@phdthesis{Hirschmueller2019, author = {Hirschm{\"u}ller, Sebastian}, title = {Beech circular hollow laminated veneer lumber sections for temporary soil nailing applications}, school = {Technische Hochschule Rosenheim}, year = {2019}, abstract = {Beech Laminated Veneer Lumber (LVL) circular hollow sections for use as temporary geotechnical soil nailing systems are developed within this thesis. Due to their permanent subsoil cement embedment, combined with high water saturation and permanent loading, the timber sections will lose strength and stiffness over time. Taking into account a duration of load factor for permanent loading of two years, it is recommended to reduce the short term tensile and bending strength of beech circular hollow sections to be used as geotechnical soil nails by 80\%. In addition to the determination of material properties on small, clear specimens and full-sized cross-sections, an appropriate surface gluing quality between the veneers is fundamental to this subsoil application of the permanently cement-embedded, engineered timber product. The circular cross-section geometry and the permanently high-alkaline environment of the structural member is not covered by presently standardised testing and conditioning methods for examining LVL surface bond line quality. Standardised test methods had to be modified to determine bonding parameters for the circular, hollow LVL sections. As cement grout ensures the bond between the wooden nails and soil for the mobilisation of a soil reinforcement effect, a reliable connection between cement and wood is required. However, soluble wood constituents may inhibit cement hydration in the contact surface between the timber nails and cement. Pull-off tests on clear LVL specimens with different cement and wood surface modifications as well as the results of large-scale push-out tests are therefore presented. But to permanently ensure the contact between the wood and cement, a high degree of saturation above wood fibre saturation is necessary to keep the hollow sections in a swollen state without moisture-dependent wood shrinking. As no publications of wood moisture development in subsoil were available, long-term tests were performed, measuring the moisture content of subsoil-stored LVL in dependence on the soil moisture content, the suction and the precipitation during a time span of one year. Besides a negative cement influence on the material strength, a positive effect of cement coating on subsoil fungal destruction was realised, resulting in a significantly increased lifetime of cement-coated wood compared to uncoated wood. For temporary soil nailing applications, fungal wood deterioration was found to be of minor importance. But the reduced material strength due to a severe alkaline attack of wood demands a re-consideration of current soil nailing design methods, usually based on a mechanical limit equilibrium analysis of a rigid body motion where just tensile forces of the reinforcement elements are considered, and accompanying forces like bending moments and shear forces are neglected. Distributed fibre optic strain measurements of a steel-reinforced soil nail wall during a time span of six weeks reveal considerable nail curvatures, which are negligible in the case of ductile soil nails with low diameters, but are a significant factor for beech circular hollow laminated veneer lumber sections of larger diameters and brittle material behaviour.}, language = {en} } @article{HirschmuellerPravidaMarteetal.2018, author = {Hirschm{\"u}ller, Sebastian and Pravida, Johann and Marte, Roman and Flach, Michael}, title = {Adhesive properties of laminated veneer lumber poles for use in temporary soil nailing: bonding performance of curved structures in a high-alkaline environment}, series = {Wood Science and Technology}, volume = {52}, journal = {Wood Science and Technology}, number = {5}, editor = {Springer,}, pages = {1289 -- 1311}, year = {2018}, abstract = {Circular hollow sections of beech-laminated veneer lumber (LVL) for the use as temporary geotechnical soil nailing systems are currently being developed. Due to their permanent subsoil cement embedment, investigations of the bond line quality of the timber sections are essential. This paper presents the bonding properties of flat and curved beech LVL after cyclic conditioning in a water-cement grout solution aimed at inducing short- and long-term alkaline attack of the timber. In total, 409 and 69 samples were tested in tensile shear tests after short-term and long-term conditioning, respectively. Three different adhesive systems, a one-component polyurethane adhesive, a melamine-urea-formaldehyde adhesive and a melamine-urea-formaldehyde adhesive modified by means of (polyvinyl)-acetate adhesive were investigated and compared. Short-term conditioning by submersion in boiling cement suspension was found to be a reliable method for testing the bonding performance rather than long-term conditioning. In the case of tensile shear tests of samples subjected to long-term treatment, wood material strength was the decisive criterion. Generally, tensile shear test samples of all investigated adhesives achieved reliable bonding for a pressing force up to 1.0 MPa. No relationship was recognised between the determined bonding failure and the wood properties tensile shear strength, wood failure percentage, fracture pattern and bulk density of veneers adjacent to the bond line. For the determination of the bond line integrity of curved veneer poles, it was necessary to test bonding quality in a combined test using curved and flat samples and to compare tensile shear strength with data determined on reference samples in the same veneer population without bond line.