Experimental behaviour of very high-strength concrete-encased steel composite column subjected to axial compression and end moment

[EN] A type of cost-effective and very high strength concrete (VHSC) with 28-day compressive strength of 100-150 MPa is developed for applications in concrete-encased steel composite column constructions. This paper experimentally investigates the structural behaviour of VHSC encased steel composite columns based on a series of pure compression and eccentric compression tests. It is found that such high-strength composite column exhibits brittle post peak behaviour and low ductility but with acceptable compressive resistance. Throughout the tests, the main failure of VHSC encased column under compressive load is brittle spalling of concrete followed by local buckling of the reinforcement bars. The splitting and slippage may occur between concrete and steel section due to bending downward action. The confinement effect by the shear stirrups designed based on normal reinforced concrete codes may not be sufficient. Composite column subjected to initial flexural cracking due to end moment load with large eccentricity may experience degradation in the stiffness and ultimate resistance so that plastic design resistance may not be achieved. Analytical studies show that the N-M interaction model based on current design codes may over-predict the combined resistance of the composite columns. Therefore, a modified elastic-plastic design approach based on strain compatibility is developed to evaluate the compressive resistance of concrete encased composite columns. The validation against the test data shows a reasonable and conservative estimation on the combined resistance of VHSC encased composite columns.Huang, Z.; Huang, X.; Li, W.; Zhou, Y.; Sui, L.; Liew, JY. (2018). Experimental behaviour of very high-strength concrete-encased steel composite column subjected to axial compression and end moment. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 323-329. https://doi.org/10.4995/ASCCS2018.2018.7034OCS32332

Experimental and theoretical study of bond behaviour between FRP bar and high-volume fly ash-self-compacting concrete

The combination of fibre-reinforced polymer (FRP) and high-volume fly ash self-compacting concrete (HVFA-SCC) reinforced is expected to solve the problem of steel corrosion in traditional structures and develop sustainable infrastructures. Bond behaviour has a strong effect on serviceability of FRP reinforced concrete structures. To achieve the acceptance of this novel composite structures in practical construction and design, it is significantly important to investigate the bond behaviour of FRP reinforced HVFA-SCC. In this study, a series of pull-out tests were carried out to investigate the bond behaviour of HVFA-SCC reinforced by FRP bar, which included bond strength, bond-slip response, and failure mode. The investigated experimental variables were reinforcing materials, surface treatment of FRP bars, bar diameters and concrete materials. The test results revealed that using HVFA-SCC resulted in higher average bond strength compared to those in the normal concrete test specimens. The reinforcing materials (steel vs. GFRP) had strong effect on bond behaviour, including bond strength, bond stiffness and failure mode. The failure mechanism of bond interaction between FRP and HVFA-SCC is dependent on friction and chemical adhesion. Subsequently, theoretical models for bond strength and development length were proposed. Finally, the parameters of analytical models of bond-slip curve are calibrated for GFRP reinforced HVFA-SCC by using the experimental data

Strength Deterioration of Concrete in Sulfate Environment: An Experimental Study and Theoretical Modeling

Sulfate corrosion is one of the most important factors responsible for the performance degradation of concrete materials. In this paper, an accelerated corrosion by a sulfate solution in a dry-wet cycle was introduced to simulate the external sulfate corrosion environment. The deterioration trend of concrete strength and development law of sulfate-induced concrete corrosion depth under sulfate attacks were experimentally studied. The damaged concrete section is simply but reasonably divided into uncorroded and corroded layers and the two layers can be demarcated by the sulfate corrosion depth of concrete. The accelerated corrosion test results indicated that the strength degradation of concrete by sulfate attack had a significant relation with the corrosion depth. Consequently, this paper aims to reveal such relation and thus model the strength degradation law. A large amount of experimental data has finally verified the validity and applicability of the models, and a theoretical basis is thus provided for the strength degradation prediction and the residual life assessment of in-service concrete structures under sulfate attacks

FRP-Confined Recycled Coarse Aggregate Concrete: Experimental Investigation and Model Comparison

The in situ application of recycled aggregate concrete (RAC) is of great significance in environmental protection and construction resources sustainability. However, it has been limited to nonstructural purposes due to its poor mechanical performance. External confinement using steel tubes and fiber-reinforced polymer (FRP) can significantly improve the mechanical performance of RAC and thus the first-ever study on the axial compressive behavior of glass FRP (GFRP)-confined RAC was recently reported. To have a full understanding of FRP-confined RAC, this paper has extended the type of FRP and presents a systematic experimental study on the axial compressive performance of carbon FRP (CFRP)-confined RAC. The mechanical properties of CFRP-confined RAC from the perspective of the failure mode, ultimate strength and strain, and stress–strain relationship responses were analyzed. Integrated with existing experimental data of FRP-confined RAC, the paper compiles a database for the mechanical properties of FRP-confined RAC. Based on the database, the effects of FRP type (i.e., GFRP and CFRP) and the replacement ratio of recycled coarse aggregate were investigated. The results indicated that the stress–stain behavior of FRP-confined RAC depended heavily on the unconfined concrete strength and the FRP confining pressure instead of the replacement ratio. Therefore, this study adopted eleven high-performance ultimate strength and strain models developed for FRP-confined normal aggregate concrete (NAC) to predict the mechanical properties of FRP-confined RAC. All the predictions had good agreement with the test results, which further confirmed similar roles played by FRP confinement in improving the mechanical properties of RAC and improving those of NAC. On this basis, this paper finally recommended a stress–strain relationship model for FRP-confined RAC

