István Sajtos

Effect of stereotomy on the lower bound value of minimum thickness of semi-circular masonry arches

ABSTRACT Constructing structural systems with the minimal required cross section of its members was a strong motivation for progress whole along the history of building. This article investigates the effect of stereotomy on the minimum thickness value of a semi-circular arch made of masonry: a material with negligible tensile strength. The arch is modeled with its center line to which the loading is assigned according to arch length. Here, instead of some scalar parameters such as the rupture angle and the location of the middle hinge on the intrados, the geometry of the stereotomy is associated with a continuous function. Stereotomy-related constraints are introduced to keep the results feasible from an engineering point of view, and it is also demonstrated that they are essential for a well-posed constrained optimization problem. The necessary condition for a non-vanishing lower bound of minimum thickness values is derived analytically considering the assumptions of limit state analysis, infinite friction, and a no-tension material model. The lower bound thickness to radius ratio (t/R) is found to be t/R = 0.0819. A numerical method is introduced to demonstrate the existence of a valid stereotomy at the lower bound. Multiple admissible stereotomy patterns are presented at various minimum thickness values (higher than the lower bound) to demonstrate that suitable stereotomy for a fixed (t/R) ratio is far not unique—in general even the location of the middle hinge and the rupture angle might vary.

Csak nyomásnak ellenálló, alakváltozásra fellágyuló anyagú falazat — vályogfalazat — teherbírása

Valyogfalazat teherbirasat hataroztuk meg kulpontos nyomasra. A teherbirast, a kiserleteknek megfelelő, csak nyomasnak ellenallo, alakvaltozasra fellagyulo anyagmodellel szamitottuk. A javasolt anyagmodell parametereinek valtoztatasaval a mernoki gyakorlatban hasznalt anyagmodellek mindegyike előallithato. A falazat teherbirasat nem lehet előirt tonkremeneteli allapotokat kivalasztva meghatarozni. A tonkremenetelt jelentő igenybevetelt a keresztmetszet nyomatek-gorbulet fuggvenyenek maximuma szolgaltatja. Megallapitottuk, hogy a tonkremenetelt jelentő allapotot nem feltetlenul jelzi előre repedes. Ugyanakkor a falazat viselkedese is valtozik, a duktilistol a ridegig, az igenybevetelek valtozasaval. Azt is megallapitottuk, hogy a falazat magsavja, ami a repedesmentes allapothoz tartozo kulpontos erők tartomanya, fugg a javasolt anyagtorveny parametereitől es a műkodő nyomoerő nagysagatol is. Javaslatot tettunk egy egyszerűbb, de elfogadhato pontossagu, a javasolt anyagtorvenyt helyettesitő, anyagtorvenyre is.

The economy of the exotic: The relation of shell architecture and industrialization in Hungary between 1949–1970

The history of shell architecture is closely linked to the rapid industrialization of the first half of the 20th century. The large spans required for industrial buildings were most suitable for the developing structural systems based on reinforced concrete shells. Present paper studies the unique features of the development of shell architecture in Hungary, in comparison to other former socialist states and the West. The significance of individual engineering qualities as opposed to the international trends is studied via the evolution of the shell roofing designed for the KOFEM Factory. The different social-political context and the relative isolation of the Soviet Sphere of interest during the second half of the 20th century generated a mild western interest toward the ‘exotic’, the architectural developments of the eastern block. As the former socialist countries are recently coming to terms with their socialist architectural heritage, this interest is awakened. The short analysis of the western recog...

Geometriai módszer alkalmazása gömbhéjak horpadásának vizsgálatához@@@Application of geometric method to study the buckling of spherical shells

A gombhejak horpadasi alakjat a kutatok jelentős resze forgasszimmetrikusnak feltetelezi. A megvaltozott alak a gombfelulet egy reszenek egy sik altal valo lemetszesevel, es a lemetszett resznek a sikra valo tukrozesevel nyerhető. Altalaban az a feltetelezes, hogy az eredeti gomb es a tukrozott gombresz csatlakozasi vonala, a horpadasi el kor alaku. Kevesen foglalkoznak az ettől elterő, de a kiserletek soran sokszor tapasztalt poligonalis horpadasi alakkal, melynel a horpadasi el valamely szabalyos sokszoghoz hasonlit. Az irodalomkutatas alapjan az erre az esetre vonatkozo megallapitasuk egysegesen az, hogy a kerdes nem megoldott, a tema tovabbi vizsgalatot igenyel. Kutatasunk celja a gombhej valodi horpadasi alakjanak meghatarozasa, tovabba a horpadast leiro teher-elmozdulas osszefugges meghatarozasa. Ehhez olyan kvalitativ modellt dolgoztunk ki, mely visszaadja a kiserletek soran tapasztalhato viselkedest. Bemutatjuk ezen kivul azt is, hogy a horpadasi el poligonalis alakja a rugalmasan agyazott sikbeli nyomott gyűrű kihajlasaval is osszefuggesbe hozhato. A cikkben az elmeleti eredmenyeket kiserleti eredmenyek tamasztjak ala. | Application of geometric method to study the buckling of spherical shells. The buckling shape of a spherical shell is assumed to be rotationally symmetric by most of researchers. The deformed shape can be obtained by a section of the sphere with a plane and by the mirror-reflecion of the cut-away part of the sphere. The intersection line between the original sphere and the mirror-reflected part of the sphere, i.e. the buckling edge is usually supposed to be a circle. Only few of the researchers suppose polygonal buckling deformations, which are different from the previous case, also they often appear in experiments. In this case, the buckling edge is close to a regular polygon. According to our literature search, researchers state that the problem needs further investigation. The aim of our research is to find the real buckling shape of spherical shells, and to determine their load-deflection relationship. A qualitative model is established to reproduce the behaviour observed in experiments. The connection between the polygonal buckling shape of a spherical shell and the buckling of a planar compresssed ring with elastic support is also shown. The theoretical achievements in the article are confirmed by experimental results.

Long-Term Strain Measuring of Technical Textiles by Photographic Method

The technical textiles are very sensitive materials. To measure the elongation of such a material needs special care. A photographic procedure has been investigated to measure the plain elongation of textile specimens. It is especially suitable for long-term measuring programs. Some experimental results measured by the described method are published.

Analysis of Adobe-Clay as an Envorinmental-Friendly Structural Material

The research topic is the analysis of adobe-clay as a structural material. The behaviour of adobe brick elements of different mixtures were examined. The bricks of various ratios of clay, straw, reed and sawdust were involved in the experiment, in which the process of drying and shrinkage was investigated. Even though only a few data have been obtained so far, some important conclusions were drawn. The first drying period was approximately three weeks long in the laboratory. The tests have shown that organic components like straw, reed and sawdust slow down the drying process. In case of each mixture, a change of weight was observed sooner than shrinkage. The aim of the research is to promote the application of this building material.