The Earth Sciences Building, a non-residential
mid-rise building, is a very impressive wood structure, from both a structural
design and a code perspective. The five-storey academic wing,
unlike the five storey concrete lab, uses wood as the primary structural material.
Hi, my name is Gary Chen and I was the project engineer responsible
for the fire safety design and building code compliance for the ESB building.
So Gary under the alternative solution provision how are you
able to get so much wood into the Earth Sciences Building?
A sophisticated fire risk analysis was carried out to demonstrate that
that building using wood construction will perform as well as non-combustible
constructions, such as steel and concrete.
And what did this analysis involve?
The analysis essentially involved looking at how the building will perform in fire and
how the resultant impact will affect the occupants in the building itself.
This is very much similar to structural engineering design, where structural engineers
look at seismic, gravity and wind forces, we as fire engineers look at the fire forces.
The fire scenarios we looked at in our analysis were based on theories of compartment fire
dynamics and it is the same test that we look at for non-combustible buildings, such as steel
and concrete, so in this case is the same. When we analyzed the ESB building we needed
to look at how the wood construction will perform relative to the goal objectives,
with respect to two possible fire scenarios: pre- and post-flashover fires.
Code consultants have solid knowledge of how wood will perform, so we know how to find
engineering building to perform at or above the level required by the building code.
Like many modern-day large buildings including that of our residential
mid-rise buildings, the Earth Sciences Building comes with a state-of-the-art
fire protection system including fire sprinklers and smoke detectors.
Yes these fire protection systems are needed in any kind of building whether
it is wood construction, concrete construction, or steel construction.
However with the ESB building we implemented additional smoke and fire separations that
we see here, to divide the building into three separate zones: the atrium which we are standing in right now,
and the north and the south wing. This will allow occupants to move from the fire
zone to the non-fire zone in the event of a fire emergency, for protection and evacuation purposes.
The floors are also fire separations so when you consider the zones and the floors we effectively
have a highly compartmentalized building, this will allow us to
address the spread of fire in this building. In addition to the one hour fire separation
we discussed earlier, we also needed to engineer these large timber column beams and wood-concrete
composite floors, for the 1-hour fire-resistance rating required by the Building Code.
This was achieved through working in collaboration with the structural engineer,
by looking at how the structure will perform, when some of the wood members have been charred.
Using appropriate fire model we can calculate how hot the fire compartment will be and how much wood
will be charred in the fire, this information can then be passed on to the structural analysis
tool to calculate the fire-resistance rating. Particularly when it comes to a large wood
building like the ESB where it has been extensively engineered by some of the
world's leading experts in the field, as we were discussing earlier the charring effect of wood is
actually something beneficial to the safety of the building, as long as wood buildings
are properly engineered it can be demonstrated that it will perform as well as concrete and
steel buildings, so there's no reason why we can't use wood in tall and large buildings.
The use wood was aligned with the goals of the project, as well as the core values of
our firm one of which is sustainability. When we started the project we started
looking at ways that we could reduce the carbon footprint of the building
wood actually sequesters a lot of carbon. When you typically look at a lab building,
they are large energy users, this building sequesters 2,600 tonnes of carbon, which
is equivalent to 262 cars off the road for one year, which is an amazing feat.
We were looking at innovation which was another goal, the wood products in this
building and the design by Equilibrium it's such an amazing feat of innovative engineering,
you can see it all throughout the building. One of the other benefits of using wood is the
beauty and the warmth of wood, it definitely has a spiritual sense or an intangible
quality for the users when they're in their offices, having this exposed wood ceiling.
This project has definitely demonstrated that the
possibilities of wood construction are on par with concrete and steel.
I'm standing on the grand staircase, in the main lobby, the staircase is made entirely of glue
laminated timber, held together with a proprietary system called the HSK, which essentially consists of a
perforated plate glued into the wood and holding the folding plates together. The stair is entirely
cantilevered off the bridge floors and goes up over the full of five storeys of the atrium.
The first element in the gravity load resisting system is the post and beam structure.
The post and beam structure is assembled very much in the same way that the buildings used
to be assembled a hundred years ago, in Gastown and other cities across Canada.
The critical element here is to avoid shrinkage, so we intentionally ensure that the columns are
continuous from the basement to the roof and the beams framing to the side of them or travel
through them at the interior column locations. So what we have here is a typical interior column
and two beam connection, so you will notice that the column and the beams were both notched
and then interlocked into each other. What this does is it allows us to bear
directly on the end fiber of the lower column. The exterior columns on the other hand can be
continuous over a single, a double or a triple storey and the beam in that case will frame into
the face of the column, and in our case we used the proprietary connector, called the
Sherpa Connector, which is an aluminum dovetail connection, which is screwed into the beam element
and the column element and can then be allowed to just lock into each other very efficiently
on site, making the erection a lot faster. You will note that in both cases there are
no metal elements exposed, in the case of the interior columns of course it's a
wood to wood connection so there are literally no metal elements at all.
In the case of the exterior connection, the Sherpa system is completely concealed and
protected by the surrounding wood material. What you see behind me is a portion of the
transfer trusses, which span across the entire width of the building over the lecture theatres.
The trusses are mostly open because of circulation requirements
and have single diagonals at the ends. The diagonal is connected to the glulam timber
frame using end bearing connections, so the steel bears directly into the end grain of the beam to
transfer horizontal forces and onto the end grain of the columns, to transfer the vertical forces
and again you see how the columns are stacked on end grain to avoid the shrinkage at the joint.
The truss top chord consists of a glulam concrete composite T-shape, the truss
bottom chord because of the eccentricity of the brace consists of a steel concrete
composite T section. So what you have is a truly hybrid truss of steel, timber and concrete.
When it came to the floor system our goal was to provide a clean and simple system with a
minimum structural depth. We used a wood-concrete composite floor system consisting of 89 millimetre
timber strand panels at the bottom, 100 millimetre enforced concrete topping at the top and 25
millimeters rigid insulation sandwiched in between to make the span of 6.4 meters from bay to bay.
The LSL panel serves as the tension cord and also provides permanent formwork for
the concrete topping. It's also the finished product for the ceiling.
The rigid insulation helps us to improve some performance of the system, plus adds structural
depth without adding any weight to the system. The reinforced concrete topping acts as the
compression cord and we were also able to place electrical and mechanical
systems within that topping. The composite action between
the timber frame panels and the reinforced concrete topping is achieved by perforated
steel plates that get glued into soft curves located at the top surface of the LSL panels.
These plates also reach into the concrete topping and once cast into that topping
they provide a stiff, yet very ductile connection between these two elements.
The lateral load resisting system consists of CNC shaped glulam chevron shaped braces.
To achieve a ductile behavior of such a system in a seismic event,
steel parts of the connection have to yield. We used triple knife plates with small diameter
tight fit beams, we over cut the slots in length where the knife plates are embedded in, to allow
connection to yield in tension and compression. The other elements of that system are designed
to have a higher capacity than that tight fit beam knife plate connection itself,
to allow the system to have an energy dissipation in that area during a seismic event.
CLT was retained for the design of the extensive canopy which wraps around the north, east and
south face of the building, the high roof as well as the link bridge between the existing ESB
main building and the new Earth Science Building. The 1,150 square metre CLT canopy is a flat plate,
which emerges from the inside of the building, cantilevering past a glulam columnated, creating
an illusion that the entire canopy is one giant single CLT piece cut to fit around the building.