An Alternative Approach for the Design of Chevron-Braced Frames

The design of steel chevron-braced frames as per Eurocode 8 is based on the idea that only the braces should buckle and yield during ground motions, while other members should remain elastic. The elastic design of the braced frames is also allowed. However, in both cases, the seismic performance of the frame may be compromised because of premature yielding/buckling of columns. This paper proposes an alternative design procedure that promotes yielding of beams in addition to yielding of braces. This mitigates the vertical unbalanced force transmitted by compressive and tensile braces to the beam and in turn reduces the internal forces of the columns. The result is the overall improvement of the seismic performance owing to the reduction of the number of cases in which failure of the columns occurs before full exploitation of the ductility capacity of the dissipative members. The proposed design procedure is validated by incremental dynamic analyses performed on a set of chevron-braced frames. In particular, the peak ground accelerations of the frames designed by the proposed procedure at the attainment of Significant Damage and Collapse Prevention limit states are determined and compared to those of frames designed according to Eurocode 8. Furthermore, frames designed according to the Eurocodes and to the proposed method are compared in terms of structural cost.

New Technique to Improve the Ductility of Steel Beam to Column Bolted Connections: A Numerical Investigation

A novel method to improve the robustness of steel end plate connections is presented in this paper. Existing commonly adopted techniques alter the stiffness of the beam or the end plate to improve the connection’s robustness. In this study, the robustness is enhanced by improving the contribution of the bolts to the rotational capacity of connections; the higher the bolts’ elongation, the higher the rotational capacity that can be achieved. However, the brittleness of the bolt material, combined with its small length, results in negligible elongation. Alternatively, the load path between the end plate and the bolts can be interrupted with a ductile element to achieve the required elongation. This can be achieved by inserting a steel sleeve with a designated length, thickness, and wall curvature between the end plate and the washer. The proposed sleeve should be designed so that its ultimate capacity is less than the force in the bolt at failure; accordingly, the sleeve develops a severe bending deformation before the failure of any connection components. Using a validated finite element model, end plate connections with various parameters are numerically investigated to understand the performance of the sleeve device. The proposed system substantially enhances the rotational capacity of the connections, ranging between 1.37 and 2.46 times that of the standard connection. It is also concluded that the sleeved connections exhibit a consistent elastic response with the standard connections, indicating the proposed system is compatible with codified elastic design approaches without modification. Furthermore, for a specific connection, various ductile responses can be achieved without altering the connection capacity nor configuration.

Application of Inelastic Method and Its Comparison with Elastic Method for the Assessment of In-Box LOCA Event on EU DEMO HCPB Breeding Blanket Cap Region

The Helium Cooled Pebble Bed (HCPB) breeding blanket, being developed by the Karlsruhe Institute of Technology (KIT) and its partners is one of the two driver blanket candidates to be selected for the European demonstration fusion power plant (EU DEMO). The in-box Loss of Coolant Accident (LOCA) is a postulated initiating event of the breeding blanket (BB) that must be accounted within the design basis. In this paper, the BB cap region is analyzed for its ability to withstand an in-box LOCA event. Initially, an assessment is performed using conventional elastic design codes for nuclear pressure vessels. However, it is thought that the elastic rules are not ‘equipped’ to assess the material damage modes which are essentially inelastic. Therefore, a non-linear inelastic analysis is further performed to better understand the damage in the material. Two predominant inelastic failure modes are thought to be relevant and addressed: exhaustion of ductility and plastic flow localization. While the design of HCPB BB has been predominantly based on the elastic design-by-analysis studies, results from the present study show that the elastic rules may be overly conservative for the given material and loading and could lead to inefficient designs. To our knowledge, this study is the first attempt to investigate the structural integrity of the European DEMO blankets under in-box LOCA conditions using the inelastic methods.

New Design of High Power Mercury Target Vessel of J-PARC

A mercury target vessel for the spallation neutron source at the J-PARC, which the mercury vessel was covered with the water shroud, was improved to realize the operation at the high beam power in two steps. In the first step to realize the stable operation at 500 kW, the basic structure of the initial design was followed and the connection method between the mercury vessel and the water shroud was changed to prevent the failure from the connection. The service operation at the beam power of 500 kW was realized in the about eight months. In the second step to realize the stable operation at 1 MW, the new structure which only rear ends of vessels were connected was investigated. The new structure which has the cooling of the mercury vessel to reduce thermal stress and the thick internal and external vessels of the water shroud to increase the stiffness for the internal pressure was adopted. The stresses in each vessel were lower than the allowable stress based on the elastic design criteria and it was confirmed that the operation with a beam power of 1 MW could be conducted.

