Seattle 3131 Elliott Avenue. Suite 600A, Seattle, WA 98121-1047 208?343?3000 August 13, 2020 Mr. David Graves, Strategic Advisor Ms. Pamela Alspaugh, Interim Director of Facilities Seattle Parks and Recreation 300 Elliott Avenue West, Suite ?[00 Seattle, WA 98119 SUBJECT: Pier 58 Waterfront Park Seattle, WA RE: Review of Pier 58 Movement Observation Report Recommendations Dear David and Pamela: This letter summarizes our observations of recent movements and responds to your requests for information and recommendations. As documented by reports dating back to 2006, the Pier 58 structure has been losing both vertical and lateral strength due to decay and corrosion of the supporting pile system. As recently as March 2019, there has been observed lateral movement. On Thursday, August 6, 2020, we were informed of a significant lateral shift in the pier. We visited the facility to observe the movement, including observation below the pier by boat. Based upon movement of transition plates at adjacent structures we observed what appeared to be recent movement of up to 12?. We recommended that the park be closed and that access be limited by the installation of cyclone fencing. We returned to the site on Monday, August 10, to further investigate the condition and to formulate an opinion of what is occurring. Ms. Alspaugh had asked us to evaluate the location of fencing along the south property line (adjacent to Pier 57 Miners Landing). We observed an additional one inch of movement. We did a row-through observation of the edges of Pier 58 along the north, east and south perimeter. It appears that the loss of vertical support at the concrete water feature (located in the northeast corner of the pier) is causing the structure to lean to the southwest, away from the corner of the pier. it appears that the piles that support the heavy concrete water feature structure are failing at their head connections and that the direction of movement is westward. This movement is being resisted by two primary elements: the adjacent structures in the south half ofthe park, and the timber piling ?cluster" that previously supported the north observatory. The entire Pier 58 structure is in a uniform state of failure. Because of the continuity of structural framing, the south half of the pier derives a portion of its stability from elements in the now-collapsing north half. Due to the angled projection of the piers into Elliott Bay, the southern portion of Pier 58 is wedged between the seawall and Pier 57 Miners Landing. There is evidence of pressure at the interface between Piers 57 and 58, and it is likely that these pressures are a direct result of the failing water feature. Civil and Structural Engineering Pier 58 August 13, 2020 Page 2 We are recommending that the entire Pier 58 be demolished. if Pier 58 were to be only partially demolished, say to the narrowest location approximately half way between the northern and southern edges, it is not certain that the southern half would remain stable. Recommended demolition, includes the ramp and deck area at the north edge of Pier 57 at the same elevation as Pier 58. We understand that there are permit issues related to the area of Waterfront Park that extends south of the property line at Pier 57 Miners Landing, and if needed these areas may be able to remain. Further investigation is required. Where the concrete water feature is failing, the timber pier structure is transferring loads to the resisting pile cluster and the south half of the pier. The observed movement of the timber structure indicates that a hinge has formed, with the center portion bulging westward. This hinging has resulted in the extreme northwest end of the pier moving towards Pier 59 Aquarium. The timber framing is not designed for these high sustained lateral loads and will likely continue to yield. Eventual failure of the resisting elements is likely as the hinging effect overcomes the north pile cluster?s ability to resist the ever?increasing loads. The consequence of this failure would be the collapse of the pier. The following are our concerns related to the collapse failure: The direction of failure ofthe north half of the pier is toward the open portion of water west of the pier. This direction of failure would likely result in the concrete water feature impacting the transformer vault on the south side of Pier 59. Damage to Pier 59 Aquarium should be limited to the transformer vault. Because the Pier 59 structure is pile supported, there is small risk of generalized failure of Pier 59. Damage to the transformer vault should be repairable. The south portion of Pier 58 currently appears to be in a stable condition under the pressures being exerted by the failing water feature. This condition could become unstable if the north pier fails. If the north pier fails, the failing pier could pull the south pier in a northerly direction, resulting in the failure of the south pier. Because of the interconnection of the south pier to Pier 57 Miners Landing, we are concerned that failure could extend into Pier 57. Recent pile replacements at Pier 57 have utilized ?stub pile? instead of driven piles, so there is not a large amount of reserve lateral capacity in Pier 57. If Pier 58 collapses, and the damage extends into the south half of Pier 58, there is the potential for some amount of apron and roof framing collapse at Pier 57 Miners Landing. The existing 6? fire main that serves the fire sprinkler room below the water feature has failed. The Aquarium is currently providing 30?minute fire watch. The following are our recommendations: 1. Continue to monitor movement of Pier 58 on a daily basis. 2. Review the support of the temporary fencing to provide a safe condition if Pier 58 fails. 3. Close Pier 57 Miners Landing to public access on the north apron and immediately adjacent building areas. 4. Close Pier 59 Aquarium south apron to public access. 5. Address access, safety and continuity of service issues related to the SCL transformer on Pier 59. 6. Restore the 6? fire main to the sprinkler system at Pier 58. 7. Demolish Pier 58 in its entirety within 90 days. Pier 58 August 13, 2020 Page 3 Please let me know if we can answer any further questions. Sincerely, oward Burton, S.E., P.E. President, Seattle Structural PS Inc. HBurton@SeattleStructural.com m/rms Waterfront Park 2020lCorresplPier 58 Review August 13. 2020 Letter