Prediction of Shear Strength of UHPC Beam with Small Shear Span to Depth Ratios Based on Modified MCFT

Ultra-high performance concrete (UHPC) has been gradually used in structure engineering due to its excellent mechanical performance, however, predicting the shear capacity of the UHPC beams is still a challenge, especially for the beams with small shear span to depth ratios. To address this issue, this paper devotes to developing a rational model to predict the shear capacity of the UHPC beams with stirrups based on the modified compression field theory (MCFT) and plastic theory. The shear force will be balanced by the stirrups, matrix, fibers and shear compression zone. The contribution of stirrups, matrix and fibers on shear capacity can be predicted by MCFT, and the contribution of compression zone is determined based on plastic theory. 12 UHPC beams was designed and tested to validate the proposed model. It can be found that the predictions agree well with test results, while the current design codes, including SETRA-AFGC and SIA, give overly conservative values for UHPC beams when the shear to span is less than 2.5.

Shear-flexural cracking strength of RC beams with external vertical prestressing rebars: Theoretical investigation and numerical simulation

This paper presents a semi-theoretical empirical formula to predict the shear-flexural cracking strength of an RC beam enhanced with the external vertical prestressing rebar (EVPR) technique. Besides, nonlinear finite element models (FEM) created by software ABAQUS were used to analyze the effect of crucial parameters on the shear-flexural cracking strength. The parameters involve shear span-to-depth ratio, concrete strength, longitudinal tension reinforcement ratio, initial pulling force and spacing of EVPRs, and the vertical stiffness of the EVPR supports. Results show that the cracking strength increased linearly with the tensile strength of the concrete and the initial pulling force. The small shear span-to-depth ratio was predominantly conducive to the cracking strength. Adequate longitudinal tension rebars contributed to the cracking strength improvement. A reasonable EVPR spacing was recommended to ensure the cracking strength. Greater vertical stiffness of the EVPR supports can ensure higher compressive stress for the RC beam to improve the cracking strength.

Seiches and the slide/seiche dynamics; subcritical and supercritical subaquous mass flows and their deposits. Examples from Swiss Lakes

Four historically documented large and potentially dangerous lacustrine waves in Swiss lakes show that these waves have been seiches (standing waves) triggered by sublacustrine slides; a statement which is in accordance with the experience of seismologists who see earthquakes triggering seiches in lakes. Nevertheless, large historical waves in Switzerland have recently been modeled as progressive shallow water waves (tsunamis), probably because the slide/seiche dynamics are not known, and experiments with subaquatic slides fail to generate seiches in test–flumes. It appears that these tests exhibit a small shear–energy/slide–energy ratio ε, if compared with the situation in lakes. These facts incite a shear–stress lemma that states that ε is the constituent factor for the slide/seiche coupling. The structure of the subaqueous mass flow deposit (MFD) in lakes Lucerne and Geneva suggests the occurrence of subcritical and of supercritical slide flows. The former would generate a contortite, a MFD with contorted bedding, the latter a debrite (mudclast conglomerate). Potential slide energy considerations are used for an estimation of the amplitudes of large seiches produced by subaquatic slides, a proceeding that yields partly similar and partly very different results, as compared with numerical tsunami simulations.

Rayleigh–Bénard Instability of an Ellis Fluid Saturating a Porous Medium

The Ellis model describes the apparent viscosity of a shear–thinning fluid with no singularity in the limit of a vanishingly small shear stress. In particular, this model matches the Newtonian behaviour when the shear stresses are very small. The emergence of the Rayleigh–Bénard instability is studied when a horizontal pressure gradient, yielding a basic throughflow, is prescribed in a horizontal porous layer. The threshold conditions for the linear instability of this system are obtained both analytically and numerically. In the case of a negligible flow rate, the onset of the instability occurs for the same parametric conditions reported in the literature for a Newtonian fluid saturating a porous medium. On the other hand, when high flow rates are considered, a negligibly small temperature difference imposed across the horizontal boundaries is sufficient to trigger the convective instability.

