1Institute of Technology, Nirma University, Ahmedabad .... FLOWCHART FOR SOFTWARE DEVELOPMENT. Fig. ... improves the quality of the company product.
Bridge Girder Design of an EOT Crane Structure—A CAD Approach A.M. Gohil1 and Y.D. Vora2 1
Institute of Technology, Nirma University, Ahmedabad 2 Government Engg. College, Gandhinagar
Abstract—Crane structure, which is made up of bridge girder and end truck, contributes heavily to the dead weight of the whole crane. Most of the materials handling equipment manufacturing industries are manufacturing equipment using conventional design procedure, which gives heavy weight of crane structure and other parts. Moreover, for the different capacities of EOT crane structure, more time is required for the design and analysis of the structure and other parts. In this paper problem of reducing the weight of box-girder at the same time increasing the productivity and to improve quality of product as required by the Indian Standard is tackled by preparing a program in Visual Basic 6.0.
design of welded box girders is well standardized using computer design programs in Visual Basic 6.0 to combine high strength with lightweight. Software prepared checks all the possible modes of failure while meeting the stringent requirement imposed by various Indian Standards. II. ANALYTICAL CALCULATION OF THE CRITICAL STRESSES AND THEIR VERIFICATION AS PER INDIAN STANDARD IS: 807 AND IS: 800
Index Terms—Bridge Girder, Camber, Duty Factor, EOT Cranes.
I. INTRODUCTION
E
lectrically-Operated Overhead Traveling (EOT) cranes are widely used to transport objects in many factories, ports, and work places. The fundamental motions of an overhead crane can be described as: object hoisting or lowering, trolley travel, and bridge traverse [1]. In order to increase the productivity of the system, it is necessary that all these motions of the crane should take place at high speeds under loaded conditions. Under most adverse conditions crane structure must resist several loads which include dead weight of bridge girder, end-truck, platform, trolley, driving system elements etc. and live load to be handled. If the crane is required to be operated outside the factories than wind load also plays an important role as there are cases of derailing and overturning of a crane due to heavy wind. Hence the crane structure must be robust enough to sustain these loads and to safely transmit the same to the foundation. Crane structure is made up of bridge girder and end-truck [2]. Bridge girder is that component of a crane structure on which trolley travels to provide the traversing motion. Bridge girder can be either double web (box) or single web design. Box girders are easily adapted to the conditions encountered in crane design because it is possible to select flange plate width, web depth, stiffener arrangement, and plate thickness to meet the exact requirements of each crane [3]. Full depth stiffeners and additional partial depth stiffeners, welded to the webs and bearing on the top cover plate; contribute to the internal strength of these girders. The 256
Fig. 1: Cross-section of Bridge Girder with usual notations Table 1: Nomenclature
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Calculations of forces, bending moment, deflection etc. is as per the simply supported beam conditions. The calculation of the state of stress in the box girder has been executed based on the formulae given below. 1. Tensile Stress
MV
... (1)
Z XX MH
... (2)
ZYY
fbt = fvbt + f hbt Permissible bending tensile stress [4],
[f bt ] = 154.5 for t ≤ 20
... (3)
... (5)
2. Compressive Stress Top flange of the box-girder is subjected to the compressive force. As top and bottom flange are of equal width, Vertical bending compressive stress, = f
vbt vbc Horizontal bending compressive stress,
... (6)
= f ... (7) hbt hbc Total bending compressive stress is sum of the above two values, f
= f + f bc vbc hbc Maximum permissible compressive stress [4] f
= 0.66
}
... (11)
⎤ hW tW ⎥ 250 1 + 0.5(hW 1) 2 ⎦
... (12)
{
hW < c , ⎡
