Frequently Asked Questions about HCB
A Hillman Composite Beam (HCB) is structural member akin to a prestressed concrete or steel beam. The fiber-reinforced polymer (FRP) outer shell provides shear strength and encapsulates the tension and compression elements. The compression element is a concrete arch. The tension element is steel reinforcement that runs longitudinally the length of the beam and ties the two ends of the concrete arch together.
Essentially, the HCB is a tied arch in a fiberglass box where 90 percent of the strength is provided by steel and concrete. The encapsulating FRP shell provides maximum protection from the elements for the steel and concrete, ensuring an extended service life and minimal maintenance.
The HCB can be used wherever steel or concrete beams are used and particularly where structures are built are in highly corrosive or caustic environments. Currently, we are manufacturing beams with span lengths up to 120 feet (34m). However, longer spans are possible. Call us or email us with your project needs.
Due to its light weight, the HCB is easily be incorporated into prefabricated bridge elements and systems (PBES) and can be set with lighter equipment. The lower weight also means that an existing steel bridge can be replaced with HCB prefabricated bridge modules without adding additional loads to the substructure. The HCB can also be installed without having to install forms for the deck, eliminating one construction process and meeting the objectives of ABC.
The HCB was originally developed for heavy axle freight railroad loadings. In general, the HCB can be designed to accommodate the same loads that any conventional beam would be designed for, such as:
- Highway Loads (Typically AASHTO, HL-93, HS-20 or HS-25, Permit Vehicles, etc.)
- Railroad Loads (Typically Cooper E-60 or E-80)
- Crane Loads
- Airport Loads
- Military Loads
- Pedestrian Loads
The HCB is a unique composite beam in that it derives most of its strength and stiffness from the high modulus concrete and steel components to provide compliance with code-specified deflection criteria such as the AASHTO requirements of L/800 or L/1000 for highway bridges.
Absolutely. Several HCB bridges currently in service are multiple span and made continuous for live load with similar details used for prestressed concrete beams.
HCB Inc. was founded by structural engineers with design, on-site construction and prefabricated bridge experience. We can assist you in the design of the superstructure or providing engineering firms that are familiar with the design of the HCB. We can assist with drawings and/or specifications for inclusion in the contract documents. Furthermore, since our background is bridge construction, we can assist with installation ideas and creating of precast bridge modules using the HCBs.
HCB Inc. can supply a generic specification that can easily be adapted for your project. We will work with you to make sure the specification meets all your requirements.
That’s your choice. The HCB can be shipped empty with the shear connectors in place and filled either in place or at another location. They can be shipped pre-filled and handled in the same manner as a prestressed concrete beam but only 1/3rd the weight, or they can be assembled into modules, with a deck, parapet or rails and other appurtenances.
Typically, neoprene bearings are used for the HCB; however, other standard bearing types can be used. Design of the bearing is the same as other conventional materials.
Yes, the HCB can be manufactured with galvanized strands and rebar to meet the “Buy American” provision of the United States Federal Aid Contracts.
Once all of the HCBs are filled, conventional bridge deck forming methods are used. For the bays between the beams, prestressed panels, SIP deck pans or removable forms anchored to the shear connectors can be used. In addition, we can offer an FRP deck form. For overhangs, standard overhang brackets are used and connected to the shear connectors with standard hangers. Alternatively, the HCB can be manufactured with flanges that form the overhang as well.
Although fiber-reinforced polymers (FRPs) are generally new to bridge engineering, they have a long history in the marine and aerospace industry. As a result, sophisticated NDT methods already exist for inspection of these materials. Further, with every bridge, we provide a design and maintenance manual, which includes NDT inspection techniques and ways to rate a bridge consistent with current NBIS bridge rating criteria. Another good reference is NCHRP Report 564, “Field Inspection of In-Service FRP Bridge Decks.”
UV radiation from the sun has been known to cause FRP laminates to fade, and it is possible for the surface of the laminate to become more brittle. To mitigate any strength concerns regarding UV radiation, we often provide pigments in the resin that prevent against UV degradation. It is also standard practice to apply UV inhibiting gel coats to either the exposed faces or all of the HCBs
Although there are typically no fire events specified in bridge codes that need to be addressed in design limit states, this is still a major concern for many owners. The resins used in the HCB shell can be tempered with bromine or aluminum tetra hydrate to achieve self-extinguishing properties. In other cases, an intumescent coating can be applied to the HCB to prevent against the errant brush fire. In any case, it should be noted that 90 to 95 percent of the HCB’s strength comes from the concrete and steel components.
The HCB uses steel and concrete to provide the bulk of the strength and along with its other inherent advantages can make the overall project cost using the HCB competitive on a first-cost basis with traditional structural members.