Damaged Steel Beams Research Articles

Influences of the bond-slip on the flexural performance of CFRP plate-strengthened damaged steel beams with intermediate debonding: A numerical study

The interfacial intermediate debonding between the steel beam and CFRP (carbon-fiber-reinforced polymer) is a considerable issue for a CFRP plate-strengthened damaged steel beam. The interfacial bond-slip property determines the interfacial debonding and thus affects the strengthening efficiency. To comprehend the influence laws of the bond-slip behavior, this study conducted a finite element (FE) modelling to assess the strengthening efficiency of the damaged steel beam using CFRP plates. The triangular and trapezoidal cohesive zone models were considered in parametric investigations. The comparisons of FE and experimental results verify the developed FE models. The FE modelling shows that the interfacial fracture energy is the most important bond-slip parameter affecting the flexural strengthening efficiency, relative to the maximum bond stress, elastic and plastic slips. The flexural capacity, ultimate deflection, and debonding load of the damaged steel beam are significantly increased with an increase in the interfacial fracture energy. However, changing the maximum bond stress, elastic slip or plastic slip only produce a minor influence under the same interfacial fracture energy. The selection of the adhesive type is critical for strengthening the damaged steel beam using CFRP plates. In this study, the debonding load, flexural capacity, and ultimate deflection are increased by 75.0%, 51.0%, and 131.1%, respectively, when Araldite-2015 adhesive with the trapezoidal bond-slip model is used instead of Sikadur-30 adhesive with the triangular bond-slip model. Moreover, the debonding load and flexural capacity are hardly increased but the ductility can be considerably improved with an increasing CFRP plate length.

Evaluation of Dynamic and Fatigue Behavior of Damaged Steel Beams Strengthened with Different Types of Techniques and a New Strengthening Method Proposal

Evaluation of Dynamic and Fatigue Behavior of Damaged Steel Beams Strengthened with Different Types of Techniques and a New Strengthening Method Proposal

Detecting Structural Deterioration: Investigating Changes in Power Spectral Density Using Deep Learning on Damaged Steel Beam Structures

Detecting Structural Deterioration: Investigating Changes in Power Spectral Density Using Deep Learning on Damaged Steel Beam Structures

Flexural strengthening of damaged steel beams with prestressed CFRP plates using a novel prestressing system

This study developed a novel prestressing system of the carbon fiber reinforced polymer (CFRP) plate to strengthen damaged steel beams, which reduced the operation space at the tensioning end, thereby extending the application range of prestressing system. Flexural tests were conducted to verify this system and investigate the effects of the adhesive layer, prestressing level, and CFRP plate area on the strengthening efficiency, and subsequently, a parametric analysis was carried out using finite element modeling to obtain more influencing rules of the unbonded CFRP plate-strengthened steel beams. The results indicated that satisfactory strengthening efficiency could be achieved by the novel prestressing system. The adhesive layer significantly affected the strain distributions of the steel–CFRP composite section, whereas it had a very slight effect on the flexural behavior of the steel beams, and the bonded and unbonded CFRP plates had a similar strengthening efficiency. Nonprestressed CFRP plate exhibited limited improvement in the flexural capacity and stiffness of the damaged steel beams under the normal service state; in contrast, the prestressed CFRP significantly increased the flexural behavior of the beams in the elastic and elastic–plastic stages owing to the high strength utilization of the CFRP plate. In addition, as the prestressing level increased, strengthening efficiency increased. Solely increasing the area or elastic modulus of the CFRP plate improved the strengthening efficiency slightly, whereas applying a prestress simultaneously clearly increases the strengthening efficiency. The strengthening efficiency increases with artificial notch depth.

