Yes, it is very important, especially if it is done within a wall system. One of the important failure modes of Brick Walls is buckling ( out-of-side). So, it depends on the displacement effects.

Yes. I agree. But, to avoid the confining effect of the loading platens, it is especially important to measure the specimen displacement in the loading direction rather than relying on the machine displacement. Hence, we need to use a Linear variable differential transformer (LVDT) to measure the vertical deformation. The LVDT is usually connected to a data acquisition system for synchronized recording of the applied load and deformation of the specimen. The corresponding strain is then estimated by dividing the recorded deformation by the gauge length.

I hope this explanation helps.

Regards,

Padalu Pravin Kumar

But, when there is no bending and we are testing specimens under axial compression, what is the difference between the measurements of LVDT and relative displacement of the loading platens?

Dear Abolfazl,

In general, the machine displacement (or the actuator displacement) includes all sources of displacement including slippages, deformations of plates and couplings, etc in addition to specimen deformation. For material testing, we use an externally mounted extensometer to avoid these deformations. If there is no way to use an external extensometer, there is a procedure called "Compliance error correction" that evaluates the errors and removes them from measured data. However, I don't think it is applicable to masonry and large-scale tests. Please check the following document for more information.

Best regards,

Dear Abolfazl Eslami

I agree with Mr. Mohammad Ali. But, this "Compliance error correction" facility is not available on all the test machines. Hence, it is always advisable to use external devices to measure specimen displacement rather than simply relying on the machine displacement.

Regards,

Padalu