Search Results (107)

Transmission towers are particularly vulnerable to extreme wind events, which can lead to structural damage or collapse, thereby compromising the stability of power transmission systems. Enhancing the wind-resistant capacity of these towers is therefore critical for improving the reliability and resilience of electrical infrastructure. This study utilizes finite element analysis (FEA) to evaluate the structural response of a 220 kV transmission tower subjected to fluctuating wind loads, effectively capturing the dynamic characteristics of wind-induced forces. A comprehensive dynamic analysis is conducted to account for uncertainties in wind loading and variations in wind direction. Through this approach, this study identifies the most critical wind angle and local structural weaknesses, as well as determines the threshold wind speed that precipitates structural collapse. To improve structural resilience, a concurrent multi-scale modeling strategy is adopted. This allows for localized analysis of vulnerable components while maintaining a holistic understanding of the tower’s global behavior. To mitigate failure risks, the traditional perforated plate reinforcement technique is implemented. The reinforcement’s effectiveness is evaluated based on its impact on load-bearing capacity, displacement control, and stress redistribution. Results reveal that the critical wind direction is 45°, with failure predominantly initiating from instability in the third section of the tower leg. Post-reinforcement analysis demonstrates a marked improvement in structural performance, evidenced by a significant reduction in top displacement and stress intensity in the critical leg section. Overall, these findings contribute to a deeper understanding of the wind-induced fragility of transmission towers and offer practical reinforcement strategies that can be applied to enhance their structural integrity under extreme wind conditions. Full article

This study investigates the fire dynamics and structural response of steel-framed warehouse racking systems under various fire scenarios, emphasizing the critical importance of fire safety measures in mitigating structural damage. Through advanced computational simulations (Fire Dynamics Simulator) and thermomechanical analysis, this research reveals that fire intensity and progression are highly influenced by the ignition point and the stored material types, with maximum recorded temperatures reaching 720 °C and 970 °C in different scenarios. The results highlight the localization of significant strain and drift ratios in structural elements near the ignition zone, underscoring their vulnerability. This study demonstrates the rapid loss of load-bearing capacity in steel elements at elevated temperatures, leading to severe deformations and increased collapse risks. Key findings emphasize the necessity of strategically positioned sprinkler systems and the integration of passive fire protection measures, such as fire-resistant coatings, to enhance structural resilience. Performance-based fire design approaches, aligning with FEMA-356 criteria, offer realistic frameworks for improving the fire safety of warehouse structures. Full article

With the widespread application of lithium-ion batteries (LIBs), safety performance has become a critical factor limiting the commercialization of large-scale, high-capacity LIBs. The main reason for the safety problem is that the electrolytes of LIBs are extremely flammable. Adding flame retardants to conventional electrolytes is an effective method to improve battery safety. In this paper, trimethyl phosphate (TMP) and trimethyl phosphite (TMPi) were used as research objects, and the flame-retardant test and differential scanning calorimetry (DSC) of the electrolytes configured by them were first carried out. The self-extinguishing time of the electrolyte with 5% TMP and TMPi is significantly reduced, achieving a flame-retardant effect. Secondly, the electrochemical performance of LiFePO₄|Li half-cells after adding different volume ratios of TMP and TMPi was studied. Compared with TMPi5, the peak potential difference between the oxidation peak and the reduction peak of the LiFePO₄|Li half-cell with TMP5 added is reduced, the battery polarization is reduced, the discharge specific capacity after 300 cycles is large, the capacity retention rate is as high as 99.6%, the discharge specific capacity is larger at different current rates, and the electrode resistance is smaller. TMPi5 causes the discharge-specific capacity to attenuate, which is more obvious at high current rates. LiFePO₄|Li half-cells with 5% volume ratio of flame retardant have the best electrochemical performance. Finally, the influence mechanism of the phosphorus valence state on battery safety and electrochemical performance was compared and studied. After 300 cycles, the surface of the LiFePO₄ electrode with 5% TMP added had a smoother and more uniform CEI film and higher phosphorus (P) and fluorine (F) content, which was beneficial to the improvement of electrochemical performance. The cross-section of the LiFePO₄ electrode showed slight collapse and cracks, which slowed down the attenuation of battery capacity. Full article

