As you all now, a typical stress-strain curve for concrete under compression can be seen in any reinforced concrete design textbook. The decreasing part of the curve (post-peak) can be obtained by testing the specimen with displacement controlled test machines.

My question is why do we prefer the strain controlled compression test instead of the stress controlled test?

We use the stress-strain curve to calculate ultimate strength capacity of the section. The reinforced concrete member which is designed according to the stress-strain curve is subjected to load such as dead loads, earthquake loads etc during its lifetime. I think that the strain controlled tests are not appropriate to model dead loads because they are constant. The stress controlled stress strain curves might be more appropriate for the dead loads and earthquake.

  • $\begingroup$ Welcome to Engineering! What about the fact that dead loads are constant makes you think they'd be best modelled by stress-controlled tests? $\endgroup$ – Wasabi Feb 27 '20 at 23:53
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    $\begingroup$ You can't measure the decreasing part of the curve in a repeatable way with stress (or force) control. As soon as you exceed the peak load, the only "control" will be the dynamics of the test specimen and the testing machine itself. If you design a structure where the dead load exceeds the peak load, you simply get structural failure! $\endgroup$ – alephzero Feb 27 '20 at 23:56

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