical wind directions in one or more quadrants. In order to determine the maximum

wind load on the building, the total load should be calculated for each of the critical directions

shown from all quadrants. Where considerable variation of pressure occurs over a surface, it has

been subdivided and mean pressure coefficients given for each of its several parts.

Then the wind load, F, acting in a direction normal to the individual structural element or

Cladding unit is:

F= ( ) Where,

= external pressure coefficient,

= internal pressure- coefficient,

A = surface area of structural or cladding unit, and

= design wind pressure element

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2.6.1 Wind Load Calculations:

Design wind speed, =

From Table 1; IS: 875 (part 3) 1987

1 = 1.0 (risk coefficient assuming 50 years of design life)

From Table 2; IS: 875 (part 3) 1987

2 = 1.035 (assuming terrain category 1)

3 = 1.0 (topography factor)

Assuming the building is situated in Hyderabad, the basic wind speed is 44 m/sec

Design wind speed,

= 44 * 1 * 1.035 *1

= 45.54 m/sec

Design wind pressure, = .() /

= 0.6 * (45.54)2= 1.244kN/m2

Permeability of building:

Area of walls = 6.5*((25x2) + (50x2)) = 975m2

Area of openings = (48x1.4x0.5) + (4x3.5x2) = 61.6m2

% opening area = 6.317%, between 5% & 20%. Hence the building is of medium permeability.

(As per IS: 875 (part 3) 1987, clause 6.2.3.2)

Wind Load on Wall:

Total wind load acting on wall can be given by product of design wind pressure and exposed

surface area. The exposed surface area of wall between each bay is calculated and total wind

load acting on the wall is calculated.

Wind Load on truss roof:

As wind load, F, acting in a direction normal to the individual structural element or Cladding unit

is given by below equation:

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F= ( )

As the roof angle is 1826 and h/w ratio is less than and equal to 0.5, the external pressure

coefficient, is given by table 6 of IS: 875 (part 3) 1987. By interpolation for the provided roof angle:

Table 2: Interpolation of external pressure coefficient

h/w Roof Angle Wind

Angle (0)

Wind

Angle(90)

0.26

Windward

side

Leeward side Windward

side

Leeward side

10 -1.2 -0.4 -0.8 -0.6

20 -0.4 -0.4 -0.7 -0.6

Here roof angle is 1826, then by interpolating we get

18.5 -0.52 -0.4 -0.715 -0.6

As buildings are of low degree of permeability, = 0.5 (As per IS: 875 (part 3) 1987,

clause 6.2.3.2)

Length of each panel along sloping roof = 1.4 x cos (1827) = 1.32m

Tributary area of each node: A= 5x1.32 = 6.6m2

Table 3: Wind load calculations

Wind

angle

Pressure

Coefficient() (-) A*

(KN)

Wind load F

(KN)

W L Windward Leeward Windward Leeward

0 -0.52 -0.4 0.5 -1.02 -0.9 8.21 -8.37 -7.38

-0.5 -0.02 0.1 8.21 -0.164 0.821

90 -0.715 -0.6 0.5 -1.212 -0.1 8.21 -9.97 -0.821

-0.5 -0.215 -0.1 8.21 -1.76 -0.821

Table 4: Loads applied on truss nodes

Wind angle Windward side (W3) Leeward side (W4)

Intermediate

node (W3)

End node.

(W3/2)

Intermediate

node (W4)

End node

(W4/2)

0 -8.37 -4.185 -7.38 -3.69

90 -9.97 -4.985 -0.821 -0.410

Loads are in KN

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2.7 SEISMIC LOAD:

Design Lateral Force The design lateral force shall first be computed for the building as a whole. This design lateral

force shall then be distributed to the various floor levels. The overall design seismic force thus

obtained at each floor level shall then be distributed to individual lateral load resisting elements

depending on the floor diaphragm action.

