. Ah we will be explaining little more on structural
designing of a glass and glass facade. Previously we have cover mostly on application side various
forms of application here we will be taking through little basic structural designing
of a glass facade. The key design basis of the glass facade is
primarily defined by 2 things primarily strength and sometime governed by deflection criteria.
And moreover to strength and design there are instances cover by building moments
like such as could be earthquake or thermal movement or any type of building moment
. And the basic design principle is design for
any it is like any others structural design like steel design or or concrete design.
The design philosophy is similar is only the material character is changing. So, it should
be design for safety and design for serviceability and design approaches when we do the
design there design factors are wind load factor a load factor live load factor there
are different factors is considered with suitable combinations. And in some instances the
design need to be check for non-linear Non-linear is critical if you are doing a
slender elements small size of the glass fence it is used for last phases the slenderness
ratio is too small then slenderness factor is critical.
The framing design. So, the first thing we start with the facade design or glass design
is The primary member which is supporting the glass in places of framing. The framing
is define primarily like any structural elements like aluminium or steel. And how the framing
is done how it is getting fabricated what is availability which define the design. And
a design of glass facade designs primarily like you are assuming the wind load or
calculating the wind load and your checking the thickness of the glass material or or
supporting frames. And your checking for a stress analysis and there are instances you
will be checking for a specific applications like a skylight application or hand railing
glass railing application where the it has to be considered for human impact load.
So, it depends on the application. And in terms of glazing and fixtures is supported
sometime by framing in a way sometime it supported by just a point fixing. So, we
should be mindful of how it is supported. Ah the the 4 factors we primarily checking
for a facade design a strength a make sure it is safe and it has adequate a safety factor
deflection and to make sure it is deflecting. And it is working in still serviceability
and safe to accept the deflection seismic earthquake or some more natural climatic
conditions and building moments. So, this is more critical for a large building tall
building a slender building using curtain wall glazing where the glazing is spreading
across the building where this building moment is more critical.
Ah we are going to explain more on strength aspects of the facade or glazing design
the This is primarily applicable for supporting framing elements of facade structures
like a framing element is in most of the case it is either steel frames or aluminium
frames . So, there we have the designer need to check for tension compression torsional
or in in many cases combination of all these 3 aspects. Tension is yes you have pulling
force of this member. A compression is it is like a column design the stress are getting
compressed. So, this in this case you have slenderness factor is more critical. And
torsional, torsional is in many cases is critical if the building individual floor height is
like a 4 meter a 3.5 meter. And it has large span of unsupported length
where torsional is very critical. And shear primarily checking for fixing connection
it is an and brackets and In many cases the curtain wall or glazing member subjected
to combined action of tension compression torsional or it could be compression and torsionals.
So, the designer should able to understand clearly that at action and where is this
check is critical. Bending check primarily bending check
is applicable to the framing elements which is supporting the glass panels It could
be vertical framing elements or horizontal framing elements The bending theory same
any beam bending theory is applicable It depends whether this member is simply supported
or it is continuous. If the glazing system is going only from
floor to floor it is not vertically continuous then the members can be designed as a simply
supporter bending element. So, most of the cases in that case if the beam is vertically
supporter, it is simple bending theory like w a square by h is applicable, which is
bending check. Bending check is you are checking the compression and tension to
make sure the member is structurally is safe for both criteria. Because the the check for
positive and negative in load the member need to be checked on both directions.
This is check, check is critical for compressive and tensile check This is critical for
a large element or maybe sometime the the framing is used for continuously for quiet
number of floors continuous there a compression is critical. Compression is critical as
a structural engineering knows when certain elements is is weak in slenderness ratio.
So, as a engineers they have to check the slenderness ratio if that falls under like
a semi compact or slender then this more detail check is required.
Ah shear check generally check for connections brackets where the components loads large
loads or transfer in a small component, where this kind of shear stress is critical
This is critically if that especially using aluminium brackets. Aluminium brackets
as slightly lower bearing stress and bending stress compare to the steel
So, the checking this checking is critical for facade and glazing applications.
Ah this is local buckling check is critical in in glazing system the most commonly
the elements used extrusions or aluminium framings. It has thin wall thickness
like one mm 0.8 or 1.5 mm thickness. In these cases, this buckling check is
critical. Because it is quite common to use a slender elements on on facade systems
In that case it could fail in local buckling or it could fail in overall buckling and
it could fail in combination of local and overall buckling. So, there are detail checks
and with various standards available to do the buckling check the buckling check is critical
on most of the facade systems. Overall buckling check is is something
similar to the steel design, if we are comparing to the I beam or open section c channel
It is not a closed section like a hollow section in this case is similar to the steel bending
theory We may have to we have to apply this to the aluminium design.
Ah there are checks available based on slenderness ratio with the slenderness ratio is very
small then it is critical to check the buckling check similar to the steel I beam
design. The buckling check is as different formula to check if it is compact section
semi compact slender elements it depending upon the aspect of this member the
various formulas is given in in analysis course. We have been so far checking for strength.