}, language = {en} } @article{HirschmuellerPravidaMarteetal.2018, author = {Hirschm{\"u}ller, Sebastian and Pravida, Johann and Marte, Roman and Flach, Michael}, title = {Adhesive properties of laminated veneer lumber poles for use in temporary soil nailing: development and evaluation of a test method for curved structures in a high-alkaline environment}, series = {Wood Science and Technology}, volume = {52}, journal = {Wood Science and Technology}, number = {4}, editor = {Springer,}, pages = {1061 -- 1092}, year = {2018}, abstract = {Innovative circular, hollow, laminated veneer lumber (LVL) beech sections for use as temporary geotechnical soil reinforcement members are currently being developed. Appropriate surface gluing quality between the veneers is fundamental to this subsoil application of the permanently cement-embedded, engineered timber product. The circular cross-section geometry and the permanently high-alkaline environment of the structural member is not covered by presently standardized testing and conditioning methods for examining LVL surface bond line quality. The sample conditioning and tensile shear test method compliant with EN 302-1 (Adhesives for load-bearing timber structures—test methods—part 1: determination of longitudinal tensile shear strength, European Committee for Standardization, Brussels, 2013) was modified to determine bonding parameters for circular, hollow LVL sections. Bond line curvature, groove cutting depth and sample geometry were found to greatly influence stress distribution, percentage of wood failure and tensile shear strength. Short-term alkaline treatment of test samples did not significantly influence the bonding performance, wood failure percentage, tensile shear strength and fracture patterns. To improve tensile shear strength, adhesives with different material rigidities were used and compared. An orthotropic, elastic numerical analysis revealed a greater influence of adherent elasticity than adhesive elasticity on the stress distribution within the bond line. With regard to determining the bond line integrity of curved veneer poles, a sample geometry compliant with EN 302-1 (2013) was developed and numerically evaluated.}, language = {en} } @inproceedings{HirschmuellerMartePravida2016, author = {Hirschm{\"u}ller, Sebastian and Marte, Roman and Pravida, Johann}, title = {Laminated veneer lumber poles for temporary soil nailing - investigation of material properties}, series = {Proceedings of the World Conference on Timber Engineering. World Conference on Timber Engineering. Vienna, 22.-25.08. Vienna}, booktitle = {Proceedings of the World Conference on Timber Engineering. World Conference on Timber Engineering. Vienna, 22.-25.08. Vienna}, editor = {Eberhardsteiner, Josef and Winter, Wolfgang and Fadai, A. and P{\"o}ll, Martha}, year = {2016}, abstract = {Within a current research project at Rosenheim University of Applied Sciences and Graz University of Technology the possibilities of using beech wood laminated veneer lumber poles as soil anchors for temporary soil nailing systems are investigated. Therefore tensile and bending properties of laminated veneers with high moisture and permanent cement contact concerning the influence of veneer bending rectangular to the fibre are determined. For investigation of material properties under different climate conditions tensile tests on small and faultless single beech wood veneers as well as tensile tests on 6 layered 3 mm samples and 9 layered 2 mm samples were carried out. Therefore all samples were stored in extreme climate conditions like high moisture content and permanent cement contact. Six layered samples with 3mm thick veneers show a slightly higher strength and stiffness under dry conditions as well as at a moisture content of the samples above fibre saturation. A strength reduction factor concerning temporary geotechnical applications is suggested which considers the influence of long term loading, veneer bending, water saturation and cement destruction on tensile properties of laminated veneer lumber poles.}, language = {en} } @inproceedings{HirschmuellerPravidaMarteetal.2016, author = {Hirschm{\"u}ller, Sebastian and Pravida, Johann and Marte, Roman and Flach, Michael}, title = {Laminated veneer lumber poles for use in temporary soil nailing. Investigation of adhesive properties.}, series = {Holzbau Forschung und Praxis. 6. Doktorandenkolloqium 2016}, booktitle = {Holzbau Forschung und Praxis. 6. Doktorandenkolloqium 2016}, editor = {Universit{\"a}t Stuttgart,}, year = {2016}, abstract = {Within a current research-project the possibility of using laminated veneer lumber beech wood poles as temporary soil anchors in foundation engineering is investigated. Within this project adhesive properties of laminated veneer lumber beech wood poles are determined. For use in temporary ground applications the influence of veneer bending, veneer thickness and intensive cement contact is concerned. As standard version two different adhesive systemsmelamine formaldehyde resin (MUF) and a 1-component polyurethane adhesive (PUR) were investigated and compared. Melamine formaldehyde resin glued samples with 3 mm thick veneers and 1.0N/mm² press force show a higher tensile shear strength but also a higher adhesive failure percentage than polyurethane glued samples. In case of melamine formaldehyde resins the closed time has a great influence on bond line quality. A long closed time reveals a low penetration of adhesive in the cells and a low embedding on the wood surface. For curved structures best results were achieved with a bonding pressure of 1.0 N/mm². A significant difference in strength between the concerned MUF and PUR adhesive system was not recognized.}, language = {en} }