Seismic Design of Bolted Connections in Steel Structures—A Critical Assessment of Practice and Research

The importance of connections in steel structures is paramount, not only because it greatly influences the cost of construction and provides room for innovations, but also due to the connections’ impact on global structural behaviour. Therefore, research into innovative connections for seismic applications and related design criteria has significantly grown in recent years. However, it has been pursued mostly on local—connection or frame—levels, leaving the system analysis and code compliance levels with a meagre investigation. Moreover, less than 1% of published papers concerning steel connections and earthquake engineering are review articles. To overcome this gap, this systematic review of more than 240 references, including scientific contributions and design codes in the field aimed to cover both recent research and current shortcomings in practice and regulations. It has been found that European design rules updated to a fully performance-based design philosophy is imminent and is deemed to bring pre-qualified joints and increased complexity. Design rules have been systematized, and current hindrances have been highlighted. A deeper look into research needs and trends showed that investigations in connections for concentrically X braced frames are still a necessity, while developments in self-centring and replaceable connections as well as in simple solutions for increasing damping are expected to modify how joints are designed, as soon as semi-rigid and partial strength connections are more easily allowed by design codes.

THE HISTORY OF THE LIMIT STATE DESIGN METHOD

This paper analyzes the 70-year history of development of the limit state design method (LSDM) focusing on the fundamentals of the design codes based on this method and considers proposals for improving the LSDM and its justification. It was also noted that the reaction of the system in any of its fixed states is not always sufficient to assess the reliability of the system, and therefore it is necessary to analyze the rate of loss of resistance of load-bearing structures. However, probabilistic considerations were not enough due to the lack of reliable statistical data in the area of extreme sections of the distribution curves and a number of other circumstances (features of control procedures, different behavior of the material in the structure and in the samples, etc.). This paper analyzes some fundamental issues that should be solved when developing the method for the nonlinear analysis.

Three airports

The airport terminals in Perm, Saratov and Kemerovo created by Asadov Architectural bureau are presented. General concepts of complexes, architectural and interior solutions for passenger terminals, as well as elaboration of design codes of administrative and technical buildings are given. Particular attention is paid to passenger comfort and safety.

Evaluation of Seismic Response Modification Factor (R) for Moderate-Rise RC Buildings with Vertical Irregular Configurations

Most international design codes consider the nonlinear seismic performance of a structure by the concept of reduction/modification factor (R). Then, an elastic static force-based method can be normally used for seismic design to create earthquake resistant RC buildings. The response modification factor (R) is sensitive to many aspects such as overall ductility, over-strength, damping, and redundancy levels. Indeed, these factors are severely affected by geometric irregularity of the structural system. So, R-value does not become a constant number for the all types of structures with the same lateral load resisting system, as many standard codes noted. It depends on types, combination, and degrees of geometric vertical irregularity. This research assesses the actual values of R for regular and familiar vertical irregularity cases in RC buildings with moment-resisting frames (MRF) systems. Also, it takes into account the reduction percent that may occurs in R-value due to these studied vertical irregularities. The vertical irregularity cases, such as set-back and soft story, are essentially needed to be studied greater than ever due to the wide propagation of these types of buildings in Egypt, recently. In addition, the potential analytical methods that may be used to calculate R-value in comparison with Egyptian code’s value. Nonlinear static pushover analysis is carried out using ETABS via three-dimensional numerical models. The findings prove that vertical irregular models have poor seismic capacities, in comparison with regular one, due to their sudden change in lateral stiffness than that with regular aspect. So, the response modification factor (R) must be re-calculated or even scaled-down before design stage with 15% and 25% for single and combined vertical irregularity, respectively. In addition, this investigation derives a vital equation between R values with vertical irregularity ratios in each studied model. This equation shall be a guide for seismic design codes, structural design engineers, and researchers. Accordingly, the response modification factor R does not become a fixed value regardless vertical irregularity aspects of the buildings, but it has a variable value that depend on their inelastic seismic performance of the lateral load resisting systems.