Folding Structure of the South Slope of the Great Caucasus in Crossing the Gorge of the River Ksani

В статье рассмотрена складчатая структура Большого Кавказа в пересечении ущелья р. Ксани, которая все еще недостаточно изучена. Вместе с тем исследование складчатости Большого Кавказа имеет решающее значение для выяснения условий формирования современной складчатой структуры региона. Цель работы. Установление важных особенностей складчатости Большого Кавказа необходимых для выявления причин и механизмов образования его структуры, представляющих еще не до конца решенную проблему. Методика исследований заключалась в весьма детальной зарисовке складчатости региона вдоль ущелья р. Ксани в масштабе 1:1000, что позволяло фиксировать все особенности изучаемой структуры. Составленный при полевых исследованиях разрез был уменьшен до 1:50000 масштаба. Полученный геолого-структурный профиль достаточно полно и точно отражает основные черты структурного строения региона. Результаты. В изученном разрезе установлен ряд новых важных особенностей складчатой структуры, сложенной из мезозойско-кайнозойских толщ. Выяснена многопорядковость и разновозрастность складчатых структур и их субширотное простирание. Структуры первого порядка являются более ранними складками и представлены асимметричными наклоненными на юг сильно сжатыми складками, шириной 1–3 км. Более поздние складки высоких порядков, осложняющие крупные структуры, тоже тесно сжаты, асимметричны и характеризуются падением осей складок на север. Размер их колеблется в широких пределах − от 0.5 м до нескольких десятков метров. Субширотная ориентировка складчатости указывает на то, что она сформировалась в другой обстановке деформации, чем основная северо-западная структура Большого Кавказа. Обсуждение результатов и выводы. Установленный характер складчатости свидетельствует о различном генезисе структур в процессе двухэтапной разноплановой деформации региона. Выяснено, что на первом доверхнеорогенном этапе дислокации (юра-средний миоцен) Кавказ испытал северо-восточное тангенциальное сжатие, вызванное придвиганием и прижатием Черноморско-Закавказского микроконтинента к Большому Кавказу. В результате в регионе была сформирована основная линейная складчатая структура северо-западного простирания, крупные региональные разломы и слоевой кливаж. На втором позднеорогенном этапе деформации (поздний миоцен-антропоген) складчатая структура Большого Кавказа испытывала косое субмеридиональное горизонтальное сжатие. Установлено, что причиной деформации явилось долготное придвигание Ксанского шоля, блока микроконтинента и его внедрение в складчатую структуру Большого Кавказа. Эти дислокации способствовали возникновению в регионе наложенной на раннюю структуру поздней малой складчатости, мелких разрывов скалывания и секущего кливажа субширотного направления. Сделан вывод, что в указанных условиях, разными механизмами дислокации была образована современная сложная складчатая структура южного склона Большого Кавказа в пересечении ущелья р. Ксани в альпийском цикле тектогенеза региона The article considers the folded structure of the Greater Caucasus at the intersection of the gorge of the river Ksani, who is still not well understood. At the same time, the study of the folding of the Greater Caucasus has crucial significance for the determination of the conditions of formation of the modern folded structure of the region. Aim. The establishment of important features of the Greater Caucasus folding essential for identification of the reason and mechanisms of its structure formation, which are not yet fully resolved problem. The research methodology was a very detailed sketching of the folding of the region along the river Ksani gorge in a scale of 1:1000, which allowed to record all the features of the studied structure. The section compiled during field studies was reduced to 1:50 000 scale. The resulting geological and structural profile sufficiently fully and accurately reflects the main features of the structural constructionof the region. Results. In the studied section, a number of new important features of the folded structure of its Mesozoic-Cenozoic strata are established. First of all is revealed, it should be noted that the fold structures are multi-order and of different ages and of sublatitudinal strike. The first-order structures are earlier folds and are represented by asymmetric southwardly declined highly compressed 1-3 km wide folds. Complicating later large structures folds of higher orders are also tightly compressed, asymmetric with the axes dipping to the north. Their sizes vary widely - from 0.5 m to several tens of meters. The sublatitudinal strike of the folding indicates that it formed in a different deformation environment than the main northwestern structure of the Greater Caucasus. Discussion of the results and conclusions. Established character of folding indicates a different genesis of the structures during the two-stage diverse deformation of the region. It was found that at the first suprahorogenic stage of dislocation (Jurassic-Middle Miocene), the Caucasus experienced northeast tangential contraction caused by the pulling and pressing of the Black Sea-Transcaucasian microcontinent to the Greater Caucasus. As a result, the main linear folded structure of the northwestern strike, large regional faults, and layered cleavage were formed in the region. At the second latehorogenic stage of deformation (Late Miocene-Anthropogene), the folded structure of the Greater Caucasus experienced oblique submeridional horizontal compression. It is established that the cause of the deformation was the longitudinal movement of the Ksani schol, a block of the microcontinent and its emplacement into the folded structure of the Greater Caucasus. These dislocations in the region contribute generation of the late low folding superimposed on the early structure, small shear faults, and crosscuting cleavage of the sub-latitudinal direction. It is concluded that, under indicated conditions, by different dislocation mechanisms was formed the modern complex folded structure of the southern slope of the Greater Caucasus at the intersection of the river Ksani gorge during the alpine cycle of regional tectogenesis

