yes / This paper presents experimental results of three continuously supported concrete slabs reinforced with basalt-fibre-reinforced polymer (BFRP) bars. Three different BFRP reinforcement combinations of over and under reinforcement ratios were applied at the top and bottom layers of continuous concrete slabs tested. One additional concrete continuous slab reinforced with steel bars and two simply supported slabs reinforced with under and over BFRP reinforcements were also tested for comparison purposes. All slabs sections tested had the same width and depth but different amounts of BFRP reinforcement. The experimental results were used to validate the existing design guidance for the predictions of moment and shear capacities, and deflections of continuous concrete elements reinforced with BFRP bars. The continuously supported BFRP reinforced concrete slabs illustrated wider cracks and larger deflections than the control steel reinforced concrete slab. All continuous BFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. ACI 440-1R-15 equations give reasonable predictions for the deflections of continuous slabs (after first cracking) but stiffer behaviour for the simply supported slabs, whereas CNR DT203 reasonably predicted the deflections of all BFRP slabs tested. On the other hand, ISIS-M03-07 provided the most accurate shear capacity prediction for continuously supported BFRP reinforced concrete slabs among the current shear design equations.

Shear failure in concrete beams are often brittle in nature and potentially dangerous without adequatereinforcing measures. In design of concrete, it is commonly recommended to install transversalreinforcement along the shear span to induce a more ductile structural response, improving the shearcapacity all together and providing sufficient warning prior to collapse. However, it is more frequentlybeing assessed whether analogous performance can be achieved in fiber reinforced concrete beamswithout stirrups, and multiple attempts in literature confirm that it is possible. This alternative technologyintroduces need for better understanding of the modeling aspects of FRC in numerical simulations, as it isbecoming more common for engineers to resort to the finite element method in quality assurance ofstructures.In this thesis, the possibility of predicting shear failure numerically in simply supported fiber reinforcedconcrete beams with flexural bar reinforcement but without stirrups was investigated by means ofnonlinear finite element analysis, using the software package ATENA 2D Engineering. The ultimate aimwas to, as accurately as possible by means of numerical analyses on representative FE-models, replicatethe results from physical three-point-bending tests on simply supported FRC beams of various sizesperformed by Minelli et al. (2014). These beams were merely equipped with flexural reinforcement andexhibited shear failure.This thesis revolved around development and comparative assessment of material models for FRC basedon the smeared crack approach, adopting two different strategies: (1) The first strategy was to calibratematerial parameters based on results from 3PBT on notched FRC beams that were carried out prior totesting of the reinforced FRC beams, as reported by Minelli et al. (2014). Nonlinear finite element analysiswas used on representative FE-models for the notched 3PBT specimens, from which material parameterswere obtained iteratively by employing inverse analysis methods proposed by Červenka Consulting s.r.o.(2). The second strategy comprised of utilizing recommended constitutive relations from designrecommendations in SS812310 and RILEM TC 162-TDF. All of the constructed material models werefinally coupled with the FE-models that represented the beams with flexural reinforcement for evaluationof their performance based on their consistency with experiment data.It was found that the material models that were generated from inverse analysis in general would haveyielded successful predictions for the occurrence of shear failure in the reinforced FRC beams, providedthat the governing post-cracking residual tensile parameters were processed with respect to relevantassumptions as to describe uniaxial tensile behavior. However, although it was possible to utilize theproposed calibration method to replicate the load-displacement data for the notched 3PBT specimens withsufficient conformity, it was not possible to arrive at only one unique solution. Instead, multiple outcomescould be obtained based on the initial choice for the input value of the uniaxial tensile strength, leading tothe conclusion that experience and the engineering judgment of the user is of high importance whenadopting this method.Regarding the material models that were derived from constitutive relations in design recommendations,satisfactory estimates for the shear capacity could be obtained from the FE-models that were based onrecommendations by RILEM. The models that were based on SS812310, on the other hand, demonstratedover-stiff behavior and they were unable to provide accurate graphical visualizations of characteristicshear cracking, although the obtained load bearing capacity overall matched the experiment data in caseswhen size effects seemingly had a minor influence. An important observation from the comparison ofthese material models was that the initial drop in tensile strength during crack initiation within an elementis crucial in modeling of FRC, as it accounts for a more realistic behavior through a gradual transitionfrom aggregate bridging mechanisms of PC to the added fiber bridging mechanisms of FRC. Forsituations with high residual tensile strengths in relation to tensile strength at crack initiation, theguidelines in SS812310 become less practical for predicting shear failure by means of NLFEA.

