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Due to the unavoidable stress concentrations and welding defects, the trapezoidal rib-to-deck welded joints of Orthotropic Steel Bridge Decks (OSBD) are prone to fatigue cracking. It is a new exploration to apply Carbon Fiber Reinforced Polymer (CFRP) sheets to strengthen the complex welded joints to improve the fatigue strength. In this paper, the comparative tests of un-strengthened and CFRP strengthened welded joints were carried out. The hot spot stress distribution under static load and fatigue behavior under cyclic load were studied, considering the influence of the number of CFRP sheet layers. The experimental results indicate that CFRP reinforcement can effectively reduce the stress concentrations at weld toe of the deck, and three-layers reinforcement has a greater effect than one-layer reinforcement. There was no significant difference in failure modes between the un-strengthened and CFRP strengthened welded joints. The fatigue cracks of all joints originated from weld toe of the deck, and then expanded along the width and thickness of the deck which caused the deck to break. CFRP reinforcement can significantly improve the fatigue life of trapezoidal rib-to-deck welded joints under the same nominal stress range and three-layers reinforcement presented a longer fatigue life. The S-N curve [Formula: see text] based on the hot spot stress range at weld toe of the deck was established, which can be applied to the fatigue strength design of un-strengthened and CFRP strengthened rib-to-deck welded joints. The mechanism that CFRP reinforcement can significantly improve the fatigue performance of welded joints can be concluded to less stress concentrations and slower growth rate of the crack. more...

Plantation softwood timber poles are associated with low natural durability, and it is also not clear what the effects of the high humidity environment on the long-term performance of composite action integrity of such a system. This paper presents a durability study for the proposed composite poles using (GFRP) glass fiber-reinforced polymer as a confinement system on wooden poles sourced from plantation softwood timber. Radiata pine poles of 6 m length were wrapped with multiple layers of 0°/90° woven roving biaxial E-glass fiber sheets through a wet layup process as confinement. The prepared GFRP softwood poles were then subjected to high humidity environmental conditions of up to 95 ± 2% relative humidity and 22 ± 2 °C temperature for a period of 30 months. Various lengths of confinement were considered in this study ranging from 0% to 70% of the span length. The poles had a span length of 5.4 m and were tested using a three-point bending test. Results showed that the proposed confinement system of GFRP-softwood provided a satisfactory long-term performance and the high humidity environment did not greatly affect the improvement in the mechanical performance that the GFRP system provided. more...

This paper presents the experimental results from nine full-scale concrete-filled double-skin tubular (CFDST) beam-columns. The test specimens exploited two fabrication strategies, featuring either hollow steel inner skins with corrugated geometry or ultrahigh-strength steel corner tubes to enhance the seismic performance of noncompact CFDST beam-columns for potential use in low-to-moderate seismicity regions. The effects of loading sequence, axial load ratio, and cross-sectional geometry were investigated. The experimental results suggested that the current AISC specification may be used to predict the axial strength of composite members with a relatively good accuracy. In the postbuckling range, conventional CFDST beam-columns and those with corrugated inner skins are prone to fracture at the corner welds of the built-up cross section. However, the latter exhibited up to two times larger drift capacities than conventional CFDST counterparts prior to losing axial load carrying capacity. Noncompact beam-columns retrofitted with ultrahigh-strength steel corner tubes exhibited a 4% lateral drift demand without experiencing more than 25% flexural strength loss. The presence of ultrahigh-strength steel increases the plastic hinge length of CFDST beam-columns by up to four times relative to CFDST beam-columns with corrugated inner skin, regardless of the employed loading history. more...

Objective This study explored the effects of sevoflurane exposure during different stages of pregnancy on the brain development of offspring. Methods Thirty-six pregnant SD rats were randomly divided into 4 groups: control, sevoflurane exposure in early (S1) pregnancy, sevoflurane exposure in middle (S2) pregnancy, and sevoflurane exposure in late (S3) pregnancy. After natural birth, the learning and memory capacity of offspring rats was analyzed using the Morris water maze experiment. The hippocampi of offspring rats were collected. The levels of interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in the hippocampus were measured by ELISA. Additionally, the Nissl bodies in the hippocampus were analyzed using Nissl staining. Immunohistochemistry was used to examine the expression of BDNF and CPEB2 in the hippocampus of offspring. Proteins related to the NR4A1/NF-κB pathway were analyzed using western blotting. Results The memory and learning capacity of offspring rats was significantly reduced in the S1 and S2 groups compared to the control group (p p > 0.05). The level of IL-1β was significantly increased (p p p p Conclusions The neurotoxic effect of maternal sevoflurane anesthesia on the brain development of offspring is higher when the exposure occurs in early pregnancy than in late pregnancy, and its mechanism might involve the NR4A1/NF-κB pathway to increase the secretion of inflammatory cytokines. more...

