Everything About Wood

Saturday, 29 October 2016

Evaluation of the mechanical properties of cross laminated timber with elementary beam theories

Published Date
30 September 2016, Vol.122:202–213, doi:10.1016/j.conbuildmat.2016.06.082

Author

I.P. Christovasilis^a,^,

M. Brunetti^b^,

M. Follesa^c^,

M. Nocetti^b^,

D. Vassallo^c^,

aAether Engineering s.a.s., Via Quintino Sella 6/A, 50136 Florence, Italy

bCNR-IVALSA, Istituto per la Valorizzazione del Legno e delle Specie Arboree, via Madonna del Piano 10, I-50019 Sesto Fiorentino (FI), Italy

cdedaLEGNO, Via Masaccio 252, 50132 Florence, Italy

Received 26 January 2016. Revised 14 June 2016. Accepted 15 June 2016. Available online 23 June 2016.

Highlights

Presents well-established theories for identification of mechanical properties.
•
Covers identification procedures for loads perpendicular and parallel to plane.
•
Bending response is well represented in terms of elastic and strength properties.
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Rolling shear strength demonstrates a significant variability.
•
Consistency identified for a combined shear failure criterion for loads in plane.

Abstract

This paper presents a study on the assessment of the mechanical properties of cross laminated timber (CLT) panels based on four-point bending tests. The most recent or well-established analytical theories have been implemented to estimate stiffness and strength properties under loads perpendicular or parallel to the principal plane of CLT panels from laboratory tests. The main objectives were to evaluate each proposed theory in predicting the associated deformation and failure mechanisms and to assess the reliability of the estimated properties with respect to the expected values and in terms of consistency among specimens with different layer configurations. The results indicate that the bending response is on average well represented in the implemented theories for the two cases of loading and in terms of both elastic and strength properties. For loads perpendicular to plane the characteristic rolling shear strength appears to have a significant variability among the different layups for all three applied methods, while for loads in plane the consideration of a combined rolling and torsional shear failure criterion provides more consistent results with respect to a less rigorous approach.

Keywords
Mechanical properties
Bending test
Parameter identification
Rolling shear

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Corresponding author.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0950061816313514

Friday, 28 October 2016

Exporting communication: Finnish Forest Academy goes Mozambique

Finnish Forest Academy. Photo: Saku Ruusila

Ms. Sílvia Maússe Sitoe and her colleagues hope that understanding the importance of forests could be improved by applying the methods used in the Forest Academy. Photo: Saku Ruusila

The Forest Academy, a programme for increasing dialogue on forest in society and highlighting the role of forests in sustainable development, is in use on three continents. Next, the Forest Academy originating in Finland will be introduced in Mozambique.

The pine forest in eastern Finland was a complete surprise to Ms. Sílvia Maússe Sitoe from Mozambique. Compared to tropical rainforest, the northern boreal forest appeared open and safe.

“The forest was like a garden, where you could never lose your way, for example. In our forests you need a machete to move ahead,” Sitoe says.

For her colleagues, Ms. Romana Rombe Bandeira, PhD at Eduardo Mondlane University, and Mr. Alberto Manhiça, researcher at the agricultural research institute IIAM, the Finnish forest was already familiar but still interesting.

“In Finland, there are three main tree species, in Mozambique more than a hundred,” Manhiça says.

In eastern Finland, the Mozambican forestry experts participated in a Forest Academy session organized by the Finnish Forest Association. The four-day course brings together a mix of decision makers and opinion leaders from all walks of society to discuss forest issues and to explore the forest sector.

The challenge of sustainable forestry

Mozambique is one of the most widely forested countries in Africa. About half of its surface is covered by forest. The share of forest industries of the country’s GDP is four percent, and a large part of the population is dependent on firewood and charcoal as domestic energy.

“Our challenge is to bring in the sustainable use of forests as a topic in public debate,” Bandeira says. “Otherwise, our forests will no longer exist after a few decades.”

