Level 1 suspended slab pours

We’re excited to share that concrete pours for the Level 1 (L1) suspended slab are underway! The first pour was done on January 25 and the remaining pours will continue until mid-April. Once all 10 pours for L1 are complete, ~2510m³ of concrete will have been poured.

Fun fact: Heidelberg Materials, Dawson Creek is supplying all of the concrete for the suspended slabs and CanaSteel Rebar Services, Dawson Creek is supplying and installing all the reinforcing steel.

Suspended slabs are upper floor concrete slabs that are not in direct contact with the ground. The slab is supported on the exterior of the building by foundation walls and on the interior by concrete columns.

In anticipation for the suspended slab pours, Graham had to complete the foundations that serve as the supporting structure of the slab. This installation involves:

• Mudsill installation – Lumber used to support shoring. Mudsills distribute the shore load across an area big enough to not exceed the allowable soil bearing pressures.
• Shore Installation – Vertical support designed to carry the weight of the formwork, reinforcing bar, concrete and live loads. All engineered to known and assumed loads. For DCDH, we are using an engineered tower system.
• Beam Installation – Aluminum beams for horizontal formwork that are supported by the shores.
• Joist Installation – Horizontal formwork installed perpendicular to and supported by the beams. The form facing material (plywood) is placed directly on the joists.
• Formwork installation – The sheathing or plywood as mentioned above is what the concrete will be placed against.

For the most part, the shoring is built in place. The beam, joist and formwork are pre-assembled as much as possible and flown in place using one of the two tower cranes on site. Infills are then completed after the prefabricated pieces are installed.

The L1 suspended slab formwork is a tower system, so after the slab section has been poured, the beam, joists, and formwork will be removed and used on future pours. The shores will be lifted and individual reshore posts will be placed for the duration of all of the suspended slab pours for all levels.

As usual, there is a lot of preparation work that goes into the suspended slab pours beforehand. In addition to engineering and picking an appropriate system, extensive planning for heating and hoarding is required to ensure the concrete cures properly. For suspended slabs, heating comes from the bottom which allows the concrete to be placed and finished and then the top of the slab is covered with tarps to keep the concrete at the right temperature and prevent moisture evaporation.

The size of the pours are also pre-planned to accommodate:

• Concrete supply capabilities – Slab sizes are based on the amount of concrete that can be received in a 6-to-8-hour window
• Reinforcing steel laps and layout – Splices in rebar can impact structural integrity and increase loads outside of design parameters
• Engineered control and expansion joints – Allow for shrinkage or movement
• Crew availability and floor requirements – Levelness, flatness and finishes all have different levels of support and manpower required
• Ambient air temperature, heating and hoarding

The Level 2 and Level 3 suspended slabs consist of 18 pours (9 per level) totalling over 5000m³ (2500m³ per level) of concrete. Level 2 is anticipated to occur from March to May and Level 3 is anticipated from April to July.