Abstract
There are frequent cases when load‐bearing reinforced concrete structures of not completed buildings are directly exposed to precipitation (rainfall, snowfall) and to environment of positive and negative temperature. Multihollowcore concrete slabs are especially vulnerable to such actions since investigations of condition of non‐conserved buildings indicate that these slabs can crack critically. Water accumulated in hollows of slabs and frozen under negative temperature can split concrete in vertical walls between hollows, inflict concrete cracking below hollows or spalling of large sections together with longitudinal reinforcement in them at the bottom of slabs. In performed investigations of condition of non‐completed and non‐conserved load bearing structures a modern method was employed for the determination of cracking in walls between hollows of slabs, using mini video‐camera. Analysis of cracking in slabs indicated that the character of cracking is governed by the quantity of water accumulated in a hollow at the moment of freezing and the level of freezing water in adjacent hollows of a slab and the compaction quality of concrete in a tensile zone of a slab as well. The analysis of pressure on the surface of hollows developed by ice set can be analysed employing a model of non‐linear analysis of COSMOS/M program and fracture mechanics of solids. Several versions of cracking in multihollowcore concrete slabs are possible, the most critical one of which is when a part of a bottom flange of a slab together with longitudinal reinforcement spalls off due to normal and shear deformations. The accomplished analysis allowed to establish kinetics of cracking for slabs and to evaluate their condition more reliably.
Highlights
completed buildings are directly exposed to precipitation
Multihollowcore concrete slabs are especially vulnerable to such actions since investigations
of condition of non-conserved buildings indicate that these slabs can crack
Summary
Lietuvos Respublikos statybos ástatyme [1] nurodoma, kad sustabdþius statybos darbus, kuriems pirkti taikomas Vieðøjø pirkimø ástatymas, nepaisant sustabdymo prieþasèiø, Vyriausybës arba jos ágaliotos institucijos nustatyta tvarka privalo organizuoti statomo statinio konservavimo darbus. Taèiau Lietuvoje dël lëðø stygiaus nemaþa dalis pradëtø ir nebaigtø statyti pastatø yra palikti neuþkonservuoti ir be reikiamos prieþiûros. Rekonstruojant pastatus techninës bûklës ávertinimas yra ypaè atsakingas, jei statinys buvo nebaigtas statyti ir prastovëjo nekonservuotas daug metø [2, 3]. Natûriniais tyrimais [2, 3] nustatyta, kad nekonservuotuose pastatuose dël lietaus vandens, pripildanèio kiaurymëtøjø perdangos plokðèiø kiaurymes, ir neigiamosios temperatûros poveikio dalies plokðèiø apatinëse lentynose atsivërë iðilginiø plyðiø, kertanèiø lentynas kiaurymiø vietose. Atidengus kiaurymes arba naudojant specialià vaizdo kamerà, skirtà vamzdþiø defektams tirti, nustatyta, kad daugeliu atvejø plyðiai buvo atsivëræ ir vertikaliosiose plokðèiø sienelëse tarp kiaurymiø. Siekiant nustatyti galimas minëtø plyðiø susidarymo vietas, programa COSMOS/M [6, 7] buvo analizuotas 6 m ilgio ir 1,2 m ploèio átemptojo gelþbetonio plokðtës, veikiamos kiaurymëse uþðàlanèio vandens slëgio, átempiø laukas. Netiesinio uþdavinio sprendimo pabaigos kriterijumi pasirinktas tempiamojo betono stipris, t. y. kai átempiai pasiekë tempiamojo betono stiprá bet kuriame plokðtës baigtiniame elemente, uþdavinys buvo stabdomas ir analizuojami átempiai plokðtës pjûvyje, kuriame veikë didþiausi tempimo átempiai
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