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International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163Volume 1 Issue 4 (May 2014) http://ijirae.com

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2014, IJIRAE- All Rights Reserved Page - 69

VALIDATION OF USE OF FEM (ANSYS) FOR

STRUCTURAL ANALYSIS OF TOWER CRANE JIB

AND STATIC AND DYNAMIC ANALYSIS OF TOWER

CRANE JIB USING ANSYSAjinkya Karpe1, Sainath Karpe2, Ajaykumar Chawrai3

[email protected] [email protected] [email protected]

1, 2, 3 (Undergraduate Student, Department of Mechanical Engineering, Sardar Patel College of Engineering, Mumbai 400058)

Prof. Sachin Rajaram Vankar4

[email protected] (Sardar Patel College of Engineering, Faculty of Mechanical Engineering, Mumbai 400058)

Abstract Tower cranes are used at construction site. Tower crane jib is suspended beam which carries load movingalong the jib. While designing components need to design crane hook & snatch block assembly, wire ropes, moving

trolley, tie rods, jib, counterweight side, mast, slewing ring. We selected jib for analysis since we wanted to validate the

use of ANSYS (FEM method) for structural design of Tower Crane Jib. Jib model was generated in ANSYS 14.5workbench and further analyzed in the same. Two models of Tower Crane jib were compared initially for axial force

and deformation developed in members of the jib and the better model was selected for further analysis. Throughoutthe analysis, the load has been applied at the end of the jib of the tower crane to generate maximum moment andstresses in the jib. Initially the results of ANSYS 14.5 were validated using analytical method for the jib (Method of

sections for trusses). Later, the results for static as well as dynamic analysis are obtained. In static analysis, cranesself weight, payload, hook weight, trolley weight and wind loading are considered whereas acceleration, braking, andangular velocity are considered in dynamic analysis,.

Keywords Tower Crane, Jib, Tie Rod, Aerodynamic Coefficient, Counterweight, FEM, Method of Sections.

1.

INTRODUCTION Cranes are widely used to transport heavy loads and hazardous materials in shipyards, factories, nuclear installations, andhigh-building construction and play an important role in production process and serve to transfer loads from one place to

another. Cranes are the best way of providing a heavy lifting facility covering virtually the whole area of the industry.Their design features vary widely according to their major operational specifications such as the type of motion, deadweights and type of the load, location of the crane, geometric features and environmental conditions. Since the crane

design procedure is highly standardized with critical components, main effort and time spent mostly for interpretationand implementation of available design standards. A tower crane is a type of crane with a hoist in a trolley which runshorizontally along gantry rails, usually fitted underneath a beam spanning between uprights which themselves havewheels so that the whole crane can move at right angles to the direction of the gantry rails. [9]

Tower cranes are a modern form of balance crane that consist of the same basic parts. Fixed to the ground on a concreteslab (and sometimes attached to the sides of structures as well), tower cranes often give the best combination of height

and lifting capacity and are used in the construction of tall buildings. The base is then attached to the mast which gives

the crane its height. Further the mast is attached to the slewing unit (gear and motor) that allows the crane to rotate. On

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2014, IJIRAE- All Rights Reserved Page -70

top of the slewing unit there are three main parts which are: the long horizontal jib (working arm), shorter counter-jib,and the operator's cab. The long horizontal jib is the part of the crane that carries the load. The counter-jib carries acounterweight, usually of concrete blocks, while the jib suspends the load to and from the center of the crane. The crane

operator either sits in a cab at the top of the tower or controls the crane by radio remote control from the ground. In thefirst case the operator's cab is most usually located at the top of the tower attached to the turntable, but can be mountedon the jib, or partway down the tower. The lifting hook is operated by the crane operator using electric motors to

manipulate wire rope cables through a system of sheaves. The hook is located on the long horizontal arm to lift the loadwhich also contains its motor. [10]

2. COMPARISONOFJIBTYPES:

FIG.2.1:TYPE1: DEFORMATION IN RIGHT ANGLE TRIANGLE PATTERN

FIG.2.3:TYPE-1AXIAL FORCE IN RIGHT ANGLE TRIANGLE PATTERN

FIG.2.2:TYPE2: DEFORMATION IN TRIANGLE PATTERN

FIG.2.4:TYPE-2AXIAL FORCE IN TRIANGULAR PATTERN

From ANSYS analysis, Type-1 gives deformation of 24.04mm and maximum axial member forces of 119.87KN

Type-2 generates deformation of 18.29mm and maximum axial member force of 102.78 KN

Hence type-2 (Triangular type) is selected for application.

3. TOWER CRANE SPECIFICATIONSTower crane specifications: [3]

1.

Hoisting 19m/min for max load 16 ton

2. Trolleying Speed 69m/min3.

Slewing 0.8 rpm4. Tower Crane height 90m5. Jib Acceleration 0 to 0.8 rpm in 30 seconds6.

