# Dictionary Definition

truss

### Noun

1 (medicine) a bandage consisting of a pad and
belt; worn to hold a hernia in place by pressure

2 a framework of beams forming a rigid structure
(as a roof truss)

3 (architecture) a triangular bracket of brick or
stone (usually of slight extent) [syn: corbel]

### Verb

1 tie the wings and legs of a bird before cooking
it

2 secure with or as if with ropes; "tie down the
prisoners"; "tie up the old newspapes and bring them to the
recycling shed" [syn: tie down,
tie up,
bind]

3 support structurally; "truss the roofs";
"trussed bridges"

# User Contributed Dictionary

## English

### Etymology

From trousse.### Noun

- A bandage and belt used to hold a hernia in place.
- A framework of beams forming a rigid structure.
- A triangular bracket in architecture.
- An old English farming measurement. One truss of straw equalled 36 pounds, a truss of old hay equalled 56 pounds, a truss of new hay equalled 60 pounds, and 36 trusses equalled one load.

#### Translations

bandage and belt

- Italian: cinto

framework of beams

- Italian: Struttura reticolare

triangular bracket in architecture

# Extensive Definition

In architecture and structural
engineering, a truss is a structure
comprising one or more triangular units constructed with straight
slender members whose ends are connected at joints.

A plane truss is one where all the members and
joints lie within a 2-dimensional plane, while a space truss has
members and joints extending into 3 dimensions.

## Truss types

There are two basic types of truss:- The pitched truss, or common truss, is characterized by its triangular shape. It is most often used for roof construction. Some common trusses are named according to their web configuration. The chord size and web configuration are determined by span, load and spacing.
- The parallel chord truss, or flat truss, gets its name from its parallel top and bottom chords. It is often used for floor construction.

A combination of the two is a truncated truss,
used in hip roof
construction. A metal plate-connected wood truss is a roof or floor
truss whose wood members are connected with metal
connector plates.

### Pratt truss

The Pratt truss was patented in 1844 by two Boston railway engineers; Caleb Pratt and his son Thomas Willis Pratt. The design uses vertical beams for compression and horizontal beams to respond to tension. What is remarkable about this style is that it remained popular even as wood gave way to iron, and even still as iron gave way to steel.The Southern
Pacific Railroad bridge in Tempe,
Arizona is
a 393 meter (1291 foot) long truss bridge built in 1912. The structure is
composed of nine Pratt truss spans of varying lengths. The bridge
is still in use today.

### Bow string roof truss

Named for its distinctive shape, thousands of bow strings were used during World War II for aircraft hangars and other military buildings.### Vierendeel truss

see Vierendeel bridge The Vierendeel truss is a truss where the members are not triangulated but form rectangular openings, and is a frame with fixed joints that are capable of transferring and resisting bending moments. Regular trusses comprise members that are commonly assumed to have pinned joints with the implication that no moments exist at the jointed ends. This style of truss was named after the Belgian engineer Arthur Vierendeel, who developed the design in 1896The beauty of this type of truss is that there is
no diagonal bracing, the creation of rectangular openings for
windows and doors is simplified and in cases the need for
compensating shear walls is reduced or eliminated.

After being damaged by the impact of plane
hitting the building parts of the framed curtain walls of the Twin
Towers of the World
Trade Center resisted collapse by Vierendeel action displayed
by the remaining portions of the frame. .

