The NEXT Beams is a regional standard that was developed by the northeast state departments of transportation and the local fabricators. Similar to other standard bridge sections, it is available from multiple fabricators and it is not proprietary.
The NEXT Beam is produced at a number of PCI Certified precast producers in the northeast. As of 2012, there are at least 4 fabricators that can produce the section. More are expected in the near future. You can contact www.PCI.org for the producers in your area.
Yes. NEXT Beam was developed by a consortium of state bridge 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 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. A NEXT beam bridge to be a more cost effective structure, reducing the overall cost of building bridges in the future.
The D Beam (Deck Beam) is a beam with an integral full-depth flange that acts as the structural bridge deck. This allows the bridge to be ready for traffic soon after the beams are 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.
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.
Intermediate diaphragms are not required for the NEXT Beams. AASHTO specifications require diaphragms at the supports where there is a joint in the deck.
NEXT Beams are typically supported on reinforced neoprene bearing pads. Details have been developed for bearing pads including a bearing that can be adjusted vertically, which may be beneficial for complex geometries. For example, on a skewed bridge with a vertical curve, the support points are out of plane, creating the need for a variable 4-point support system. The adjustable bearing will solve this problem.
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. These span ranges are approximate since they are based on certain design parameters such as parapet weight and overlay options. Actual span capabilities should be checked for each situation based on the actual design parameters. Please consult the Drawings section in the typical details for more information.
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 concern is with regard to cracking at release in the fabrication plant. Experience with double tee beams has shown the potential for longitudinal cracking in the top flange near the interior stem surfaces. Additional reinforcement has been placed in this region; however the potential for the development of these cracks is still present.
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.
The accommodation of vertical curve profiles can be handled in several ways (as with any precast concrete product). The thickness of the deck on NEXT F Beam bridges can be varied. The thickness of the top flange on NEXT D Beams can be varied; however this comes at a higher cost due to the need for more complex forming in the fabrication plant. Another option is to vary the thickness of the overlay to provide the desired profile.
The beams can be set to match the roadway cross slope. This is not normally done with prestressed I-Beams due to issues with stability. The large lateral stiffness of the NEXT Beam allows for this approach, which greatly simplifies the installation. Roadway crowns can be accommodated at the joints between the beams.
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.
Guidelines for the Live Load Distribution Factors for F, E and D Beams are found on sheet NEXT 01 of the NEXT Beam Detail Sheets.
Yes. This would be done the same way as any prestressed concrete 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, or the top flange could be dapped with projecting reinforcing. The positive moment reinforcement would be strand extensions.
The design of the deck is based on a normal stringer bridge. It is recommended that the top flange not be used in the deck design. The deck can be designed by treating each stem as an individual beam with the deck spanning between stems.
The design of the deck is based on a normal stringer bridge. The deck can be designed by treating each stem as an individual beam with the deck spanning between stems. The reinforcing shown on the typical details should work for most scenarios; however it should be checked for each design.
The connection shown on the typical details was developed based on research for deck bulb tee beams. The headed reinforcing bars were found to be fully developed with the specified lap length and bar spacing. The headed bars were placed just below mid-depth in order to provide both positive and negative moment capacity. The slight lowering of the bars was done to provide slightly more positive moment capacity since the connection is mid-way between the stems (positive moment region).
The PCI Northeast committee felt that it is important to use only one layer of bars in order to reduce fabrication costs. Multiple rows of bars can be used; however the costs will increase.
The design of the connection should be based on the moments generated using a standard AASHTO strip method. The deck can be designed by treating each stem as an individual beam with the deck spanning between stems. Once the positive moment is calculated at the joint, the section can be checked assuming that the projecting bars are fully developed. The reinforcing shown on the typical details should work for most scenarios; however it should be checked for each design. If more moment capacity is required, the bars can be lowered to achieve more moment capacity.
The design of integral abutment bridges using NEXT beams is the same as any stringer bridge. Sample details are included in the typical details.
Bridges using the F Beam will have a monolithic deck.
The D Beam has grouted mechanical connections provided (studs) that are. This joint provides continuity as well as a seal. This connection has been researched and tested to provide resistance to long-term fatigue loading and leakage. The joint was tested through two million cycles of loading and then successfully subjected to a ponding test.
The NEXT F Beam has a composite concrete deck cast on top; therefore any agency standard wearing surface treatment can be used, including bare concrete.
The NEXT D Beam has an integral deck cast into the beam. While not necessarily required, a wearing surface (either thin concrete or bituminous) is recommended in order to provide the smoothest riding surface. If bituminous overlays are used, a waterproofing membrane should be applied prior to paving. Refer to agency standards for acceptable overlay options.
There are several options, including one with a precast curb illustrated in the typical drawings.