Puidust I-talade painde- ja nihkekandevõime empiiriline uurimine kolmandas kasutusklassis

Käesolevas lõputöös uuriti katseliselt Masonite tüüp H200 kergtalade nihke- ja paindekandevõimet esimeses ja kolmandas kasutusklassis. Nihkekandevõime katsete tulemused ja purunemispildid olid nii esimeses kui ka kolmandas kasutusklassis ootuspärased. Paindekandevõime katsete tulemused esimeses kasutusklassis olid ootuspärased, aga kolmandas kasutusklassis ilmnes, et määravaks sai erinevalt esimeses kasutusklassis tehtud katsetest hoopis survevöö purunemine. Survevöö purunemise tingis, hoolimata C30 tugevusklassi puidu suuremast survetugevusest võrreldes tõmbetugevusega, puidu niiskumisel kahanev survetugevus ja katsekeha kiivumine. Katsetulemuste analüüsi käigus arvutati katsetulemuste alusel põik- ja paindekandevõime statistilised piirväärtused 95% tõenäosusega (5-protsentiil). Piirväärtuste järgi leiti niiskuse ja koormuse kestuse mõju arvestav modifikatsioonitegur kmod nii esimesele kui ka kolmandale kasutusklassile, mis annab võimaluse hinnata katsekehade nihke- ja paindekandevõimet nimetatud kasutusklassides. Kuna standardis EVS-EN 1995-1-1:2005+A1+NA+A2 puudub katsekeha puitlaastplaadist seinale rakendatav kmod väärtus kolmandas kasutusklassis, annab käesolev töö empiirilise esialgse kmod väärtuse, mis on vajalik normatiivse nihkekandevõime teisendamisel arvutuslikuks. Katsekeha arvutuslik paindekandevõime on standardi järgi leitav, kuna saepuidust vöödele on antud kmod tegur ka kolmandas kasutusklassis. Katsete tulemusel leitud tegurid ja nende võrdlemine standardis EVS-EN 1995-1-1:2005+A1+NA+A2 toodud teguritega kinnitas töös kasutatud metoodika sobivust ja näitas, et tegurite suhted ning väärtused on empiiriliselt õiges suurusjärgus Tuginedes eelpool toodud andmetele on võimalik hinnata märgunud Masonite kergtala tüüp H200 kandevõime vähenemist ja vastavalt lõputöös toodud tulemustele otsustada milliseid meetmeid (koormuse vähendamine, ümberpaigutamine, toestamine) tarvitusele võtta, kui talad on paiknenud kolmandas kasutusklassis. Edasiste uuringute käigus tuleks täiendavate katsete abil täpsustada vastavaid modifikatsioonitegureid, viies katseid läbi erinevates koormuse kestusklassides ja veelgi ekstreemsemates kolmanda kasutusklassi tingimustes. Samuti tuleks uurida, kas katsekehade märgumine on mõjutanud nende kandevõimet peale niiskuse välja kuivamist ja kuidas mõjutavad kandevõimet bioloogilised tegurid ning katsekehade läbikülmumine.

In today’s world, the construction sector is increasingly raising awareness of the importance of a green mindset and sustainable, resource-efficient use of materials throughout the entire life cycle of a building. Timber, as a renewable and recyclable material, has been a traditional building material on one hand, while on the other hand, there is potential for its use to be expanded even further. The popularisation of wood as a building material has been driven in part by increasingly stringent environmental regulations, the pursuit of carbon neutrality, and the growing expertise in constructing reliable and energy-efficient timber buildings. A great example of this mindset is the adoption of wooden lightweight beams in construction. Compared to solid wood cross-sections, I-beams have significantly reduced material consumption and construction time without compromising strength properties. The decisive factor in choosing the thesis topic was the fact that although different manufacturers only allow the use of I-beams in service classes 1 and 2, there have been situations on construction sites where I-beams or elements made of beams have been left unprotected from the weather and, as a result, have become wet. Although manufacturers allow for short-term wetting of I-beams in their guidelines, they do not specify the permitted time frame or moisture content. The purpose of the thesis is to experimentally study how the transverse force and bending resistance of timber I-beams is affected by their presence in service class 3, and to find out which moisture and load duration effect factor kmod should be used for the I-beam selected for the tests in service class 3. The sought-after factor taking into account the effect of moisture and load duration would allow to evaluate the load-carrying capacity of wetted beams and to find the design bending and transverse force bearing resistance in service class 3. The results of the transverse force resistance tests and the failure patterns were as expected in both service class 1 and 2. The results of the bending resistance tests in service class 1 were as expected, but in service class 3 it appeared that, unlike the tests performed in service class 1, the decisive factor was the failure of the compression flange. The compression flange failed due to the decreasing compressive strength and bending of the test specimen when the timber became wet. During the analysis of the test results, the statistical limit values of the transversal and bending resistance were calculated with a probability of 95% (5th percentile) based on the test results. According to the limit values, the modification factor kmod, which takes into account the effect of humidity and load duration, was found for both service class 1 and 2, which gives the opportunity to evaluate the transverse force and bending resistance of the test specimens in the mentioned service classes. The factors found as a result of the tests and their comparison with the factors given in the standard EVS-EN 1995-1-1:2005+A1+NA+A2 confirmed the suitability of the methodology used in the study and showed that the ratios and values of the factors are empirically in the right order of magnitude. According to the results presented in the thesis, it is possible to evaluate the reduction of the load-carrying capacity of the wetted masonite I-beam type H200 and to decide what measures (load reduction, relocation, support) should be taken if the beams are located in service class 3. In the course of further studies, the respective modification factors should be specified with the help of additional tests, by carrying out tests in different load duration classes and even more extreme conditions of service class 3. It should also be studied whether the wetting of the test specimens has affected their load-carrying capacity after the moisture has dried out, and how biological factors and freezing of the test specimens affect the load-carrying capacity.