Composite structural systems are widely used in the construction industry, effectively combining the properties of the constituent materials. Classical examples include here steel - concrete composite members, which combines the tensile strength and ductility of steel with the compressive strength and stiffness of concrete. Hybrid systems, on the other hand, combine elements of different materials, or of same materials but different characteristics, allowing for tailored deformation/strength/ductility demands or different interaction levels between different parts for optimized structural performance, improved construction cost, low environmental impact, and longer durability. Examples include concrete core systems combined with steel framing, dual steel frames made of High Strength Steel (HSS) and Mild Carbon Steel (MCS), or more recent developments, like steel and cross-laminated timber (CLT) hybrid constructions, or hybrid steel- Fiber Reinforced Polymer (FRP) composite systems. This paper summarizes a series of research projects and practical applications of hybrid systems, all with direct involvement of the authors. Particularly, the structural connections between the members made of different materials are examined. Some of the structural solutions detailed in the paper have been confirmed by full scale laboratory tests but also by advanced numerical simulations. The paper aimed also to demonstrate the efficiency of hybrid systems over classic homogeneous or composite ones, but also the inherent technical difficulties faced by designers, due to the lack of consistent design provisions. There are also emphasized some further developments based on the activities presented in the paper.

Light steel based composite (sandwich) panels are largely used for the envelopes of different kinds of buildings. Owing to their non-combustible properties, new generations of sandwich panels are made with mineral wool insulation materials. Even less efficient than classic foam cores in terms of thermal conductivity, these panels are still efficient for energy consumption. Under extreme loading conditions, such as those generated by external blast events, sandwich wall panels may experience substantial damage under both positive and negative pressure regimes. This study presents experimental and numerical results obtained from sandwich panels with a mineral wool core subjected to transverse loading up to complete structural failure. Numerical models were developed and calibrated using the SAP2000 structural analysis and design software to observe and replicate behavior. Using previous studies on blast resistance, numerical models were further used to preliminary evaluate the response of the mineral wool sandwich panels against close in detonations.

Abstract Steel faced sandwich panels with polyurethane foam core PUR are widely used for façade systems, due to their high strength‐to‐weight ratio and very good thermal properties. For ordinary civil engineering applications, their design is generally controlled by stiffness rather than strength, excepting the under pressure (suction) due to wind, where pullover failure of the fasteners may occur. Accordingly, the ductility and energy absorption demands are not generally specified. For extreme loadings, like those generated by blast, they may suffer extensive damage or destruction, with high potential for collateral risk to occupants. The paper addresses the behavior of sandwich panels under extreme out of plane loads, and factors that may enhance their ductility and energy absorption capacity. Numerical models are calibrated against relevant test data and employed in a parametric study. Appropriate end fastening and lateral stiffness at the supports are particularly effective in increasing the ductility and prevent premature failure of the wall panels.

Steel frame structures are widely used in various types of constructions. With much longer experience and tradition in practice, the Moment Resisting Frames (MRF) and Concentrically Braced Frames (CBF) were the predominant lateral load resisting systems for many decades, thanks to their architectural versatility and high ductility (MRF) or high lateral stiffness (CBF), respectively. On the other hand, the much newer Eccentrically Braced Frame EBF system, may be a viable alternative, thanks to an appropriate combination of stiffness and ductility. In this study, we investigated the effect of composite action between the link beam and the concrete slab on the monotonic and cyclic response of EBFs with long links. The results indicated an increase of initial stiffness and yield resistance of the system, but a small impact on the ductility. Also, the simple detachment of the concrete slab from the beam by the lack of shear studs does not fully eliminate the composite action in links, which may affect both the local and global behavior.

Local damages to key structural members may originate from different causes, including localised fires or earthquakes, and, as far as the affected area remains small and the damage is contained, the risk is reduced. However, if the structure does not have the capacity to absorb the damage and bridge over the lost components, progressive collapse may be initiated, with serious consequences for the life of the occupants and the costs of losses. Even if some inherent structural properties, like redundancy and ductility, bring a beneficial contribution to the resistance of structures subjected to such scenarios through the activation of alternate load paths, these properties can be affected when working under elevated temperatures, and thus structural integrity can be at risk. This paper investigates the cumulative effects of seismic events and elevated temperature on the progressive collapse resistance of two-way frames with steel and composite steel-concrete floors. Numerical models are calibrated against relevant test data. The results show that, even if fire protection is an effective way in increasing the resistance of structural components under elevated temperatures, the failure may propagate due to the attainment of the bearing capacity of the surrounding elements and connections that are still at ambient temperature. Also, the interaction between concrete slabs and steel beams may provide additional capacity to stop the progressive collapse.

