Automated design of gantry girder

DEPARTMENT OF APPLIED MECHANICS SARDAR VALLABHBHAI NATIONAL INSTITUTE OF TECHNOLOGY

SURAT-395007

PRESENTED BY

PRAVEEN KUMAR , an undergraduate student

DR. S. N DESAI, Head Of Department, AMD

INTRODUCTION

The travelling over head cranes are

commonly used in factories,

workshops, and heavy industrial

buildings to lift and move loads from

one point to other. The movement of

load is of three dimensional nature.

The cranes is required to lift heavy

mass vertically and horizontally, also

the crane with load is required to

move along the length of the shed.

This crane moves on rails which are at

its ends. The rails are provided on a

girder called gantry girder.

COMPONENTS OF OVER HEAD TRAVELLING CRANE RUNWAY

The crane : crane girder, crab, trolley, hoist, power

transmitting devices and a cab which houses

the controls and operator

Crane rails and their attachments

The gantry girder

The gantry girder supporting columns or brackets

The crane stops

MOVEMENTS

crab

Movement of loads

Wheel carriage

Crane rail

FORCES

Braking

surge

crab

Crane load + hook load

Wheel load

braking

Wheel load surge

Wheel load

surge

Wheel load

surge

Crane frame weight

Vertical Forces

Vertical forces acting on the gantry girder are the vertical reaction from the

crane girder and self weight of the gantry girder.

The maximum wheel load is due to the weight of the crane girder, the crab

and the crane capacity and occurs when the crab is nearest to the gantry

girder. The effect of impact has to be included

Fatigue Effects

Gantry Girders are subjected to fatigue effects due to moving loads.

Normally light and medium duty cranes are not checked for fatigue

effects if the number of cycles of load is less than 5 x10106.

Foe heavy duty cranes , the gantry girders are to be checked for

fatigue loads (IS 1024 and IS 807)

Horizontal Forces

Horizontal forces are of two types:

Longitudinal Forces are those which act parallel to the gantry girder. Lateral

Forces are those which act in a direction perpendicular to the gantry girder.

a. Longitudinal Forces

These are caused due to the starting/stopping or acceleration/deceleration

of the crane. These produce thrust along the longitudinal direction of the

gantry girder. These are transferred at the rail level. Therefore, the gantry

girders are subjected to moments due to these forces.

b. Lateral Forces

These are caused due to the starting/stopping or acceleration deceleration

of the crab. These produce thrust normal to the gantry girder. These

produce bending moment in the girder in a horizontal plane.

L

C

W

L/2

C/4

W

L/2

(2.l – C)

2𝑤

𝐿

2𝑤

𝐿

(L/2-c/4)^2

Shear force and equation

𝑤𝐿

4

Maximum bending moment

bending moment

= WcL3 [(3a/4L)-(a3/L3)]/(6EI)

STRUCTURAL FEATURES OF GANTRY GIRDER

Design of gantry girder is a classic example of

laterally unsupported beam

Its is subjected to in addition to vertical loads

and horizontal loads along and perpendicular

to its axis Traction

Braking

Impact on crane stops

Loads are of dynamic nature and produce

vibrations

Compression flange requires critical attention

SELECTION OF GANTRY GIRDER

(a) shows a wide flange beam with out any reinforcement and

may be used for short spans and very light crane loads.

(b) a cover plate is used on the compression face which improves the

lateral buckling strength of the beam and provides larger moment of

inertia about the vertical axis against the lateral loads.

(c) a channel has been used instead of the cover plate to further

increase Ivv.

(d) the channel is used just below the compression flange of the wide

flange beam and is supported by brackets to increase the torsional

stiffness of the girder.

(e),(f) show plate girder sections used for longer spans and heavier crane

loads.

