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Steel-concrete composite structures are widely adopted in civil engineering attributed to the large span-to-depth ratio, light weight and rapid construction. However, long-term behavior of these structures attacked by environmental agents has not been fully investigated. This study presents an experimental study on monotonic and fatigue behavior of steel-concrete composite beams subjected to corrosion. Ten specimens were prepared using accelerated artificial corrosion and tested under four-point bending with a special focus on the effect of corroded studs. Different failure modes were observed for the specimens tested by static and fatigue loading. Corrosion was demonstrated detrimental effect on both monotonic load-bearing capacity and fatigue life of the specimens. The residual bending stiffness also decreased with corrosion rates.

This study presents an experimental study on the static and fatigue behavior of steel-concrete composite beams subjected to negative bending moment. A total of 10 specimens were tested, with a special focus on the effect of corroded studs. The load-carrying capacity, beam stiffness and fatigue life of specimens having different corrosion rates were evaluated. Test results showed that the specimens subjected to monotonic loading failed by local buckling while fatigue loading led to shear fracture of the studs and crack initiation followed by propagation in the steel beam. Corrosion of shear connectors had a significantly detrimental effect on the load-carrying capacity and stiffness of the composite beams. As the corrosion rate increased, the fatigue life of the beams was dramatically declined by up to 29.69%. The residual bending stiffness and slip stiffness decreased as the fatigue cycles elapsed.

This paper investigates the preparation and assessment of mortar-phase change materials (PCM) systems to gain a full understanding of using the heat stored in PCMs to delay or prevent ice formation in concrete. Desirable PCMs and light weight aggregates (LWA), which act as carriers of the PCMs, were first selected based on their thermal and physical properties. LWAs containing PCMs were prepared and assessed for different combinations of materials. Cyclic freeze-thaw mass loss, latent heat attenuation, and FTIR tests were conducted to characterize the stabilities of the LWA-PCMs. The thermal performances of the mortars containing LWA-PCMs were investigated using a longitudinal guarded comparative calorimeter (LGCC) that was operated under quasi-steady state conditions during the cooling/heating process. The results confirmed that PCMs can be steadily absorbed in LWAs without chemical reactions or great losses in latent heat when the LWA-PCMs were coated in a certain way. Cement paste was recommended to coat the surface of the LWA-PCMs for better compatibility with the system than that of traditional coating materials. The ability of the PCM to delay or prevent ice formation in mortar was verified from the exothermic/endothermic events associated with the phase transformations of the pore solution and PCM. In the present study, when up to 50% vol. of the LWA was replaced as carriers of PCM, the heat released by the PCM was sufficiently high to inhibit ice formation.

This paper investigates damage and healing of cementitious materials based on fly ash (FA) with a special focus on the effect of repeated loading on the self-healing performance. In total, ...

Corrosion and high temperature are two main detrimental factors that degenerate the mechanical properties and lead to decrease both in strength and durability of steel. The combined influence of corrosion and high temperature on the mechanical properties of grade D36 marine steel is proposed in this study. A series of tests were conducted to determine the post-fire mechanical properties of corroded marine steel. Specimens were corroded by a saltspray test, and then heated to 500 °C or 900 °C. Afterward, stress–strain curves, elastic modulus, yield stress and ultimate strength of the specimens were obtained from tensile coupon tests. Three-dimensional laser scanning was used to evaluate the impact of corrosion. The microstructure and fracture morphology analyses were carried out by metallographic microscope and scanning electron microscope (SEM), respectively. It was found that corrosion and high temperature have significant influence not only on the mechanical properties, but also on the microstructures and corresponding fracture morphology of grade D36 marine steel.

This paper presents a numerical study on the stress intensity factor (SIF) and fatigue behavior of carbon fiber-reinforced polymer (CFRP) strengthened steel plates with center inclined cracks under uniaxial tensile fatigue loading. Effects of prestress level in CFRP and initial crack inclination angle were investigated. Results indicated that the CFRP laminates could reduce the mode I SIF and effective SIF range, thereby enhancing the fatigue life of the steel plates. The strengthening was more efficient by using the prestressing technique. It was found that fatigue life was approximate for specimens with an identical crack projection length on the plane perpendicular to the load. This indicated that the effect of the initial crack inclination angle on the fatigue crack propagation life of the steel plate was limited when subjected to a unidirectional load. The findings of this study can be adopted as a reference for the repair of existing metallic structures with inclined cracks.

