The plethora of calculations structural engineers undertake to determine whether a structure will withstand an earthquake or be reduced to firewood could fill up a wall, not unlike John Nash’s handiwork in “A Beautiful Mind.”

Sometimes, however, it really only takes a bit of common sense.

Facing an incredibly intrusive retrofit that might have cost more than $20 million, Sherith Israel called on illustrious San Francisco engineer Sig Freeman. He cracked back some panels, inspected the inner structure and figured the 100-year-old synagogue must be stronger than the city reckoned, as it had survived the last two major earthquakes with hardly a brick shaken asunder (and this wasn’t just some sort of geographical oddity — neighboring buildings were demolished in the 1906 quake).

Of course, it’s a bit more complicated than that. But the plan germinated by Freeman’s assessment may yet save Sherith Israel tens of millions of dollars and years of painstaking construction work — and has already spared congregants from being forced into temporary facilities following a February deadline the synagogue would have otherwise failed to meet.

As reported previously in j., the synagogue hopes to pull an end-around and avoid San Francisco’s rigid Unreinforced Masonry Building Codes and instead retrofit using state historical building codes, which are more open to less obtrusive methods of construction.

San Francisco officials gave Sherith Israel permission to file a state codes application late last year, and are currently assessing whether or not to grant the synagogue permission to commence its retrofit. David Newman, Sherith Israel’s president, says he has no idea how long it will take for the city to get back to him with an answer; when asked to give a ballpark estimate, he could only offer “when they tell us.”

But synagogue officials are confident enough that they’ve already hired a development consultant to begin planning for a capital campaign.

Gary Ho, the head of the city’s UMB program, said that fewer than five unreinforced masonry San Francisco structures have applied to use state codes.

Had the city turned down the synagogue’s application, Sherith Israel, like all the other unreinforced masonry buildings in San Francisco, would have been vacated on Feb. 15.

The city UMB codes would have required Sherith Israel to tear through the interiors of the synagogue walls, add steel bracing and then, in the most costly and tedious move of all, replace the shredded walls and all the historic artwork on them. State guidelines, however, would allow the synagogue to drill from the tops of the walls down and place long steel bracings within the walls without having to rip through them.

Sherith Israel will also require “tension ties” in its attic.

“When you’ve got something heavy on top of a building — like a dome — the walls want to fall away from each other” during a quake, noted Newman.

“Especially under stress, tension ties hold the tops of the walls in a relative position.”

The synagogue would also need to buttress a retaining wall and undertake some minor foundation work, as well as tackle some deferred maintenance (during Freeman’s spelunking exploration, he discovered some minor damage from The Big One in ’06). Newman is wary to put a price tag on the construction plan, but is highly doubtful it will come in under $10 million.

Newman — who repeatedly used the phrase “when the city gives us approval,” never “if” — said that even in the best of circumstances it will be several years before retrofitting is completed, which gives him plenty of lead time on that capital campaign.

So if … rather, when the city gives the thumbs-up, Sherith Israel will then submit full conceptual drawings, meaning there may be several months or even a year between city approval of the synagogue’s plan and the issuance of a building permit.

Newman is optimistic that the actual retrofitting can be done in about a year, meaning that “if the timing is right, we can do it between High Holy Days and High Holy Days.”