The self-weight of the beam and the weight of the slab and haunch act on the non-composite simple span structure, while the weight of barriers, future wearing-surface, and live loads with impact act on the composite continuous span structure. Full continuity is assumed for continuous model and no time effects are considered.

Using simple static, values of shear forces and bending moments for a typical interior beam under self-weight of beam and weight of slab and haunch is computed. For these calculations, the span length (L) is the design span (29700 and 32400 mm). However, for calculations of stresses and deformation, at the time prestress is released, the overall length of the precast member is used as illustrated later in this example. The shear forces and bending moments due to barrier self-weight, future wearing surface and live load are calculated based on the continuous span lengths, 30000, 33000, and 30000 mm.

Shear Forces and Bending Moments Due To Dead Loads

Dead Loads [LRFD Art. 3.3.2]

DC = Dead load of structural components and non-structural attachments

1. Dead loads acting on the simple span structure:

   Loads auto-computed by the program:

   Beam self-weight = 12.325 kN/m

   10mm haunch self-weight = (0.010)(1.225)(23.56) = 0.289 kN/m

   190mm slab self-weight = (0.190)(3.60)(23.56) = 16.115 kN/m

   Loads modeled by the user:

   10mm non-structural slab-weight = (0.01)(3.60)(23.56) = 0.850 kN/m

   Note: A 10 mm haunch thickness is assumed in the computations of dead load.

2. Dead loads placed on the continuous structure:

   LRFD Art. 4.6.2.2.1 states that permanent loads (curbs and future wearing surface) may be distributed

   uniformly among all beams if the following conditions are met:

   • Width of the deck is constant. OK
   • Number of beams, Nb, is not less than four (Nb = 4) OK
   • Beams are parallel and have approximately the same stiffness. OK
   • The roadway part of the overhang de < 910 mm, where de = 1300 – 150/2 – 400 = 825 mm. OK
   • Curvature in plan is less than (curvature = 0.0). OK
   • Cross-section of the bridge is consistent with one of the cross-sections given in the LRFD Table 4.6.2.2.1. OK

   These criteria are satisfied, but for this example the barrier and wearing surface loads are distributed among the 4 beams in the ratio of the Dead Load distribution factor. Dead load distribution factor for Beam 2:

   $=\frac{BeamTributaryWidth}{OverallBridgeWidth}=\frac{3.60}{13.40}=0.269$

   Barrier weight = (2 barriers)(4.378 kN/m) = 8.756 kN/m

   DW = Dead load of future wearing surface

   $0.050\times 12.600\times 23.56=14.843kN/m$

Unfactored Shear Forces and Bending Moments

Using simple static, values of shear forces and bending moments for a typical interior beam under self-weight of beam and weight of slab and haunch is computed. For these calculations, the span length (L) is the design span (29700 and 32400 mm). However, for calculations of stresses and deformation, at the time prestress is released, the overall length of the precast member is used as illustrated later in this example. The shear forces and bending moments due to barrier self-weight, future wearing surface and live load are calculated based on the continuous span lengths, 30000, 33000, and 30000 mm.