Structural testing testing steel truss under static load experiment purpose and requirement for testing steel truss

LIST OF FIGURESFigure 1 Steel truss diagram...6 Figure 2 Steel truss experiment under static load...7 Figure 3 Hydraulic pump...8 Figure 4 Switch and Balance Unit SB10 Figure 5 Vishey me

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY OFFICE FOR INTERNATIONAL STUDY PROGRAMS

STRUCTURAL TESTING

Student : Do Tan Kiet

ID number : 1852490

Adviser : Assoc Prof Ho Duc Duy

Subject code : CI4011

Ho Chi Minh City, November 2022

Overall, I would like to express my great appreciation to Assoc GS Ho Duc Duy about the valuable knowledge and valuable advice that he has taught and shared during this course.

Signature

EXPERIMENT 1: TESTING STEEL TRUSS UNDER STATIC LOAD 6

1.1 Experiment purpose and requirement for testing steel truss: 6

1.1.1 Experiment: 6

1.1.2 Requirement for testing steel truss: 6

1.2 Experimental diagram: 6

1.3 Apparatus: 7

1.3.1 Hydraulic pump: 7

1.3.2 Strain measurement equipment: 8

1.3.3 Dial indicator: 10

1.3.4 Load cell: 11

1.4 Procedure: 11

1.4.1 Preparation: 11

1.4.2 Testing procedure: 11

1.5 Testing result: 12

1.6 Calculated data: 12

1.7 Theoretical calculation of stress, strain, deflection: 13

1.7.1 Modeling the steel truss using SAP2000: 13

1.8 Result and discussing: 17

1.8.1 Comparison between testing method and SAP modelling method: 17

1.8.2 Discuss the result between testing and SAP modelling method: 23

1.8.2.1 : Comment on chart result: 23

1.8.2.2 Cause of differences: 23

EXPERIMENT 2: REINFORCED CONCRETE BEAM 25

2.1 Experimental purpose: 25

2.2 Experimental diagram: 25

2.3 Apparatus: 26

2.4 Procedure: 27

2.4.1 Preparation: 27

2.4.2 Testing procedure: 28

2.5 Testing result: 28

2.6 Calculated data: 29

2.6 Theoretical calculation of stress, strain, deflection: 30

2.6.1 Reinforcement concrete theory: 30

2.6.1.1: Initial data: 30

2.6.1.2: Deflection: 31

STRUCTURAL TESTING SUBJECT QUESTION 36

LIST OF FIGURES

Figure 1 Steel truss diagram 6

Figure 2 Steel truss experiment under static load 7

Figure 3 Hydraulic pump 8

Figure 4 Switch and Balance Unit SB10 Figure 5 Vishey measurement P3500 8

Figure 6 Strain gage 10

Figure 7 Dial indicator 10

Figure 8 Steel truss 10

Figure 9 Load cell 11

Figure 10 Axial force of the steel truss for case F 1 =1.5kN 16

Figure 11 Deflection node I 18

Figure 12 Deflection Node II 19

Figure 13 Strain gage 1 20

Figure 14 Strain gage 2 21

Figure 15 Strain gage 3 21

Figure 16 Strain gage 4 21

Figure 17 Strain gage 5 22

Figure 18 Strain gage 6 22

Figure 19 Strain gage 7 22

Figure 20 Concrete beam diagram 25

Figure 21 Reinforced concrete beam testing at the laboratory 26

Figure 22 Hydraulic jack and load watch for applying and controlling load 27

Figure 23 Switch and Balance Unit SB0 and P3500 27

Figure 24 General dimension for all 30

Figure 25 Loading action on beam according to the first level of load (i=1) 32

Figure 26 Moment distribution of beam according to the first level of load (i = 1) 32

Figure 27 Case of loading RC beam 34

LIST OF TABLES Table 1 Result of deflection and strain for the 1st experimental testing 12

Table 2 Result of deflection and strain for the 2nd experimental testing 12

Table 3 Calculated result of deflection and strain for the 1st experimental testing 13

Table 4 Calculated result of deflection and strain for the 2nd experimental testing 13

Table 5 Average the calculated result of deflection and strain for the experimental testing 13

Table 6 Summarize the result of deflection and axial force from ETABS 17

Table 7 Summarize the result of deflection and strain value according to elastic theory 17

Table 8 Comparison the deflection result between testing method and SAP2000 18

Table 9 Comparison the strain result between testing method and SAP 19

Table 10 Result of deflection and strain for the 1st experimental testing 29

Table 11 Result of deflection and strain for the 2nd experimental testing 29

Table 12 Calculated result of deflection and strain for the 1st experimental testing 29

Table 13 Calculated result of deflection and strain for the 2nd experimental testing 30

Table 14 Average the calculated result of deflection and strain for the experimental testing 30

Table 15 Summaries the calculation of stiffness factor  33

EXPERIMENT 1: TESTING STEEL TRUSS UNDER STATIC LOAD

1.1 Experiment purpose and requirement for testing steel truss:

1.1.1 Experiment:

Become familiar with the method of testing a bar structure, know how to use

measuring devices to determine experimentally stress and displacement

Determine the stress in the truss rod, deflection, displacement of the truss Fromthere, compare the results between theory and experiment when considering:

• Stress (expressed through strain) of truss rod

• Deflection and displacement at some positions on the steel truss

1.1.2 Requirement for testing steel truss:

• Measure strain  at some representative bars in the array

Stress  and internal force N in truss bars.