Global Buckling Investigation of the Flanged Cruciform H-shapes Columns (FCHCs)

In China, increasing the application ratio of hot-rolled H-shapes has become a severe problem that the government, academia, and engineering circles must vigorously address. Research on reasonable hot-rolled H-shapes built-up columns is one of the primary methods. After reviewing the various combination columns in the existing research, the paper proposes the new flanged cruciform H-shapes columns (FCHCs) made of three hot-rolled H-shapes. Using comprehensive imperfections given by the design standard, GB50017-2017, the paper analyzes the global buckling of FCHCs subjected to the axial compression load. The global buckling factor obtained is compared with the current national design code. Comparative analysis of seventy-two specimens of Q345 and Q460 steel found that the global buckling mode of FCHCs was flexural bending buckling around the axis of symmetry, and global torsional buckling and local buckling did not occur. Furthermore, the corresponding column curves in current design codes overestimate the dimensionless buckling strength of the novel FCHCs. Therefore, designers need to drop a class to select the global buckling factor within a specific range. Finally, new column global buckling curves are proposed based on a non-linear fitting of the numerical results according to the current national design codes.

Design Forces of Horizontal Braces Unlocated at Middle of Columns considering Random Initial Geometric Imperfections

The horizontal bracing forces of column-bracing systems derived from past studies and current design codes were considered only located at middle of columns. Actually, the horizontal braces used to reduce the out-of-plane effective column lengths are frequently designed not to locate at middle of columns. In this paper, a large number of column-bracing systems with the horizontal braces unlocated at middle of columns were modelled and analyzed using the finite element method, in which the random initial geometric imperfections of both the columns and the horizontal braces unlocated at middle of columns were well considered by the Monte Carlo method. Based on the numerical calculations, parametric analysis, and probability statistics, the probability density function of the horizontal bracing forces was found, so that the corresponding design forces of horizontal braces unlocated at middle of columns were proposed which were compared with the design mid-height horizontal bracing forces in the previous study and the relevant codes. The results indicate that the design forces of the horizontal braces located at 0.6 column height are smaller than the mid-height horizontal bracing forces in the previous study while the design forces of horizontal braces located at 0.7 column height are larger than the mid-height horizontal bracing forces in the previous study. The proposed design forces of the horizontal braces located and unlocated at middle of columns are both smaller than the mid-height horizontal bracing forces stipulated in GB50017-2017, Eurocode 3-1992, and AS4100-1998. The above conclusions provide references for the engineering applications and further related code revisions.

Estimating the Basal Heave Stability of Narrow Braced Excavations

Engineering practices indicate that narrow braced excavation exhibits a clear size effect. However, the slip circle method in the design codes fails to consider the effect of excavation width on basal heave stability, causing waste for narrow excavation. In this paper, numerical simulation for basal heave failure of excavation with different widths was performed by FEM with SSRT (shear strength reduction technique). The results revealed that the failure mechanism of narrow excavation is different from the complete slip circle mode. In addition, the safety factor decreases increasingly slowly as the excavation widens and stabilizes when approaching the critical width. Subsequently, the corresponding computation model was presented, and an improved SCM (slip circle method) was further developed. Finally, the engineering case illustrated that it can effectively optimize the design, which exhibits clear superiority.

Overview of Thermal Hydraulic Optimization and Verification for the EU-DEMO HCPB BOP ICD Variant

When progressing from the International Thermonuclear Experimental Reactor (ITER) to the Demonstration Fusion Reactor (DEMO), a system for transferring plasma heat exhaust to a power conversion system is necessary for the so-called Balance of Plant (BOP). During the preconceptual phase of the EU-DEMO project, different BOP concepts were investigated in order to identify the main requirements and feasible architectures to achieve that goal in the most efficient way. This paper comprises the investigations performed during the DEMO preconceptual design phase (p-CDP) and compares the different variants. The main aspect was focused on the helium-cooled pebble bed (HCPB) breeding blanket (BB) concept. After all assessments were performed, the indirect coupled design (ICD) was chosen as the reference configuration for the DEMO HCPB BOP for further development and optimization. The ICD provides decoupling using a molten salt storage loop, which accumulates thermal power during plasma pulses that are released during dwell periods. The work is supported by simulations using design codes EBSILON and MATLAB/SIMULINK, providing the basis for the next design phase.