11 Types of Cerches according to Equilibrium, Conformation and Origin

The Types of trusses Can vary depending on the balance, conformation and origin or designer. Known as flat lattice, space or as lattices and reinforcements, in terms of engineering are rigid structures armed by straight rods at their ends that have a triangular shape.

This type of configuration has the property to support loads in its plane, especially those that act on the unions or nodes.

Types of trusses

Consequently, its application in the construction is of great importance, because it is an articulated and indeformable system that is not cut or flexed. This implies that its elements actively participate in terms of compression and traction.

Unlike the square, this triangular formation is not unstable, so it can be applied in works of small or large magnitude.

The trusses can be composed of various materials, the most used being wood, metal and reinforced concrete.

Depending on the use that you want to give this type of frame, they are generally applied in the construction of warehouse roofs, industrial warehouses, aircraft hangars, churches, stadiums, bridges or beam systems.

Classifications of types of trusses

According to its balance function

A truss may be totally isostatic or statically determined relative to the mechanical equilibrium applied to the external shape of the structure. The same happens with the internal elements, which are evaluated in their reactions and efforts to know their stability. The categories resulting from this evaluation have been established as follows:

A) Isostatic

This concept refers to a kind of structure that can be analyzed by the principles and formulas that make static values ​​known. As mentioned, its nature is determined statically, so that the removal of some of the components that bind the framework as such would cause catastrophic failure throughout the system.

B) Hyper-static

The essence of this type of configuration is its state of equilibrium, which means that the bending moment has a value equal to 0 in each of the bars that make up the system.

In spite of this condition, the truss can present instability conditions by the type of design with fixed knots that can resemble an isostatic structure.

According to its conformation

This type of truss presents a flat structure that is composed of articulated knots and that they present several forms:

A) Simple

This truss is a statically defined conformation, whereby the number of rods and the number of articulated joints must satisfy the appropriate formula. It presents the known form of a triangle and its calculation is based on graphical static and the balance of the knots.

B) Composite

Like the previous one, they present a structure with static determination that can be designed from 1 or 2 simple trunks. In this case, both structures are joined by an additional bar at a common point so that they remain fixed. They may also include 3 additional rods or an inner shell that meets the equilibrium criteria.

C) complex

Since they belong to the category of hyperstatic, its difference is that it does not exclude previous models and includes all other geometries. Although it is composed of fixed joints, its calculation can be done by the Heneberg method or the matrix method of stiffness. The first is more approximate, while the second is much more accurate.

Depending on your origin or who designed them

On the other hand, some commonly used trunks bear the names of their creators, who studied them or the city where they were first applied. These include:

A) Cercha Long

This variant appeared in 1835 and is related to Stephen H. Long. It is a design in which the horizontal cords of up and down are united by vertical uprights. The whole set is braced by double diagonals and resemble some X enclosed by pictures.

B) Howe Cercha

Although it had already been used before, this structure was patented in 1840 by William Howe. Also known as Belgian, it uses vertical uprights between the upper and lower lace and is applied a lot in wood. In this design is composed of diagonal bars receive the compression and other vertical that support the traction.

C) Certt de Pratt

Created by Caleb and Thomas Pratt in 1844, it is a variation of the previous model but with a more resistant material: the steel. It differs from the Howe truss in the direction of the bars, which form a V. In this case the vertical rods receive the understanding and the diagonals suffer the traction.

D) Cerren de Warren

Patented in 1848 by the English Willboughy Monzoni and James Warren, this structure is characterized by forming isosceles or equilateral triangles, giving the same length to the diagonals. Compression and tensile forces are present in these cross members due to the application of vertical loads at the upper knots.

E) Cercha K

It is usually applied to bridge design and owes its name to the orientation of a vertical element in combination with the oblique parts. It is presented as triangles that leave the center and its design allows to improve the performance of the compressed diagonals.

F) Cercha Baltimore

Another characteristic model of the bridges of this city. Incorporates more support at the bottom of the structure. This prevents collapse by compression and controls distention. Its sections look like 3 triangles in 1 linked by a horizontal bar.

It is important to note that although these structures can be both triangular and rectangular. This is clearly exemplified in gable, scissor and flown roofs. When using the uprights, incorporating these vertical elements into bridges, ceilings and vaults give it a slightly more square appearance.

References

  1. Muzammar, Chemma (2016). Types of Trusses. Recovered from es.slideshare.net.
  2. Mariana (2013). Hypostatic, isostatic and hyperstatic structures. Retrieved from prezi.com.
  3. Open Course Ware (2006). Structures type: function, general forms, elements... University of Seville. Recovered from ocwus.us.es.
  4. Tecun (undated). Flat shutters. University of Navarra, School of Engineers. Retrieved from dadun.unav.edu.
  5. Construmática (without date). Parts of a truss. Recovered from construmatica.com.


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