Service load is the load a structure is expected to carry in normal use, combining its own weight (dead load) with the people, vehicles and other loads that come and go (live load), without the safety factors applied in strength design.
Engineers use two kinds of load. Factored, or ultimate, loads are increased by load factors to make sure a member will not fail. Service loads are the real, everyday loads, used to check how the structure behaves: how much it deflects, how wide cracks open, and whether floors vibrate.
Why service loads matter in parking structures
- Durability. Crack widths under service load control how much water and deicing salt reach the reinforcement, which drives corrosion and long-term repair cost.
- Deflection and drainage. A deck that sags under everyday load can pond water and defeat the drainage slopes.
- Design live load. ASCE 7 (Table 4.3-1) sets the uniform live load for passenger vehicle garages at 40 psf and a concentrated load of 3,000 lb applied over a 4.5 in by 4.5 in area. Check the edition adopted locally.
The Parkonomics view
Strength design keeps a garage standing; service-load design keeps it in business. Most of the money a parking structure costs over its life goes to repairs driven by cracking, leaking and corrosion, all of which are service-load questions. Ask the design team how they checked serviceability, not only strength.
Related terms: Factored Load, Ultimate Load, Concentrated Load, Live Loads, Floor Diaphragm
Further reading: The Evolution of U.S. Parking Structures in 2026