hey guys welcome back to the channel today is a quick video on the things you need to know
about bracing domestic dwellings i'm going to be going over the principles of bracing design
ceiling diaphragm and show you a couple of bracing options that you can use in specific situations
let's get started with this diagram. Wind produce horizontal loads on buildings
that must be transmitted through the structure to the foundation
in a conventionally constructed house these loads are transmitted to the ground by a complex
interaction between the walls ceiling and roof structure and floor structure
so what we've got here is wind force on the roof are transferred to the ceiling diaphragm
and then carry it down to the floor via bracing walls. The same applies to the wind
force on the top half of this wall which are carried to the ceiling and down to the floor
through the bracing walls the wind force on the bottom half of this wall represented by the yellow
arrows are transmitted to the floor diaphragm and down to the footings through bracing walls
the same principle applies to the wind force acting on the ground floor wall so you can
see here that the wind force on the top half of this wall are transferred to the floor diaphragm
then it engages the bracing wall and the load is carried down to the footing and finally the force
acting on the bottom half of this wall are carried direct to the ground via the wall and footing
to illustrate this explanation better and reinforce how important the diaphragm system
is have a look at the image on the right hand side here we're able to visualize how the ceiling will
distribute the wind loads carried from the wall to the bracings now let's have a look at the image on
the left imagine that the ceiling has been removed without the diaphragm system the wind force will
not be distributed out to the bracings and the walls will become unstable and try to bow out
think of a cardboard box as soon as you start cutting off the sides the box becomes less
rigid and more unstable you will come across a situation like that in two-story buildings
where a full height void region exists between the first floor and ground floor these void regions
commonly fall within stairwells and entrancy lobbies in this case a wind beam can be used
to resist the horizontal wind loads and prevent the wall from bowing out
let's have a look at a couple of issues that you might encounter when you're designing a house as
i explained before in the first slide of the presentation half of the wind load acting on
the wall is transferred to the floor and the other half goes through the ceiling to the bracing wall
when it gets to the bracing panel it creates a racking force and it's carried down to the
foundation you can also imagine this bracing panel as a cross bracing for wind forces coming from
this direction this rod here will be in tension and this other one will buckle away in compression
now what happens if we cut off this panel to install a garage door for example the
load path will remain the same until it gets to the lateral panel which now has only these two narrow
sections of wall to resist the racking forces so how can we deal with this type of problem
we've got a couple of solutions the first one if you can leave between 600 or 900 millimeters
of wall you might get away with plywood bracing at both ends these would be the cheapest options that
you can provide to your client if the portion of wall left is between 250 and 600 millimeters
you might get away with k frame or power truss to carry the loads down to the foundation
k frame is a steel truss frame that can be made of shs welded together while power truss is a
proprietary lightweight metal truss frame on the other hand if the width of the wall left
is less than 250 millimeters you might have to consider designing a portal frame system
the portal frame can be either in timber or steel
the idea behind this option is to create a frame rigid enough to provide high lateral capacity
the portal frame can be made of hollow sections like shs or rhs or open sections such as ubs ucs
or pfcs another important point i would like to touch upon is the spacing of bracing walls as1684
presents a table with the maximum distance between bracing walls according to wind classification
ceiling depth and roof pitch the shallower the ceiling diaphragm the closer the bracing the
bracing walls need to be an easy way to understand this concept is imagining the house as a wind beam
the deeper the beam the higher its capacity to distribute the forces out without deflecting too
much if you have a look at this deep diaphragm the force can still reach the bracing panel
while in the shallow diaphragm the forces cross the whole ceiling without engaging the bracings
as a final comment for the ceiling diaphragm to work properly the ceiling sheeting must have
direct fixing to the roof or ceiling framing okay so for instance suspended ceilings will
not work as a diaphragm and if you wish to use suspended ceilings you will have to look for
an alternative solution to brace the structure maybe speed brace or another type of bracings
so that was it for today hope you learned something new if you have any questions
or suggestions just drop a comment below and thanks for watching and i'll see you next time