Refine
Year of publication
- 2018 (12) (remove)
Document Type
Has Fulltext
- no (12)
Is part of the Bibliography
- no (12)
Keywords
- Bauproduktenrecht (5)
- Timber engineering (4)
- Innenausbau (2)
- Laminated veneer (2)
- Stahl-Leichtbau (2)
- Temporary soil nailing (2)
- Trockenbau (2)
- Unterdecken (2)
- Außenwand (1)
- Bauphysik (1)
Institute
- Fakultät für Holztechnik und Bau (12) (remove)
Soil nailing systems are a common way to stabilize slopes and construction pits. Their design is usually based on the mechanical equilibrium of a rigid body motion and therefore, only tensile stresses are considered and accompanying forces like bending (shear stresses) in the soil nails are neglected. Continuous strain measurements along nails could verify this assumption, but may not be performed using conventional sensing technologies.
This paper reports about monitoring of a soil nailed slope stabilization using distributed fiber optic sensing. Soil nails in different anchoring horizons were instrumented and autonomously monitored over several weeks, in which the construction pit was excavated continuously. After the excavation, the final load bearing capacity of one selected nail was determined within a classical geotechnical load test. In addition to the field measurements, the bending behavior of the instrumented nail system was analyzed under laboratory conditions.
The presented studies demonstrate the high potential of distributed fiber optic sensing systems and their capability to extend traditional measurement methods in foundation engineering applications.
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.
This paper investigates the long-term tensile properties of laminated veneer lumber (LVL) beech sections coated with cement and exposed to fungal decay. A set of LVL coupon (dog-bone) samples was stored in compost, tested in tension after 6 and 12 months and compared to reference samples stored at 20 °C and 65% relative humidity. Results showed that after 26 weeks of compost exposure, a fungus of the Ascomycota genus was identified in cement-coated samples using a molecular biology polymerase chain reaction (PCR) technique, which analyses the internal transcribed spacer (ITS) region of the ribosomal DNA. However, no visual deterioration was noticed.
Still in cement-covered samples and after 12 months of exposure, a common white rot fungus was determined by DNA chip technology, but no fungal wood decay was visible in areas where the applied coating had a thickness of at least 5 mm. Decay in uncoated LVL samples was significant with the samples having an average residual strength equal to 7%. This compares to the tensile strength of coated samples, which only decreased by 65% relative to the reference samples. Strength and stiffness of coated samples did not differ significantly between 6 and 12 months of exposure. Preliminary investigations tend to show that the strength reduction in cement-coated samples is due to an alkaline degradation of the wood. The observed influence of the coating thickness on the visual fungal decay can probably be ascribed to the protection mechanism due to a physical fungal barrier with a high pH.
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.
Der Beitrag stellt den Grundgedanken des europäischen Bauproduktenrechtes dar. Dieses zielt mit der Bauprodukteverordnung (EU 305/2011) auf eine europaweit einheitliche Angabe von Leistungen von Bauprodukten hinsichtlich ihrer wesentlichen Merkmale. Das CE-Zeichen auf Bauprodukten hat dadurch eine ganz andere Bedeutung als CE-Zeichen nach anderen EU-Richtlinien. Denn es werden (abgesehen von Schwellenwerten) keine konkreten Anforderungen an die Leistungen von Bauprodukten gestellt. Deswegen müssen Bauwerks-Planer im Planungsprozess die Bauwerks-Anforderungen in Anforderungen an die Bauteile und Anforderungen an die Bauprodukte "übersetzen". Diese sollten nach den wesentlichen Merkmalen formuliert werden. Die Verwender der Produkte müssen Produkte auswählen, deren Leistungen den Anforderungen entspricht.
Der Beitrag stellt die bauordnungsrechtlichen Anforderungen an Unterdecken allgemein und speziell die brandschutztechnischen Anforderungen an Unterdecken für Rohdecken mit Unterdecken sowie an das Brandverhalten von Unterdecken ohne Feuerwiderstand z.B. in Versammlungsstätten dar. Zudem werden die Randbedingungen für die Nachweisführung mit nach EU-Bauproduktenverordnung CE-gekennzeichneten Bauprodukten und Bausätzen oder Bauarten nach nationalem Bauordnungsrecht dargelegt.