How does a structural engineer check engineering drawings

Join Matt Cornell as he checks the drawings for a single storey concrete masonry (bessa block) home to be built in a cyclone region. He goes through the process of checking a set of structural engineering drawings with some tips for checking and good construction.

Today we’re going to go through the process that I normally
follow when I’m checking a set of engineering plans.

So a job comes into – a set of plans come into the office and they’ve asked us to do the engineering.

One of my engineers has done up some engineering drawings.

Here you can see the engineering, the AutoCAD file here. They’ve set up a form 15 ready for me to fill in. I’m doing the checking.

So a lot of the works already been done. There’s a checking folder already as you can see, so first thing I’m going to do is is check to see what the client has actually asked for.

So we’ll open up that email and here it is. So it came in
to quotes. It says “Dear Cornell Engineers, can I get you to do the engineering for this house please. I need it as soon as possible. (typical) I have attached the floor plans, truss plans and soil tests. Let me know if you have any questions.”

So see there’s the attachments. The sample house, truss plan the soil report, house plans and the truss reactions.

Okay so excellent. Let’s just close that for a minute, and we’re going to go back and have a look.So our system inside the office is when
we receive these plans, we put them into the receive folder the latest plans are always in the receive folder. So those attachments have been saved in here so let’s have a quick look at the house plans.

Okay so it’s a sample house there’s a set of notes, some more notes, a site plan. You’ll just realise that some of the details have been removed from this set of plans for privacy and this job is a little bit old so some of the standards that have been referenced on these
drawings are probably out of date now but for the purpose of this exercise it’s a pretty clear indication of what sort of plans we get.

So here we go a floor plan. We can see the garage, it’s one, two, three, four bedrooms with an alfresco, meals area, family room so this is a nice house. You can see this hatching around outside that indicates concrete masonry walls and if we zoom in here we’ll see that the walls have actually been dimensioned as190 thick so that’s a 200 series concrete block wall and that’s pretty consistent around the outside of the house with the exception of the alfresco.

Obviously it’s a probably, there’s a down pipe there, but there’s a timber post in that corner. Let’s see what else we’ve got in this set. So this is the window layout so maybe there’s a bit more information on the windows on this plan compared to the previous plan.

The elevations – so this is when the house is finished the building designer wants us to be able to, see what the house is going to look like when it’s finished.

So the important things here for an engineer are a) how high the wall is and that’s the garage so don’t forget that number is for a set down slab so 2.44 meters or two thousand four hundred forty millimeters
to the ceiling height and this is the elevation although the line doesn’t line up with anything but that’s the ceiling in behind and that’ll become a little bit clearer when we get to the cross section.

So four elevations front, rear, left and right elevations and we
can see also that the roof sheeting is metal and there’s windows and doors and that’s all fairly standard.

Here we go with the cross-section. So this is the building designer’s indication of the trusses – won’t necessarily be true – we have some information from the truss designer. We’ll use that in preference to how the trusses are actually shown but as far as the ceiling height, here we go at two hundred and forty millimetres from the slab is there so that’s how high when you’re standing on the slab that’s how high the ceiling will be.

The internal walls he says are 70mm pine stud frames. The outside walls we know already are concrete masonry, 190 core filled concrete masonry blocks. Okay
and what else we got going on. So that’s

pretty much the last page of this set.
This is an abbreviated set for the

purpose of this example. Um so let’s see
what else we’ve got.

Here’s the soil test and remember a lot
of the stuff their personal stuff

private information has been removed from this.

So scrolling through and again this is an old soil test and some of
the ways the soil testing were done have changed a little bit in this time.

In any case so the soil test has given us a photo from the street to help us confirm that this is the right allotment. They’ve given us the site address back on this previous page which you won’t see because it’s been removed for privacy and they’ve done some soil testing and they’ve actually in this case used a Atterburg Limits which are liquid limit plastic, plasticity index and linear shrinkage to classify the site – to determine how reactive the clay’s are on this site.

Okay so those numbers are important to us but not as important as the results which is this one – they estimate that seasonal changes in in moisture content in the order of 20 to 40 millimeters a moderately reactive site so they reckon there’s at least 100 kPa so it’s nice firm soil and they’ve called it a class “M” site to AS2870-2011 so there we have class and moderately reactive site

There’s some information on the profile so when they did the testing here’s what they found as they dug down to the depth that they went to – two meters. Borehole termination at two meters and there’s the profile. So the top 200 millimetres is silty sand fill overlying sandy gravelly clay fill, silty sand – alluvial and sandy clay – alluvial so natural soils down starting at about 500 millimetres depth

Second bore hole because they need to do to both of them should be in the footprint of the house silty sand fill overlying sandy gravelly clay fill overlying sandy clay so it reviewing this information as a matter of course as structural engineers at the end of the day we’re relying on the soil test but we’d like to make sure as much as possible that the information that we’re using is correct and if we see a discrepancy we’re going to bring it to the soil testers attention.

