As shown in the image, I have done a vibrating wire type strain gauge and pressure cell (not shown in the image) instrumentation on full scale form. the objective is to measure the lateral pressure of the concrete on the form while concrete was poured and until later initial setting time. Though the interest was to measure only the concrete pressure. As an additional information I measured strain too.
There is a doubt in the measured pressure. I checked the calibration and raw data. It seems everything is OK. But the measured values are far less than the expected theoretical value. Fortunately, We have concrete strain measurement. But unfortunately I do not know how to use the strain data to back calculate and get the lateral pressure.
Is there a standard formula available to calculate lateral concrete pressure from the measurements of lateral concrete strain?
In the drawing shown, I will assume it is a vertical concrete cross section of a form. When wet concrete is placed in the form the forces are fairly uniform on both form faces, and the internal friction in the concrete mixture makes the concrete perform as if it is a uniform solid, and the forces are thus distributed fairly uniformly over the area of each form face. However ,when a concrete vibrator is inserted into the wet concrete, and it is turned on, the concrete suddenly changes from a uniformly distributed solid to a triangularly distributed force like water on the face of a dam. the deeper down in the form, the higher the water pressure of the concrete. When concrete is being liquified by a vibrator, the forces are far higher that when the concrete is acting as a solid, and the maximum force is occurring at the bottom of the form. Tall forms tend to explode the form ties if the concrete is not placed in relatively thin layers, and each layer vibrated separately, just barely going into the prior layer. Concrete is typically around 144 to 150 LBS per cubic foot of front face area, until a vibrator is applied, then the force increases dramatically especially at the base of a tall form.
You could demonstrate this by using long form ties with calibrated springs on the form ties that could be filmed when the vibrator is applied to the concrete.
4 form ties in a square with 8 calibrated springs and a video camera would be very instructive.
MWC
I agree with Michael Clark. The lateral pressure on form depends on water cement ratio , pouring rate of concrete into the form work , arrangement of reinforcement, workability of concrete.
If two sensors connected by calibrated straingauge placed at a given location out of which one is fixed and other is allowed to translate due to lateral pressure of flowing concrete acting on a certain area ( ( force acting on this area will create strain in staringauge) may help.
You have to know one thing that the stress and strain are accurate for static condition loading. But when we talk about vibration then finite elements method are necessary to obtained. For the design or analysis use finite element method ,
And one important thing --
If we go for simply beam ,column, slab and find the lateral loading by the effect of vertical load then we have to know mixing , pouring rate etc . . This criteria are not applicable for lateral loading by the effect of vibration.
Thank you..
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