Search Results (16)

The interfacial shear performance between ultra-high-performance concrete (UHPC) and normal concrete (NC) is a critical factor in determining the overall performance of composite structures. This paper systematically reviews the research progress on the interfacial shear performance of UHPC-NC, revealing the core mechanisms of bond strength (dominated by mechanical interlocking with chemical bonding as a supplementary factor). It compares the advantages and disadvantages of single-shear, Z-shaped shear, double-shear, and inclined shear tests, clarifying the influence patterns of key parameters such as interface roughness, matrix wetness, curing conditions, and fiber content. This study found that interface treatment is the most significant factor in improving shear strength. Roughening or grooving treatments can increase the strength by more than 40%~80%, while the combination of rebar planting and grooving can further enhance ductility. The matrix wetness (saturated and moist) and UHPC age (within 7 days) need to be strictly controlled to avoid differences in shrinkage stress. Prediction models based on mechanics, finite element analysis, and experimental data each have their advantages and disadvantages and should be selected based on actual working conditions. To address common issues in practical engineering, such as insufficient interface roughness, shrinkage cracking, and fatigue degradation under cyclic loading, it is recommended to adopt composite interface treatment techniques (such as roughening + rebar planting), prestressing design, and optimized fiber distribution (with a steel fiber content of 1.5%~2.5%). This paper provides the theoretical basis and practical guidance for the design optimization and construction control of UHPC reinforcement projects and composite structures. Full article

The seismic performance of an electric power system is crucial for maintaining the functionality of urban communities following an earthquake. In thermal power plants, the RC frame–shear wall structure plays a key role in providing seismic resistance to the main building’s longitudinal structural system. This study presents the results of a series of pseudo-dynamic tests on a two-span, four-story frame–shear wall model with a scale of 1/8. The prototype structure was a seven-story, seven-bay longitudinal RC frame–shear wall from the main workshop of a large thermal power plant. The cracking process, yielding sequence, hysteresis curves, and skeleton curve were obtained. Based on the test results, the energy dissipation, equivalent viscous damping coefficient, ductility and deformation, stiffness degradation, dynamic response, and displacement response were analyzed. The results showed that the RC frame–shear wall structure exhibits a high energy dissipation capacity and excellent seismic performance, and the shear wall significantly influences the structural bearing capacity and deformation performance. These findings offer valuable guidance for the seismic design of RC frame–shear wall structures in high-rise and large factory buildings. As the shear wall absorbs the majority of seismic forces and minimizes the concentration of plastic deformation, strengthening critical weak areas—such as increasing the horizontal distribution of rebars or improving the concrete strength at the shear wall base—can enhance overall structural performance and seismic resilience in industrial buildings subject to seismic loading. Full article

Inhibitors for the prevention of corrosion in reinforced concrete are chemical substances able to reduce carbon steel reinforcements corrosion without altering the overall properties of concrete. Today, many commercially available substances have a negative impact on human safety during either the inhibitor synthesis, their handling or application in field. Green corrosion inhibitors are nontoxic, biodegradable and environmentally biocompatible substances. They are generally made of extracts from natural plants or waste, which are abundantly available in several countries. The majority of green inhibitor molecules usually contain multiple bonds, aromatic rings, polar functional groups and electronegative atoms as P, N, S or O; the latter are able to coordinate with metal cations to form protective layers on the metallic surface of the reinforcements, so as to inhibit the development (initiation and/or propagation) of the corrosion process. In this review, the most recent achievements on the study and investigation of green corrosion inhibitors for concrete structures are presented and discussed. Inhibitors are classified based on their nature and inhibition mechanism. The inhibition effectiveness of the substances is compared with the well-established effective nitrite-based inhibitor, distinguishing between accelerated and long-term tests. Based on the available data, a summary of corrosion inhibitors efficiency is reported. Full article

In view of the complexity of the pile foundation underpinning structure system and the stringent requirements of the construction process, this paper briefly describes the necessity of introducing epoxy resin reinforcing adhesive of planting rebar in the design of pile foundation underpinning beam structure to improve the mechanical properties of the reinforced beam new and old concrete joint surfaces and proposes a new type of pile foundation replacement beam system construction method by “chiseling + prestressed reinforcement + epoxy resin reinforcing adhesive”. This paper uses an actual pile foundation underpinning project of an urban overpass as a prototype, designs and creates a model structure with a similarity ratio of 1/6, and performs repeated progressive static loading tests to study the load carrying capacity, displacement change, and other properties of the strengthened replacement structure, as well as analyses and distorts the overall working performance and failure mode of them. On this basis, the prototype structure’s finite element analysis model was built, and the finite element analysis results were compared with the test results to obtain the mechanical properties and deformation characters of the actual pile foundation underpinning structure system corresponding to the actual underpinning beam load. This paper’s study can lay the theoretical and experimental foundation for the smooth development of similar projects. Full article

