Pleskan T. A.

National Research Irkutsk State Technical University

General review of construction of outer shells and their classification

Introduction

Architecturally, shells are structural elements which allow us to crystallize difficult and unconventional moulds. Shells are used for covering big areas without transitive pylons. It allows us to schema buildings as rationally and economically as it possible. Solidity and tastefulness of constructions, harmony and expression of mould are achieved with the help of sells. There are three-dimensional, hanging, reticulate and membranous shells of reimpositioned concrete, metals, and wood, polymeric, textile and composition materials in architectural practice. Shells are advantageous for architects and designers.

For example, during the project conception of refurbishment of art museum in Irkutsk, a new idea started up. It was the idea of arrangement of space on courtyard of museum complex with canopy sells. But there were questions about exploiter of shells, special aspects of their designing and possibility of shells to serve additional functions. There are plans for some additional functions such as: lighting, arrangement of expositional street area, using constructions as hardscape elements.

The aim of this research is an analysis of rationality of using shells as a spatially-organized element.

The history of shell structure

From the standpoint of structural mechanics shell is a body confined with two surfaces. The distance between these surfaces (shell thickness) is smaller than other amounts of this body. They (shells) allow spanning considerable area without interior support, but just by means of self-supported feature of construction. At that stiffness of shells is achieved by means of geometry of structure in process of engineering design without increase in weight of material.

Grid shells can be broken down into several categories: thin-shell structures, hyperboloid structures and complex amorphous reticulated structure. It is worth to distinguish slewing shells such as cylindrical, spherical, cone-shaped, toroid-shaped and so on. These shells are used construction solution more often because of some undeniable advantages.

In 1896 Russian architect-engineer V.G. Shukhov invented and patented three types of base grid shells (three-dimensional, hanging and hyperboloid structures) and developed the basic theory of shells. However, because of complexity of calculation, high quality requirement to the material and technical supplying grid shells began to be widely used only at the end of XX century. V.G. Shukhov used steel hyperboloid shells with lozenge load carrying grillage. Load carrying grid shells are performed of metal, composition material and wood. Until mid-XX century load carrying grid shells had been used very rarely because of complexity of calculation, high quality requirement to the material and compliance with the requirements of matching. For All-Russia industrial and art exhibition in 1896 in Nizhny Novgorod V.G. Shukhov built eight huge thin-shell structures exhibition pavilions with grid shells structure and first in the world grid shells tower of extraordinary beauty. It was bought by benefactor U.S.Nechaev-Maltsov after exhibition and was carried to his estate Polibino (Lipetsky region), where it has saved until present days. The main feature of Shukhov’s shells is using hyperboloidal forms and consequently the opportunity of gathering them from long rectilinear elements which do not have knees.

We had unique experience of investigation, development and using long thinwalled wooden cylindrical shell vault in building. From 1931 they had been used in one- or multi-wave cover of mill buildings with bay about 100 meters. Famous architects such as Buckminster Fuller, Norman Foster, Frank Gehry, Nicholas Grimshaw, Santiago Calatrava made substantial contribution to implementation of load carrying grid shells. Grid shells have got plenary recognition and wide spreading in progress architecture during last two decades by cybernation of calculation practice of constructions and advent of a new building materials and technologies. In XXI century grid shells have become one of the main means of form making of mould-breaking buildings, including skyscrapers and masterwork in “high-tech” style. In building practice reinforced concrete shells (by the way, several accidents have happened recently in Russia) are getting out by grid shells gradually. Steel grid shells of buildings and structures are operated in our climate without accidents. Shukhov’s grid shells do not destroy without rust protection from 70 to 100 years.

The main difference of modern grid shells from hyperboloid constructions is using node connection. As a result a construction may be built of short elements, which connect in nodes. Band of a tower of such construction has broken form but not straight line as it is in Shukhov’s shells.

Classification

Despite the diversity of constructions the most acceptable classification is the static type-work classification – spacing and unspaced. Such classification holds water as coincides with classification of geometrical form shells. Obviously as any others the classification on picture 1 generalizes and simplifies occurrence and does not take into account possible variants of designing. For example, using in building unspaced folded cover and walls and welded them together flexurally we will get framed bent so that spacing construction.

Unspaced constructions:

1. Curl

2. Shell of zero curvature (cylindrical and cone-shaped)

Spacing constructions:

1. Cope (glib, wave, curly, cloistered and intersecting)

2. Bowl (with different geometry of cover) on round or ellipsoid plan

3. Shallow shell on polygonal annular foundation (positive or negative curvature)

4. combined (complex) of fragments of shells similar or different curvature.

Speciality of constructions from thin-shell structure and curls (as it was said by P.L.Nervy) is the fact, that their carrying force is function of their geometrical form. Changing a curvature of a shell and its camber of arch will change its rigidness without increasing of material consumption. Right choice of geometrical form supplies activity of the biggest part of structural section on axial stress, leaving activity on stretching and shift to the special elements of the construction - diaphragm plate, body of shield and end beam. In spite of original form of space constructions, all of these determinate their economical efficiency, which increases with enlargement of ceil bays.

Speaking about functions of shells, it is impossible to disregard constructions have been developed recently, which have define qualities such as permselective membranes, self-adapting shells.

In most cases there is not clear separation of shell’s functions. Shells is structures with explicit tendencies to combining functions of constructions and it is their the best reference.

Reference list:

1. Product spatial structures recommended for public buildings with large spans. - L .: Stroyizdat, 1977.

2. The modern space construction (concrete, metal, wood, plastic) / Ed. Y.A. Dykhovichny and E.Z. Zhukovsky. - M .: Higher School, 1991.

3. Thesis: "Nonlinear parametric vibrations of shells and a zero Gaussian curvature." - Candidate of Physical and Mathematical Sciences O.S. Bakashkina, 2004.