Verbundverhalten von Vollgewindeschrauben in Brettschichtholzbauteilen

Bond behaviour of self‐tapping screws being used as reinforcement in glue‐laminated timber elements – Part 2: Analytical and numerical investigations as well bond model derivation for the calculation of anchorage length In favor of the investigation of bond behaviour, force transfer and anchorage length of self‐tapping screws, several tests have been realized at the Chair of Structures and Structural Design in cooperation with the Institute for Building Material Research of the RWTH Aachen University. The experimental investigations comprise more than 160 pull‐out tests of screws with long embedment length and over 84 load distributions tests. Additionally, several tests displaying the effect of longitudinal cracks in the surrounding wood as well as the effect of the screw tip have been conducted. Through various analyses of the bond behaviour, the experimental investigations form the basis for the calibration and evaluation of the numerical models and allow a prediction of the force transfer of the screws in glue‐laminated elements. Design rules that enable the application of the self‐tapping screws as reinforcement in timber elements have been derived from the knowledge obtained in the experimental and numerical investigations. This paper, which results from a research project funded by the German Research Foundation [1], presents the results of investigations on the bond behavior of self‐tapping screws in glue‐laminated timber elements. Part 1 elaborates on the experimental investigations [2] whereas part 2 illustrates the numerical analyses and presents a bond model, which enables the design of the anchorage length and the safe application of the screws as reinforcement in timber elements.     

Untersuchung von Schlosssprengungen an ausgeführten Ufereinfassungen mit kombinierten Spundwänden

Interlock failure of combined sheet pile walls In addition to multiple combinations of king piles and intermediate sheet piles the installation method of combined sheet pile walls can differ as well. The installation has to adapt to the boundary conditions of the construction work considering soil conditions, profile and interlock system, interlock protection, driving equipment, driving assistance etc. Despite the established construction of combined sheet pile walls interlock failure occurs. In this paper, the installation aspects of combined sheet pile walls in northern Europe are compiled and analyzed for the occurrence of interlock failure.     

Ausbau des Stichkanals nach Salzgitter von SKS‐km 3,550 bis 14,918

Expansion of the branch channel to Salzgitter from SKS‐km 3,550 to 14,918 The branch channel to Salzgitter will be extended to the waterway category Vb in the next years. This will enable inland waterway vessels with a width of 11,45 m and a loaded draft of 2,80 m to run it without limitations. The reaches Wedtlenstedt and Üfingen will be extended in most areas to a trapezoidal cross section with a width at water level of 36,90 m and a water depth of 4,00 m. The exit basins of the locks will be extended on one side. Overall about 1 000 000 m² of soil will be moved. About 300 000 m² of clay sealing and 460 000 m² of rip‐rap will be installed. Three culverts have to be replaced by new constructions to adapt to the new cross section of the channel. In addition two bridges will be modified to allow for a clearance of 5,25 m. At present the plan approval procedure is carried out. It is expected to achieve the plan approval order in 2017. The construction is planned to start in 2018. Completion is scheduled for 2024.     

Characterizing the effects of fines on the liquefaction resistance of silty sands

Recent earthquakes in New Zealand and Japan indicate that evaluating the liquefaction potential of silty sands remains an area of difficulty and uncertainty in geotechnical engineering. This paper presents a comprehensive experimental study along with analysis and interpretation in the framework of critical state soil mechanics, with the aim to address the complicated effects of fines. Two series of sand-silt mixtures, formed by mixing two different base sands with the same type of non-plastic silt, were tested under a range of packing density, confining pressure and silt content, and a unified correlation was established between the cyclic resistance and the state parameter that collectively accounts for the effect of packing density and confining pressure. The proposed correlation is independent of packing density, confining pressure, fines content and base sand, and allows prediction of the cyclic resistance of silty sands under different states. Furthermore, the mechanism of the fines-content induced reduction of cyclic resistance and the mechanism of the base-sand effect observed from the tests are elaborated in the sound theoretical context. The present study suggests that the critical state soil mechanics is a rational and appealing framework for liquefaction analysis of both clean and silty sands.     

Particle loss: An initial investigation into size effects and stress-dilatancy

Drained triaxial tests have been performed to explore the effect of particle loss on shearing behaviour and critical states in granular mixtures. The mixtures comprise Leighton Buzzard sand (d₅₀ = 0.8 mm), to which was added 15% by mass of salt particles of different nominal sizes: 0.063 mm, 0.25 mm and 0.5 mm. Shearing behaviours before and after particle loss (by dissolution) were compared. A good fit is observed between the test data and a stress-dilatancy relationship for the post-dissolution tests, highlighting the ability of the stress-dilatancy analysis as a means to interpret the effects of particle loss on shearing. It was noted that critical state strength parameter M is determined by the post-dissolution grading regardless of size of removed particle. However, the duration of contractant volumetric strain increased with the larger removed particles (0.25 mm & 0.5 mm) even when initial specific volumes were virtually identical. It is suggested that a loose volumetric state is reached if the sand particle network is initially disrupted by the amount and/or size of salt particles, which following dissolution results in structural or fabric phenomena that are not reflected in scalar volumetric measures such as specific volume.