A shell is a type of structural element which is characterized by its geometry, being a three-dimensional solid whose thickness is very small when compared with other dimensions, and in structural terms, by the stress resultants calculated in the middle plane displaying components which are both coplanar and normal to the surface. Essentially, a shell can be derived from a plate by two means: by initially forming the middle surface as a singly or doubly curved surface, and by applying loads which are coplanar to a plate's plane which generate significant stresses.

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Shell may refer to:

Architecture and design

Business

Chemistry and Physics

Computing

A shell corporation is a company which serves as a vehicle for business transactions without itself having any significant assets or operations. Some shell companies may have had operations, but those may have shrunk due to unfavorable market conditions or company mismanagement. A shell corporation may also arise when a company's operations have been wound up, for example following a takeover, but the “shell” of the original company continues to exist.

Shell corporations are not in themselves illegal, and they do have legitimate business purposes. However, they are a main component of the underground economy, especially those based in tax havens. They may also be known as international business companies, personal investment companies, front companies, or "mailbox" companies.

Shell companies can also be used for tax avoidance. A classic tax avoidance operation is based on the buying and selling through tax haven shell companies to disguise true profits. The firm does its international operations through this shell corporation, thus not having to report to its country the sums involved, avoiding any taxes.

In computing, a shell is a user interface for access to an operating system's services. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer's role and particular operation.

The design of a shell is guided by cognitive ergonomics and the goal is to achieve the best workflow possible for the intended tasks; the design can be constricted by the available computing power (for example, of the GPU) or the available amount of graphics memory. The design of a shell is also dictated by the employed computer periphery, such as computer keyboard, pointing device (a mouse with one button, or one with five buttons, or a 3D mouse) or touchscreen, which is the direct human–machine interface.

CLI shells allow some operations to be performed faster in some situations, especially when a proper GUI has not been or cannot be created. However, they require the user to memorize commands and their calling syntax, and also to learn the shell-specific scripting language, for example bash script. CLIs are also easier to be operated via refreshable braille display and provide certain advantages to screen readers.

In universal algebra and in model theory, a structure consists of a set along with a collection of finitary operations, and relations that are defined on it.

Universal algebra studies structures that generalize the algebraic structures such as groups, rings, fields and vector spaces. The term universal algebra is used for structures with no relation symbols.

Model theory has a different scope that encompasses more arbitrary theories, including foundational structures such as models of set theory. From the model-theoretic point of view, structures are the objects used to define the semantics of first-order logic. For a given theory in model theory, a structure is called a model, if it satisfies the defining axioms of that theory, although it is sometimes disambiguated as a semantic model when one discusses the notion in the more general setting of mathematical models. Logicians sometimes refer to structures as interpretations.

In database theory, structures with no functions are studied as models for relational databases, in the form of relational models.

The structure of a thing is how the parts of it relate to each other, how it is "assembled".

Structure may also refer to:

In architecture:

In engineering:

In art:

In biology:

In chemistry:

Structural engineers are most commonly involved in nonbuilding structures, as well as building structures, but they can also be involved in the design of machinery, medical equipment, vehicles or any item where structural integrity affects the item's function or safety. Structural engineers must ensure their designs satisfy given design criteria, predicated on safety (i.e. structures must not collapse without due warning) or serviceability and performance (i.e. building sway must not cause discomfort to the occupants).

Structural engineering theory is based upon applied physical laws and empirical knowledge of the structural performance of different materials and geometries. Structural engineering design utilizes a number of simple structural elements to build complex structural systems. Structural engineers are responsible for making creative and efficient use of funds, structural elements and materials to achieve these goals.

Structural Engineer (Professional)

Structural engineers are responsible for engineering design and analysis. Entry-level structural engineers may design the individual structural elements of a structure, for example the beams, columns, and floors of a building. More experienced engineers may be responsible for the structural design and integrity of an entire system, such as a building.