Assessing the seismic performance of buildings from various epochs is essential for guiding retrofitting policies and educating occupants about their homes’ conditions. However, limited resources pose challenges. Some approaches focus on detailed analyses of a limited number of buildings, while others favor broader coverage with less precision. This paper presents a seismic risk assessment method that balances and integrates the strengths of both, using a comprehensive building survey. We propose a low-cost indicator for evaluating the structural resilience of individual buildings, designed to inform both authorities and property owners, support building rankings, and raise awareness. This indicator classifies buildings by their taxonomy and uses analytical capacity curves (2D or 3D studies) obtained from consulting hundreds of studies to determine the ultimate acceleration (agu) that each building type can withstand before collapse. It also considers irregularities found during the survey (to the exterior and interior) through structural modifiers Δ, and adjusts the peak ground acceleration the building can withstand, agu, based on macroseismic data from past events and based on potential retrofitting, Δ+. Although this method may not achieve high accuracy, it provides a significant approximation for detailed analysis with limited resources and is easy to replicate for similar constructions. The final agu value, considered as resistance, is then compared to the seismic demand at the foundation of the building (accounting for hazard and soil conditions at the building location), resulting in a final R-value. This paper provides specificities to the methodology and applies it to selected areas of the City of Lisbon, clearly supporting the advancement of a more sustainable society. Full article

The rapid development of underground engineering contributes significantly to achieving China’s “dual carbon” strategic goals. However, during the construction and operation phases, this engineering project faces diverse risks and challenges related to disasters. Consequently, enhancing the evaluation capability for underground engineering resilience is imperative. Based on the characteristics of resilience evaluation and enhancement in underground engineering, this study defines the concept and objectives of resilience evaluation for underground space engineering and analyzes corresponding enhancement methods. By considering aspects such as the magnitude of collapse disaster risk in underground engineering, its vulnerability, resistance capacity, adaptability to disasters, recovery ability, and economic feasibility, a comprehensive index system for evaluating the resilience of collapse disaster risks in underground engineering has been established. This research suggests that disaster risk management should shift from passive to active prevention. Through resilience evaluation case applications, it is possible to improve the design objectives of underground engineering towards “structural recoverability”, “ease of damage repair”, and “controllable consequences after a disaster”. The integration of intelligent static assessment models based on artificial intelligence algorithms can effectively enhance the accuracy of resilience evaluations. Furthermore, dynamic assessments using multiple data fusion techniques combined with numerical simulations represent promising directions for improving the overall resilience of underground engineering. Full article

Epidemics spread through shipping networks and have dual characteristics as both biological sources of infection and triggers of cascading failures. However, existing resilience models fail to capture this dual and coupled dynamics. To minimize the cascading impacts of epidemics on global shipping networks, this paper proposes an innovative resilience assessment framework that considers the interaction between epidemic transmission and the shipping network cascading failure. First, a weighted shipping network topology is constructed based on route flow characteristics to quantify route frequency, stopping time, and the number of infected people, and the epidemic transmission across ports is modeled with an improved SEIR model, which contains a heterogeneous infectivity function and a dynamic transmission matrix, revealing a dual transmission mechanism inside and outside the ports. Second, a two-stage cascading failure model is developed: a direct failure triggered by infected people exceeding the threshold and an indirect failure triggered by the dynamic redistribution of loads. The load redistribution strategy is optimized to reconcile the residual port capacity and the risk of infection. Finally, a multidimensional resilience assessment framework covering structural destruction resistance, network efficiency, path redundancy, and a cascading failure propagation rate is constructed. Example validation shows that the improved load redistribution strategy reduces the maximum connected subgraph decay rate by 68.2%, reduces the cascading failure rate by 88%, and improves the peak network efficiency by 128.2%. In case of multi-source epidemics, the state of the network collapse can be shortened by 12 days if the following recovery strategy is adopted: initially repair high connectivity hubs (e.g., Port of Shanghai), and then repair high centrality nodes (e.g., Antwerp Port) to achieve a balance between recovery efficiency and network functionality. The research results reduce the risk of systemic disruptions in maritime networks and provide decision-making tools for dynamic port scheduling during pandemics. Full article

