Updated, Dec. 14

The Mercer Island School District released a summary of the latest earthquake safety review of the former North Mercer middle school buildings Wednesday morning, confirming fears that walls in a portion of the building currently used by Youth Theatre Northwest could collapse in a catastrophic earthquake.

Structural engineering consultant PCS Structural Solutions issued a Dec. 11 report on reviewing the wall reinforcment to columns, roof and concrete foundation designed to withstand an earthquake at both buildings on the North Mercer Campus. PCS vice president Jim Collins reported engineers used magnetic sensors to check for additional support for the walls and discovered an addition to the south of the North Mercer Gymnasium — called the "Music Building Addition" — lacked any reinforcement to the exterior masonry walls. The addition is a series of large rooms used by YTN as classrooms and a "second stage" for performances by smaller ensembles and younger members.

The addition, according to the report, is covered by a wood roof and supported by a 2-by-8 wood frame superstructure sheathed with plywood. The exterior walls are a veneer wall constructed with concrete masonry units (CMU) (sometimes referred to as "cinder block") that "rely on the tensile strength of masonry units, mortar and grout to provide structural support." But the masonry wall, said the report, are not anchored to the structural wood stud wall.

According to the report:

"ln an MCE (Seattle Fault) type seismic event the wood superstructure would perform less than new construction and likely sustain structural damage. The masonry veneer, assuming lack of anchorage as indicated by field test, would fall away from the building. The veneer is a localized lifefsafety issue and does not affect the overall seismic performance of the building."

Youth Threatre Northwest Executive Director Manny Cawaling said he would reserve comment on the report until it was presented to school board directors at their next meeting.

School board directors asked for the additional report to help them decide if there is a "Life/Safety" issue, which could result in serious injury or death of the building's occupants. The board must now decide whether or not to reinforce the building, which a citizen's panel on facilities planning did not recommend for immediate redevelopment in their report earlier this fall.

Concerns about the building are one of several issues the Mercer Island School Board will consider at their Dec. 15 meeting.

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Original Story:

The Mercer Island School Board may be forced to close buildings used by Youth Theatre Northwest that drew additional scrutiny following a seismic safety review of the facility last month in the event of a major earthquake.

As first reported by Mercer Island Patch in November, an independent study comissioned by the Mercer Island School District revealed concerns about the theatre's south classrooms at a Nov. 29 board meeting (PDFs of the study and the Dec. 15 school board agenda are attached).

The school board allowed additional study of the building after MISD Superintendent Dr. Gary Plano alerted them of the possibility that lives could be at risk if the masonry walls were not re-inforced and failed in a major earthquake.

The report anticipated that, in an extreme earthquake or "Maximum Considered Earthquake" (MCE) event (a 2 percent probablity of being exceeded in 50 years), the south classroom area of the North Mercer Performing Arts/Gymnasium "has the potential for collapse, with the lack of positive anchorage of the wood roof structure to the walls." The MCE standard is the latest design standard for new school construction. It also noted the walls appeared to be the only load-bearing structures in the building.

"Without reinforcing, the walls will continue to fall apart in the event of a major earthquake," stated the report.

A "major" earthquake is defined as having a 10 percent probability of being exceeded in 50 years, or likely every 450 years. The report concluded that it was unclear if the necessary reinforcement to prevent collapse was present in that part of the building — even during a less severe earthquake.

"It raises a concern of life safety, said Plano. "We may need more money to reinforce the walls, or closing the building may be necessary because we could risk collapse ... The building was built using the 1958 building code and hasn't been renovated since then. It's a dilemma that we have to face."

A recommendation from the 21st Century Facilities Planning Committee (21 CFPC) to review the structural integrity of all buildings prompted the report, which was conducted by PCS Structural Solutions. YTN's buildings are leased from the school district.

According to YTN, the building affected houses the threatre's Studio Stage, Craft Room and Blue Room. The Studio Stage is the theatre's "second stage" and features performances by younger thespians — such as a planned spring performance of Peter Rabbit — which may be moved to an alternative location.

"We will find solutions," said YTN executive director Manny Cawaling. "We're all in this together." 

A 2 percent probablity every 50 years means there is a 50 percent chance every 2,500 years that an earthquake of that magnitude could strike Mercer Island. Geologists recently discovered Mercer Island is situated directly over the Seattle Fault, and a shallow earthquake could cause significant damage to local buildings.

"We're grappling with the big issues, Cawaling said. "We'll figure out a solution, but we're looking for a little help. We trust the school board, and we thank them. They care a lot about the kids on MI and I really appreciate working with them."

The additional testing and analysis on the YTN building will be presented to the Board and community at the School Board meeting to be held this Thursday, Dec. 15, at 6 p.m. in the school district board room.

(Ed. Note: An earlier version of this story appeared to imply engineers found that interior walls of the "Music Building Addition" could collapse. This was incorrect — only the exterior walls were found to be susceptible to falling in a catastrophic earthquake. Additional techincal seismic information was also added to the most recent version of this story.)