This article proposes a new type of basalt fiber–reinforced polymer (BFRP) bar–reinforced seawater sea sand glass aggregate concrete (SSGC) beam with broad application prospects in ocean engineering. Crushed tempered glasses were utilized as coarse aggregates in the concrete mixture to realize the efficient and harmless recycling of waste glass. First, the bond behaviors between the BFRP bars and SSGC with different glass aggregate replacement ratios were investigated. Then, four-point bending tests were conducted to investigate the flexural performance of the SSGC beams completely reinforced with BFRP bars. Based on this, the tested flexural strengths were compared with the calculated strengths to evaluate whether the existing specifications were still applicable to the design of the BFRP bar–reinforced SSGC beams. Test results showed that although the compressive strength of the SSGC gradually decreased with increased glass aggregate content, the bond performance between BFRP bars and SSGC did not follow the same degradation pattern. There were no obvious differences in the form of the bond–slip curves between BFRP bars and different types of SSGC. With increasing glass aggregate content, the ultimate bearing capacity and energy consumption of BFRP bar–reinforced SSGC beams decreased. All calculated ultimate flexural capacities were higher than the experimental values, which shows that the application of existing specifications to BFRP bar–reinforced SSGC beams needs to be studied further. more...

Pre-stressed unbonded retrofit (PUR) CFRP strengthening of steel structures is becoming a common method of strengthening metallic structures. This paper presents a comprehensive study on the use of... more...

Circular hollow steel (CHS) members have been regarded as structural elements of choice for use in civil infrastructure. Despite the risk of seismic damage of steel structures during an earthquake due to its cyclic characteristics, studies on the cyclic strengthening of CHSs have been minimal. In the present study, a new finite element (FE) modelling approach is developed and applied to study the cyclic performance of carbon fibre reinforced polymer (CFRP) strengthened CHS specimens. The modelling techniques are first validated using results from the authors’ previous experimental work. A detailed parametric study is then carried out to evaluate the effects of CFRP bond length, CFRP layer numbers, ratio of thickness of CFRP to thickness of CHS, CHS member diameter-to-thickness ratio and steel grade on the cyclic performance of the CFRP strengthened CHS members. Results confirm the significant effects of these parameters on the cyclic performance of CFRP strengthened CHS members. The efficiency of CFRP strengthening increases with an increase in the ratio of the thickness of CFRP to the thickness of CHS and also with an increase in the diameter-to-thickness ratio of CHS specimens. Conversely, the efficiency of CFRP strengthening reduces with an increase in the steel grade. Moreover, the ultimate moment capacities obtained from the FE analyses of the bare and CFRP strengthened CHS specimens agree reasonably well with the theoretically predicted values. more...

This article presents an investigation on the durability of different glass-fibre-reinforced polymer composites when subjected to harsh outdoor conditions, including freeze/thaw cycles, ultraviolet radiation and moisture, as well as when used with seawater sea-sand concrete for construction applications. To achieve this, the effects of a number of parameters, including the environment of exposure, exposure time, profile cross-sectional configuration and orientation of fibres, on the mechanical properties of different glass-fibre-reinforced polymer composites were studied. To investigate the degradation of the mechanical properties, three-point bending, compression and tension tests were conducted on both reference and conditioned samples. Moreover, scanning electron microscopy analyses were performed to examine the contribution of microstructural deterioration to the damage mechanisms of the conditioned composites. Finally, the test results were used to develop empirical regression models to predict the level of retention of mechanical properties of different composites under different environmental conditions. The findings showed the maximum flexural, compressive and tensile strength reductions to be 35%, 48% and 37%, respectively, with regards to the pultruded profiles exposed for 3000 h to freeze/thaw cycles followed by 90 days of seawater sea-sand concrete immersion, while the flexural strength reductions recorded for the vacuum-infused samples subjected to 2000 h of freeze/thaw cycles followed by 90 days of seawater sea-sand concrete immersion were 28%, 72% and 56% for the unidirectional, woven and chopped strand mat laminates, respectively. more...