• Measure deflection  at some positions on the truss

• Compare experimental and theoretical results

1.2 Experimental diagram:

Figure 1 Steel truss diagram

 The steel truss has trapezoid shape, including 5 spans, each span has 0.5m in height and 1m in length

 Structure of truss steel bars as in the following table:

 Piston diameter: 5.6 cm

 Gusset plate thickness: 4-5mm

Specifications Area(A)(cm2) X-axial moment ofinertia Jx (cm4) E (N/cmModulus2)Chord and

Interior

1.3 Apparatus:

Figure 2 Steel truss experiment under static load

with 1 Hydraulic pump

2 Strain measurement equipment

2 sides of the steel truss as showed in the above figure

 The load acting on the 2 sides

of the truss is calculated as follow:

F=(v × π d42)÷ 2

where: v: Pressure value that read on gauge (daN/cm2)

1 2

4

d: Diameter of the piston (mm).

Figure 3 Hydraulic pump

 The testing uses the 20 tons’ hydraulic pump with the piston diameter

(d = 56mm)

 The process of loading and unloading of the hydraulic pump equipmentshould be processed by each loading level After unloading the pressure

to zero, wait about 10 minutes to continue to operate

1.3.2 Strain measurement equipment:

Figure 4 Switch and Balance Unit SB10

 Switch and Balance Unit SB10:

• Including 10 channels plus open position that allow to measure up to 10 strain gages at the same time The equipment consists a switch button to determine each value of strain gages The channel switch of the SB-10 has an open position to allow the use of additional SB-10’s with a single P-3500 strain indicator

• The combination of a P-3500 and SB-10 allows the operator to intermix, in a single 10- channel system, quarter, half and full bridge circuits

 Vishay measurement P3500:

• The model P-3500 Vishay measurement is a portable,

battery-powered instrument with unique features for use in stress analysis

testing and for use with strain gauge-based transducer

• The value extracted from the electronic meter of the device showed

the negative value is for the strain gage location that are under

compression, and positive value for tensioning

 Strain gage:

 Based on tensest effect, when the conductor is mechanically deformed, the resistance also changes The valueextracted from the Vishay

measurement based on the following formula: ε g=∆ R g / R g

GF

Figure 6 Strain gage

1.3.3 Dial indicator:

Small displacement gauges:

 The type of gauge used in the experiment is an electronic clock That scale is mm Minimum division 0.01mm.

 In the experiment, install 2 clocks to measure the deflection of 2 button positions in the steel frame Corresponding to the increasing or decreasing displacement of each node position that we set the clock up or down

Figure 7 Dial indicator

Figure 8 Steel truss

1.3.4 Load cell:

 An electronic weighing load cell are used toinstall electronic scales These load cells areusually made of allow steel with variousshapes, loads and sizes This equipment iswidely used in many industrial and civil fields

 The load cell is connected to the hydraulicpump, then the hydraulic pump will transferpressure to the load cell, through the steel balland then acting to the structure

Figure 9 Load cell

1.4 Procedure:

1.4.1 Preparation:

The experiment was performed in a group of 15 members The tasks of each member are as follow:

+) Duyen: Setup and read switch and Balance Unit SB10.

+) Minh Duy: Set up and read data from Vishay measurement P3500.

+) Chi Huy: Adjusting the hydraulic pump into the specific pressure level that the instructor has already required.

+) Phuc Dat: Set up and checking the dial micrometer value 1.

+) Dai Duong: Set up and checking the dial micrometer value 2.

+) Others on the team were responsible for assisting with the lighting, taking pictures of the equipment, and checking the metrics.

1.4.2 Testing procedure:

Step 1: Check and re-measure the truss bars with a steel ruler and caliper.

Step 2: Arrangement of deflection and strain gauges (already arranged in

advance) Adjust the deflection gauges to 0 Place the deflection gauges in the correct position to be measured and always touch the steel frame when the load

is increased.

Step 3: Control the hydraulic jack from 0 to 1.5-3-4.5-6 kN by continuously pushing the hydraulic jack below the truss.

Step 4: When it reaches to the required stress level, recording the 2 values of deflection from the dial indicators and strain value of 7 strain gage from Vishey measurement.

Step 5: When the forced reached the maximum required value (6 kN), unloading the hydraulic pump to zero, and wait for 10 minutes and continue the above procedure to measure the second time.

1.5 Testing result:

After testing for 2 times, the results from laboratory experiments will be

summarize in these following table The force value is calculated as:

F=(v × π d42)÷ 2=(v × π × 5.64 2)÷ 2

Table 1 Result of deflection and strain for the 1st experimental testing.

