Crane Girders Prezentare

8/12/2019 Crane Girders Prezentare

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6. Crane girders

6.1. General elements

In order to accomplish the technological flux inside the workshop structure, this has to be

provided with crane (gantry) girders upon which the cranes travel carrying different materials (with

the help of the crab). Thus, the floor is empty free to be used for different industrial activities.

When the loads transported weight light (!..."! k#), the system that is used consists in

overhead travelling cranes. These cranes are made up of powerful hot rolled profiles (I) suspended

at the bottom chord of the roof truss $runway girders, along the bay of the structure (fig.%). &o, the

crane girder moves along the bay, being itself suspended at the bottom flange of the two profiles.

'ig. %. verhead crane girders for industrial buildings (small lifting capacity)

When the lift capacity is bigger ("!..."!! k#), the cranes travel on two parallel runway

girders, whose supports are the brackets of the structural columns.

The runway girder is composed by the rail and the crane girder.

6.2. Design of the crane girders

rane girders are made up of hot rolled steel profiles$usually special powerful profiles of

Western *uropean or +.&.. profiles or of build up cross sections, obtained from thick plates

welded with continuous fillet welds. -attice girders may be used also when the bays are big and the

lift capacity of the crane is small, but generally this solution is avoided because of the fatigue

phenomenon.


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'ig.. &ection of runway girders for cranes with different lifting capacity/ a)$ crane girders made of hot rolled

sections for small lifting capacities and small bays/ b)$ plate girders made of thick steel plates and knee

braced girders for heavier weights and bigger bays0 c)$ runway girders for heavy and very heavy weights and

big bays

'ig.. rane girders for light and medium weights and very big bays/ a)$ hot rolled sections0 b), c) $ hot rolled

section with tie$rod at the flange in tension0 d)$ hot rolled section with lattice girder at the bottom flange.

rane girders may be continuous or simply supported.

Simply supported gantry girders -are easier to build up at the building site, but they use a

bigger 1uantity of steel.

Continuous crane girders- need a bigger amount of manual labour at the building site but the

distribution of the bending moments is more rational and the deflection is smaller. When the spans


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are not e1ual negative reactions on the supports of the smaller spans may appear so on the bigger

spans the simply supported girders will be adopted.

The crane girders made up of hot rolled cross sections (simple or compound) are used for

smaller bays and lighter cranes (2 m , 34"!...%!! k#). 'or bigger bays and lifting capacities of the

cranes (56% m,3!! k#) crane girders are made up of build$up cross sections (fig. ).

'ig. 7. lternative static systems adopted for the crane girders

&pecial hori8ontal girders are used if they are needed, in order to take the crab effect. These

girders may be either build$up sections or lattice girders. The build up cross sections are made up of

a web which is corrugated steel sheet, one flange being the top flange of the runway girder and the

other flange being a hot rolled steel profile (channel or beam). The corrugated steel sheet is also

used as a passing platform (cat$walk) between two running columns and for that it has to be

stiffened.


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'ig. ". 9unway girders with continuous platform made of thick steel sheet between two running columns

If the bays are big the deflection of the profiles (+ or I) is diminished with the help of ties

(knee braces) put at "...2 m distance between the stiffeners and the bottom flange of the crane girder

or, in some situations an elastic restraint for the profile is used (fig. 2).


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'ig. 2. :nee$braced runway girders for limiting the deflections

The special girders used to take the crab effects may be lattice girders. Their width may be

%....%." m and the walking platform is made of timber planks or corrugated sheet put on the lattice

system (hori8ontally). The internal lattice system is triangular with supplementary struts. The angles

of the ties are small (a4"o...!o), the number of the ;oints being diminished. The members are

obtained by angles which are positioned so as to permit the corrugated sheet to be put on.

special case is the platform between two crane girders that sits on the internal columns and

which, in this situation, is common for both girders. In order to insure the stability in the plane of the

crabs, the girders are provided with transversal bracing. The distance between the bracing is

(!....!."")-T. 'or bigger bays (-T % m) hori8ontal bracing elements are necessary to be

provided at the bottom flanges of the crane girders.

6.3. The rails of the runway girders

The rails insure the process of travelling of the cranes and transmit the stresses from the

wheels of the cranes to the crane girders.

The width (b) of the rail is determined with the relationship/

b P

D R

=

max

% (%)

where/

Pmax$the maximum load on the wheel of the crane0

D$the diameter of the wheel0

9l$the strength of the material for local crush (9l47


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The value of bmay be also expressed depending on the width of the crane at the internal part

of the wheel rim (br) / b = br-(15...16mm.