Prestressing plays a pivotal role in ensuring the tightness and integrity of prestressed concrete containment in nuclear power plants. The prestress loss reduces the compressive stress in concrete resulting from the prestressing strands and increases the risk of containment leakage under severe accident conditions. Therefore, the accurate prediction of prestress loss is essential for the design and in-service management of prestressed concrete containment. Unlike one-way beams or girders in building structures and bridges, two-way prestressing systems are used in prestressed concrete containment. In the current simplified method for evaluating time-dependent prestress loss, the interaction of concrete creep in two directions resulting from the two-way prestressing strands and the influence of the steel liner and mild steel rebars in two directions are neglected. In this study, based on the principle of creep superposition, the age-adjusted effective method for the creep estimation of concrete, and considering concrete shrinkage, concrete creep, and the relaxation of prestressing strands, as well as the influence of the steel liner and mild steel rebars in two directions, a sectional analysis is performed for prestressed concrete containment with bonded prestressing strands, and equations for calculating the two-way time-dependent prestress losses are derived. The results of the two-way time-dependent prestress losses predicted by the derived equations are compared with those of tests in the literature, and great agreement is achieved. Finally, a case study is given to show the application of the proposed method for the prediction of prestress loss in prestressed concrete containment in the nuclear power plant. Full article

The use of full lightweight ceramsite concrete (FLWCC) for the repair of ordinary concrete (OC) structures has a good application prospect in the field of engineering structural strengthening. However, the interface here is less studied at present. For this purpose, 10 sets of FLWCC (new concrete)–OC (old concrete) specimens were produced for the shear test to test the bonding properties of the interface. The results showed that the damage form was changed from brittle damage to ductile damage after strengthening. It was proven that planting rebars in the interface could improve the shear performance. The interface shear strength increased with the number of rebars and it had a better effect after the number was more than 2. The strength was related to the rebar diameter and the maximum was obtained when the diameter was 8 mm. The most suitable spacing of the bars was 80 mm. The one-way analysis of variance (ANOVA) showed that the number of rebars had the greatest effect on shear strength followed by rebar diameter, while the effect of the spacing of the bars was less pronounced. Moreover, Fib’s (2010) specification of the interface shear strength formula could be used for the calculation of FLWCC–OC. Full article

Molecular dynamics (MD) is an important method for studying the molecular and atomic scale of cement (geopolymer)-based composites which provides an effective method for the optimal design of cementitious materials. In this paper, the research progress of MD simulation in Portland cement and geopolymer-based materials is discussed in detail, including molecular structure models of calcium silicate hydrate, calcium aluminosilicate hydrate, sodium aluminum silicate hydrate gel, and auxiliary experimental techniques. The basic mechanical properties of calcium silicate hydrate, calcium aluminosilicate hydrate and sodium aluminum silicate hydrate in Portland cement-based materials (CBM) and geopolymer-based materials are reviewed. In addition, the dynamic simulation of the interface between CBM and reinforcement materials such as rebar, synthetic fibers, plant fibers and nanoparticles is also discussed. Through the macroscopic experimental results of cement (geopolymer)-based materials and the performance analysis of an MD microscopic model, MD helps to better explain the macroscopic properties of materials, and can quickly and conveniently analyze the mechanical properties, transport properties and interface properties of composite materials, so as to improve the fine design of cement (geopolymer)-based materials. Existing structural models and force fields are affected by environment and time, and MD simulation shows great differences in application range and characterization ability. It is necessary to further study and reveal the internal mechanism for improving concrete performance through a large number of experiments and MD simulation, and lay a theoretical foundation for preparing the next generation of (super) high-performance concrete. Full article

