The aim of this paper is to contribute to the classification of structural timber in the ex-YU region into strength-class system through the application of experimentally obtained archive data in ...order to provide a realistic framework for most commonly used II grade (according to JUS) structural coniferous timber. The analysis of archive data was carried out on a sample of 150 specimens of structural size and based on the set of statistical requirements prescribed by EN standards, taking into account the change in disposition of loading in laboratory testing in the past and now. Statistical procedures prescribed by EN standards are given through calculation steps together with necessary adjustment factors that cover the size and number of specimens. The presented procedures given for structural-size specimens are also applicable to small clear specimens, so that a more comprehensive research and additional new examinations could be conducted with the available archive data simultaneously with the harmonization of the visual classification rules applied in the ex-YU region. The paper emphasises the direct dependence of the consistent application of the visual grading rules required by the relevant EN standard on strength-class system.
Cilj ovog rada jest pridonijeti klasifikaciji konstrukcijskog drva na području bivše Jugoslavije u sustavu klasa čvrstoće primjenom eksperimentalno dobivenih arhivskih podataka kako bi se dobio realan okvir za najčešće upotrebljavano konstrukcijsko crnogorično drvo razreda II (prema JUS-u). Analiza arhivskih podataka provedena je na skupini od 150 uzoraka konstrukcijske veličine, i to na temelju skupa statističkih zahtjeva sadržanih u regulativi EU-a, pri čemu je uzeta u obzir promjena rasporeda opterećenja u laboratorijskim ispitivanjima u prošlosti i danas. Statistički postupci propisani EN normama dani su putem koraka izračuna, zajedno s potrebnim faktorima prilagodbe koji pokrivaju veličinu i broj uzoraka. Predstavljeni postupci dani za uzorke konstrukcijske veličine primjenjivi su i za male čiste uzorke, tako da bi se proširena kampanja s postojećim arhivskim podatcima i dodatnim novim ispitivanjima mogla provoditi istodobno s usklađivanjem pravila vizualne klasifikacije konstrukcijskog drva u bivšoj Jugoslaviji. U radu je naglašena izravna ovisnost dosljedne primjene pravila vizualnog ocjenjivanja kvalitete drva koja zahtijeva relevantna EN norma o sustavu klasa drva prema čvrstoći.
In Europe the structural timber building product cross laminated timber (CLT) is regulated via European Technical Assessments (ETAs), which require large and voluminous test campaigns to obtain. So ...far, there is no standardised CLT strength class system nor a set of harmonised properties. Such a strength class system and tabulated values could be accompanied by a set of so-called load-bearing models, analogous to the current regulations for glued laminated timber (GLT). The aims of this contribution are to comprehensively analyse the first known load-bearing model for out-of-plane bending of CLT from 2006 and to validate and benchmark this approach with possible further candidates. The aim is to initiate the establishment of a European strength class system for CLT based on its out-of-plane bending properties, for a more reliable, regulatory compliant structural building product and for enhancing its market acceptance. Therefore, a comprehensive analysis of various potential influencing parameters on out-of-plane CLT bending properties is effected by means of stochastic-numerical investigations as well as a large amount of test campaigns, the latter in the form of a retrospective study. The first approach from 2006, in particular in its adapted version, is successfully validated and confirmed as a valuable candidate for the future regulation of CLT due to its overall more accurate and more reliable strength predictions compared with the other candidates. In addition, models for the density and the modulus of elasticity parallel to the grain, as currently defined for glulam, are confirmed to be applicable also for CLT. An analysis of the variation in the properties of the base material and CLT motivates additional efforts towards grading and quality assurance in order to meet the expectations of the nominal strength class of boards and to fulfil minimum requirements for finger joint quality to better utilise the high performance of CLT and to increase its reliability.
•validation of the first load-bearing model for out-of-plane CLT bending strength and benchmark with other potential models;•main influencing parameters on out-of-plane CLT bending properties identified via three-dim. stochastic-numerical models;•analyses of tests on different timber species, layups, etc., knowing the tensile properties of the boards and finger joints;•identifying further efforts on quality assurance to better utilise the high mechanical properties of CLT;•load-bearing model for out-of-plane CLT bending strength, MOE and density proposed as a basis for CLT strength classes.
