This issue of Structures and Buildings features one commentary (Perry, 2025) and six papers covering a diverse range of topics, including reserve capacity and vertical extension potential in steel-frame buildings, hybrid passive energy-dissipating devices, seismic performance of joints in coal ash slag concrete frames, progressive collapse analysis of L-shaped CFST column frames, experimental investigation of wet joints in precast concrete segmental bridges, and the analysis and optimisation of spherical hinges in swivel construction.
Buildings account for approximately 34% of global energy consumption and 37% of associated greenhouse gas emissions. Reusing existing structures is a key strategy for transitioning to a circular economy and achieving decarbonization targets. Among reuse strategies, vertical extensions have gained attention; however, these are often constrained by the need to accommodate additional loads, which must be supported by reserve structural capacity or strengthening measures. Previous research has highlighted structural under-utilisation in existing buildings and proposed various sources contributing to reserve capacity. However, a comprehensive understanding of how these factors influence a building’s ability to be extended remains limited. Addressing this gap, Gillott et al. (2025) analyse 11 scenarios modelling different sources of under-utilisation in the design and reappraisal of 11,252 hypothetical steel-frame office buildings. Their findings demonstrate that, across the 11 scenarios, between 9% and 89% of cases were extendable without requiring structural strengthening. Optimal Eurocode (EC) designs revealed an average reserve capacity of 10%, increasing to around 20% for designs based on British Standards.
Hybrid dampers, which combine multiple energy dissipation devices to enhance strengths and minimise weaknesses, have been widely studied for their ability to significantly improve seismic performance by reducing roof displacement, drift, inter-story deformation, floor acceleration, and base shear. However, despite extensive experimental and theoretical investigations, their application in concrete structures remains underexplored. In response to this gap, Almajhali and Alhaddad (2025) provide a comprehensive evaluation of passive energy dissipation systems integrating various types of dampers, from early developments to present advancements. Their research highlights the superior vibration control properties of hybrid dampers and underscores their potential for broader development, design, and implementation in buildings.
The use of coal ash slag as a partial replacement for cement is gaining attention as a sustainable approach to reducing the environmental impact of the construction industry. However, its effect on seismic performance requires further investigation. Ma et al. (2025) conduct an experimental study on the behaviour of joints in concrete frame beams and columns incorporating 20% coal ash slag as a cement replacement. Their findings reveal that joints without coal ash slag exhibit 10.3%–16.2% higher ductility, whereas those with 20% coal ash slag show a 14% improvement in bearing capacity.
Since the late 1960 s, the structural resistance of buildings to progressive collapse has been a critical area of research for improving construction safety. L-shaped columns composed of concrete-filled steel tubes (L-CFST) are becoming increasingly popular, particularly in China. In this issue, Zhang et al. (2025) develop a macro joint model to assess the progressive collapse resistance of L-CFST frames, accounting for joint performance. Their results indicate that CP-FBSP (flush beam-flanged side-plate connections reinforced with cover plates) significantly enhance the tie capacity of frame structures. Additionally, the study highlights the influence of the steel beam span–depth ratio on the progressive collapse resistance of L-CFST column frames.
Precast concrete segmental bridges (PCSBs) have seen rapid development due to their advantages in construction speed, environmental impact reduction, quality control, and cost efficiency. However, a critical component of these structures is the joint used in the closure section. Su et al. (2025) conduct an experimental investigation into the wet joints of PCSB closure sections. Their findings indicate that, under cyclic loading, damage accumulates in the wet joint, leading to plasticity development, residual deformation, strength attenuation, and stiffness degradation. Furthermore, their results show that increasing the prestressing level can effectively delay cracking, improving joint performance.
The construction phase is one of the most critical stages in a bridge’s lifespan. Among various construction methods, the swivel technique has been widely adopted due to its suitability for complex terrains and high-traffic areas. In swivel construction, the spherical hinge plays a crucial role due to its unique structural characteristics. However, current methods for calculating contact stress in spherical hinges often overlook forces exerted by curved surfaces. To address this issue, Nie et al. (2025) propose a refined model that accurately analyzes the stress state of spherical hinges, improving the precision of existing calculations.
We extend our gratitude to all the authors, reviewers, and readers, and we encourage discussions on any of these papers.
