Automated design of gantr gantry y girder girder
DEPARTMENT OF APPLIED MECHANICS SARDAR VALLABHBHAI NATIONAL INSTITUTE OF TECHNOLOGY SURAT-395007
PRESENTED BY
PRAVEEN KUMAR , an undergraduate student 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, 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.
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, 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
Wheel carriage
Movement of loads Crane rail
FORCES Wheel load
braking
surge surge
crab
Wheel load
Braking
Crane load + hook load
surge Crane frame weight Wheel load
Wheel load surge
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 x10 106 . 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.
C 2
(2.l – C)
L Shear force and equation 4
C/4 Maximum bending moment
W
W 2
L/2
L/2
(L/2-c/4)^2
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
Affected length 3.5 x (rail depth + flange thickness) Rail depth “k” distance of I
section
Affected length
Welded or rolled gantry girder Affected length 3.5 x(rail depth + cover plate thickness + gauge distance) Rail depth “k” distance of I
section Affected length
bolted or riveted gantry girder
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
COLUMN BRACKET WITH LIGHT LOADS
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
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
When Top flange lateral bracing not of adequate strength add diaphragm Web of gantry girder should not be connected to columns by diaphragm – fatigue failure risk
Separate diaphragm for each beam
Diaphragm: Should not be connected this way, instead thorough diaphragm should be used
stepped columns
BRACINGS Laterally and longitudinally
Most effective, simplest X bracings
Limit
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 (M z) Apply multiplication factor 1.5 for live load and dead load Calculate the Maximum Shear Force
Approximate
I ZZ
15.6W ( L c)
Z p
LE
2 [2 L 2 L
1.4 M /
c
c
2
]
f y
Classify the section (plastic, compact, semi-compact) Calculate I z , Z z, Calculation of plastic sectional modulus (Z pz, Zpy)
Check for local moment capacity
M d b Z p f y / m 0 1.2 Z e f y / m 0 Combined local capacity check M z M dz
Check for buckling resistance
M y
M dy
1
M d Z p f bd 2 L LT / r y EI y h f 1 1 M cr C 1 2 20 h f / t f 2( L LT )
0.5
2
LT = b Z p f y / M cr
1.2 Z e f y / M cr
LT 0.5 1 LT LT 0.2 LT LT
1
2 2 LT LT LT
0.5
f bd = LT f / m0
1.0
2
M z
Biaxial bending
M dz
M y M dy
1
V 0.6V d
Check for shear
V d
=
Av f yw /( 3 m0 )
Check for deflection
Weld design
strength of weld
=
0.7 s
3 mw
q
VA y / I Z
f u
l
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
Screen shots….