Cement is widely used as the primary binder in concrete; however, growing environmental concerns and the rapid expansion of the construction industry have highlighted the need for more sustainable alternatives. Geopolymers have emerged as promising eco-friendly binders due to their lower carbon footprint and potential to utilize industrial byproducts. Geopolymer mortar, like other cementitious substances, exhibits brittleness and tensile weakness. Basalt fibers serve as fracture-bridging reinforcements, enhancing flexural and tensile strength by redistributing loads and postponing crack growth. Basalt fibers enhance the energy absorption capacity of the mortar, rendering it less susceptible to abrupt collapse. Basalt fibers have thermal stability up to about 800–1000 °C, rendering them appropriate for geopolymer mortars designed for fire-resistant or high-temperature applications. They assist in preserving structural integrity during heat exposure. Fibers mitigate early-age microcracks resulting from shrinkage, drying, or heat gradients. This results in a more compact and resilient microstructure. Using basalt fibers improves surface abrasion and impact resistance, which is advantageous for industrial flooring or infrastructure applications. Basalt fibers originate from natural volcanic rock, are non-toxic, and possess a minimal ecological imprint, consistent with the sustainability objectives of geopolymer applications. This study investigates the mechanical and thermal performance of a geopolymer mortar composed of metakaolin and red mud as binders, with basalt powder and limestone powder replacing traditional sand. The primary objective was to evaluate the effect of basalt fiber incorporation at varying contents (0.4%, 0.8%, and 1.2% by weight) on the durability and strength of the mortar. Eight different mortar mixes were activated using sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) solutions. Mechanical properties, including compressive strength, flexural strength, and ultrasonic pulse velocity (UPV), were tested 7 and 28 days before and after exposure to elevated temperatures (200, 400, 600, and 800 °C). The results indicated that basalt fiber significantly enhanced the performance of the geopolymer mortar, particularly at a content of 1.2%. Specimens with 1.2% fiber showed up to 20% improvement in compressive strength and 40% in flexural strength after thermal exposure, attributed to the fiber’s role in microcrack bridging and structural densification. Subsequent research should concentrate on refining fiber type, dose, and dispersion techniques to improve mechanical performance and durability. Examinations of microstructural behavior, long-term durability under environmental settings, and performance following high-temperature exposure are crucial. Furthermore, investigations into hybrid fiber systems, extensive structural applications, and life-cycle evaluations will inform the practical and sustainable implementation in the buildings. Full article

This study evaluates the seismic fragility and code compliance of reinforced concrete buildings in Turkey following the 6 February 2023 Kahramanmaraş earthquake. Sixty representative buildings were modeled in SAP2000, consisting of thirty structures designed according to TEC-1975 and thirty according to TEC-1998. These models were subjected to three-dimensional nonlinear time history analyses using ground motions scaled to match the seismic characteristics of the earthquake. Structural performance was assessed by comparing calculated displacement demands with capacity thresholds defined by modern code provisions. The results show that buildings designed under TEC-1998 generally performed better than those constructed according to TEC-1975, particularly in terms of deformation capacity and collapse resistance. Fragility curves and exceedance probabilities were developed to quantify damage likelihoods across different performance levels. When compared with post-earthquake field observations, the analytical models produced lower collapse rates, which may suggest the presence of widespread code noncompliance in the actual building stock. These findings highlight the critical importance of ensuring adherence to seismic design regulations to improve the resilience of existing structures. Full article