So they’ve done some testing on this material they have done a particle size distribution, they provided an aerial photo with the location of where those bore holes and we’ll see that those bore
holes are within the footprint of the building and then there’s just some standard notes.

Okay so I’m looking at a Class M soil test and the only other thing
we haven’t looked at is truss plan and here it is .

Nice colorful one but the thing and you can see the outline of the building. They’re relying on those outside walls, those concrete masonry walls as the load-bearing walls and also as the tie-down walls for and some cases where it’s unclear where there’s
big trusses spanning across the building and they’ve used the walls of the alfresco.

They’ve also nominated these walls will be load-bearing as well and
they become a little bit more apparent when you see those X’s across the wall so they’re internal tie-down points on internal walls and here is another one but this one’s a timber wall so a load-bearing wall, some X’s showing that these trusses are sitting on to those walls here’s the third one we’re going to take that into account when we do our checking of the drawings to make sure our engineer has taken all that into account.

So this is now ready for checking. Let’s see where we’ve got those checking drawings in the checking folder. Okay we’re going into the checking folder now so the AutoCAD drawings are there, the Form 15 is ready. We’ve gone through the received and the emails. Now we’re ready to start going through our own engineering drawings.

So let’s open these up. A quick run through the drawings that Cornell Engineers provides for a single-story concrete masonry house. This is a house in a cyclonic area, a Region C area but let’s just have a quick look at the layout of the plans.

First is our project specific notes and rather than call these standard notes we call them project specific notes because each and every note is read and checked to make sure that it’s relevant to this site and we’ll come back to this.

Some notes on safe design for the building contractor and
the homeowner to take into account to ensure that the Builder and the site remains safe. That’s just part of workplace health and safety and how we contribute to that.

Okay so sheet S4, is our footing and slab plan and shows the layout of the footings and slabs how, thick the slabs are. We’ll come back to that as well.

We have one page of details. This tells the Builder and the concreter exactly how we want those footings laid out and how we want them built.

The bracing plan is the essentially the wall framing plan with some extra notes on where the bracing is. So these areas the hatched walls are going to be plywood bracing walls and then there’s some tie down or a hold hold up details but cyclone areas mainly tie down details so there’s a lot of emphasis on on tie rods and then finally some bracing details.

So as checkers we’re going to start at the top and work down.

We’ll start with the very top thing which is the roof sheeting which we don’t need to check but the next thing that’s supporting the roof sheeting is the roof battens.

So we’ll have a quick look at the note for the roof battens. 35 by 70 MGP12 roof battens at 600 centres and there’s a connection which is a batten screw to each truss. That looks good.

Next we specify the trusses. They’re obviously being designed by the trust manufacturer and we’ve already seen those those plans.

If a different truss manufacturer is used that’s fine but we want them to use an internal pressure coefficient of 0.7 and minus 0.5 and the truss manufacturers is going to do the design of the truss to truss connections. Finally the truss bracing is going to be specified by the truss manufacturer and the ceiling is going to be pine battens.

Then there’s some notes for the wall framing. We’ve shown the load-bearing walls, the walls that are helping support the roof – we want them to be 90 wide so we specified 35mm x 90mm frame which is
essentially about a 4 inch frame in the old terms.

We’ve got tie down specified – M12 tie rods beside openings, corners, 900 maximum centers. We have non load-bearing walls, these other walls that aren’t actually taking load including the bracing walls actually, can be 70mm stud and the MGP10 is a
slightly lower specification for strength.

For the timber studs because they’re non-structural. They’re not really holding up any roof. This is the bit that explains what the hatching on the walls is. That’s the bracing walls and we talked about the capacity of 6.4 kilonewtons per meter and then we say that we want the builder to connect the bracing walls to the roof frame and that is using the details on the last page. So that’s that little bit covered.

