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RE: Diaphragm

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Gary:
I looked to Bemo Manual and they also say 5 feet spacing. So I will try
to reduce spacing of joists and keep it within limits as you mentioned.
But how can I defend it to the client since it has large cost
implications?. How about providing purlins at a spacing of 5' and
keeping joists at a spacing of 10'. Does it help to keep joist spacing
at 10'?.
The minimum design load is 25 psf. 
Thanks for your help and regards
Ashraf

-----Original Message-----
From: Gary L. Hodgson and Assoc. [mailto:ghodgson(--nospam--at)bellnet.ca] 
Sent: Tuesday, May 30, 2006 3:05 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Diaphragm

Ashraf,
I had the same feelings as Daryl when I saw a spacing of 10 ft between 
joists. Of course, we are used to snow loads,
(here in Niagara Falls 39 psf on a flat roof), but I would think you 
should be designing for a minimum of 20 psf (that
is code here in Ontario).  This probably covers construction loads, 
etc.  My Butler Manual recommends a spacing of
5 ft for their MR24 standing seam roof, but they don't say why or what 
are the ramifications of larger spacings.  I have
walked on a ss roof with 5'-6" spacing and it was like walking on mush.

The contractor told me to stay over the purlins.
       In your case, the flat bar bracing depends on local conditions 
and abilities of the work forces.  Bridging is not bracing;
rather it is individual bracing of the joists to stabilize them during 
construction, as individual joists have a tendency to roll over easily.

The Can. Institute of Steel Const emphasizes that bridging is not
bracing.
Gary


Ashraf, Mohammed (Qatar) wrote:
> Gary:
> I've joists spaced at 10 foot and span of joists is about 74 foot.
> Joists are supported on steel girders and girders are supported on
> concrete columns spaced at 30 foot spacing. Hence I think flat bar
> spacing will be a better choice. What do you say?. Is this called as
> bridging?. 
> Thanks and regards
> Ashraf
>
>
> -----Original Message-----
> From: Gary L. Hodgson and Assoc. [mailto:ghodgson(--nospam--at)bellnet.ca] 
> Sent: Monday, May 29, 2006 3:05 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Diaphragm
>
> Ashraf,
> You can install X-bracing angles under the steel joists from col to 
> column; or you can install flat bar bracing on top of
> the joists, under the deck.  This pretty well has to be field welded
and
>
> needs to be pulled tight--details to work out
> with the erector. The angle braces are usually bolted with connection 
> plates at the columns.  Count on some of the
> angles not being correct and they will need to be field-welded--this 
> depends on the quality of the fabricator and his
> detailer.
> Gary
>
> Ashraf, Mohammed (Qatar) wrote:
>   
>> Gary,
>> Thanks. You are right and I am not comfortable with the diaphragm
>>     
> action
>   
>> of metal roofs. I am planning to use open web joists to support the
>> standing seam metal roof as shown in the client documents. But if I
>>     
> want
>   
>> to put X-bracings in the roof, how can I provide it?.
>> Regards
>> Ashraf
>> -----Original Message-----
>> From: Gary L. Hodgson and Assoc. [mailto:ghodgson(--nospam--at)bellnet.ca] 
>> Sent: Monday, May 29, 2006 2:39 PM
>> To: seaint(--nospam--at)seaint.org
>> Subject: Re: Diaphragm
>>
>> Ashraf,
>> For a building that size, I would put in X-bracing in the roof.  The 
>> CISC has stated that for large buildings,
>> diaphragm action is not reliable.  However some eminent engineer 
>> (Galambos?) has disagreed with that.
>> Gary
>>
>> Ashraf, Mohammed (Qatar) wrote:
>>   
>>     
>>> Thanks GM. I am using IBC 2003 code.
>>> A brief description of building is given below for your info.
>>> The building is of 107x60 m in plan size and maximum 17m height with
>>> roofs at different levels.
>>> The columns are of concrete and most of the beams are of steel. Roof
>>>     
>>>       
>> is
>>   
>>     
>>> of steel deck type. I have about 7 braced frame in the x-direction
>>>     
>>>       
>> (107m
>>   
>>     
>>> is in x-direction). The span of frames vary from 10 to 22m. In the
>>> y-direction there are 7 columns @ a spacing of 10m. Only 3 bays are
>>> braced. The height of braced bay is 8m and span is 10m.
>>> The maximum size of diaphragm comes around 60x22m. 
>>> What can I do to make this system more rigid?. Since I am using Open
>>>     
>>>       
>> Web
>>   
>>     
>>> Joists to support metal deck, does bridging help me to make the
>>>       
> system
>   
>>> more rigid?.
>>> Thanks and regards
>>> Ashraf
>>>
>>> -----Original Message-----
>>> From: Gerard Madden, SE [mailto:gmadden(--nospam--at)maddengine.com] 
>>> Sent: Saturday, May 27, 2006 9:43 AM
>>> To: seaint(--nospam--at)seaint.org
>>> Subject: RE: Diaphragm
>>>
>>> Most likely not. I'm assuming the walls are concrete or steel braced
>>> frame.
>>> Unless the metal deck has concrete fill, it will be considered
>>>     
>>>       
>> flexible
>>   
>>     
>>> diaphragm. See the UBC/IBC for the definition of Rigid Diaphragms
and
>>> Flexible
>>> Diaphragms. The deflection of the diaphragm would need to be less
2.5
>>> times
>>> the deflection of the vertical resisting elements of the lateral
>>>     
>>>       
>> system
>>   
>>     
>>> to consider it rigid and at best your would have a partially rigid
>>> diaphragm
>>> but with those plan dimensions, you would need several interior
lines
>>>     
>>>       
>> of
>>   
>>     
>>> lateral resistance and you must also be careful to make sure that
>>>       
> your
>   
>>> diaphragm
>>> span ratios are not too great to violate whatever code your
structure
>>> falls
>>> under.
>>>
>>> -gm
>>>  
>>>   
>>>     
>>>       
>>>> -- Original Message --
>>>> Subject: Diaphragm
>>>> Date: Sat, 27 May 2006 09:14:22 +0300
>>>> From: "Ashraf, Mohammed (Qatar)"
<mohammed.ashraf(--nospam--at)worleyparsons.com>
>>>> To: <seaint-ad(--nospam--at)seaint.org>
>>>> Cc: <seaint(--nospam--at)seaint.org>
>>>> Reply-To: <seaint(--nospam--at)seaint.org>
>>>>
>>>>
>>>>
>>>> "This email is to be read subject to the disclaimer at the end of
>>>>       
>>>>         
>> this
>>   
>>     
>>>>     
>>>>       
>>>>         
>>> message
>>>   
>>>     
>>>       
>>>> or attached to this message."
>>>>
>>>> Hello all,
>>>>
>>>> I have building of 107mx60m in plan size and maximum height of 17m.
>>>>
>>>> The roof is of seamless metal deck from Bemo USA or other
>>>>       
>>>>         
>> manufacture.
>>   
>>     
>>>> The metal deck is supported by open web joists. The maximum span of
>>>> joists is 22m.
>>>>
>>>> Can I take this deck as rigid diaphtragm?.
>>>>
>>>> Thanks in advance,
>>>>
>>>> Ashraf
>>>>
>>>>
>>>>
>>>>
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