How far can you span with flitch beam? (Design with online calculator)

The maximum you can span with flitch beam depends a lot on the size of the beam, the load conditions, the type of material and supporting conditions. But typically you can span a flitch beam can span a maximum of 25 feet. To go beyond, you need to give support to the beam.

Flitch beams are created by sandwiching two steel plates with a layer of wood. Typically, structural steel, a kind of steel intended for use in building applications, is used to make steel plates.

A structural grade of timber, such as Douglas fir or southern pine, is used to create the wood layer. Bolts or other fasteners are used to join the steel plates with the wood layer.

Flitch beams are utilized in a range of construction-related applications. In buildings and other constructions, where they can carry heavy loads while yet offering some degree of flexibility, they are frequently utilized as structural beams. They can also be used to reinforce existing structures or to provide additional support to structures that are subjected to heavy loads.

One of the main advantages of flitch beams is that they combine the strength and durability of steel with the inherent structural properties of wood. The steel plates provide the beam with lateral stability and resistance to bending, while the wood layer provides the beam with resistance to compression and tension.

The combination of these properties allows flitch beams to support heavy loads while also being able to withstand the stresses of construction and use.

You might also want to read my other article that give details about flitch beam.

General steps for installing a flitch beam:

• Measure and mark the location where the beam will be installed. This should be done using a tape measure and a pencil or chalk.
• Cut the wood layer to the appropriate length using a circular saw or other wood-cutting tool.
• Cut the steel plates to the same length as the wood layer using a metal-cutting saw or other tool.
• Place the steel plates on either side of the wood layer, and align the edges of the plates with the edges of the wood.
• Secure the steel plates to the wood layer using bolts or other fasteners. It is important to use sufficient fasteners to ensure that the beam is adequately supported.
• Install the flitch beam in its intended location using a crane or other lifting equipment. The beam should be placed on top of supports such as steel columns or concrete piers.
• Secure the beam to the supports using bolts or other fasteners. Again, it is important to use sufficient fasteners to ensure that the beam is adequately supported.
• Check the beam for level and alignment, and make any necessary adjustments.

Types:

There are several types of flitch beams, the specific type of flitch beam used in a project depends on the specific design and load requirements.

1. Simple flitch beams consist of one wood layer and two steel plates.
2. Double flitch beams consisting of two wood layers and three steel plates.
3. Composite flitch beams consisting of a wood layer and two steel plates, with one or more additional layers of wood or other materials.
4. Multi-web flitch beams consisting of a wood layer and two steel plates, with one or more additional steel plate

How far can you span with flitch beams?

The separation between the points of support on which a flitch beam is resting is known as its span. The maximum span of a flitch beam can vary depending on:

• The size of the beam
• The distance between the supports
• The kind of wood and steel used
• The weight that the beam is anticipated to hold

The size of the beam

The maximum span is significantly influenced by the size of the beam since larger beams can often span greater distances than smaller beams.

The width and depth of the wood layer are commonly used to describe a beam’s dimensions, and they can be stated in inches (for example, 4″ x 6″) or millimeters (e.g. 100mm x 150mm).

The distance between the supports

The greatest span is also significantly influenced by the space between the supports. The maximum spread of the beam will often decrease as the distance between the supports rises. For instance, a beam supported at intervals of 4 feet would often be able to span a greater distance than a beam supported at intervals of 2 feet.

The kind of wood and steel used

The type of wood and steel used in the flitch beam will also affect its maximum span. Different types of wood and steel have different structural properties, and some may be better suited for certain applications than others. For example, southern pine is a commonly used type of wood in flitch beams due to its strength and durability. Structural steel is a common choice for steel plates, as it is designed for use in construction applications.

The weight that the beam is anticipated to hold

Finally, the loads that the beam is expected to carry will also impact the maximum span. Beams that are subjected to heavy loads will generally have a shorter maximum span than beams that are subjected to lighter loads. It is important to consult a structural engineer or other professional to determine the appropriate span for a flitch beam based on the specific design and load conditions.

Maximum Span of flitch beam

In comparison to other beam types and made, flitch beams are capable of spanning more and supporting heavy loads. Just a built-up wood member alone can span nearly 70% of what you can span with a flitch beam. A simple 2×12 or 2×8 flitch beam is far more rigid and strong than a 4×4 timber beam.

We generally design flitch beam for the moment, just like other beams. Let’s do an example of a flitch beam that’s supporting a roof. We’ll first calculate the moment or flexural stress on the beam and then using the beam size we’ll check if it can support that loading or not.

A typical flitch beam made with 2×10 or 2×12 timber members sandwiching grade 50 steel can span anywhere between 15 to 20 feet. But the actual span may vary depending on the design, load requirements, and the size of the beam.

