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Localized corrosion often occurs on steel members due to paint peeling led from insufficient durability of the coating material or human collision, which may significantly reduce the load carrying capacity and safety performance of the structures. The effects of the parameters such as localized corrosion penetration, circumferential corrosion ratio, longitudinal corrosion ratio, slenderness ratio and eccentricity of mechanical behaviors of locally corroded circular steel tubes under compression were studied experimentally and numerically. Based on the test results and the finite element analysis, a calculation method was proposed for predicting load carrying capacity of the corroded specimen under compression. It is found that localized corrosion did not change the failure modes of test specimens, and all of them failed in the limit point buckling mode. The factors affecting the degradation of load carrying capacity and stiffness of localized corrosion specimens from high to low were corrosion time, circumferential corrosion ratio and longitudinal corrosion ratio. The most unfavorable localized corrosion modes of load carrying capacity and stiffness were H3L3-270 and H3L1-270, respectively. The load carrying capacity degradation of members increases with the increase of the localized corrosion ratio, circumferential corrosion ratio and longitudinal corrosion ratio, while decreases with the increase of the eccentricity. The formula proposed can be used to predict the load carrying capacity of locally corroded circular steel tube members under compression.

In order to achieve a comprehensive and accurate evaluation of the safety of compression members made of circular steel tubes, image processing technology is commonly utilized to extract the morphology of the steel tubes before and after rust removal. The obtained results have validated the feasibility and applicability of employing digital cameras and image processing technology to analyze the images of the steel tubes before and after rust removal and to extract useful structural mechanics features. The feature values of the apparent morphology before rust removal grow with the increase of the corrosion depth, while after rust removal, the feature values first increase and then decrease with the growth of the corrosion depth. Based on this fact, a simplified equation is proposed to quantify the relationship between the feature values of the apparent morphology before and after rust removal and the corrosion depth. In continuing, a simple, fairly accurate, and comprehensive safety evaluation methodology for corroded circular steel tubes under compression is established. Finally, an example is illustrated to check the applicability and effectiveness of the proposed approach.

Ensuring adequate tightening of bolted joints is necessary since they are more prone to corrosion in a harsh environment under insufficient preload. To this end, this paper first conducted an accelerated electrochemical corrosion experiment to expedite the corrosion process of bolted connections over different periods. The results show that as the corrosion time is extended, the overall dimensions of the bolt system remarkably decrease. Moreover, according to the mass loss of the bolted joints in 3.5% NaCl solution, the rate of corrosion continuously changes. Then, a real-time monitoring approach based on active sensing was utilized to evaluate the corrosion conditions of bolted joints. The stress wave generated by one piezoceramic transducer propagates through the bolted joints and is captured via another transducer that acts as a sensor. The energy corresponding to the stress wave signal declines during the corrosion process, and the normalized wavelet packet energy index is used to evaluate the degree of damage to the bolted joints. Overall, the health status of the bolted joints is significantly affected by the corrosion time. The proposed active sensing method can accurately monitor the corrosion process of bolted joints. The experimental results verify the feasibility and practicality of the real-time, piezoceramic transducer-enabled method for monitoring the structural health of corroded bolted joints.

In the real civil structures, material deterioration, overloading and environmental corrosion inevitably lead to sensor performance degradation or sensor fault. Sensor performance degradation or sensor fault usually introduce observable changes in the measured structural responses, which may be incorrectly interpreted as structural damage. This paper proposes a novel approach to quickly distinguish sensor fault from structural damage and locate the faulty or degraded sensors. Two steps are involved in this approach. In the first step, the root mean square of the generalized likelihood ratio test (GLRT) is used to detect and localize the structural damage or degraded sensors. In the second step, a new index is proposed used along with the statistical process control chart to distinguish sensor performance degradation from structural damage. The proposed index is the percentage of the extreme value of the largest principal component scores of the generalized likelihood ratio, which not only has excellent noise tolerance but also can distinguish sensor performance degradation from structural damage. The applicability and efficiency of the proposed approach are validated by numerical studies on a planar 11-element truss structure and experimental studies on a simply-supported steel beam in the laboratory. The results demonstrate that the proposed approach can locate the damage accurately when taking into account of sensor performance degradation and environmental noise in the measurements. The proposed index is able to accurately and quickly determine the source of the novelty in the responses.