Numerical Simulation of the Degree of Protection for K9 Artillery Position under Explosion Scenario Using METT+TC

This study proposes a method to evaluate the protective performance of an existing K9 artillery position according to various explosion scenarios. Thus, a commercial software package AUTODYN was used to create a 3D model of the existing artillery position. Following the mission, enemy, terrain and weather, troops and support available, time available, and civil consideration (METT+TC) analysis, a total of three blast loading scenarios were selected. According to the results, the wall rotation angle of a near-miss explosion was within the standard of 2°; considering contact explosions, the rotation angles were also within 2°. This confirmed that the K9 artillery position under examination for protective performance was within the elastic design range. Considering the final evaluation and combining the results, the walls and slabs of the K9 artillery position were determined to be able to withstand the corresponding blast pressures and have no issues in protective performance. Meanwhile, due to the limitations of the actual blast tests for evaluating the protective performance of civilian protective structures and those of the ROK Armed Forces, these tests were replaced with numerical analysis-based evaluations. However, due to the lack of specified procedures for numerical analysis based on finite element analysis, there were several difficulties in practice. Therefore, this study aims to provide a basic procedure for evaluating the protective performance of protective structures in the future by presenting analytical and blast loading conditions which are necessary for evaluating protective performance.

Study of Topology Optimized Hammerhead Pier Beam Made with Novel Preplaced Aggregate Fibrous Concrete

This study aims to study topology Optimized Hammerhead Pier Beam (TOHPB) designed with a density-based technique. TOHPB is made with Preplaced Aggregate Fibrous Concrete (PAFC), which comprises two main preparation processes. First, the fibers and coarse aggregates filled into empty formwork to develop a skeletal system. Second, voids in the skeletal system are filled with cement grout; hence a type of PAFC was obtained. Besides, alleviating the self-weight of the concrete beam is a top priority of design engineering without compromising its strength and durability. The effect of topology optimization in association with the safety of factors and elastic design case is considered in this study. Explicitly, (i) compliance is scaled down to a minimum under a perimeter on the utilized material (ii) the principle Drucker-Prager is employed to impose the stress limitations even though utilization of material is minimized. The problem is designed with imposed stress limitation and generates keys that involve an essential part of post-processing before fabrication. In total, ten TOHPB were prepared with and without the combined shape of crimped-hooked end steel fiber. Two different types of fiber reinforcement schemes were used; first, the fibers were reinforced to full beam cross-section; then, the fibers were reinforced to the top half of the beam cross-section. Results revealed that the TOHPB beam reinforced full cross-section exhibited better ultimate load performance than that of the beam with half reinforced cross-section.

Comparative Evaluation of Plastic Design Methods for Fatigue Assessment of a Nuclear Class 1 Piping Nozzle

Design-by-analysis (DBA) procedures for Nuclear Class 1 pressure vessels such as those prescribed within ASME Boiler and Pressure Vessel Code (BPVC) Section III, provide rules to demonstrate assurance against fatigue failure. Two general assessment routes exist, linear finite element analysis (FEA) with stress categorization and elastic-plastic penalty factors, or nonlinear FEA with direct multiaxial strain evaluation. Whilst the elastic design route possesses many practical advantages, it is widely acknowledged to be very conservative, sometimes unacceptably so. At the cost of additional analysis effort, plastic design methods can provide a more appropriate evaluation of fatigue usage, potentially avoiding unnecessary design modifications and reducing the burden of in-service inspection requirements. This paper presents and compares various strain measures proposed for ASME III plastic fatigue analysis within the technical literature. A case study of a typical pressurized water reactor (PWR) main coolant line (MCL) piping nozzle subjected to pressure and thermal loads is presented. The influence of strain measure selection on the FE-derived strain concentration (Ke) factors is examined. Some important considerations for calculation of realistic Ke factors in ASME III are further discussed.

PERFORMANCE BASED SEISMIC DESIGN OF STRUCTURES – A REVIEW.

This paper presents an overview of the current state of knowledge with regard to literature on Performance based seismic design method. Performance-based earthquake engineering (PBEE) comprises the design, evaluation, and construction of structures performing during design earthquakes and extreme earthquakes to the desires / needs of owners, user, society and environment. The general promise of performance based design is to produce engineered structures with predictable performance during future earthquakes. Presented in this paper is an updated literature review of the Performance -based Seismic design (PBSD) method. Performance based Seismic design is an elastic design methodology done on the probable performance of the building under different ground motions. The derivatives of the PBSD method, known as the Performance ¬based Plastic design (PBPD) and Displacement-based seismic design (DBSD) method that has been widely recognized as an ideal method for use in the future practice of seismic design has also been reviewed.