Concrete Structures In Civil Engineering Research Articles

Calculation of the mechanical properties of high‐performance concrete employing hybrid and ensemble‐hybrid techniques

AbstractThis study aims to execute machine learning methods to predict the mechanical properties containing TS and CS of HPC. They are essential parameters for the durability, workability, and efficiency of concrete structures in civil engineering. In this regard, obtaining the estimation of the mechanical properties of HPC is complex energy and time‐consuming. Due to this, an observed database was compiled, including 168 datasets for CS and 120 for TS. This database trained and validated two machine learning models: SVR and RT. The models combine the prediction outputs from the meta‐heuristic algorithms to build hybrid and ensemble‐hybrid models, which include dwarf mongoose optimization, PPSO, and moth flame optimization. According to the observed outputs, the ensemble models have great potential to be a recourse to deal with the overfitting problem of civil engineering, thus leading to the development of more supportable and less polluting concrete structures. This research significantly improves the efficiency and accuracy of predicting vital mechanical properties in high‐performance concrete by integrating machine learning and metaheuristic algorithms, offering promising avenues for enhanced concrete structure design and development.

Probabilistic calibration of environmental reduction and partial safety factors for the design of reinforced concrete beams strengthened by flax fibre reinforced polymers based on two-factor accelerated degradation tests

The main topic of this article is the probabilistic-based calibration of environmental reduction and safety coefficients for the design of reinforced concrete civil engineering structures repaired or strengthened by externally bonded flax fibre reinforced polymers (FRP). In view of the poor feedback on the durability of flax fibre composite materials used in civil engineering and the impossibility of conducting performance tests over several years, a two-factor accelerated test campaign based on the stimulation of composite degradation by increasing both temperature and humidity conditions was conducted. Flax-FRP (with a bio-based epoxy matrix) laminates and Flax-FRP-strengthened concrete slabs have been exposed over a period of two years to various couplings of temperature (from 20 °C to 60 °C) and humidity (from 50 % of relative humidity to water immersion), according to an asymmetrical Hoke design of experiments. Similar specimens were also exposed to outdoor natural ageing (climate of Lyon, FR) over a period of three years. Series of tests (more than 320 tests) aimed at monitoring the evolution of the degradation of mechanical characteristics (tensile capacity, tensile stiffness, shear strength, pull-off strength) directly associated with the possible modes of failure of structural elements repaired by composites, were carried out on control and aged specimens. A degradation model of these mechanical characteristics considering the competition of two mechanisms - inducing non-monotonic degradation-, and the influence of the temperature and the humidity - through the Eyring model -, was then developed and finally extended to consider the variability of the degradation under different climatic zones. On this basis, a reliability-based approach was adopted to propose environmental reduction and safety coefficients calibrated for Flax-FRP found within four international design guides (Fib bulletin 40, ACI-440, AFGC and TR55 guides). Finally, we showed the necessity to provide adaptable coefficients according to the climatic conditions in which the Flax-FRP elements will be installed.

Autonomous Wireless Sensors Network for the Implementation of a Cyber-Physical System Monitoring Reinforced Concrete Civil Engineering Structures

This paper presents an autonomous Wireless Sensors Network as the hardware basis for implementing a Cyber-Physical System. The Wireless Sensors Network is composed of Sensing Nodes and Communicating Nodes. The Sensing Nodes can wirelessly transmit data measured in reinforced concrete using Non-Destructive Testing methods over several tens of meters. These are battery-free, and are powered and controlled wirelessly and remotely by a radiative electromagnetic Wireless Power Transfer system tuned by the Communicating Nodes. Each Communicating Node covers a volume of at least 11 meters in all directions for the Wireless Power Transfer. The Wireless Sensors Network meets the requirements of the Simultaneous Wireless Information and Power Transmission paradigm by using a single antenna in the Sensing Nodes (concurrently for power harvesting and data transmission). The proposed system is designed for the Structural Health Monitoring of reinforced concrete civil engineering structures, but can be adapted to other applications, especially in harsh environments.

