S1 – Timber Redesign Office Building

Structural drawings were created to show the layout of the building. Building 12 is L-shaped using CLT walls and glass panels as the envelope. The glass panels are present on the sections G to J and 6 to 9 facades on the 1st and 2nd floor of the building for openness and welcomes natural light. On the top and left side of the building, the two rectangles represent the staircases and the large rectangle at the bottom right represents the core, depicting the location of the elevator shaft. The black dots represent the columns of the building.

The drawing below shows a clear beam layout. The beams within the building are represented using red lines. The blue lines represent the 365×608 beams used for the largest span of 9.45m.

The drawing below displays the elevation view of the building from the east side. The panels with a diagonal pattern represent glass, the panels without a pattern represent CLT.

The drawing below displays the elevation view of the building from the north side. The panels with a diagonal pattern represent glass, the panels without a pattern represent CLT.

The main part of the design was to size every structural member and ensure that they were safe for use and occupancy, as well as service limit state conditions. The sizing process for each member is: consider the tributary spans affected, convert to a linear distribution, factor every load using ULS design, find maximum axial, shear, moment and deflections that are safe in accordance with the National Building Code 2019. Then, designing the section in accordance to a 90 min fire rating, highlighted by Wood Design Manual 2017. After assessing the loads and the sizes of all the members throughout the building, the values were run through the WoodWorks software to model the connections. Only the members with the maximum loads were designed and used throughout the building.

IMPORTANT: Please visit Our Photo Gallery at the bottom of the page to view the visual representation of each structural member designed. Here are the size specifications for each member:

• Slabs: Made from NLT. 140mm thickness for floors 1-5 and 184mm thickness for the roof.
• Beams: Made from Glulam. 365x608mm for the beams having a span of 9.45m, 365x532mm for the beams having a span of less than 9.45m , 265×342 for redundant beams.
• Columns: Made from Glulam. 365x456mm for floors 1 to 3, 365×342 for floors 4 and 5.
• Exterior Walls: Made from CLT. 175mm thickness throughout.
• Core and Stairs: Made for DLT. 2×8 inch panel thickness throughout.
• Connections: Made from Steel bolts. 4 different connection types specified in our photo gallery.

While there are advantages in using timber, it also has some challenges. These challenges have always impacted the construction industry but have a greater impact on timber designs. Therefore, additional efforts were required with respect to the following risks and challenges.

• Fire Rating: The biggest concern that arises from using timber over concrete and steel is that it does not perform as well in the case of a fire. Using the Wood Design Manual 2017, the building was adequately designed for a high fire rating of 90 minutes of fire evacuation. The common problem was that to satisfy the fire rating requirements, members had to be heavily over-designed. Smaller cross-sections could have been used for most members if fire safety protocols were not considered.

• Deflections: Since wood has a lower stiffness, it performs poorly in resisting deflections. This was particularly challenging when designing for long spans. For example, referring to the structural drawing, the span between 6 and 7 is 9.45m, which is the longest span, a 365x608mm was used. This beam is atypical and would need to be custom-made. However, for all the other beams, 365x532mm was used instead.

• Vibrations / Lateral Forces: The most important aspect when designing floors and beams are the vibrations, usually governing its design. To reduce the magnitude of vibrations, a thin 50mm concrete cover was added atop the slabs. A moisture barrier is added between the concrete cover and the slab to prevent moisture damage from the concrete cover. Another design challenge is lateral force resistance. Since this building is proposed to be assembled in Calgary, high wind and earthquake loads are negligible, thus, the cores are sufficient to support the lateral loads.

In the original design of Building 12, the cores were made of concrete. In the proposed concept shown in Figure 7, Nail-laminated timber (NLT) cores were proposed as a timber alternative. In the actual redesign of the building, Dowel-laminated timber (DLT) cores were used instead due to their better fire rating. As such, the thickness of the cores was reduced.

From floors 1-3 and floors 4-5, the column sizes are 365x456mm and 365x342mm, respectively. The columns are continuous for each set of floors; however, a connection was required between floors 3 and 4. It was proposed to have a steel hollow structural section (HSS) with welded plates which are then screwed into the columns, as shown in our “column to column” drawing. This is an unnecessary complex connection requiring more designing and a simpler connection can be used instead. As such, the connection is made of 3 welded steel plates which are then bolted to the column.

A beam with a span of 9.5m was required, however, readily available glulam beams do not meet the adequate moment resistance. As a solution, a stronger material such as a steel beam was suggested. To be consistent with the wood aesthetic, the use of a steel beam was not aesthetically engaging. As an alternative method, beams from neighboring spans were extended and connected using bolts, as shown in our “beam to beam” drawing. On the other hand, it was not a viable option with respect to the continuous columns. This is due to the beams being crushed by the columns because of the anisotropic nature of wood. Another alternative method was to have 2 separate beams going from side to side. This method would increase the resistance of the beams almost doubling its resistance. The drawback is that it would require more bolts going through the columns which would weaken the column. Therefore, the better option was to have a beam with a higher cross-sectional area which is not readily available and would require being custom made.

The concept requires a curved glulam roof. However, a curved glulam roof is not feasible option due to a large span and the size unavailability of any curved glulam beam. Even if, the longest curved glulam beam was used and connected using steel plates, the calculations would be too complex, and it proved as such. Therefore, the alternative option was to have the columns erected up to the roof and have the columns bear the loads leading to a roof with slanted sides instead of a curved roof as shown in our “roof truss” drawing.

Due to the thickness of the girder, the use of bolts as a connection is inadequate since it is weakening the girder. The addition of bolts to the girder, weakens the girder causing splitting in the girder. Therefore, the solution was to use a top hanger connection, that is hanging the beam directly on top of the girder, eliminating the use of holes in the girder.