For this year’s Tilt-Up Concrete Association (TCA) annual convention held in Kansas City, Mo., TCA members came together to demonstrate the versatility of tilt-up and present a lasting contribution to the community. In April 2011, the TCA chose to work with the Missouri Korean War Veterans Memorial Commission, and the Kansas City Parks and Recreation Department, on a memorial to honor Korean War veterans. The project is a park structure that was donated to the city following the annual convention.
Local TCA professional engineering firm member Needham and Associates Inc., Lenexa, Kan., served as engineer of record for the project and graciously offered its services pro bono. TCA contractor member, Summit Concrete, Lee’s Summit, Mo., accepted the challenge of building the memorial and also contributed its services. As the project continued to increase in scope and complexity, the Missouri Korean War Veterans Memorial Commission hired JE Dunn to serve as general contractor, which also provided its services at no profit. In June 2011, the project team met for the first time in Kansas City with less than four months to go before the deadline.
Various factors, including the approval of concrete sample panels, delivery of images to be embedded in the memorial (to be used in the creation of the form liners), and fundraising efforts delayed the start of construction a few weeks and threatened to jeopardize the planned dedication ceremony which had already been promoted.
In July 2011, construction began, with just two months before the opening of the 2011 TCA Annual Convention and the planned dedication. Coincidentally, the date set for the dedication coincided with the day marking the arrival of American troops in defense of South Korea in 1950. “In Korea the day is celebrated still,” says Young Kim, A Korean-American and friend of Jim Shultz, co-chair of the Missouri Korean War Veterans Memorial Board of Directors. “It’s called Ku Yi Pal Su Bok in Korean, or September 28th, Recapturing Seoul.”
Beyond the programmatic elements of the project associated with the remembrance of those who served in the Korean War, the project was charged with demonstrating the versatility, applicability, and beauty of tilt-up concrete construction. These efforts can be seen in the exploitation of the inherent benefits of tilt-up.
The articulation of the edges of the tilt-up panels and the use of them to mediate between the horizontal and vertical planes of concrete not only highlights the effectiveness of manipulating the one formed edge of a tilt-up panel, it aids in the reading of the overall form as a continuous ribbon.
The outside faces of the memorial were treated with a retardant prior to concrete placement in order to expose aggregate on the surface of the panel. The result is a texture that is familiar and one that gives depth to the surface. The interior of the structure and all of the edges were polished.
Openings in the walls and roof break up the mass of the large panels and provide additional layers of light and transparency. Reveals in the surface of the panels on both the interior and exterior reinforce the geometry of the structure and again aid in reducing the scale of the panels.
Large stainless steel plaques inscribed with more than 900 names of those from the State of Missouri who paid the supreme sacrifice and gave their lives in defense of South Korea are inset on the interior of the structure. On the exterior of the memorial, two large images—one on the outside face of each wall—are cast into the concrete. Grooves of varying depths and widths capture light cast on the structure to reveal the dynamic images. Their appearance changes with the light and viewing angle affording visitors a variety of experiences and becoming an interactive element of the design.
In panel design theory, the engineer typically designs the vertical column strip assuming that the panel acts like a one way flexural member using slender wall theory. This project, however, had very few vertical load paths. To account for the unusual load paths, Needham’s Karen S. Hand, P.E., designed reinforcing in four planes: two vertical, one horizontal, and one plane at a 45-degree angle. The first analysis was done using only the vertical strips but the nature of the roof loads and shape of the panel left the overall design difficult to grasp. In order to finalize the design and determine how the panels would behave, Hand built a finite element model in a structural analysis and design software (STAAD). This allowed her to look for the stress risers in the panels to account for the odd geometry and reinforcing load paths. Hand notes, “This project was the most geometrically complex project I have ever worked on.”
The structure has only two parallel wall panels so the lateral in-plane loads are resisted by fixed base connections. To ensure extra stability of the panels, special heavy-duty base connections were used. The panel was designed with outrigger “feet” to increase the moment arm and keep the panel more rigid than the standard fixed base connection. These were placed at 2 feet on center and welded to a large embed cast into the footing. This also ensured that the connections were robust enough that temporary bracing could be removed prior to the erection and placement of the roof panel. This was essential in the sequencing of the project since the flatwork around the panels and finished grading needed to move forward while the roof panel was being finished.