Steel structures under dynamic loading are prone to fatigue damage and a considerable number of metallic infrastructure in the world are structurally deficient. The fatigue behavior of defected steel beams mechanically retrofitted by different high-strength materials was experimentally studied in this work. The steel beam was I section with an artificial cut at the mid-span and tested under fatigue loading. The specimens were strengthened on the tension flange by carbon fiber reinforced polymer (CFRP) laminate, high strength steel (HSS) plate or SafStrip (SAF) plate. Three mechanical anchorage schemes were designed to test their efficiencies. The fatigue crack propagation was recorded to explore the crack growth rate. Strain gauges were installed on the strengthening material to monitor the strain development. The stress intensity factor (SIF) at the crack front was calculated based on analytical solution and numerical simulation; then, the results were compared with experimental findings. It was demonstrated that the strengthening significantly increased the fatigue life of the beams. The attached strengthening materials not only globally shared a portion of the far-field load on the cracked steel section but also provided a local constraining effect, both of which reduced the crack mouth opening displacement (CMOD) and SIF. The different CMODs resulted from the different retrofitting configurations indicated significant variation in the crack constraining effect caused by various retrofitting systems, which cannot be neglected in analytical modeling.

In recent years, externally bonded carbon fibre–reinforced polymer has been considered an innovative way to strengthen steel structures attributed to its high strength-to-weight ratio, excellent corrosion resistance and fatigue performance. This article presents an experimental and numerical study on the fatigue behaviour of defected steel beams strengthened with carbon fibre–reinforced polymer laminates, with a special focus on the effect of interfacial debonding. Analytical modelling and numerical simulation confirmed that the interfacial debonding had a pronounced effect on carbon fibre–reinforced polymer strain and stress intensity factor at the crack front. After introducing interfacial debonding from experimental findings into the numerical analysis, the fatigue life and crack propagation versus cycle numbers of the specimens compared well with the test results. Based on the current experimental program, specimens with Sikadur 30 were more prone to debonding failure; therefore, Araldite 420 is suggested for strengthening schemes.

This paper presents a numerical study on the fatigue behaviour of edge cracked steel plates strengthened with carbon fibre reinforced polymer (CFRP) laminates based on the boundary element method. The models were first validated by a comparison with experimental data in the literature, followed by a further investigation into the effects of initial damage degree, bond configuration and crack type on the fatigue behaviour of retrofitted specimens. Results indicated that CFRP overlays could effectively slow down crack growth and extend fatigue life of edge cracked steel plates, regardless of the initial damage levels. It seems better to adopt an early repair considering the total fatigue life. Double-sided repair showed significant superiority over single-sided repair when equivalent composite materials were used. For the repair configuration presented herein, the strengthening was more efficient for edge cracked steel plates than centre cracked steel plates.

Corrosion is a major cause of durability deterioration for reinforced concrete (RC) structures. This paper investigated the random evolution process of corrosion in steel bars under a constant corrosion current density. A probabilistic prediction model was developed combining a continuous-time Markov chain model with the Faraday law. The model parameter, state interval, which represents the difference between the actual adjacent corrosion depths, was calibrated by test data and statistically studied. Markov model predicted results showed that the corrosion depth followed the Poisson distribution while the longitudinal nonuniformity factor of corroded steel bars R, which was defined as the ratio of the average cross-sectional area to the minimum one, followed the Gumbel distribution. The probability distribution parameters of the factor R were determined by Monte-Carlo simulation. The corrosion depth and the factor R predicted by the Markov model agreed well with the experimental data.

The multiple damaging and healing of cracks in cement paste by microcapsules was experimentally investigated under various flexural loading scenarios. The crack formation in the loading process was detected in situ using the acoustic emission (AE) technique, in which passive and active sensing modes were combined to provide complementary information on the overall damage and local cracking. The AE analysis was conducted based on the differentiated features of the signals in terms of the temporal and spectral descriptors to distinguish the cracking mechanisms. The results indicate the alleviated damage of the specimens due to healing of cracks based on the active sensing mode. The time-dependent hits and cumulative energy demonstrate new cracking sources in the healing specimens. The changes in the variation of hits (versus amplitude) and the AE energy (versus duration time) reveal that the new cracking sources were the failure of the pre-attached crack space by the adhesive according to the calibration. The distinguished characteristics of the maximum frequency of the waveforms provide further insights into the cracking mechanisms of matrix and interface. The plot of the average frequency (AF) versus the RA index illustrates that the cracking modes contribute to the characteristic spectrum.

The bending fatigue test results on cracked rectangular hollow section (RHS) steel beams repaired with prestressed carbon fiber-reinforced polymer (CFRP) plates are presented. The steel bea...

This paper presents a numerical simulation on the collapse behavior and structural stability of a reinforced concrete superlarge cooling tower subjected to strong winds. Results demonstrate...

This paper presents a numerical simulation and theoretical analysis on the collapse behavior of a reinforced concrete super-large cooling tower induced by failure of columns. The finite-ele...

This paper presents an experimental study on the fatigue behavior of cracked steel beams strengthened using different patch systems and high-strength materials. These materials included normal modulus carbon fiber–reinforced polymer (CFRP) laminate, high-strength steel (HSS) plate, and SafStrip (SAF) plate. Adhesive bonding and mechanical anchorage were selected to attach these overlays. A digital image correlation (DIC) system was adopted to detect stress distribution at the vicinity of the crack front. Different failure modes were observed for specimens with different retrofitting schemes. Test results showed that, in comparison with control specimens without strengthening, application of these retrofitting materials significantly retarded crack propagation and extended fatigue life of defected steel beams. The stiffness decay and crack mouth opening displacement (CMOD) were also reduced in repaired cases. Based on the fatigue cycles when the crack propagated to half-height of the steel beam, CF...