In this paper, we describe how, through the combination of field testing and finite element simulation, the bonding and anchoring performance of small-diameter rebar under the action of medium and low cycle fatigue load was studied and the corresponding conclusions were obtained: ① Through the test, the performance parameters of the 6 mm and 8 mm rebar planting specimens were obtained after the rebar was subjected to 10,000, 50,000 and 100,000 times of medium and low cycle fatigue loading at depths of 10d, 15d and 20d. The analysis shows that the medium and low cycle fatigue load has a significant effect on the elastic ultimate load, elastic ultimate slip and ultimate slip of the small-diameter rebar planting specimens. With the increase in fatigue loading times, the elastic ultimate load of the rebar specimen decreased continuously, and the elastic ultimate slip and ultimate slip showed an increasing trend. By increasing the anchor depth, the influence of fatigue load on the anchoring performance parameters of the rebar planting specimen can be reduced. Under the influence of the upper ultimate condition of 100,000 times of fatigue loading, the ultimate load and failure mode of the planted bars basically did not change compared with the control specimens without fatigue loading. ② Based on the performance parameters of the rebar planting specimens obtained from the field test, the bond–slip constitutive relationship of the adhesive–rebar interface of the small-diameter rebar planting under the medium and low cycle fatigue load is analyzed and proposed. The F-U relationship of the spring element under the fatigue load is defined to simulate the bond–slip behavior of the adhesive–rebar interface. The finite element simulation results are in good agreement with the field test results. ③ Through a large number of finite element numerical simulation results, the elastic ultimate load calculation formulas of 6 mm and 8 mm diameter rebar planting specimens under medium and low cycle fatigue loads are obtained. Full article

The construction industry is on the lookout for cost-effective structural members that are also environmentally friendly. Built-up cold-formed steel (CFS) sections with minimal thickness can be used to make beams at a lower cost. Plate buckling in CFS beams with thin webs can be avoided by using thick webs, adding stiffeners, or strengthening the web with diagonal rebars. When CFS beams are designed to carry heavy loads, their depth logically increases, resulting in an increase in building floor height. The experimental and numerical investigation of CFS composite beams reinforced with diagonal web rebars is presented in this paper. A total of twelve built-up CFS beams were used for testing, with the first six designed without web encasement and the remaining six designed with web encasement. The first six were constructed with diagonal rebars in the shear and flexure zones, while the other two with diagonal rebars in the shear zone, and the last two without diagonal rebars. The next set of six beams was constructed in the same manner, but with a concrete encasement of the web, and all the beams were then tested. Fly ash, a pozzolanic waste byproduct of thermal power plants, was used as a 40% replacement for cement in making the test specimens. CFS beam failure characteristics, load–deflection behavior, ductility, load–strain relationship, moment–curvature relationship, and lateral stiffness were all investigated. The results of the experimental tests and the nonlinear finite element analysis performed in ANSYS software were found to be in good agreement. It was discovered that CFS beams with fly ash concrete encased webs have twice the moment resisting capacity of plain CFS beams, resulting in a reduction in building floor height. The results also confirmed that the composite CFS beams have high ductility, making them a reliable choice for earthquake-resistant structures. Full article

Strengthening concrete structures with ultra-high performance concrete (UHPC) can both improve the bearing capacity of the original normal concrete (NC) structure and prolong the service life of the structure due to the high strength and durability of UHPC. The key to the synergistic work of the UHPC-strengthened layer and the original NC structures lies in the reliable bonding of their interfaces. In this research study, the shear performance of the UHPC–NC interface was investigated by the direct shear (push-out test) test method. The effects of different interface preparation methods (smoothing, chiseling, and planting straight and hooked rebars) and different aspect ratios of planted rebars on the failure mode and shear performance of the pushed-out specimens were studied. Seven groups of push-out specimens were tested. The results show that the interface preparation method can significantly affect the failure mode of the UHPC–NC interface, which is specifically divided into interface failure, planted rebar pull-out, and NC shear failure. The critical aspect ratio for the pull-out or anchorage of planted rebars in UHPC is around 2. The interface shear strength of straight-planted rebar interface preparation is significantly improved compared with that of the chiseled and smoothened interfaces, and as the embedding length of the planted rebar becomes longer, it first increases greatly and then tends to be stable when the rebar planted in UHPC is fully anchored. The shear stiffness of UHPC–NC increases with the increase of the aspect ratio of planted rebars. A design recommendation based on the experimental results is proposed. This research study supplements the theoretical basis of the interface design of UHPC-strengthened NC structures. Full article

Cactus plants are prevalent in hot terrain locations. The spines in the cactus plants have an important function in preventing water evaporation. The strong pointed spines serve to distribute heat and prevent internal moisture loss owing to high heat. This paper addresses the biomimicking of a cactus plant to a reinforced concrete column. Columns are one of the most predominant elements in a structure and are responsible for maintaining the stability of the structure. Under the occurrences of fire, columns are the most affected, and the failure of the same could eventually steer to global collapse of the structure. In this study, various geometries were adopted based on the cactus plant, and the heat dissipation characteristics were studied. Finite element analysis was used to determine the optimal form based on the heat dissipation. The optimized shape was tested experimentally using a high-temperature localized heating element. Five column specimens were considered for experiments and named C (conventional nonheated column), C1 (conventional heated column), C2 (mimicked column), C3 (mimicked column with rebar in cone), and C4 (mimicked column with rebar in cone (quenching)). The heat-dissipating nature was observed, and the structural aspects were tested aftermath. The results reveal that the quenched specimen depicts better heat dissipation than the other specimens and eventually maintains the stability of the specimen throughout the height. Full article