[ f s ] p = 92.7 ⎢1.3 − ⎣
{
}
4. Bearing Stress
fb =
RV AB
... (13)
[( f
f cb × f y cb
)
n
+ (fy )
n
]
1
[ f b ]p
= 185.4
... (14)
5. Equivalent Stress Equivalent stress,
... (4)
[ fbt ] = 147.15 for t > 20
[ f bc ] p
⎣
⎤ c tW 2 ⎥ 250 1 + 0.5(c hW ) ⎦
Permissible bearing stress [4],
Total bending tensile stress is sum of the above two stresses,
f
⎡
Bearing stress,
Horizontal bending tensile stress, f hbt =
hW > c ,
[ f s ] p = 92.7 ⎢1.3 − For
Bottom flange of the box-girder is subjected to the tensile force. Vertical bending tensile stress, f vbt =
For
... (8)
fe =
... (9)
3. Shear Stress
2
2
2
... (15)
Permissible equivalent stress [4],
[ f e ] p = 224.16 for t ≤ 20 [ f e ] p = 216.31 for t > 20
... (16) ... (17)
6. Torsional Shear Stress Torsional shear stress,
⎛ hW ⎞ + tF ⎟ × T ⎜ 2 ⎠ τs = ⎝ IP
... (18)
7. Longitudianl Direct Stress Longitudinal direct stress,
fl =
n
f bt + f b + f bt × f b + 3 × f s
FHLLL M HLLL + AT Z XX
... (19)
Permissible longitudinal tensile stress [4],
[ f l ]p [ f l ]p
= 147.15 for t ≤ 20
... (20)
= 139.3 for t > 20
... (21)
Shear stress,
RV fs = 2 × AW Permissible shear stress [4],
8. Duty Factor ... (10)
All the permissible stresses mentioned in remark 1) to 7) above i.e. Permissible tensile stress, permissible compressive stress, permissible shear stress, permissible bearing stress,
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permissible equivalent stress & permissible longitudinal tensile stress should be multiplied by duty factor to get the final permissible stress. Duty factor is the fraction of a period during which crane remains in operation during its whole life period. Duty factors are different for four classes of cranes mentioned in Ref. [5] Designed stresses should be below the final permissible stresses arrived as above.
IV. PROGRAM OUTPUT
9. Rigidity consideration Deflection is maximum at the center. Permissible deflection [5],
[δ ]p
= l 900
... (22)
Fig. 3: Selection of a program to run
Vertical deflection should be less than permissible deflection, For EOT crane, while fabricating the webs of the box girder plates are given curvature in opposite direction of deflection to neutralize the effect of deflection due to loading. This curvature provided is known as camber.
camber = l 1000 [5]
... (23)
III. FLOWCHART FOR SOFTWARE DEVELOPMENT
Fig. 4: Input to the bridge girder program
Fig. 2: Flowchart for design of a bridge girder
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Fig. 5: Sectional properties of bridge girder
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Fig. 6: Forces on bridge girder
Fig. 7: Bending moments on bridge girder
V. CONCLUSION In this paper, software prepared satisfies the safety consideration as stipulated by various Indian Standards at the same time section designed gives the minimum weight of the bridge girder. It is also possible to check the section of interest so it gives flexibility to the designer. This ultimately increases the productivity of a designer and also improves the quality of the company product. More work is required to incorporate the temperature load which is the case of a foundry crane. Also seismic loads are excluded while designing a crane which can play a major role in locality high prone to earthquakes. REFERENCES
Fig. 8: Stresses and deflection for bridge girder
[1] Rudenko, N., Materials handling equipment, Envee publishers, New Delhi, 1979, pp. 20-23. [2] Alexandrov, M.P., Materials handling equipment, Mir publishers, Moscow, 1981, pp. 59-77, pp. 253-261, pp. 357-385. [3] Kazimi, S.M.A., and Jindal R. S., Design of Steel Structure, Prentice Hall of India, New Delhi, 1988, pp. 407-408. [4] IS: 800, Code of Practice for Use of Structural Steel in General Building Construction, Bureau of Indian Standards, New Delhi, 1984, pp. 19-22, pp. 29-35, pp. 44-47, 67-73. [5] IS: 807, Code of Practice for Design, Manufacture, Erection and Testing (Structural portion) of Cranes and Hoists, Bureau of Indian Standards, New Delhi, 1992, pp. 9-24.
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