Understanding what happened to Pier 58

Late afternoon this past Sunday a portion of Pier 58, better known as Waterfront Park, collapsed as construction workers were beginning the work to carefully dismantle and remove it.  Let’s look at what led to the collapse, where things stand now, and what happens next.

 

 

Waterfront Park was built in 1974 at Pier 58, between Miner’s Landing (Pier 57) and the Seattle Aquarium (Pier 59). There have been several changes and refurbishments along the way, including removal of the two original observation towers, the addition of a Seattle City Light electrical vault in 2006, and a rebuilt seawall over the past two years. The pier covers just over 48,000 square feet, in a crescent shape with the southern terrace wedged in between Pier 57 and Miner’s Landing and the northern terrace extending to the northwest paralleling the Aquarium.

Pier 58 Waterfront Park, standing on the south terrace looking north.

While most of Pier 58 is wood, a large section of the northern terrace is concrete, with multi-level plazas, planters for trees, and the well-loved FitzGerald Fountain. On the underside, the wooden areas are supported by pilings made out of creosote-treated wood, and the concrete areas are held up by a combination of steel H-beams and steel “monotubes” filled with concrete. Underneath the concrete areas is a “pump house” feeding an under-the-pier sprinkler fire suppression system.

After a series of pier collapses between 1979 and 1990, the Seattle Department of Construction and Land Use (now SDCI) issued a Director’s Rule establishing a mandatory waterfront pier maintenance program, including required inspections of all the wood pier components (deck and pilings) every five years.

Pier 58 had all the SDCI-required inspections. Most of the attention was paid to the wooden pilings, which as can be expected were showing steady deterioration over the years. Pilings are rated as to how much of their original strength remains, from 100% (good as new) down to 0% (failed).

Here’s a chart that shows how the wooden pilings on Pier 58 were rated over the years:

Source:
Source: Seattle Structural PS Inc. Piers 58, 59 and 60 Timber Piling Inspection, 2016

The 2006 report found some timber pilings reaching the end of their useful life, corrosion on the H-pilings and monotube pilings, and also rust on some of the concrete beams on the underside of the north terrace (signifying that the reinforcing steel inside the concrete was corroding). It recommended a list of repairs to be made immediately, at a cost of about $950,000, or a full set of repairs to return the pier to near-design-capacity for up to $1.5 million — including $340,000 to repair and strengthen the monotubes and $100,000 to repair the “cathodic protection” system for the H-steel piles. Alternatively, it estimated that demolition would cost in the $300,000 to $450,000 range, and suggested that the city faced a major decision point on the future of the pier. If the repairs were not made, then it recommended placing load limits on the wooden portions of the pier by restricting the size and weight of vehicles.

The 2011 report also found that there was heavy corrosion on many of the steel and monotube pilings supporting the concrete area of the north terrace.  Around the time of the 2011 report, two things were happening: first, the city (and country) were just starting to work their way out of the Great Recession; second, the plans for remaking the waterfront were just starting to come together. The Seattle Waterfront plan included demolishing the aging Pier 58 and building a new pier to replace it. With that context, the city chose not to spend large amounts of money on ongoing maintenance for the existing Pier 58 (which would include piecemeal replacement of wood pilings as their condition worsened). Having communicated the budget restrictions, the 2001 report focuses on increasing the load restrictions: banning all vehicles, discouraging large groups of people from congregating in any area of the pier, conducting annual load tests, and planning to remove the south observatory tower. It also recommended annual row-through inspections underneath the pier to monitor for ongoing deterioration. It also included the following ominous conclusion:

The concrete superstructures of the north and south terraces, the north terrace apron, and the promenade will eventually need to be repaired, replaced, or demolished. The north terrace in particular has serious reinforcing steel corrosion that may not be accelerating at this time but is on-going. All of these areas are supported by Monotube piles and steel H-piles that have serious corrosion. The cost of repairs or replacement would be high.

In response, the city put load restrictions in place, and stopped hosting concerts on the pier. There is no indication that they started annual row-through inspections at that time. UPDATE: a spokesperson for Seattle Parks and Recreation says, “Specific row through inspections were not done annually, though staff were underneath the pier a few times each year for other work, and communicated any concerning observations.”

