3.5 Serviceability

Introduction to serviceability

The final limit state for beams is serviceability. "A serviceable structure is one that performs satisfactorily,not causing any discomfort or perceptions of unsafety for the occupants or users of the structure" LRFD Steel Design Second Edition -- William T. Segui . A beam is serviceable when it satisfies certain deflection limits.This is so there are no visible sags or deflections that lead to a flexible beam. If the beam is too flexible, itcould have a problem with vibrations.

Deflection limits

The deflection of a beam depends on the loading and support conditions. A list of deflection formulas can be found inPart 5 of the Manual starting on page 5-162. After finding the deflection for the beam inquestion, compare it to the maximum allowable total (service dead load plus service live load) deflections. These aredependent on the function of the beam.

• Plastered construction:
  $\frac{L}{360}$
• Unplastered floor construction:
  $\frac{L}{240}$
• Unplastered roof construction:
  $\frac{L}{180}$

where, $L$ is the span length.