ASCE705S.xls

Rating:
12

Description


Program Description:
"ASCE705S" is a spreadsheet program written in MS-Excel for the purpose of flat roof snow loading analysis for buildings and structures per the ASCE 7-05 Code. Specifically, coefficients and related and required parameters are selected or calculated in order to compute the net design snow loads, including snow drift due on lower roofs and rain-on-snow surcharge.
Program Assumptions and Limitations:
1. This program specifically follows Section 7.0, Snow Loads, of the ASCE 7-05 Standard, "Minimum Design Loads for Buildings and Other Structures".
2. This program assumes only snow loading analysis for buildings with a flat roof, or low slope roof <= 5 degrees. (Note: for reference, a 1:12 roof slope equates to 4.76 degrees, and the program allows a slope up to 1.05:12.)
3. This program addresses only balanced snow loading, snow drifts on lower roofs, and rain-on-snow surcharge loading. Unbalanced roof snow loads are not considered.
4. This program assumes the possibility of either leeward or windward snow drifts, and the larger of the two calculated drift heights per the code is used as the design drift height. Leeward drift results from snow blown off a high roof onto a lower roof. Windward drift results from snow blown against a projection or wall below a high roof.
5. This program determines any rain-on-snow surcharge loading when applicable. Rain-on-snow surcharge loading of 5 psf is not required for ground snow loads, pg > 20 psf, nor for roof slopes (in degrees) >= W/50, where "W" is equal to the horizontal distance (in feet) from the eave to the ridge on the building. This program conservatively combines the rain-on-snow surcharge loading with snow drift loading. However, per Code, rain-on-snow surcharge loading need not be combined (superimposed) with snow drift loading.
6. This program contains numerous “comment boxes” which contain a wide variety of information including explanations of input or output items, equations used, data tables, etc. (Note: presence of a “comment box” is denoted by a “red triangle” in the upper right-hand corner of a cell. Merely move the mouse pointer to the desired cell to view the contents of that particular "comment box".)

 

Useful Web Resource
I was given a couple of websites which you might find convenient for determining the basic wind speed and ground snow load
for any location in the continental United States per the ASCE/SEI 7-05 Code, so I thought I'd pass them along.
The website links are as follows:
http://www.windspeedbyzip.com/
http://www.groundsnowbyzip.com/
You must register to make use of either website, but you only have to register at one, not both of the websites.   
Once you register at one of them, you will automatically have access to information from the other one.
The two websites allow you to input either the street/city/state address or just the zip code.   
The resulting location latitude and longitude are given.  Regular (street), satellite, and hybrid maps are available as well.

Calculation Reference
ASCE 7-05 Code Snow Load

 

Calculation Preview

Submitted On:
08 May 2012
File Size:
302.00 Kb
Downloads:
742
File Version:
1.7
File Author:
Alex Tomanovich
Rating:
12