This article presents an experimental investigation on the durability behaviour of seawater sea sand concrete and seawater sea sand concrete–filled fibre-reinforced polymer/stainless steel tubular stub columns. Effects of NaCl of seawater on the strength of seawater sea sand concrete and on the deterioration of fibre-reinforced polymer were studied. Accelerated degradation tests were conducted on fibre-reinforced polymer rings exposed to a combined environment of 3.5% NaCl solution and seawater sea sand concrete. Obvious hoop strength reductions were observed in glass fibre-reinforced polymer and basalt fibre-reinforced polymer rings after 6-month exposure at 60°C. Seawater sea sand concrete–filled glass fibre-reinforced polymer tubular stub columns were exposed to an indoor environment (i.e. aged in air at room temperature) for a maximum duration of 2.5 years and no degradation was found by comparing the axial compressive test results from unexposed and exposed specimens. Seawater sea sand concrete–filled stainless steel tubes did not show any deterioration in strength after a 2.5-year exposure to an indoor environment or a 1.5-year immersion in NaCl solution. This study indicated that a hydrothermal environment (e.g. full immersion in solution) is much more aggressive to fibre-reinforced polymer than a dry environment. The reliability of using accelerated degradation test data to estimate the long-term performance of fibre-reinforced polymer–related structures in a real environment may need further research. more...

Rectangular hollow section (RHS) steel members are commonly utilized in various mechanical and civil engineering applications, but they have shown to be quite vulnerable under cyclic loading. In both onshore and offshore infrastructure, steel members can be subjected to cyclic loading produced by earthquakes, currents, wind and waves. Considering multiple factors, such as design errors, the influence of environmental conditions, an increase in applied loads and material deterioration, steel members may require strengthening to withstand cyclic loadings. This study presents numerical simulations using Finite Element (FE) modelling techniques to analyse carbon fibre reinforced polymer (CFRP) strengthened RHS steel members subjected to cyclic loading to predict their behaviour and modes of failure. The predicted results are compared with available results from experimental tests to validate the numerical models and ensure their accuracy. Results imply that CFRP strengthened RHS steel members demonstrate enhanced cyclic performance in which the moment-rotation hysteresis behaviour, secant stiffness and the energy dissipating capacity are improved compared those in bare steel RHS members. Furthermore, the effects of section thickness, bond length of CFRP, number of CFRP layers, wrapping orientation of CFRP and elastic modulus of CFRP on the response of these structural members are also investigated through detailed parametric studies. more...

High-strength steel (HSS) has been increasingly applied in structural engineering, while the work on residual stress of HSS sections is still insufficient. Limited research is available for welded H-sections above 690 MPa while with a plate thickness of more than 10 mm. This paper deals with the residual stress distributions of welded H-sections with flame-cut edges, which are fabricated from HSS plates with yield strength of 690 MPa and 960 MPa and thickness of 10 mm–20 mm, using both experimental and numerical method. The experiments showed that the welded tensile residual stresses in the weld region are not significantly affected by sectional dimensions and steel grade. Verified by comparing with the experimental results, three-dimensional (3D) finite element (FE) models using sequentially coupled thermal-stress analysis was adopted for parametric study of compressive residual stress of welded H-sections made of 690 MPa HSS. The results showed that the compressive tensile stress is negatively correlated with plate thickness as well as width-thickness ratio. Through regression analysis, formulae were proposed for estimation of compressive residual stress in the flange and web, respectively. Finally, residual stress distribution model was developed, which was proved effective by comparing with the experimental and FE results. more...