Here’s a collection of photographs of corroded pilings and beams from the 2011 report:

The 2016 report only inspected the wooden pilings; it makes only passing mention of the steel and monotube pilings, and provides no update on their condition other than copy-and-pasting the above warning from the 2011 report. The news on the wooden pilings was not good, though: the deterioration had continued if not accelerated, and a large fraction of them were critically near their end of life. At this point, the plan to replace Pier 58 around 2022 was established (and budget constraints continued), so the report continues to focus on recommendation to continue the load restrictions — though it renewed its urging that the city conduct annual row-through inspections.

Between 2016 and 2020, the Seattle Waterfront renovation plan advanced, the seawall was replaced, and funding was secured to replace Pier 58 in 2022 (part of a long sequence of carefully orchestrated projects in the master plan). But on August 6 — five weeks ago — the trouble started when the water main feeding the Pier 58 fire suppression system broke. Seattle Structural, the company that had conducted the 2011 and 2016 inspections, was called out, and discovered that the pier had shifted sideways (aka “lateral movement”) up to twelve inches, opening up a gap between the structure and the seawall. Lateral movement is a very bad sign: piers are designed for vertical strength, but minimal lateral strength — enough to withstand wind, waves, and earthquakes (though it had been noted in the earlier inspection reports that Pier 58, as built in 1973, was not up to current earthquake code anyway). The city responded by immediately closing Waterfront Park, fencing off the pier, and requesting that Seattle Structural return in the following days to do a full inspection to determine the cause of the lateral shift.

On August 10th, Seattle Structural found the cause, as described in their summary letter on August 13:

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 the movement is westward. This movement is being resisted by two primary elements: the adjacent structures in the south half of the 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 the 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.

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 northern edge of Pier 57 at the same elevation as Pier 58…

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.

In English:

  • The monotube and H-steel pilings supporting the concrete area of the north terrace, and particularly the fountain, failed at the point where they connect to the platform above, and the concrete terrace is sliding westward out into Elliott Bay — pulling the rest of the pier with it. But the pull is being resisted by the southern terrace, and by the cluster of extra wooden pilings where the old north observatory tower used to stand.
  • The thin part of the pier between the north and south terraces has turned into a hinge, with the south terrace twisting counter-clockwise and putting pressure on Pier 57 and the north terrace twisting clockwise and moving closer to Pier 59. This is putting enormous lateral pressure on the pier, beyond what it was built to withstand even when its pilings were in good shape (which they are decidedly not now). The movement of the pier is the beginning of the failure of the pier under that stress, at which point it will collapse — probably all of it because the northern terrace was partially supporting the southern terrace.
  • The pier is failing: it is in a very slow process of collapsing.

Seattle Structural recommended several steps:

  1. Continue to monitor the movement of Pier 58 daily;
  2. Review the perimeter fencing to ensure that it will remain up if the pier collapses;
  3. Close the north apron of Pier 57 “and immediately adjacent building areas”;
  4. Close the Pier 59/Aquarium south apron/access road to public access;
  5. Address the potential issues if the electrical vault were to be impacted by the collapse of the pier;
  6. Reconnect the fire-suppression system;
  7. Demolish Pier 58 within 90 days.

The city (a combination of the Parks Department, the Office of the Waterfront, and SDOT) kicked into gear. They issued a $120,000 emergency contract to Seattle Structural to design and plan the complicated process of safely demolishing a pier already in the process of self-demolishing, and another emergency contract to Orion Marine Construction to do the demolition and salvage work. The Orion contract was issued on August 26 for $4.3 million, calling on the company to work six days a week on the project. Orion’s first barge arrived at the site on September 4. In the meantime the pier was being monitored daily, and digital monitoring equipment was installed that would give an audible alarm if movement above a certain threshold was detected.