Design Seismic Base Shear The total design lateral force or design seismic base shear (Vb) along any principal direction

shall be determined by the following expression:

Vb= Ah W

Where,

Ah = horizontal acceleration spectrum = (Z*I*Sa)/ (2*R*g)

W = seismic weight of all the floors

Fundamental Natural Period The approximate fundamental natural period of vibration (T,), in seconds, of a moment-resisting

frame building without brick in the panels may be estimated by the empirical expression:

Ta=0.075 0.75 for RC frame building

Ta=0.085 0.75 for steel frame building

Where,

h = Height of building, in m. This excludes the basement storeys, where basement walls are

connected with the ground floor deck or fitted between the building columns. But it includes the

basement storeys, when they are not so connected. The approximate fundamental natural period

of vibration (T,), in seconds, of all other buildings, including moment-resisting frame buildings

with brick lintel panels, may be estimated by the empirical Expression:

=0.09

Where,

H= Height of building

d= Base dimension of the building at the plinth level, in m, along the considered direction of the

lateral force.

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Distribution of Design Force Vertical Distribution of Base Shear to Different Floor Level

The design base shear (V) shall be distributed along the height of the building as per the

following expression:

=

2

2

=1

Qi=Design lateral force at floor i,

Wi =Seismic weight of floor i,

hi =Height of floor i measured from base, and

n=Number of storeys in the building is the number of levels at which the masses are located.

Distribution of Horizontal Design Lateral Force to Different Lateral Force Resisting

Elements in case of buildings whose floors are capable of providing rigid horizontal diaphragm

action, the total shear in any horizontal plane shall be distributed to the various vertical elements

of lateral force resisting system, assuming the floors to be infinitely rigid in the horizontal plane.

In case of building whose floor diaphragms cannot be treated as infinitely rigid in their own

plane, the lateral shear at each floor shall be distributed to the vertical elements resisting the

lateral forces, considering the in-plane flexibility of the diagram.

2.7.1 Base shear Calculations

=0.09

H= 10.7m

D=25m

T= 0.09 x 10.7/ 25 =0.171s

The building is located in Type II medium soil, From Fig 2 in IS 1893 for T= 0.171s

Sa/g=2.5

=

2 (/)

Z=0.1(Zone factor)

I=1 (Importance Factor Table 6)

R=4 (Response reduction Factor)

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= 0.031

= x W = 0.031x 120027.6

=3720.8 KN

CHAPTER 3

WORKING WITH STAAD.Pro

3.1 Input Generation:

The GUI (or user) communicates with the STAAD analysis engine through the STD input file.

That input file is a text file consisting of a series of commands which are executed sequentially.

The commands contain either instructions or data pertaining to analysis and/or design. The

STAAD input file can be created through a text editor or the GUI Modeling facility. In general,

any text editor may be utilized to edit/create the STD input file. The GUI Modeling facility

creates the input file through an interactive menu-driven graphics oriented procedure.

Fig 3.1: STAAD input file

3.2 Types of Structures:

A STRUCTURE can be defined as an assemblage of elements. STAAD is capable of analyzing

and designing structures consisting of frame, plate/shell and solid elements. Almost any type of

structure can be analyzed by STAAD.

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A SPACE structure, which is a three dimensional framed structure with loads applied in any

plane, is the most general.

A PLANE structure is bound by a global X-Y coordinate system with loads in the same plane.

A TRUSS structure consists of truss members which can have only axial member forces and no

bending in the members.

A FLOOR structure is a two or three dimensional structure having no horizontal (global X or Z)

movement of the structure [FX, FZ &MY are restrained at every joint]. The floor framing (in

global X-Z plane) of a building is an ideal example of a FLOOR structure. Columns can also be

modeled with the floor in a FLOOR structure as long as the structure has no horizontal loading.

If there is any horizontal load, it must be analyzed as a SPACE structure.

3.3 Generation of the structure: The structure may be generated from the input file or

mentioning the co-ordinates in the GUI. The figure below shows the GUI generation method.

Fig 3.2: GUI

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3.4 Material Constants:

The material constants are: modulus of elasticity (E); weight density (DEN); Poisson's ratio

(POISS); co-efficient of thermal expansion (ALPHA), Composite Damping Ratio, and beta angle

(BETA) or coordinates for any reference (REF) point. E value for members must be provided or

the analysis will not be performed. Weight density (DEN) is used only when self-weight of the

structure is to be taken into account. Poisson's ratio (POISS) is used to calculate the shear

modulus (commonly known as G) by the formula,

G = 0.5 x E/ (1 + POISS)

If Poisson's ratio is not provided, STAAD will assume a value for this quantity based on the

value of E. Coefficient of thermal expansion (ALPHA) is used to calculate the expansion of the

members if temperature loads are applied. The temperature unit for temperature load and

ALPHA has to be the same.