Hygrothermal resistance of pultruded carbon, glass and carbon/glass hybrid fiber reinforced epoxy composites

The hygrothermal resistance of pultruded fiber reinforced polymer (FRP) composites is the key concern when applying in the reinforcement or strengthening of concrete structures in civil engineering. In the present study, the hygrothermal properties of pultruded carbon, glass and carbon/glass hybrid fiber reinforced polymer (CFRP, GFRP, C/GFRP) composite plates were investigated experimentally through the immersion in deionized water at 40 °C, 60 °C and 80 °C as long as 135 days. Water absorption, thermal properties, mechanical properties and microstructure analysis were conducted to evaluate the long-term hygrothermal evolution. It was found that the water absorption response of three kinds of composite plates represented the initial Fick’s diffusion response and a followed long-term deterioration response. Immersed in deionized water led to an obvious degradation of thermal and mechanical properties up to 29.5% for short beam shear strength (SBSS) of C/GFRP, 25.8% for three point bending strength (TPBS) of GFRP and 43.1% for glass transition temperature (Tg) of C/GFRP, respectively. The diffusion of water molecule in the plate brought about the reversible effect of resin plasticization and irreversible effect of resin relaxation. Furthermore, the irreversible interface debonding of fiber/resin aggravated the degradation of SBSS. Based on the Arrhenius accelerating theory, the long-term life of SBSS decreased to stable level of 87.90% (CFRP), 76.64% (GFRP) and 72.43% (C/GFRP), respectively. Meanwhile, the stable retentions of TPBS were 85.99% (CFRP), 77.32% (GFRP) and 81.40% (C/GFRP), respectively.

Experimental Investigation on Effective Distances of Acoustic Emission in Concrete Structures

As one of the non-destructive testing (NDT) methods, acoustic emission (AE) can be widely applied to the field of engineering and applied science owing to its advantageous characteristics. In particular, the AE method is effectively applied to monitor concrete structures in civil engineering. For this technology to be employed in a monitoring system, it is necessary to investigate the propagation characteristics of the AE in structures. Hence, this study investigates the characteristics of AE in concrete structures to evaluate the field applicability of AE monitoring systems. To achieve this goal, experiments employing an AE system are conducted for concrete structures 20 × 0.2 × 1.2 m in length, width, and height, respectively, to explore the AE parameters according to the impact energy. Among all AE parameters, absolute energy is determined to be most sensitive factor with respect to the impact energy. In addition, the attenuation effect of the AE wave is quantitatively evaluated according to the wave propagation distance. Moreover, the concept of effective distance is newly suggested based on the experimental results. The effective distance is shown to increase as the impact energy increases, although the increased effective distance is limited because the damaged AE signal is of high frequency. This study helps improve the field applicability of AE monitoring systems by suggesting suitable AE sensor spacing, which contributes to promote the practice of technology.

A Review on Inspection and Maintenance of FRP Structures

FRP is extensively used today in all domains like concrete structures in Civil engineering, spacecraft in Aerospace Industry. It is also used in elevator and bridge cables. Although FRP has some remarkable properties, it undergoes fatigue and damage and sometimes, undetectable defects are formed. Defects like de-lamination or voids occur due to manufacturing errors, or exposure to external environmental factors can result in BVID. Thus, FRP structures have to undergo inspection to ensure its continued use and safety. The inspection and maintenance methods most commonly employed in FRP structures are NDT or Non-Destructive Testing and CM or Condition Monitoring. The integral part of both, NDT and CM is SHM. NDT is a type of inspection method wherein the sample is tested without damaging it whatsoever. NDT is commonly used for reasons such as low cost, high reliability. The techniques involving NDT are Acoustic Emission Testing, Thermography, Ultrasonic Testing, Eddy-Current testing, Radiography. This paper discusses and reviews the various types of Inspection Techniques in NDT and SHM.

Reverse time migration of acoustic waves for imaging based defects detection for concrete and CFST structures

Abstract Ultrasonic non-destructive testing (NDT) technology has been widely used for defect inspection of concrete structures in civil engineering. However, most of the current data processing methods can only provide qualitative information regarding the existence of concrete inner defects. In this study, an ultrasonic inner defects inspection approach with a high-resolution imaging method which combines travel time tomography (TTT) and reverse time migration (RTM) is proposed for concrete and concrete-filled steel tube (CFST) columns. TTT estimates a reasonable distribution of ultrasonic velocity over the cross-section of the concrete and CFST columns from the first arrival time of the ultrasonic transmission signal. The velocity distribution is used as an input of the initial model for RTM to image the defects inside the concrete and CFST column cross-sections with a high resolution. Numerical experiments demonstrate that the air cavity inside the concrete and CFST columns, and the debonding between the concrete core and the steel tube of the CFST column can be identified clearly, and that the location, size and shape of both defects can be determined accurately. It is concluded that the proposed defect detection approach with a high-resolution imaging method is efficient for the non-destructive inspection of concrete and CFST structures using ultrasonic waves.