We’ve got a single sided plywood bracing wall detail for 6.4 kilonewtons per meter how thick the plywood has to be how it’s
nailed off so that’s all really good and how the builders got a few options here for how he can connect this bracing wall to the roof frame so I’ve got that covered as well so good work by the guys because we know it’s 200 series concrete masonry walls we know that the builder is going to need details on how to connect the roof trusses by the trust manufacturers to those concrete masonry walls and here’s our details. This shows how we would like the building to connect them so I’ve talked about threaded rods and talked about his picture of the plate that’s going to go over the trusses where there’s roof beams we want them to bolt the roof beams to the concrete masonry wall using this detail. Wwhere there’s trusses

to roof beams so out on that Alfresco area well we want them to use a looped strap to connect the trusses to the roof beam.

We know that there’s some internal load-bearing walls so here we have a detail for rods tie rods running down the middle of the wall of the load-bearing wall and connecting the bottom chord of the truss which is where the trust manufacturer allows us to connect to and when there’s an internal concrete masonry wall which is that wall on the alfresco – that’s the detail we want the Builder to use and finally there’s a detail here for how we want the framing tied down because it’s so important to get load from the roof down to the ground.

We show the load path not directly but it’s all there so a truss or a rafter sitting on the wall is connected to the lintel which connects out to the outside beside the opening through a tie rod for uplift down to the slab and then a couple of studs jamb studs they’re called beside the opening to hold the roof up over that area.

The last one we haven’t checked how to look at is this alfresco roof beam to a timber post so going back a page here’s that connection we’ve got a post in the middle a post on the outside edge we’ve called up that roof beam size there’s an rb2 it’s 195 by 65 Hyne beam roof beam the rest of the openings.

Around the concrete masonry the have been called up as bond beams one one six SBB one one success and there’s a BB216 for the big garage opening which is a bit wider we’ve got a detail with two sixteen top
and bottom and here’s the information

the building needs to build that where
the timber frames are but the outside

perimeter concrete masonry walls we
don’t want there to be any movement we

in fact we want there to be a good
amount of strength transfer between the

timber frames and the concrete masonry
walls so here we’ve told the Builder

fixed timber frames to concrete masonry
wall with one m12 cam set which is an

m12 epoxy bolt bolt that’s glued into
the concrete masonry at top plates at

the top of this wall and at them in
height and that’s going to stop those

walls moving around independently of
each other and that is pretty much our

standard night we use that and we expect
to see those bolts on all these internal

walls where they about the perimeter
walls you can see there’s another post

in the middle of the the entry roof and
a roof beam size so going through

checking this I would give that a quick
check to make sure I’m comfortable with

that size and finally I can see there’s
an l1 size here so I imagine here we go

there’s an internal load-bearing wall
lintel and that would be built according

to that lintel detail for the timber
which is this one little tie-down detail

on this next page and that actually
looks like a cavity slider so that’s a

bit tricky that l1 has suspended right
across over the top of cavity a little

trick for um for those who aren’t used
to checking these sorts of things so

this layer we’re pretty comfortable I’m
pretty comfortable that the guys have

got the floor plan the walls all pretty
much in the same location as as the

building’s owner because we start with
the building designers drawings when we

put these plans together we actually
copy the building designs information

into our plans and sometimes we actually
overlay these two claims just to make

sure they all work so well
I’m pretty confident are the same as the

building design or in a full design
check I’d probably do a quick check to

make sure we’ve got all the openings in
the right spot and that we’re referring

to the latest set of building designers
plans we’ve got doorway in the entry

we’ve got some the lintels over the
openings I’ve got got roof beams out in

the alfresco area and posts and the post
size has been called up there so that’s

really good
so I think British pretty happy with

this bracing plan so we’re working our
way down and the next thing we’re going

to check is that slab plan so let’s get
and zoom out of here and head over to

the slab plan so now this is a class-m
site and the engineer has done a great

job of identifying this is an M site and
the requirements according to a is 20

things that are really important to us

to make this house for the homeowner and
for the Builder to observe to give this

house the best chance to resist
foundation movement ground movement and

that’s a whole thing that we’ve got a
lot of information of on that on our

website so the main specification of the
reinforcement in the concrete 200 series