<p dir="ltr">A key challenge in the assessment of the stability of fractures in rock is the identification of precursory geophysical signatures of shear failure. Accurate estimation and prediction of shear failure along rock discontinuities is crucial to prevent failure of geotechnical structures and potential natural hazards, such as landslides and earthquakes. Active seismic monitoring, such as compressional (P) and shear (S) waves, has been used to monitor the evolution of contact area and contact stress along rock discontinuities. Past laboratory experiments determined that changes in the amplitude of the transmitted, reflected, and converted P- and S-waves can be used to assess local changes in contact area and fracture specific stiffness, and to identify precursory events to shear failure of rock fractures. Those studies have identified the peaks (maxima or minima) in wave amplitudes as the seismic precursors to shear failure. Past studies were performed on dry artificial rock discontinuities with homogeneous and well-matched contact surfaces. However, in nature, rock discontinuities are not always homogeneous and well-matched, and are often found below the water table. In addition, at large depths, e.g. in enhanced geothermal systems (EGS), fractures are subjected to high temperatures.</p><p dir="ltr">The objectives of this research are to: (1) characterize the geophysical response of rock fractures during shear for dry and saturated conditions at room temperature, and saturated conditions at elevated temperatures; and (2) detect and identify seismic signatures of shear failure/slip for each of the three conditions. To achieve the goal of the research, a novel shear test apparatus was designed and built to test saturated jointed rock specimens under normal and shear loading, with a back pressure and at elevated temperatures, while also being capable of housing seismic transducers to monitor simultaneously the mechanical and geophysical response of the rock joints during shear. The system consisted of a sealed and heated pressure chamber and a biaxial compression frame. The pressure chamber was also used to perform B-value tests on cylindrical rock specimens to determine the minimum magnitude of back pressure required for fluid saturation.</p><p dir="ltr">Laboratory direct shear tests were performed on tension-induced fractures in Indiana limestone and Sierra White granite specimens with non-homogeneous rough contact surfaces. The contact surfaces were created by axial splitting of prismatic rock blocks. Shear tests were conducted on the rock fractures at a constant displacement rate in the pressure chamber, which enabled control of effective normal stress, pore water pressure, and temperature. During the tests, transmitted and converted P- and S-waves propagated across rock fractures and their changes in wave amplitude were monitored to assess the evolution of local contact areas during shear and detect precursory changes in wave amplitudes prior to shear failure.</p><p dir="ltr">Seismic precursors were observed in the wave amplitude data from all tests conducted under the three conditions. Precursors were most identifiable in the transmitted S-wave data. For all three conditions, the transmitted S-wave showed the same form of a seismic precursor; a peak (maximum) in wave amplitude was observed prior to the peak shear strength, as local contact surfaces interlocked and failed before macroscopic shear failure. However, the transmitted P-wave and converted waves (P-to-S and S-to-P) exhibited different behavior compared to the transmitted S-wave and depended on the test conditions. While, for dry conditions, the transmitted P-wave and converted waves still exhibited seismic precursors as peaks in their wave amplitudes, they did not display an observable peak for saturated fractures at room temperature, but rather either a very slight increase or a continuous reduction in amplitude. Instead of observable peaks, an abrupt change in the rate of reduction in the transmitted P-wave and converted amplitudes was observed that either coincided or occurred close to the peak in the transmitted S-wave amplitude. Thus, an onset of dramatic change in the reduction rate can be also taken as a seismic precursor to shear failure. This phenomenon can be explained by the large stiffness of the highly incompressible fluid, water, which leads to a decrease in P-wave sensitivity to changes in the normal fracture stiffness that arise from rock asperities under saturated conditions.