Flexural behaviour of strengthened damaged steel beams using carbon fibre-reinforced polymer sheets

This paper presents the test and finite element analysis results of a study on the flexural behaviour of damaged steel beams strengthened with carbon fibre-reinforced polymer (CFRP) sheets. The test results showed that the yield load, ultimate load and elastic stiffness of the steel beams with 100% loss of tension flange were 68.3%, 73.8% and 13.5% greater than the yield load, ultimate load and elastic stiffness of the steel beam with 28% loss of the web after static loading. The yield load and elastic stiffness of the steel beam after overloading were 8.7% and 24.5% greater than the yield load and elastic stiffness of the steel beam without overloading. The damage level had a significant effect on the yield load, ultimate bearing capacity and elastic stiffness of the steel beams regardless of whether the steel beams were under static loading or overloading. The damaged steel beam could be repaired by CFRP sheets, the increased layers of CFRP sheets could improve the yield load, ultimate bearing capacity and elastic stiffness of the steel beams, and the strains of CFRP sheets would decrease because of overloading. The numerical analysis results showed that compared with the steel beam without overloading, the deflection and strains of the steel beam after overloading were much smaller. The yield load and the elastic stiffness increased with the increment of the overloading amplitude, and the increment of overloading number could reduce the yield load and elastic stiffness. All the yield loads of the steel beams after overloading were greater than the yield loads of the steel beams without overloading, but the ultimate bearing capacities were smaller.

Flexural Behavior on Damaged Steel Beams Strengthened with CFRP Sheets Subjected to Overloading

This paper presents results of testing and numerical analyses of damaged steel beams strengthened with carbon-fiber reinforced polymer (CFRP) sheet and subjected to overloading. The test results showed that as cyclic times increase, the yield load and stiffness increase, but the ultimate bearing capacity decreases to a certain extent. Applying prestress could improve the ductility of the girder. The damage level greatly influenced the girders with overloading, and the increase in damage degree reduced the stiffness, yield load and ultimate load. The numerical calculation showed that the yield load would decrease by 0.4–0.8 kN when the cyclic times increase by 100 times. The yield load would increase by 1–2 kN and the ultimate bearing capacity would decrease by 0.6–1.2 kN when the overloading amplitude increased by 0.02 Pu. The increase in damage degree would obviously reduce the yield load and ultimate bearing capacity of the steel beam after overloading. The yield load and ultimate bearing capacity could be increased by approximately 3 kN when the CFRP sheet thickness increases by 0.05 mm.

Test and Numerical Analysis on Damaged Steel Beam Strengthened with Prestressed CFRP Sheet

This paper presents the experimental and numerical analysis of damaged steel beams strengthened with prestressed CFRP sheet or only strengthened with CFRP sheet. The test results showed that damaged level had a significant effect on the stiffness, yield load, and ultimate bearing capacity. And using prestressing CFRP sheet to strengthen damaged steel beam could increase the ultimate bearing capacity. The numerical analysis results showed that the damaged level had a significant effect on the stiffness and ultimate bearing capacity. The strengthened steel beam with the damaged level could exceed the steel beam without damage by about 10% in the ultimate bearing capacity. The ultimate bearing capacity would increase about 8% when the flange or web thickness increased per 1 mm. The ultimate bearing capacity would increase about 3% when the thickness or width of CFRP sheet increased per 0.05 mm or 10 mm. The bearing capacity would increase about 1.5% when the prestressed degree increased about 7%.

Study on the Flexural Fatigue Performance of CFRP-OFBG Plate Reinforced Damaged Steel Beams

This paper studies the flexural fatigue performance of damaged steel beams strengthened by carbon fiber reinforced plastic-optical fiber bragg grating (CFRP-OFBG) plates. By analyzing the test beam's failure mechanism under cyclic loading and the strain data monitored by the CFRP-OFBG panel in real-time, a life prediction model based on cumulative fatigue damage is proposed. The test results show that CFRP-OFBG plate reinforcement effectively reduces the fatigue crack growth rate of damaged steel beams and increases the fatigue life of damaged steel beams by 22.46%. The analysis and test results show that the minimum error between the calculated value of the life prediction model and the test value is −24.13%, and the maximum error is −5.61%. This study provides some suggestions for improving the service life of existing fatigue-damaged steel beams and establishing a simple fatigue life evaluation model.