concrete masonry walls is here and we
talked about bars where the vertical

bars are which are these dots on the
plan so each one of these dots

roundabout is exactly where we would
expect the vertical reinforcement to be

placed in those walls on site we want
extra bars beside big openings this is

how we we specify the heavier bars the
end 16 bars and I’d expect this probably

some yeah here we go over beside the
garage door which is a bigger opening

it’s got a bit more load on it and don’t
forget in cyclonic areas we’ve got a

design for the loads from the garage
doors bearing on these these door

openings so there’s a little bit of
extra rinsed reinforcements and strength

in around the garage door to to
strengthen the frame around the roller

doors or the panel lift doors in this
case probably these diagonal bars are

crack control bars we call up as per a

l 12 which is the low ductility
reinforcement placed at the reentrant

cornice and we’ve got that required of
that requirement rather wherever we’ve

shown these three bars on the diagonal
so one two three four five places the

slab thickness is shown in the hexagon
and the same reinforcement is shown

directly underneath SL 82 is eight mil
bars of 200 mil centers both ways and it

comes in the sheet of fabric and you can
buy that from Bunnings or from your

reinforcement supplier and that’s the
specification the way that the builders

used to reading it so the 30 mil cover
is how high in the slab that mesh needs

to be it needs to be 30 from the top of
the slab and from the size incidentally

and in the alfresco area which gets wet
and dry and and and ranked and leaned on

and gets hosed off we need a little bit
more protection to the reinforcement

same size reinforcement but we need 40
mil cover so 40 mil of concrete on top

over the reinforcement before you hit
the slab on top of the slab so strip

footing depth we said has been
calculated in accordance with the

engineering principles rather than the
straight team to comply principles and

we can use that as structural engineers
we’re allowed to use section 4 of a s

structural engineer who knows what

they’re doing in relation to these jobs
a quick check if we weren’t recording

I’d be checking the spacing of our
internal footings our SF ones and so I

have a quick look here we know that
there’s a 4 meter spacing requirement to

be 4 metres from the outside of a slab
and we know that at changes in direction

that we want strength internal beams
running both ways so here’s one here we

know we want this edge beam to continue
as an SF one and the designers done a

great job of that and in this location
with this direction we want this EB one

to continue as an SF one so again he’s
done a great job there

in all those locations and all these
locations all these internal corners

you’ll see an SF one coming off in one
direction and in the other direction

that gives strength to that corner and
that’s a requirement of a is 2870 a lot

of engineers have trouble with that with
that requirement but it’s really very

simple where there’s an internal corner
like that we want bars to continue to

provide the strength the continuity in
fact of the SF one through to the EB one

and that gives the house again the best
chance of performing well when there’s

ground movement this is the set down on
area this is the garage area remember

and it’s set down a little bit lower
than the house so that the homeowner can

wash out that area if they want to so
this is the symbol that we use to show

that this area is slightly higher
slightly higher than the garage area of

the garage is slightly lower than the
main floor slab we’ve got another same

sort of symbol out here in the in the
entry slope but the house slave again is

higher than the entry step so now a
quick scan through all those details on

a normal checking if wasn’t recording
I’d be checking these EB ones the

dimensions that we’ve provided the
dimensions that we’ve provided for the

SF one 300 by 300 in this case it makes
sure they’re aligned on the main part of

the plan the sat down dimensions there’s
two types SF 2 and SF 3 where the patio

is so we’ve called that EB 2 where they
saw cut joints where there’s shower

rebates and I don’t think I mentioned
that but they’re shown in these

locations so in the middle of the slab
according to the floor plan there’s a

shower in this area and we’ve actually
made the slab a little bit lower there

and that’s the detail finally where we
want BB 1 to continue as as SF 1 we’ve

given a detail for that as well so the
engineer’s done a really good job on

this one finally we just kind of make
sure that these project specific notes

are specific to the project so in this
case some of the information has been

removed for the recording but
we’ve given the Loddon plan number the

site has some fall it’s not it and we’ve
asked the Builder to refer any problems

to us there’s not overly inflows it’s
not trees near the house that the site

conditions are as per the saw test and
that there aren’t any sewer mains

adjacent to the building and notes for
the concrete masonry are here we

reference a is 3700 which was the
Australian standard and the year

applicable at the time this job was done
we talked about the mortar

classification the strength of the core
fill and that we want the corners all

bonded we talked about how we want the
soil placed and compacted under the

Neath the house including the sand and
the fill this directly underneath the

slab which as we saw in the details is a
little bit higher than the natural

ground we talked about our requirements
for in the concrete section our

requirements for the concrete so it’s n

we’ve gone actually upper grade n 25

concrete we talked about how we want the
reinforcement or how the reinforcement

has been shown diagrammatically we
talked about the grades of steel and the

Australian standards that they had to be
supplied to and we talked about most

importantly or one of the important
things how to cure the concrete to give

the concrete the best chance to perform
to harden beef rather than cracking over

