Search Results (47)

A novel endplate bolted rigid joint is proposed in this study for connecting circular concrete-filled steel tube (CCFT) columns to wide-flange (WF) steel beams. The seismic performance and potential failure mechanisms of the proposed joint were investigated through quasi-static cyclic tests and finite element (FE) simulations. This study aims to address several engineering challenges commonly observed in existing joint configurations, including an irrational force-resisting mechanism, complicated detailing and installation, on-site construction difficulties, constraints on beam size, and limited repairability. By optimizing the force transfer path, the new joint effectively reduces the number of critical tension welds, thereby enhancing the ductility and reliability. The experimental results indicate that the joint exhibits adequate flexural strength, stiffness, and ductility, with stable moment–rotation hysteresis loops under cyclic loading. Moreover, full restoration of the joint can be achieved by replacing only the steel beam and endplate, facilitating post-earthquake repair. FE analysis reveals that, under the ultimate bending moment at the beam end, multiple through cracks develop in the high-strength grout—which serves as a key load-transferring component—and significant debonding occurs between the grout and the surrounding steel members. However, due to confinement from adjacent components, these internal cracks do not compromise the overall strength and stiffness of the joint. This research provides an efficient and practical connection solution, along with valuable experimental insights, for the application of CCFT columns in moment-resisting frames located in high seismic zones. Full article

This study develops a quantitative framework to assess performance degradation and damage evolution in CRTS I ballastless track slabs. Based on the impact-echo method, the internal void distribution characteristics of the new and old track slabs were obtained. The track slabs were sampled separately by drilling cores to verify the distribution of voids, and uniaxial compression tests were conducted simultaneously to quantify the attenuation of bearing capacity. The on-site wheel–rail force and temperature field data were monitored, based on the established three-dimensional finite element model of CRTS I ballastless track, and the damage distribution characteristics of the track slab under different load combinations after performance degradation were studied. The results show the following: (1) As the performance of the track slabs gradually deteriorated, it was reflected in the increasing internal void distribution area from 0.5% to 3.6%, corresponding to a 22.4% decrease in core strength. (2) The on-site monitoring results showed that the average wheel–rail force was 84.5 kN. The temperature gradient range varied from −50.4 °C/m to 100.0 °C/m, exceeding the allowable value of the design specifications. (3) The actual damage distribution of the track slab after performance degradation under different load combinations significantly increased at key stress locations such as near fasteners, convex abutments, and anchor holes of prestressed steel bars, which required special attention in actual maintenance and repair. Full article

The conservation of experimental building materials that were introduced during the 20th-century currently represents one of the main challenges in building restoration. Fair-faced concrete is especially affected by durability problems and requires careful assessment to implement effective conservation methods, even more so when the building has artistic and expressive value. In addition, the literature in this field is still limited and case studies are very rare. In this paper, the Partisan Ossuary Monument, a brutalist monument at the Certosa of Bologna, was studied and analysed in order to find the most effective restoration techniques, especially for its concretes, which have a particularly expressive texture. The aim was to combine both the preservation of the aesthetics and functional quality of the building with the use of existing technologies in this field. Firstly, archive research was carried out to discover the original building techniques and the materials used. The literature on the Monument was studied to unveil the expressive role given to the concretes’ surface finishing. Then, after an on-site investigation, all the materials used in the Monument and the degradation processes were analysed and mapped out. Significant samples of the Monument were manually collected whilst limiting invasiveness. Then, diagnostic tests were carried out to identify the causes of degradation and to comprehend the nature of certain superficial finishes. Several techniques were used, i.e., X-ray diffraction, optical microscopy, and FT-IR spectrometry. Finally, guidelines were drafted for possible future restoration, merging all the results from the previous phases of this study with compliance with heritage structures’ restoration requirements. Many technologies commonly used for the repair of concrete structures could not be applied to this Monument due to its features. Hence, new solutions were studied and proposed. The results obtained may contribute to an increased awareness of the need to restore 20th-century heritage buildings in order to limit degradation and partial reconstruction. Many concrete heritage buildings of this period suffer from the same problems, and this paper could offer an important starting point for future research. Full article

