Help identifying design criteria - Exisitng concrete/wood platform over SF Bay connected to Levy

[MikeSFBay]

I am putting together a proposal for the existing pedestrian platform shown in the google image attached. The structure and Levy are both open to the public 24/7. I assume as part of the lease agreement the Hotel (Client) is responsible for servicing this structure. I would appreciate feedback on setting up my design criteria (assuming my proposal is executed). The PDF is annotated with existing conditions and end-use environment. Let me know if you need more information before responding. The structure consists of a series of concrete frames (width of the walkway) with glulam beams framing into seated steel plate buckets, which are in turn bolted into the sides of the existing concrete beams. A group of these steel buckets appear to be suffering from substantial rust, although I did not observe delamination. The concrete columns are founded in the bay (into what type of foundation I do not know) and the glulam beams bear on concrete pads at the street level. The scope of work includes designing/specifying replacement glulam beams for existing that are rot (one of the interior glulam beams has completely sheared off it's concrete beam-supported bucket (yikes!! Sorry I don't have photos--it's a terrible sight to see)). I read the 11 page Technical Note, Preservative Treatment of Glued Laminated Timber, Number S580D, July 2013 and understand the basic pressure-treated options available based on the end-use service condition of the glulam beam. I assume this is a marine application and all the glulam supplier websites I visited say no to the use of naturally durable species (Cedar, etc) for use in Marine applications so I'm thinking I need to specify an approved artificial treatment. Also, are there any AASHTO requirements and what is an appropriate engineering term (name) for this structure?

Thanks,

Mike (PE in California)

 

[thaidavid40]

I don't know if the original beam seats were galvanized or not, but I would strongly suggest that they be at least galvanized, if not stainless steel (preferably grade 316). I don't know what the RFP calls this structure, but I would call it a public observation pier. Ostensibly, no vehicles would be allowed, but I would design as a minimum for the weight of a small service vehicle, given the width of the walkway. The supporting frames are what I would call walkway support bents (a la vehicular bridge terminology). If there is no vehicular traffic on this, then I don't see where any AASHTO requirements would be called for. Good luck -
Dave

Thaidavid

 

[SlideRuleEra]

Agree with thaidavid40, I would call the structure an "Observation Pier". Suggest making the first item in the proposal a detailed evaluation of the substructure by a qualified inspection agency. No need to proceed with a superstructure design if there are foundation problems.

As for general requirements, I consider a live load of at least 100 PSF justified since large groups of people could gather for events and photographs.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[MikeSFBay]

I like the evaluation idea and using a small vehicle load as well. I don't think the hotel will have a problem with the glulam beams being pressure treated so I think I will not specify naturally durable wood. Should I have a third party evaluate the rusted seats or better off replacing them all?

Thank you both for the response.

 

[KootK]

I had my own boardwalk/pier design adventure recently. I found this Aussie document to be very useful with regard to vehicle loadings and durability concerns: Link. This definitely isn't identical to your situation but you may find it useful none the less.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SlideRuleEra]

Mike - I suggest having the (qualified) third party inspect everything that potentially will be reused. Got to do "due diligence" to protect yourself.

Some years ago I was involved in the design of a lengthy elevated pedestrian walkway. The suggestion to include provisions for ATV is good, and we did so on our project. FWIW, after consideration we selected a John Deere "Gator" as a reasonable representative vehicle. Manufacturer's technical info, such as axle loading, wheel base, etc., is readily available.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[BUGGAR]

Do you have a design lifespan? I suggest that the San Francisco Bay is a pretty severe marine environment for glulams expected to last any length of time. Notice how all the piers around S.F. that have survived (excluding those lost to fires) are made of heavy timber.

 

[MikeSFBay]

BUGGAR, I do not know what the design life span is and I can only guess that the platform has not been serviced in at least 5 years, likely more. The concrete bents appear to be in a serviceable condition and I observed only minor cracking and little discoloration (on the beams). This is a good question to be addressed with the client. The contractor notified me that he spoke with the City and they have certain standards applicable to SF Bay Area marine structures that should be followed. I will learn more in the upcoming week and share. The link KootK provided above contains a section regarding fire, which I had not considered. I have to look into this as well, especially with treated timber, considering environmental consequences if treated timber catches fire over the Bay.

KootK, excellent resource. I browsed through it and will look into the particulars. It does a good job of capturing the intent of my OP, which was to determine the design criteria for this project. Thanks!

 

[MikeSFBay]

SlideRuleEra, I mentioned the use of a qualified third party professional to inspect the structure to the contractor and he agrees. I do not want to get in a situation where we do a surgical job and leave the platform in a potentially hazardous condition by not revealing all the existing conditions that also require servicing. I have a feeling this is going to come down to a cost consideration with the Client (as opposed them magically agreeing to replace all the potentially deficient components in one go). We will see. A middle ground would work for me where we have the inspection to at least provide a health report of the structure. Otherwise we would have to rely on my observations to determine which additional scope is required. And I'm not a qualified inspector by any means.

 

[MikeHalloran]

- I don't know what word they use in SF, but in Louisiana, the berm that keeps the water away from the valuable real estate is called a 'levee', and is pronounced like Eugene Levy's last name.

- If a Crown Victoria will physically fit on the pier, you will find one there someday.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeSFBay]

Thanks for the spell check Mike. Thought it was off. I wonder if Eugene is a qualified inspector.