Verifying Basic Information on Engineering Calculations

[jar546]

**NOTE - This is informational only since we have some difference of opinion as to what the purpose of plan review is and how far we are suppose to take it. Today I had one such example of why we need to be familiar with the basics to ensure the correct submission was made. Yes having an engineer or architect would be preferable but that is not always possible in 90+% of municipalities. Here we go.

I have a condo on a barrier island in a 170mph wind zone. The entire island has been deemed Exposure Category D. A new impact slider is being installed on the 5th floor of a 126' tall high-rise condo. The initial submission for wind pressures from the GC came from his PE and looked like this: (partial view)



Unfortunately he used the wrong Exposure Category of C and has the building height way, way off at 45'. This changes the pressures significantly, enough that it may require a different product to meet the positive and negative pressures. After rejecting this from the PE, he was thankful that the error was caught and resubmitted calculations that had at least the correct data. This is important to us because we now have in our possession the design requirements for this installation that shows the correct Wind, Exposure and Roof heights and the pressures are now more consistent with similar projects with similar sized sliders.

Here is the revised calculation (partial):



The design pressures need to be a minimum of +59.64psf and -75.39psf

Unfortunately the slider proposed has a maximum pressure rating of:


This is why I feel it is so important to verify as much as you can within the scope of your job. Around here it is expected that you do this at a minimum. Thoughts?

 

[RLGA]

It may not be a plan examiner's responsibility to verify every component on a building, whether a structural engineer or not, but if the plans examiner does notice a discrepancy, I would bet that the design professional would be appreciative of that feedback.

In your situation above, the architect may have selected a slider based on the first set of calculations prepared by the structural engineer. When the errors in the calculations were caught during the plan review and corrected by the structural engineer, the architect may not have been aware of the change in pressures; thus, the slider selection was not changed.

Had this gone to construction (since this is a high rise, I would venture to say there are many sliders on the project) and there were multiple failures, the architect would likely be found liable and the structural engineer would probably escape any legal action, even though it was probably the incorrect calculations that may have caused the problem to begin with.

I have to admit that my statement above is conjecture, but is conceivable.

 

[e hilton]

The tenants would have sued the developer and builder, and only the lawyers would have benefitted.

what are the +59\-75 numbers? Is ‘plus’ for facing into the wind, and ‘minus’ for facing away?

 

[RLGA]

The tenants would have sued the developer and builder, and only the lawyers would have benefitted.

what are the +59\-75 numbers? Is ‘plus’ for facing into the wind, and ‘minus’ for facing away?

The tenants would have sued everyone.
The positive pressure is for a wind force pushing against the slider (windward side). The negative pressure is the suction force trying to pull out the slider (leeward side).

 

[TheCommish]

Forchantly for me I do not live in an extreme wind zone, I do however check the basics assumption of all designs and micro lam beam calculations, point load path, snow load. Some of the mentioned are an extreme problems on 1 & 2 family homes as people import plans for lesser snow load area to Massachusetts, decide they want open space layout, and miss loads from above on to beams.

On the commercial side see my previous comment on the need for a good code summay submittal by the RDP

 

[steveray]

See exposure and wind speed incorrect often.

 

[e hilton]

I was doing a retail finishout on miami beach a couple if years ago, scope included flood barriers. Third party inspector, who was pretty good, kicked back the submittal due to incorrect data: the vendor had used fresh water data in the calcs. The product was galvanized so i didn’t see the issue, until he pointed out that sea water is more dense and imparts a heavier load on the panels.
Ok, that’s technically correct, but the difference is only 0.025 kg/l and the panels are only 4 ft high. The actual increase in pressure is negligible.

 

[jar546]

I was doing a retail finishout on miami beach a couple if years ago, scope included flood barriers. Third party inspector, who was pretty good, kicked back the submittal due to incorrect data: the vendor had used fresh water data in the calcs. The product was galvanized so i didn’t see the issue, until he pointed out that sea water is more dense and imparts a heavier load on the panels.
Ok, that’s technically correct, but the difference is only 0.025 kg/l and the panels are only 4 ft high. The actual increase in pressure is negligible.

Understood, but,...regardless, the data submitted was incorrect. Think deposition.

 

[mark handler]

I have that issue with seismic zones
Common correction, "...cannot do that in seismic zones D,E,F...."