Many countries around the world are in a race against time to decarbonise their energy systems. One of the avenues being explored in detail is Offshore Renewable Energy (ORE), with technologies such as wind, wave, and tidal. All of these technologies are in their infancy within the marine environment and required heavy Research and Development (R&D) to make them commercially viable. With so much demand for these industries, the supply chain is heavily constrained. A solution that has shown great potential to alleviate the pressure on the supply chain is the use of Wire Arc Additive Manufacturing (WAAM) for the use of onsite repair or manufacture for components. This is due to its ability to produce large-scale parts, with low emissions and at a lower cost than other Additive Manufacturing (AM) processes. The opportunity to use this technology could result in shorter downtimes and lead to a reduction in the Levelised Cost of Energy (LCOE). However, knowing that offshore structures are subject to cyclic loading conditions during their operational lifespan, fatigue properties of new materials and manufacturing processes must be well documented and studied to avoid any catastrophic failures. An issue often seen with WAAM is the presence of residual stresses. This study looks at fatigue cracking on Compact Tension C(T) specimens that have undergone laser shock peening and rolling, surface treatment processes that form compressive residual stresses at the surface of the material. In this study, the influence of fatigue overloading on the residual stress distribution in surface-treated WAAM specimens is evaluated and the effectiveness of the post-processing techniques on the subsequent fatigue behaviour is explored. Full article

During the long-term operation of the DC grounding electrode of the converter station, there are often hazards such as heating and aging of the coke layer, and burning and corrosion at the connection between the feed rod and the cable, resulting in break problems at the connection between the cable and the feed rod. Currently, the operational status monitoring of grounding electrodes primarily relies on daily tracking of well temperature, humidity, and water level characteristics; periodic testing; and on-site excavation. However, the above methods cannot accurately obtain the breakage location information at the connection between the cable and the feed rod. To address these issues, this paper first analyzes the current distribution law in the feeder rod of the DC grounding electrode. Subsequently, it studies the impact of localized fractures in the DC grounding electrode on the surface potential distribution characteristics. Finally, an Operation State Detection Method (OSDM) based on potential distribution is proposed and validated through case studies, demonstrating high measurement accuracy. The results indicate that OSDM can effectively monitor the operational status of DC grounding electrodes, providing a reference for their maintenance and repair. Full article

This paper presents an experimental study on the elastic support in a discrete rail fastening system used in a ballastless tram track structure. The study focuses on the elastic support of the anchor element, specifically the Pm49 baseplate. These elements significantly influence environmental pollution along tram routes, such as vibration (at low frequencies) or noise (at high frequencies), as well as static and dynamic rail deflections. The authors outline a methodology for identifying the static and dynamic characteristics of the discrete elastic support in laboratory conditions. The procedure follows the European standard EN 13146-9 for track category A (tramway), as classified according to the European standard EN 13481-5. The study analyzes how the thickness and density of the tested materials affect stiffness. Additionally, it examines the correlation between parameters identified easily on-site (thickness, Shore hardness and density) and laboratory-determined parameters (static and dynamic stiffness), which are costly and time-consuming to measure. The research confirms that prototype prefabricated vibration isolation baseplate pads made of styrene butadiene rubber (SBR) granules, recycled from end-of-life car tires, can achieve equivalent basic static and dynamic parameters, compared to underlays made of two-component polyurethane (PU) resin. This aligns with the strategy of promoting sustainable materials in construction. The innovative and prefabricated SBR rubber baseplate pads can also be used in repair and maintenance works (regardless of weather conditions), as they enable the quick launch of tram traffic. The results of the research included in this article can be used by other scientists, recycled rubber producers, tram track designers or construction site engineers. Full article

Metal additive manufacturing in space is a cutting-edge technology that is designed to meet the needs of space exploration and space station construction. This technology is capable of customizing and repairing key metallic parts in a space microgravity environment, providing the feasibility for long-term space tasks. It enables astronauts to perform on-site repairs and replace broken parts, significantly reducing the risk of mission failure on the International Space Station or during future deep space missions. Further, this technique opens new possibilities for constructing space bases by directly utilizing the materials from space, thereby reducing reliance on Earth’s resources. However, metal additive manufacturing in space faces challenges due to the unclear underlying mechanisms that lie in (I) the significant differences in the melting behaviors of materials in a space microgravity environment compared to those on Earth; and (II) extreme environmental factors, i.e., radiation and temperature fluctuations, that influence the metal additive manufacturing process and, consequently, the properties of the manufactured materials. This review provides a comprehensive analysis of those mechanisms underlying metal additive manufacturing in space, based on published works. Emphasis is placed on aluminum, titanium, iron, and copper-based metals. Our work may offer valuable guidance for reducing mission costs, improving safety, and enabling the on-demand production of complex components in the harsh environment of space by using metal additive manufacturing. Full article

