Award Winning Shoring Key to Success
By Mark Palmatier | January 11, 2021
Originally built in 1962, Climate Pledge Arena (originally known as Key Arena) is located in the heart of the historic Queen Anne district of Seattle. To take advantage of its prime but densely populated location, the arena was built down into the ground, with a pavilion-like sloping roof that has become a staple of the Seattle skyline. As part of a $700 million remodel, the Seattle Center Arena would get entirely new facilities, meaning the entire interior structure of the arena would be demolished and rebuilt from the ground up. With the majority of the arena built underground, this meant the existing concrete retaining walls would no longer have the concrete floors to support them and would require soil anchors be installed for support. In order to install those new soil anchors, an 18,000 lb micro pile drilling machine had to be driven on the existing slabs. However, the drill rig was a load the slab was never designed to support.
Due to the rapid pace of construction, it was immediately clear that coordination and clear communication would be required for the project to succeed. DHC was met on site by scaffolding contractor Performance Contracting, Inc., as well as representatives of both the general contractor and the structural engineer (SEOR) for the structure. The site to be shored was walked extensively, with each party noting critical locations that either needed to be shored, to be left open for access, or obstructions that needed to be worked around. The area of highest concern was over the Event Level ramp. The SEOR made it clear the Main Concourse slab above the ramp need to be shored to support the drill rig. At the same time, the general contractor was adamant that the ramp had to stay open and unimpeded in order for construction to stay on schedule. With demolition well underway, the ramp saw a constant stream of dump trucks as material was moved out of the stadium. The scope was to design a shoring system that fully supported the upper slab while taking up no space on the floor below.
After exploring some initial options, it was eventually determined that the most feasible way to adequately support the Main Concourse slab while simultaneously leaving the ramp open would be to essentially build a “tunnel” in the shoring; the slab itself would be shored up using modular cuplok scaffolding, which would then be set onto large steel beams spanning the width of the access ramp. After confirming the type of drill rig that would be used, DHC performed a detailed moving load analysis of the drill rig to model the loading that would be applied to the shoring. This drastically reduced the load on any one shoring beam, allowing for the use of lighter, more easily erectable beams.
Due to the slab above the ramp dropping as the ramp descended, as well as the presence of concrete beams at awkward angles, the modular, flexible nature of cuplock scaffold was used to its fullest as the main support of the Main Concourse slab. To support the steel beams on either side of the ramp, RMD Kwikform Super Slims were used as vertical post shores. While originally designed for use in falsework and concrete wall pouring applications, the Super Slims had high axial capacity and DHC had experience in using them in shoring applications. By bracing them to each other, as well as anchoring them to concrete wall and ramp for stability, a stabile base for the shoring tunnel was created that took up less than a foot of width. Once fully installed, the tunnel shoring allowed for the tie back installation to successfully move forward without any hinderance to the demolition work.
Mark Palmatier, PE – Branch Manager – (707) 537-8282
Jasper Calcara, PE – President – (760) 436-9756