Introduction to HCB

Recently invented by John R. Hillman, Hybrid-Composite Beams (HCBs) are a new approach to structural design that incorporate four materials in such a way as to maximize the efficiency of each material.  A concrete arch serves as the main compression reinforcement, with steel strands tying the arch and carrying tension forces.  The space between the arch and the steel is filled with stiff, lightweight foam.  A Fiber Reinforced Plastic (FRP) box encases the system and adds shear reinforcement.  The Virginia Department of Transportation is interested in using HCBs in bridges and funded a project at Virginia Tech to better understand the behavior of the beams.

Fig. 1: HCB Components

The HCB was originally developed as a system to be used for rapid replacement of short span railroad bridges.  The developer received funds from the Highspeed Rail IDEA program and the NCHRP IDEA program to further the development of the system, fabricate proto-types and test them in the laboratory.

There are several advantages of the HCB versus the more traditional girders i.e. prestressed concrete girders (PCGs) and steel girders. First, the concrete arch inside the frp box can be cast on site. This decreases the time and cost of transporting the HDBs by allowing for more than normal beams per truck load. It is believed the erection costs will be lower considering smaller cranes can be used for lifting and setting of the beams. Moreover, the FRP shell adds a great deal more corrosion resistance to the steel reinforcement than commonly used concrete. This should decrease the long-term maintenance concerns and expenses as well increase the overall safety.