Superfine cement is widely used in building reinforcement and repair, special concrete manufacturing, and environmental protection engineering due to its high toughness, high durability, good bonding strength, and environmental friendliness. However, there are some problems in superfine cement slurry, such as high bleeding rate, prolonged setting time, and consolidated body volume retraction. In this article, on the premise of using the excellent injectability of superfine cement slurry, the fluidity, setting time, reinforcement strength, and volume expansion rate of novel expansive superfine cement slurries with varying proportions were analyzed by adding expansion agent UEA, naphthalene-based water reducer FDN-C, and triisopropanolamine accelerating agent TIPA. The results show that under most mix ratios, the bleeding rate and fluidity of the novel superfine cement slurry initially increase and decrease with rising water-reducing agent dosage. The initial setting time generally decreases with accelerating agent dosage, reaching a minimum value of 506 min, representing a 33.68% reduction compared to the benchmark group (traditional superfine cement). Under normal conditions, the compressive strength of the net slurry consolidation body is positively correlated with expansion agent dosage, achieving maximum strengths of 8.11 MPa at three days and 6.93 MPa at 28 days; these values are respectively higher by 6.7 MPa and 2.6 MPa compared to those in the benchmark group. On the seventh day, the volume expansion rate of the traditional superfine cement solidified sand body ranges from −0.19% to −0.1%, while that for the corresponding body formed from the novel superfine cement is between 0.41% and 1.33%, representing a difference of 0.6–1.43%. After the on-site treatment of water and sand-gushing strata, the core monitor rate of the inspection hole exceeds 70%. The permeability coefficient of the stratum decreases to a range between 1.47 × 10⁻⁶ and 8.14 × 10⁻⁶ cm/s, resulting in nearly a thousandfold increase in stratum impermeability compared to its original state. Hence, the findings of this research hold practical importance for the future application of such materials in the development of stratum reinforcement or building repair. Full article

Good-quality metallurgical bonding and a high degree of automation are critical for using laser cladding technology in on-site repairs. At present, most of the on-site repairs are carried out manually, which can bring about problems such as complicated operation procedures, uneven repair quality, and personnel injuries. In this study, a surface repair method that combined laser cleaning with cladding (LCC) was proposed. First, the plates were scanned with a high-frequency pulsed laser to remove the surface impurity layer. The surface was then coated with Inconel 625 powder while irradiated with a continuous laser for the cladding. Both the macro-morphology and microstructure of the surface were examined, and mechanical property tests were also conducted. The metallographic and scanning electron microscope images indicated that, compared to the manual polishing and laser cladding process, the LCC specimens had a better metallurgical bonding quality and a thicker clad layer. The average hardness of the clad layer on the LCC specimens was high at 256.47 HV, 36.2% higher than that of the Q345R substrate. Compared to the Q345R specimens of the same size, the LCC specimens showed an increased impact on the energy absorption, yield strength, and tensile strength. This study provides a new approach for improving the automation and cladding quality of on-site repairs. Full article

This paper presents two original methods for monitoring and evaluating concrete specimens/structures affected by external sulfate attack (ESA). The first is a drying method developed to assess the penetration depth of sulfate ions in a concrete structure, as this parameter is a relevant indicator of the progress of the ESA. This method has been specifically designed for on-site investigations. The second experimental method involves the use of optical fibers capable of measuring the swelling response of specimens to ESA in real time. According to the results obtained, these two new methods seem likely to be used to complement or replace traditional methods such as inductively coupled plasma (ICP) for determining the penetration depth of sulfate ions or as extensometers for measuring swelling. These traditional methods (ICP and extensometers) are generally considered painful and time-consuming, whereas, because of its simplicity, the proposed drying method will enable experts to regularly inspect concrete structures and make informed decisions on the measures to be taken to repair or prevent further damage induced by ESA, while the second method appears promising for experimental studies involving the monitoring of a large number of ESA-affected specimens. Full article

This study aims to investigate the factors and consequences of gas deflagration accidents in metro shield tunnels based on on-site investigation and numerical analysis. We built a numerical model and detection process for an underground shield tunnel subjected to an internal explosion from an actual accident. The tunnel geometry under consideration is the same as that used for the metro line. Concerning the limitations of research on the failure and recovery mechanism of shield segmental linings under the action of internal explosion load, an explosion accident of a shield segmental lining under construction caused by the shield tunneling machine destroying natural gas pipelines was discussed, in which the structure failure characteristics during the explosion and the structure repair method after the explosion were investigated. An interval repair scheme was proposed, which provides experience for the treatment of similar engineering accidents. To investigate the gas explosion within the tunnel during the accident, the finite element software Ansys LS-DYNA with the arbitrary Lagrangian–Eulerian (ALE) technique was employed to simulate the explosion scenario. Dynamic analyses were carried out to reproduce the blast scenario. The stress distribution within the segmental lining as well as the lining’s deformation were calculated. The potential applications of the treatment and planning of comparable engineering mishaps were discussed in the study. Full article

