Interactive Sample Project: Pedestrian Bridge

Step 13: Analysis: Dead Load

  • Earlier we only took into account the live load and now need to factor in the dead load of the beam and its deck.
  • The dead load is defined as the weight of a structure and the materials that are permanently attached to it. [4]
    Bridge Dead Load (weight of beams and weight of the bridge deck):
    wd = γbeamAbeam + γdeckAdeck = ( lb/in3)( in2) + ( lb/in3)(45 in2) =  lb/in.
  • Combined live and dead load:
    w = wl + wd = 8.854 lb/in +  lb/in =  lb/in.
  • Recalculate Mmax and Sreq with the total load to check S ≥ Sreq:
    Mmax = w  L2 ∕ 8 = ( lb/in)(96 in)2∕ 8 =  lb·in,
    Sreq = Mmax ∕ σallow = ( lb·in) ∕ ( ksi) =  in3
    S =  in3 ≥ Sreq =  in3. Ok
  • Recalculate δmax with the total load to check δmax ≤ δo:
    δmax = 5w L4 ∕ (384 E I) = 5( lb/in)(96 in)4 ∕ [384( ksi)( in4)] =  in
    δmax =  in ≤ δo = 0.192  in. Ok
< < Back to Step 12: Concept Design Analysis Continue to Step 14: Cost Analysis >>


This material is based upon work supported by the National Science Foundation under Grant No. 0633602. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).


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