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New Advances in Strengthening of Structural Timber
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New Advances in Strengthening of Structural Timber

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: closed (20 April 2024) | Viewed by 16137

Special Issue Editor

Prof. Dr. Paweł Kossakowski

E-Mail Website
Guest Editor
Faculty of Civil Engineering and Architecture, Department of Strength of Materials and Structural Analysis, Kielce University of Technology, Al. Tysiaclecia Panstwa Polskiego 7, 25-314 Kielce , Poland
Interests: strength of materials; structural analysis; timber structures; bridge engineering; fracture mechanics; damage mechanics; computational mechanics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Although wood is one of the oldest construction materials, it has been successfully used to this day. Its relatively high strength combined with low density makes wood a well-known building and structural material. However, in many situations, timber structures need to be repaired and strengthened. This is mainly due to the properties of wood, which are influenced by a number of factors that can reduce the values of mechanical parameters of this material, especially for long-life structures. In addition, the properties of wood are often inappropriate for structures exposed to high loads.

Increasing the load-carrying capacity and stiffness of timber structural elements is usually achieved by introducing reinforcements into elements, whether old or new. This reinforcement usually takes the form of rods, sheets (uni-, bi-, or multi-directional reinforced), laminates, or profiles. The conventional material from which these reinforcing elements are made is steel or other metals such as aluminium. Composite materials—such as aramid, glass, carbon or basalt fibres—responsible for carrying the load immersed in the resin matrix have now become a popular solution. In order to increase efficiency, traditional passive reinforcement of the structure can be replaced by active reinforcement, the key advantage of which is introducing the initial precamber of the element. Much research has been conducted on wood strengthening, and many methods and technologies have been developed, but much remains to be done. This applies primarily to new wood-based materials and innovative timber structural elements as well as novel reinforcing materials.

This Special Issue covers new developments in the field of structural timber strengthening. Topics include theoretical and practical studies focused on the analysis, description, and optimisation of the novel methods and technologies which have been developed and applied recently for strengthening different types of structural elements made of wood. Original research papers, reviews, and short communications reporting the results of experimental, theoretical, and/or computational work on any aspect of research in the subject scope are welcome. We look forward to receiving your contributions.

Prof. Dr. Paweł Kossakowski
Guest Editor

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Keywords

  • timber
  • wood
  • strengthening
  • composites
  • timber structures
  • wood composites
  • fibres
  • retrofitting
  • failure modes

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Published Papers (9 papers)

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Editorial

Jump to: Research

6 pages, 172 KiB  
Editorial
New Advances in Strengthening of Structural Timber
by Paweł Grzegorz Kossakowski
Materials 2024, 17(11), 2545; https://doi.org/10.3390/ma17112545 - 24 May 2024
Viewed by 786
Abstract
As one of the oldest building materials, wood is still widely used today [...] Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)