External explosions, either accidental or intentional, pose a serious threat to the communities but also a challenge to the structural engineers. Such threats include detonation of high energy explosives (e.g., improvised explosive devices), which can cause structural failures (local damage of structural/nonstructural members or even global failures) and serious injuries or deaths. This risk can be minimized by increasing the standoff distance, but also through structural conception and design, e.g., avoiding brittle materials especially on the facades, adopting specialized construction techniques and detailing. The study investigates the capacity of light steel building facades to resist the effects of close-range explosions and main parameters affecting the ultimate strength and deformation capacity. Pressure-impulse P-I curves are derived from numerical analyses performed with Etabs finite element based structural analysis and design program. Numerical models are calibrated against benchmark tests obtained in a full-scale experimental program.

Many buildings or other types of constructions remain unfinished at various stages, put on hold, or suffer serios time delays from the schedule. Before resuming the works, these constructions may require extensive structural assessment to determine the condition of the structure, identify the damages, and provide recommendations for intervention. This paper summarizes the intervention works for the retrofitting of an existing 11 story building made with a hybrid system of reinforced concrete walls, steel frames, and composite floor decking. The building is located in a marine environment and moderate seismicity area. The constant exposure to aggressive conditions caused different extents of damage, and most affected were the composite floor steel decking. Experimental tests were carried out to validate a strengthening solution for the composite floor slabs based on adding a new concrete layer and post-installed shear studs. Numerical models have been calibrated against test data. Additional requirements were considered, i.e., reducing the potential for progressive collapse and improving global behavior for seismic response (torsional stiffness, floor diaphragm effect).

The robustness of multi‐story steel frame buildings and, in general, of any construction structure, is an important issue, with a particular impact on the safety of people and the built environment. However, as has been seen from many previous catastrophic events, there is still a need for an improvement in design provisions that will allow structural engineers to ensure adequate structural robustness. In the particular case of steel frames, the structural joints at the ends of the beams play a key role when the frames are subjected to extreme events, as these joints may be subject to load conditions not foreseen by the design process under classical “load conditions”. The consequences can be aggravated in case of cascading or multiple events, e.g., seismic aftershocks, explosion or localized fire after an earthquake. If their capacity is exceeded, the building will be exposed to unacceptable damage and risk levels. On this aim, a quantitative definition of the residual characteristics of beam‐to‐column joints is of significant importance. The study presents the results obtained on a set of T‐stub elements subjected to monotonic, cyclic and combined protocol (cyclic plus monotonic). The influence of several parameters, including the loading protocol, the plastic deformation demands in cyclic loading, and the geometry of T‐stub elements is also investigated. Numerical models calibrated based on experimental data are used in a parametric study.

Floating modular energy islands (FMEIs) are modular, interconnected floating structures designed to collectively produce, store, convert, and transport renewable energy. This review aims to establish a foundation for developing innovative approaches to sustainably harness multi-energy sources in offshore environments. It leverages existing technological expertise while exploring new solutions to address specific challenges associated with FMEIs. The review initially presents existing technologies for floating energy structures and assesses their applicability to FMEI. The structural materials that could be utilised for the construction of a floating energy island are subsequently reviewed. Next, the offshore construction technologies suitable for FMEI are reviewed. Finally, studies on the life cycle assessment of hybrid energy systems are examined, highlighting the environmental advantages of integrating multiple renewable energy sources, thereby underscoring the potential of FMEIs.