</p><p dir="ltr">Even though the seismic wave amplitude generally contains a seismic precursor to shear failure, some exceptions exist: the wave amplitudes also depend on the local characteristics of the frictional area. No peak or seismic precursor in wave amplitude is observed prior to failure when the contact area between the fractures surfaces decreases because of dilation/opening. In addition, a delay peak in amplitude after shear failure may be observed when the fracture surfaces contain an initial large void or aperture in the region probed by the sensor. These exceptions may occur at a relatively low effective normal stress (2 MPa) and may disappear when a better contact has been established between the fracture surfaces by increasing the effective stress. Direct shear tests under an effective stress of 6 MPa, but at 50^oC, showed that both the transmitted P-waves and converted waves exhibited peaks in their amplitudes prior to the failure. However, these exceptions still require further exploration for the systematic identification and detection of seismic precursors.</p><p dir="ltr">The research shows that seismic monitoring is an effective tool to monitor the shear behavior of discontinuities, to provide an assessment of the local behavior of the frictional surface under the transducer, and to predict failure of the discontinuity. It can be used for dry, saturated discontinuities and for a wide range of pore pressures and temperatures. Other potential applications include fault monitoring, and even possibly earthquake prediction with additional research.</p>

Reinforced masonry (RM) shear walls are a common lateral load-resisting system for building structures. The seismic design guidelines for such systems are based on relatively limited experimental data. Given the restrictions imposed by the capabilities of available experimental equipment, analytical modeling is the only means to conduct systematic parametric studies for prototype RM wall systems and quantify the seismic safety offered by current design standards. A number of modeling approaches, with varying levels of complexity, have been used for the analysis of reinforced concrete (RC) and masonry wall structures. Among the various methods, the truss analogy is deemed attractive for its conceptual simplicity and excellent accuracy, as indicated by recent studies focusing on RC walls. This thesis uses an existing modeling method, based on nonlinear truss models, to simulate the behavior of fully grouted reinforced masonry shear walls. The modeling method, which was originally created and used for RC walls, is enhanced to capture the effect of localized sliding along the base of a wall, which may be the dominant mode of damage for several types of RM walls. The truss modeling approach is validated with the results of quasi-static cyclic tests on single-story isolated walls and dynamic tests on a multi-story, three-dimensional wall system. For the latter, the truss model is found to give similar results to those obtained using a much more refined, three-dimensional finite element model, while requiring a significantly smaller amount of time for the analysis. Finally, truss models are used for the nonlinear static analysis of prototype low-rise walls, which had been analyzed with nonlinear beam models during a previous research project. The comparison of the results obtained with the two modeling methods indicates that the previously employed beam models may significantly overestimate the ductility capacity of RM squat walls, due to their inability to accurately capture the shear-flexure interaction and the effect of shear damage on the strength of a wall. / Master of Science