Research

Jump to: Editorial

12 pages, 5851 KiB  
Article
Mechanical Properties of Wooden Elements with 3D Printed Reinforcement from Polymers and Carbon
by Jan Dedek, David Juračka, David Bujdoš and Petr Lehner
Materials 2024, 17(6), 1244; https://doi.org/10.3390/ma17061244 - 8 Mar 2024
Cited by 3 | Viewed by 859
Abstract
The research presented in this article aimed to investigate the differences in mechanical properties between solid structural timber and the same reinforced element in three different ways. A three-point bending test was performed on wood elements reinforced with carbon-fiber-reinforced polymer (CFRP), 3D printed [...] Read more.
The research presented in this article aimed to investigate the differences in mechanical properties between solid structural timber and the same reinforced element in three different ways. A three-point bending test was performed on wood elements reinforced with carbon-fiber-reinforced polymer (CFRP), 3D printed polycarbonate (3DPC) lamellas, and 3D printed polycarbonate with carbon fiber (3DPCCF) lamellas. In this comparison, the bending strength was large for CFRP samples, which have 8% higher performance than samples with 3DPCCF and 19% higher performance than samples with 3DPC. Conversely, when factoring in theoretical manufacturing costs, the performance of 3DPCCF is almost three times that of CFRP and 3DPC. In addition, 3D materials can be used for more complicated reinforcement shapes than those discussed in the paper. Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)
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24 pages, 12600 KiB  
Article
Bending Behavior of Hybrid Timber–Steel Beams
by Peter Haase, Simon Aurand, Jakob Boretzki, Matthias Albiez, Carmen Sandhaas, Thomas Ummenhofer and Philipp Dietsch
Materials 2024, 17(5), 1164; https://doi.org/10.3390/ma17051164 - 1 Mar 2024
Cited by 1 | Viewed by 1995
Abstract
Driven by climate change and the need for a more sustainable construction sector, policy is increasingly demanding and promoting timber hybrid construction methods. In the German state of Baden-Württemberg, every new public building has to be of timber or timber hybrid construction (Holzbauoffensive [...] Read more.
Driven by climate change and the need for a more sustainable construction sector, policy is increasingly demanding and promoting timber hybrid construction methods. In the German state of Baden-Württemberg, every new public building has to be of timber or timber hybrid construction (Holzbauoffensive BW). The objective of multi-story buildings with large floor spans can only be achieved in a resource-efficient way by hybrid constructions combining timber and steel components. A research project recently completed at the Karlsruhe Institute of Technology was aimed at the development and systematic investigation of hybrid bending beams in which an advantageous combination of the materials steel and timber is used. For this purpose, steel profiles are integrated into timber cross-sections in a shear-resistant manner by adhesive bonding. As part of the experimental, numerical and analytical investigations, different cross-sections of steel and timber, as well as different construction materials, were considered (GL24h, LVL48p, LVL80p, S355 and S420). The results of large-scale four-point bending tests illustrate the potential of this new hybrid construction method. Depending on the geometry and material combinations tested, the bending stiffness could be increased by up to 250%, and the load-carrying capacity by up to 120%, compared to a glulam beam with identical dimensions. Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)
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20 pages, 11691 KiB  
Article
Assessment of the Technical Condition of Timber Structural Elements Using Sclerometric Tests
by Justyna Jaskowska-Lemańska and Daniel Wałach
Materials 2023, 16(18), 6152; https://doi.org/10.3390/ma16186152 - 10 Sep 2023
Cited by 2 | Viewed by 1100
Abstract
The technical assessment of wooden elements is the primary step in their repair and reinforcement design. Normative requirements currently mandate additional tests, including semi-destructive ones, beyond traditional visual assessment. Despite the growing feasibility of semi-destructive tests for qualitative assessments, there remains a paucity [...] Read more.
The technical assessment of wooden elements is the primary step in their repair and reinforcement design. Normative requirements currently mandate additional tests, including semi-destructive ones, beyond traditional visual assessment. Despite the growing feasibility of semi-destructive tests for qualitative assessments, there remains a paucity of data enabling quantitative assessments. This study investigated the hardness of structural timber, specifically pine, spruce, and fir, from Central Europe using sclerometric methods. The outcomes of these tests were compared with those of conventional destructive tests and correlational relationships were established. A strong correlation was found between the sclerometric tests and density (r = 0.62 ÷ 0.82), while a range of strong to moderate correlations was found (r = 0.40 ÷ 0.70) for mechanical characteristics (bending and compressive strength). The correlation strength varied among different wood species, with the strongest for pine and the weakest for spruce. All established relationships were compiled into 40 functions to facilitate their future utilization in quantitative assessments during the technical evaluation of wooden objects. The study also examined the influence of wood defects on the derived correlations by considering the knot index. Sclerometric methods accurately reflect the physico-mechanical properties of elements with a small or medium defect content. However, for wood with a high proportion of defects (knots), the correlations are very weak (r = 0.23 ÷ 0.52, including statistically insignificant results). This research offers new insights into the potential of semi-destructive methods in the structural evaluation of wooden elements, highlighting the need to account for wood species and defect content. Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)