Feasibility of Reusing Damaged Steel Beams in Temporary Structures

This study addresses the feasibility of reusing pre-damaged steel beams in temporary structures. The extensive structural investigation of notch-damaged, unrepaired, and laterally unsupported steel beams was performed experimentally and numerically. The simply supported specimens were tested in two-point loading with the study parameters being the location and size of the notch. Some beams had one notch on one edge of the tension flange at different locations, and some beams had two notches on both edges of the tension flange. Three-dimensional numerical models were generated to simulate the behavior of the test beams. After verifying the model, the numerical analysis was extended to cover additional different notch depths and widths. The study showed that the capacity of beams with single notch was more influenced by the notch depth increase than it was by the increase in the notch width. Beams with double notches exhibited an even more pronounced and distinct decrease in the capacity as the notch depth and width increased. This investigation supports the feasibility of reusing pre-damaged steel beams in temporary structures under service loads and certain levels of damage, where the behavior of such beams is within the elastic range and the beam maximum defection is less than the allowable one.

Rehabilitation of thin walled steel beams using CFRP fabric

This paper discusses the structural behaviour of damaged steel I-beams rehabilitated using carbon fibre reinforced polymers (CFRP) fabric. The damage was simulated by thinning the bottom flange of the steel beams. A total of eight beams were tested under four-point bending load. The study found that both yield and ultimate load capacities of a damaged steel beam can be fully restored to the level of undamaged beam if adequate number of CFRP fabric layers is used and the debonding failure is avoided. The structural behaviour of rehabilitated steel beams was successfully modeled using commercially available finite element software and a good correlation was obtained between the finite element output and the lab specimen's results.

Fatigue Performance Analysis of Damaged Steel Beams Strengthened with Prestressed Unbonded CFRP Plates

A study was experimentally and numerically conducted to investigate the fatigue performance of notched steel beams strengthened with prestressed unbonded carbon-fiber-reinforced polymer (CFRP) plates. The experimental study included several large-scale edge-notched steel beams that were strengthened by unbonded CFRP plate with different prestress levels and then tested under cyclic fatigue load. The experimental results indicated that the proposed anchorage and prestressing system is feasible and reliable, and the prestress effect is significant not only for life extension but also in the stiffness decay reduction of the specimens. The highest prestressing level leads to over eightfold increase in the fatigue life of specimens. Furthermore, an analytical model was proposed to determine the effects of prestress level on the fatigue life of reinforced specimens based on a modified Paris’ law. Relative to the experimental results, the predicted results from the analytical model are satisfactory. Moreover, the regression analysis of the experimental results determined that the recommended values of parameter n and C in the modified Paris’ law were 3.0 and 2.72×10−12.

Numerical study on notched steel beams strengthened by CFRP plates

Carbon fibre reinforced polymer (CFRP) externally bonding is an efficient and effective method to strengthen damaged steel beams, and thereby prolong their service life. However, debonding failure, which requires accurate predictions to ensure safety, can occur before the full usage of CFRP. In this study, the notched steel beams strengthened with CFRP plate were simulated by finite element method where the mixed-mode cohesive law was employed to determine the interfacial stress. The load–deflection curves and strain development at different load levels from experimental study were used to verify the validity of the numerical model. The interfacial stress distribution with increasing load was analysed, and good correlation with theoretical calculations at elastic stage was observed. In contrast to the previous elastic analytical study, the plastic behaviour of the CFRP strengthened notched steel beams was revealed. More importantly, interfacial crack initiation, propagation and debonding were accurately simulated. This simulation method can be used to predict debonding process in actual engineering applications. In addition, parametric analysis was conducted to assess the effects of notch depth, CFRP elastic modulus and CFRP thickness. The ultimate load and ductility decreased substantially with increasing notch depth. Furthermore, although increased bearing capacity was achieved by increasing the CFRP elastic modulus and thickness, ductility decreased and premature debonding failure occurred more easily.

