I received an answer from NIST about UPS in the 81st floor of WTC2.

I wrote in my blog an article about lead batteries in the South Tower.
This is the link to my article:

http://11-settembre.blogspot.com/2007/02/ups-on-81st-floor-of-wtc2.html

Now I receive this email from Mr. Michael Newman Spokesman, NIST WTC Investigation:

"Date : 17/03/2008 19:23
Sender : Michael E. Newman

Re: Question about UPS in WTC2

Enrico,
Modifications were made in 1991 to reinforce the 81st floor of WTC 2 in an area occupied by the United Parcel Service.

Modifications were made in 1999 to floor 81 in an area of the floor occupied by Fuji Bank to accommodate the weight of an uninterruptible power supply.

Both of these modifications are documented in the section of the NIST WTC Investigation Report known as NCSTAR 1-1C (go to http://wtc.nist.gov/NISTNCSTAR1-1C.pdf ).

What is perhaps confusing is that both modifications were made to areas where there are two-way trusses (the corners of the building) and the acronyms (UPS for "United Parcel Service" and "uninterruptible power supply") are the same.