FACULTY OF CIVIL AND ENVIRONMENTAL

ENGINEERING

DEPARTMENT OF STRUCTURE AND MATERIAL

ENGINEERING

LAB MATERIAL

REPORT

Subject Code BFC 21201

Code & Experiment Title BUCKLING OF STRUTS

Course Code 2 BFF/1

Date 03/10/2011

Section / Group 2

Name MUHAMAD ASYRAF BIN AB MALIK (DF100108)

Members of Group 1.MUHAMMAD IKHWAN BIN ZAINUDDIN (DF100018)

2.AHMAD FARHAN BIN RAKAWI (DF100142)

3.IDAMAZLIZA BINTI ISA (DF100128)

4.AINUN NAZHIRIN BINTI ABD JALIL (DF100076)

Lecturer/Instructor/Tutor EN MOHAMAD HAIRI BIN OSMAN

Received Date 17 OCTOBER 2011

Comment by examiner

Received

STUDENT CODE OF ETHIC

(SCE) DEPARTMENT OF STRUCTURE AND MATERIAL

ENGINEERING

FACULTY OF CIVIL & ENVIRONMENTAL ENGINEERING

UTHM

We, hereby confess that we have prepared this report on our effort. We also admit not to receive

or give any help during the preparation of this report and pledge that everything mentioned in the

report is true.

___________________________

Student Signature

Name : MUHAMAD ASYRAF AB MALIK

Matric No. : DF100108

Date : 17/10/2011

_______________________

Student Signature

Name : MUHAMMAD IKHWAN ZAINUDDIN

Matric No. : DF100018

Date : 17/10/2011

___________________________

Student Signature

Name : AHMAD FARHAN RAKAWI

Matric No. : DF100142

Date : 17/10/2011

___________________________

Student Signature

Name : AINUN NAZHIRIN ABD JALIL

Matric No. : DF100076

Date : 17/10/2011

___________________________

Student Signature

Name : IDAMAZLIZA ISA

Matric No. : DF100128

Date : 17/10/2011

1.0 OBJECTIVE

1.1 To examine how shear force varies with an increasing point load.

1.2 To examine how shear force varies at the cut position of the beam for various loading

condition.

2.0 LEARNING OUTCOME

2.1 The application the engineering knowledge in practical application.

2.2 To enhance technical competency in structural engineering through laboratory

application.

2.3 To communicate effectively in group.

2.4 To identify problem, solving and finding out appropriate solution through laboratory

application.

3.0 INTRODUCTION

A compressive member can fail in two ways. The first is via rupture due to the direct

stress and the second is by an elastic mode of failure called buckling. Short wide

compressive member tends to fail by material crushing.

When buckling occurs the strut will no longer carry any more load and it will simply

continue to buckle i.e its stiffness then becomes zero and it is useless as a structural

member.

4.0 THEORY

To predict the buckling load Euler buckling formula is used. The crictical value in

Euler Formula is the slenderness ratio, which is the ratio of the length of the strut to

its radius of gyration (L/K).

The Euler formula become inaccurate for struts with L/K ratio of less than 1.125 and

this should be taken into account in any design work.

Euler buckling formula for pin struts:

Pe=π2EI/L

2

Where;

Pe = Euler buckling load (N)

E = Young’s Modulus (Nm-2)

I = Second moment of area ( m4

)

L = length of strut ( m )

5.0 APPARATUS

Buckling of Strut Digital Display Force

Steel Strut

Buckling of Strut Equipment

6.0 PROCEDURES

Part 1

1. Fit the bottom chuck to the machine and remove the top chuck (to give two pinned ends).

Select the shortest strut, number 1, and measured the cross section using the vernier

provided and calculated the second moment of area, I,for the strut. ( bd3/12)

2. Adjust the position of the sliding crosshead to accept the strut using the thumbnut to lock

off the slider. Ensure that there is the maximum amount of travel available on the hand

wheel threat to compress the strut. Finally tighten the locking screw .

3. Carefully back- off the handwheel so that the strut is resting in the notch but not

transmitting any load. Rezero the forcemeter using the front panel control.

4. Carefully start to load the strut. If the strut begin to buckle to the left, “flick” the strut to

the right and vice versa (this reduces any error associated wih the straightness of strut).

Turn the hand wheel until there is no further increase in load (the load may peak and then

drop as it settles in the notches).

5. Record the final load in Table 1. Repeat with strut numbers 2, 3, 4 and 5 adjusting the

crosshead as required to fit the strut.

Part 2

1. To study the effect of end conditions, follow the same basic procedure as in part 1, but

this time remove the bottom chuck and clamp the specimen using the cap head screw and

plate to make a pinned-fixed end condition.

2. Record your result in Table 2 and calculate the values of 1/ L2 for the struts.

3. Fit the top chuck with the two cap head screws and clamp both ends of the specimen to

make a pinned –pinned end condition. Calculate the new values of 1/L2.

