What are those round disks along the top of the façade?

AS WE PREPARE for our waterproofing contractor to refresh the stucco of the façade (and then cover it with an elastomeric coating) this summer, my attention has been drawn to the 8 disks displayed across the front of our sanctuary, near the roof line (see photo). 

(As usual, click/tap on an image to enlarge it.)

 
“What are those disks?” I have been wondering. Are they aesthetic features, or are they structural elements? If structural, what are they made of, and what is their internal structure? Does their integrity need to be checked periodically? 

The Historic Structure Report (2003) used the label “seismic plates” to describe them. So that’s the label I used in annotating the photo, above. Below the jump, I share my doubts that this label is correct.…

In April, I wrote to the structural engineer Jim Farasatpour, who has advised us in the past. I showed him that photo and I asked for his comment. He replied:

Yes, they are indeed [a] structural member and they are called seismic plates. These must have been part of some sort of seismic upgrading [that] was done back then.  Basically they are the end of the “wall-ties”.   

We have learned that certain buildings in an earthquake, the exterior walls will separate from the roof (or floor) structure and cause [a] total collapse of the building. So, the retrofit building code required to literally tie the roof (or floor) to the exterior walls. And these ties are made of steel rod/plate that extend inside the building and connect to the roof structural members and puncture through the exterior façade; and to hold them together (hold the wall to the roof structure) we install these sort of washer plates.

Jim’s answer is enlightening as to prevailing practice. However, as I have thought more about the matter, I have become skeptical that for this building, there was ever a seismic retrofit per se. There’s simply no other evidence of it. 

Furthermore, there is some counterevidence. First, those disks do not appear on the east or the north sides of the building—only on the west and south. 

Second, on the south side, the wall is already tied to the roof via the tied trusses that rest on top of the pilaster posts. 

Third, according to the HSR architectural drawing of the south side (which might not be accurate), the position of the plates’ center is actually above the roof, on the parapet portion. (However, the as-is drawing might not be accurate in that particular detail.) 

South elevation - upper detail

Transverse section
(red line extends behind the center of a disk)

Perhaps the disks are helping to anchor only the portion of the wall (including parapet) above those posts? That seems unlikely.

Could these disks simply be aesthetic elements? Until today, I had no photograph or description from 1948 to verify whether those disks were part of the original construction, which would tilt the balance toward the “aesthetic” explanation.

Then today I found evidence online that those disks were indeed original—not part of a seismic retrofit. In the photo below, I highlight one of them via a magnifying glass.

September 1948

(For more on the Santa Monica History Museum’s archive of Mishkon photos, see my post here.)

Consequently, for now I am inclined to think that the disks are cosmetic elements.

Jim’s response on May 30

Jim was kind enough to read over the above post and offer further thoughts, as follows:

Even though they might be from the original construction, still I do believe that they serve a structural purpose. If I understand the historical picture correctly, most of these plates happen at the top of the columns — indicating some sort of fastening of the top of these columns to the rest of the structure. Remember in those days we certainly did not have some of the (manufactured) connectors that readily we use in our wood structures today.

Another potential scenario [on the south wall] could be that they are “parapet braces,” which are very common applications and code-mandated for parapets.