Design Snow Load

[EngrUzair]

ASCE 7 provides ground snow loads values for the design of structures, located in various parts of the USA. Where we can find  snow load data related to various regions of Pakistan?

[Waqar Saleem]

See Pakistan Building Code SP2007 ,chapter 5, Div II 

[EngrUzair]

waqar sahib!

 

Chapter 5 Division II of Building Code of Pakistan (Seismic Provisions-2007) provides the following information only:

 

1. Which load combinations are to be used for snow load.

 

2. How the snow load reduction factor can be calculated.

 

It however DOES NOT tell us recommended values of snow load (in psf or kN/m^2 etc) to be used for the design of building roofs in various areas of Pakistan. Snow does not fall in all areas  of Pakistan. Moreover, snowfall intensity is not the same in different hilly area. For example, Murree receives much more snow, as compared to Quetta. As such, design snow load for these two cities will certainly be different. 

 

I am interested to know where can I find design snow load values, applicable for structural design of building roofs located in Murree, Quetta and other hilly areas of Pakistan.

[Waqar Saleem]

snow fall data u may get from the MET department or use any conservative value based on the snow pattern of the area .

[EngrUzair]

 

... or use any conservative value based on the snow pattern of the area .

 

Waqar sahib!

 

Can you give some practical example, how a "conservative" design snow load value can be selected for a particular city? What should be the design snow loads for Quetta and Murree? 

 

IMHO, as structural engineers, we are responsible to design safe and economical structures. Using unlikely heavy loads, will result in larger structural members or more reinforcement, thereby making the structure uneconomical. As such, selected loads should be very realistic.

 

In this purview, I am interested to know how the other structural engineers are selecting snow load values for various hilly areas of Pakistan? I think, seniors should share their experience here to tell us about  what snow load values they have used for their designs?, and what criteria they adopted to determine the selected snow load value? This sharing of knowledge would certainly help the younger engineers to decide at least about selection of reasonable design snow loads, in absence of standard or code-recommended values.

[UmarMakhzumi]

I have done some search in my content dump, and I found ground snow values(kN/m^2) as well as wind speed values(m/s) based on IBC 2006, International Building Supplement. The values are for Karachi, Islamabad, Peshawar and Lahore only.

 

Here are the two pre-notes that go with the attached tables:

 

1) Ground snow loads. OBO site-specific snow load data shall be as specified in the project statement of

work (SOW). Use the values in Table 1609 only when such data is not specifically given in the SOW.

 

2) Basic wind speed. OBO site-specific basic wind speed data shall be as specified in the project

statement of work (SOW). Use the values in Table 1609 only when such data is not specifically given in

the SOW; however, the minimum basic wind speed (3 second gust) shall be 40 m/s.

 

 

Here are the two foot-notes that go with the attached tables:

 

Note 1: To convert the snow load value in kN/m2 to psf, multiply the kN/m2 value by 20.89. Snow loads shall be

rounded to the nearest 5 psf.

 

Note 2: To convert wind speed value in m/s to mph, multiply the m/s value by 2.237. The wind speed shall be

rounded to the nearest 5 mph.

 

Now regarding design values for places like Murree or Northern Pakistan, which receives biggest chunk of snowfall, my personal recommendation would be to use values for Fort McMurry, Alberta, Canada. You can use this link(http://www.jabacus.com/engineering/load/snowload.php) to quickly calculate snow load for Fort McMurry or any city in Canada.

 

To establish a baseline, you can do a comparison of average annual snowfall for Fort McMurry(or whatever city you selected: Edmonton, Saskatoon and Regina would be some good choices in addition to Fort McMurry) to the area that you are designing to get a feel for how conservative your number are.

 

You may have to some search on google for Pakistani Cities average snowfall data but it would be worth it. Do share it here if you come across any.

 

This sums up my 2 cents.

 

Thanks.

 

[EngrUzair]

Aoa.

 

Sir Umar! Thanks for indirectly reminding me to check my own record dump, as I have found relevant portions of international building supplement to 2009 IBC available with me as well. However, the database includes the same four pakistani cities, as mentioned in your post.

 

I think, I will have to obtain basic snow load data from MET department (as waqar saleem has already pointed out earlier), and to transform it into a reference database table, useful for structural designers. This is however a time-cosuming job and being too busy now-a-days, I will work on it sometimes later. The progress & results of this research will insha-allah be updated on this forum, whenever some noteworthy achievement is made in this regard.

[UmarMakhzumi]

W.salaam..

It would be great if you could get the data. Finally, we would be able to reference something.

Thanks in advance.

[EngrUzair]

Aoa.

I have received snow fall data of Skardu for the last ten years, in connection with a project. It is attached here for the benefit of all.

Regards

 

[UmarMakhzumi]

Great share Uzair. 

Thanks.

[EngrUzair]

AA. Some progress has been made in this connection and snow fall data regarding Murree area has been collected from Met Department. 

According to the received information, only 'Number of Days of Snow Fall' data is available for the years from 1973-2004. However, daily recorded snow fall thickness in inches is available for the years from 2005-2016.

According to this data, calculated maximum snow fall in one go of 4'-9" was observed in Murree during Feb 2005, whereas 2nd highest snow fall of 4'-1" was observed in Jan 2005.

Images of year wise snow fall record from 2005 to 2016 are attached below, for the benefit of all.

Regards.

[UmarMakhzumi]

This is great. Thanks so much for the update.

[EngrUzair]

AA. Snowfall data of Murree, for the period from Jan 2017 to Mar 2020 has received. It is attached below for the information of all those interested. Data for the earlier period has already been uploaded in a previous post.

Regards.

[Simple Structures]

With snow loading design, always consider the "Drifting Snow" loading cases  also - this often causes building failure.

 

 

[UmarMakhzumi]

This is a good point. Snow drift should also be calculated for all structures especially for canopies as they can be lightly framed!

Thanks.

 

Edited October 17, 2020 by UmarMakhzumi