3.5 Supports:

Supports are specified as PINNED, FIXED, or FIXED with different releases (known as FIXED

BUT). A pinned support has restraints against all translational movement and none against

rotational movement. In other words, a pinned support will have reactions for all forces but will

resist no moments. A fixed support has restraints against all directions of movement.

Translational and rotational springs can also be specified. The springs are represented in terms of

their spring constants. A translational spring constant is defined as the force to displace a support

joint one length unit in the specified global direction. Similarly, a rotational spring constant is

defined as the force to rotate the support joint one degree around the specified global direction.

3.6 Loads:

Loads in a structure can be specified as joint load, member load, temperature load and fixed-end

member load. STAAD can also generate the self-weight of the structure and use it as uniformly

distributed member loads in analysis. Any fraction of this self-weight can also be applied in any

desired direction.

Joint loads:

Joint loads, both forces and moments, may be applied to any free joint of a structure. These loads

act in the global coordinate system of the structure. Positive forces act in the positive coordinate

directions. Any number of loads may be applied on a single joint, in which case the loads will be

additive on that joint.

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Member load:

Three types of member loads may be applied directly to a member of a structure. These loads are

uniformly distributed loads, concentrated loads, and linearly varying loads (including

trapezoidal). Uniform loads act on the full or partial length of a member. Concentrated loads act

at any intermediate, specified point. Linearly varying loads act over the full length of a member.

Trapezoidal linearly varying loads act over the full or partial length of a member. Trapezoidal

loads are converted into a uniform load and several concentrated loads. Any number of loads

may be specified to act upon a member in any independent loading condition. Member loads can

be specified in the member coordinate system or the global coordinate system. Uniformly

distributed member loads provided in the global coordinate system may be specified to act along

the full or projected member length.

Area/floor load:

Many times a floor (bound by X-Z plane) is subjected to a uniformly distributed load. It could

require a lot of work to calculate the member load for individual members in that floor.

However, with the AREA or FLOOR LOAD command, the user can specify the area loads (unit

load per unit square area) for members. The program will calculate the tributary area for 14

these members and provide the proper member loads. The Area Load is used for one way

distributions and the Floor Load is used for two way distributions.

Fixed end member load:

Load effects on a member may also be specified in terms of its fixed end loads. These loads are

given in terms of the member coordinate system and the directions are opposite to the actual load

on the member. Each end of a member can have six forces: axial; shear y; shear z; torsion;

moment y, and moment z.

Load Generator Moving load, Wind & Seismic:

Load generation is the process of taking a load causing unit such as wind pressure, ground

movement or a truck on a bridge, and converting it to a form such as member load or a joint load

which can be then be used in the analysis.

Moving Load Generator:

This feature enables the user to generate moving loads on members of a structure. Moving load

system(s) consisting of concentrated loads at fixed specified distances in both directions on a

plane can be defined by the user. A user specified number of primary load cases will be

subsequently generated by the program and taken into consideration in analysis.

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Seismic Load Generator:

The STAAD seismic load generator follows the procedure of equivalent lateral load analysis. It

is assumed that the lateral loads will be exerted in X and Z directions and Y will be the direction

of the gravity loads. Thus, for a building model, Y axis will be perpendicular to the floors and

point upward (all Y joint coordinates positive). For load generation per the codes, the user is

required to provide seismic zone coefficients, importance factors, and soil characteristic

parameters. Instead of using the approximate code based formulas to estimate the building period

in a certain direction, the program calculates the period using Raleigh quotient technique. This

period is then utilized to calculate seismic coefficient C. After the base shear is calculated from

the appropriate equation, it is distributed among the various levels and roof per the

specifications. The distributed base shears are subsequently applied as lateral loads on the

structure. These loads may then be utilized as normal load cases for analysis and design.