Die Zielstellung des Forschungsvorhabens ist die Entwicklung und Erprobung von speziellen Indikatoren, welche im Zuge einer Probebelastung für die sichere Beurteilung der Tragfähigkeit von Massivbaukonstruktionen mit geringem Ankündigungsverhalten geeignet sind. Der Begriff "Ankündigung“ bezieht sich dabei auf die beim Belastungsversuch wichtige Bestimmung der Versuchsgrenzlast, deren Überschreiten zu inakzeptablen Schädigungen führt und daher mit ausreichender Sicherheit ausgeschlossen werden muss. Durch den Einsatz und vor allem die Kombination moderner Messverfahren kann eine wesentliche Verbesserung der Informationsqualität während des Belastungsversuches erreicht werden. Eine Echtzeitauswertung der Messergebnisse erlaubt die Definition objektiver Kriterien der Versuchsgrenzlast. Dadurch soll zukünftig gewährleistet werden, dass bereits minimales nichtlineares Strukturverhalten unmittelbar während des Versuches festgestellt und damit die Versuchsgrenzlast nahezu schädigungsfrei ermittelt werden kann. Den Kernpunkt der Sensorik und Datenverarbeitung bilden flexibel einsetzbare photogrammetrische Verfahren zur automatisierten hochgenauen flächenhaften Erfassung von Schädigungen bei Probebelastungen aus Bilddaten von Digitalkameras mit permanenter Rechnerverbindung. Durch die Anwendung von speziellen Verfahren der Bildanalyse kann die Auswertung der Bilddaten weitestgehend automatisiert werden und in Echtzeit während des laufenden Versuchs erfolgen. Durch Subpixeloperatoren und geeignete Kalibrierverfahren können Genauigkeiten im Bereich weniger Mikrometer erzielt werden. Dieser Abschlussbericht gibt einen Überblick über die bisher durchgeführten theoretischen und experimentellen Untersuchungen zur Anpassung und aufgabenspezifischen Entwicklung der gewählten Messverfahren (Photogrammetrie und Schallemissionsanalyse). Diese wurden in Tastversuchen und Schubversuchen an Stahlbetonbauteilen ohne Bügelbewehrung erprobt und erlauben durch die Kombination der Messinformationen Schlussfolgerungen auf eine messbare Vorankündigung auch bei nicht-duktilen Massivbaukonstruktionen.

Die Zielstellung des Forschungsvorhabens ist die Entwicklung und Erprobung von speziellen Indikatoren, welche im Zuge einer Probebelastung für die sichere Beurteilung der Tragfähigkeit von Massivbaukonstruktionen mit geringem Ankündigungsverhalten geeignet sind. Der Begriff "Ankündigung“ bezieht sich dabei auf die beim Belastungsversuch wichtige Bestimmung der Versuchsgrenzlast, deren Überschreiten zu inakzeptablen Schädigungen führt und daher mit ausreichender Sicherheit ausgeschlossen werden muss. Durch den Einsatz und vor allem die Kombination moderner Messverfahren kann eine wesentliche Verbesserung der Informationsqualität während des Belastungsversuches erreicht werden. Eine Echtzeitauswertung der Messergebnisse erlaubt die Definition objektiver Kriterien der Versuchsgrenzlast. Dadurch soll zukünftig gewährleistet werden, dass bereits minimales nichtlineares Strukturverhalten unmittelbar während des Versuches festgestellt und damit die Versuchsgrenzlast nahezu schädigungsfrei ermittelt werden kann. Den Kernpunkt der Sensorik und Datenverarbeitung bilden flexibel einsetzbare photogrammetrische Verfahren zur automatisierten hochgenauen flächenhaften Erfassung von Schädigungen bei Probebelastungen aus Bilddaten von Digitalkameras mit permanenter Rechnerverbindung. Durch die Anwendung von speziellen Verfahren der Bildanalyse kann die Auswertung der Bilddaten weitestgehend automatisiert werden und in Echtzeit während des laufenden Versuchs erfolgen. Durch Subpixeloperatoren und geeignete Kalibrierverfahren können Genauigkeiten im Bereich weniger Mikrometer erzielt werden. Dieser Abschlussbericht gibt einen Überblick über die bisher durchgeführten theoretischen und experimentellen Untersuchungen zur Anpassung und aufgabenspezifischen Entwicklung der gewählten Messverfahren (Photogrammetrie und Schallemissionsanalyse). Diese wurden in Tastversuchen und Schubversuchen an Stahlbetonbauteilen ohne Bügelbewehrung erprobt und erlauben durch die Kombination der Messinformationen Schlussfolgerungen auf eine messbare Vorankündigung auch bei nicht-duktilen Massivbaukonstruktionen.

