Pier/column development length

[BridgeEI]

A sr. engineer has been checking a set of plans that I had done a while back and questioned the development length of the reinforcing in the column to the pier cap. I used the basic development length, but did not include any modification factors. Would you use the basic development length or apply the factors to it? No damage has been done, just a QC check, i'm just frustrated that I would have missed that....

 

[asixth]

Were they modification factors that increased or decreased the development length and what was the bar size which you were devloping?

 

[crossframe]

Generally that will depend on the specifics. Bars lapped or just embedded? Epoxy coated or not? All splices at same location? There's usually nothing wrong with extra embedment as long as the bars fit, but the modification factors are there for a reason.

Even if you don't use the modification factors, you should make it clear to a checker that you know you're not using them and the rationale behind it. A senior engineer will not know what you were thinking "a while back."

 

[BridgeEI]

The bars are epoxy coated and are just embedded into the cap, they aren't lapped or tied to any other bars. The factors would increase the development length. I have no problem w/ adding extra steel, after all it can't hurt until a certain point anyways. I have sets of plans (from more experienced engineers) that show it both ways. Anyways I'm just adding the extra length to the bars and will keep this is the back of my head for future projects.

 

[asixth]

Epoxy coated reinforcement should have the modification factor applied to it because of the reduced bond strength. Was the bridge stamped for construction and had the reinforcement been scheduled before the QC check pick up the error.

As for the two sets of plans that show it both ways. You should make the assessment of whether the details are correct. Like yourself, I spend endless hours reviewing design drawings 'by others' to find an industry standard ways of doing things. Personally I hate seeing two sets of plans design the same element differently, particular when the plans are coming from the same office.

 

[tumbleleaves]

If you don't mind me asking, why were the bars epoxy coated? I have not designed a significant bridge structure in years+, and never used epoxy. So your response would educate and benefit me.

My present memory (though hazy) was that the development length was increased even beyond the "factors", since EQ was always controlling (in my limited experience) and it was necessary that the plastic moment functioned.

 

[BridgeEI]

Final plans hadn't been submitted so there wasn't any harm done, just bruised ego's. Preference of the DOT, the cost is virtually the same as non epoxy coated.

 

[NashBridges]

In response to tumbleleaves, we epoxy coat all bars in northern Utah. This is done to minimize corrosion due to the heavy use of salts for road maintenance.

If BridgeEI's bridge is in a seismic zone (SDC C or D) and you are applying AASHTO's Guide Specifications for LRFD Seismic Bridge Design (2009), then your requirement for development length should be based upon section 8.8.4 of that guide specification. Interestingly, you find that the embedment length is smaller than what is recommended by the AASHTO LRFD Bridge Design Specifications. However, it is recommended that the column longitudinal reinforcing be exteneded "as close as practically possible" to the face of the cap beam.

 

[tumbleleaves]

Epoxy coated appears to cost about two or three times as much per pound?

I have shied away from specifying epoxy coated bars because my understanding was that they needed special handling and inspection. My understanding was that if the coating is damaged the bar can corrode at an accelerated rate where it was damaged. I specified galvanized bars in the few and minor instances where additional protection was required.

However, I suspect galvanized bars are likely cost prohibitive (for other than minor use), and the sacrificial coating may be depleted by continuous ionic exposure.

I remember being very conservative with plastic moment design. Also, I take the AASHTO code with a grain of salt and was sorry to see the old spec's go.