'ig. =. 9unway girders with platform sustained of steel lattice girder


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'ig. >. ?ifferent systems of fixing the rails on the crane girder/ a), b), c)$ s1uare steel sections0 d), e)$ :@ type

of rails0 f)$ railway rails

In fig.> some possibilities for assembling the rail to the top flange of the crane girder are

presented. In the b) case the rail is welded at the flange with continuous fillet weld but this may be

used only for light working conditions as putting the rail right in the centre of the cross section and

removing it whenever it is necessary is a difficult operation. The c) case, adopted when the crab

effects are smaller is easier to be used. The d) case is adopted when the cranes have big lifting

capacities.

s the transportation lengths are small (2...> m) the tolerances between the units of rail are

numerous. The welding between the units is done with butt welds (aluminium$thermal method).


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6.4. The buffers of the runway girders

They are provided for the case that the crane would come too close to the end of the runway

girder and the braking system would not act in time.

single crane is considered for the design of buffers. The force transmitted to the buffers

(!b) is expressed with the relationship/

"

#$!

b

.

= Ak#B ()

where/

#$ the speed of the crane when it bumps into the buffer in mCs. It is taken as a ratio from the

maximum speed (!.=vmax). This is due to both the fact that the speed at the ends of the runway

girders is automatically diminished and the fact that the rail is inclined in that 8one0

'ig. 5. Types of buffers of the crane

f 4 !.% m for flexible suspension and 3 "! k# (working groups I, II, III) and f 4 !. m for

the other cases0

D$ mass of the maximum vertical pressure force from the crane on the rail determined with

the following relationships/

a) $ in the case of the flexible suspension when the maximum lift load 3 is not taken into

account because of dissipation of impact energy due to balancing the load in the hook/


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)(%

%max

P

P

cP

p

%

c%&&

gg

Pn$

+=

= AkgB (7)

b) $ in the case of the rigid suspension/

P

P

cPP %

c%

&'&gPn$

%

max )(A

% ++==

AkgB (")

The notations are/

g$ gravity acceleration0

&p$ weight of the crane Ak#B0

&c$weight of the crab Ak#B0

'$ lifting capacity of the crane Ak#B0

%p$ span of the craneAmB0

c%$ minimum distance between the crab and the axis of the rail AmB (see &T& >!!$>)

!t will not go over the following values/

7!! k#$ I working group cranes0

%!! k#$ II and III working groups cranes0

!!! k#$ IE and E working groups cranes.

6.5. The comutation of the crane girders

This includes the following stages/

a)$estimation of loads0

b)$computation of the maximum stresses0

c)$choosing the dimensions of the cross section0

d)$strength and stability checking0

e)$other checking (stiffness, fatigue).

2.!.3.5.1. "ctions and combinations

a. +niform distributed loads Ada#CmB0

%) weight of the crane girder/

%& )= ( ... )%" ! (2)

) weight of the rail (including an extra weight of the angle cleats used for the connections

with mechanical fasteners, aprox. %"F)/

%",%=>"!

=ss

*( (=)


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)(%%

, cbc

cp

t &'+"n

nn! += (%)

&o/

7!

c

t

&'!

+= $ flexible suspension

7!

c

t

&'!

+= $ rigid suspension

where/

n@$ number of the wheels of the crane that transmit the crab effect ( 4 )0

nc $ number of wheels of the crab( 4 7)0

nc,b$ number of wheels of the crab that the brake acts on simultaneously ( 4 )0

f G friction factor ( 4 !.%)0

k G suspension factor0 for flexible suspension, k4%,! and for rigid suspension, k4,!

7) hori8ontal forces that appear because of the stacking phenomenon see fig./

)

& & ' %

-

P c P=

+ +

( )

%!! (%7)

.The influence of the T force is automatically taken into account by considering the dynamic

coefficient .


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actions and the dynamic coefficient the hori8ontal loads, this last coefficient depending on the

working group of the crane, maximum load in the hook, the type of suspension (table below). If two

cranes travel on a single span, 0is diminished with !.% (see table )

. The design values of the actions in the fundamental group of actions are obtained by

multiplying with/

%,"$dead loads (self weights)0

%,"$live loads0

%,$vertical actions from crane (@max)0

%.$hori8ontal actions from crane and crab ('l, 't)0

7. ccording to the fundamental group of actions, the variable actions will be taken together

with the corresponding value of partial safety factors.

". The coefficients that take into account the simultaneous effects depend on the number of

cranes that act at a certain moment and on the working group of the biggest crane considered (table)

6.6. The comutation of the ma#imum stresses

The design values for the maximum stresses are obtained from the following situations/ a)

Dmax, Tcor0 b)Tmax, Dcor.

