A7.1. Concept design 1 – Steel bars
The first concept proposes the introduction of steel members as steel bars, fully enclosed in the GFRP deck, attached to the bottom of the top skin and the top of the bottom skin in every core cell (see Figure 22). Below, the advantages and disadvantages posed by this design are described
Figure 22 – GFRP deck with steel bars; drawing not on scale
• Advantages
o The steel bars will be flexible (due to their small thickness), therefore, they will bend in the mould and follow the curvature of the bridge deck;
o The shape of the steel members will be standard (i.e. no additional grooves or holes) because the resin will be able to flow around it through the GFRP skins;
o The contribution of the steel members to the bending stiffness of the deck is maximum due to the fact that the bars are placed far from the neutral axis;
o Stress concentrations are relatively low due to the fact that steel members are evenly spread all over the cross section.
• Disadvantages
o Design challenges
The steel members need to be fully connected to the GFRP skin in order to contribute to the section’s stiffness. This needs to be achieved with either an adhesive bond or with mechanical means.
o Procurement challenges
Steel members need to be procured. The size of the members will be standard in order to keep the costs and delivery times low;
Foam blocks with a different runner pattern will be required in order to ensure proper spreading of the resin.
Lead time will increase due to the waiting time until steel member delivery.
Production of custom made steel members and foam blocks will cause an increase in costs;
o Manufacturing challenges
At least two cranes will be required to place the steel members into position due to their weight and size;
The production time will increase (with approximately 30 minutes for every steel member) due to the need to place additional elements;
The steel members will need to be placed on one side of the core cell in order to allow the central grooves to transport the resin along its normal course;
The design of the webs will be different in order to accommodate the steel bars. Wrapping each foam block will no longer be possible as it is presently being done because the steel member will be continuous in the longitudinal direction. Therefore, a new technique will have to be developed and tested.
Any changes in the manufacturing process pose risks and need to be tested and therefore cannot be implemented immediately.
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A7.2. Concept design 2 – Steel sheets
The second concept design is similar to the first one. The difference is that the steel bars are wider so that they fill the entire width of the core cell. As before, the steel sheets will be present both at the top and bottom of the cross section (see Figure 23).
Figure 23 – GFRP deck with steel strips; drawing not on scale
• Advantages
o The steel bars will be flexible (due to their small thickness), therefore, they will bend in the mould and follow the curvature of the bridge deck;
o The contribution of the steel members to the bending stiffness of the deck is maximum due to the fact that the bars are placed far from the neutral axis;
o Stress concentrations are relatively low due to the fact that steel members are evenly spread all over the cross section;
• Disadvantages
o Design challenges
The steel members need to be fully connected to the GFRP skin in order to contribute to the section’s stiffness. This needs to be achieved with either an adhesive bond or with mechanical means
o Procurement challenges
Steel members need to be procured. The size of the members will be standard in order to keep the costs and delivery times low;
The shape of the steel members will need to be custom made. Holes and grooves will be required in order to allow the transport of resin to the skin;
The edges of the steel members will need to be chamfered in order to protect the fibres that will be wrapped around them;
Production of custom made steel members will determine longer lead time;
Foam cores with a different pattern will be required in order to ensure the resin is spread uniformly;
Production of custom made steel members and foam blocks will cause an increase in costs;
o Manufacturing challenges
At least two cranes will be required to place the steel members into position due to their weight and size.
The production time will increase (with approximately 30 minutes for every steel member) due to the need to place additional elements,
The fabrication of the webs will be different because the foam cores will need to be wrapped in glass fibres separately while the steel will be a continuous member along the full length of the bridge
Any changes in the manufacturing process pose risks and need to be tested and therefore cannot be implemented immediately
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A7.3. Concept design 3 – Rectangular hollow profiles
The last concept proposes the introduction of steel rectangular hollow sections only in the outermost core cells (see Figure 24), thus acting as the beams supporting the concrete slab on a traditional bridge.
Figure 24 – GFRP deck with rectangular hollow steel profiles; drawing not on scale
• Advantages
o Only two steel profiles are required;
o The steel members can easily be placed after all the foam cores are positioned in the mould and the GFRP plies can simply be wrapped around them;
o There will be no changes to the central part of the section since the steel is only present at the sides;
o No adhesive bond is required since the neutral axis of the steel members is the same as that of the deck section. Therefore, when the bond fails, the steel provides the same amount of bending stiffness;
o The steel members can remain empty, therefore, less foam blocks are required;
o The rectangular sections can increase the torsional rigidity of the section.
• Disadvantages
o Design challenges
The steel is concentrated at the sides which will focus the stresses around them.
o Procurement challenges .(will cause an increase in costs and delivery / production time)
Steel members need to be procured. The size of the steel profiles will not be standard since it needs to match the depth of the deck.
In case the necessary size cannot be manufactured, separate sheets need to be bought and welded together
The outer faces of the steel beams will need to feature holes and grooves in order to allow the transport of resin to the skin.
The edges of the steel members will need to be chamfered in order to protect the fibres that will be wrapped around them
The beams will need to be pre-cambered since they are rigid and they will not bend under their own weight on the mould.
Lead time will increase due to the need of customized steel profiles
Procurement costs will increase due to the need of customized steel profiles o Manufacturing challenges
At least two cranes will be required to place the steel members into position due to their weight and size.
The production time will increase (with approximately 1 hour for every steel member) due to the need to place additional elements
The steel members will need to be airtight during the vacuum process in order to prevent resin from entering them. Additionally, a pressure difference may cause deformations of the steel beam.
Any changes in the manufacturing process pose risks and need to be tested and therefore cannot be implemented immediately
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