Gantry Girder
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Transcript of Gantry Girder
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