Structural performance of notch damaged steel beams repaired with composite materials

An experimental program and an analytical model using ANSYS program were employed to estimate the structural performance of repaired damaged steel beams using fiber reinforced polymer (FRP) composite materials. The beams were artificially notched in the tension flanges at mid-spans and retrofitted by FRP flexible sheets on the tension flanges and the sheets were extended to cover parts of the beams webs with different heights. Eleven box steel beams, including one intact beam, one notch damaged beam and nine notches damaged beam and retrofitted with composite materials, were tested in two-point loading up to failure. The parameters considered were the FRP type (GFRP and CFRP) and number of layers. The results indicated that bonding CFRP sheets to both of the tension steel flange and part of the webs, instead of the tension flange only, enhances the ultimate load of the retrofitted beams, avoids the occurrence of the debonding and increases the beam ductility. Also the numerical models give acceptable results in comparison with the experimental results.

Applications of Fiber Reinforced Polymer Composites

Fueled by the need to surpass the limitations of conventional materials, recent years have seen a large increase in engineering applications of advanced fiber reinforced polymer (FRP) composite materials in many major industries, such as aerospace and defense, automotive, construction, marine, and oil and gas. FRP composites are very attractive for these applications due to their highly favorable material properties, including high strength-to-weight and stiffness-to-weight ratios, and corrosion resistance. Studies conducted to date have demonstrated the numerous advantages offered by FRP composites in various engineering applications. However, there are still a number of technical and implementation issues that need to be resolved prior to broader uptake of the application of FRP composites by some engineering communities such as civil construction. This special issue is aimed at disseminating the most recent advances and developments in this exciting field. A total of 17 paperswere submitted to the special issue and after a rigorous peer-review process six of themwere accepted to appear in the issue as original research articles. These six papers deal with a range of topics on the structural behavior of composite members/structures and mechanical properties and development of composite materials. The studies on the former investigate the dynamic behavior of composite FRP bridge systems and flexural behavior of previously damaged steel beams repaired with FRP. The studies on the latter are concerned with the development of ecoefficient engineered cementitious composites, mechanical properties of carbon fiber composites obtained using different molding techniques, and properties of high-density and ultra-high molecular weight polyethylene and heat-treated bamboo fiber composites. We hope that some of the most recent advances on the development and applications of FRP composites that have been disseminated in this special issue will be of interest to readers and contribute toward the advancement of research in the field.

Theoretical and experimental study on notched steel beams strengthened with CFRP plate

CFRP external bonding is an alternative technique to repair or strengthen notch damaged steel beams. However, the premature debonding failure caused by the stress concentration at the notch location reduces the effectiveness of this reinforcement technique. This paper presents an integrated closed-form solution for obtaining the interfacial shear and normal stresses in steel beams strengthened with a CFRP plate. Simple expressions of the maximum interfacial stresses at the notch locations, the adhesive hollows and the plate ends are given. A parametric study indicates that the maximum stresses at the notch locations increased with the notch depth and the applied bending moment on notched cross-sections, but reduced with the thickness of the adhesive. An experimental study of model-scale CFRP bonded steel beams was conducted as well. The test results show the strength of the notched beam can be improved almost twice by the CFRP plate strengthening, while the brittle fracture caused by intermediate debonding initiated from the notch location limits the ductility enhancement of the retrofitted beams. The good agreement between the longitudinal strain distributions in the CFRP plate obtained from the tests and the corresponding analytical results demonstrates the validity of the theory.