In the present study, a strengthening design approach is proposed for the mixed mode I/II fatigue crack arrest in existing structural steel members using prestressed unbonded carbon fiber reinforced polymer (CFRP) composites. Through the analytical formulation of mode I and II stress intensity factor ranges, a design model is proposed to determine the strengthening solution, including the required prestressing level and/or the cross-sectional area of the reinforcement, which would ensure the complete arrest of an existing mixed mode I/II fatigue crack in a steel member. In parallel, sets of stepwise high-cycle fatigue tests were carried out on reference unstrengthened and prestressed CFRP-strengthened precracked steel plates of grade S355J2+N under various mode mixities. The experimental results revealed that the maximum tangential stress (MTS) criterion fairly predicts the state of the mixed mode I/II fatigue cracks (i.e., crack arrest or growth) in unstrengthened specimens, while the proposed design model provides a conservative estimation of the mixed mode I/II fatigue threshold in prestressed CFRP-strengthened specimens. Furthermore, the crack propagation characteristics of grade S355J2+N steel, i.e., Paris’ law parameters (C and m) and the crack closure parameter (U), were determined and demonstrated to be independent of the material rolling direction. Based on the analytical and experimental results of the current study, it can be concluded that the proposed model can be used for the safe design of strengthening solutions, which is an increasing need to extend the service life of existing fatigue-damaged steel structures; certain recommendations are provided in this regard for practical strengthening applications. more...

The major factors contributing for the longitudinal failures in large-diameter cast iron water pipes are identified as corrosion and internal water pressure. Evidence of deteriorating pipeline integrity due to fluctuations of internal pressure loading was reported. This study aims to investigate the fatigue resistance of cast iron pipes and to identify the pipes in a water network that are at high risks of fatigue damage. Stress-controlled fatigue tests were conducted on coupons prepared from exhumed cast iron pipes. A correlation between tensile fatigue stress and cycles to failure was developed based on experimental results. A methodology was proposed to identify critical factors for initiating a through-wall crack in cast iron water pipe considering the impact of fatigue. A sensitivity analysis was conducted with relevant factors, and the relative impact of those factors to cause a premature failure was assessed. The operating pressures and stress ratios caused by pressure transients and long-term soil corrosion rate were identified as the key contributing factors for severe fatigue damage. more...

In this article, the flexural durability of three types of seawater sea-sand concrete beams that were fully reinforced with steel bars, 304 stainless steel bars, or fiber-reinforced polymer bars were comparatively tested. Beam specimens were conditioned in a 40°C seawater wet–dry cycling environment and a 50°C seawater immersion environment for up to 9 months with an interval of 3 months. The test results showed that in the absence of an additional current (even if the temperature is elevated), the flexural properties of the seawater sea-sand concrete beams reinforced with steel bars and stainless steel bars after 9 months of conditioning did not show any degradation trends. However, for the carbon fiber–reinforced polymer bar–reinforced beams (top bars and stirrups are both basalt fiber–reinforced polymer bars) conditioned in the high-temperature and high-humidity environment considered, the failure modes changed from concrete crushing in the pure bending section to concrete crushing at loading points in the shear span with a maximum reduction of 30% in the ultimate load-carrying capacity. In addition, the crack distribution of conditioned carbon fiber–reinforced polymer bar–reinforced beams became sparse, and the crack width increased significantly, with a maximum of 2.2 times. In addition, obvious sudden load drops were observed in the tested load–displacement curves. more...

The primary objective of this study was to develop a new type of hybrid beam with excellent durability. This new type of beam was designed to be suitable for rapid in-situ construction in an offshore environment. It composed of seawater sea-sand concrete (SWSSC) and a prefabricated ultrahigh performance concrete (UHPC) shell, and was reinforced with basalt FRP (BFRP) bars or steel-FRP composite bars (SFCBs). Two types of production methods for the UHPC shell were designed and compared. The main objective was to test the mechanical properties of the proposed hybrid beams and to verify the feasibility of the proposed preparation processes. Traditional monotonic four-point bending test methods and 3D digital image correlation (DIC) measurements were performed simultaneously. The test results showed that the shear cracks reduced significantly due to the existence of UHPC shell. Because the depths of the UHPC sidewalls were ¾ of the beam depth, the bending strength of the test beam was not substantially improved, but the cracking load and energy absorption improved by approximately 70% and 24%, respectively. The integrity of the hybrid beam prepared by the rotation method was better than that of the hybrid beam prepared with a prefabricated U-shaped UHPC shell. more...

