The new supply of multifamily housing delivered in 2021 is expected to increase by around 17% to 334,000 units.
A growing trend in multifamily construction is the use of cold-formed steel (CFS) framing above one and two-story podiums. Since CFS framing allows for the construction of multifamily structures at heights greater than other materials, successful CFS-framed projects feature a properly designed, detailed and constructed podium structure.
This article provides an overview of podium design. But first, let’s address this question: Is there a need for multifamily projects to go skyward?
Vertical construction with cold-formed steel
Increasingly, the answer is yes. Since 2010, more people in the world live in urban than in rural settings. In 2020, 56.2 percent of the world population was urban — approximately 4.4 billion people. Since urban space is limited, building owners must meet the demand to go vertical.
Not all architects, engineers and contractors are aware of CFS framing’s high strength and ductility. Some may think of CFS as a light-gauge material only suitable for interior drywall partition framing and a framing backup for a variety of exterior building finishes.
Is CFS suitable for load-bearing support of a 10-story building? Yes.
- CFS’s gravity and lateral-resisting properties make it perfect as the load-bearing material for mid-rise structures
- Research from the Steel Framing Industry Association (SFIA) demonstrates that CFS has a height capacity of up to 40-stories, although 10-story structures using CFS C-studs and joists is common
The SFIA Matsen Tower has opened the door to a new way of incorporating CFS framing into high-rise buildings.
Overview of podium systems
According to STRUCTURE, podiums are typically constructed using structural steel or cast-in-place reinforced concrete, though regional variations and some construction cost models favor podiums made with post-tensioned concrete, and even precast and pre-stressed concrete.
The design considerations for each of these podium types is unique. Such considerations may include achieving certain architectural expressions, providing for mechanical, electrical, plumbing and fire protection and ensuring sufficient structural system analysis and design.
Structural steel was used for the podium to construct the Sheridan College Student Residence near Toronto, Canada.
STRUCTURE provides the following overview of 3 typical podium systems:
Structural Steel Podium
- Can be located directly below the walls and designed to meet the requisite strength and serviceability limits, allowing the remaining framing at the podium level to be designed only for a single level
- Not susceptible to additional long-term deflection considerations
- Typically lighter than concrete solutions, a benefit that can reduce foundation loads
Reinforced Concrete
- Offer flexibility in the arrangement of the supported superstructure
- Require important considerations related to both initial detailing and long-term performance
- Primary concern is long-term deflection, particularly where vertically stiff, multi-story bearing walls are supported
Post-Tensioned Concrete
- Preferred structural system for podium slabs in certain regions because of cost savings
- Added economy accompanies heightened trade coordination and, for many practitioners, analytical complexity
- Inherently powerful at minimizing deflections and controlling cracks due to their precompression and load balancing
Free Project Assistance for Cold-Formed Steel Framing
The podium structural system for a multi-family residential development can impact nearly every part of the project. System selection, design, and detailing should balance structural efficiency with serviceability, architectural needs, MEP and FP coordination, local contractor experience and constructability, says STRUCTURE.
Do you have additional questions or need support for a new or existing project? BuildSteel offers free project assistance for building professionals in the U.S. and Canada:
- Central source for consultation on code-compliant design of non-residential and multi-family structures
- Industry experts with decades of knowledge on CFS
- National network of manufacturers, suppliers, and contractors (U.S. and Canada)
Submit your project or question.