Reliability Analysis of Bond Behaviour of CFRP–Concrete Interface under Wet–Dry Cycles

Effective bonding between adherents plays a key role in retrofitting concrete structures in civil engineering using fibre-reinforced polymers (FRPs). To ensure structural safety, it is critical to develop design codes, which account for uncertainties of materials, the environment, and load, to estimate bond behaviour under long-term exposure to harsh environments. Therefore, a reliability analysis was performed to study the bond behaviour of FRP–concrete interface under wet–dry cycles and sustained loading. Thirty double-lap, shear-bonded carbon FRP (CFRP)–concrete composite specimens were tested after wet–dry cycles and sustained loading exposure. The fracture energy Gf of the bond behavior between CFRP and concrete was directly obtained from the measured local bond-slip curves. Five widely used test methods were adopted to verify the possible distribution types of Gf. Based on the best fit distribution of Gf, a reliability index β was then calculated for the specimens. The effects of wet–dry exposure and sustained loading on β were analysed separately. The effects of the mean and standard deviation of the load on β were compared. It was found that the mean had a greater impact on reliability than the standard deviation, but neither changed the regulation of the exponential reduction of β with increasing wet–dry cycle time. Their impact was significant for a small number of wet–dry cycles but insignificant for more than 4000 wet–dry cycles.

Effect of sustained load and seawater and sea sand concrete environment on durability of basalt- and glass-fibre reinforced polymer (B/GFRP) bars

Recently, in responding to the resource shortage and steel corrosion, the combination of seawater and sea sand concrete (SWSSC) and fibre reinforced polymer (FRP) bars was proposed to replace the traditional reinforced concrete structures in civil engineering. For FRP bars in the real service condition of concrete structure, the synergistic effect of sustained load and corrosion environment needs to be considered. This paper presents an investigation on the durability of basalt- and glass-fibre reinforced polymer bars exposed to a SWSSC environment under different sustained stress levels. Scanning electron microscopy was employed to study the degradation mechanism of FRP bars.

Hydrogen-Assisted Micro-Damage in Cold-Drawn Pearlitic Steels: Resembling Donatello Wooden Sculpture Texture

This paper deals with hydrogen embrittlement of cold-drawn pearlitic steel wires to be used in prestressed concrete structures in civil engineering. Special attention is given to the micro-level of hydrogen degradation, i.e, the hydrogen-assisted micro-damage (HAMD) that takes place in pearlitic steels in the form of the so-called tearing topography surface (TTS). It is shown that the appearance of this special topography evolves with the degree of cold drawing in the steels (level of cumulative plastic strain undergone by the wires) from standard TTS in hot rolled pearlitic steels (not cold-drawn at all) to a special hydrogen damage topography (HDT) consisting of a sort of enlarged and oriented TTS in heavily cold-drawn pearlitic steels (prestressing steel wires), thereby resembling Donatello wooden sculpture texture (DWST).

Development of a mechanical strain amplifying transducer with Bragg grating sensor for low-amplitude strain sensing

Vibration-based damage identification is a well-known method to support health monitoring of civil engineering structures. Damage in such structures can be identified by measuring changes of the natural frequencies, damping factors or modal displacements of the structure. However, this approach suffers from the low sensitivity of these natural frequencies and modal displacements to certain types of damage. Modal strains and curvatures can be more sensitive to local damage, but direct monitoring of these quantities with sufficient spatial resolution is not possible with current measurement techniques due to the very small strain levels (sub-microstrain) caused by ambient or operational excitation. To deal with this issue, we propose a novel mechanical transducer equipped with an optical fiber Bragg grating (FBG) sensor that enhances the sensitivity to strain with a factor larger than 30. The principle of operation of the transducer exploits a symmetric cantilever structure that enlarges the strain experienced by the FBG sensor compared to the strain applied to the transducer itself. We carried out dynamic and static tests to verify the ability of the strain-amplifying transducers to measure small-amplitude strain levels and to evidence the potential for carrying out FBG based modal strain measurements on concrete civil engineering structures.

МЕТОДИКА РАСЧЕТА НА ПРОЧНОСТЬ НОРМАЛЬНЫХ СЕЧЕНИЙ ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ ГИДРОТЕХНИЧЕСКИХ СООРУЖЕНИЙ, УСИЛЕННЫХ ВНЕШНИМ АРМИРОВАНИЕМ НА ОСНОВЕ УГЛЕРОДНЫХ МАТЕРИАЛОВ

The way to strengthen concrete structures in civil engineering by adding external reinforcement using carbon fiber composites is widely spreading in recent years. A method for calculating the strength of reinforced concrete in hydro technical constructions with reinforcing by carbon fiber composite materials was invented with the aim to justify the solutions of strengthening concrete structures. It was taken into consideration that the characteristic features of mass reinforced concrete structure with sand operating loads which including backpressure of water in the cracks and in opened construction joints. It has evolved the relations for calculation of strength in normal cross section of bending reinforced concrete member of hydro technical constructions which strengthening with external reinforcement by carbon fiber.

