Multi-unit residential construction continues to see an increasing demand for living units above a one- or two-story podium. The demand is primarily driven by maximizing residential unit density within permissible building heights for a particular construction type. Architecturally, the podium’s primary purpose is a horizontal separation between different occupancies, creating open space for parking, retail, or amenity space on the lower floor(s). Yet, for the structural engineer, the podium level is expected to transfer significant loads from the density of the program above the podium to a different structural system below. While “stick-built” construction is historically wood-framed, the prevalence of cold-formed steel is increasing the structural demands on the podium level due to the ability to construct as many as ten stories of residential (Figure 1). While the design focus is often the structural efficiency of the residential units, due consideration is required for a properly designed, detailed, and constructed podium structure.

STRUCTURE magazine published Structural Design and Coordination of ICC 500 Tornado Shelters in July 2020, summarizing when a storm shelter is required, design criteria, and lessons learned. The authors of the July 2020 article provide guidance on design criteria, including the significantly increased basic wind speed, the increased internal pressure coefficient which presumes a breach in the building envelope, the increased directionality factor, and increased minimum roof live load, among other design criteria. To supplement the information in the previous article and illustrate the implications of storm shelter design criteria, the Table summarizes and compares wind load design parameters for a fictitious building used conventionally or as a storm shelter.

Multi-Unit Residential Construction

Pre-fabricated, structural cold-formed metal framing (CFMF) bearing walls are a trending construction system and an economical alternative to structural steel or reinforced concrete systems for mid-rise construction. CFMF wall systems are particularly desirable for 6- to 12-story multi-family apartments or condominiums, student housing, senior living, and hotels. Vertically-aligned residential demising and partition walls allow the CFMF to stack like timber-framed or concrete masonry unit (CMU) bearing wall construction. However, CFMF wall buildings are less height restrictive than timber due to steel’s higher strength and not as labor-intensive as CMU because of pre-fabrication. Additionally, CFMF systems integrate wall panels as the structural system in what would typically be non-structural, stick-built partition walls. …