Walking Columns on the Laurel Rittenhouse Square Project
About walking columns
A walking column refers to a structural column that is not vertically aligned between floors, meaning that the column above does not sit directly on top of the column below. Instead, the column "walks" or shifts horizontally from one level to another over a series of floors. This gradual transition distributes the load more evenly instead of shifting it all at once.
With extensive experience in structural engineering, IMEG has been at the forefront of designing and implementing solutions for complex projects. Their expertise is reflected not only in their work on high-profile developments but also in their commitment to knowledge sharing through industry lectures. Recognizing the need for advanced analytical tools, IMEG integrated IDEA StatiCa solutions into their workflow four years ago, enhancing their ability to tackle challenging structural designs with greater precision and efficiency.
\[ \textsf{\textit{\footnotesize{Walking Columns – A Proposed Design Methodology October 20, 2021, Presented by: Clifford Schwinger, PE}}}\]
Theory in practice
What do Seminole Hard Rock Hotel & Casino in Hollywood, Vancouver House in Vancouver, or The Laurel Rittenhouse Square in Philadelphia have in common? Overcoming challenges using walking columns and design by IMEG engineers.
\[ \textsf{\textit{\footnotesize{Vancouver House, The Laurel Rittenhouse Square, Seminole Hard Rock Hotel and Casino}}}\]
While the focus at Seminole Hard Rock Hotel and Vancouver House was primarily on the architectural shape when using walking and sloping columns, at The Laurel Rittenhouse Square, walking columns were used to expand the upper floors westward while preserving a historic building at the base. It is a recent project by IMEG.
The Laurel Rittenhouse Square is a 50-story, 583,000-square-foot ultra-luxury residential tower and the tallest residential building in Philadelphia. Designed by Solomon Cordwell Buenz and engineered by The Harman Group (now IMEG), it features 65 condominiums, 184 apartments, and a three-story podium with retail and dining space.
\[ \textsf{\textit{\footnotesize{The Laurel Rittenhouse Square in Philadelphia}}}\]
A key structural challenge was preserving an adjacent three-story historic building while maximizing floor area. To achieve this, engineers implemented walking columns, gradually shifting load-bearing columns over four floors to support the 40-plus stories above.
Engineering Challenges
Currently, there is no established ACI 318 methodology for designing walking columns. Structural engineers must, therefore, primarily use an approach based on fundamental structural engineering principles and experiences. That can be tricky, because walking columns may have unique conditions. However, these are discontinuity regions, and thus, the columns are designed according to how the code addresses such areas - the Strut-and-Tie method (SaT), even though ACI does not explicitly mention walking columns. Therefore, more senior engineers are needed to consider all the inputs and conditions that factor into the calculation. The SaT method relies on an initial assumption. However, if this assumption is incorrect, it may not accurately reflect reality, making experience essential.
Solutions and results
IMEG implemented IDEA StatiCa Detail to conduct a comparative analysis against ACI 318-14 strut-and-tie hand calculations. This approach was critical in validating key structural behaviors and ensuring compliance with engineering best practices.
IDEA StatiCa Detail played a pivotal role in assessing the transmission of loads across multiple floors, evaluating the impact of kick forces applied to floors from column walks, and identifying potential tension-splitting zones resulting from bottle struts. Such insights are essential for optimizing design solutions and mitigating structural risks.
\[ \textsf{\textit{\footnotesize{Hand calculation of walking column}}}\]
The software enhanced the reliability of engineering decisions in complex scenarios by providing a more refined analysis of stress distributions and force interactions.
\[ \textsf{\textit{\footnotesize{Model and results of walking column in IDEA StatiCa Detail}}}\]
Since January 2021, IMEG’s Philadelphia office has integrated IDEA StatiCa software into its workflow to analyze non-standard structural elements and to deliver solutions for complex architectural challenges.
IDEA StatiCa Detail provides a solution for analyzing discontinuity regions (D-regions) using the nonlinear Compatible Stress Field Method (CSFM). This method allows engineers to gain a deeper understanding of the actual structural behavior, including load distribution patterns, stress concentrations, and reinforcement demands in concrete elements.
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Conclusion
Walking columns represent a unique structural challenge that requires a cautious approach. IMEG has demonstrated expertise in this field, applying advanced methodologies and tools like IDEA StatiCa to verify other methods. By successfully integrating walking columns in high-profile projects such as The Laurel Rittenhouse Square, IMEG has shown how engineering ingenuity can overcome architectural and structural obstacles.
As the industry continues to evolve, the use of walking columns will likely become more refined, with advanced software solutions playing a crucial role in ensuring safe and efficient designs.
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