Robustness of multi-story buildings, and more globally, of any construction, is an important matter when the safety of built environment is considered. However, as seen from past natural or human-made originated accidents, an improvement of the design process allowing us to ensure an appropriate structural robustness is still required. The consequences can be aggravated in case of cascading events, e.g., seismic aftershocks, explosion or localized fire after an earthquake. The study presented in the paper investigates the robustness of multi-story steel frames following the loss of a column. The case study structures were designed for the envelope of seismic and persistent design situation demands, considering low seismicity conditions of the site. For the perimeter locations, the structures had adequate resistance to prevent the progressive collapse, due to the large overstrength resulted in beams and joints from either non-seismic or seismic design situations. For the interior spans designed for gravity loads, the solution with partial strength joints also provided the capacity required to resist the loss of a column, with maximum load multipliers, λ, larger than unity. On the contrary, if the beams (and end connections) are designed to provide only the minimum tying resistance specified in the codes, the progressive collapse initiates.

End plate bolted joints are frequently used in seismic resistant multi-story steel frame structures. Their flexural behavior can range from flexible and partial strength to stiff and full strength. For partial strength joints, the main source of ductility is the T-stub macro-component. While most studies and design provisions envisaged the response under single critical events, e.g., strong earthquakes, experience shown they may be vulnerable in a multi-hazard environment, e.g., earthquake aftershock, or column loss (due to fire or explosion) after earthquake. The study presents the results obtained on a set of T-stub elements subjected to monotonic and cyclic loading, single or in sequence monotonic after cyclic. The influence of several parameters including the loading protocol and plastic deformation demands, are also investigated. Numerical models are calibrated against test data.

Explosions produced in urban or industrial areas due to accidental or intentional detonation of explosives are low-probability but high-impact events. If standoff distance from buildings or other constructions is small, explosions can cause structural failures and serious injuries or deaths of occupants. Although heavy/stiff enclosure systems were long considered appropriate to protect buildings against explosive threats, lighter and flexible steel-based systems, which are increasingly used for modern buildings, may also provide satisfactory performance. The study presents the results of full-scale blast tests on liner tray walls attached to a steel frame building. Walls were tested against increasing blast charges until failure. Due to very high peak pressures and very short durations, the loading regime could be classified as impulsive. The ultimate strength is given by the failure of the end fasteners, after large bolt hole elongations coupled with the pull-through of the end fasteners. If the insulation and outer cladding are lost, the liner trays are directly exposed to blast and the seaming fasteners at overlapping sheets are prematurely lost. As a result, the wall panels work mostly independently, as one-way elements. On the contrary, if the outer cladding protects the seaming fasteners, the overlapping provides additional capacity due to membrane effect (two-way behavior). Numerical models were calibrated using test data and were further used to obtain more information about liner tray behavior under blast.

Steel plate shear walls (SPSW) are efficient lateral load resisting systems, with high ductility and initial stiffness properties. When coupled with moment resisting frames (MRF) in sharing the seismic induced lateral loads, they can provide more resilient systems, if the later provide the restoring forces to recenter the structure. If the damage is localized in easily replaceable panels, repairing is easier and costs less. In the paper, dual SPSW-MRF systems are investigated for evaluating their seismic performances (plastic mechanism, global ductility, residual drift, recentering). Numerical models employed nonlinear shell approach for SPSW and bar elements for MRF and were calibrated against experimental data. Several repair/replacement sequences of damaged panels were investigated. For low to moderate damages induced during a seismic event, the MRF provides the structure recentering capacity. For significant damages however, plastic deformations in MRF prevent the structure from returning to its initial positions, as it remains with residual story drifts. Such residual drifts do not, however, mean that the building will be demolished, as the structure is still reparable but probably at higher costs.

Floating Modular Energy Islands (FMEIs) are modularized, interconnected floating structures that function together to produce, store, possibly convert and transport renewable energy. Recent technological advancements in the offshore energy sector indicate that the concept of floating offshore energy islands has the potential to become more cost-effective and more widespread than previously anticipated. This review is specifically meant as a basis for the development of new approaches to the sustainable exploitation of multi-energy sources in the offshore environment leveraging the know-how of existing technologies and, at the same time, exploring new solutions for the specific challenges of FMEIs. The paper critically analyzes the current state of data-driven approaches and structural health monitoring techniques in the offshore energy sector. It also covers topics such as met-ocean data, loads estimation, platform dynamics, coupling actions, nonlinear dynamics of mooring lines, modelling considerations, and control of electrical subsystems. It is believed that this systematic and multidisciplinary review will facilitate synergies and further enhance research and development of offshore renewable energies.