Sr.no. Choice Condition

1. I-section MOT cranes

2. I-sections with plates/channels spans up to 8 m and 50 kN cranes

3. Plate girders spans from 6 to 10 m

4. Plate girder with channels, angles etc. spans more than 10 m

5. Box girders with angles Span more than 12 m

REQUIRED FEATURES

Single span gantry girders are desirable

Span, short and beam depth large

Beam capable of taking localized loads, web crushing not critical

Full penetration of groove weld between web and top flange

of welded plate gantry girder

Use of continuous welds rather than intermittent weld

Rail depth

“k” distance of I

section Affected

length

Rail depth

“k” distance of I

section

Affected length

Welded or rolled gantry girder

bolted or riveted gantry girder

Affected length

3.5 x (rail depth + flange thickness)

Affected length

3.5 x(rail depth + cover plate

thickness + gauge distance)

Intermediate stiffeners underside of top flange and down the

web

0.75tw

tw

Lateral loads are resisted by the channel (or plates/ angles)

plus the top flange of the beam and vertical loads are resisted

by both beam and channel (or plates/ angles)

If clamps are used to fasten the rails above the girder, it is

necessary to select member sizes that accept the required

spacing

PROBLEMS

Prevent abrupt changes in cross sections

Prevent Cantilevered gantry girder

While using high strength steel, check deflection as section

may get smaller

End rotation and deflection

Stretching of rails

opening of splice joints

column bending

skewing of crane girders

undulating crane motion

Column The crane girders are supported either on brackets connected to

columns of uniform section with brackets or on stepped columns

Column bracket stepped columns

Impact considered in design of brackets

Stiffeners at end of beam to prevent web buckling

Design bolts to resist longitudinal loads

Design bolts to resist longitudinal loads

shims used (bracket and bottom of flange) to re-level gantry girders

Lonitudnal forces causes torque on columns with brackets,

horizontal struts used to minimize it

COLUMN BRACKET WITH LIGHT LOADS

STEPPED COLUMN

Used when bracket use turns uneconomical

Gantry column oriented in such a way that its strong axis resists

wind , seismic, lateral crane loads

Web of gantry girder should not be connected to columns by

diaphragm – fatigue failure risk

When Top flange lateral bracing not of adequate strength add

diaphragm

Separate diaphragm for each beam

stepped columns

Diaphragm:

Should not be connected

this way, instead thorough

diaphragm should be

used

BRACINGS

Laterally and longitudinally

Most effective, simplest X bracings

Limit 𝑳

𝒓 𝐫𝐚𝐭𝐢𝐨 𝐭𝐨 𝟐𝟎𝟎

Bracings should never be of rods

Locate braces near Centre of runway- allows contraction and thermal expansion

knee Bracings should never be used

Types of bracings

Crane stops

Prevents crane moving past rail end

Located at any location

Gaps (25 mm per every 30m) are provide between and of rail

and face of stop to accommodate thermal expansion and

creep

Height of stop = 450 to 750 mm above rail top

2 types “ typical crane stop and heavy duty stop

Design steps

Calculate the Maximum Wheel load, assume size of girder

For depth = L/12 and width = L/30

Calculate the Maximum Bending Moment Due to Vertical Forces (Mz)

Apply multiplication factor 1.5 for live load and dead load

Calculate the Maximum Shear Force

]2222[)(6.15

cc

LLLE

cLW

ZZI

yp fMZ /4.1

Approximate

Classify the section (plastic, compact, semi-compact)

Calculate Iz , Zz, Calculation of plastic sectional modulus (Zpz, Zpy)

00 /2.1/ myemypbd fZfZM

1dy

y

dz

z

M

M

M

M

Check for local moment capacity

Combined local capacity check

bdpd fZM

LT crypb MfZ / crye MfZ /2.1

22.015.0 LTLTLTLT

0.1

15.022

LTLTLT

LT

5.02

2

2

1/

/

20

11

)(2

ff

yLT

LT

fy

crth

rL

L

hEICM

Check for buckling resistance

=

fbd = LT fy /m0

1dy

y

dz

z

M

M

M

M

Check for shear dVV 6.0

dV )3/( 0mywv fA =

Check for deflection

lf

s

mw

u

37.0

ZIyVAq /

Weld design

strength of weld =

Biaxial bending

Automated design inputs…..

Loads :-

Crane Capacity Wc

No. Of Eot Cranes

Self Wt. Of Crane Excl. Trolly

Self Wt. Of Troley,Hook Etc.

Minimum Hook Approach, rail hieght

Distance Between Wheel Centre C

Minimum Distance Between Cranes

Span Of Crane Between The Rails

Span Of Gantry Girder

Fy, E

Selection of sections

Diameter of wheel

Weld size

Screen shots….

THANK YOU