Material ST 63

7. Max. capacity at the end of jib 2 tons

8.

Radius of tower crane 78m

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4. SELECTIONOFCROSSSECTIONS

1. The top member of the jib was kept circular since it undergoes tensile loads.

2. The bottom members of the jib were kept I sections since I sections have better resistance against bucklingfailure.

3.

The side members were made up of L section since they have good strength against bucking and bending (due to

wind loading)

5.

VALIDATIONOFJIBRESULTS:(FOR STATIC ANALYSIS WITHOUT WIND LOADING)

L section: Total Length = 574.06 m Cross-sectional area = 0.000186 m2

I section:Total length = 169.1 m Cross-sectional area = 0.003272 m2

Circular cross-section:Total length= 82.5 m Cross-sectional area = 0.002827 m2

Total Volume of Jib = 574.060.000186+169.10.003272+82.50.002827= 0.893 m3

Density of Structural Steel= 7850 Kg/m3

Mass = Density Volume =78500.893 Kg

Total Mass of Jib = 7010 KgUDL of Jib = mass of jib/jib length = 7010/85.25 = 82.229 Kg/m = 806.34 N/mTotal Length of I section for counter weight = 116.42 mArea of counter weight side I-section = 0.0112 m2

Counter weight mass=10235.6 KgUDL on counter weight side of jib = mass/length = 10235.6/25.25

= 405.372 Kg/m = 3975 N/m

Fig.5.1 : Free body diagram of crane Jib Fig.5.2 :Forces in critical section of jib

Fig.5.3 : Axial forces in critical section of the jib (ANSYS)

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Tie rod Calculations:Taking moment about R,2085.25+ 27.8268 + 40.92125.375 = T115.26

T1= 301 KN100.3712.625 + 16025.25 = T213.2T2= 402.058 KN

Forces in Critical Members of Jib:

For simplicity members are considered in 2D and later they are split into 3D. The analytical results obtained for axial

forces should be twice the actual force in a member since the calculations are done in 2D for each member and

later split into 2 since there are 2 members in 3D to share that load.

Taking moment about A,

2033 + 27.8217.25 = R23.5R2= 325.68 KN (compressive)Taking moment about B,2031.5 + 27.8215 = R13.5R1 = 299.228 KN (Tension)

Taking moment about C,

2030 + 27.8215.75 + = 325.683.5 R32.757R3= 36.89 KN (Tension)

Taking moment about D,2028.5 + 27.8212.75 = 299.2283.5 - R42.757R4= 44.46 KN (Compressive)Arrangement of members in jib is such that R3 members creates compressive force of 3.34KN (0.5R3 cos79.57) in

member R5 and at the same time R4 members creates tensile force of 3.98KN (0.5R4cos79.57).Hence, force acting on member is R5= 3.98-3.34 = 0.640 KN (Tensile)Horizontal imbalance on top of jib:T1cos1 T2 cos2= Imbalance (H)1 = angle between jib and tie rod T1= tan

-1(16/50.75)

2 = angle between counter weight side of jib and tie rod 2 = tan-1

(16/25.25 )H = 301cos17.5 402.058cos32.36

H = -52.544 KN (-ve sign indicates H is in the direction of counter weight side)Moment at Top of Jib:Moment = Imbalanceheight = 52.54416 = 840 KN.mMoment = Imbalanceheight = 52.54416 = 840 KN.m

6. RESULT TABLE

Members Area10^(-3)m^2

ANSYS Analytical

% errorAxial force (in

KN)

Stress (in

MPa)

Axial force (in

KN)

Stress

(in MPa)

T1 5.026 320.61 63.78 301 59.88 6

T2/2 5.026 194.76 38.75 201.029 39.99 3.1

R1 2.827 298.05 105.41 299.228 105.83 .4

R2/2 3.272 154.17 47.11 162.83 49.76 5.3

R3/2 0.186 18.641 107.52 18.44 99.16 7.9

R4/2 0.186 16.047 86 22.23 118 27.11

R5 0.186 0.632 3.397 0.640 3.44 1.25

Table 6.1: Comparison of analytical and ANSYS jib results

The above table shows that the ANSYS results are validated and hence it can be used for further analysis

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7. STATIC ANALYSIS:Forces applied:

1. Self weight2.

Live Load (at the end of the jib 2 tons)3.

Wind Load

Wind loading calculations:

Section 1:Wind loading calculations on L section of Jib (considering perpendicular wind direction) (length= 3.87 m)Force due wind, F = A p C f [2]

where, p = 0.613Vs210-3 ( KPa )

Vs = 20 m/s (wind velocity) [6]Projected area of L section, A= 0.18m

2

p= 0.61320210-3

p= 245.2 PaCf= 1.9 [2](shape factor based upon aerodynamic drag coefficient for L section)

Substituting these values in above force equation,

F = 84 NThis 84N force acts on one L section member.Section 2: Wind loading calculations on I section of Jib (length = 3m )

Force due wind, F = A p Cf [2]p = 0.613Vs210

-3( KPa )

Vs = 20 m/s [6]

Projected area of L section, A= 0.69m2

p= 0.61320210

-3

p= 245.2 Pa

Cf= 1.6 [2](shape factor based upon aerodynamic drag coefficient for I section)Substituting these values in above force equation,

F = 270 NThis 270N force acts on one I section member.

