Bridge Beams FAQ

Below are some questions that we are asked on a regular basis.

An I-beam is a beam with an I-shaped cross-section. The horizontal elements of the “I” are flanges, while the vertical element is the web. The web resists shear forces while the flanges resist most of the bending moment experienced by the beam. Beam theory shows that the I-shaped section is a very efficient from for carrying both bending and shear loads in the plane of the web. I beams are used in Structural Engineering and bridge design projects.

A concrete slab is a common structural element of modern buildings. Horizontal slabs of steel reinforced concrete, typically between 100 and 500 millimetres thick, are most often used to construct floors and ceilings, while thinner slabs are also used for exterior paving.

GRC is glass fibre reinforced concrete. GRC panels suit all forms of structures, providing both a practical and economical way of supporting freshly poured in situ concrete in composite bridge decks. They are often used to span the short distances between bridge beams on site.

An arch bridge is a type of bridge that relies on a curved, semi-circular structure for its support. Unlike post and beam bridges, which support loads on columns placed in the water along the entire bridge length, an arch bridge can span great distances while still leaving wide openings for water flow and water traffic.

A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into space, supported on only one end. The roadway of the bridge is held in place by cantilevers, which are long structures, or arms, projecting out into the water, but which are anchored on only one end. In a cantilever bridge, there are the outer beams, the cantilevers, and the central beam. The outer beams are attached firmly to shore, while the cantilevers are then attached to these outer beams. The cantilevers projecting out from the outer beams, or supporting piers on the opposite shores, are then joined by a central beam.

A box beam is a rectangular-shaped precast and prestressed concrete beam. These beams may be side by side or connected laterally and are used to from a bridge deck with or without a cast-in-place slab or topping. The units act similar to a slab. They act as a beam when spread and when a cast-in-place slab is used.

M stands for the moment in the beam and Y is the distance from the point where you are calculating the stress to the neutral axis. MY beams are used in Structural Engineering and bridge design projects.

U beam is a U-shaped, uni-directional, pre-stressed, quartz fiber reinforced beam for bridges. It is resistant to twisting and flexing. U beams are used in Structural Engineering and bridge design projects.

Because concrete is both a very durable and versatile material it is perfect for the manufacture of a wide range of bespoke concrete solutions as it can be pre-frabricated offsite making it a very cost effective and time efficient process . Engineers and architects are using precast and prestressed concrete for unique construction projects e.g.: replacing rail bridges, aquaducts, tunnel projects, framed buildings, carparks, stadia, motorways, waste water treatment plants and lots more.

Typical applications of the Y beam are for medium and long span bridges and commercial developments.

Span tables allow bridge designers and engineers to choose an appropriate size bridge beam and stress grade to achieve spanning needs. Shay Murtagh have created span tables for a variety of prestressed concrete bridge beams to meet Eurocode Standards in accordance with the European Union. If you would like to know more about concrete beam span tables you can download our Eurocode Bridge Beam Manual.

Precast prestressed concrete beams are widely used in today’s bridge construction industry where speed and ease of erection are of paramount importance. Over the years, the precast prestressed concrete beam spans have increased due to improvements in material properties, the introduction of new girder shapes, larger prestressing strands, and advances in design methods. There are many shapes and sizes including: i beams, u beams, y beams, my beams, w beams, mye beams, ye beams, t beams, ty beams, tye beams, m beams, um beams and box beams.

The four main factors are:

  • span (simple, continuous, cantilever)
  • material (stone, reinforced concrete, metal, etc.)
  • placement of the travel surface in relation to the structure (deck, pony, through)
  • form (beam, arch, truss, etc.)

In pre-cast bridges, concrete segments like beams, decking and flanges are constructed offsite normally at the precast manufacturing plant and then transported and hoisted into place. As the new segment is suspended in place by the crane, workers install steel reinforcing that attaches the new segment to preceding segments. Each segment of the bridge is designed to accept connections from both preceding and succeeding segments. Precasting bridges allows engineers to construct a bridge quite quickly for time –precious projects like active rail bridges who cannot afford much downtime making it a highly cost effective solution.

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