Here we are checking for a deflection . A deflection check is critical to make sure
the member is deflecting as what a engineer is assuming.
Ah and this is going to be deflecting for wind loads or sometime it could be for a live
load to the members glass and glass elements need to be check for these different criteria
is primarily driven by the wind loads could be a negative wind load or positive wind load.
Here we are checking for a deflection deflection of deflection check is needed for glass
and glass supporting framing elements. A diffraction generally follow the beam deflection theory
for a framing elements and for glass checking it it follows a plate analysis theory for
glass checking. The beam deflection theory it could be either
continuous beam or simply supported beam if it is more complex it require a computer
analysis. So, that the behaviour of the beam is able to predict correctly Like
any other structural element you there is allowable deflection criteria is specified.
Allowable deflection criteria is specified mainly for serviceability conditions aesthetic
conditions as defined in the design of this elements. And actual deflection is
predicted then the engineer need to check actual deflection is within the allowable
limit then this framing elements are are members is considered as structurally adequate.
Ah we will be talking little more on other impact of this facade or glazing system
This one other aspect is natural conditions or seismic or it could be different things
like a building movement on many different aspects In particular, to seismic how
it. In fact, the facade system we can study little more detail the seismic has many
different impact on the facade as we all know the seismics induce lot of building
movements Sometime the building is accelerated too fast and the materials which is attached
to building may not able to sustain or take this additional loads .
And it could be imposing the seismic could be imposing on a very tall buildings like
inter storage drift or sway beyond the limits. And seismic could also impose lot
of different shaped building movement. It is like one floor is not moving the upper
floor or top floor is moving too too much movement. And the seismics put lot of dynamic
load to the building envelops framing or glass element. And it also give so much
of additional loads to the serviceability of this framing system bracket system
the glass cladding panel which is supporting.
Ah continuing with the loads relevant to the building or could be seismic on earthquake.
The predominant force which is imposed on to the glass panel facade system is
in plane forces, but you can see here when the building is drifting or or swaying
it is going to put the horizontal loads on this glazing element. And this system need
to be verified for in plane load as structural engineer should be aware the facade system
or it is material is is very strong element in supporting the out of plane loads like
a wind load which is acting on a plane. Ah it may be weaker on it is own plane on this
minor axis loading. So, the buildings sway may impose minor axis which need to be checked
during the design. Here we are explaining other impact or the
framing how the framing will perform if the building is swaying or drifting. It
could be due to earthquake or due to the just a wind load or or sometime even a gravity
load. So, the building high rise building we all know it will sway on it due to that
height of the building or slenderness factors of the building , but this building sway how
it will impact on the glass facade if the framing it could also give a various modes
of acceleration. It could the frame could have this kind of a impact or it may
be linearly leaning towards this. So, when the frame moves it will put lot of
stress on the glass panel or or any other cladding material which is holding this
as a structural engineer they have to check this.
Here we could even little more detail video showing how this building sway you
will impact the framing elements in particular, as you can see the building swaying when
the framing changes to red. It is highly stressed as you can see this frame is imposing lot
of loads on onto this members when it is swaying you can see here. Which is this video is showing
primarily this this linear sway condition. This condition the frame will have more impact
relying on that weaker axis bending. Continuing with building movement the facade
system you can see a typical section detail of the facade system the glass here. And it
has a framing arrangement and there is a bracket which is holding this panels. So,
this is a primarily if you take a curtain wall glazing system for a commercial building
generally this system is adapted. You can see is a glass building the glass is used
at this level when you see from the floor level is different. At the face of the
beam it has a darker band here which is using a different glass combination.
But the system is it is a prefabricated is called unitized curtain wall system or prefabricated
panellized the system . Each glazing panel you can see prefabricated and it is it is
fixed to the building with the bracket here. And this is a fixed with interlocking arrangement
of aluminium extrusions. This is no limit on the extrusions shape design in it is
quite common to you customize these faced based on individual project needed . And and
this video will explain you how it is moving horizontally. In our previous slide we have
seen the building moving sway, when the building is moving on a sway this is will
impact on the horizontal movement of this joints.
And continuing with this the moment when the building is moving be the engineer need
to carefully check the joints Unlike other building materials like concrete
wall there is no primary joints on on on the surface except where it is interfacing
but curtain wall or glazing or cladding has lots of joints along the face of the building.
Hence the joint design is one of the critical here the joints are needed mainly for building
movement or thermal movement for various natural conditions there should be a good
joint design. So, that the joints are not cracking or failing during the service of
the building and there should be 2 way of doing a join design horizontal joints and
vertical joints. Vertical joints is mainly on the floor horizontal
joints on the panel joints This calculation is showing how do we design a thermal moment.
Thermal moment for any glazing system is primarily effect of change in temperature
which is delta t and what is the width of the panels. So, how wide is the panel, if
the panel is much wider and it has to move lot of a horizontally and the thermal expansion.
