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Department of Civil Engineering

International University (IU)

MECHANICS OF MATERIALS LABORATORY

Department of Civil Engineering
Room 506, International University – Viet Nam National University HCMC Quarter 6, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Viet Nam. Phone: 848-37244270. Ext 3425 Fax: 848-37244271 www.hcmiu.edu.vn

Mechanics of Materials Laboratory
Course Outline No. ST01 ST02 ST03 ST04 ST05 ST06 Assessment • • Attendance: 10% Group Report: 90% (Each Lab Session: 15%). The report will be submitted 1 week after the lab session. Topic Bending Stress in a Beam Steel Bars under Pure Tensile Forces Torsion of Circular Sections Buckling of Struts Continuous and Indeterminate Beams Redundant Truss

Please provide the following parts in your report: • Introduction (purpose of the experiment) • Theory • Experimental Results • Analyzing the Experimental Results • Conclusions

Group Allocation Group A Group B Group C Group D

Schedule Group A & B No Lab ST01 ST02 ST03 ST04 ST05 ST06 No Lab Group C & D No Lab ST02 ST01 ST04 ST03 ST06 ST05 No Lab

W1 W2 W3 W4 W5 W6 W7 W8

Department of Civil Engineering

International University (IU)

ST01: BENDING STRESS IN A BEAM

Department of Civil Engineering
Room 506, International University – Viet Nam National University HCMC Quarter 6, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Viet Nam. Phone: 848-37244270. Ext 3425 Fax: 848-37244271 www.hcmiu.edu.vn

1.

Introduction

The Bending Stress in a Beam experiment introduced students to stress and strain, bending moment, section properties and the bending equation. 2. Theory

Considering the simply supported beam as shown in Figure 1, there are two point loads ( W / 2 ) applying to this beam.

Figure 1 Beam set-up and schematic The applied bending moment (M) is calculated as:

M = where: M=Bending moment (Nm) L=Span length as shown in Figure 1 (m) From the bending equation, we have:

WL 2

(1)

M σ = I y where: I=Second moment of area of the section (m4)

(2)

σ =Stress (Nm-2)
y= Distance from the neutral axis (m)

From the Hooke’s law, we have:
E=
1

σ ε

(3)

where:
ε = Strain

E = Young’s modulus for the beam material (given as 69GPa in this experiment) 3. Experimental Apparatus

The experimental apparatus consists of the following parts:

• • • • •

A loading assembly as shown in Figure 2 The structural test frame to support the loading assembly as shown in Figure 3. The Digital Force Display to measure and displace force electrically. The Digital Strain Display to measure and displace strains. Automatic Data Acquisition Unit and software to record all measured data (strains and force) to the computer system.

Figure 2 Bending Stress in a Beam Experiment

2

Figure 3 Bending stress in a beam experiment in the structures frame 4. Experimental Procedures

• • • • • • •

Ensure the beam and Load Cell are properly aligned. Turn the thumbwheel on the Load Cell to apply a positive (downward) preload to the beam of about 100 N. Zero the Load Cell using the control. Take the nine strain readings at the zero force and fill in Table 1 at the zero force column. Increase the load to 50 N and record all nine of the strain readings. Repeat the procedure in 50 N increments to 250 N. Finally, gradually release the load and preload.

3

Table 1 Results for Experiment

Gauge number 1 2 3 4 5 6 7 8 9

0

50

Load (N) 100 150

200

250

5.

Analyzing the Experimental Results

• • • • • •

Correct the strain reading values for zero (be careful with your signs!) and convert the load to a bending moment then fill in Table 2. From your result plot a graph of strain against bending moment for all nine gauges (on the same graph). What is the relationship between the bending moment and the strain at the various positions? What do you notice about the strain gauge readings on opposite sides of the section? Should they be...
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