Influence of the foundation slab on vibration reduction in buildingsTo prevent secondary airborne noise in buildings caused by vibrations from nearby rail traffic, appropriate measures, such as elastic bedding of buildings, are required. The stiffness of the building, particularly its foundation, relative to the wavelengths of the dynamic excitation in the ground has a significant influence on the transmission of vibrations and, consequently, on the sound radiated by the slabs and walls within the building. It is frequently claimed that increasing the stiffness of the base plate can reduce vibration transmission into the building to such an extent that elastic bedding of buildings is no longer necessary. This question was investigated in the studies described below, which employed various modeling approaches to determine the vibration reduction achieved by a stronger base plate for buildings supported elastically or rigidly on the ground. It is shown that while this measure can significantly reduce vibrations of the base plate itself, it has little effect on the much more relevant vibrations in the floor levels.
Holz-Beton-Verbunddecken (HBV-Decken) kombinieren die Leichtigkeit und Nachhaltigkeit von Holz mit dem Schall- und Brandschutz von Beton. Verbundmittel wie Kerven gem & auml;ss CEN/TS 19103 erfordern zus & auml;tzliche Abhebesicherungen zur Aufnahme von Exzentrizit & auml;tsmomenten. In einem Forschungsprojekt wurde die Frage untersucht, inwieweit eine getr & auml;nkte textile Naturfaserbewehrung Betonstahl nachhaltig ersetzen kann. Ziel war es, durch die exzentrische Anordnung der textilen Bewehrung die Biegetragf & auml;higkeit der Betonplatte so zu aktivieren, dass die Abhebesicherungen reduziert werden. Dauerhaftigkeitsuntersuchungen nach ISO 10406-1 (60 degrees C, alkalisches Milieu) zeigten eine hohe Best & auml;ndigkeit der Naturfaserbewehrung; der maximale Festigkeitsverlust betrug 12,6%. Push-out-Tests nach DIN CEN/TS 19103 belegten, dass eine textile Bewehrung ohne Abhebesicherungen eine Verlagerung des Versagensmechanismus vom Biegeversagen zum Schubversagen der Kerve erm & ouml;glicht. Zudem konnten die Bemessungslasten einer HBV-Decke mit betonstahlbewehrter Betonplatte, Kerven und Abhebesicherungen erreicht werden. Gro ss ma ss st & auml;bliche 4-Punkt-Biegeversuche best & auml;tigen die Tragf & auml;higkeit der Verbindung. Allerdings zeigten die Versuche Herausforderungen bei der Betonverdichtung im Kervenbereich, was zu einer ausgepr & auml;gten Streuung der Kervensteifigkeit mit einem Variationskoeffizient von 70 % f & uuml;hrte. Die Ergebnisse verdeutlichen das Potenzial von Naturfasertextilien f & uuml;r leistungsf & auml;hige, nachhaltige HBV-Decken. Load-bearing behaviour of TCC ceilings with textile natural fibre reinforcement and notched jointsTimber-concrete composite (TCC) slabs combine the lightweight, sustainable properties of timber with the acoustic and fire protection benefits of concrete. Since connections such as notches require additional lift-off restraints to handle eccentric moments according to CEN/TS 19103, this research investigated impregnated textile natural fibre reinforcement as a sustainable alternative to steel. The aim was to activate the flexural capacity of the concrete slab by placing textiles eccentrically, thereby reducing the need for lift-off restraints. Durability tests in an alkaline environment (60 degrees C) according to ISO 10406-1 confirmed sufficient resistance, with a maximum strength reduction of 12.6%. This enables a reduction in concrete cover, resulting in leaner, more resource-efficient constructions. Local push-out tests demonstrated that multi-layer textile reinforcement successfully shifted the failure mechanism from flexural failure to shear failure within the notch, achieving maximum loads comparable to those with steel reinforcement. Large-scale four-point bending tests validated the load-bearing capacity of the connection. However, practical challenges in concrete compaction around the notch area resulted in considerable variation in notch stiffness (coefficient of variation: 70%). Overall, the results confirm the high potential of natural fibre textiles for efficient and sustainable TCC construction.
