Automated design of gantry girder

DEPARTMENT OF APPLIED MECHANICSSARDAR 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

Crane girder

FORCES

Braking

surge

crab

Crane load + hook load

Wheel load

Crane girder

braking

Wheel loadsurge

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 EffectsGantry 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 x10.

Foe heavy duty cranes , the gantry girders are to be checked for fatigue loads (IS 1024 and IS 807)

Horizontal ForcesHorizontal 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 ForcesThese 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)

2𝑤𝐿

2𝑤𝐿

(L/2-c/4)^2

Shear force and equation

𝑤𝐿4

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 sectionAffected

length

Rail depth

“k” distance of I section

Affected length

Welded or rolled gantry girder

bolted or riveted gantry girder

Affected length3.5 x (rail depth + flange thickness)

Affected length3.5 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 railsopening of splice joints

column bendingskewing of crane girdersundulating 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 𝐫𝐚𝐭𝐢𝐨 𝐭𝐨𝟐𝟎𝟎

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 girderFor 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 loadCalculate the Maximum Shear Force

]2222[)(6.15

ccLL

LE

cLWZZI

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

fycr th

rL

L

hEICM

Check for buckling resistance

=

fbd = LT fy /gm0

1dy

y

dz

z

M

M

M

M

Check for shear dVV 6.0

dV )3/( 0mywv fA =

Check for deflection

lf

smw

u

37.0

ZIyVAq /

Weld design

strength of weld =

Biaxial bending

Automated design inputs…..

Loads :-

Crane Capacity WcNo. Of Eot CranesSelf Wt. Of Crane Excl. TrollySelf 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