4. Enter the result into Table 3

7.0 RESULTS

Strut

Number

Length

(m)

Buckling Load

(N)

Experiment

Buckling Load

(N)

Theory

1 0.32 -92 88.65

2 0.37 -56 66.31

3 0.42 -24 51.46

4 0.47 -13 41.09

5 0.52 -16 33.57

Table 1

Strut

Number

Length

(m)

Buckling Load

(N)

Buckling Load

(N)

Theory

1/L2 ( m-2)

1 0.32 -196 177.30 9.77

2 0.37 -106 132.62 7.30

3 0.42 -105 102.92 5.67

4 0.47 -101 82.19 4.53

5 0.52 -48 67.14 3.70

Table2

Strut

Number

Length

(m)

Buckling Load

(N)

Buckling Load

(N)

Theory

1/L2 ( m-2)

1 0.32 -397 354.60 9.77

2 0.37 -284 265.24 7.30

3 0.42 -252 205.85 5.67

4 0.47 -174 164.38 4.53

5 0.52 -155 134.29 3.70

Table 3

8.0 DATA ANALYSIS

Part 1

To calculate Buckling Load (N) Theory ( pinned-pinned end condition)

Pe = π2

EI/L2

I = bd3

= π

2 ( 69 x 10

9 ) ( 13.33 x 10

-12 )

12

0.322

= 88.65 N = ( 0.02 ) ( 2 x 10 -3

)

12

= 13.33 x 10 -12

m

Part 2

To calculate Buckling Load (N) Theory ( pinned-fixed end condition)

Pe = 2π2

EI/L2

= 2π2 ( 69 x 10

9 ) ( 13.33 x 10

-12 ) I = bd

3

0.322 12

= 177.30 N = ( 0.02 ) ( 2 x 10 -3

)

12

= 13.33 x 10 -12

m

Part 3

To calculate Buckling Load (N) Theory ( fixed-fixed end condition)

Pe = 4π2

EI/L2

= 4π2

( 69 x 109 ) ( 13.33 x 10

-12 ) I = bd

3

0.32

2 12

= 354.60 N = ( 0.02 ) ( 2 x 10

-3 )

12

= 13.33 x 10 -12

m

9.0 DISCUSSION

Part 1:

1) Examine the Euler buckling equation and select an appropriate parameter to establish a

linear relationship between the buckling load and the length of the strut. Write the

relationship below.

Based Eular formula and Table 1, 2 and 3,

Pe = Euler buckling load (N), L = length

We can consider that when L is bigger, Pe will be small, relation between

buckling load and the length of the strut is inversely proportional in linear condition.

2) Calculate the value and enter them in Table 1 with an appropriate title.

Show on Table 1 using formula: ( )

3) Plot a graph to prove the relationship is linear. Compare your experimental value to those

calculated from Euler formula by entering a theoretical line onto the graph. Comment on

the result.

Graph plotted = In the graph paper.

Base on the graft that we plotted, the difference to the end of the pins for the

results of gradient experiments is 1.46 and the slope of the theoretical calculation results

of 1.28. Difference to the fixed -pin end of the gradient experiment results were 1.33 and

gradient theory results of the calculation is 1.29. In addition, the differences for fixed-

fixed end conditions are for the gradient experiment results are 1.25 and theoretical

calculations are the result of the slope is 1.25. This experiment result shows that the slope

is greater than the slope of the calculation results. In practice, the buckling of the

experiment is higher than theoretical.

4) Explain that the Euler Formula can predict the buckling load or not.

Euler Formula can predict the buckling load, because the ratio between the

Buckling Load (N) and the 1/L² (m) is consistence within the graft, and show accurately

that inversely proportional as approve at point 0,0 when the length is 0, then the buckling

Load should be 0.

Part 2:

1. Plot separate graphs of buckling load versus 1/ L2 and calculate the gradient of each line.

Graph Plotted = In Graph Paper.

Gradient in the graph plotted.

2. Fill the table below showing the comparison between experimental and theoretical ratio

by end condition

Pinned-Pinned Pinned-Fixed

Fixed-Fixed

Experimental

Gradient

1.46 1.33 1.25

Experimental

Ratio

1.46/1.46 = 1

1.33/1.46 = 0.911 1.25/1.46 = 0.86

Theoretical Ratio 1.28/1.28=1 1.29/1.28 = 1.008

1.25/1.28 = 0.98

Notes:

1. *Use the experimental gradient fom Part 1

2. Experimental ratio = Exp. Gradient / gradient of pinned-pinned.

3. Theoretical ratio can be obtained from Euler Formula for pinnedfixed and fixed-fixed.

3. Comment on the experimental and theoretical ratio.

From the table, experimental ratio is not consistence with the usage of end of

connection, we basically we know that the fixed end is much stronger than the pins end as

per theoretical ratio value. This shows the more force should be imposed on the members

of the joint fixed-fixed end compared to the pin-pin connection. When one of the end is

changed from pin end to fix end, the ratio is two times larger than the pinned-pinned, it

the same case happed when both of the end changed to Fixed-fixed end. The experimental

ratio is not consistence with theoretical ratio because there was several errors when

conduct the experiment, such as the screw is not tightens carefully, the sliding crosshead

are not tighten to the experiment apparatus.

4. What conclusion can you made from the experiments.

Based from the experiment of Buckling of Strut, we can conclude that Fixed end is

much stronger than the Pinned end and more force should be imposed on the member of

the joint fixed-fixed end connection, but in other criteria the usage in fixed end

connection usually apply for concrete beam or column connection, The Pinned end is

used for Steel connection because, usually fixed end connection is for permanent

connection, steel always use bolt and nut rather than weld fabricating connection.

10.0 CONCLUSION

Based from the experiment of Buckling of Strut, we can conclude that Fixed end were

much stronger than the Pinned end and more force should be imposed on the member of the

joint fixed-fixed end connection, but in other criteria the usage in fixed end connection usually

apply for concrete beam or column connection. The Pinned end is used for Steel connection

because,it is usually fixed end connection is for permanent connection..