For decades, ferrocement has been used to repair, strengthen, and even build structural components because it is a long-lasting and reasonably priced material. However, onsite ferrocement jacketing is time-consuming and labour-intensive. Alternatively, prefabricated ferrocement jacket installation eliminates these shortcomings. Therefore, this study utilises wearable prefabricated ferrocement jackets to repair and strengthen axially loaded sub-standard low-strength concrete elements. In order to repair cracked specimens and strengthen existing intact specimens, two types of wearable prefabricated jackets are proposed, ‘L’ shape and ‘U’ shape. Besides a control specimen, two preloaded and two unloaded square concrete specimens were utilised to repair and strengthen using the Prefabricated Ferrocement Jacketing system. The test results and crack patterns show that all the jacketed specimens performed better than the control specimens in terms of load-bearing capacity, ultimate axial and lateral deflection, and ductility. In terms of load-bearing capacity, the unloaded strengthened specimens showed significant results consistently. Based on the results, the proposed solutions were found to be effective in solving the problem of typical square ferrocement jackets. Full article

In ancient buildings, timber members may require specific on-site interventions, including reinforcement or repair and sometimes the insertion of reinforcing material into grooves routed in the original sound wood. The required number, positions, and dimensions of grooves and the strengthening materials may differ according to the desired increases in bending stiffness and strength. The modulus of elasticity (MOE) of each beam is of key importance: the MOE is typically a point of weakness for wood and is considered a constant characteristic of each beam. However, taking into account the wood lost for the groove, whether the needed incisions affect the stiffness is unknown. As such, in this study, 12 old beams were accurately measured, and their static and dynamic MOEs were calculated before and after groove formation to simulate the typical processes of reinforcing interventions. One groove was routed along the length of each beam and progressively deepened in three steps. The results of tests showed how the MOE is affected by the groove depth, decreasing by up to one-third (34.1%), and that beam stiffness cannot be regarded as constant. Beam stiffness depends on the features of the beam, mainly the pith, fissures, and slope of the grain, as well as its structural integrity. Beam stiffness is strongly influenced by the cuts upon it. This study proves how the weakening effect of grooves created on-site can be assessed using the dynamic MOE and roughly predicted with a visual survey. The grooves required for strengthening beams must be thoroughly evaluated, considering the potential reduction in the mechanical properties of the beam, which goes well beyond the wood lost during cutting. Full article

Naval vessels face multiple risks that can damage their hulls during navigation, leading to on-site repairs through the shield metal arc welding (SMAW) process and underwater wet welding (UWW). This paper presents a weldability study to identify the optimal heat input parameters to improve ASTM A131 DH36 welded joints quality, development, and sustainability. This study analyzes the influence of heat input on the microstructure and mechanical properties of underwater wet welding fillet joints welded with shield metal arc welding at 4 m water depth in a real-life environment located at the bay of Cartagena (Colombia). The methodology involves nondestructive and destructive tests, including visual inspection, fillet weld break, scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers hardness, and shear strength tests. The welds microstructure is composed of ferrite, pearlite, retained austenite, bainite, and martensite; the hardness values range from 170 HV1 to 443 HV1, and the shear strength values range from 339 MPa to 504 MPa. This indicates that high thermal inputs improve the weld quality produced by the underwater wet welding technique and can comply with the technical acceptance criteria of AWS D3.6, making them more sustainable, with less welding resources wastage and less impact on marine ecosystems. Full article

Repairing potholes is a task for municipalities to prevent serious road user injuries and vehicle damage. This study presents a low-cost, high-performance pothole monitoring system to maintain urban roads. The authors developed a methodology based on photogrammetry techniques to predict the pothole’s shape and volume. A collection of overlapping 2D images shot by a Raspberry Pi Camera Module 3 connected to a Raspberry Pi 4 Model B has been used to create a pothole 3D model. The Raspberry-based configuration has been mounted on an autonomous and remote-controlled robot (developed in the InfraROB European project) to reduce workers’ exposure to live traffic in survey activities and automate the process. The outputs of photogrammetry processing software have been validated through laboratory tests set as ground truth; the trial has been conducted on a tile made of asphalt mixture, reproducing a real pothole. Global Positioning System (GPS) and Geographical Information System (GIS) technologies allowed visualising potholes on a map with information about their centre, volume, backfill material, and an associated image. Ten on-site tests validated that the system works in an uncontrolled environment and not only in the laboratory. The results showed that the system is a valuable tool for monitoring road potholes taking into account construction workers’ and road users’ health and safety. Full article