Classification of timber for various commercial purposes is essential for its proper application in order to ensure the reliability and economic use. Visual grading of structural timber is commonly ...used in a number of EU countries, with different grading national standards optimized for locally available wood. Countries in the ex-YU region are traditional partners in wood trade and had the same standards for visual grading, but in most of the regions these standards are not completely compliant with EN requirements. Consequently, that leads to the fact that the most of regionally available structural timber is not assigned into strength classes, which is the starting point for the limit-state concept in design of timber structures. The aim of this paper is to emphasize the lack of strength classification of structural timber in the ex-YU region, which is a prerequisite for the design of timber structures made by civil engineers. Based on an overview of visual classification types with regional experience in grading, relevant EN standards, and differences in design concepts with possible consequences of grading approach, it can be concluded that "quality" grades and "strength" classes are not easily comparable.
Klasifikacija drvne građe za različite komercijalne namjene ključna je za njezinu pravilnu upotrebu kako bi se zajamčila sigurna i ekonomična uporaba. Vizualno ocjenjivanje konstrukcijskog drva obično se provodi u mnogim zemljama EU-a uz pomoć različitih nacionalnih standarda ocjenjivanja optimiziranih za lokalno dostupno drvo. Zemlje bivše Jugoslavije tradicionalni su partneri u međusobnoj trgovini drvom i imale su zajedničke standarde za vizualno ocjenjivanje drvne građe, ali u većini njih ti standardi nisu u potpunosti usklađeni s EN zahtjevima. To posljedično rezultira činjenicom da većina regionalno dostupnoga konstrukcijskog drva nije razvrstana u klase čvrstoće, što je polazište za koncept graničnog stanja u projektiranju drvnih konstrukcija. Cilj rada jest upozoriti na nepostojanje klasifikacije čvrstoće konstrukcijskog drva na području bivše Jugoslavije, a to je preduvjet za projektiranje drvnih konstrukcija, što je posao građevinskih inženjera. Na temelju tipova vizualne klasifikacije i regionalnih iskustava u ocjenjivanju, relevantnih EN normi te razlika u konceptima projektiranja s mogućim posljedicama pristupa ocjenjivanju, zaključeno je da ocjene razreda kvalitete i klase čvrstoće u promatranim zemljama jednostavno nisu međusobno usporedive.
The paper demonstrates improved structural low-frequency vibroacoustic performance of cross-laminated timber (CLT) floor panels by informed selection of the wood material. The use of wood species and ...strength classes that are not traditionally assigned to CLT panels was investigated in order to study their influence on dynamic characteristics and vibroacoustic response metrics. The potential of each of the orthotropic material properties to alternate the vibration response was examined to determine the governing parameters of the low-frequency vibroacoustic performance. The effects on transfer mobility response functions, and eigenfrequencies and mode shapes were used for a rigorous performance study of the panels. It was found that using laminations with stiffness properties typical for hardwoods ash, beech, and birch can significantly improve the performance of a CLT floor panel, and they outperform laminations of typical softwood strength classes.
Background and Objectives: The aim of this study was to determine the effects of different stand densities on wood density (WD), global modulus of elasticity (MOE), and bending strength (MOR) in ...35-year-old Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst) stands, representing the hemiboreal forest zone. Materials and Methods: Scots pine and Norway spruce sites, representing different stand densities of 3000–3100; 2000–2100 and 1000–1100 trees per hectare, were chosen. Visually healthy model pine and spruce trees were selected, and diameter at breast height (DBH) was measured for model trees; the competition index was calculated; the MOE and MOR were evaluated by the Standards EN 408:2006 and EN 384:2016, at 12% moisture content; WD and the knot diameter were measured; and the strength class of wood was determined by the Standard EN 338:2009. To predict wood quality characteristics based on stand and tree characteristics, linear regression models were developed. Results and Conclusions: Higher stand density led to a significant change in the main wood properties of both conifer species. The highest mean WD, MOE, and MOR were obtained at the sites with the highest stand density. The MOE and MOR were highly correlated, but relatively weak correlations were found between MOE and MOR with tree DBH and WD. Despite the lower quality of Scots pine wood, the Norway spruce wood from more dense sites corresponded to the strength class of C16, according the strength grading of softwoods. The linear regression models did not perform well in describing the relationship of wood properties with stand and tree characteristics. The models for MOR accounted for the highest variation of 62–65% for both Scots pine and Norway spruce. These relationships can be expected to change with increased stand age or with the inclusion of specific crown parameters.