Construction-induced deformations in Berlin SandsUrban excavation pits and foundation systems are frequently constructed in close proximity to existing buildings and infrastructure. In this context, the reliable prediction and limitation of deformations affecting adjacent structures are of critical importance. Although modern numerical analysis methods enable a sound assessment of structure-induced ground movements, the installation processes of retaining systems and foundation elements are generally neglected or represented only in a highly simplified manner. Construction-induced effects, such as ground relaxation during diaphragm wall installation, densification resulting from drilling operations, or loosening caused by unintended soil loss, are strongly influenced by the quality of construction execution and there-fore often cannot be adequately captured by numerical calculations alone. Consequently, the additional deformations arising from these installation processes are typically estimated in engineering practice based on empirical experience. This paper presents monitoring data on construction-induced deformations obtained from urban construction projects in Berlin and develops a practical approach for estimating the influence of construction activities on ground deformations.
Bei der dynamischen Simulation von Zug & uuml;berfahrten & uuml;ber Eisenbahnbr & uuml;cken im Hochgeschwindigkeitsbereich zeigt sich h & auml;ufig eine erhebliche Diskrepanz zwischen berechnetem und real gemessenem Systemverhalten, insbesondere hinsichtlich der vertikalen Br & uuml;ckenbeschleunigungen. F & uuml;r diesen Unterschied k & ouml;nnen vereinfachte Rechenmodelle verantwortlich gemacht werden, denen zugunsten einfacher Handhabung konservative Annahmen zugrunde liegen. Als ein ma ss gebender Einflussfaktor gilt das Lehr'sche D & auml;mpfungsma ss des Br & uuml;ckentragwerks. Oftmals ist eine experimentelle Bestimmung an realen Tragwerken erforderlich, weil die im aktuell g & uuml;ltigen Eurocode angegebene Gr & ouml;ss e als untere Grenze gilt. Der vorliegende Beitrag untersucht die Frage, inwieweit die in dynamischen Versuchen eingesetzte Sweep-Rate einen Einfluss auf die Bestimmung des D & auml;mpfungsma ss es aus & uuml;bt. Es wird gezeigt, dass eine ungeeignet gew & auml;hlte Sweep-Rate zu systematischen Verzerrungen f & uuml;hrt, die bei Anwendung & uuml;blicher Auswertungsverfahren eine nicht konservative, d. h. zu hohe Absch & auml;tzung des realen D & auml;mpfungsma ss es zur Folge haben. Aufbauend auf den gewonnenen Erkenntnissen wird ein Fehlerkriterium formuliert, aus dem eine empfohlene maximale Sweep-Rate abgeleitet wird. Zudem wird gezeigt, wie aus verzerrten Messdaten aufgrund einer zu hohen Sweep-Rate das tats & auml;chlich zugrunde liegende D & auml;mpfungsma ss rekonstruiert werden kann. Analysis of linear sine sweeps of railway bridgesIn dynamic simulations of high-speed train passages over railway-bridges a considerable discrepancy is frequently observed between the calculated and the measured structural response, particularly with regard to the vertical bridge accelerations. Simplified computational models, which rely on conservative assumptions for the sake of practical applicability, can be responsible for this. One of the governing influencing factors in this context is the damping ratio of bridge structure. Since the value specified in the currently valid Eurocode represents a lower boundary, experimental determinations on real structures are often required. This contribution investigates the extent to which the sweep rate used in dynamic tests to determine a structure's response affects the determination of the damping ratio. It is shown that an improper sweep rate can lead to systematic distortions resulting in a non-conservative, i.e., excessively high, estimation of the actual damping ratio, when using common evaluation methods. Building on these findings, an error criterion is formulated from which a recommended maximum sweep rate is derived. In addition, it is demonstrated how the true underlying damping ratio can be estimated from distorted measurement data.
The Working Group for Excavations of the German Geotechnical Society (DGGT) has regularly published recommendations for analysis, design and construction of excavation enclosures since 1968. The present report provides an overview of the current activities of the working group. During the reporting period, the focus was on the participation in commenting on the drafts of the new Eurocode 7 and Eurocode 0. Further topics include simplifications in the use of the FEM, the integration of a safety and monitoring concept in the design of struts, minor editorial corrections in Section 8.3 and proposals for abbreviations in the second generation of EC 0 and EC 7.