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16 pages, 12401 KiB  
Article
Study of Complexity of Numerical Models of a Strengthened Timber Beam
by Michał Szczecina
Materials 2023, 16(9), 3466; https://doi.org/10.3390/ma16093466 - 29 Apr 2023
Cited by 6 | Viewed by 1750
Abstract
Laboratory research of wood–CFRP (carbon fiber reinforced polymer) structural elements, especially beams, is a scientific issue undertaken by many scientists. Research is often complemented with numerical analysis with the use of complex finite element method (FEM) models. Modern FEM software offers models that [...] Read more.
Laboratory research of wood–CFRP (carbon fiber reinforced polymer) structural elements, especially beams, is a scientific issue undertaken by many scientists. Research is often complemented with numerical analysis with the use of complex finite element method (FEM) models. Modern FEM software offers models that can reproduce such properties and phenomena as orthotropy and plasticity of wood and CFRP, delamination and mechanical behavior of adhesive layers, and damage of a strengthened element. The author of the paper reproduces numerical laboratory research of a four-point bending test of a glulam beam strengthened with CFRP tape. The main goal of the numerical research is an analysis of how the complexity of the FEM model influences the results of calculations, especially stress, deflection, and bearing capacity of the glulam beam. In some cases, a simpler model can be satisfactory, especially for a structural engineer, who takes into account serviceability limit states (permissible deflection of a structural member) and assumes that stress should not exceed the yield stress of timber. Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)
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18 pages, 8591 KiB  
Article
Flexural Properties in Edgewise Bending of LVL Reinforced with Woven Carbon Fibers
by Neda M. Sokolović, Ivana Gavrilović-Grmuša, Vladislav Zdravković, Jelena Ivanović-Šekularac, Darko Pavićević and Nenad Šekularac
Materials 2023, 16(9), 3346; https://doi.org/10.3390/ma16093346 - 24 Apr 2023
Cited by 5 | Viewed by 2020
Abstract
This paper presents the results of experimental testing of the bending strength and modulus of elasticity in edgewise bending of unreinforced and reinforced seven-layer LVL (laminated veneer lumber) poplar veneer panels. The aim of the research is to determine the influence of woven [...] Read more.
This paper presents the results of experimental testing of the bending strength and modulus of elasticity in edgewise bending of unreinforced and reinforced seven-layer LVL (laminated veneer lumber) poplar veneer panels. The aim of the research is to determine the influence of woven carbon fibers on the improvement of the bending properties and modulus of elasticity of LVL bending in the plane of the plate, as well as the influence of adhesives on the bending properties of the composite product, in order to test the potential of using this newly obtained material as a structural element. Bending was performed on small-scale samples. The main research task is the examination of three types of reinforcement, which differ from each other in position, orientation, and number of layers of reinforcement, using two different types of adhesives: epoxy adhesive and Melamine Urea Formaldehyde Resins (MUF). The composite material was produced in four different combinations in relation to the orientation and position of the reinforcement in the layup. The applied reinforcement is defined through three different configurations (EK1, EK2, and EK3) and a fourth control sample (EK4). Each configuration was produced by applying the two previously mentioned types of adhesives. The research findings showed that in the case of samples produced by applying CFRP (carbon fiber reinforced polymer) using epoxy adhesive, it significantly affected the increase in bending strength and flexural modulus of elasticity. The average improvement in bending strength is 32.9%, 33.2%, and 38.7%, i.e., the flexural modulus of elasticity is 54.1%, 50.7%, and 54.7%, respectively, for configurations EK1, EK2, and EK3, compared to control sample EK4. During the testing, the test samples from reinforced panels EK1 and EK2 showed partly plastic behavior up to the fracture point, while the diagram for the test samples from reinforced panels EK3 shows elastic behavior to a considerable extent, with a significantly smaller plastic behavior zone. This research proved the impossibility of using melamine-urea formaldehyde adhesive to form a composite product based on veneer and carbon fabric. The greatest contribution of this work is the experimentally verified and confirmed result of the possibility of applying poplar veneer to design structural elements in LVL using epoxy adhesive. Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)
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12 pages, 3234 KiB  
Article
Static Analysis of Wooden Beams Strengthened with FRCM-PBO Composite in Bending
by Piotr Kazimierz Sokołowski and Paweł Grzegorz Kossakowski
Materials 2023, 16(5), 1870; https://doi.org/10.3390/ma16051870 - 24 Feb 2023
Cited by 5 | Viewed by 1473
Abstract
The article presents an analysis of the static work of bent solid-wood beams reinforced with FRCM–PBO (fiber-reinforced cementitious matrix–p-phenylene benzobis oxazole) composite. In order to ensure better adhesion of the FRCM–PBO composite to the wooden beam, a layer of mineral resin and quartz [...] Read more.