Bandeira and her colleagues hope that understanding the importance of forests could be improved by applying the methods used in the Forest Academy. They point out that the sustainable use of forests is guaranteed by law in Mozambique, but in practice there is a lot to improve.

Mozambique’s 43 million hectares of natural forest are owned by the state. Forestry is mainly carried on by international companies, which also operate tree plantations, cultivating tree species such as eucalyptus.

The private land ownership in Finland was a surprise to the Mozambican guests of the Forest Academy. Families own more than half of the 23 million hectares of forest in Finland, while the share owned by companies is somewhat over ten percent. “Private ownership certainly has its advantages, as it spreads the responsibility in forest management,” says Sitoe.

Two decades of Forest Academy

This year, the Forest Academy for decision makers celebrates its 20th anniversary. In Finland, as many as 1,300 decisions makers have taken part in the programme. According to Ms. Tiina Rytilä, director of the academy, the most important task of the discussion forum is to highlight the role of forests in the development of society.

“The Forest Academy supports the forestry sector in public debate by strengthening the networks between sectors, by providing topical and compact information and by bringing different perspectives into the forest debate,” says Rytilä.

Participants to the Forest Academy are invited from various sectors of society – from politics, business, non-governmental organizations, government, media – which ensures a diverse participant base with varied opinions. The discussions take place in conference rooms, in the forest and during visits to forest businesses all around Finland. The most recent course was held in Joensuu in eastern Finland.

According to Rytilä, the concept of the Forest Academy for decision makers is especially suitable for countries wishing to boost the use of renewable natural resources in a way that is accepted as sustainable by the whole society. In addition to Mozambique, the Finnish Forest Academy is already in use in Latvia, Costa Rica and Tanzania.

It was the Natural Resources Institute Finland, Luke for short, that brought Mozambique and the Forest Academy together. With the Eduardo Mondlane University and the IIAM Institute, Luke is developing Mozambique’s forest research in a project called Forecas.

“One element of the project is to strengthen the role of the forest sector by providing information to and developing communication with the decision makers. The Forest Academy combines all this,” says Rytilä. “I hope that the Forest Academy will help to create an open discussion culture and enable people to participate in the development of the forest sector.”

The Finnish Forest Association also publishes the forest.fi webzine.

For further information log on website :
http://www.smy.fi/en/artikkeli/its-all-organic-finns-could-certify-almost-all-picking-areas-of-wild-berries/?ed2f26df2d9c416fbddddd2330a778c6=vbvvzjvv-vgzkkczv

Minister’s round table to improve forest biodiversity

Photo: Erkki Oksanen

In a discussion forum with an unprecendented range of participants, a common will and concrete ways to protect forest biodiversity in Finland are being sought.

Storms may be brewing up in Finnish forests in the near future. At the same time as logging is increasing, funding for protection will be cut. All this is reflected in public debate as a conflict between bioeconomy and biodiversity.

Measures for the protection of biodiversity are now being looked for by more actors than ever before. Nearly thirty organisations and companies are involved in round table discussions, representing the forest owners, the forest and environmental organizations, the industry, the research community and the authorities.

A common will is being looked for in discussions convened last spring by Mr. Kimmo Tiilikainen, the Finnish Minister of Agriculture and the Environment. It is believed that an invitation from the minister himself was successful in bringing all forestry and environmental organizations around the same table this time.

Among the significant actors, only Greenpeace Finland is missing – in spite of having been invited. According to Mr. Matti Liimatainen, in charge of forest issues in Greenpeace, the organisation does not participate in discussions that have no goals or no mandate to decide on concrete protection measures. The organization is just starting its own “Protecting Finnish forests” campaign.

From words to action

“Forests are linked to a lot of emotion and a desire to act. Even if people have the same aims, the discussions often run along familiar grooves,” says Mr. Timo Lehesvirta, Director, Forest Global, at UPM. According to him, there was a clear need in Finland for the new discussion forum and the dialogue it enables. Because all forest actors are involved, discussions and encounters will also lead to action.

