Out-of-plane web deformation

Abstract on Out-of-Plane Web deformation and Relative Arch Movement of Hybrid-Composite Beams Based on Photogrammetry
by
Margret Grace Mascaro

http://vtechworks.lib.vt.edu/handle/10919/18750

Ultimate load test on 09.20.13 on a signal HCB girder

Ultimate load test on 09.20.13 on a signal HCB girder. This single girder carries load of 138 kips, comparing to the AASHTO design truck of 72 kips . Considering the fact that the truck load will distribute into multiple girders rather than being taken by one, HCB is definitely a strong structure!

HCB ABAQUS Modeling

Enjoy.

What is FRP Laminate?

No doubt, the most interesting part of HCB is its implementation of FRP? So what is FRP?

Fibre-reinforced plastic (FRP) (also fibre-reinforced polymer) is a composite material made of a polymer matrix reinforced with fibres. FRPs are typically organized in a laminate structure, such that each lamina (or flat layer) contains an arrangement of unidirectional fibres or woven fibre fabrics embedded within a thin layer of light polymer matrix material (Figure 1). The fibres, typically composed of carbon or glass, provide the strength and stiffness. The matrix, commonly made of polyester, Epoxy or Nylon, binds and protects the fibers from damage, and transfers the stresses between fibers[1].

The above right picture is a piece of FRP cut from HCB, showing that fibers orientated at 45 and 0 degree directions in different lamina.

Why FRP? Because of the high strength of these fibers, FRP can reach the same of higher strength than steel, but 1/10 lighter---------------consider using FRP in a air-plane, how much fuel can be saved in one year?-----------------and hence, save the expense of the labor in the transportation and the erection of the bridge( figure 2). Also, FRP could save on the painting over its life span because of its nice anti-corrosion property.

Research on HCB shear resistance

What if you substitute the web panels of  a steel bridge with concrete of same thickness？

It will crush under truck load? Right?

Well, there is essentially the same substitution in a HCB, considering the 3100 ksi elastic modulus of FRP--------concrete is normally 3000-5000 ksi. And the thickness of HCB web panel is less than 0.15 inch. But, a single HCB girder can handle more than 130 kips of load.

What makes the flexible FRP web capable to carry the weight of 2 trucks? We are digging into that and preparing a journal paper. Basically, post-buckling strength is the answer to the question.

Our discovery of this FRP post-buckling mechanism may not only be beneficial for our HCB design, but also helpful for other FRP applications -------i.e. aerospace engineering----------potentially.

Simulating strands corrosion for testing on October. 25. 2013

We are introducing damage to some strands embedded in the bottom slab of HCB. Basically, we want to simulate the bridge condition after decades of service and strands corroded with rust, and thus, better know the performance of HCB in its life span.

Testing on Oct.25.13. 

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.