At this year’s PTI Conference held in Fort Worth, CCL gave a presentation on vertical post-tensioning in shear walls as used on the River House development. The project, the tallest building in Grand Rapids, Michigan USA, comprised a 38 storey all post-tensioned building featuring vertical bonded post-tensioning within the walls to enhance the building’s performance under wind loads.
Post-tensioning was used to overcome a number of structural design and construction challenges faced on the project. At design stage, finite element modelling revealed that the building would be subject to high drift and the walls would experience excessive tension under wind loads. Traditional reinforced concrete shear walls were initially considered but were unable to provide enough capacity. The decision was therefore taken to use vertical post-tensioning. This would add axial compression to overcome tension stresses and allow the use of uncracked section which reduces drifts down to permissible code values.
From a construction perspective, the geometry of the walls was variable. Post-tensioning tendons had to sweep around door openings, and limited space was achievable to provide access to the post-tensioned anchors. In order to meet these requirements, a flexible post-tensioning system was used. A small round duct was provided to accommodate sectional transitions and tendon sweep at openings, and to overcome the problem of restricted access, small anchors were used along with special multistrand stressing equipment. This was comparable in size to the more compact monostrand equipment, which made its handling and usage on site more practical.
In short, vertical post-tensioning in the shear walls provided a successful solution, which was able to accommodate design requirements and allow construction to be completed on time and without complication.