Floor Beam Deflection At Elevators

[abusementpark]

Anybody know what the floor deflection criteria should be (if any) at the entrance of elevators at elevated floors?

I have a project where the elevator entrance is located near the mid-span of a floor beam that is spanning 43 feet into a girder with a 24 foot span. I am starting to get concerned about the accumulated deflection, even though my floor deflection criteria is fairly stringent (l/400 for total load).

For starters, I'd be curious to know if the dead load deflection is accounted for when the elevator is installed and calibrated (or whatever they do). For example, if the 2nd floor is supposed be at EL. 16'-0", but it is actually 15'-11 1/4" in the field, do they account for that in the installation?

 

[Agent666]

One question is the structure around the lift enclosure load bearing? Columns or walls, etc? This would be the usual scenario for the shafts construction, so will the door location really deflect in this scenario more than the axial shortening of the columns/walls, if anything the nearby beam deflection will be constrained and load up the load bearing elements more than a tributary area approach might suggest. You certainly want to avoid the lift rails carrying the differential floor loads if there is not a load bearing shaft being constructed.

But yes I believe they will match the actual as built elevation when they commission the lift. If in doubt ask the proposed lift supplier, they have to accommodate normal constructional tolerances after all in all installations.

 

[abusementpark]

The lift enclosure is not load-bearing (it is just partition walls). This is steel framed structure and the elevator was located in the middle of framing bay, away from columns.

 

[Agent666]

I've never seen anyone attempt that type of configuration without a dedicated structural shaft (like posts and breaking the beams to be supported from these posts). How are the lift rails and the associated horizontal loading supported (usually at floors and at mid storey) if its just a non-loadbearing partition?

Lift guys usually want to connect to primary structure and their usual rail connection detailing does not allow for any significant differential deflection between floors (like sliding connections to ensure the rail isn't trying to prop the floor above or below for the relative vertical deflection that's going to occur when one floor is more heavily loaded after initial installation).

I'd run whatever you are thinking past your lift supplier as they may have come across and dealt with this particular scenario before, or it may be deemed not to be an issue. My experience is they are usually quite inflexible though, they just sell lifts and they expect the shaft to be deliver to meet their exact requirements which means the interstorey floor to floor height remains essentially more or less constant. They would need to know the maximum differential deflection, live + worst long term creep/shrinkage, etc vs no live load and limited creep/shrinkage on adjacent floor. The total deflection isn't the concern, its the differential deflection that can occur from the point at which the lift is calibrated.

Anything out of the ordinary and you need to get their buy in and there would be additional cost potentially if special detailing is required.

Considering the car is calibrated to a given elevation at installation, and then this floor elevation changes, it would seem there is high potential with this configuration to have a variable lip/step occurring. Given the lip size is variable depending on the load on the adjacent floors its not like you can adjust the car stop elevation to suit over time, if loading changes, lip height changes. This would seem like a potential issue from a serviceability perspective.

 

[BUGGAR]

I have seen projects where the floor is depressed around the elevator entrance and the final floor height set with a pour-back or tile or whatever after the elevator is in .

 

[MotorCity]

I have not seen any criteria for this specified in elevator load drawings. Quite honestly, I have not treated these beams any differently than any other floor beam with regards to deflection.

Usually use L/360, no complaints yet. More often than not, actual deflections don't come close to our theoretical deflections that we calculated since those are based on "worst case" scenario.

I would assume that the actual stop position of the elevator at each floor could be tweaked to match finish floor elevation.

 

[abusementpark]

Thanks guys. I ended up speaking with an elevator supplier who said he had never of floor deflection being an issue, so that gives me some confidence. Also, AISC DG #3 seems to indicate the criteria is no worse than for interior partitions.