Steel Framing, Steel Plates, Composite Steel
The new 6-story, Krause Gateway Center, located in downtown Des Moines, IA is a 160,000 sq-ft modern office building that serves as the headquarters for the Krause Group of companies. The $151 million building was designed by the world-renowned Renzo Piano Building Workshop to provide employees with a highly collaborative work environment through the use of open space and light. Additionally, massive roof overhangs serve both artistic and functional purposes by increasing efficiency and when paired with the green roof, aims to achieve LEED certification. Finally, the structure includes a double height (29 ft) lobby that features some of the tallest window in North America and is situated adjacent to the Pappajohn Sculpture Park, making the area a destination for the public as well as those who work there.
"Using RISA-3D to model the structure was valuable, but being able to create and apply various load types exactly where we needed them on the structure was essential in understanding how the structure would perform."
— Thomas Reynolds, PE
The architecture of the building created a variety of interesting design challenges for the engineers at Silman. The focal point of the building is the perimeter cantilevered framing known as the “nosing”. This two-story exterior cantilever spans anywhere from 9ft to 19ft beyond the main supports and as a result, produce significant deflections and torsion at the outriggers. Furthermore, at various levels, floors were either set back from the floor below, larger than the floor below or rotated such that the structure was no longer in line with the floor below. This variability in geometry was the reason that a structural steel system was chosen. Overall, the gravity system consists of composite steel beams and columns supported by over 450 one-hundred ton axial capacity auger cast concrete piles while the lateral framing of the building includes a hybrid system with moment frames, braced frames and cable-tied super columns all working together to resist the wind and seismic loading.
One of the most critical factors contributing to the success of the project was the long-standing relationship between Silman and Renzo Piano Building Workshop. This relationship allowed the engineer to work collaboratively with the architect during early design to ensure that the architects vision was maintained. In order to accomplish the various engineering challenges that the project posed, Silman utilized RISA-3D in both early design studies and final engineering design. The cantilevered “nosing” sections in particular were created as full plate models in order to understand the stresses and compound deflections. The interior, free floating stairs were also modeled, analyzed and designed in RISA-3D using plates in order to understand the diaphragm action within the system. Overall, this atypical office building proved to be a unique engineering challenge that Silman, with the help of RISA-3D, was equipped to handle.
Images 1-3: Applied Art