And there were indeed small amounts of additional movement in the intervening weeks: according to city officials, about 1/4 inch per week. But on September 11, that changed: there was a significant increase in pier movement. The city and the two companies quickly confirmed the demolition plan, which would prioritize removing the concrete area of the north terrace since it was the apparent source of the lateral movement. They also accelerated the schedule to seven days a week beginning the following day (last Saturday, the 12th). On Saturday demolition began, starting with non-structural items on and around the concrete part of the north terrace: planters and other decorative items — some of which were intended to be eventually re-installed on the replacement pier, including portions of the FitzGerald Fountain. A safety plan was in place that limited the number of workers on the pier at any given time, required the workers to wear personal flotation devices, instituted daily safety briefings so that precautions could be modified from day to day as the project advanced, and kept tight control on the site. Unfortunately, the nature of the work required workers to be out on the pier: the pier components (including the concrete) needed to be cut into smaller pieces and then attached to a crane so that they could be lifted out. But the contractor has chosen an approach and tools to break it apart (saw-cutting) that minimizes the weight of equipment on the pier.

A picture of Pier 58, taken one hour before the partial collapse on September 13. Photo credit: Alexey Merz

Then on Sunday afternoon, it happened. As you can see from the video provided by the city, the section of concrete pier underneath the trees gave way and fell straight down, pulling the rest of the concrete area down behind it. In all, about 15,000 square feet of pier (just under a third) collapsed into the water, including the fountain and the pump house. There were seven workers on the pier at the time; the movement alarm went off as intended, and five of the workers made it off safely. Two went into the water just south of the north terrace, and were quickly pulled out even before the fire department arrived on the scene. SFD medics treated them for injuries and then transported them to Harborview, where they were in stable condition.

There was no damage to Piers 57 or 59, to the seawall, nor to the electrical vault (which you can see still standing in the top right corner of the video, right at the edge of the collapsed area).


What happens from here? The city and the two contractors have several immediate tasks:

  • Ensure that the site (and the adjoining piers) are safe.
  • Establish a new baseline for the demolition project, and assess the best sequence to move forward with the demolition project. The remaining pier is still on the verge of collapse, and it is just as urgent, if not more so, to safely demolish it as soon as possible.
  • The new challenge: now instead of cutting up and removing the pier, they must cut up and remove a big pile of concrete that is sitting underwater — currently surrounded by unstable wooden pier. According to the city, the submerged pieces of concrete are still too big to be hauled out by crane, so the hard work just got harder.

The city and Orion are still reviewing the incident, and they have been joined by the state Department of Labor and Industry, which apparently often comes out to sites after major incidents to investigate the situation for workers.

It’s still an emergency demolition, but they don’t yet have a new plan or timeline for finishing the job.

Longer term, there are some interesting issues to be sorted out.  As for the replacement pier, the partial collapse of the old pier probably doesn’t change the plan or the timeline; while the demolition was accelerated, building the new pier wasn’t (it’s partially dependent on Waterfront LID funding).

This incident also raises an important policy question: whether SDCI’s thirty-year-old director’s rule mandating the waterfront pier inspection and maintenance program needs to be updated. Clearly there’s a demonstrated need for it to extend beyond just the wooden components of piers. And I expect that SDCI and the Office of the Waterfront will want to review the inspection status for all the waterfront piers to ensure that they have been looked at recently and are in decent shape.

And there are still some hard questions that need to be asked about this specific incident. The city was on notice for nearly 15 years that the pilings — including the non-wooden ones — were in bad shape, and yet it deferred nearly all maintenance because it knew it would eventually demolish the pier, opting instead to lighten the load on the pier instead in the hope that they could squeeze a few more years out of it. And it appears that they did the bare minimum required inspections on the pier, which were not sufficient given the well-known deterioration that was occurring.

There is much more to coming in the ensuing weeks and days.


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One comment

  1. It appears possible that the crane which was attempting to lift the concrete barrier (attached to the pier) actually shifted and distorted the entire pier to the point that the portion to the left (in the video) broke first. The video shows the crane cables under considerable tension. The crane operator would normally apply some tension until that piece was cut free. Perhaps the crane operator was in a hurry to separate that piece and applied excessive lifting force. In the world of construction, contractors are required to stabilize shifting structures before sending workers out onto them or into them. There is a clear failure here to follow the correct procedure. Prediction: L&I will slap their wrist with a minor fine, just like the Seattle Tower Crane failure. The two questions which will get swept under the rug are: 1. How much lifting force was being applied at the time of failure? 2. What structural basis did the Contractor use to verify that the structure was sufficiently stabilized for workers to enter?

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