here we have our notes for structure of
timber and we’ve referenced reference is

construction we talked about rejecting

the wrong kind of timber abnormally
green or split timber we’re using MGP

twelve of junk joint and group jd4 or
better so now that timber supplier knows

what kind of timber to supply I’ve
talked about bolts and screws that

they’re all detailed in accordance with
a is 1720 talked about plywood that

needs to be stamped as structural grade
plywood these couple of the notes bolts

in contact with CCA which probably don’t
doesn’t apply to this house and if

there’s no other details given if we

given a detail on connection details or
or tie down or how walls connected to

each other then the Builder is to refer
to a s 16 a 4.3 2010 but the Australian

standard for residential timber frame
construction relevant at the time of

this record the timeless job was done
and then finally we’re checking to make

sure that the wind speed is right so I
know from local knowledge on this job

that it was Regency it was in a cyclone
area there’s trained cat category –

there’s no buildings around this is pup
beg your pardon partially shielded one

or two buildings but generally fairly
flat land topographic factor talks about

is in relation to how flat or or how
much slope there is on land

there’s no factor there’s no no no
increase in wind due to topographic so

it’s T zero and we’ve classified the
site as C 2 so the the Builder now knows

what the wind speed is for this building
and you can check that to make sure the

trusses are supplied correctly that the
glazing the the windows are supplied for

the correct wind classification and here
we talk about that internal pressure

coefficient that we had on the other
page as well

the floors are designed on the balcony
for 2 kPa which is about 200 kilograms

per square meter the internal floor
inside the house is designed for 1.5 kPa

and the roof is designed for about 25
kilograms per square meter and the truss

manufacturer is going to take that into
account and make sure that he’s going to

make sure he provides trusses that are
strong enough to take 25 kilograms per

square meter which is really just a
maintenance load of builders working on

the roof we don’t expect anyone to be
living up there so there you have it

we’ve started at the back of this set
and we’ve worked away from from the top

down we’ve worked through the roof
through the walls through to the slab

and then we’ve checked our project
specific notes to make sure all that

and is relevant and correctly specifies

how this how the Builder needs to build
this house so we are just about done the

only thing that’s left now is for the
rpq engineer to fill in to fill in the

form 15 which the compliance certificate
to say that the engineering complies we

and with what australian standards so
let’s get clean this up a bit so don’t

forget this is an old form 15 this is an
old job in general and this form is

actually being changed slightly but the
information is pretty much the same we

talk about what street address so the
street address for the actual house

london plan which is the surveyors plan
numbers and what local government this

building is being built in these are the
things that we are responsible and that

we’re saying do comply the footings the
slab the concrete masonry walls 10 posts

warframe we’ve spoken about all these
things the wall bracing the lintels over

the windows the roof beams add in the
patio the alfresco in the entry and how

the roof trusses are being tied down to
these to the walls for our single-story

residents as shown on their drawings so
that all looks great

the Australian standards that we’ve
referenced in this design are these ones

and these are all correct and current at
the time of the job that the job was

done we use they’ll concrete masonry
associations single leaf masonry design

manual we’ve confirmed here the wind
speed in case this piece of paper gets

separated from the drawings the Builder
can use this to confirm what the wind

speed is for this building pressure
coefficients talked about the roller

doors quickly but this is a whole
different video that the door frames are

compliant with a is four five oh five we
talk about our drawings so this is what

we’re actually certifying or this is the
documents that we that we’ve used to

consider this design our drawings floor
plans by the building designer the site

tests site report the truss plan and
reaction report

we leave this one blank and then I fill
in my details I work at Cornell

engineers our DTaP contact details will
appear here I’ll sign in this pot spot

and I’ll put the date in the day that I
sign this form and then that gets PDF

and sent to the Builder along with these
plans and now that we’re happy with them

I’ll tell you what we’re going to go
over here create a new folder

this is how we do it internally at

Cornell engineers put the date in in
Reverse date location so one 2016 zero

five one four 14th of May 2016
so we’re just kind of move those plans

in there didn’t do that very well did I

okay so now those pains are in issued
and once I’ve signed that form 15 this

job is ready to go to the Builder and go
get built he’s already got this

information because he’s already given
us this information but we keep it on

file just in case anyone needs it so
look thank you very much for joining me

I’m at Cornell we’ve just been through
the design checking process on a sample

house plant we’ve started with an email
from the Builder we’ve had a look at the

plans that we were received and the
other information that we’ve received

we’ve put gone through the drawings that
our engineer has prepared and we’ve been

really happy with them it’s been a good

the plans are being put into issued and
the rpq engineer this is a Queensland

job signs our form 15 turns it into a
PDF and sends it off to the Builder who

then sends it to the certifier for
building approval thank you very much

for joining us I hope you got something
out of this if you have any questions

leave them in the comments below and we’ll see if we can help you thank you very much