Wind Load Generator:

The STAAD Wind Load generator is capable of calculating wind loads on joints of a structure

from user specified wind intensities and exposure factors. Different wind intensities may be

specified for different height zones of the structure. Openings in the structure may be modeled

using exposure factors. An exposure factor is associated with each joint of the structure and is

defined as the fraction of the influence area on which the wind load acts. Built-in algorithms

automatically calculate the exposed area based on the areas bounded by members (plates and

solids are not considered), then calculates the wind loads from the intensity and exposure input

and distributes the loads as lateral joint loads.

3.7 General Comments:

This section presents some general statements regarding the implementation of Indian Standard

code of practice (IS: 800-1984) for structural steel design in STAAD. The design philosophy and

procedural logistics for member selection and code checking are based upon the principles of

allowable stress design. Two major failure modes are recognized: failure by overstressing, and

failure by stability considerations. The flowing sections describe the salient features of the

allowable stresses being calculated and the stability criteria being used. Members are

proportioned to resist the design loads without exceeding the allowable stresses and the most

economic section is selected on the basis of least weight criteria. The code checking part of the

program checks stability and strength requirements and reports the critical loading condition and

the governing code criteria. It is generally assumed that the user will take care of the detailing

requirements like provision of stiffeners and check the local effects such as flange buckling and

web crippling.

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Allowable Stresses:

The member design and code checking in STAAD are based upon the allowable stress design

method as per IS: 800 (1984). It is a method for proportioning structural members using design

loads and forces, allowable stresses, and design limitations for the appropriate material under

service conditions. It would not be possible to describe every aspect of IS: 800 in this manual.

This section, however, will discuss the salient features of the allowable stresses specified by IS:

800 and implemented in STAAD. Appropriate sections of IS: 800 will be referenced during the

discussion of various types of allowable stresses.

Multiple Analyses:

Structural analysis/design may require multiple analyses in the same run. STAAD allows the

user to change input such as member properties, support conditions etc. in an input file to

facilitate multiple analyses in the same run. Results from different analyses may be combined for

design purposes. For structures with bracing, it may be necessary to make certain members

inactive for a particular load case and subsequently activate them for another. STAAD provides

an INACTIVE facility for this type of analysis.

3.8 Post Processing Facilities:

All output from the STAAD run may be utilized for further processing by the STAAD.Pro GUI.

Stability Requirements:

Slenderness ratios are calculated for all members and checked against the appropriate maximum

values. IS: 800 summarize the maximum slenderness ratios for different types of members. In

STAAD implementation of IS: 800, appropriate maximum slenderness ratio can be provided for

each member. If no maximum slenderness ratio is provided, compression members will be

checked against a maximum value of 180 and tension members will be checked against a

maximum value of 400.

Deflection Check:

This facility allows the user to consider deflection as criteria in the CODE CHECK and

MEMBER SELECTION processes. The deflection check may be controlled using three

parameters. Deflection is used in addition to other strength and stability related criteria. The local

deflection calculation is based on the latest analysis results.

Code Checking:

The purpose of code checking is to verify whether the specified section is capable of satisfying

applicable design code requirements. The code checking is based on the IS: 800 (1984)

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requirements. Forces and moments at specified sections of the members are utilized for the code

checking calculations. Sections may be specified using the BEAM parameter or the SECTION

command. If no sections are specified, the code checking is based on forces and moments at the

member ends.

CHAPTER 4

DYNAMIC ANALYSIS OF FOOD GRAIN STORAGE

HOUSE USING STAAD.Pro

Plan:

Fig 4.1: Plan of Warehouse

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Floor area of building: 50x25m

Capacity: As per Specifications of Grain godowns - NABARD

No of stacks:

6 Nos 7x6.75m

9 Nos 10x6.75m

Assuming each stack is approximately 3300 bags of 50 kg which sums up to 2500t.

Span length of A-type trusses (meters) = 25

Spacing between trusses (meters) = 5.0

Roof slope=1 in 3,

Column height = 6.5(meters)

Wind zone = Hyderabad

Permeability = Normal

Class of structure = B

Rise of truss = 4.2m

Elevation:

Fig 4.2: Elevation of Warehouse

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3D Image:

Fig 4.3: 3-D Image of warehouse

4.1 Physical parameters of building:

Length = 10 bays @ 5.0m = 50.0m

Width = 1 bay =25.0m

Height = 6.5m + 4.2m rise of truss = 10.7m

Grade of concrete and steel used:

Used M30 concrete and Fe 415 steel

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4.2 Generation of member property:

Fig 4.4: Member property

Generation of member property can be done in STAAD.Pro by using the window as shown

above. The member section is selected and the dimensions have been specified.

