# Types of Truss Structures

Trusses are an extremely strong, well-accepted, cost effective option for the construction of various structures. To maximise the efficiency of the strucutre (which is often meaured in material used or labour), an appropriate truss type should be selected for design. Today we will explore what types of structures are out there and how they can benefit your design.

## Pratt Truss

A Pratt Truss has been used over the past two centuries as an effective truss method. The vertical members are in compression, whilst the diagonal members are in tension. This simplifies and produces a more efficient design since the steel in the diagonal members (in tension) can be reduced. This has a few effects - it reduces the cost of the structure due to more efficient members, reduces the self weight and eases the constructability of the structure. This type of truss is most appropriate for horizontal spans, where the force is predominantly in the vertical direction.

Below is an example of a Pratt Truss, constructed and analysed using our SkyCiv Truss Calculator. Compressive members are shown as green and tension as red.

**Advantages**

- Aware of member's behaviour - diagonal members are in tension, vertical members in compression
- The above can be used to design a cost effective structure
- Simple design
- Well accepted and used design

**Disadvantages**

- Not as advantageous if the load is not vertical

**Best Used For:**

- Where a cost effective design is required
- Where a mix of loads are applied
- Where a simple structure is required

## Warren Truss

The Warren Truss is another very popular truss structure system and is easily identified by its construction from equilateral triangles. One of the main advantages of a Warren Truss is its ability to spread the load evenly across a number of different members; this is however generally for cases when the structure is undergoing a spanned load (a distributed load). It's main advantage is also the cause of it's disadvantage - the truss structure will undergo concentrated force under a point load. Under these concentrated load scenarios, the structure is not as good at distributing the load evenly across its members. Therefore the Warren truss type is more advantageous for spanned loads, but not suitable where the load is concentrated at a single point or node.

An example of a Warren Truss, and its axial forces under a distributed load is shown below. The structure was built and analysed using SkyCiv Truss Calculator. Compressive members are shown as green and tension as red.

*Source:*Warren Truss Calculator

**Advantages**

- Spreads load fairly evenly between members
- Fairly simple design

**Disadvantages**

- Poorer performance under concentrated loads
- Increased constructibility due to additional members

**Best Used For:**

- Long span structures
- Where an evenly distributed load is to be supported
- Where a simple structure is required

## K Truss

The K Truss is a slightly more complicated version of the Pratt Truss. It's main difference is that the vertical members have become shortened - improving it's resistance against buckling. It does however have similar pros and cons to the Pratt Truss and although it is not widely used, it is a strong design. One of it's main disadvantages is that the members don't always behaive as expected. A member may be in compression under one load scenario and in tension under another. This can mean the structure may not be able to be optimally designed - since

An example of a K-Truss setup and its reaction under an applied load is shown below. Learn more about our SkyCiv Truss Calculator. Compressive members are shown as green and tension as red.

**Advantages**

- Reduced compression in vertical members
- Possible reduction in steel and cost if designed efficiently

**Disadvantages**

- Slightly more complex
- Increased constructibility due to additional members

## Howe Truss

Howe trusses are essentially the opposite of Pratt trusses in terms of geometry. In fact, looking at a Pratt truss upside-down will visualize a Howe truss of sorts. The entire structure is still relatively the same, but the diagonal braces are now occupying the opposite or the unoccupied joints. This switch in position of the diagonal members has a very important effect structurally.

A Pratt truss (above) and a Howe Truss (below)

Previously, we discussed how Pratt trusses have their vertical members in compression and diagonal members in tension upon the application of a gravity loads at the joints of the top chord. For Howe trusses, the reverse becomes true as diagonal members are now in compression, while the vertical loads are in tension.

*Source:*Howe Truss Calculator

As they are similar in structure with Pratt trusses, their uses are generally the same. To maximize the efficiency of the truss, the truss can be loaded at the joints of the bottom chord. Roof trusses can be loaded with a ceiling loads for example.

Another thing to note is that, depending on the geometry and loading, Pratt trusses can have more unloaded members than Howe trusses.

## Fink Truss

The Fink truss in its most basic form has web members that follow a V-pattern which can be repeated several times. As the top chords are sloping downward from the center, the V pattern becomes noticeably smaller. As Fink trusses rely more on diagonal members, they can be very efficient at transmitting loads to the support.

Derivatives of the Fink truss include the Double Fink and the Fan truss types. Double Fink trusses are essentially Fink trusses that repeat the pattern twice on either side. If the most basic Fink truss can be characterized by a double-V, then a double fink would look like a double-W. Fan trusses are essentially Fink trusses that have its web members ‘fan out’ from the joints at the bottom, usually the addition of vertical members.

A Fink (top), a Double fink (middle), and a Fan Truss (bottom)

*Source:*Fink Truss Calculator

## Gambrel Truss

In the exterior, a gambrel truss have two different slopes, where the slope gets steeper from the center. Due to outward-protruding shape, gambrel trusses can be effective to be fitted with a hollow center, which can be used as a storage area. As such, the upper section of a barn is usually shaped in a gambrel. In the case of a barn, as the members are usually constructed with wood, the structure acts more like a frame than a truss. Derivatives of the gambrel include the Mansard roof, which is also called a French roof, hence its popularity in France.

### SkyCiv Truss Software

SkyCiv offers two truss software; one Free Truss Calculator to model and analyze the internal forces of a truss structure. SkyCiv also offers powerful 3D Structural Analysis Software to model your 3D trusses and frames.

OR

**Sam Carigliano, PEng**

CEO and Co-Founder of SkyCiv

BEng (Civil), BCom

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