So, this simple formula here we will show you the horizontal movement required for this
curtain wall glazing system is around proximately 10 mm.
Ah similar to horizontal design it should also be checked for vertical design. Vertical
design is is critical if the curtain wall is going continuously to the tall building
and it is passing several floors above. And it should be checked for 2 things vertical
horizontal movement and as well as inter story drift.
Inter story drift is mainly from a floor to floor drift is happening on the side ways
due to the building sway. A lot of standards is allowing this like a h over 500. So, floor
hight divided by 500 which the engineer need to be understanding this requirement. So,
that he can design the joint such that it will not crack or a fail during the building
moment . And the joint design needed primarily for this factor it could be due to the thermal
inter story building design and installation tolerances because it is most of the facade
system it is not a casting in situ a various components coming and and is getting fixed
the site. So, the engineer should be aware of a tolerances.
Floor deflection the floor will be deflecting due to the live load or in some cases if the
slender building then the torsion maybe a critical factors for a joint design.
It is still we are continuing with the joint designing facade system has no definite rule
for using the particular standard profile unlike a steel design . In steel design we
have a standard profile like a I beam c channel section channel section angular section
or hollow section, but curtain wall the engineer should be familiar with what is
availability and what is possible what is a limitation here .
And you can see in this the profiles which is supporting the facade or system has
no definite shape of the profile it could be a many different shape here. And the primary
concept here is the there is aluminium framing which is supporting the glass and the glasses
supported with structural sealant or it may be some time has a mechanical fixing. And
the shape of this aluminium profile could be very different from project to project
and each panel shape is defined by many different factors it could be a opened section like
c channel here or it could be a hollow section here .
We have just passed through the vertical joint design this slide is showing the
horizontal joint design. The horizontal joint designs primarily happening
or the floor joints here or it could be somewhere in between. And this horizontal joint generally
happen mainly it follows the floor slab of the or noise] beam level of the building and
you can see this is the picture is taken an actual project site On a curtain wall
this is a joint if this is a floor here what you can see this u type of like a channel
profile is sit fixed at the bottom there is one more profile which is coming at the top.
And what it does here is is different panel is fixed. So, it allows panel to move as you
can see in this video the panels need to be moving vertical direction here and this vertical
moment will take here of that floor to floor movement.
And you can see the panels here is not moving panel above is vertical sliding. So, it is
it is called vertical joint design. Horizontal joint design . This is same detail
as we have seen previously the joints need to be taking care of the same aspect a differential
live load floor deflection insulation tolerances. The horizontal one more aspect is critical
is that a creep or shrinkage and column shortening this is a long term. This 2 are long term
effects which will impact the framing elements of the facades. So, the facade system
need to be designed for joint design. Typically, if you combine all these impact
the engineer should be aware apart 15 to 25 or 30 mm is need to be design all the horizontal
joints. So, that will define how the joint design is designed for the project.
There is multiple ways these joints are design, it could have the capping here it has
no capping here or is just exposed glass joint here but the principal remain same here
there will be a joint here the glue line joint here . You can see this picture has
a different joint line here. It primarily allow the horizontal panels of moving. So,
that the glass panels or cladding panels not cracking due to the building moment.
Another aspect of thermal movement that we have seen previously here is thermal movement
design is it is the same formula is adapted here Delta t times panel and and thermal
expansion. So, the engineer should arrive and make sure he check for combination of
floor moment and and vertical movement. A factor of safety as typical to any other
steel design or concrete design is applicable to facade elements being and glass cladding
panels or framing elements as bracket detail. The safety factor is for a framing elements
is generally 1.5 time of safety factor and for glass element the safety factor is is
much higher like 3 or sometime 5 it depends on the glass types or which standards
is being used. Ah the general design criteria or may you
call as a best practice for framing elements The framing elements on facades is generally
aluminium framings this 3 different types of loads is is applicable here as dead load
mainly the glass panel or a cladding panel. Live load just due to that the glazing element
or impact to the human load or if it is used on a skylight there are maintenance load
human loads to be consider and wind load Wind load for a frame elements is given
an allowable deflection criteria span over 175 or 20 mm maximum, but again this depending
upon where it is used for windows system or if it is used on curtain wall system this
is different. And this is slightly a less strengthen as
compared to a steel design generally span over 240. Aluminium has is much more
ductile materials compared to the steel. Hence the allowable deflection is given much more
higher . So, as less strengthened as compare to a steel deflection criteria . And a similar
to the framing element here it shows the glass and glazing element or cladding element.
It has a dead load criteria mainly dead load criteria is not a major factor. It need to
be check for a wind a live loads if it has a human impact such as glazing used at the
lower level the seal level or the hand railing glass railing this is critical
For wind load checking glass deflection there is no definite control of the deflection the
reason being deflection control is not something or a safety concern. It is more of serviceability
aesthetics and a perception So, there is no definite control on the deflection as
a industry practice it is taken like a span over 90, or 20 mm maximum allow span is consider
as a shortest span or whichever the span is the glasses deflecting .