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roof Truss bearing on Brick masonry with anchor bolt

roof Truss bearing on Brick masonry with anchor bolt

roof Truss bearing on Brick masonry with anchor bolt

(OP)
Hi,

I've been wondering about roof truss for a long time.
I can do the truss design, it's not a big deal but what bugs me is the support!

I was thinking of supporting the truss on brick wall on either side, but as the wind load is taken into account i am doubtful if the brick mortar joints can take enough tension..
Even if it can, i was wondering how much weight of brick masonry contributes to the anchorage (is it a function of type of bond between brick units?) & how deep should the anchor bolt be placed?
any idea regarding support?

Guys i need some reference to masonry design & design of anchor bolts. any help will be highly appreciated.
Thank you :)
 

RE: roof Truss bearing on Brick masonry with anchor bolt

You give very few details.....

Most trusses rest on a sill plate attached to the wall.

Very few "brick" walls can carry much load - they are usually veneered to a wood or masonry block structural wall. The sill plate attaches to one of these.

Get some help...

RE: roof Truss bearing on Brick masonry with anchor bolt

Among other things here...

You do need to get engineering help - brick mortar joints should not have to take tension - reinforcing steel does that..

 

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: roof Truss bearing on Brick masonry with anchor bolt

A single course of brick wall (without column posts) is not so good in compression, or for that matter, resisting lateral loads esp. applied at the top either.

From "BigInch's Extremely simple theory of everything."

RE: roof Truss bearing on Brick masonry with anchor bolt

(OP)
Okay,
Problem is we are from different part of world and look at masonry in different forms. I haven't yet come across veneered masonry.
Most of buildings in south east asia have load bearing wall (1 brick thick masonry on mortar)

But in this case the wall is half brick thick, 1 brick thick pier shall be provided(as biginch expected) at supports to carry compression,(which i don't think will fail in compression).

As MiketheEngineer stated, the truss end will rest on bearing plate to distribute load on masonry pier.

I'm worried about uplift; which imparts tension on joints. sadly,i can't use re-bars (as expected by msquared48) so mortar has to take tension(thought limited).

i need some design example for anchor bolt.how deep should i drill it into masonry (bond strength between cement & bolt, cement & masonry)? should i use expansive cement to ensure adequate grip between bolt,cement and masonry?

 

RE: roof Truss bearing on Brick masonry with anchor bolt

As Mike said, mortar doesn't take tension, reinforcement does.  That is why masonry walls crack so much do to foundation movement or other movement that imparts tension to portions of the masonry.  Any net uplift will crack the mortar joints and could cause the wall to fail.

RE: roof Truss bearing on Brick masonry with anchor bolt

I would question drilling vertically into the "thin" brick wall you seem to describe to distribute the tension.

I would recommend strongly considering a LONG strap on the inside of the wall with thru-bolts to the outside of the wall to take out the uplift.  

Seems like you are literally trying to bear the truss end on a thin ribbon of brick.  That would make me nervous, real nervous.

Can you post a section at the bearing location?

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: roof Truss bearing on Brick masonry with anchor bolt

PujanG,
The system as you described it may be common where you are, but it has no technical basis.  The closest thing to it that is used in some countries would be a single skin brick wall spanning horizontally between piers.  The brick can resist a degree of bending in the horizontal direction, provided it is not stack bonded.  The piers then have to be reinforced to resist uplift tension and bending due to the lateral loading.  Direct tension loading perpendicular to bed joints is not allowed by any Code that I know of.

Half brick elements should not be considered as structural.

Reinforcing bars are available in all Southeast Asian countries.  The will to build adequately is often what is lacking.  Some of the construction I have seen there is truly scary.   

RE: roof Truss bearing on Brick masonry with anchor bolt

You are looking to "engineer the details" without securing the engineering of the global structure.  That makes no sense. Perhaps you are at the wrong website.

From "BigInch's Extremely simple theory of everything."

RE: roof Truss bearing on Brick masonry with anchor bolt

(OP)
Tadeng: thank you for your opinion.

Mike: I can't really define "thin", i thought 1 brick thick wall should be thick enough for the purpose.
I really like the idea of through-bolts & straps.
Again, as per my understanding load propagation will be [truss end uplift>tension on straps> shearing of through bolts,
Through-bolt held against uplift by weight of masonry above it]
I think masonry at the level of through bolt suffers  tension if the height of masonry above isn't adequate.
So how do i assess the adequate height?
Bond of masonry units(English/Flemish. & so on) contribute to arch action. Is there any such provision regarding tributary area of masonry that contributes as dead load over thru-bolt?

Hokie66: I've not heard of anyone designing Masonry on direct tension. Well, I'm not trying to design it in tension either, but i'm kinda lost.
An anchor bolt drilled in Masonry pier is likely to suffer tension. My question is "how deep should i drill the anchor bolt to ensure that the uplift is balanced by the weight of masonry?"
I think, if i drill it too shallow, either it fails in bond or the weight of masonry won't be good enough to balance uplift.
If the weight won't be enough to balance uplift, mortar will suffer serious tension. Isn't it?
So, i'm not trying to make mortar take tension, rather trying to ensure it doesn't take tension.

BigInch: Sir, i respect your emotions.:)
 

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