 
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Comments: 9
ATomanovich 8 years ago
It was brought to my attention in the "ASCE705S.xls" spreadsheet workbook, for the rather rare case when the actual length of lower roof is less than the calculated snow drift length, the spreadsheet was reducing the magnitude of the snow drift to a value of zero at the edge of the roof. This was incorrect. Per ASCE 7-05 Section 7.7.1, when length of lower roof is less than calculated length of snow drift, the snow drift shall be truncated at the far edge of roof, and not reduced to zero there.
Thus, for this special case I had to create another result, in the form of the weight of the snow drift at the low end (minimum value). Please note that for this rather rare case, the illustration shown at the bottom of the calculation sheet will not actually depict the snow drift value at the low end (edge of building) correctly. Sorry, there's really not an easy nor convenient way to address that particular case, and to me it's not worth the effort trying to address it. The user will just have to be aware of it.
This workbook is now version 1.7.
ATomanovich 8 years ago
It was brought to my attention in the "ASCE705S.xls" workbook in the "Snow Load" worksheet that was a wrong cell reference pertaining to the calculation for the snow drift sketch off to the right of the main calculation page. Here the user could input a distance from the end where the drift is a maximum value, and determine what the value of the drift is at that distance away. The calculation in Cell AC41 was using the actual calculated drift length, "w", when it should have been using the "w(use)" value of the drift, which is the minimum of either "w" or "w(max)". The error would show up only when the value of "w(use)" was controlled by the value of "w(max)".
I have made the appropriate cell reference correction, and the version of this workbook is now 1.6.
ATomanovich 9 years ago
For some people, there has been some confusion in the "Snow Load" worksheet, distinguishing between the use of the maximum drift height, "hd(max)" and the design drift height, "hd". I have added a variable named "hd(max)" to distinguish between "hd(max)" and "hd" for determining the proper usage of each one in eventually calculating the drift width, "w" and the weight of the drift at the high end, "pd".
Below is the logic that I have used for the revised worksheet from the second paragraph of ASCE 7-05 Section 7.7.1.
I don't know about the rest of you, but to me that paragraph typifies some of the confusing and convoluted verbiage that is often found in building codes.
hd(max) = maximum of (hdL or hdw)
If hd(max) <= hc then w = 4*hd(max) and hd = hd(max) (where hc = clear height)
If hd(max) > hc then w = 4*hd(max)^2/hc and hd = hc
The current version is now 1.5.
ATomanovich 11 years ago
In the "ASCE705S.xls" workbook, it was brought to my attention that the comment box in cell C36 in the "Snow Load" worksheet pertaining to rain-on-snow loading was an apparent "leftover" from the version of this workbook for the ASCE 7-02 Code. What I typically do when a new version of a particular code comes out is use the workbook for the previous code version and edit it as required. Obviously, I forgot to edit this particular comment box. The programming logic did reflect the change in the code on that subject.
I have corrected that comment box, and the current version of this workbook is now version 1.4.
ATomanovich 11 years ago
Useful Web Resource
I was given a couple of websites which you might find convenient for determining the basic wind speed and ground snow load
for any location in the continental United States per the ASCE/SEI 7-05 Code, so I thought I'd pass them along.
The website links are as follows:
http://www.windspeedbyzip.com/
http://www.groundsnowbyzip.com/
You must register to make use of either website, but you only have to register at one, not both of the websites.
Once you register at one of them, you will automatically have access to information from the other one.
The two websites allow you to input either the street/city/state address or just the zip code.
The resulting location latitude and longitude are given. Regular (street), satellite, and hybrid maps are available as well.
ATomanovich 11 years ago
It was discovered in all 3 snow loading workbooks (ASCE705S.xls, ASCE702S.xls, and ASCE798.xls) that the sketch at the bottom of the calculation page as well as the sketch off of the calculation page to the right were displaying the calculated snow drift length, "w", when they should have been displaying the actual snow drift length to be used, "w(use)". The actual snow drift length to be used is the minimum of either the calculated value "w" or the maximum value "w(max)" per the Code.
At some point I will just drop the ASCE798.xls workbook, since most folks are probably using either the ASCE 7-05 or ASCE 7-02 Codes in their work.
For now I have made the corrections to the sketches in all three workbooks, and they are all now version 1.3.
ATomanovich 11 years ago
It was brought to my attention that in the "ASCE705S.xls" workbook on snow loading, I inadvertently had the user input cell for "Type of Roof" locked, so that the input pick box could not be utilized. Thus, you were stuck with the "Monoslope" roof selection.
I have made the correction and the workbook is now version 1.2.
drhall 11 years ago
Thanks.
ATomanovich 12 years ago
The section pertaining to rain-on-snow surcharge, Section 7.10 of the ASCE 7-05 Code, has been revised from how it read in the ASCE 7-02 Code. At first, I believed that there was room for interpretation of ASCE 7-05 Section 7.3, because of the way it has been revised and worded. It states basically that the flat roof snow load shall be computed per Equation 7.1 as pf = 0.7*Ce*Ct*I*pg, but not less than the minimum pf = I*pg when pg <= 20 psf nor pf = 20*I when pg > 20 psf. Section 7.10 states that the rain-on-surcharge, when applicable, is to be added to the balanced snow load case. So to me, there in lied the interpretation issue. Does the balanced snow load case referred to in Section 7.10 mean "pf" as calculated solely per Equation 7.1, or does one follow through literally the complete provisions of Section 7.3, where the minimum value of "pf" is also to be considered? In version 1.0 of the "ASCE705S.xls" workbook, I originally opted to take the latter interpretation, which would result in higher (conservative?) design balanced snow loads.
With clarification received and passed on to me from one of the guys who posed these questions to the ICC, they stated that there was really no intent in the revisions made to the ASCE 7-05 Code to increase the balanced snow loading when considering rain-on-snow surcharge from what the ASCE 7-02 produced. An excerpt of that question and answer clarification received from the ICC is shown below.
A2. Not to our knowledge.
In summary, it appears that the only real change in snow loading using ASCE 7-02 versus ASCE 7-05 is the roof slope criteria for when to consider rain-on-snow surcharge. In ASCE 7-02, it applied only to roof slopes of less that 1/2" per foot, whereas in ASCE 7-05 it applies to roof slopes of less than W/50 degrees.
I have made the necessary revisions, and the "'ASCE705S.xls" workbook is now version 1.1.