Needham detailed the steel embedment items as well, specifying a shelf connection. Deformed bar anchors, instead of headed studs welded to plates and channels, provide substantial strength in the design of the connections. Tincher’s Welding, Harveysburg, Ohio, fabricated the embeds and personally delivered them to Kansas City.
The lifting and bracing design was done by Scott Collins, P.E., assistant chief engineer for Meadow Burke. The complex geometry of the panels made the lifting design especially difficult. The panel geometry caused the panels’ center of gravity to shift drastically to one side. This was remedied using special crane rigging to rebalance the lift points back onto the panels’ center of gravity.
With only two months to build the memorial and with a number of events occupyied the memorial site in Washington Square Park, the Summit Concrete team decided to cast the tilt-up panels on recyclable casting slabs in their nearby yard. The process of forming the panels was complicated. The overall shape of each of the three main panels (two wall panels, one roof panel) was a parallelogram with 45-degree angles. But the two faces of the panel were designed to be misaligned. At the bottom of the panel the faces were offset 8-inches in one direction and at the top 8-inches in the other direction. The edge of the panel in-between the two faces was to be triangulated creating a faceted edge.
All of this was done within the 8-inch-tall edge forming; the faces of the panels were flat. This is typical of most tilt-up concrete construction, but the way in which the edges were designed and formed was not typical. Because of the manner in which each panel interacted with the next, there was virtually zero tolerance and the schedule didn’t allow for mistakes.
Roger Meyer, Tony Turner, and other Summit Concrete team members began forming the panels and realized quickly that the angularity of the form coupled with the faceting of the edges created conditions that were not simple to construct. Adjustments to the design were made as needed, but many pieces of the project were already set into motion and the panels would have to accommodate insets, such as plaques and signage, rather than altering the design of those elements.
Fabricated and donated by Innovative Brick Systems of Denver, Colo., ShadowCast formliners were used to cast the images in the exterior faces of the panels. To create the liners, photographic images were carved into a wooden “tool” or mold using a CNC milling machine. Then each mold was used to create the elastomeric liner. Innovative Brick Systems was able to create the very large, one-piece liners. They were durable and easy to work with and fortunately fit like a glove into the areas defined by reveal strips that wrapped the image and were already in place.
Once the first wall panel was formed, including reveals, insets, and embedded images, Summit began to place the reinforcement. The reinforcement layout was congested and support of the heavy custom-embedded structural elements was tricky. The decision was made to apply the retarder to the slab with the reinforcement in place because of the complexity and density of the reinforcement layout—a very tedious job.
Hardware to accommodate last-minute modifications to the lifting design was rushed to the site courtesy of White Cap Construction Supply, the Meadow Burke distributer in the Kansas City area that contributed the hardware and other rental items at no charge.
Once everything was in place, a final layer of insets and reveals to be cast on the top face of the panel was secured to the top of the forming and the panel was poured.
On a traditional tilt-up project, the next step would be to lift these panels into place. On this project, however, the design called for the inside, or top side, of each panel and its edges to be polished. Summit Concrete got a crash course in polishing from Bledsoe Rentals, the company providing the equipment, and they began to work the surface of the panel. After hours of work, the panels were lifted onto a steel frame where they were situated vertically so that work on polishing the edges could begin. They were then transported to the site on this frame in the vertical position and lifted into place.
What started as an effort to demonstrate the benefits of tilt-up concrete construction quickly turned in to something so much more. Not only is this project a testament to the versatility, applicability, and beauty of tilt-up construction, it is a demonstration of the generosity, pride, and good will of TCA members. Most importantly, it continues the legacy of Korean War Veterans and recognizes those who paid the supreme sacrifice and gave their lives in defense of South Korea.
Mitch Bloomquist was project manager on this project for the Tilt-Up Concrete Association.