The NEXT Beam is efficiently designed to minimize labor in both the manufacturing plant and at the job site. The lack of draped (harped) strands is a significant benefit during fabrication. The elimination of deck forming in the field saves significant time during construction and also provides an instant platform for work, making for a much safer project. PCI Northeast Committee anticipates the NEXT beam bridge to be a more cost effective structure, reducing the overall cost of building bridges in the future.
Yes. NEXT Beam was developed by a consortium of engineers from all six New England states and New York and members of the Northeast region of PCI. In addition, the DOT bridge offices of New Jersey, Delaware, and Maryland are open to its use, making it attractive in design/build projects. Further, Pennsylvania DOT has accepted an alternate version of the F beam (using smaller diameter prestress strand).
The NEXT Beam is a good choice for bridge spans between 30 and 90’.
The NEXT Beam can range from a length of 30-90 ft and a width of 8-12 ft for the NEXT F beams and 8’-10’ for the NEXT D Beams. Please consult the Drawings section in the technical binder for more details.
The D Beam (Deck Beam) is a beam with a full-depth flange, on which a membrane and wearing surface can be field-applied, enabling it to be ready for traffic almost immediately after the bridge is erected.
The F Beam (Flange Beam) is a beam with a partial-depth flange which serves as the formwork for a conventional cast-in-place reinforced concrete deck. This results in a monolithic deck surface at the expense of a few extra days of site construction. The top flange of the F Beam eliminates the need for deck forming (including the overhang), which is a tremendous time saver.
Engineers in New England and New York have used PS Beam (www.lrfd.com) to design NEXT Beam bridges. ConSpan by Leap (www.bentley.com) and PG Super (www.pgsuper.com) are also viable software packages; PG Super was used to develop the load tables in this manual.
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Construct the abutments. The bridge seats should be cast to match the cross slope of the final roadway.
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Erect the NEXT beams. The beams should be installed to the spacing shown on the plans with ½-in.width joints between the beams.
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Form the deck ends and side faces, and place deck reinforcing (precast concrete curbs or parapets set in grout beds can be considered in place of side forms).
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Cast the bridge deck and deck facia. It may be possible to pre-pour the end diaphragms in the fabrication shop prior to shipping.
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Install bridge railing system.
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Install membrane waterproofing and pavement overlay.
Intermediate diaphragms are not required for the NEXT Beams. AASHTO specifications require diaphragms at the supports where there is a joint in the deck.
The flanges of the NEXT Beam can be cut back from the end of the beam in order to facilitate the placement of the concrete end diaphragm. The maximum amount of the flange cutback shall be 6”.
Bridges using the F Beam will have a monolithic deck.
The D Beam has grouted mechanical connections provided (studs) that are similar to Inverset. This joint provides continuity as well as a seal. The research team that developed the D Beam considered long term fatigue loading and leakage. The joint was tested through two million cycles of loading and then successfully subjected to a ponding test. Our details recommend a waterproofing membrane and overlay to guarantee a waterproof deck. The overlay (bituminous or thin concrete) is recommended to accommodate misalignment due to field tolerances or differential camber.
NEXT Beam sits on a reinforced neoprene bearing pad.
The PCI NE Bridge Tech Committee is currently developing further details for bearings, including an adjustable bearing, which may be beneficial for more complex geometries. For example, on a skewed bridge with a vertical curve, the support points are out of plane, creating the need for a 4-point support system. The adjustable bearing will solve this problem.
CIP parapets are handled no different from a standard precast bridge. If you would like to consider a precast curb or parapet there is a sample detail in the Standards for the NEXT beam on this website.
The AASHTO LRFD Bridge Design Specifications are not clear when it comes to the calculation of live load distribution factors for a double tee beam with a composite concrete deck. The PCI Northeast Bridge Technical Committee has contacted the original authors of the specification and found that this type of structure was not specifically investigated during the development of the code. In lieu of more precise information, the following approach for calculation of live load distribution factors was suggested.
Please reference, AASHTO LRFD 4.6.3.1 Distribution of Live Loads Per Lane for Moment in Interior Beams. For the calculation of NEXT Beam F Interior Distribution Factor use Cross Section Type K – Precast Concrete I or Bulb-Tee Sections (AASHTO LRFD Table 4.6.2.2.2b-1) with the following modifications, ‘One Design Lane’ and ‘Two or More Design Lanes’:
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Treat each stem as an individual beam and calculate Distribution Factors for each stem based on the average stem spacing.
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Multiply those factors by two and apply it to the entire NEXT beam section (i.e. S = S/2 and DF final = DF x 2).
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The Corresponding NEXT F Beam Moment Correction Distribution Factors and Shear Distribution Factors would follow this same methodology
This method produces more conservative live load distribution factors when compared to calculations using the full beam width in the equations. Until further notice, please implement these changes on all current and future designs.
Yes. The PCI Northeast set 30 degrees (AASHTO skew convention) as a preliminary maximum limit, but it may be possible to exceed this value. The value will be refined as more skewed bridges are built and experience is gained.
The widths of the NEXT Beams can be adjusted readily in fabrication to accommodate gentle curves. The flanges of the exterior NEXT Beams can be curved (in plan) to produce a curved roadway geometry.
The widths of the NEXT Beams can be adjusted readily in fabrication to accommodate roadways which are tapered in plan. The flange width of the NEXT Beams can be tapered, creating a slightly ‘pie shaped’ beam which would be used for splayed layouts.
One of the main reasons the NEXT beam was developed was to handle multiple utilities, unlike the box beam which can only handle a few. Utility supports can be coordinated with the Manufacturer and be cast into the beam at the time of fabrication to expedite installation time out in the field.
Yes. This would be analogous to achieving continuity using NEBT beams. The negative moment reinforcement can be cast into the deck on the NEXT F design. For the NEXT D design, mechanical couplers could be considered. The positive moment reinforcement would be strand extensions.
A sample detail can be downloaded as part of the Standards for the NEXT beam.
The NEXT Beam is produced at a number of PCI Certified precast producers in the U.S. You can contact www.pcine.org for the producers in your area.
