Shear response of reinforced concrete members without stirrups under bendingThis contribution presents a new model to determine the shear capacity of reinforced concrete members under bending without shear reinforcement. The main idea of the model is the consideration of principal stress in the region of crack tips of the flexural cracks due to bending. A potential band for the formation of a critical shear crack that tends to connect the tips of existing flexural cracks can be assumed. The width of this band decreases with the increasing of the bending moment and gets larger when the shear force becomes higher. This means the bending moment affects positively the shear capacity. With the new model the shear capacity and the crack pattern in previous shear tests with different structural systems and loading conditions can be explained, which is generally not possible with the existing models.

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Der vorliegende Aufsatz berichtet über experimentelle Untersuchungen zum Einfluss des statischen Systems und der Belastungsart auf das Querkraftverhalten von Biegebauteilen ohne Querkraftbewehrung. Zehn rechteckige Stahlbetonbalken mit drei statischen Systemen und zwei Belastungsarten wurden hierbei getestet, wodurch nahezu alle in der Praxis möglichen M/V‐Kombinationen erfasst werden konnten. Die Ergebnisse zeigen erhebliche Unterschiede in der Querkrafttragfähigkeit von Schubfeldern unterschiedlicher M/V‐Kombinationen. Die Querkrafttragfähigkeit von Einfeldbalken unter Gleichlast ist höher als jene von vergleichbaren Balken unter Einzellast. Ferner ist die Querkrafttragfähigkeit von Krag‐ und Mittelstützen von Durchlaufbalken unter Gleichlast deutlich höher als die Querkrafttragfähigkeit von Einfeldbalken. Im Allgemeinen kann mit den Versuchsergebnissen festgestellt werden, dass die zugehörige Biegebeanspruchung die Querkrafttragfähigkeit eines Bauteils positiv beeinflusst. Weiterhin spielt das Rissbild infolge Biegung eine entscheidende Rolle für die Querkrafttragfähigkeit bei schubschlanken Stahlbetonbauteilen. Shear tests on reinforced concrete beams with different M/V‐combinations This paper presents an experimental investigation on the effect of structural system and load configuration on the shear behavior of flexural reinforced concrete (RC) members without shear reinforcement. A total of ten rectangular beams with three structural systems and two load configurations were tested. With the chosen test set‐up, almost all M/V‐combinations commonly encountered in practice can be investigated. The test results indicate significant differences of the shear capacity of members with different M/V‐combinations. The shear capacity of the simply supported beam under a uniform load is higher than that of similar beams under a concentrated load. Moreover, the shear capacity of the cantilever and continuous beams under uniform load is significantly higher than that of simply supported beams. Generally, it can be concluded that the co‐existing flexural action has a positive influence on the shear resistance of a RC member without shear reinforcement. Furthermore, the flexural crack pattern plays an important role in the shear resistance of slender RC members.

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Development time, survival, reproduction, and sex ratio were determined for the predatory mite Neoseiulus longispinosus (Evans) at six constant temperatures (20, 25, 27.5, 30, 32.5 and 35 oC) reared on citrus red spider mite Panonychus citri (McGregor). No predatory mite reached adulthood at 35oC. All female and male immature stages of N. longispinosus developed significantly faster as the temperature increased from 20to 30 oC, but development slowed down as the temperature exceeded 30 oC. The mean total developmental time of females was longest at 20 °C (9.73 days), followed by 25oC (5.67 days), 27.5oC (4.46 days), and 32.5 oC (4.55 days) and was shortest at 30oC (3.69 days). The oviposition rate and lifetime fecundity were highest at 27.5 oC (2.80 eggs/female/day and 43.76 eggs/female, respectively) and lowest at 20 oC (0.78 eggs/female/day and 21.64 eggs/female, respectively). However, temperature had no influence on the sex ratio of offspring with the proportion of females ranging from 0.62 to 0.65. The intrinsic rate of increase (r) of N. longispinosus averaged 0.323, 0.303, 0.267, 0.189 and 0.107 females female−1 day−1 at 30, 27.5, 32.5, 25, and 20°C, respectively. These values suggested that the most optimal temperatures for the population growth of N. longispinosus were between 27.5 and 30oC.