Experimental studies on concrete-filled stainless steel (SS) circular stub columns (in the form of fully filled and double-skin) have been reported in the last 10 years, but there is still a lack of theoretical model to predict the complete load-axial strain curve of such stub columns under axial compression. This study presents a load-axial strain model for concrete-filled SS tubes, which takes account of the interaction between the encasing tube and concrete core. A dilation model is first proposed in which the dilation rate is expressed as a function of axial strain and outer tube diameter-to-thickness ratio. The theory of metal plasticity in the form of deformation type is adopted to calculate the bi-axial stresses in the SS outer tube. The SS inner tube is assumed to be under uni-axial compression and continuous strength method (CSM), which is suitable for strain hardening material such as SS, is adopted. The effect of SS tube buckling on reducing the axial stress and confining stress is considered in the model. Numerical procedures are proposed to generate the complete load-axial strain curve which involve an incremental process. Finally, the predicted load-axial strain curves are compared with the experimental results obtained by the authors and other researchers, and a good agreement is achieved. more...

This paper summarizes the strengthening of a historically significant 122-year-old roadway metallic bridge using nonprestressed bonded carbon fiber reinforced polymer (CFRP) plates. Prior to the bridge strengthening, sets of laboratory tests were conducted to characterize the mechanical properties, glass transition temperature, and CFRP-to-steel bond strength of two different epoxy adhesives (linear and nonlinear) commonly used for structural retrofitting. Furthermore, the field application complexity, as well as the short- and long-term efficiency of the developed nonprestressed bonded system, was compared with the existing flat prestressed unbonded retrofit (FPUR) system. Short-term measurements, including sets of truck-loading tests performed before and after strengthening, demonstrated that the tensile stresses were reduced by approximately 15% and 44% in the bridge cross-girders after strengthening by the proposed nonprestressed bonded and FPUR systems, respectively. The long-term measurement results, obtained from a wireless sensor network (WSN) system installed on the bridge, revealed that because of the mismatch of the steel-CFRP thermal expansion coefficient, diurnal temperature changes can cause significant thermal-induced stress cycles in the nonprestressed bonded CFRP plate. These diurnal cyclic stresses must be considered in the design of bonded CFRP strengthening solutions. more...

Experimental research on the behaviour of conventional construction materials subject to extreme loading condition of post-impact-fire has indicated the effect of rate dependent loading history on the temperature performance of these materials. In order to analyse and design structures to withstand such combined loading, it is desirable to develop models that can reflect the mechanical properties of materials under initial impulsive loading and subsequent elevated temperature. In this study, a rate-pre-damage-temperature dependent empirical expression is proposed to predict the residual strength of partially damaged steel-concrete and fibre rein-forced polymer-concrete composite materials, in the form of concrete-filled steel tubes (CFST) and Concrete filled carbon-fibre reinforced polymer tubes (CFFT), at high temperatures up to 600 °C. The developed model is calibrated and validated on the basis of actual experimental data published by the authors. The proposed expression proves to be capable of successfully reproducing material strengths by considering the extent of high strain rate induced pre-damage together with temperature exposure. more...

This paper presents a critical characterization of the uncertainty of bond strength models of adhesively bonded carbon fiber-reinforced polymer (CFRP)-to-steel joints. A model factor e was defined as the ratio of a tested ultimate load to the corresponding predicted value. A database consisted of 414 CFRP-to-steel single/double-lap shear tests was collected and two frequently used bond strength models were used in the evaluation. The statistics of e indicated a high level of both the mean value and coefficient of variation (COV). The model factor was found to be highly dependent on input parameters rather than purely random. A systematic part (f) was consequently introduced by a multiple regression analysis to remove this kind of correlation, leaving a residual lognormally distributed random variable (e*). After the critical characterization, performance of the model factor was significantly improved. Afterwards, a reliability analysis was performed to compare the model performance given the condition whether the model factor was properly considered or not. The merit of the critical calibration of the model factor is highlighted in the reliability analysis. The resistance factor for the two bond strength models was calibrated given a target reliability index βT of 3.5. The sensitivity analysis indicated that the adhesive tensile strength is the most influential parameter to the reliability index among all the input parameters. more...