If the crane girder is simply supported, maxim maximorum value of the bending moment and

maxim value of the shear force are determined according the rules in the &tatics (fig. ).In the case of the continuous crane girder, the maximum values of the sectional efforts (D, T) will

be obtained with the help of the influence lines.

enerally we take into account the effects from two cranes in the most unfavourable

situations. s on the girder there are also uniform distributed loads, although their effects are

negligible, they have to be taken into account. &o, the coefficients 1 and 2are used in order to

amplify the bending moment and the shear force respectively.

ccording to the above specifications the values of$max3max and )max3maxare/

$ P %i i

$

)max max ,max.= % %

J (%")

) Pi i

)

max max ,max.= %


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The crab effects (surge) will be a bending moment in the hori8ontal plane, the position of the

hori8ontal transversal forces!tbeing the same with that of the convoy of forcesPmax/

= )$

ic!t %!$ .% (%2)

6.!. Choosing the dimensions of the cross section of the crane girder

They are the same used for a girder having a build up cross section only specific measures

have to be taken for the deflection/

+4"or'%

" ) "!!,2!!

max


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'ig. %%. ?etermination of sectional efforts from vertical actions on the crane girder (the simply supported

case)


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'ig. %. oefficients for the determination of sectional efforts and deflections of continuous girders under

mobile forces (influence lines)


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'ig. %7. Daximum sectional efforts$influence lines


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'ig. %7. ontin.


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The top flange has to be dimensioned also from the point of view of putting the rail

on it/

)!...%"

( " mmeeb

btop +++ (%5)

'ig. %". onstructive detail for the top flange of the crane girder

6.$. %trength &erifications

Case 1. The crane girder without platform

The hori8ontal longitudinal forces !tis taken by the top flange along with a part from the

web of the girder (fig. ). The stresses are/

'ig. %2. &chemes for the determination of stresses in the cross section of a girder for which the top flange

carry hori8ontal actions from the surge effect of the crab


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yy

s(P(P

yy

s(P(P

5

6$

5

6$

K,,

,,

% 0 == 0

yy

i(P(P

yy

i(P(P

5

6$

5

6$

K,,

7

,,

0

== (!)

66

i!!

66

s!!

5

t$

5

b$ tttt

=

=

0

%

0

s

P!p!

-

!==

.% J (%)

Rtx

P

i

l

= max,

ii

cor

t*

)

==7.

hecking the normal stresses and the plane combined state of stress/

R

R

!t(P

!p(P

%.%%,

%%

%

,

%%

+=

+=

()

!l!t(P ..

,

.. ++=

ec* R,K .

%%= +

J () Rmllec* ++=

,

,

KK

,

where m4%.% for the simply supported girder and %." for the continuous girder0 the normal

stresses are considered with their algebraic sign (L or$)

ll R., 0 R" 0 R

l!

l

(P++

..,

,

. (7)

7 7=

P (,

0

ec* R, .7 7

7

%%= +

(")

Case 2. The crane girder with platform made of continuous corrugated steel sheet

'ig. %=. ?iagrams for the determination of the stresses for the girders when the top flange carries the surge

effects from the crab


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The forces!tare taken by the hori8ontal cross section made the steel platform, the channel

(+#@) or beam( I#@) on which is welded and the top flange of the crane girder (fig6)The stresses

are/

% 7P P , ,........

are the same as for the case 1

%%%%%%

""

%% 00

66

!t!t

66

!t!t

66

!t!t

5

y$

5

y$

5

y$ ===

(2)

s

l!!

-

!ll

==

% (=)

iii

l

C

t*

)

tx

P

7

$

==

==

7.

max

." 00

(>)

hecking the stresses/

R

R

!t(P

!p(P

%.%%,

%%

%

,

%%

+=

+=

0 l

!

l

(P

.,.

,

.. ++= (5)

ec* R

%%K .= + 0

ec* l l m R

M = + + (!)

RRR (P"ll ,

7, 00

0

ec* R7 7

7

%%= + .0

Rt!

+="""

(%)

ther verifications of the crane girders like overall buckling, local buckling of the web and

of the flanges, fatigue, are the same as for the build up cross sections (according to &T& %!%!>C!$

=>).

Case 3. The crane girder with the platform made of a truss

This system is adopted when their space for the platform is bigger or the depth of the column

at the inferior part is greater. It is considered that the hori8ontal forces from crab surge act between

the ;oints of the truss forces, so there are bending moments at the flange in compression/

$

! aloc

! cc =

%! ()

The value of the axial effort (P! $4 t ,

is determined generally with the analytical

methods.


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The stresses are/ % 7

P P , ,.... using the same relationships as in the case 2, see also the

figure ( ).

0

%i

66

loc!p

66

loc! t

5

$b

5

$tt ==

0

-

4

-

4 tt

t

tt

!!

s

!!!

=== "% 0 ()

C

l

!! ll"7.,..%

,,,

== (7)

are the same as in the case 2.

hecking the stresses/

Rtt !!(P

++=

%%

,

%%0 tt

!!(P ..

,

.. ++= (")

The other relationships are identical as in the case 2

'ig. %>. ?iagrams of stresses for runway girders with platforms sustained by steel lattice girders

6.1'. Details of assembling( welding( bolting at building site and suorts on the column of the

crane girders


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'ig. %5. ?etails of build up section of crane girders/ welding the flanges to the web, end posts fixing

'ig. !. urrent stiffeners on the webs of crane girders0 transversal and longitudinal


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'ig.

Crane Girders Prezentare

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