Types of Truss

Back to Bridges     Back to Home Page

Introduction and List of Truss Types

Clear diagrams of numerous truss types may be seen here.

More good diagrams of trusses may be seen here and here.

Photographs of some truss types may be seen here.

Many diagrams may be seen here here.

Trusses for roofing may be seen here.

Evolution of trusses.

Truss bridge design.

 

Here is a list of truss types.

Baltimore truss

Bollman truss

Bowstring truss

Burr truss

Camelback truss

Childs truss

Fink truss

Haupt truss

Howe truss

K truss

King Post truss

Lattice truss

Lenticular truss

Multiple King Post tr

Long truss

Partridge truss

Pennsylvania truss

Pratt truss

Queen Post truss

Scissors truss

Smith truss

Town truss

Warren truss

Wernwag truss

Whipple truss

Whipple bowstring

For most of these truss types, further subdivisions are possible.  Most truss bridges possess two trusses, one each side of the deck, though a few have only one, on the centre line, and some have three, one at each side and one in the middle.  

Another variation is in the line of the top and bottom, which are normally straight.  But some trusses have a degree of arching of the top surface, while others are curved below.  Lenticular trusses are curved top and bottom.  In all cases the purpose is to provide greater depth where the bending moment is greatest, around mid-span.

The next set of diagrams shows examples of straight and curved Warren type trusses with verticals.

In the simplest type of truss bridge the two trusses are essentially one dimensional, stiffness in the third dimension being provided by the deck.  The trusses must possess enough rigidity to prevent buckling out of their plane.  This is especially important when the trusses are above the deck, and the compression member is free.

In larger truss spans, both the top and the bottom members are joined by cross members, which may themselves be in truss form.  The span is then like a box girder in truss form.

Those trusses that are deeper in the middle than at the ends have been designed in response to the variation of bending moment along a beam.  For short spans this complication may not be worthwhile.

Cross-sections through these various types are shown below.

Click here to download a program which allows you to investigate the behaviour of a kingpost truss.  The truss is assumed to have a weight that is negligible with the load.  The load can be moved about, and the height of the truss can be varied.

from Brantacan

History

During the 18th and 19th centuries, particularly in the USA, numerous types of truss were invented and patented, attempting to get the best from the available materials, which were successively wood, cast iron, wrought iron and steel.  Methods of jointing were also a factor in some designs, and we must not forget that in those days, the sizes of parts was important as well, because large and heavy parts were difficult to transport.  The problems were greatly exacerbated by the arrival of the railways - loads increased by a large factor.

Before wrought iron became available, bridge failures were not rare, because of the use of cast iron, with its very limited tensile strength.  In compression, by contrast, it is a strong material.

As usually happens when we try to classify things, there may be some confusion between types of truss, because numerous variations were created.  In some cases, arches were added to trusses, sometimes made of laminated wood, creating a degree of redundancy and indeterminacy.  In the USA, wooden trusses were often built in the form of covered bridges, the wooden roofs and sides being added for protection to the bridge from the elements.

Mathematical analysis was not always applied in the early days, and some trusses were indeterminate.

from Brantacan

Lattice Truss or Town Truss

This truss was invented by Ithiel Town and patented in 1820.  It was used with timber and iron.  In timber bridges, nails could be used at all the crossing points, for quick assembly.  There is a great deal of redundancy in the Town truss, which is advantageous where there is a risk of members failing.  Some iron examples are shown below.

BrockWeirXZE.jpg (164386 bytes) BrockweirLattice406.jpg (104582 bytes) BrockWeirLattice405.jpg (120047 bytes)   GlasgowTruss198.jpg (113556 bytes)

from Brantacan

Town Truss - please see Lattice Truss

from Brantacan

Warren Truss

The Warren truss is very simple - an outline filled with zigzags, though some Warren truss include vertical members as well.  Not only is it seen in bridges, it is often seen in crane jibs and in guyed masts.  In conjunction with closed box section members, and welded construction, the Warren truss can look very tidy.  Here are some examples -

WorcsR6.jpg (59066 bytes) HuntshamA.jpg (224926 bytes) ChepstowBrunel287.jpg (126340 bytes) TrussA38DL.jpg (219534 bytes)

MWood.jpg (76347 bytes) Tuffley2.jpg (97160 bytes) DuxfordTruss2.jpg (108310 bytes) Crane1.jpg (21378 bytes)

Look in these pictures and in real bridges for deck type, pony type and through type, and for Warren with-verticals and Warren without-verticals.

from Brantacan

Back to Bridges     Back to Home Page