In seismic risk analyses, collapse assessment is of critical importance, as it leads to most injuries and fatalities, as well as significant economic losses. In this paper, the seismic collapse response of some 3D prototypes representative of the 1970s Italian reinforced concrete building stock has been analyzed. The considered prototypes have been selected based on two of the most important typological parameters, namely the number of storeys (three types: 2-, 4-, and 6-storey) and the design level (two types: gravity load design, representative of pre-code types, and earthquake-resistant design with low lateral load intensities without anti-seismic details, representative of low-code types). Incremental non-linear dynamic analyses have been performed along the two in-plane directions using a set of 20 real signals scaled up to collapse. The inter-storey drift ratio values at collapse have been analyzed to estimate the mean and dispersion values of the best-fitting distribution functions. These results can be used as capacity thresholds for assessing seismic performance in numerical analyses. Fragility curves have also been derived using different intensity measures to estimate the exceedance probability of collapse, accounting for their inherent efficiency, to be used in seismic risk analyses. Results have been compared to provide valuable insights into the influence of the considered typological parameters on collapse. Full article

In the seismic design of steel moment-resisting frames (MRFs), the panel zone region can significantly affect overall ductility and energy-dissipation capacity. This study investigates the influence of panel zone flexibility on the seismic response of steel MRFs by comparing two modeling approaches: one with a detailed panel zone representation and the other considering fixed beam-column connections. A total of 30 2D steel MRFs (15 frames incorporating panel zone modeling and 15 frames without panel zone modeling) are subjected to nonlinear time–history analyses using four suites of ground motions compatible with Eurocode 8 (EC8) soil types (A, B, C, and D). Structural performance is evaluated at three distinct performance levels, namely, damage limitation (DL), life safety (LS), and collapse prevention (CP), to capture a wide range of potential damage scenarios. Based on these analyses, the study provides information about the seismic response of these frames. Also, lower-bound, upper-bound, and mean values of behavior factor (q) for each soil type and performance level are displayed, offering insight into how panel zone flexibility can alter a frame’s inelastic response under seismic loading. The results indicate that neglecting panel zone action leads to an artificial increase in frame stiffness, resulting in higher base shear estimates and an overestimation of the seismic behavior factor. This unrealistically increased behavior factor can compromise the accuracy of the seismic design, even though it appears conservative. In contrast, including panel zone flexibility provides a more realistic depiction of how forces and deformations develop across the structure. Consequently, proper modeling of the panel zone supports both safety and cost-effectiveness under strong earthquake events. Full article

To analyze the impact of capacity uncertainty on the seismic collapse fragility of reinforced concrete (RC) frame structures, a fragility analysis framework based on seismic reliability methods is proposed. First, incremental dynamic analysis (IDA) curves are plotted by IDA under a group of natural seismic waves. Subsequently, collapse points are identified based on recommendations from relevant standards, yielding the probability distribution of the maximum inter-story drift ratios (MIDRs) at collapse points. Then, the distribution of the MIDRs under various intensity measures (IMs) of artificial seismic waves is calculated by using the fractional exponential moments-based maximum entropy method (FEM-MEM). Next, the structural failure probability is determined based on the combined performance index (CPI), and a seismic collapse fragility curve is plotted using the four-parameter shifted generalized lognormal distribution (SGLD) model. The results indicate that the collapse probability is lower considering the capacity uncertainty. Compared to deterministic MIDR limits of 1/25 and 1/50, the median values of the structure’s collapse resistance increased by 13.2% and 87.3%, respectively. Additionally, the failure probability obtained by considering the capacity uncertainty is lower than the results based on deterministic limits alone. These findings highlight the importance of considering capacity uncertainty in seismic risk assessments of RC frame structures. Full article

Reinforced concrete (RC) walls are mainly used in RC structures to resist gravity and lateral forces. These structural elements may need to be upgraded to withstand additional forces and extend their life cycle. Therefore, it is crucial to provide effective strengthening techniques using low-cost sustainable materials under optimal conditions to rehabilitate RC walls. This study presents an experimental and numerical investigation of reinforced normal concrete (NC) walls strengthened with near-surface mounted (NSM) steel bars, confined with or without an externally bonded reinforced (EBR) galvanized steel sheets (GSSs). A total of six RC walls were constructed, loaded, and tested to failure. The examined parameters included the type of strengthening technique, materials used, and the position and configuration of the strengthening. Both EBR and NSM techniques were applied using GSSs and steel bars, respectively. The configurations were introduced in vertical and horizontal positions to resist gravity and lateral forces, respectively. The experiments revealed that these parameters significantly influenced the crack control, energy absorption, mode of collapse, and ultimate load capacity. Nonlinear three-dimensional finite element models were developed and verified against experimental results, achieving a validation accuracy of 95% on average. This was followed by a parametric study investigating the effect of confinement with or without vertical reinforcements. Both experimental and numerical results confirmed that the strengthening could increase the ultimate load capacity from 20% to 38%. Full article

