Stress Strain Relationships for Steel and Concrete

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EN1029 Laboratory: Compression Tests

Objective
To plot stress-strain relationships for steel and concrete when tested in compression.

Equipment to be used
Avery Testing Machine & Compression Press

Experiment instructions
You will be supplied with two “identical” steel cylinders (specimens A & B), three “identical” concrete prisms and three “identical” concrete cubes. Measure the specimens and draw dimensioned sketches of the specimens. One of the steel specimens, A, will have electrical strain gauges (and cabling) attached.

1. [Watch Clip 1] Place the steel specimen A, with the gauges attached, in the Avery Testing Machine [see “Pictures.pdf” on Learning Central] and apply compressive loads in increments of 5kN. Record the corresponding changes in length of the specimen via the strain readings. [Readings of loading and unloading given in “Results.pdf” on Learning Central.] The maximum load applied should not exceed 50kN. Unload in steps of 5kN and again note values of load and strains. Note too the residual strain after unloading.

2. [Watch Clip 2] Remove specimen A from the test machine and place specimen B in the compression press machine [see “picture.pdf” on Learning Central]. Increase the load until failure occurs (typically, go up to around 500kN). Note the maximum load, and the shape and sizes of specimen B after the test.

3. [Watch Clip 3] Place one of the concrete cubes in the compression press and measure the shortening of the specimen with a dial gauge for increasing load. Remove the dial gauge and test to failure, recording the maximum load. Repeat with the other two cubes (which should be identical) but record only the failure loads. [Clips 5 & 6 – from Expedition Workshed - also show concrete cube test at failure point.] (Note that although the “design strength” of the concrete was 30 N/mm2, that is the expected strength at 30 days, whereas the specimens were tests at age of less than a week, and they had thus not yet reached full strength.)

4. [Watch Clip 4] Repeat the concrete cube experiment with the concrete prism.

Report writing
Use the report template. Detail what happened in the experiments and how the objective of the exercise was met (or not). Plot and explain the stress-strain relationships for steel and concrete compression test. Obtain the ultimate stresses and also the values for Young’s modulus and the type of failure observed and comment on the values obtained.

Reference
1. Ormandy, P.G., 1968 “An Introduction to Metallurgical Laboratory Testing”, Pergamon Press. 2. BS1881 Part 4, 1970, Methods of Testing Strengths of Concrete. Steel Specimens
Specimen A (load within Elastic Limit)
|Load (kN) |Micro-Strain (x 10-6) |Axial shortening (mm) |Strain |Stress (kN/mm2) | |0 |0 |0 |0 |0 | |2 |-19 |9.49 x10-4 |1.90 x10-5 |4.10 x10-3 | |5 |-46 |2.30 x10-3 |4.60 x10-5 |10.25 x10-3 | |10 |-93 |4.65 x10-3 |9.31 x10-5 |20.49 x10-3 | |15 |-141 |7.05 x10-3 |1.41 x10-4 |30.74 x10-3 | |20 |-187 |9.34 x10-3 |1.87 x10-4 |40.98 x10-3 | |25 |-234 |11.69 x10-3 |2.34 x10-4 |51.23 x10-3 | |30 |-270 |13.49 x10-3 |2.70 x10-4 |61.48 x10-3 |...
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