Bottom Chord: LSA 100x100x6LD

Struts & Ties : 90x90x6LD

Bracings : 90x90x6

4.3 Supports:

The base supports of the structure were assigned as fixed. The supports were generated using the

STAAD.Pro support generator.

4.4 Materials for the structure:

The materials for the structure were specified as steel with their various section sizes as per

standard IS code of practice.

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4.5 Loading:

The loadings were calculated partially manually and rest was generated using STAAD.Pro load

generator. The loading cases were categorized as:

Self-weight

Dead load due to non-modeled elements

Live load

Wind load

Seismic load

Load combinations

Self-weight

The self-weight of the structure can be generated by STAAD.Pro itself with the self-weight

command in the load case column.

Dead load due to non-modeled elements

As calculated impervious section 2.5

Weight of roofing material = 2570.1kg (25.7kN)

Miscellaneous loads = 437.5kg (4.37kN)

Total Dead load = 25.7+4.37 = 30kN

Dead Load on each intermediate panel = 30

= 30/10 = 3kN

Dead Load on end panel = 3/2 = 1.5kN

Dead load due to RCC wall of 230mm thickness in kN/m = 0.2x6.5x19 = 24.7kN/m

Live load

As calculated in previous section 2.5

Imposed Load on each intermediate panel = 3.89kN

Imposed Load on end panel = 3.89/2 = 1.94kN

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Wind load

As calculated in previous section 2.6.1

Wind load on truss roof

Table 4.1:Wind load on truss roof

Wind angle Windward side (W3) Leeward side (W4)

Intermediate

node (W3)

End node.

(W3/2)

Intermediate

node (W4)

End node

(W4/2)

0 -8.37 -4.185 -7.38 -3.69

90 -9.97 -4.985 -0.821 -0.410

Loads are in kN

Seismic load:

STAAD.Pro has a seismic load generator in accordance with the IS code mentioned.

Description:

The seismic load generator can be used to generate lateral loads in the X and Z directions only. Y

is the direction of gravity loads. This facility has not been developed for cases where the Z axis

is set to be the vertical direction using the SET Z UP command.

Methodology:

The design base shear is computed by STAAD in accordance with the IS: 1893(Part 1)-2002.

V = Ah*W

Where, Ah = (Z*I*Sa)/ (2*R*g)

STAAD utilizes the following procedure to generate the lateral seismic loads.

User provides seismic zone co-efficient and desired "1893(Part 1)-2002 specs" through

the DEFINE 1893 LOAD command.

Program calculates the structure period (T).

Program calculates Sa/g utilizing T.

Program calculates V from the above equation. W is obtained from the weight data

provided by the user through the DEFINE 1893 LOAD command.

The total lateral seismic load (base shear) is then distributed by the program among

different levels of the structure per the IS: 1893(Part 1)-2002 procedures.

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General format:

DEFINE 1893 LOAD

ZONE f1 1893-spec

SELFWEIGHT

JOINT WEIGHT

Joint-list WEIGHT w

1893-Spec= {RF f2, I f3, SS f4, (ST f5), DM f6, (PX f7),

(PZ f8), (DT f9)}

Where,

Zone f1 = Seismic zone coefficient.

RF f2 = Response reduction factor.

I f3 = Importance factor depending upon the functional use. of the structures,

characterized by hazardous consequences of its failure, post-earthquake functional needs,

historical value, or economic importance.

SS f4 = Rock or soil sites factor (=1 for hard soil, 2 for medium soil, 3 for soft soil).

Depending on type of soil, average response acceleration coefficient Sa/g is calculated

corresponding to 5% damping

ST f5 = Optional value for type of structure (=1 for RC frame building, 2 for Steel frame

building, 3 for all other buildings).

DM f6 = Damping ratio to obtain multiplying factor for calculating Sa/g for different

damping. If no damping is specified 5% damping (default value 0.05) will be considered

corresponding to which multiplying factor is 1.0.

