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Ascent is the tallest mass timber tower
Ascent / Milwaukee, WI

Jun 21, 2022 Ricky McLain

When engineering mass timber high-rise buildings, vertical material movement is an important consideration.

Column shrinkage, joint settlement, beam crushing, and creep are all potential causes of vertical structure movement in a mass timber building, and their impacts can be more pronounced in tall structures due to cumulative effects. The main concerns are the impact of deformations on vertical mechanical systems, exterior enclosures, and interior partitions—as well as differential vertical movement of timber framing systems relative to other building elements such as concrete core walls and exterior façades.  

Vertical movement occurs in all buildings, regardless of height and structural materials used. The key to mitigation is to understand all potential sources of movement, calculate the sum of those predicted, and provide connection details that minimize movement and its effects while allowing for field adjustability.  

Ascent, Milwaukee, Wisconsin

In mass timber buildings, particularly tall mass timber buildings, it is common for the vertical lateral force-resisting systems to be non-wood—e.g., concrete shear walls or steel braced frames. As the primary vertical elements in a tall mass timber building, the timber columns significantly impact the net vertical movement of the building. However, column-to-column, beam-to-column, and floor panel-to-column connections can also play a significant role. The net vertical movement of timber columns and connections need to be considered, along with the movements of these elements relative to other building systems—which may not be moving to the same degree or in the same direction (e.g., timber column movement relative to concrete core wall movement). 

WoodWorks recently published a paper that addresses these topics, co-authored with the engineering firm Fast + Epp. The paper:  

  • Analyzes reasons for vertical movements in tall timber buildings (both short and long term) 
  • Provides methods of calculating anticipated movement 
  • Compares calculated movement to on-site verified movement 
  • Highlights detailing options that help minimize vertical movements 
  • Discusses vertical movement strategies implemented on several tall mass timber projects completed in North America, including Brock Commons in British Columbia and INTRO in Cleveland