Jeonghyeon Lim

Mountain railways are constructed on terrains with steep gradients and operate under unique conditions as they climb slopes at low speeds using rack rails. Recently, mountain railway systems in the form of embedded rail systems (ERSs) have been developed to minimize environmental damage caused by the construction of new roads. However, the use of ERS in mountain railway tracks is still limited, and research on their safety and behavior is lacking. Therefore, this study was conducted to evaluate the safety profile and behavioral responses of mountain-ERS under a steep gradient condition of 180‰. The effects of using high-strength concrete materials for precast concrete panels were investigated in this study, and the safety profile and behavioral response of mountain-ERS based on changes in the gradient and after adjusting the thickness of the subgrade of mountain-ERS was assessed. Under load conditions, the maximum tensile stress in the concrete elements did not exceed the tensile strength of the concrete. In the structural behavioral analysis, the patterns of stress variation were analyzed by applying stress to the concrete elements. The safety assessment and behavioral analysis results obtained in this study are considered valuable foundational research data for analytical studies on mountain-ERSs.

At construction sites, various types of temporary equipment and structures are used for safety and work efficiency. However, various temporary equipment-related accidents frequently occur for many reasons, including inappropriate installation, usage, and material and structural imperfections. A mobile scaffold is one of the most commonly used indoor temporary equipment for work in high places. In general, the main structural members of the mobile scaffold, such as the mainframes, horizontal members, braces, caster wheels, outriggers, and handrails, are installed on the construction site for this purpose. This means that the load-carrying capacity of the equipment can vary depending on the assembly details. In Korea, there are safety certification standards applied for frequently used temporary equipment, such as scaffolds and shoring. However, the standards concern the strength criteria for the member itself, rather than the global load-carrying capacity. Therefore, it is difficult to review whether the fabricated mobile scaffold has sufficient load-carrying capacity, or to confirm the structural safety considering the various uncertainties affecting the structural performance. In this study, rational safety certification standards and evaluation methods are suggested for fabricated mobile scaffolds. The suggested safety certification standards present structure-level criteria for checking the load-carrying capacity, horizontal stiffness of the structure, and overturning risk. It is expected that the structural performance for safety can be directly checked based on the suggested safety certification standards and performance evaluation methods during the safety certification stage.

If bending and torsional moments are applied to an I-shaped beam member, the coupling of those two forces could reduce the bending moment capacity of that member. Therefore, the interaction between bending and torsional moments is an important issue for horizontally curved members that are always simultaneously subjected to bending and torsion. In this study, the behavior of the horizontally curved steel I-beam was investigated through numerical analysis. The ultimate state of sharply curved members that showed large displacement was defined in accordance with the stiffness reduction ratio to consist of strength curves. Based on the analysis results, interaction curves were established, and a strength equation was derived. The uniform torsional moment capacity, curvature, and slenderness parameters were considered in the equation, which were the main factors that affected the ultimate strength of curved members. The curvature effect was considered individually, so that the strength of the straight or curved girder could be estimated with a unified equation. To verify the accuracy of the suggested equation, experimental studies were also conducted. Consequently, the suggested equation shows very good agreement with the test results, and is expected to provide useful information for the design of curved members.

A fabricated mobile scaffold has various components, including vertical members, horizontal members, braces, work plates, and castor wheels. In Korea, the structural performance of each member must be validated based on member-level structural safety criteria; this means that rigorous evaluation methods are required to secure the system-level structural safety of the fabricated mobile scaffold. To suggest rational system-level structural safety criteria and effective evaluation methods, the characteristics of the structural behaviors of the assembled structure must be investigated first. Unlike other temporary equipment, it is a product that requires convenience of use and ease of movement. Therefore, to secure the safety and usability of the structure, it is necessary to evaluate the ultimate behavior of a mobile scaffold fabricated with various material and structural types. In an experimental study, the ultimate mode and load-bearing capacity were investigated, and the appropriateness of the required performance of the mobile scaffold was reviewed. Three types of experimental test models with different materials (steel and aluminum) and stories (single-story and three-story erection) were selected and examined for vertical loads. Based on the experimental results, the ultimate behavior characteristics of the fabricated mobile scaffold were analyzed, and the ultimate load was identified.