Seismosoft | Earthquake Engineering Solutions

Mx, My and Mz are simply the lumped masses which you wish to be considered in each of the three orthogonal directions.

Mxx, Myy, and Mzz are the rotary inertias about each of the respective axes.

So if you have, in fact, used the formulas shown as your input to Mx, My, and Mz, then this is incorrect. The formula you listed is for Mxx, Myy, Mzz.

The Mx, My, and Mz values are simply the lumped mass, i.e., the weight divided by gravity in the appropriate units.

With no detailed information on the experimental setup, I cannot possibly attempt an explanation as to why your model periods are different from the experimental values.

quote:Originally posted by huffte

Mx, My and Mz are simply the lumped masses which you wish to be considered in each of the three orthogonal directions.

Mxx, Myy, and Mzz are the rotary inertias about each of the respective axes.

So if you have, in fact, used the formulas shown as your input to Mx, My, and Mz, then this is incorrect. The formula you listed is for Mxx, Myy, Mzz.

The Mx, My, and Mz values are simply the lumped mass, i.e., the weight divided by gravity in the appropriate units.

With no detailed information on the experimental setup, I cannot possibly attempt an explanation as to why your model periods are different from the experimental values.

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Sir the details of experimental are elaborated below in a presentation
Experimental Setup
https://drive.google.com/file/d/0B7rekW ... sp=sharing

The dead mass on circular column was put in increments (as shown in above presentation for reference)of 25%, 50%, 75% and 100%.
so lets say i want to find the time period for 100% mass i.e, 19.24 tons then in Mx , My and Mz i should enter a value of 19.54 tonne ?? and what about for the rest of 3 cells asking for Mxx , Myy and Mzz ..do they need to be filled or should i leave them as zero ???

Thanks in advance

I calculated the the values of Mx, My, Mz and Mxx , Myy and Mzz for the above case as shown below in following picture. Is this approach right ?? although i am still far away from the time period calculated experimentally.

https://drive.google.com/file/d/0B7rekW ... sp=sharing

quote:Originally posted by zsaeed

I calculated the the values of Mx, My, Mz and Mxx , Myy and Mzz for the above case as shown below in following picture. Is this approach right ?? although i am still far away from the time period calculated experimentally.

https://drive.google.com/file/d/0B7rekW ... sp=sharing

Using above formuale and putting values for all Mx, My, Mz, Mxx, Myy and Mzz i got the following results tabulated.

https://drive.google.com/file/d/0B7rekW ... sp=sharing


The good thing is that the results of Column without CFRP and Column with single CFRP layer matched the experimental results but still when i move from Single CFRP layer to Double CFRP layer, my results no longer matches the experimental results..

If experimental results are reporting longer periods for the retrofitted condition compared to the original unwrapped column, then clearly there is something beyond simply the initial uncracked elastic period being reported.

Wrapping a column with FRP would not decrease the stiffness of the column, which for the same mass, is what would have to happen in order for the period to lengthen (get higher).

Does your experimental report explain how a single layer of FRP could increase the stiffness (decrease the period as indicated in your table) while a double layer decreased the stiffness (increased the period)?

zsaeed, what type of FRP did you use in experiment? Was it unidirectional FRP with the fiber perpendicular to column axis i.e., fibers in the circumferential direction)?

If you used FRP with bidirectional or more direction fibers, then obviously simply use of con_frp won't work since it will neglect the effect of longitudinal fibers on column stiffness.

quote:Originally posted by huffte

If experimental results are reporting longer periods for the retrofitted condition compared to the original unwrapped column, then clearly there is something beyond simply the initial uncracked elastic period being reported.

Wrapping a column with FRP would not decrease the stiffness of the column, which for the same mass, is what would have to happen in order for the period to lengthen (get higher).

Does your experimental report explain how a single layer of FRP could increase the stiffness (decrease the period as indicated in your table) while a double layer decreased the stiffness (increased the period)?

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Actually the Experimental work has been done by a researcher during his Phd studies and i am doing a numerical simulation of it.. i was also amazed to observe this abnormal behavior that when a single CFRP layer is wrapped on a column it causes a decrease in time period (normal expected trend) but when the similar column was wrapped with double CFRP layer the time period got increased to a much higher value as compare to column with a single CFRP layer (abnormal trend) and column without a CFRP layer...
i will ask the question to the Phd scholar , might be he had some thing new in his mind and will discuss his thoughts and finding on this platform as well ...

quote:Originally posted by fakharifar.mostafa

zsaeed, what type of FRP did you use in experiment? Was it unidirectional FRP with the fiber perpendicular to column axis i.e., fibers in the circumferential direction)?

If you used FRP with bidirectional or more direction fibers, then obviously simply use of con_frp won't work since it will neglect the effect of longitudinal fibers on column stiffness.

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Yes Sir the FRP used unidirectional and fibers were oriented perpendicular to longitudinal direction of column..
Pictures represent the above mentioned samples while doing experimental work

https://drive.google.com/file/d/0B7rekW ... sp=sharing


https://drive.google.com/file/d/0B7rekW ... sp=sharing

"i was also amazed to observe this abnormal behavior that when a single CFRP layer is wrapped on a column it causes a decrease in time period (normal expected trend) but when the similar column was wrapped with double CFRP layer the time period got increased to a much higher value as compare to column with a single CFRP layer (abnormal trend) and column without a CFRP layer..."

What you mean by amazed?

How much deviation between different result you define as much higher?

I have been using this software around 5-6 years, and from my experience let me tell you, you SHOULD NOT get so much deviation when you increase the number of layers from 1 layer to 2 layers.

Think about it and use your engineering judgement. FRP is a thin wrap that works upon concrete dilation (cracked cross section), that's why it is categorized as passive confinement. How could you think such jacket with small out of plane membrane stiffness could affect the structural fundamental period of vibration significantly when increased from 1 to 2 layers. That's why confining pressure from FRP wraps in rectangular cross section is not as effective as circular cross section.

I would agree with your results if it was either conventional steel jacket or concrete jacket.

I hope this helps you furthering your work. Good luck.

zsaeed hi,

First, the experimental results do seem a bit strange indeed. From experience, we would expect the decrease in the period (i.e. the increase in the stiffness) both with the single and the double FRP layers to be very small. However, these results (and the explanation for these values) is something that you should discuss with the people that have carried out the experiment, and cannot be really explained by the people in the forum, as we do not know the details of the experiment.

Secondly, you should realise that the models behaviour in the program is just a way to simulate reality and it should not be confused with reality, i.e. the actual experimental results. In order to understand your model in the PC and the results that you get, you should understand first the assumptions that have been made. One of these assumtions lie in the concrete material models and their way of treating confinement. According to the models the confinement (modeled only through the confinement factor) affects the maximum stress, the strain at the maximum stress and the descending branch of the material model. But it only marginally affects the initial stiffness, which is in line with most of the experiemental results in the literature. In your model, if you go to the Materials module of the pre-processor, and observe the hysteretic curves of the confined and uncofined con_ma material models, you will realise that the initial ascending branch of both is essentially the same (e.g. they both cross the point with coordinates at strain=0.001 - stress=14MPa).

Thridly, the differences between the unwrapped and wrapped with a single layer models are attributed to the fact that you are using different concrete material models (con_ma and con_frp) and the different ways these models calcualate the initial stiffness. Going from the single FRP to the double FRP model, has no significant difference in the initial stiffness, because I suspect that you are using the same con_frp model.

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