Experimental Study on Shear Capacity of High Strength Reinforcement Concrete Deep Beams with Small Shear Span–Depth Ratio

This study aimed to investigate the shear capacity performance for eight deep beams with HTRB600 reinforced high strength concrete under concentrated load to enable a better understanding of the effects of shear span–depth ratio, longitudinal reinforcement ratio, vertical stirrup ratio and in order to improve design procedures. The dimension of eight test specimens is 1600 mm × 200 mm × 600 mm. The effective span to height ratio l0/h is 2.0, the shear span–depth ratio λ is 0.3, 0.6 and 0.9, respectively. In addition, the longitudinal reinforcement ratio ρs is set to 0.67%, 1.05%, 1.27%, and the vertical stirrup ratio is taken to be 0%, 0.25%, 0.33%, 0.5%. Through measuring the strain of steel bar, the strain of concrete and the deflection of mid-span, the characteristics of the full process of shear capacity, the failure mode and the load deflection deformation curve were examined. The test results showed that the failure mode of deep beams with small shear span–depth ratio is diagonal compression failure, which is influenced by the layout and quantity of web reinforcement. The diagonal compression failure could be classified into two forms: crushing-strut and diagonal splitting. With decreasing of shear span–depth ratio and increasing longitudinal reinforcement ratio, the shear capacity of deep beams increases obviously, while the influence of vertical web reinforcement ratio on shear capacity is negligible. Finally, the shear capacity of eight deep beams based on GB 50010-2010 is calculated and compared with the calculation results of ACI 318-14, EN 1992-1-1:2004 and CSA A23.3-04, which are based on strut-and-tie model. The obtained results in this paper show a very good agreement with GB50010-2010 and ACI 318-14, while the results of EN 1992-1-1:2004 and CSA A23.3-04 are approved to be conservative.

Querkrafttragfähigkeit von Brückenträgern aus Spannbeton mit geringen Querkraftbewehrungsgraden/Shear Capacity of Prestressed Concrete Bridge Girders with Small Shear Reinforcement Ratios

Zusammenfassung Neben gestiegenen Verkehrslasten führen strengere normative Regeln zu höheren Anforderungen an Spannbetonbrücken. Viele ältere Spannbetonbrücken im Bestand weisen daher rechnerische Defizite bei der Querkrafttragfähigkeit auf. Durch experimentelle und theoretische Untersuchungen konnten im Zuge eines Forschungsprojekts für die Bundesanstalt für Straßenwesen (BASt) verfeinerte Berechnungsansätze für Querkraft erarbeitet werden. In diesem Beitrag werden am Institut für Massivbau der RWTH Aachen (IMB) durchgeführte Großversuche an Spannbetondurchlaufträgern vorgestellt. Die Träger mit Rechteck- oder I-Profil wiesen geringe Querkraftbewehrungsgrade auf und wurden durch Gleichstreckenlasten beansprucht. Auf Basis der Forschungsergebnisse wurde ein verfeinertes Bemessungsmodell entwickelt, das aus einem modifizierten Fachwerkmodell mit additivem Betontraganteil besteht und gegenüber dem Ansatz nach aktueller Nachrechnungsrichtlinie weitere Querkrafttragreserven berücksichtigt.

Astrophysical implications of double-layer torsional oscillations in a neutron star crust as a lasagna sandwich

In the crust of a neutron star, global torsional oscillations could occur in two elastic layers. The outer and inner layers are composed of spherical and cylindrical nuclei and of cylindrical holes (tubes) and spherical holes (bubbles), respectively, while between these two layers, a phase of slab-like (lasagna) nuclei with vanishingly small elasticity is sandwiched. In this work, we update systematic calculations of the eigenfrequencies of the fundamental oscillations in the inner layer by newly allowing for the presence of tubes. We find that the frequencies still depend strongly on the slope parameter of the nuclear symmetry energy, L, while being almost independent of the incompressibility of symmetric nuclear matter. We also find that the fundamental frequencies in the inner layer can become smaller than those in the outer layer because the tube phase has a relatively small shear modulus and at the same time dominates the inner layer in thickness. As a result, we can successfully explain not only the quasi-periodic oscillations originally discovered in the observed X-ray afterglow of the giant flare of SGR 1806–20 but also many others recently found by a Bayesian procedure.