### King post truss

One of the simplest truss styles to implement, the king post consists of two angled supports leaning into a common vertical support. The queen post truss, sometimes queenpost or queenspost, is similar to a king post truss in that the outer supports are angled towards the center of the structure. The primary difference is the horizontal extension at the centre which relies on beam action to provide mechanical stability. This truss style is only suitable for relatively short spans.### Town's lattice truss

American architect Ithiel Town designed Town's Lattice Truss as an alternative to heavy-timber bridges. His design, patented in 1835, uses easy-to-handle planks arranged diagonally with short spaces in between them.## Statics of trusses

A truss that is assumed to comprise members that are connected by means of pin joints, and which is supported at both ends by means of a hinged joints or rollers, is described as being statically determinate. Newton's Laws apply to the structure as a whole, as well as to each node or joint. In order for any node that may be subject to an external load or force to remain static in space, the following conditions must hold: the sums of all horizontal forces, all vertical forces, as well as all moments acting about the node equal zero. Analysis of these conditions at each node yields the magnitude of the forces in each member of the truss. These may be compression or tension forces.Trusses that are supported at more than two
positions are said to be statically indeterminate, and the
application of Newton's Laws alone is not sufficient to determine
the member forces.

In order for a truss with pin-connected members
to be stable, it must be entirely composed of triangles. In
mathematical terms, we have the following necessary condition for
stability:

- m \ge 2j - r \qquad \qquad \mathrm

When m=2j - 3, the truss is said to be statically
determinate, because the (m+3) internal member forces and support
reactions can then be completely determined by 2j equilibrium
equations, once we know the external loads and
the geometry of the truss. Given a certain number of joints, this
is the minimum number of members, in the sense that if any member
is taken out (or fails), then the truss as a whole fails. While the
relation (a) is necessary, it is not sufficient for stability,
which also depends on the truss geometry, support conditions and
the load carrying capacity of the members.

Some structures are built with more than this
minimum number of truss members. Those structures may survive even
when some of the members fail. They are called statically
indeterminate structures, because their member forces depend on
the relative stiffness
of the members, in addition to the equilibrium condition
described.

## Analysis of trusses

Because the forces in each of its two main
girders are essentially planar, a truss is usually modelled as a
two-dimensional plane frame. If there are significant out-of-plane
forces, the structure must be modelled as a three-dimensional
space.

The analysis of trusses often assumes that loads
are applied to joints only and not at intermediate points along the
members. The weight of the members is often insignificant compared
to the applied loads and so is often omitted. If required, half of
the weight of each member may be applied to its two end joints.
Provided the members are long and slender, the moments
transmitted through the joints are negligible and they can be
treated as "hinges" or
'pin-joints'. Every member of the truss is then in pure compression
or pure tension – shear, bending moment, and other more complex
stresses
are all practically zero. This makes trusses easier to analyze.
This also makes trusses physically stronger than other ways of
arranging material – because nearly every material can hold a much
larger load in tension and compression than in shear, bending,
torsion, or other kinds of force.

Structural
analysis of trusses of any type can readily be carried out
using a matrix method such as the matrix
stiffness method, the flexibility
method or the finite
element method.

### Forces in members

On the right is a simple, statically determinate flat truss with 9 joints and (2 x 9) − 3 = 15 members. External loads are concentrated in the outer joints. Since this is a symmetrical truss with symmetrical vertical loads, it is clear to see that the reactions at A and B are equal, vertical and half the total load.The internal forces in the members of the truss
can be calculated in a variety of ways including the graphical
methods:

- Cremona diagram
- Culmann diagram

Or the analytical Ritter method (method
of sections).

### Design of members

A truss can be thought of as a beam where the web consists of a series of separate members instead of a continuous plate. In the truss, the lower horizontal member (the bottom chord) and the upper horizontal member (the top chord) carry tension and compression, fulfilling the same function as the flanges of an I-beam. Which chord carries tension and which carries compression depends on the overall direction of bending. In the truss pictured above right, the bottom chord is in tension, and the top chord in compression.The diagonal and vertical members form the truss
web, and carry the shear
force. Individually, they are also in tension and compression, the
exact arrangement of forces depending on the type of truss and
again on the direction of bending. In the truss shown above right,
the vertical members are in tension, and the diagonals are in
compression.

In addition to carrying the static forces, the
members serve additional functions of stabilizing each other,
preventing buckling. In
the picture, the top chord is prevented from buckling by the
presence of bracing and by the stiffness of the web members.