Application of Nonlinear Model Updating for a Reinforced Concrete Shear Wall

The detection of changes in vibrational behavior has long been applied as a potential means of damage detection. However, existing damage diagnosis techniques are primarily limited to linear models in which the stiffness of some of the elements is reduced to represent damage. Although these methods appear to be adequate for locating and quantifying the present damage in the structure, they are not sufficient for determining future performance of the structure, which can only be determined using nonlinear models. This paper focuses on the challenging task of updating nonlinear models for reinforced concrete civil engineering structures. A nonlinear hysteretic material model is applied to accurately portray the fundamental hysteretic behavior of concrete structures. A systematic methodology to perform damage detection and, more importantly, update the nonlinear model for prediction is proposed. This new method is designed to use low-level ambient vibration data to detect changes in the modal parameters. With the acquired modal information, the damage parameters that control the nonlinear material model are updated. The final updated nonlinear model may be utilized not only to evaluate the structure’s current damage state but also to predict its future behavior. A concrete shear wall is analyzed numerically to demonstrate the proposed method.

Dynamic properties of concrete under severe environmental condition

Exposure to environmental conditions can significantly influence the mechanical behavior of concrete structures in civil engineering. In this study, the effect of environmental factors, such as moisture and temperature, on the strain-rate sensitivity of concrete mixtures was systematically investigated. The strain rate varied from 10−5s−1 to 10−2s−1. From the investigation it was concluded that moisture content had a significant influence on the strain-rate sensitivity of concrete. With regard to concrete with low moisture content, temperature had little influence on the rate-dependent behavior; while for fully saturated specimens, a significant influence was observed. These phenomena were attributed to the meso-scale bonding properties of the concrete matrix. Equations were derived to characterize the ultimate strength increment of concrete with strain rate under different environmental conditions. An explanation to the dynamic failure mechanisms of concrete based on the experimental findings was proposed.

Ductility components and limits of FRP-plated RC structures

The structural design of the vast majority of reinforced concrete civil engineering structures relies on the inherent ductility of the members to accommodate changes in load patterns, to absorb energy and to give prior warning of failure. It is such an important fundamental behaviour and requirement, that it simply cannot be ignored in practice without a quantum change in the existing design procedures. The quantifiable ductility of unplated reinforced concrete members is based on the ultimate rotation at concrete crushing failure; this proviso cannot be applied to FRP-plated RC members as the FRP may fracture or debond prior to concrete crushing. Hence, the necessity to quantify or model the ductility of a member at all stages from the initial loading to the end failure is the subject of this paper.

Electrical resistivity measurement applied to cracking assessment on reinforced concrete structures in civil engineering

Non-destructive evaluation appears more and more important in the civil engineering economic stakes. In this context electrical resistivity measurements get sensitivity to parameters allowing to assess concrete structures conditions. This article analyses the ability of the resistivity measurement to study cracks in concrete. Its ability to detect and to locate cracks and spalling is shown with on site measurements on a damaged slab. Then specific studies on such disorders allow to distinguish the influence of their characteristics. The sensitivity of the method to cracks depth, according their moisture conditions, is assessed by computation. Experimental works on a reinforced concrete beam, ideally cracked, confirmed these results. Some assumptions based on measurements realised on a size-one structural component allow to assess the general influence of crack opening and bridging degree between crack lips. Qualitative results show the similar effects on measurement of various cracking parameters. Prospective works presented in the paper lead us to say that electrical resistivity method applied to civil engineering structures is a relevant tool for the assessment of structural damage.

General recommendation for loading tests of load-bearing structuresin situ

This provisional recommendation outlines the main principles of static load tests and long-term observations which must be conducted in-situ on monolithic or precast load bearing structures, on structural parts, on buildings or concrete, reinforced concrete, precast concrete civil engineering structures, whatever shape and whatever use. Additional guidelines are appended for loading tests of structures of special shape, use or aim. The objective of the tests is to obtain a practical knowledge of the real behaviour, bearing capacity, safety, deformation and failure of load bearing structures and their structural members. This recommendation was agreed upon at the meeting of the committee for in-situ structural tests (number 20 tbs) which was held in Liege, 1st to 3rd June 1975. /TRRL/