1913 One-Way Slab 1

[JohnnnyBoy]

We are doing an analysis of an existing wharf structure built in 1913 that utilizing a one-way slab to transfer the load to timber pilecaps and bearing piles.

I am trying to complete a rough analysis for a one-way slab to ensure it can handle the current building code loads (canada). The issue I am running into is that the concrete was poured using round beach stone and smooth rebar. I am a fairly new engineer and have only dealt with the new generation of concrete codes. Does anyone have a guide I could follow (1910 era) that would help me in the analysis of the slab.

Further, there is many areas of spalling on the underside of concrete so these would need to be handles differently. (Concrete repairs)

 

[r13]

Do not bother use the old code, as your effort is bring it up to date. Take a core sample and analyze the bar grade, and strength of the concrete, then analyze the slab using the resulting data.

The linked paper, titled "A Guide to Historical Reinforcement", issued by Steel Reinforcement Institute of Australia (SRIA), is for your information use. Link

 

[Tomfh]

Agree with retired13. Assess the steel and concrete strength and take it from there.

There’s also the issue of stress development. Old round bars take longer to develop than deformed bars. From memory my Hool and Johnson Concrete Engineers Handbook from that era specified development lengths roughly twice that of deformed bars.

 

[catsndogs]

The normal live loads on a wharf are far greater than anything in the building code. And I imagine that the slab you're looking at is massive. Commentary L of NBCC would allow a structural assessment based on satisfactory past performance. That doesn't mean you can add concentrated loads anywhere you want. You'll have to plan that carefully. But perhaps it is better to start by determining whether the remaining service life of the structure is appropriate for whatever use you have in mind for it.

 

[robyengIT]

Google : FHWA - HRT - 16 - 012
furthermore attached doc

 

[Settingsun]

Here on the other side of the world, the concrete deck was often added many many years after the wharf was constructed, poured on top of the original timber deck. Not sure whether the same could be the case in Canada but worth checking if you're just assuming the deck is as old as the wharf.

Whatever the age of the slab, it may have been designed conservatively compared with current ultimate limit state procedures. Be careful not to compromise the durability by not checking whether soffit cracks are widened by increased loads.

 

[r13]

But perhaps it is better to start by determining whether the remaining service life of the structure is appropriate for whatever use you have in mind for it.

Yes. the above is a sound suggestion. As you didn't mention any noted problem of the current structure, therefore the capacity likely is there, and the system has worked satisfactory for the past/present use. Then, it is a wise move to assess how much damage you are going to deal with, can those damaged areas/elements be restored for durability without doubt, and will that efforts be cost-benefit effective, before been distracted by all those calculations.

 

[kipfoot]

As others have suggested, use modern codes and material properties appropriate for the time of construction for your rough analysis. This linked file is from Kidder Parker, a bit later than your construction, but you'll see that concrete strengths topped out at 3000 psi. (the subsequent pages give some background in working stress design, if you're interested) This will get you started, but testing core samples will give you better justification when the owner's spending real money.

Other things to consider:
[ul]
[li]Spalling is commonly related to rusting steel. A thorough sounding of the concrete may be in order;[/li]
[li]If you're patching this old concrete, be mindful that it's important to have compatibility of patch material. A new material at 6000 psi will have a different E and different thermal properties than the original conc.[/li]
[li]Your new use may require a loading that is significantly less than the original design use.[/li]
[/ul]

 

[NorthCivil]

my thought: material properties of the concrete will vary a lot across the field of the slab. how many core samples will you need to take to get a good overall idea? and how many cores are we keen to punch into a 100 year old slab?

 

[r13]

NorthCivil's concerns are valid, unfortunately at least a few cores needs to be collect for calibration purpose (exact number shall be determined by the lab), and accompanied with NDT method as noted below.

Existing Structures
NDT methods can be helpful to map compressive strength variations in a concrete structure. To do so, a combination of Ultrasonic Pulse Velocity (UPV) and Rebound (Schmidt) Hammer can be used to evaluate the in-situ compressive strength of concrete. A minimal number of concrete cores should be drilled within the concrete in order to calibrate the employed NDT methods. The compressive strength map would be generated using the employed NDT methods based on the former calibration. Breysse (2012) presents a comprehensive literature review about non-destructive evaluation of concrete strength.

Hope the above helps.

 

[STrctPono]

I have analyzed lots of bridges over 80 years old and quite a few over 100 years old. The oldest bridge that I ever had to analyze was from 1911 so I appreciate this project. Bridges are very much like piers/wharves in many ways.....

1. How do you know that the pier utilized smooth rebar? Do you guys have as-built drawings for it? If plans are available, in my experience, they will probably be in rather rough shape and might be hard to read. I would be very interested to see the existing as-builts if you have any. Any way you can post them?
2. I am surprised to hear that they used smooth bar because even in the early 1900's before rebar was standardized, all the individual proprietary manufacturers of reinforcing steel understood that incorporating deformations of some kind onto the surface of the bar improved mechanical bond and development length. For all the old bridges that I have analyzed, I have never had one with smooth bars.
3. Unless the as-builts specifically state it or you have done destructive testing the general rule of thumb for bridges, is that for a structure that old, use 2,500 psi concrete and 33,000 psi steel. Now, if this wharf were a privately owned wharf (not one maintained by a government agency) I may even be more conservative because whoever built the wharf may not have had any standards to follow.
4. Nevertheless, CRSI has published a "Comprehensive and Invaluable Treatise on all Forms of Steel Reinforcement Employed in the Design and Construction of Reinforced Concrete of Long Ago." I think you may find this interesting with useful information.
Link
5. When trying to figure out how the spall affects the capacity...... The way FHWA does it is that the Feds assign different condition factors to structural elements based on their condtion. For instance, a GOOD condition would have a condition factor of 1.0. A FAIR condition would have a condition factor of 0.95. And a POOR condition would have a condition factor of 0.85. If you have very large noticeable areas of concrete spalling with lots of reinforcing steel section loss then you may be able to analyze the capacity of those areas based on the amount of remaining steel. This will require Engineering Judgement.

 

[Agent666]

Codes like ASCE 41 for the assessment of existing structures will also contain general guidance on concrete strengths, reinforcement strengths for the assessment of existing structures. My local codes for this sort of thing basically provide values to use, typically for the ocncrete take 1.5 times the specified strength, and for rienforcement 1.08 times the specified strength to get to a probable strength. I believe ASCE41 uses similar principles/relationships.

Remember that given that its a wharf structure and general age (>100 years old) that testing for carbonation depth and chloride ion ingress might be quite important to establish current durability state to see if this needs to be addressed.