Fig.7.1 : Static forces applied to the jib Fig.7.2: Direct Stresses developed due to static loading

Section 3: Wind loading calculations on circular cross-section (length = 3m )

Force due wind, F = A p Cf[2]p = 0.613Vs

210

-3( KPa )

Vs = 20 m/s [6]Projected area of L section, A= 0.18m

2

p= 0.61320210

-3

p= 245.2 Pa

Cf= 1.1 [2](shape factor based upon aerodynamic drag coefficient for circular section)Substituting these values in above force equation,

F = 48 N

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This 48N force acts on one circular section member.This wind load is then transferred on to the nodes of the individual members.

Wind load on upper node (nodes on upper circular of jib) is 48+42+42 = 132 NWind load on lower node (nodes on lower I section) is 270+42+42 = 354 N

8. DYNAMIC ANALYSIS:Forces Applied:

1. Static Forces

2. Angular Velocity (0.8 rpm)

3.

Acceleration Load (0 to 0.8 rpm in 30 sec)

The jib was analysed for acceleration only since the braking force applied was assumed equal to the acceleration forceapplied. The forces on each member were distributed on the respective nodes.

Calculations for tangential acceleration and centripetal force:

Table. 8.1 :tangential and centripetal force calculation

Where m is mass of jibr is radius of members (from the mast of tower crane i.e. centre of rotation of jib)

is angular accelerationw is angular velocity

Fig.8.1.: Dynamic Loading on jib in ANSYS Fig.8.2 :Direct Stresses in Jib

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9.

RESULTS:STATIC ANALYSIS:Maximum Stress induced: 99.6 MPaF.O.S: 355/99.6 = 3.56

DYNAMIC ANALYSIS:Maximum Stress induced: 229.69 MPa

F.O.S: 355/229.69 = 1.54

10.CONCLUSION:

1.

Wind loading was observed to be major criteria in the design of structure for the Tower Crane.2.

As the computed stress values in the jib are smaller than the allowable stress of Material (Structural Steel) of the

components, it is observed that the jib crane is safe according to I.S norms [6].The analytical and FEA (ANSYS)results are very close. The results obtained from FEA analysis show that the boundary conditions have beenchosen correctly.

3. Use of FEM method for structural analysis of Tower Crane Jib is validated and hence a lot of computing timecan be saved for the calculation of jib forces.

REFERENCES:

[1]

Trusses, theory and in LEGO, T. J. Avery, c. 2001[2]

Mechanical Engineering Department/ Carlos III University/ Cranes

[3] STT 403 concise tower crane manual/ Manufacturer: Fushun Yongmao Construction Machinery C Ltd. China[4]

Fracture Mechanics, Theory and Applications by Majid Mirzaei[5]

Zeid, I. (1991) CAD/CAM Theory and Practice, McGraw-Hill, Delhi.

[6] Indian Standard Code of Practice for Design of Tower Cranes. (IS: 6521)[7]

Assist. Prof. Gerdemeli I, Assoc. Prof. Kurt S, Tasdemir B; Design and analysis with Finite element method of JibCrane

[8] Bechtel Rigging Handbook , edition 2

[9] Ismail Gerdemeli, Serpil Kurt, Okan Deliktus; Finite Element Analysis of Tower Crane[10] http://en.wikipedia.org/wiki/Crane_(machine)#Tower_crane

[11] Boris Visocnik, Stojan Kravanza; Slewing Port Mechanism[12] Yehiel Rosenfeld; Automation of existing cranes-from concept to prototype[13] Zhang Yang, Zhao Jianzhi, Yao Junjun; Static structural finite element analysis of tower crane based on FEM[14] Lanfeng Yu;Calculation method and control value of static stiffness of tower crane[15] Atul Suman, Jyoti Vimal, Vedansh Chaturvedi; Principal Stress analysis of Luffing Jib using Solid Works-12[16] Robert Huntington Durfee Analysis and Design of a triangular cross section truss for a highway bridge (M.E

Thesis, Virginia Polytechnic Institute and State University)[17] Hillary Skinner, Tim Watson, Bob Dunkley, Paul Blackmore Tower Crane Stability[18] Richard Isherwood, Robert Richardson; The effect of wind loading on the jib of a luffing tower crane (Health and

Safety Centre)[19] N.D. Zrnic, V.M. Gasic, S.M. Bosnjak; Dynamic responses of a gantry crane system due to a moving body

considered as moving oscillator

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