Apartment Building Collapse - Part 2

[Sym P. le]

Apartment Building Collapse - Part 1

 

[Sym P. le]

City of Davenport Iowa - Information Update as of September 7, 2023 | Report Details Causes of Partial Collapse of 324 Main Street, City releases study by SOCOTEC Engineering and White Birch Group LLC

1. Root causes of collapse:

1.1 Inadequate Capacity of Wall System
1.2 Inadequate Shoring


2. Proximate causes of collapse:

2.1 Improper Understanding of Original Building Construction
2.2 Inadequate Construction Documents
2.3 Neglect of Composite Wall
2.4 Inadequate Oversight of Repairs
2.5 Inherent Weakness of West Wall
2.6 Inadequate Repair Techniques
2.7 Inadequate Frequency and Type of Maintenance

 

[IRstuff]

TLDR

https://www.iowapublicradio.org/ipr...ntable-davenport-building-collapse-and-deaths

pursuant to 2.1 above, the people working on the building apparently thought the brick was veneer, rather than structural

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

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[Sym P. le]

SSE May 24, 2023

Select Structural Engineering assumes no liability on construction or demolition means and methods.

Clearly, SSE is referring first to the two window openings and adjacent pilasters south of the infill door and secondly to the plain wall area north of the door. In the first instance, they loose the scope of the structural implications but then return focus to exactly that for the area north of the door. This may have been misleading to the "contractor" though no apparent effort was made to shore the structure in either case. I doubt anyone can mistake the bracing as an adequate measure to support any part of the structure other than to mitigate safety concerns of falling materials (not whole wall sections).

SSE supervised successful repairs further south complete with shoring, so I'm reluctant to conclude they were unaware of appropriate measures and question whether the "contractor" was competent to undertake the task. I do question the propriety of extending adjacent outer wythe remediation without a means of ensuring the structural capacity of the cross section.

The issue of the outer wythe being a veneer or structural is a significant concern. Any competent professional should have been up to speed on the structural implications. Yes it is structural, yes it had been compromised by inadequate previous repairs. It is not surprising that many uniformed onlookers have concluded that it is a non structural veneer. The one caveat is that window openings are not structural in the initial structure.

I suspect SSE is not completely in the clear w.r.t. liability, but at least they included a c.y.a. clause for comfort.

 

[IRstuff]

Regardless of what they say, "multiple wythes" removed is damning.

The removal of multiple wythes of masonry during the repair work in the three days preceding the collapse severely compromised the western bearing wall and caused it as well as the areas it supported to collapse on May 28, 2023.

The engineers and masonry contractors responsible for repairs to the Building repeatedly misidentified the structural bearing wall as a nonstructural system. As such, they underestimated the significance of the observable signs of distress in the wall, delayed necessary repair work, designed and installed a weaker replacement system, and removed significant portions of the wall without first installing adequate temporary shoring.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Sym P. le]

Given that multiple wythes were already compromised from inside and out, the structure was already fully compromised. "Removing" becomes a matter of semantics. I wonder if the engineer is just going to claim that the "contractor" barged ahead without them.

The point loads of the east-west beams under five stories seem to be the main point of failure. Also, I didn't catch whether the plumbing stacks were part of the original building design or hacked in as a plumbing upgrade. They further compromised the bearing capacity under the beam point loads allowing the upper floors to sag and bulge the outer wythe time and again.

 

[KRZ.13]

Sym P. le points out that SSE supervised successful repairs further south complete with shoring, but it should be mentioned that the mason on the earlier repairs was not the mason performing the work when the building partially collapsed. Recall that the owner of the building has a disagreement with BSM over a change order (likely the additional cost associated with the City's requirement for a brick veneer to match the historical envelope of the building). The inspection photos taken by the city also illustrate that the degree of shoring drastically decreases between the two projects. If I recall correctly from the permits pulled at the address, BSM took out the permit for the work performed on the south end of the building, but the owner took out the permit for the work leading up to the collapse, which raises the question of whether or not the owner decided to self-perform the work with their own crew. I didn't see anywhere in the WBG/SEI report where they discussed the interior beam shoring or the installation of the W6x15 and concrete pilaster the Select Structural called for. Was that work performed prior to the brick removal or not? I do disagree with the WBG/SEI report that Engineers thought that the wall was a nonstructural system. Both firms recognized that the wall as a whole was a load bearing structural system, but I gather they were under the impression that outer weathering wythe was the problem. I will caveat that with the SSE February 28th Addendum Figure 3, which proposed an exterior grouted CMU wall with a void between the interior and exterior CMU and didn't account for the City's requirement that the new exterior masonry match the existing appearance of the building.