Due to the softening at the heat-affected zone (HAZ) in ultra-high strength steels (UHSS), the mechanical properties can deteriorate depending on the steels’ grade, welding heat input, and its associated cooling rate. Hence, a design based on the properties of the base material (BM) may not be appropriate, and there is a need to retain the lost properties of the weldment. This study presents an effort to strengthen butt-welded UHSSs using ultra-high modulus (UHM) carbon fiber reinforced polymer (CFRP) plates. Although the rehabilitation and strengthening of steel structures using CFRPs have been available during the last two decades, they have not been used to strengthen higher grades of steel such as UHSSs. For this aim, a series of tensile tests were carried out on butt-welded UHSSs strengthened with adhesively bonded UHM CFRP plates on both sides of the weldment. Two welding processes, i.e. the gas metal arc welding (GMAW) and laser welding, were implemented separately to join the plates. Microhardness measurements and tensile tests were carried out for the experimental part, as well as finite element (FE) analysis of the joints. The results were also compared with other available methods, i.e. high-frequency mechanical impact (HFMI) treatment and TIG-dressing (tungsten inert gas) of the weld toe that are commonly used to increase the fatigue life of UHSS joints. It was found that CFRP strengthening can not only retain the lost properties of the weldment but can also increase the joint strength up to 32% compared to the BM, and a considerable 50% higher stiffness. In contrast, the other methods (HFMI and TIG-dressing) had no impact on the tensile characteristics of the weldments. Post-print / Final draft more...

This literature review has examined the use of FRP composite materials as a potential retrofitting technique for civil structures. Importantly, the various material properties, bond mechanisms, durability issues and fatigue resistance have been discussed. Studies exploring the performance of CFRP repaired steel have strongly indicated its potential as a rehabilitation material. These systems offer many improvements over the current bulky and less chemically resistant methods of bolting or welding steel plate patches. This review has established and highlighted the factors that affect CFRP/steel bond durability, namely surface preparation, curing, corrosion, fatigue loading, temperature and moisture ingress through studies that focus on their effect. These studies, however, often focus on a single influencing factor or design criteria. Only limited studies have investigated multiple parameters applied simultaneously, even though they commonly occur together in industrial practice. This review aimed to summarise the numerous influencing parameters to give a clearer understanding of the relevance of CFRP repaired steel structures. more...

An old steel bridge located in Melbourne, Australia, was strengthened with carbon fibre-reinforced polymer (CFRP) laminates. A prestressed unbonded CFRP system was used in strengthening the bridge. A long-term wireless monitoring system was installed on the strengthened girders to monitor the strain evolution of the CFRP laminates, the temperature readings on the adhesive layer and air temperature. Short-term monitoring devices were also mounted on the girders for the purpose of on-site measurement. The on-site measurements were recorded when the bridge was subjected to a 42.5-ton loaded truck before and after strengthening. The results showed significant decreases in the bending stresses at the bottom of the girders when prestressed un-bonded CFRP laminates were used. This paper presents a linear finite element modelling of the bridge with the CFRP strengthening system. The results were validated using field measurements and a parametric study was carried out to understand the effect of change in temperature on the stress development on the steel girders. The paper also presents details of the bridge modelled with the prestressed unbonded strengthening sys-tem. The results showed good validation of the model, and the insignificant effect of the change of temperature on the prestressed strengthened girders more...

Seawater and sea sand concrete (SWSSC) is a highly attractive alternative to normal concrete (NC) that requires huge amounts of fresh water and river sand. However, reinforcements of stainless steel (instead of mild steel that is used in NC) may be required for SWSSC. This article reports investigation of stress corrosion cracking (SCC) of AISI 316 stainless steel (SS) in simulated SWSSC and NC environments, with and without addition of silica to SWSSC and NC, employing slow strain rate testing (SSRT) at 25 and 60 °C. For the purpose of comparison, SCC of SS was also investigated in simulated seawater (SW) solution. SS showed no SCC at 25 °C in any of the test solutions. Indications of SCC were seen in SW at 60 °C, but no features of SCC in SWSSC and NC at 60 °C, as suggested by scanning electron microscopy (SEM) fractographs. While the absence of SCC in SWSSC and NC is attributed to the highly passivating alkaline condition, its absence in SWSSC also indicates the role of alkalinity to predominate the deleterious role of chloride content of SWSSC. However, the addition of silicate to SWSSC or NC triggers transgranular SCC to SS at 60 °C, as evidenced by the fractography. more...