Artificial intelligence and its diverse applications are examples of emerging new technologies that have so far been shown to be successful in merging scientific applications. Generally, intelligent ...systems outperform their traditional counterparts in solving non-linear tasks. Artificial neural network (ANN) models are usually designed and used to arbitrate these non-linear problems; as they mimic the structure and function of a biological brain. In this paper, an intelligent classification system is proposed to decide the result of a routine and laborious civil engineering quality control process. The ANN model is specifically designed, implemented and tested in order to classify the compressive strength grade of different concrete mixes as low, normal or high strength. Concrete elements of varying compressive strength classes and qualities, are required to be used for different purposes and under different environmental conditions. The grade of the concrete’s strength is highly dependent on many non-linear factors and it is often conventionally determined by using civil engineering methods involving the destruction of concrete samples. Our aim is to classify the concrete strength without destructing any samples. Experimental results in this work show high efficiency in correctly classifying the compressive strength.
The paper presents the results of experimental tests and the process by which a batch of spruce timber elements is sorted in a strength class with reliability.
RESUMO Como consequência dos fatores edafoclimáticos, as propriedades da madeira podem ser influenciadas de acordo com a região de desenvolvimento da árvore. O objetivo do presente trabalho consistiu ...em verificar a influência da região de extração de lotes da madeira de Tatajuba (Bagassa guianensis), provenientes de duas diferentes regiões do Brasil (Alta Floresta e Bonfim do Sul, municípios dos estados de Mato Grosso e Roraima, respectivamente), ao teor de umidade de 12%, em algumas de suas propriedades físicas e mecânicas. Para cada um dos lotes foram determinadas duas propriedades físicas e cinco propriedades mecânicas, de acordo com a norma ABNT NBR 7190:1997. Para avaliar a influência da região de extração nas propriedades, foi realizada a análise de variância de Kruskal-Wallis, considerando resultados significativos (valores não equivalentes) aqueles que atendiam à condição P-valor < 0,05. De acordo com os resultados da análise estatística, os diferentes lotes da mesma espécie de madeira apresentaram valores médios das propriedades estudadas equivalentes em relação ao conjunto composto por todas as madeiras, porém, os valores médios da resistência na compressão paralela (fc0) e da densidade aparente não foram significativos entre as duas regiões. Os valores característicos da fc0 foram diferentes para os lotes das duas regiões, ao teor de umidade de 12%, implicando em classes de resistência diferentes (D50 – Alta Floresta e D60 – Bonfim do Sul).
En las últimas décadas en Europa se ha promovido la promulgación de Códigos de Práctica, Directivas y Normas Armonizadas de obligado cumplimiento para los países miembros, que afectan a la madera en ...la construcción y que son imprescindibles para favorecer al material en su uso estructural. Debido al carácter dinámico intrínseco a las normas, y necesario para su funcionalidad, éstas sufren modificaciones en el tiempo por lo que es necesario confrontarlas con el material realmente existente. En este trabajo se realizó un muestreo representativo en el País Vasco sobre una de las especies de madera más habituales en la construcción en España como es el pino radiata (Pinus radiata D.Don), buscando la veracidad de lo disponible en el mercado tanto en calidades como en dimensiones, y se aplicó la metodología normalizada y estipulada para su caracterización. Además, en cada una de las piezas se aplicaron los criterios de clasificación visual establecidos en la norma española UNE 56.544 para la estimación de calidades. En los resultados se presentan las conclusiones obtenidas tras la aplicación de las últimas variaciones de la normativa para la determinación de las propiedades mecánicas, las cuales están implicadas en los análisis de la caracterización estructural de la madera y condicionan la asignación resistente final. Abstract In the last decades in Europe the promulgation of Practice Codes, Directives and Harmonised Standards of obliged fulfilment for the member countries was promoted. They affect to wood in construction and are essential to improve the material in the structural use. Due to the dynamic character proper of standards, and necessary for their functionality, these suffer modifications in the time that are necessary to check in the really existing material. In this work, a representative sampling on one of the usual species of wood in the construction in Spain, as it is the radiata pine, was carried out, looking for the veracity of the available material in the market both in qualities and sections. The standard methodology stipulated for the characterization was applied. Additionally, in each piece, the visual classification criteria established in the Spanish standard UNE 56.544 for the estimation of the strength grades, was applied. The results set forth the conclusions obtained after the application of the last changes of the regulation for the determination of mechanical properties, which are involved in the analyses of the structural characterization of timber and determine the final strength assignation.