Force

(kN)

Deflection value from

dial indicators (mm) Strain value from P3500 (με)

Deflection value from

dial indicators (mm) Strain value from P3500 (με)

- The displacement value rounded to 2 decimal places

- The positive value (+) of strain corresponding to tension, and the negative value (-) of strain is for compression

1.6 Calculated data:

 The testing result are assumed that the initial displacement and strain values still existed since this is the old steel truss and has been used for various of experiments.

 Therefore, these values should be converted by subtracting the original value to consider the initial displacement and strain to be 0

 Assumed that the results at the initial stage i = 1.

Table 3 Calculated result of deflection and strain for the 1st experimental testing

1.7.1 Modeling the steel truss using SAP2000:

Step 1: Modeling the grid system (notice that the units are kN and meter)

Step 2: Define the material (According to TCVN 5575:2012)

Step 3: Define the section properties (According to the given information).

Step 5: Assign the section properties corresponding to each chord on the truss.

Step 6: Assign joint forces at 2 points on the truss (the force has calculated in Table 5) Then start running and analysis the result and repeat this step for next joint forces acting on the truss

1.7.2 Result from SAP2000:

Figure 10 Axial force of the steel truss for case F 1 =1.5kN

Comment on the axial forces result:

- The top chords are tended to be in compression with a negative value (-) and the lower string tends to be in tension with a positive value (+) However, the middle chord of the upper and lower truss has the highest longitudinal force value.

- The four interior chords located in the middle of the truss have a very small number of axial forces

Table 6 Summarize the result of deflection and axial force from ETABS

Force

(kN)

Deflection value

fromSAP2000 (mm) Axial force value N from SAP2000 (kN)

1.5 0.242 0.268 1.219 0.035 1.219 -4.48 -4.49 1.189 1.189

3 0.443 0.536 2.657 0.063 2.657 -8.97 -8.97 2.379 2.379 4.5 0.647 0.759 3.759 0.078 3.579 -12.46 -12.46 3.532 3.532

+ N: Axial force for each chord (N)

+ A: Cross-sectional area of each steel chord (mm2)

+ E: Elastic modulus of steel (N/mm2), taken E = 210000N/mm2

For easier comparison, the theoretical result of strain will be converted into  which has the same unit corresponding to the measurements on the test equipment

1.8 Result and discussing:

1.8.1 Comparison between testing method and SAP modelling method:

a Deflection

Table 8 Comparison the deflection result between testing method and SAP2000

Node F(kN) ExperimentDeflection (mm)SAP2000 %

0 1.5 3 4.5 6 0

Table 9 Comparison the strain result between testing method and SAP

Experiment SAP2000

Figure 14 Strain gage 2

Figure 15 Strain gage 3

Figure 16 Strain gage 4

Figure 17 Strain gage 5

Figure 18 Strain gage 6

Figure 19 Strain gage 7

1.8.2 Discuss the result between testing and SAP modelling method:

-100

-90 -80 -70 -60 -50 -40 -30 -20 -10

1.8.2.1: Comment on chart result:

Overall, there is a significant difference in both deflection and strain value between the two testing methods and SAP2000

 For deflection, the highest difference between the two methods is 78% Besides,the graph between the two methods shows the same trend (deviation value ofboth methods increases in proportion to the load)

In addition, the test method gives a deviation value is higher when comparedwith value extracted from SAP2000

However, the results in SAP2000 show more linear increase than experimentalmethod This may be due to the experimental procedure, the error during theexperiment process, resulting in non-linear results when compared withSAP2000 results

 For strain values, the highest difference between the two methods is up to 99%and as low as 3% The biggest difference comes from the result of tensionmeasurement 2, with the test method results are much larger than the SAP2000results This can come to the fact that the normal force result extracted fromSAP2000 for strain gauge position 2 is N = 0 kN is considered to be nodeformation, but in the strain test, strain also occurs gauge 2 (test value fornegative strain value for strain gauge 2 means that the bars are undercompression)

 Due to the force part

 Due to mechanical processing the beam model is not accurate in

both cross section and working structure

b) Since strain gauges are very sensitive, it is very difficult to get to zero

initially, so usually accept a non-zero number, leading to error in

calculation So, each reading of the data will lead to a larger error

c) Due to the careless reading of the number as well as the installation of

the meter

d) Due to the error of the length measure Error of displacement and

strain gauges (error number of instruments-objective error)

Although the measured data is not close to the theory, but through the

process of experimenting myself

Learned many useful lessons, learned more measuring devices such as

tensormet, clock measure displacement equipment, and especially

understand how to do experiments in reality construction site that helps usavoid surprises when working in reality In the past the process also draws a lot of experience, knows how to adjust the equipment measured and errors are common.

- Errors made during the experiment made the measurement results inaccurate as accurate as placing non-vertical gauges made vertical

displacement measurement to tilt displacement measurement, the gauges are so sensitive that the initial adjustment does not going to 0 makes the measurement and reading of numbers inaccurate many times leading to errors adjusting the device at the beginning is very important