Ziel des Folgeantrages war die Entwicklung der photogrammetrischen Messtechnik zur onlinefähigen Anwendung bei In-situ-Belastungsversuchen. Dies wurde mit den in Kapitel 3 beschriebenen Ansätzen erfolgreich umgesetzt. Die gewählte künstliche Texturierung der Bauteiloberflächen stellte sich als sehr geeignet heraus, um bereits kleinste Strukturveränderungen beobachten und visualisieren zu können. Durch die Verwendung einer Industriekamera konnte die onlinefähige Bildanalyse und simultane Darstellung der Ergebnisse auf dem Bildschirm umgesetzt werden. Durch die Verwendung von Dreiecken und der Ermittlung der Hauptverzerrung jedes dieser Dreiecke wurden Bereiche hoher lokaler Dehnungen (Rissentwicklung) frühzeitig detektiert. Diese frühe und automatisierte Erkennung der Rissentwicklung ermöglicht und verbessert die Beurteilung des Tragzustandes des zu untersuchenden Bauteils erheblich. Für die Beurteilung des Tragverhaltens von Stahlbetonbauteilen ohne oder mit zu geringer Bügelbewehrung wurden neben der Photogrammetrie die Schallemissionsanalyse, herkömmliche Verformungsmesstechniken und abschnittsweise Verformungsmessungen mit Neigungssensoren durchgeführt. Es zeigte sich, dass gerade die Kombination dieser Messverfahren zu einer erheblichen Verbesserung der Information über den Tragzustand des untersuchten Bauteils führte.

No description available.

Historical accidents and experimental investigations have made apparent that blast loaded concrete members are prone to fail in brittle shear rather than a ductile flexure mode. Air blasts from accidental detonations or explosives may cause severe damage to buildings and infrastructure and it is of great importance that load carrying members can withstand the impulse that arise to avoid progressive collapses. The aims of this thesis are, through explanation of blast loads as dynamic loads acting on structures and measuring of the effects of blast loads on reinforced concrete beams with shear reinforcement, to understand the mechanisms governing shear failure. Two hypotheses are therefore tested: That for a reinforced concrete beam with shear reinforcement, the mechanism governing dynamic shear failure is similar to that of static shear failure and that blast induced shear failure in reinforced concrete beams can be prevented through a sufficient amount of shear reinforcement. To meet the stated aims and test the hypotheses, a literature study was conducted together with numerical simulations using explicit non-linear finite element analysis software LS-Dyna.Previous experimental investigations on blast loaded reinforced concrete beams have displayed a possible shift in failure mode from a ductile flexural failure at static loading to a brittle shear failure at dynamic loading. The shifting may be a property of higher exciting frequencies of blast loads, inducing modes of vibration with larger portions of shear energy. The results obtained from the numerical analyses indicated that an increased ratio of shear reinforcement reduces the risks of a brittle shear failure as well as decrease beam deflections and concrete strains, while increasing strains in the tensile reinforcement.Analysis of the shear capacity and shear reinforcement design through methods given in Eurocode 2 and FKR 2011 were considered as supplementary to the FE analysis. FKR 2011 provided accurate estimations of the maximum dynamic support reactions. Eurocode 2 uses a more conservative approach resulting in lower values of the design shear strength.The conclusions are that for the given beam and blast load, brittle shear failures may be prevented through reduction of the spacing and increase of the bar diameter of the shear reinforcement. The increased plastic strain of the tensile reinforcement as well as measurements of shear crack widths, support reactions and strains in the concrete suggests that the beams with large ratio of shear reinforcement exhibit more ductile behaviour without reaching failure. / Historiska händelser och experimentella undersökningar har gjort gällande att betongelement utsatta för luftstötvåg är benägna att gå till spröda skjuvbrott snarare än sega böjbrott. Luftstötvågor från oavsiktliga detonationer eller explosivt gods kan orsaka svåra skador på byggnader och anläggningar och det är därför viktigt att bärande strukturer kan motstå impulsen som uppstår för att fortskridande ras ska undvikas. Målen med detta examensarbete är att, genom att förklara det dynamiska beteendet hos luftstötvågor som belastar konstruktioner och