Editing Structural engineering (section)

==Structural elements==
{{main|Structural element}}

[[File:Bending.svg|thumb|right|A [[statically determinate]] simply supported beam, bending under an evenly distributed load]]

Any structure is essentially made up of only a small number of different types of elements:
* [[Columns]]
* [[Beam (structure)|Beams]]
* [[Plate (structure)|Plates]]
* [[Arch]]es
* [[Thin-shell structure|Shells]]
* [[Catenaries]]

Many of these elements can be classified according to form (straight, plane / curve) and dimensionality (one-dimensional / two-dimensional):

{| class="wikitable" style="border-collapse: collapse;"
|-
!style="background: #eeeeee;" |
!style="background: #eeeeee;" colspan="2" align="center" |One-dimensional
!style="background: #eeeeee;" colspan="2" align="center" |Two-dimensional
|-
!style="background: #eeeeee;" |
!style="background: #eeeeee;" |straight
!style="background: #eeeeee;" |curve
!style="background: #eeeeee;" |plane
!style="background: #eeeeee;" |curve
|-
|(predominantly) bending
| align="center" |[[Beam (structure)|beam]] || align="center" | continuous [[arch]]
| align="center" |[[Plate (structures)|plate]], [[concrete slab]]  || align="center"| [[planar lamina|lamina]], [[dome]]
|-
|(predominant) tensile stress
| align="center"|rope, tie || align="center"|[[Catenary]]
|colspan="2" align="center" | [[Thin-shell structure|shell]]
|-
|(predominant) compression
|colspan="2" align="center" | [[Pier (architecture)|pier]], [[column]]
|colspan="2" align="center" | [[Load-bearing wall]]
|}

===Columns===
{{Main|Column}}

Columns are elements that carry only axial force (compression) or both axial force and bending (which is technically called a beam-column but practically, just a column). The design of a column must check the axial capacity of the element and the buckling capacity.

The [[buckling]] capacity is the capacity of the element to withstand the propensity to buckle. Its capacity depends upon its geometry, material, and the effective length of the column, which depends upon the restraint conditions at the top and bottom of the column. The effective length is <math>K*l</math> where <math>l</math> is the real length of the column and K is the factor dependent on the restraint conditions.

The capacity of a column to carry axial load depends on the degree of bending it is subjected to, and vice versa. This is represented on an interaction chart and is a complex non-linear relationship.

===Beams===
{{Main|Beam (structure)|l1=Beam}}
[[File:The Little Belt Bridge (1935).jpeg|thumb|[[Little Belt Bridge|''Little Belt'']]: a [[truss bridge]] in [[Denmark]]]]

A beam may be defined as an element in which one dimension is much greater than the other two and the applied loads are usually normal to the main axis of the element. Beams and columns are called line elements and are often represented by simple lines in structural modeling.
* [[cantilever]]ed (supported at one end only with a fixed connection)
* simply supported (fixed against vertical translation at each end and horizontal translation at one end only,  and able to rotate at the supports)
* fixed (supported in all directions for translation and rotation at each end)
* continuous (supported by three or more supports)
* a combination of the above (ex. supported at one end and in the middle)

Beams are elements that carry pure bending only. Bending causes one part of the section of a beam (divided along its length) to go into compression and the other part into tension. The compression part must be designed to resist buckling and crushing, while the tension part must be able to adequately resist the tension.

===Trusses===
{{Main article|Truss}}
[[File:McDonnell-Planetarium.jpg|thumb|The McDonnell Planetarium by [[Gyo Obata]] in [[St Louis, Missouri]], USA, a concrete shell structure]]
[[File:gateway arch.jpg|thumb|upright|The 630 foot (192 m) high, stainless-clad (type 304) [[Jefferson National Expansion Memorial#The Gateway Arch|Gateway Arch]] in [[St. Louis|St. Louis, Missouri]]]]

A [[truss]] is a structure comprising members and connection points or nodes. When members are connected at nodes and forces are applied at nodes members can act in tension or compression. Members acting in compression are referred to as compression members or [[strut]]s while members acting in tension are referred to as tension members or [[Tie (engineering)|ties]]. Most trusses use [[gusset plates]] to connect intersecting elements.  Gusset plates are relatively flexible and unable to transfer [[bending moment]]s. The connection is usually arranged so that the lines of force in the members are coincident at the joint thus allowing the truss members to act in pure tension or compression.

Trusses are usually used in large-span structures, where it would be uneconomical to use solid beams.

===Plates===
{{Main|Plate (structure)}}

Plates carry bending in two directions. A concrete flat slab is an example of a plate. Plate behavior is based on [[continuum mechanics]]. Due to the complexity involved they are most often analyzed using a finite element analysis. 

They can also be designed with yield line theory, where an assumed collapse mechanism is analyzed to give an upper bound on the collapse load. This technique is used in practice<ref>{{cite web |title=Assessment of a Pair of Reinforced Concrete Roof Slabs |url=http://www.ramsay-maunder.co.uk/downloads/precast_roof_slabs.pdf |website=Ramsay-Maunder.co.uk |publisher=Ramsay Maunder Associates |date=2011 |access-date=2022-03-08 }}</ref> but because the method provides an upper-bound (i.e. an unsafe prediction of the collapse load) for poorly conceived collapse mechanisms, great care is needed to ensure that the assumed collapse mechanism is realistic.<ref>{{cite web |url=http://www.ramsay-maunder.co.uk/downloads/l_shaped_landing.pdf |title=Reappraisal of a Simply Supported Landing Slab |website=Ramsay-Maunder.co.uk |publisher=Ramsay Maunder Associates |url-status=live |archive-url=https://web.archive.org/web/20160304071038/http://www.ramsay-maunder.co.uk/downloads/l_shaped_landing.pdf |date=2011 |archive-date=2016-03-04 |access-date=2022-03-08 }}</ref>

===Shells===
{{Main|Thin-shell structure}}
{{See also|Gridshell|Space frame}}

Shells derive their strength from their form and carry forces in compression in two directions. A dome is an example of a shell. They can be designed by making a hanging-chain model, which will act as a catenary in pure tension and inverting the form to achieve pure compression.

===Arches===
{{Main|Arch}}

Arches carry forces in compression in one direction only, which is why it is appropriate to build arches out of masonry. They are designed by ensuring that the [[line of thrust]] of the force remains within the depth of the arch. It is mainly used to increase the bountifulness of any structure.

===Catenaries===
{{Main|Tensile structure}}

Catenaries derive their strength from their form and carry transverse forces in pure tension by deflecting (just as a tightrope will sag when someone walks on it). They are almost always cable or fabric structures. A fabric structure acts as a catenary in two directions.
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===Seismic base isolators===
{{Main|Vibration control}}

[[Base isolation]] is a collection of structural elements of a building that should substantially [[decouple]] the building's [[superstructure]] from the shaking ground thus protecting the building's integrity and improving its [[seismic performance]]; see, e.g., the shake table testing of a kind of ''' seismic base isolators''' called [[Earthquake Protector]]s. This technology, which is a kind of seismic [[vibration control]], can be applied both to newly designed buildings and to seismic upgrading of existing structures. Normally, excavations are made around the building which is separated from its foundation. Steel or reinforced concrete beams replace the connections to the foundation, while under these, the isolating pads, or '''seismic base isolators''', replace the material removed. While the [[base isolation]] tends to restrict the transmission of the ground motion to the building, it also keeps the building positioned properly over the foundation.
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