Because U-shaped steel beams filled with concrete have the advantages of reduced construction period and superior structural performance, they have been widely used as structural elements. In this study, the flexural behavior of newly developed bolt-connected U-shaped steel and concrete composite beams under a negative bending moment was experimentally evaluated. The main test variables were bolt spacing in bottom steel plates and types of U-shaped steel sections. Test results showed that the flexural behavior of the composite beams is determined by the plate-buckling mode of bolt-connected bottom steel plates. Composite beams with a greater bolt spacing than that in the standard AISI S100-16 experienced early plate buckling of the bottom steel plates, resulting in reduction of flexural stiffness and maximum flexural strength. Thus, the buckling mode of bolt-connected bottom plates should be considered for bolt-connected U-shaped composite beams under a negative bending moment. The longitudinal lips of U-shaped steel sections can increase the flexural performance of composite beams due to anchorage performance of the steel sections with lips.

In reinforced concrete columns, both constructability and structural safety should be considered in selecting the anchorage details of transverse reinforcement. For the simple installation of peripheral hoops, in this study, L-shaped ties were proposed to replace the conventional closed hoops with 135° hook anchorages. The L-ties can be easily installed from the side of columns by temporarily moving a longitudinal bar. Cyclic lateral loading tests were performed on five reinforced concrete columns to verify the effect of the L-ties on the shear resistance and buckling resistance of longitudinal bars after concrete cover spalling. The main test parameters included the types of transverse reinforcement, aspect ratio of columns, and straight extension of hooks. The test results demonstrated that the strength, deformation capacity, and energy dissipation of the columns using L-ties were comparable to those of columns using the conventional closed hoops because 135° hooks at both ends in the L-ties were anchored in the core concrete. The straight extension of the 135° hook anchorages with 6db provided a sufficient anchorage performance despite following concrete cover spalling. Furthermore, nonlinear behaviors of the columns were discussed by comparing the nonlinear modeling parameters specfied in current standards to evaluate postyield deformation capacities.

Concrete-filled U-shaped steel beams can be alternatives to conventional composite beams with I-section steel. In this study, a novel U-shaped composite beam is proposed, with a bolt assembly of two Z-shaped steel and a bottom plate. Focusing on the negative flexural behavior of bolted U-shaped composite beams, two experimental programs were carried out: (1) monotonic negative bending on six beam-to-girder connections (or continuous beams); and (2) cyclic positive and negative bending on two beam-to-column connections. In the specimen design, the degrees of composite action were considered for both headed stud anchors in the slab and bolts in the bottom section. The proposed bolt assembly was expected to provide fully and partially composite actions for positive and negative moment, respectively. The test results showed that the flexural mechanism of the bolted U-shaped composite beams occurred typically with local buckling of the bottom plate and the bottom flanges of the Z-shaped steel. The positive and negative flexural strengths of the proposed composite beams were evaluated based on AISC design practice, addressing the degrees of composite action and the plate local buckling. The structural performance of the test specimens was further evaluated with respect to the flexural stiffness and deflection. On the basis of the test results, design considerations for the bolted U-shaped composite beams were recommended.

Monitoring and preserving natural habitats has become an essential activity in many countries today. As a native tree species in Korea, Paulownia coreana has periodically been surveyed in national ecological surveys and was identified as an important target for conservation as well as habitat monitoring and management. This study explores habitat suitability models (HSMs) for Paulownia coreana in conjunction with national ecological survey data and various environmental factors. Together with environmental variables, the national ecological survey data were run through machine learning algorithms such as Artificial Neural Network and Decision Tree & Rules, which were used to identify the impact of individual variables and create HSMs for Paulownia coreana, respectively. Unlike other studies, which used remote sensing data to create HSMs, this study employed periodical on-site survey data for enhanced validity. Moreover, localized environmental resources such as topography, soil, and rainfall were taken into account to project habitat suitability. Among the environment variables used, the study identified critical attributes that affect the habitat conditions of Paulownia coreana. Therefore, the habitat suitability modelling methods employed in this study could play key roles in planning, monitoring, and managing plants species in regional and national levels. Furthermore, it could shed light on existing challenges and future research needs.

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address