Roman Marte

Long-term material properties of circular hollow laminated veneer lumber sections under water saturation and cement alkaline attack

ABSTRACT Innovative beech laminated veneer lumber (LVL) circular hollow sections for the use as temporary geotechnical soil nailing systems are currently being developed. Due to the permanent subsoil cement embedment, combined with high water saturation and permanent loading, the timber sections will lose strength and stiffness over time to a degree currently unknown. This paper presents the tensile and bending material properties of flat and curved beech LVL under various periods of immersion in a water–cement grout solution aiming at inducing both water saturation and long-term alkaline attack of the timber. In total, 824 and 279 samples were tested in tension and bending, respectively. Results show that samples manufactured from 3 mm thick veneers result in tensile strength and stiffness 17% and 24% higher, respectively, than samples manufactured from 2 mm thick veneers. A reduction in the initial bending and tensile strength of up to 70% was found after 90 days of water saturation and cement contact. 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 anchors by 80%.

Geodetic and fibre optic measurements of a full-scale bi-axial compressional test

Earth filled dams are commonly used as flood prevention dams and for hydroelectric power plants. Their stability is critical for an uninterrupted operation and a reliable protection from catastrophic incidents. During the operation, dams are subjected to lateral loading by hydrostatic pressure. In order to predict the deformation behaviour the material parameters have to be known accurately. Therefore, Graz University of Technology carried out a series of life-size experiments to determine the material parameters of an earth filled dam. Controlled vertical load was applied in these experiments and the resulting deformations were measured with geodetic and fibre optic methods. Single points on the slope were continuously tracked with robotic total stations. In addition, the whole dam surface was monitored using a scanning total station. Finally, relative movements between points on the dam were measured with fibre optic sensors based on fibre Bragg gratings. The achievable measurement precision and the relation between acting load and resulting deformation is investigated in detail for every measurement technique. The authors show in their evaluation that absolute deformations can reliably be detected with the geodetic methods. However, individual loading steps cannot be resolved because of the limited precision of the geodetic measurements. Our results demonstrate that the sensitivity of the monitoring system can be significantly increased with the fibre optic sensors and the scanning data also contribute to assess the stability of the experiment set-up.

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

AbstractInnovative 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.