The Finnish Association for Nature Conservation is represented at the round table by its president, Mr. Risto Sulkava. He stresses the importance of a balance between conservation and the commercial use of forests.

“This is where you need to start. If bioeconomy is to increase the use of wood, it is necessary to increase nature conservation and boost the best practices of nature management in forestry, too. This trio will have to stand or fall together,” says Sulkava.

All for one

The round table participants are strikingly united in thinking that the government should not have cut the funding to the Metso biodiversity programme. Last spring, a petition on behalf of the valued programme followed an initiative taken by the round table members.

According to Ms. Liisa Rohweder, Secretary General of WWF Finland, the goal of the round-table discussion should be that the Finnish government would restore the funding to Metso to its previous level. “Everybody is for it. The funding allocated to Metso is relatively small compared to, for example, a number of harmful state subsidies.”

Next year, some forests will be protected by voluntary donations in honour of the centenary of Finnish independence. The idea is that private forest owners can donate their land for conservation, and the state will match this with forests of its own.

As for how much forest, or what kind and where situated, will be donated, is to be determined later in the autumn. It could be, for example, a hundred hectares in each of the Finnish regions.

The round-table participants interviewed by forest.fi agreed that the forest conservation campaign for Finland’s centenary year 2017 has a great symbolic value. On a more practical level, though, a new national park called Hossa in Eastern Finland will be opened to honour the centenary, as was pointed out Mr. Antti Otsamo, Sustainable Development Manager at Metsähallitus.

Searching for market-oriented solutions

In addition to the joint round-table discussion, the participants want to find concrete solutions for forest protection and sustainable forestry. The themes discussed include how to increase the volume of decaying wood, as well as the Multi-forest project, which attempts to eliminate bottlenecks from nature management in forestry.

“The round table provides a basis for developing projects jointly by a wide range of actors and to exchange information on best practices,” says Mr. Tomi Salo, Forest Director at the Finnish Forest Industries Federation (FFIF). According to Salo, the forum provides all actors a valuable opportunity to gauge their own programmes against the public debate on forests. The round table meetings have discussed the connections between the FFIF’s environmental programme and the Multi-forest project, among other things.

Mr. Juha Hakkarainen, forest director at the Central Union of Agricultural Producers and Forest Owners (MTK), believes that forest debate needs more courage and proactiveness. “In addition to what we have succeeded with, we should find new, fresh ways to take forest biodiversity forward.”

“If the state cannot find the money, we should look for market-oriented solutions for conservation”, Hakkarainen says. As a possible solutions, he mentions the commercialization of ecosystem services, habitat banks and a foundation for the protection of forest biodiversity that everyone could invest in.

“The state has an important role in protecting biodiversity, but this does not exclude the role of the private sector and citizens.”

Those interviewed for the article also included Mr. Pekka Kallio-Mannila, Corporate Responsibility Manager at Stora Enso, and Mr. Sixten Sunabacka, CEO at Tornator.

Nearly thirty organisations are involved in round table

Association of Finnish Local and Regional Authorities (AFLRA)
Bioenergy Association of Finland
Birdlife
Central Union of Agricultural Producers and Forest Owners (MTK)
Finnish Energy
Finnish Environment Institute SYKE
Finnish Forest Association
Finnish Forest Centre
Finnish Forest Industries
Finnish Nature League
Finnish Sawmills Association
Finnish Society for Nature and Environment
Finnish Association for Nature Conservation
Forestry Management Association of Southern savo
FSC Finland
Metsä Group
Metsähallitus – State Forest Enterprise
Ministry of Agriculture and Forestry
Ministry of Economic Affairs and Employment
Ministry of the Environment
Natural Resources Institute of Finland
PEFC Finland
Stora Enso
Svenska lantbruksproducenternas centralförbund SLC
Tornator
University of Helsinki
University of Eastern Finland
UPM
WWF Finland

Researchers: Harvesting can be increased sustainably – if nature management is not forgotten

According to the researchers, the decline in the area of controlled burning should ne turned. Photo: Jari Leskinen

According to researchers, the nature management needed includes increasing decayed wood by leaving retention trees and other methods, controlled burning and the activities defined in the Metso biodiversity action programme.