Effects of Different Moisture-Permeable Packaging on the Quality of Aging Beef Compared with Wet Aging and Dry Aging

The objective of this study was to investigate the effects of six different aging methods (four types of moisture-permeable packaging, wet aging, and dry aging) and aging time (0, 7, and 14 d) on the quality of aging beef, especially physicochemical properties. The weight loss, aerobic bacterial counts, yeast counts, and mold counts increased with the increase of moisture permeability and aging time. However, shear force, hardness, cohesiveness, and chewiness followed an opposite trend with increasing moisture permeability. The values of L* and b* appeared to decrease in the dry-aged samples compared with those of the others. In addition, water content in dry-aged samples for 7 and 14 d showed a significant decrease. The higher myofibril fragmentation index was observed in dry-aged samples for 7 and 14 d compared with groups using moisture-permeable packaging. Meanwhile, the percentage of bound water and free water appeared to decrease with the increase of moisture permeability. Thus, different moisture-permeable packaging was able to control different levels of water loss and effectively reduce microbial contamination compared with dry aging. The changes of both myofibrillar fragmentation index (MFI) and distribution of water indicated that moisture-permeable packaging affected the structure of myofibrils, which influenced the shear force

Axial stress-strain behaviour of pre-damaged square concrete column repaired with FRP jackets

This paper presents the results of an experimental study on the behaviour of pre-damaged concrete square columns that have been strengthened with carbon fibre-reinforced polymer (CFRP) wrap. Tests were conducted on 46 concrete columns involving variations of corner radius ratio, damage degree, and confinement pressure. The effect of corner radius on the main parameters of stress-strain curve for FRP strengthened pre-damaged specimens, such as compressive strength, strain capacity, initial elastic modulus, was investigated. The test results demonstrated that the efficiency of repairing damaged columns significantly depends on the corner radius ratio, the strength gain after FRP-strengthening decreases as the corner radius ratio reduces. Using those test data, new ultimate strength and ultimate strain model are proposed. The proposed models involved the effect of both corner radius and damage level, showing good agreement with the experimental results

An emergency task autonomous planning method of agile imaging satellite

Abstract As the number of satellite emergency imaging tasks grows, the main goal of satellites becomes putting forward solutions and meeting users’ demands in a relatively short time. This study aims to investigate the problem of emergency task planning for agile satellites. Through the analysis of the problem and its constraints, a model of emergency task autonomous planning was implemented. According to the characteristics of emergency tasks, a strategy to deal with the tasks of different emergency levels and various quantities was proposed. We put forward three algorithms for quick insertion of emergency tasks, i.e., emergency task insertion algorithm (ETIA), general emergency task insertion algorithm (GETIA), and general emergency task planning &insertion algorithm (GETPIA). The experimental result showed that the strategy and algorithms can not only respond quickly to observation tasks but also produce effective planning programs to ensure the successful completion of observation tasks

Experimental study of bond-slip performance of corroded reinforced concrete under cyclic loading

Reinforced concrete structures exposed to marine environment often sustain high levels of chloride-induced reinforcement corrosion, which causes reinforcement corrosion and resulting in degraded performance under cyclic service loading. This article studied the dynamic bond performance between corroded reinforcing and concrete under force controlled loading. Tests were carried out to evaluate the cyclic bond-slip degradation with different reinforcement corrosion levels. A series of 30 specimens with various corrosion levels of rebar and stirrup were made. The specimen was cast as concrete cube with the dimension of 200 mm, and a steel rebar was centrally embedded with two stirrups around. The embedded steel rebar and stirrups were corroded using an electrochemical accelerated corrosion technique. The corrosion crack opening width and length were recorded after completion of artificial corrosion. Then, cyclic loading test was carried out; three different force levels of 24, 36, and 48 kN were adopted. The effects of reinforcement corrosion rate on crack opening, maximum slip, energy dissipation, and unloading stiffness were discussed in detail. It was found that both reinforcement corrosion rate and crack opening would have significant effects on cyclic bond performance. Further studies are urgently needed to quantify these effects to the cyclic bond performance

Axial stress-strain behaviour of pre-damaged square concrete column repaired with FRP jackets

This paper presents the results of an experimental study on the behaviour of pre-damaged concrete square columns that have been strengthened with carbon fibre-reinforced polymer (CFRP) wrap. Tests were conducted on 46 concrete columns involving variations of corner radius ratio, damage degree, and confinement pressure. The effect of corner radius on the main parameters of stress-strain curve for FRP strengthened pre-damaged specimens, such as compressive strength, strain capacity, initial elastic modulus, was investigated. The test results demonstrated that the efficiency of repairing damaged columns significantly depends on the corner radius ratio, the strength gain after FRP-strengthening decreases as the corner radius ratio reduces. Using those test data, new ultimate strength and ultimate strain model are proposed. The proposed models involved the effect of both corner radius and damage level, showing good agreement with the experimental results