Flat slabs supported by columns without beams are widely used in construction owing to their economy and efficiency. However, brittle punching shear failure at slab–column connections can cause progressive collapse. UHPC has a higher tensile strength than NSC and, when appropriately reinforced with steel fibers, exhibits strain hardening after initial cracking. These properties make Ultra-High-Performance Concrete (UHPC) ideal for durable, thin, low-cost bridge decking and heavily loaded elements and an excellent choice for improving slab–column connections that have experienced punched shear failure. This study explores the impact of UHPC layers on the punching shear behavior of reinforced concrete slabs. Sixteen slab specimens were tested with variations in UHPC layer thickness, placement, and column shape. Results demonstrate that incorporating UHPC layers significantly enhances punching shear resistance, increasing ultimate load capacity by 27–91% compared to reference specimens. Notably, thicker UHPC layers (75 mm) and bottom-placed layers exhibited superior performance in terms of ductility and toughness. Square columns outperformed circular ones in resisting punching shear. Additionally, thicker layers reduced initial stiffness, while debonding issues in 25 mm layers adversely affected structural performance. This research provides valuable insights for optimizing UHPC configurations to improve the punching shear resistance of concrete slabs, offering promising solutions for high-load structures in modern construction. Full article

Transmission lines are usually located outdoors and are subjected to wind loads year-round. When a fire occurs, transmission towers are exposed to the combined effects of fire and wind loads. This paper investigates the impact of high temperatures on the bearing capacity of transmission tower-line systems under wind load and explores the effects of uneven horizontal spacing distribution and changes in the elevation of the target tower on the bearing capacity of the tower-line system. The failure criteria for transmission tower components at high temperatures were determined by considering the constitutive relationship of steel at ambient temperature and the variation patterns in material strength and elastic modulus with temperature. A finite element model of the transmission tower-line system was established using ABAQUS (2023). This paper studied the effects of temperature, uneven horizontal spacing distribution, and changes in the elevation of the target tower on the response of the transmission tower-line system by comparing collapse-resisting wind speeds and collapse processes under various conditions. The research indicates that the load-bearing capacity of the transmission tower-line system decreases as temperature increases. When the temperature exceeds 400 °C, the collapse-resisting wind speed of the transmission tower drops sharply. At temperatures above 600 °C, the transmission tower may collapse even at the annual average wind speed. In addition, the uneven horizontal spacing distribution and changes in the elevation of the target tower have an adverse effect on the stability of the transmission tower-line system. It is recommended to choose steel materials with higher fire resistance or apply fire-resistant coatings to existing steel, and to avoid extremely uneven spacing distributions and excessively high target tower elevations. Full article

Roof separation, destabilization and collapse of multilayer roof structures are difficult to control in large mining height gob-side entries due to severe mining pressure. In the 22301 working face in Tunlan Mine, a mining height of 4.75 m posed great challenges to gob-side entry retaining techniques. Through mechanical analysis, the strata movement of a multilayer roof structure was investigated, and numerical analysis was conducted to identify key aspects of the supporting scheme, e.g., ensuring the stability of immediate roof above the filling area, transferring the resistance from the cemented backfill to the roof structure and maintaining self-supporting capacity. A new support strategy was proposed and applied in industrial settings, with entry stability evaluated by monitoring the deformation characteristics, roof separation values and overall support performance. The results showed that the gob-side entry retaining technique was successful in Tunlan Mine, providing valuable insights for similar techniques in large mining height gob-side entries. Full article