I found it was much less stressful to rent the stairs and scaffolding that the stairs are apart of.

Note that you also have to design the stairs for a minimum concentrated load of 1000 lbs.

Standard Building Code Table 1203.1 specifies 100 psf min.  Table 1203.3 specifies 300 lb stair tread load at an area of 4 sq in at center of tread.

All codes that I am familiar with calls for 1(00 PSF) live load plus the concentrated load. I had to comply with OSHA requirements when safety guys asked for it during a design for a platform at a military installation.

At first I did not believe them; but after reading and review, they were correct. You will find that most of the steel stair designs do meet the OSHA loads unless you have some really wide tread long flights of stairs.

Good luck

Which code states that the stairs shall be designed for uniform load plus concentrated load?  I may have overlooked it in the SBC and OSHA 1910.24(c), at least the way I interpret it, doesn't require the concentrated load in addition to the uniform load.  

29 CFR 1910.24(c) states; Fixed stairways shall be designed and constructed to carry a load of five times the normal live load anticipated but never of less strength than to carry safely a moving concentrated load of 1,000 pounds
See:
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9716&p_text_version=FALSE#1910.24(c)

Therefore, with respect to the design calculation, the normal live load is spread over the whole stair tread area and the moving concentrated load is considered to be a point load applied at a location on the stair system where the maximum stress would be experienced by the system (the 1000 lbs loading criteria is a minimum).

The design of fixed stairways and their components must be based on their ultimate strength [yield stress (FY) or ultimate stress (FU)] and not on the allowable stresses as given in the Allowable Stress Design method of the American Institute of Steel Construction, Ninth Edition.