A discrete-event simulation (DES) model was developed to enhance the reinforcing bar (rebar) fabrication efficiency for multiple simultaneous projects at different sites. The production volume and procedure of the actual rebar fabrication plant were compared to the simulation model to ensure its accuracy. By determining the loss rate and necessary processing time, the fabrication plan was then optimized. The rebar type and machine features, which influence the loss rate and time required for rebar fabrication, were configured as the parameters in a discrete-event simulation model. The model considers a situation in which a rebar fabrication plant simultaneously delivers rebars to multiple sites. In this manner, the model can quantify the loss rate and time required in the fabrication process. The determination of the loss rate according to the import ratio of raw steel, site combination, and length can help optimize the rebar fabrication plan and increase work efficiency. In the considered scenario, a two-site combination and import ratio of raw steel of 2:1 (8 m:10 m) was noted to corresponded to the maximum decrease in the loss rate and required time. By extending the proposed approach to the complete rebar process (processing–transportation–construction), the plant member production process can be optimized. Full article

Nuclear power is a major source of electricity in the international community. However, a significant problem with nuclear power is that, if a severe nuclear accident occurs, radiation may leak and cause great damage. As such, research on nuclear safety has become increasingly popular worldwide. In this paper, the structural integrity of a reactor cavity during a steam explosion—one kind of the aforementioned severe nuclear accidents—was evaluated. Steam explosions are primarily caused by fuel–coolant interactions (FCI), and result from issues in the cooling system that discharges the melt from the reactor core to the outside. A steam explosion can damage the nuclear power plant, and radiation leakage, the greatest concern, may occur. In the Chernobyl or Fukushima Daiichi accidents, significant radiation leakages resulted in damages extending beyond the country of origin. In this paper, a steam explosion was simulated using values given by the transient analysis code for explosive reactions (TRACER-II)—the only steam explosion code in Korea. The walls of the reactor cavity were modeled after the APR-1400 currently operating in Korea. The integrity of the concrete, rebars, and liner plate in the reactor cavity during a steam explosion was evaluated in terms of stress and ductile failure strain limits. Full article

Reinforced concrete (RC) is by far the most widely used composite material in the world. Despite the enormous economic importance of RC construction, there is a lack of viable concepts for its digital fabrication. While 3D printing of plain concrete has been pushed forward by a growing research community in recent years, methods for integration of steel reinforcement have only scarcely been researched and little attention has been payed to meet the practical requirements of construction sites and prefabrication plants. Therefore, full-scale implementations of current approaches are hardly available. Based on both, a sound review of R&D for digital fabrication of RC structures and an analysis of practical requirements, the present paper proposes a novel 3D printing process for RC structures, called Additive Manufacturing of Reinforced Concrete (AMoRC), viable for real-world application. In this hybrid process, consisting of an intermittent stud welding process and a continuous concrete extrusion process, segmented steel reinforcing bars are joined to form a three-dimensional reinforcement mesh and simultaneously encased with extruded concrete. The paper describes the conceptual design and development of the process and demonstrates the results of preliminary investigations on its feasibility. As AMoRC enables the operation of rebar welding and concrete extrusion process with synchronized feed rates, combination of both processes in one hybrid print head for digital fabrication of RC is a key-advantage of the proposed method. Full article

The article concerns the assessment of technical condition of the precast loggia wall in a large panel building after 25 years of use as well as the cause of its damage. As a result of the study, cracks and losses of the concrete cover were found. Corrosion products were visible on exposed reinforcing rods. The reinforcement distribution and concrete cover thickness in loggia wall were estimated using a rebar detector. The corrosion assessment of reinforcement was performed using a semi non-destructive galvanostatic pulse method that allows the location of areas of corrosion and estimate the reinforcement corrosion activity. The phase composition of the concrete cover was analyzed. The test results showed an insufficient thickness of the concrete cover as the main cause of loggia wall damage. The research indicated that manufacturing errors made in the prefabrication plants affect the technical condition of precast elements and may lead to the damage of the structure well before the expected of its service life. In the case of manufacturing errors causing the implementation of an element with a concrete cover that does not meet the standard requirements for thickness and tightness, it is recommended to use protective coatings to increase the element’s durability to the designed level. Full article