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trussess are they trust worthy gerald.janvier 11-10-2007
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Posted by on November 10, 2007, 3:56 am
i am currently in charge of erecting truss for a workshop. the clear
span is 45 meters. the truss , itself reached our site in parts, and
we had to do some welding before hoisting them up. these ones seemed
not to be straight - and in fact they were not straight - when we put
them all up. but placing the purlins and other joineries, now they are
having a better alignment.
but my concern is will this be ok, or the truss will become crooked
and cause problems.

also as far as trusses are concerned (of any longer span, say more
than 20 meters) what about their life in general. do they fail, and if
they do so in what manner?

here in india the temp is between around 47 to 49 deg cel during the
day and when it drops low it even goes to eight or nine deg cel during
winter.


Posted by tbasc@bellsouth.net on November 10, 2007, 7:32 am
On Nov 10, 3:56 am, gerald.janv...@gmail.com wrote:
> i am currently in charge of erecting truss for a workshop. the clear
> span is 45 meters. the truss , itself reached our site in parts, and
> we had to do some welding before hoisting them up. these ones seemed
> not to be straight - and in fact they were not straight - when we put
> them all up. but placing the purlins and other joineries, now they are
> having a better alignment.
> but my concern is will this be ok, or the truss will become crooked
> and cause problems.
>
> also as far as trusses are concerned (of any longer span, say more
> than 20 meters) what about their life in general. do they fail, and if
> they do so in what manner?
>
> here in india the temp is between around 47 to 49 deg cel during the
> day and when it drops low it even goes to eight or nine deg cel during
> winter.

I would have the engineer who designed the trusses and the connections
you made do a field check.
The engineer should have answers on your other questions too.
T


Posted by Michael Bulatovich on November 10, 2007, 2:43 pm

>i am currently in charge of erecting truss for a workshop. the clear
> span is 45 meters. the truss , itself reached our site in parts, and
> we had to do some welding before hoisting them up. these ones seemed
> not to be straight - and in fact they were not straight - when we put
> them all up. but placing the purlins and other joineries, now they are
> having a better alignment.
> but my concern is will this be ok, or the truss will become crooked
> and cause problems.
>
> also as far as trusses are concerned (of any longer span, say more
> than 20 meters) what about their life in general. do they fail, and if
> they do so in what manner?

1) Anything will fail if it is overloaded.
2) Presuming perfect installation, first by exceeding deflection limits,
then by collapse.
--


MichaelB
www.michaelbulatovich.ca



Posted by Chuck News on November 11, 2007, 4:00 am

>
>>i am currently in charge of erecting truss for a workshop. the clear
>> span is 45 meters. the truss , itself reached our site in parts, and
>> we had to do some welding before hoisting them up. these ones seemed
>> not to be straight - and in fact they were not straight - when we put
>> them all up. but placing the purlins and other joineries, now they are
>> having a better alignment.
>> but my concern is will this be ok, or the truss will become crooked
>> and cause problems.
>>
>> also as far as trusses are concerned (of any longer span, say more
>> than 20 meters) what about their life in general. do they fail, and if
>> they do so in what manner?
>>
>> here in india the temp is between around 47 to 49 deg cel during the
>> day and when it drops low it even goes to eight or nine deg cel during
>> winter.
>
> What you've described sounds like *bar joists* with intermediate supports.
> Yes, they can fail.
> Life expectancy? Unknown.

This is to be considered as a 'long span' structural element 45 meters ( 148
ft ). It is called a joist girder. It also could be designed as a
Vierendeel truss where the web members are vertical and designed where
connection joints are subject to moments. If designed correctly it could
last quite a long time. Construction/installation can be critical. Many
lines of bridging will be necessary to brace the bottom chord since the
girder truss will be quite deep.
The joist girder needs to be designed for the expected loads and a proper
safety factor. The top chord and bottom chord will be large and the
diagonal web members are designed for compression, tension and shear will be
critical. Connections are critical. With the temperature difference
mentioned expansion and contraction of the members needs to be considered as
well as the end bearings. Expansion and contraction also increases member
stress. It is possible that if contraction is not considered the ends could
slip off at the bearing connection and fail at the end support. Fire
protection also is needed.
Hope this helps.

CID...


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