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RE: Diaphragm

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Gary:
Thanks for your solution.
Regards
Ashraf
-----Original Message-----
From: Gary L. Hodgson and Assoc. [mailto:ghodgson(--nospam--at)bellnet.ca] 
Sent: Wednesday, May 31, 2006 2:32 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Diaphragm

Ashraf,
It is all a matter of economics: joists versus purlins.  If your joists 
are spanning 74 ft, then they are long span steel joists and it is 
probably cheaper to use light beams or cold-rolled members for your
purlins.
Gary

Ashraf, Mohammed (Qatar) wrote:
> 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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