PX f7 = Optional period of structure (in sec) in X direction. If this is defined this value

will be used to calculate Sa/g for generation of seismic load along X direction.

PZ f8 = Optional period of structure (in sec) in Z direction. If this is defined this value

will be used to calculate Sa/g for generation of seismic load along Z direction.

DT f9 = Depth of foundation below ground level. It should be defined in current unit. If

the depth of foundation is 30 m or below, the value of Ah is taken as half the value

obtained. If the foundation is placed between then ground level and 30 m depth, this

value is linearly interpolated between Ah and 0.5Ah.

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Calculation of Shear Force, Bending Moment for Gravity Loads:

Fig 4.5: Deformed shape

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Shear force diagram:

Fig 4.6: SF in X direction

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SF in Z direction:

Fig 4.7: SF in Z direction

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Bending Moment Diagram:

Fig 4.8: Bending Moment

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Mode Shapes:

Mode shape 1:


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Mode shape 2:


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Mode shape 3


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Mode shape 4


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CHAPTER 5

DYNAMIC ANALYSIS

5.1 Time History Analysis:

Time History is a record of the ground acceleration at defined time segments for a specific

earthquake in a certain direction. The record is usually normalized and therefore needs to be

multiplied by the acceleration due to gravity or a factor thereof.

5.2 Response Spectrum Analysis

Response spectrum method of analysis shall be performed using the design spectrum specified,

or by a site-specific design spectrum mentioned.

Differences between Base Shear obtained from Time History analysis and

Response Spectrum Analysis and manual base shear calculations

In the time history method, the structure is subjected to time wise variations of

ground motions, and the response of the structure is determined by integrating the

equations of motion in a step-by-step manner.

Having established the structural model and the input motions, the time history

analysis per se is considered exact and yields accurate data. On the other hand, the

response spectrum concept is relatively simple and the computations are not as

involved as the time history method.

The speed advantages of running a Response Spectrum analysis over a full Time History analysis can be substantial. In design, the Response Spectrum analysis

can provide an even greater speed advantage, due to the fact that the design check

does not need to be done at each time segment.

For this building, base shear due to Time history is higher in magnitude as

compared to Response spectrum. Since response spectrum is approximate

method, such difference in calculation of base shear is experienced.

Base Shear due to

Response Spectrum

Base Shear due to

Time History

Manual Base Shear

At ground 2685.9 KN 1342.95 KN 3805.78KN

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6. Conclusion:

1) Due to wind load alone the warehouse structure was subjected to uplift as it can be deduced

from the deflection profile. Hence, the weight of sections to be increased to make the structure

stable.

2) For time history analysis for elcentro ground motion, the structure was stable as the structural

members were subjected to uniform bending and shear due to symmetry of the structure.

3) Its been observed that the base shear due to time history is less compared to response

spectrum because response spectrum is calculated for the total design and the total maximum

displacement and shall include simultaneous excitation of the model 100% of the most critical direction

of ground motion

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7. References

1. SP-38(S & T):1987 - Handbook of typified design for structures with steel roof trusses,

Bureau of Indian Standards.

2. IS: 875[Part 1]:1987, Code of practice for design loads-Dead loads, Bureau of Indian

Standards.

3. IS: 875[Part 2], 1987, Code of practice for design loads-Imposed loads, Bureau of Indian

Standards.

4. IS: 875[Part 3], 1987, Code of practice for design loads-Wind loads, Bureau of Indian

Standards.

5. IS 1875:1992, Carbon Steel billets, Blooms, Slabs and Bars for forging-specifications,

Bureau of Indian Standards.

6. SP-64(S & T): 2001, Explanatory Handbook on Indian Standard Code of Practice for

Design Loads, Bureau of Indian Standards.

7. IS 277:2003, Galvanized steel sheets (Plain and corrugated)-specification, Bureau of

Indian Standards.

8. IS 607:1971, Code of practice for construction of Food grain Storage Structures,

NABARD.

9. Ram Chandra (2007),Design of Steel structure Vol.-1,Scientific publisher

case project

Documents

india fig

gui fig

components of warehouse

plan of warehouse fig

elevation of warehouse

deformed shape fig

staadpro analysis

staad input file fig