The inclusion of the elements shown is largely an
engineering decision based upon economics, being a balance between
the costs of raw materials, off-site fabrication, component
transportation, on-site erection, the availability of machinery and
the cost of labor. In other cases the appearance of the structure
may take on greater importance and so influence the design
decisions beyond mere matters of economics. Modern materials such
as prestressed
concrete and fabrication methods, such as automated welding, have significantly
influenced the design of modern bridges.

Once the force on each member is known, the next
step is to determine the cross
section of the individual truss members. For members under
tension the cross-sectional area A can be found using A = F
× γ / σy, where F is the force in the member, γ is a
safety
factor (typically 1.5 but depending on building
codes) and σy is the yield tensile
strength of the steel used. The members under compression also
have to be designed to be safe against buckling.

The weight of a truss member depends directly on
its cross section -- that weight partially determines how strong
the other members of the truss need to be. Giving one member a
larger cross section than on a previous iteration requires giving
other members a larger cross section as well, to hold the greater
weight of the first member -- one needs to go through another
iteration to find exactly how much greater the other members need
to be. Sometimes the designer goes through several iterations of
the design process to converge on the "right" cross section for
each member. On the other hand, reducing the size of one member
from the previous iteration merely makes the other members have a
larger (and more expensive) safety factor than is technically
necessary, but doesn't require another iteration to find a
buildable truss.

The effect of the weight of the individual truss
members in a large truss, such as a bridge, is usually
insignificant compared to the force of the external loads.

### Design of joints

After determining the minimum cross section of the members, the last step in the design of a truss would be detailing of the bolted joints, e.g., involving shear of the bolt connections used in the joints, see also shear stress.## See also

- Andreini tessellations, the only 28 ways to fill 3D space with trusses that have identical joints everywhere
- Brown truss
- Geodesic dome, a truss in the shape of a sphere
- Girder
- Mechanics of structures
- Serrurier truss, a truss form used for telescopes
- Space frame
- Stress:
- Structural steel
- Tensegrity truss, a truss where no compression member touches any other compression member
- Truss bridge
- Truss rod, a guitar part

## References

## External links

- Historic Bridges of Michigan and Elsewhere With a focus on metal truss bridges, this site provides photos, information, maps, and links
- "Preventing Injuries and Deaths of Fire Fighters Due to Truss System Failures," National Institute for Occupational Safety and Health, Accessed September 13, 2007
- Classical Truss Theory
- An Introduction to Historic Truss Bridges
- truss bridge designer simulation (requires Java)
- Trusses in 20th-century architecture
- Vierendeel bridges (in Dutch)
- Residential trussed roofs Australia
- Structural Building Components Association
- Truss Types Visual Guide at Structural Wiki. Line diagrams and names of 30+ truss types.

truss in Catalan: Gelosia (estructura)

truss in German: Fachwerk

truss in Spanish: Celosía (estructura)

truss in Esperanto: kradtraba skeleto

truss in Hebrew: מסבך

truss in Italian: capriata

truss in Dutch: vakwerk

truss in Japanese: トラス

truss in Polish: Kratownica

truss in Russian: Ферма (конструкция)

truss in Swedish: Fackverk

# Synonyms, Antonyms and Related Words

bale,
band, bandage, belt, bend, bind, bind up, bindle, bolt, bouquet, brace, budget, bundle, bundle up, chain, cinch, deck, deflate, disarm, do up, enchain, fagot, fardel, fasces, fascine, gag, gird, girdle, girt, girth, hamstring, handcuff, hobble, hog-tie, knock out,
lace, lash, leash, manacle, muzzle, nosegay, pack, package, packet, paralyze, parcel, posy, prostrate, quiver, roll, roll up, rope, rouleau, sheaf, silence, splice, strangle, strap, swaddle, swathe, throttle, tie, tie up, truss up, wire, wrap, wrap up