Experimental study on the fatigue behaviour of cracked steel beams repaired with CFRP plates

For the repair of damaged steel beams, Carbon Fibre Reinforced Polymers (CFRP) are effective under monotonic loads, but less information is available under fatigue loading. In this paper, fatigue tests were performed on nine CFRP reinforced cracked steel beams. The fatigue crack propagation curves showed that CFRP strips reduce the fatigue crack growth and extend the fatigue life. Experimental results also revealed the presence of a debonded area between the reinforcement and the steel substrate at the crack location. Debonding clearly has a detrimental effect on the reinforcement effectiveness. Finally, numerical and analytical studies are performed and compared to the experimental findings.

Using locally pre-stressed reinforcing bars to restore the capacity of severely damaged steel beams

This paper investigates the behaviour of damaged steel beams repaired using locally pre-stressed reinforcing steel bars. Regular reinforcing bars are welded to the beam’s web at both ends and then pretensioned using a manual screw jack to increase the effectiveness of the repair. Six beams with different bar diameters and levels of pre-stress were repaired and tested under three-points bending. Results showed that the level of pre-stress controlled the beams’ stiffness, while restoration of their ultimate load-carrying capacity was governed by the bar size. Significantly higher repaired capacities were achieved by this method than by other published methods used for the strengthening of steel beams.

The compensation technique of tensile force effect on the electro-mechanical impedance method for structural health monitoring

In this article, the external axial tension applied on structure was considered in electro-mechanical impedance method. An experiment was performed to study the effect of external axial force on the electro-mechanical impedance–based structural health monitoring. The axial tensions were applied on both healthy and damaged steel beam pasted by surface-bonded piezoelectric transducers. The study results showed that the electrical admittance (the inverse of impedance) curves had an obvious tendency of decline with the increase in tension; thus, this effect would mislead the judgment of health status. Then, the artificial neural network based on radial basis function was introduced to compensate the effect of tension on EMI method. Numerical examples showed that artificial neural network method can prevent the root mean square deviation index from changing with increase in tension. An additional experiment was performed to verify the artificial neural network method. The same conclusion as the first experiment was obtained. The reasonable experiment result demonstrated that artificial neural network method has its generality for application.

Impedance-based damage monitoring of steel column connection: numerical simulation

This study has been motivated to evaluate the practicality of numerical simulation of impedance monitoring for damage detection in steel column connection. In order to achieve the objective, the following approaches are implemented. Firstly, the theory of electro-mechanical (E/M) impedance responses and impedance-based damage monitoring method are outlined. Secondly, the feasibility of numerical simulation of impedance monitoring is verified for several pre-published experimental examples on steel beams, cracked aluminum beams, and aluminum round plates. Undamaged and damaged steel and aluminum beams are simulated to compare to experimental impedance responses. An aluminum round plate with PZT patch in center is simulated to investigate sensitive range of impedance responses. Finally, numerical simulation of the impedance-based damage monitoring is performed for a steel column connection in which connection bolts are damaged. From the numerical simulation test, the applicability of the impedance-based monitoring to the target steel column connection can be evaluated.

Debonding Mitigation of CFRP-Strengthened Steel Beams with Silyl-Modified Polymer and CFRP Wrap Anchorage

AbstractThis paper presents an innovative strengthening methodology for damaged steel beams with carbon-fiber-reinforced polymer (CFRP) sheets. Emphasis is placed on controlling premature CFRP debonding using an emerging material called silyl-modified polymer (SMP) in conjunction with its hybrid bond application with a conventional epoxy adhesive. The hypothesis proposed is that the low-modulus SMP addresses stress singularity along the CFRP-steel interface, while the high-modulus epoxy preserves interfacial capacity. CFRP anchorage assists the efficacy of such a hybrid bond configuration. A two-phase experimental program is conducted to evaluate the performance of various CFRP-strengthening schemes, including element- and structural-level investigations (i.e., interface and beam tests, respectively). Test results reveal that the SMP bond mitigates CFRP debonding that is commonly observed in epoxy bond. The strengthening systems employed significantly improve the flexural behavior of the test beams in ter...