mätning av de effekter som uppstår av luftstötvågor på armerad betong med tvärkraftsarmering, förstå de mekanismer som ligger till grund för skjuvbrott. Som påföljd testas två hypoteser: Att mekanismerna som ligger till grund för dynamiska skjuvbrott hos armerade betongbalkar med tvärkraftsarmering är liknande som för de som styr statiska skjuvbrott, och att skjuvbrott till följd av luftstötvågor kan förhindras genom att förse balken med tillräcklig tvärkraftsarmeringsinnehåll. För att nå målen och testa hypoteserna så genomfördes en litteraturstudie tillsammans med numeriska simuleringar med explicit icke-linjär finita elementanalys i kommersiella programvaran LS-Dyna. Tidigare experimentella undersökningar av armerade betongbalkar utsatta för luftstötvåg har visar på en förflyttning i brottmod, från sega böjbrott vid statisk belastning till spröda skjuvbrott vid dynamisk belastning. Förflyttningen kan härstamma från luftstötvågens frekvensinnehåll som framkallar högre vibrationsmoder med större andel skjuvenergi.De erhållna resultaten från de numeriska analyserna indikerar att ett ökat tvärkraftsarmeringsinnehåll minskar risken för spröda skjuvbrott, minskar utböjning och töjningar I balken samtidigt som töjningar i dragarmeringen ökar.Analyser av tvärkraftskapaciteten och dimensionering av tvärkraftsarmering genom metoder givna i Eurocode 2 och FKR 2011 användes som komplement till finita elementanalysen. FKR 2011 gav träffsäkra uppskattningar av de dynamiska störreaktionerna grundade i dynamisk jämvikt. Emellertid var Eurocode 2 det mer konservativa tillvägagångssättet, vilket resulterade i lägre dimensionerande tvärkraftskapacitet. Slutsatserna som drogs var att, för den givna balken och luftstötvågen så kunde spröda skjuvbrott motverkas genom minskning av avstånden mellan tvärkraftsarmeringen och ökning av stångdiametern. De ökade plastiska töjningarna i dragarmeringen tillsammans med mätningar av skjuvsprickornas bredd, stödreaktionerna och töjningarna i betongen föreslår att balkarna med högt tvärkraftsarmeringsinnehåll visar på ett segare beteende utan att gå till brott.

The geological disposal of nuclear waste, in underground openings and the long-term performance of these openings demand a detailed understanding of fundamental rock mechanics. A full scale field experiment: Äspö Pillar Stability Experiment was conducted at a depth of 450 m in sparsely fractured granitic rock to examine the rock mass response between two deposition holes. An oval shaped tunnel was excavated parallel to the σ3 direction to provide access to the experiment and also provide elevated stress magnitudes in the floor. In the tunnel floor two 1.75-m diameter 6-m deep boreholes were excavated so that a 1-m thick pillar was created between them. In one of the holes a confinement pressure of 700 kPa was applied and in the other displacement transducers were installed. The pillar volume was monitored by an Acoustic Emission System. Spatially distributed thermocouples were used to monitor the temperature development as the pillar was heated by electrical heaters. The excavation-induced stress together with the thermal-induced stress was sufficient to cause the wall of the open borehole to yield. The temperature-induced stress was increased slowly to enable detailed studies of the rock mass yielding process. Once the rock mass loading response was observed, the rock mass was unloaded using a de-stress slotting technique. This thesis focuses on the in-situ study of the rock mass response to coupled mechanical thermal loading and thermal-mechanical unloading. The experiment, its design, monitoring and observations are thoroughly described. An estimate of the yielding strength of the rock mass is presented and compared with laboratory test and results from other rock mass conditions reported elsewhere in the open literature. General conclusions about the effect of the confining pressure and the observations from the unloading of the pillar are also presented. Important findings are that the yielding strength of the rock mass has been successfully determined, low confinement pressures significantly affects the onset of yielding, the primary mode of fracture initiation and propagation is extensional, no significant time dependency of the yielding process was observed. The unloading studies also indicated that what appeared to be shear bands likely was a propagating zone of extensile failure that weakened the rock so that displacements in the shear direction could occur. / <p>QC 20100622</p>