End Regions

Cast-in-place construction allows for the easy formation of edge beams and cut-off walls for the support of the cut reinforcement. Cut reinforcement is not assumed for precast construction as precast forms do not easily accommodate edge beams and cut-off walls. The following suggested edge beam and cut-off wall reinforcement and dimensions must be verified by the designer and increased if necessary.

In situations where a skewed culvert unit may control slab thickness requirements for the project, designers are encouraged to investigate edge beam design, in accordance with the LRFD Specifications, as an alternative to increasing slab thickness. In addition, if the skewed unit is located at the fascia of the bridge, the Multiple Presence Factor, MPF, may be reduced from a value of 1.2 to 1.0.

Cast-in-place culverts with skewed ends require additional stiffening of the top and bottom slabs by what is most commonly called an "edge beam" in the top slab and a "cut-off wall" in the bottom slab. An edge beam is very similar to a headwall in that it may be used to anchor guide railing posts or retain earth fill. Its main purpose, however, is to stiffen the top slab of cast-in-place culverts that lose their rigid frame action as a result of having a skewed end. A cut-off wall will stiffen the bottom slab as well as prevent water from undermining the culvert. A cut-off wall is usually required on culverts with no skew also.

For single cell cast-in-place culverts with skewed ends use a minimum 1'-6" wide by 1'-0" high (measured from the top of the top slab) edge beam for the top slab. The end of the bottom slab is suggested to have a minimum of a 1'-6" wide by 4'-0" high (measured from the bottom slab invert) cut-off wall placed directly beneath it.

The single cell edge beam should have a minimum of 4 - #8 longitudinal bars (bar marks S1 and/or S2) in the bottom of the top slab. The cut-off wall should have a minimum of 4 - #8 longitudinal bars placed in the top of the bottom slab. In addition, the top slab edge beam should have a minimum of 4 - #5 longitudinal bars (bar marks G1 and/or G2) placed as shown below with #5 stirrups at 1'-0" centers. Note that the S1 bars are intended for both edges, if the edges have the same skew, and the left edge otherwise. The S2 bars are intended for the right edge The same logic is applied to the G1 and G2 bars.

For multiple cell cast-in-place culverts with skewed ends it is suggested to use a 1'-6" wide by 1'-0" high edge beam for the top slab. The end of the bottom slab should have a minimum of a 1'-6" wide by 4'-0" high cut-off wall poured directly beneath it.

The multiple cell edge beam is typically reinforced with a minimum of 8 - #6 longitudinal bars (bar marks S1 and/or S2). A minimum of 4 - #6 bars are usually placed in both the top and bottom of the top slab edge beam as well as in the top and bottom of the bottom slab cut-off wall. In addition, the top slab edge beam should have a minimum of #5 stirrups at 1'-0" centers.