Design of flitch beam

So, how do we do a flich beam calculation for a flat roof?

Inputs

We’re going to take a flat roof that is 6 meters by 4 meters. For distributing the load, we’ve divided the span here with a flitch beam, and the roof is spanning now from left to right rather than from top to bottom. The span of the roof is 3 meters.

Factored load: So, the first thing to do is to just look at what our loadings are going to be, and just for the purposes of this calculation, I’m going to say that the factored load (that’s the load after we’ve applied a load factor to it) is 2 kN/m2 on that roof.

`Factored load on the roof = 2 kN/m2 (kilo Newtons per meter square = Factored Area loading on the roof)`

Line Load: So, what’s the line load going to be, which is the load that goes along the line of that beam?

Well, it’s going to be 3 m x by 2 kN/m2, and the reason for that is because we’re taking a part of the roof as the contribution of load on our flitch beam.

`Line load on the beam = 3x 2 = 6 kN/m2`

Where 3 is the dimension of the roof.

Moment:

The next thing we need is the moment, and the simple formula for the moment is

`Moment = wl2/8 (this formula is valid only for simply supported beam. It means that it's supported at each end and has a uniformly distributed load along the full length.`

l  = dimension of roof i.e. 4 meters (span of the beam).

So, we can write moment as

Moment = 6 x 4 x 4 / 8 = 12.12 kN.m => Design moment for the flitch beam

So that is the moment and that’s the value which you’re going to use to design the flinch beam.

Flitch beam size

We have a steel plate, let’s say it’s 10 by 120 in mm and let’s say the timbers are 50 by 125 in mm. So how do we work out the strength of this flitch beam?

Restraint timber: Well, the simplest way of doing it is to use the timber simply as a restraint which means that this beam can’t really buckle any ways, and as long as we also have timbers trimming in from either side here, so we’ve got our roof timbers trimming.

If we don’t need to worry about buckling, then we can develop the full bending strength of this beam and use a very simple formula for that.

Bending Strength of beam

So the bending strength; we can write as:

`Bending strength (MR) = fy x (bd2/6) ; where  bd2/6  = z`

Out steel beam we’re using, let’s say it has a yield strength of 275 and the thickness is 10 mm which the depth is 120; so, we can write bending strength (Mr) as:

Mr = 275 x (10 x 275x 275)/6

So we can see here straight away that the depth is the most important thing because that’s the squared value, the width of the steel doesn’t matter so much which is why a flitch beam is so effective because you’ve got most of the steel within the depth rather than in the breath.

Mr = 6.6 x 106N.mm

So, converting N.mm to kN.m we can write it as:

`Mr = 6.6 x 106N.mm / (1000 x 1000) = 6.6 kN.m`

Check

That means this beam is capable of supporting only 6.6 kN.m bending moment. But if you see above in our roof configuration we need a beam of size for supporting 12 kN.m; so that’s half of what we need.

Now, what we can do is increase the width of flitch plate to 20 mm instead of 10; so that will give us a resisting strength of 12.12 kN.m.

Flitch Beam Design Calculator

Bending Strength of Flitch Beam (kNm):

1. Flitch beams are sturdy, long-lasting, and capable of bearing heavy loads.

2. Flitch beams, which combine the strength of steel with the natural structural qualities of wood, can be more economical than other types of beams.

3. Flitch beams have some flexibility, which enables them to endure construction and use-related pressures.

4. A vast number of uses for Flitch beams exist, including the building of bridges, buildings, and other structures.

1. Flitch beams might be more difficult to fabricate and install than other types of beams.

2. If the steel plates in a flitch beam are not adequately protected, they may corrode.

3. Flitch beams are often heavier than other types of beams, making them more difficult to handle and install.

4. Because the wood layer is sensitive to moisture damage and decay, flitch beams may require more care than other types of beams.

Conclusion:

Finally, flitch beams are structural components made of a wood layer sandwiched between two steel plates. They are sturdy and resilient, capable of supporting heavy weights while yet allowing for considerable flexibility.

Flitch beams are frequently utilized in the construction of bridges, buildings, and other structures, and they can be used to strengthen existing structures or to give extra support to structures subjected to significant loads. Flitch beams’ key advantages are their strength and durability, flexibility, cost-effectiveness, and versatility. However, they can have certain drawbacks, such as complexity, weight, possible maintenance costs, and corrosion risk.

Saad Iqbal is a professional civil engineering and freelance write. He's passionate about structures, construction management, and home improvement topics. He's been working as a Senior Engineer in a consultant firm for over 8 years. Besides he loves writing informative and in-depth content focused on construction and home-related topics. You can catch him at his linkedin page or reach out via our contact us page.