Recent studies on the application of carbon fibre reinforced polymer (CFRP) materials to defected steel structures have demonstrated the potential for significant reduction of stress intensity factor (SIF) values at crack tips leading to extended fatigue lives. However, most of the previous research relied on experimental and numerical methods, which were either expensive or time-consuming. In this paper, the SIF values at crack tips of steel plates strengthened with bonded composite materials were evaluated using linear elastic fracture mechanics. The analysis was based on the classical solution of SIF values of plain steel plates, considering load share effect and geometry correction factor change resulted from the overlay patch. The effect of different parameters were demonstrated and compared with experimental results, including initial damage degrees of specimens, geometric and mechanical properties of retrofitting materials and bond locations. Good agreement with the experimental data indicated that this approach could conservatively predict the SIF values with reasonable accuracy. A parametric study on variables including the CFRP modulus, the bond width and bond length was conducted based on this method to further investigate their effect on the SIF values.

Although carbon fibre reinforced polymer (CFRP) materials have proven effective in strengthening steel structures especially when used to improve fatigue behaviour, further study is required to investigate their effectiveness when applied at different stages of crack propagation in steel elements. This paper presents a numerical study on CFRP retrofitted steel plates with different degrees of damage using the boundary element method (BEM). The numerical results compared well with the experimental data, which demonstrated that the BEM is reliable for crack propagation analysis of CFRP laminate retrofitted steel plates. Finally, a parametric analysis was conducted to investigate the influence of bond length, bond width, CFRP stiffness and adhesive shear modulus on stress intensity factor (SIF) values.

An experimental and analytical study was conducted to further investigate the effectiveness of the carbon fibre reinforced polymer (CFRP) plates in extending fatigue life of steel structures. Different lengths of artificial cracks were introduced to represent different degrees of fatigue damage. The experimental results demonstrated that the CFRP patches could effectively slow down the crack growth and prolong the fatigue life. A theoretical model was developed to predict the fatigue life of tested specimens. Thereafter, a parametric study was carried out to investigate the fatigue behaviour of steel plates with a wider range of damage degrees. This study extends the understanding of CFRP repair at different stages of crack propagation and provides some useful suggestions for the strengthening method.

This paper reports an experimental study on the use of carbon fiber-reinforced polymer (CFRP) sheets to strengthen non-load-carrying cruciform welded joints subjected to fatigue loading. Failure modes and corresponding fatigue lives were recorded during tests. Scatter of test results was observed. Thereafter, a series of numerical analyses were performed to study the effects of weld toe radius, the number of CFRP layers and Young's modulus of reinforced materials on local stress concentration at a weld toe. It was found that fatigue life of such welded connections can be enhanced because of the reduction of stress concentration caused by CFRP strengthening. Parametric study indicates that the weld toe radius and the amount of CFRP are the key parameters influencing the stress concentration factors and stress ranges of the joint. Enhancement of modulus for adhesive and CFRP sheets can also be beneficial to the fatigue performance to some extent.

In this paper, steel plates with longitudinal weld attachments strengthened by carbon fiber reinforced polymer (CFRP) laminates on one side were analyzed based on the boundary element method and compared with test data from the literature. Good agreement with the data indicated that the numerical analysis was reliable for estimation of the fatigue crack propagation of CFRP-bonded steel plates with longitudinal weld attachments. The effects of double-sided strengthening, double-sided weld attachment and CFRP stiffness on the fatigue behavior of retrofitted welded joints were also investigated. The results showed that double-sided strengthening was much more efficient than single-sided application. It was observed that the crack propagation of steel plates with weld attachments on both sides was accelerated compared with those with attachments on only one side. In comparison with steel plates without a weld attachment, the retrofitting efficiency, in terms of the fatigue life extension ratio, was si...

Strengthening steel structures using carbon fiber reinforced polymer (CFRP) materials has attracted much attention in recent years owing to their potential for fatigue crack repair and their convenience in construction. However, little is known about the efficiency of this strengthening method when applied to steel plates at different crack propagation stages. An experimental study was carried out on notched steel plates strengthened using CFRP laminates. 20 specimens were tested to evaluate the fatigue performance of the strengthened steel plates with emphasis on various degrees of initial damage, simulated by different lengths of slots, including 2%, 10%, 20%, 30% and 40% of the plate width. The effects of the retrofitted configuration and CFRP stiffness were also investigated. The "beach marking" technique and crack propagation gauges were adopted to monitor the fatigue crack propagation. The experimental results were very encouraging, demonstrating that the CFRP patches could effectively slow crack growth and extend fatigue life, regardless of the initial damage levels. More effective strengthening was found by using ultra-high modulus CFRP laminates, covering the initial cracks with CFRP and repairing at an earlier stage (i.e. smaller damage level).