Design vs Cost

Design options are literally endless. Employing these options intelligently adds a great deal of design interest to a project with only minimal cost increases.

The following design strategies should be considered:

  • Panels can contain more than one concrete face mix.
  • Panels can be produced with multiple finishes. The combination of finish methods will determine the cost impact.

  • Design an appendage to an existing form. Doing so will cost less than adding a full form, yet will provide an attractive building detail.
  • Set windows back from the building’s face at one or two column bays or at certain levels.
  • Add a few small ornate pieces at the entrance or as site walls. The small panels will be more expensive per square metre, but a few of them amortized over the entire project will add a minimal additional charge ($15,000 increase over,say, 3000 square metres = a $5 premium).

On steel-frame structures, gravity and lateral support brackets (for precast connections) should be in the structural steel fabricator’s scope of work and should be shop-welded to the structural-steel columns rather than field-welded. It is much less expensive to shop-fabricate and shop-weld them than to hoist and field-weld heavy support brackets.

Architectural precast offers many cost advantages over other cladding materials. Precast is produced all year round in a controlled, cost-efficient production environment. In addition, precast can be installed year round even in harsh winter conditions. This eliminates the need for costly winter weather protection and contributes significantly to compressing the overall building schedule.

Architectural precast can enclose the project quicker than any other cladding material. Typically, more than 100 square metres can be installed each day (10 pieces per day at 10 square metres each). The installation speed of precast panels can shave months from a construction schedule, thus reducing construction financing cost. Precast spandrel panels are commonly used as a vehicle-impact restraint in parking structures in addition to providing a perimeter design feature. Doing so eliminates the need for an upturned cast-in-place concrete beam or a cable system.

Size

Architectural precast panels can span great distances (5 metres to 20 metres) and be connected directly or adjacent to structural columns. This advantage allows the designer to control the gravity loads to reduce the structural-framing costs.

Load

Precast can be stacked onto a foundation. This way, all precast gravity loads of a multi-storey building can be transferred vertically through each panel and ultimately onto the foundation. Where this design is used, the structural-steel frame resists the precast panel wind loads only, permitting the frame steel to be lighter and less expensive. This design must allow for building drift.

Multi-level

In high-rise construction, vertical precast panels can span multiple floors. Multiple vertical floor spans of precast panels require gravity loads to be supported at only one floor per panel (every two or three floors.) That way, the majority of the floors can be designed without the need to support the gravity loads of the exterior skin, reducing the overall structure’s cost. This approach may not be practical in high seismic zones due to drift requirements.

Mitigating the costs of other building materials

Routinely, precast panels provide support for gravity and wind loads of other material, such as windows, curtain walls and storefronts. This capability reduces the framing cost of these adjacent cladding materials and reduces structure costs. More expensive traditional materials can be replaced with cost-efficient architectural precast. Precast can be coloured and textured to mimic natural stone.

Planning ahead with Wilco Precast

Early in the design phase, the designer should evaluate all the factors influencing the economics of a particular architectural precast concrete project. To arrive at an optimised solution, the designer will need to seek early consultation with Wilco Precast.

We should be challenged to suggest options for creating a good economical design that also satisfies the designer’s aesthetic requirements. If possible, the designer should visit Wilco’s manufacturing plant, as well as visit projects under construction. This way the designer can become familiar with the manufacturing and installation processes.

Such tasks as mould fabrication, challenges to casting and finishing specific designs or shapes, relative material costs, handling methods at the plant and jobsite, and approaches for connecting panels to a structure are important to fully understand in order to optimise the cost of the precast concrete.