The Natural Resources Institute Finland and the Finnish Environment Institute have prepared an evaluation of the sustainability of Finland’s forest use for the Round Table discussions led by Mr. Kimmo Tiilikainen, Minister of Agriculture and the Environment. The evaluation focuses on ecological sustainability, the safeguarding of which is also what the discussions aim at.

The evaluation consists of a description of the present state of forest use, the assessment of future development and proposals for action needed. The researchers behind the evaluation are Mr. Taneli Kolström, Director at the Natural Resources Institute Finland, and Mr. Petri Ahlroth, Director at the Finnish Environment Institute.

Timber stock in Finnish forests is increasing

Future development is evaluated on the basis of three scenarios. The first is based on the present harvesting level, the second on the higher harvesting level defined in the current forest policy and the third on the highest sustainable level of harvesting.

The researchers consider that the timber stock in Finnish forest will increase in all scenarios. In the “current forest policy” scenario, the timber stock will increase from the current figure of just under 2,100 million cubic metres to just above 2,500 million cubic metres by 2055.

On the other hand, the harvesting areas do not expand to a similar extent, thanks to the fact that the forests are becoming denser. The area of thinnings undertaken each year would only increase by 2,000 hectares from the current figure of 465,000, and the area of regeneration fellings would grow by 18,000 hectares from the current figure of 155,000.

The total area of Finnish commercial forests is around 20 million hectares.

The amount of stout timber would also increase in all scenarios, although only after a short decline.

In the “current forest policy” scenario the volume of stout coniferous trees – that is, with a stem diameter of more than 30 centimetres at a height of 1.3 metres – would almost double, and the volume of broadleaved trees would increase 2.5-fold in southern Finland and even threefold in northern Finland.

Also the age structure of Finnish forests is, according to the researchers, appropriate for increased harvesting.

KulotusPalonRajaaminen_PhotoRistoHoglund — Controlled burning of especially groups of retention trees creates decayed and burned wood in the forest, which is essential for many endangered forest species. Photo: Risto Höglund

Amount of decayed wood can be increased

In consequence, it is possible to increase the amount of decayed wood, which is a critical factor for several forest habitats and endangered species. This means that the favourable development already observed could continue.

This may be illustrated by the amount of deadwood that could be used as fuelwood, if for nothing else, which reached it lowest level in the 1970s. This was because in the 1960s people still used to remove all trees brought down by winds for use as fuelwood, but since then they have largely been left lying in the forest.

As a result, the amount of usable deadwood in the forests in southern Finland has increased fourfold since the 1960s and by a quarter in northern Finland.

The amount of decayed wood has also increased due to the practice of leaving retention trees in the forest in connection with regeneration fellings, as is required by forest certification. This practice was started in the late 1990s.

Since then, the amount of decayed wood has increased only slightly, by about 3 to 3.5 cubic metres per hectare in southern Finland. In protected forests the increase has been clearly larger.

The researchers strongly recommend that the amount of decayed wood in the forests should be increased. This should be achieved by leaving retention trees and by making sure that valuable habitats are spared in commercial forests.

Metso programme must be safeguarded

The area of habitats spared in connection with fellings has clearly increased during the past few years. The researchers also recommend that controlled burning is increased, as many endangered species thrive on scorched wood or in wildfire sites.

The area of controlled burning has significantly decreased during the last few years, probably because it is a very expensive method. At its highest, the area of controlled burning was close to 7,000 hectares in 1998–2002, as against to only 2,000 hectares in 2008–2012.

In addition to what is recommended, it is equally interesting to see what they researchers do not recommend. They say nothing about increasing strict forest protection, except by the means mentioned in the Metso biodiversity action programme. According to them, it is extremely important that the Metso programme is implemented according to plan.

The funding for the Metso programme has faced severe cutbacks due to poor state finances. The forest sector and the environmental organisations have jointly demanded the cuts to be revoked, but to no result.