The article presents an analysis of the static work of bent solid-wood beams reinforced with FRCM–PBO (fiber-reinforced cementitious matrix–p-phenylene benzobis oxazole) composite. In order to ensure better adhesion of the FRCM–PBO composite to the wooden beam, a layer of mineral resin and quartz sand was applied between the composite and the wooden beam. Ten wooden pine beams with dimensions of 80 × 80 × 1600 mm were used for the tests. Five wooden beams, unreinforced, were used as referenced elements and another five were reinforced with FRCM–PBO composite. The tested samples were subjected to a four-point bending test in which the static scheme of a simply supported beam subjected to two symmetrical concentrated forces was used. The main purpose of the experiment was to estimate the load capacity, the flexural modulus and the maximum bending stress. The time needed to destroy the element and the deflection were also measured. The tests were carried out based on the PN-EN 408: 2010 + A1 standard. The material used for the study was also characterized. The methodology and assumptions adopted in the study were presented. The tests confirmed a significant increase in destructive force by 141.46%, maximum bending stress by 118.9%, modulus of elasticity by 18.32%, time needed to destroy the sample by 106.56% and deflection by 115.58% compared to the reference beams. The unusual method of wood reinforcement presented in the article can be considered as innovative, characterized not only by a significant load capacity margin exceeding 141%, but also by simplicity of application. Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)
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22 pages, 12239 KiB  
Article
Application of Digital Image Correlation to Evaluate Strain, Stiffness and Ductility of Full-Scale LVL Beams Strengthened by CFRP
by Michał Marcin Bakalarz and Paweł Piotr Tworzewski
Materials 2023, 16(3), 1309; https://doi.org/10.3390/ma16031309 - 3 Feb 2023
Cited by 11 | Viewed by 2401
Abstract
Due to limitations of traditional measuring methods, a necessity of verification of applicability of optical measuring systems in different fields of science is required. The paper presents the application of a non-contact, non-destructive ARAMIS optical system in the analysis of static work of [...] Read more.
Due to limitations of traditional measuring methods, a necessity of verification of applicability of optical measuring systems in different fields of science is required. The paper presents the application of a non-contact, non-destructive ARAMIS optical system in the analysis of static work of unstrengthened and strengthened laminated veneer lumber beams (LVL) with composite materials, subjected to a four-point bending test. The beams were strengthened with Carbon Fiber Reinforced Polymer (CFRP) sheets and laminates. The sheets were bonded to the external surfaces in three configurations differing in the number of layers applied and the degree of coverage of the side surface. The CFRP laminates were glued into predrilled grooves and applied to the underside of the beams. An adhesive based on epoxy resin was used. The scope of the work includes analysis of the strain distribution, stiffness and ductility. The analysis was performed on the basis of measurements made with an optical measurement system. The strain analysis indicated a change of the distribution of the strain in the compressive zone from linear for the unstrengthened to bilinear for the strengthened beams. The stiffness increase was equal from 14% up to 45% for the application of the CFRP laminates in the grooves and CFRP sheets bonded externally, respectively. Similar improvement was obtained for the ductility. Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)
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12 pages, 7670 KiB  
Article
Strengthening of Full-Scale Laminated Veneer Lumber Beams with CFRP Sheets
by Michał Marcin Bakalarz and Paweł Grzegorz Kossakowski
Materials 2022, 15(19), 6526; https://doi.org/10.3390/ma15196526 - 20 Sep 2022
Cited by 14 | Viewed by 2010
Abstract
This paper presents the results of experimental research on full-size laminated veneer lumber (LVL) beams unreinforced and reinforced with CFRP sheets. The nominal dimensions of the tested beams were 45 mm × 200 mm × 3400 mm. The beams were reinforced using the [...] Read more.
This paper presents the results of experimental research on full-size laminated veneer lumber (LVL) beams unreinforced and reinforced with CFRP sheets. The nominal dimensions of the tested beams were 45 mm × 200 mm × 3400 mm. The beams were reinforced using the so-called U-type reinforcement in three configurations, differing from each other in the thickness of the reinforcement and the side surface coverage. An epoxy resin adhesive was used to bond all the components together. A four-point static bending test was performed according to the guidelines in the relevant European standards. The effectiveness of the reinforcement increased with the level of coverage of the side surface and the level of reinforcement. The average increases of bending resistance were 42%, 51% and 58% for configurations B, C and D, respectively. The average value of bending stiffness increased for the beams of series B, C and D by 15%, 31% and 43%, respectively. Their failure mode changed from brittle fracture initiated in the tensile zone for unreinforced beams to more ductile fracture, initiated in the compression zone. The influence of the coverage of the side surface by the CFRP sheet and reinforcement ratio on the mechanism of failure and effectiveness of strengthening was studied in the article. Full article
(This article belongs to the Special Issue New Advances in Strengthening of Structural Timber)
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