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TOPIC: BOEF.xls
#3273
ATomanovich (User)
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BOEF.xls update to version 1.5 3 Years, 8 Months ago Karma: 53  
I've made some additions to the "BOEF.xls" spreadsheet workbook, for beam on elastic foundation analysis.

First, off of the main calculation page to the right and below, I have added the ability to convert a given subgrade modulus (k) value derived from a geotechnical plate load test to what would be more applicable for the full size footing or strip of mat that is being analyzed. The references used are listed above the calculations. There is a noted limitation to this adjustment in the subgrade modulus, and it is always advised to consult the geotechnical engineer on the project for advice and recommendation on this subject.

Second, I also added the minimum soil bearing pressure and the percent bearing area resulting from the analysis. This, along with the additional comment boxes that I've added, should help the user determine the applicability and validity of a particular analysis using this spreadsheet.

For those of you who may not have ever tried or used this spreadsheet before, you might want to give it a try and become familiar with its capabilities. Sometimes we don't have the time (due to schedule) nor the need (preliminary engineering) for a more sophisticated FEM analysis. If this spreadsheet is used wisely and within its limitations, it will give you very acceptable results, efficiently. Plus, and maybe most importantly, it can help you understand the effects of a flexible vs. a rigid foundation/soil system, and give you quick insight on the thickness to use for a particular footing or mat when relative rigidity has been "casually" assumed initially in analysis, as is often done. Paying close attention to the plotted bearing pressure diagram will help you see just how flexible or rigid the footing or mat really is. When a "semi-rigid" to "rigid" condition is desired, you will be striving for a relatively linear distribution for the bearing pressure diagram.

The current version of this workbook is now version 1.5.
 
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#3274
ATomanovich (User)
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BOEF.xls update to version 1.6 3 Years, 8 Months ago Karma: 53  
Oops!....."BOEF.xls" Spreadsheet Workbook - Update (version 1.6). Well, this has to be a personal record for the least elapsed time between updates on a particular workbook. Maybe age and "high mileage" is finally catching up with me. (lol)

It was just brought to my attention that in the calculations for adjusting the subgrade modulus, in cell M65 where the spreadsheet was computing the final adjustment for a rectangular configuration the program logic was using the maximum of prior calculated values between sand or clay, instead of using the specific prior calculated value for either sand or clay. I have made the necessary correction in the program logic in cell M65 to select the value for whichever soil type was selected.

To summarize, what these calculations do for adjusting the subgrade modulus is first take the given k1 value from the geotechnical plate load test for the given plate width, B1, and then based on the soil type, sand or clay, convert it to a value reflecting a square footprint of BxB, where B is the assumed foundation or mat strip width. Then, the value adjusted for BxB is adjusted once again to reflect the actual footprint, LxB, where L is the input length and B is the assumed width.

As stated in the calculations and from the designated references, the adjustment equations deteriorate when the ratio of B/B1 > 3, and at that point a recommendation from the geotechnical consultant is advised.

The current version of this workbook is now version 1.6
 
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#3713
AMMamore (User)
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Re:BOEF.xls update to version 1.6 2 Months, 1 Week ago Karma: 0  
Hello Alex. This is my first time of using BOEF spreadsheet. I am designing a beam t support the load cells of a truck scale. What I notice is that the value of maximum deflection of the beam is not changing as I change the depth of the beam. Can you try to see if there is an error in your deflection formulas.

Thanks,
File Attachment:
File Name: BOEF.xls
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#3714
ATomanovich (User)
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Re:BOEF.xls update to version 1.6 2 Months, 1 Week ago Karma: 53  
The value of the maximum deflection should always change when the thickness of the beam or slab/mat strip. It does just that for me in Version 1.6.

Why don't you email me and I'll make direct contact to will take a look at it for you.

While it's possible that there could be an issue, this spreadsheet has been used by countless people around the world for several years and I've never heard of an issue like the one that you are having. Of course, there is always a first time for everything, as the saying goes.

Alex
 
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Last Edit: 2017/10/04 20:50 By JohnDoyle[Admin].
 
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#3715
ATomanovich (User)
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Re:BOEF.xls update to version 1.6 2 Months, 1 Week ago Karma: 53  
Albert,

You cannot compare a beam supported only at both ends with a beam continuously supported on an elastic medium. Yes, as we all know, the deflection is proportional to the cross section moment of inertia for a beam supported only at both ends, but that is definitely not the case for a continuously supported beam. For a beam on elastic foundation, the beam stiffness and the stiffness of the supporting elastic medium work together to determine how “rigid” or “flexible” the entire system is.

In your example problems, the less thick beam is already “semi-rigid” while the thicker beam is “theoretically rigid”. Once a beam/support system, is at least relatively rigid, then the applied loads are distributed basically linearly, as they would absolutely be in a “theoretically rigid” beam/support system. Thus, increasing the thickness of the beam would not have much effect on the deflection and bearing pressure. You should also remember to account for the difference in self weights when changing the thickness of the beam or slab/mat strip, as the thicker beam would result in a slightly larger defection and bearing pressure. However, increasing the thickness of the beam would obviously increase the shear capacity and lessen the reinforcing requirements for an assumed concrete cross section.

In any beam on elastic foundation analysis, I always pay particular attention to the resulting bearing pressure diagram. Linearity of the diagram is the dead giveaway of how rigid the particular beam/support system actually is.

Finally, a very important part of any beam on elastic foundation analysis, when used for analyzing a strip of a slab or mat, is the actual strip width that is input to be used in the analysis. Off of the main calculation page to the right, there is some suggested criteria that I present to help keep you from being either way too conservative or unconservative in the analysis. Increasing the slab or mat thickness would allow for an increase in the assumed strip width to be used in the analysis.

I hope this helps.

Alex
 
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Last Edit: 2017/10/10 17:21 By ATomanovich. Reason: Typo error for \"Off\" and \"of\" in last paragraph.
 
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#3716
AMMamore (User)
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Re:BOEF.xls update to version 1.6 2 Months ago Karma: 0  
Thank you, Sir Alex, for your explanation. That clarifies my question.
 
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