Constructions should be able to remain stable for their designed lifetime, from 50 to 100 years, even more. As climate change intensifies, extreme weather events such as temperature variation, humidity, heavy rainfall, floods, and windstorms become more frequent and more severe. These events pose a significant threat to conventional building designs and infrastructures. Consequently, there is a growing demand for climate-resilient constructions that can withstand extreme weather conditions. Protecting infrastructure and buildings to cope with these threats is a complex challenge. Building materials, design, and construction techniques need to be adapted to ensure the durability and safety of structures in the face of changing climatic conditions. The safety margins and robustness of constructions for undesired events in technical regulations and standards should therefore be continuously re-evaluated so that the designed level of reliability is maintained. To control by design, alternatively to traditional prescriptive design codes, where the building must conform to a set of given requirements that results in a hard-to-quantify performance, a Performance-Based Design (PBD) method might apply to explicitly define and achieve the desired structural performance. Based on the review and analysis of dedicated literature and research reports related to this complex problem, potential technical solutions are discussed. Also, two real study cases, one caused by extreme wind and the other by extreme drifted snow, are presented.

The growth of industrialization and the rapid expansion of densely populated urban areas have increased the risk caused by technological and man-made hazards. In particular, the accidental or intentional detonation of high explosives (e.g., improvised explosive devices IEDs), can cause damages to buildings and infrastructures and severe harm people. These risks can be minimized by a better planning, design, and construction, e.g., avoiding brittle construction materials, especially within the building envelope, and adopting more robust construction techniques. The study presented in the paper investigates the capacity of light steel-based wall panels to resist the effects of external explosions. The experimental results showed the ultimate capacity of the wall panels is strongly dependant on the initial design conditions and panel-to-structure fastening solution. A numerical model has been also calibrated using Etabs program.

During the 2023 earthquake sequence in Kahramanmaraş (Turkey) several failures were recorded in industrial buildings consisting of prefabricated reinforced concrete (RC) columns and rafters, ranging from significant damage of structural elements to total collapse of the roofs. The findings of the Greek field mission following the event are presented and comparison to similar failures recorded during the 2012 Emilia earthquakes (Italy) is made. The main cause of failure is attributed to the poor column-rafter connection. To that end, methods to strengthen the connection are proposed. For buildings where the RC rafters have collapsed with the columns still standing at their original position, the possibility to install steel truss rafters with sufficient connection to the RC corbels is examined. Numerical analyses are performed to validate the feasibility of the proposed actions.

The explosions produced in industrial/chemical facilities, such as hazardous material storage facilities, are events with low probability but high destructive potential. When occurring in a densely populated area, such explosions can lead to extensive damage of nearby buildings or infrastructures, resulting in high economic costs and human injuries and fatalities. The explosions may be the result of an accident but may also be intentional. As the pressure released by the external explosions decreases exponentially with the distance to the target, increasing the stand-off distance is one of the most effective ways to mitigate the effects against structures. In addition, the local resistance of the facade elements must be increased to prevent or limit the spread of damage. Even though these issues are well known and understood, there are relatively few provisions in the current European practice. The destructive effect of the high velocity debris projected by the explosion should also require attention, as they can cause severe harm to people. The study presented in the paper investigates the capacity of light steel-based building facades to resist the effects of near field blasts. The experimental results showed the ultimate capacity of the wall panels is strongly dependent on the initial design conditions and panel-to-structure fastening solution.

Light weight steel-based panels are largely used for the envelope (walls, roofs) of different kind of buildings. They are typically designed from the weather-related conditions of the site (climatic actions, thermal comfort). Despite their low weight, they have adequate load carrying capacities under transverse loads. However, under extreme loading conditions, like the high intensity pressures associated with external explosions, the panels can be heavily damaged or detached from the structure. The study presented in the paper describes the results obtained on liner tray walls tested for transverse loading until complete failure. The test program included also shear tests on end fastenings. The liner trays were arranged as single span systems supported on side beams and loaded at the mid-span. After a quasi-linear response, the maximum flexural strength is reached. Then, due to a local instability, there is a drop in capacity, followed by an increase in response capacity due to development of catenary forces. If the end fasteners have adequate resistance, the ultimate capacity in the catenary stage can be significantly higher than the peak flexural capacity. The ultimate capacity depends also on the in-plane stiffness of the support columns.