Unfactored Column Loads 1

[onetimedeal]

In my area, building engineers typically indicate "unfactored column loads" in column schedule under each column.

1. What are these column loads for? Who will use these loads and for what applications?

2. What should be included in this "unfactored column loads"? Pu = 1.0DL + 1.0LL?

3. What if I use these columns as frame columns which also resist lateral loads? Shall I also include the additional axial loads due to lateral loads? Pu = 1.0DL + 1.0LL + 1.0E?

Thank you for your input.

 

[spats]

I assume you're talking about steel columns. Maybe it's design loads for the base plates?

 

[cap4000]

I have over the past 30 years in New Jersey always included the service axial loads in my column schedules. I also show the roof and floor loads. The lateral loads I separate out and draw the steel rigid frame involved with the E or W and show those loads on that elevation. I think its just a book keeping issue. If the building ever undergoes any major renovations the loads are indicated for a comparison.

 

[onetimedeal]

These are concrete buildings and concrete columns.

 

[civilperson]

Renovations and changes in proposed use require structural analysis with columns and footing very expensive to upgrade.

 

[whyun]

Where do you practice engineering?

I am a California engineer and we typically don't specify unfactored loads, or any loads, on the column schedule.

In the Structural Calculations, however, we indicate unfactored dead load, unfactored live load, and unfacfored seismic load for each column. Then we use the governing factored load combination to design the concrete element (column dimensions, reinforcing, ties etc). Governing unfactored load combinations are used to design the size of the foundation.

 

[onetimedeal]

I practice engineering in DC, VA, and MD area. All concrete buildings including garages show this unfactored load.

Some engineers intent to put larger numbers for this load. Since I do not really know what and who will use these numbers, it makes me concern about what numbers should I put in.

County structural reviwers typicall do not ask for design calculations unless they found something really out of wack. However, we do design columns with factored loads and foundations with unfactored loads for sizing and reinforcement.

 

[asixth]

I have seen construction drawings issued with working loads provided in the schedule. I do find it unneccessary to list each column with the working loads which have been exported from your analysis (rounded to the nearest integer). I think it would serve a better purpose if the listed working load is in fact the maximum working load a column type can take with the minimum out-of-alignment eccentricity.

I guess with BIM coming to the forefront of design, in the future we will see the design axial forces listed with each element of the structure.

A problem does arise when horizontal forces are taken into consideration because the additional moment that is transferred into the column can significantly reduced the capacity of that column if you are in the compression failure region of your interaction diagram.

Onetimedeal lists an interesting load combination of 1.0DL + 1.0LL + 1.0E. I myself practice in a very low seismically intra-plate region of the world where we use 1.0DL + 0.4LL + 1.0E for our seismic analysis (static pushover). The reason for the reduced LL factor is to allow for the fact that unless the load is fixed to the structure, it will not contribute to the mass of the system.

 

[DaveAtkins]

It's hard to list total unfactored loads, because of the various load combinations. The controlling load combination might be DL + 0.7EL, or it might be DL + 0.75LL + 0.75(0.7EL), or it might be
DL + 0.75(0.2SL) + 0.75(0.7EL), or it might be
0.6DL - 0.7EL.

DaveAtkins

 

[hokie66]

My experience with listing service loads for columns, and that was in the same area where onetimedeal practices, was before USD, so all loads were unfactored. The load listed was full dead load plus live load for which the column was designed. So at the bottom lift, it was the load for which the footing was designed. Quite a useful number to know, I think.

 

[Lion06]

asixth-
Can't you include only 40% LL in the mass of your structure while still accounting for 100% LL for the gravity loads? If the controlling load combination is 1.0DL + 1.0LL + 1.0E, I don't think you can arbitrarily take off 60% LL to reduce the mass on the structure. I can see doing it to only reduce the mass, but I think it needs to be there when calc'ing the gravity loading (again, if the controlling load combination calls for it).

 

[onetimedeal]

Thanks, Guys/Ladies

We have very interesting doscussion here. Based on my opinions, I would like to list the footing design loads in the column table because that is what the column and foundation were designed for.

Like hokie66 said, the unfactored loads were used before USD. I just don't see any reason to put unfactored loads and no one can actually use it for any reasons.

I think I might take them out of the column schedule or use column/footing design loads. It might be out of ordinary but I believe that makes more sense.

 

[hokie66]

You just need to be clear on what information you are actually showing on the drawing. If they are factored loads, give the factors, because our code writers have a habit of changing factors.