The integration of discrete wavelet transform and independent component analysis (DWT-ICA) method can directly identify time-varying changes in linear structures. However, better metrics of structural seismic damage and future performance after an event are related to structural permanent and total plastic deformations. This study proposes a two-stage technique based on DWT-FastICA and improved multiparticle swarm coevolution optimization (IMPSCO) using a baseline nonlinear Bouc–Wen structural model to directly identify changes in stiffness caused by damage as well as plastic or permanent deflections. In the first stage, the measured structural dynamic responses are preprocessed firstly by DWT, and then the Fast ICA is used to extract the feature components that contain the damage information for the purpose of initially locating damage. In the second stage, the structural responses are divided at the identified damage instant into segments that are used to identify the time-varying physical parameters by using the IMPSCO, and the location and extent of damage can accordingly be identified accurately. The efficiency of the proposed method in identifying stiffness changes is assessed under different ground motions using a suite of two different ground acceleration records. Meanwhile, the effect of noise level and damage extent on the proposed method is also analyzed. The results show that in a realistic scenario with fixed filter tuning parameters, the proposed approach identifies stiffness changes within 1.25% of true stiffness within 8.96 s; therefore, it can work in real time. Parameters are identified within 14% of the actual as-modeled value using noisy simulation-derived structural responses. This indicates that, in accordance with different demands, the proposed method can not only locate and quantify damage within a short time with a high precision but also has excellent noise tolerance, robustness, and practicality.

Due to the long-term service, Chinese ancient timber buildings show varying degrees of wear. Thus, structural health monitoring (SHM) for these cultural and historical treasures is desperately needed to evaluate the service status. Although there are some FBG sensing-based SHM systems, they are not suitable for Chinese ancient timber buildings due to the differences in architectural types, structural loads, materials, and environment. Besides, a technical gap in Fiber Bragg grating (FBG) sensing-based column inclination monitoring exists. To overcome these weaknesses, this paper develops an FBG sensing-based structural health monitoring system for Chinese ancient Chuan-dou-type timber buildings that aims at monitoring structural deformation, i.e., beam deflection and column inclination, temperature, humidity, and fire around the building. An in-situ test and simulation analyses were conducted to verify the effectiveness of the developed SHM system. To validate the long-term-operation of the developed SHM system, monitoring data within 15 months were analyzed. The results show good agreement between the developed SHM system in this paper and other methods. In addition, the SHM system operated well in the first year after its deployment. This implies that the developed SHM system is applicable and effective in the health state monitoring of Chinese ancient Chuan-dou-type timber buildings, laying a foundation for damage prognosis of such types of timber buildings.

To better protect ancient wooden structures, this paper presents a dual-indicator prediction model that is applicable to assessment on the safety of wooden structures with consideration of bioerosion. More specifically, the dual indicator includes bearing capacity index and deformation capacity index. The former is achieved by combining the Gerhards model and the time-varying bioerosion model. The latter is implemented by employing the Weibull model to fit the development tendency of monitoring data. This dual-indicator prediction model was finally applied to an existing ancient wooden structure, i.e. the Seven Literary World, to predict the remaining service life (RSL). For the Seven Literary World, the RSL of the most components predicted by the deformation capacity index is much shorter than that predicted by the bearing capacity index. Taking the shortest RSL of all components as the RSL of the overall structure, the RSL of the Seven Literary World is 96.6 years. Besides, for bearing-capacity-based RSL prediction, the RSL without considering bioerosion reaches to 7803 years, which is much larger than that considering bioerosion, i.e. 287 years. The results show that the proposed dual-indicator prediction model can comprehensively predict the future service state of structures, and it will much overestimate RSL of wooden structures if bioerosion is neglected.

Compared with the conventional drainage strengthening techniques, the precast concrete segment assembly strengthening method (PCSAM) is regarded as a fast, more economical, and traffic-friendly underwater strengthening method for damaged bridge piers and piles, as the drainage procedure can be omitted. However, this method still has some disadvantages, such as strength loss of the filling material, debonding of the interface due to shrinkage of the filling material, poor connection effects, and poor durability of the segment sleeves. To solve these problems, the PCSAM is improved in this study by using self-stressed anti-washout concrete (SSAWC) as the filling material and by developing a lining concrete segment sleeve (LCSS) by referring to the design theory for shield lining segments. Six specimens are designed and prepared with consideration of the influential factors, such as the self-stress, thickness of the filled concrete, and concrete strength of the LCSS, then the monotonic axial compression test is carried out to investigate the improvements in the axial compression properties of the specimens. Accordingly, extended parametric analyses are performed based on the established numerical models. Finally, the calculation formula for the bearing capacity is proposed based on the analysis results. The results indicate that the SSAWC can provide initial confining compressive stress in the core region of the piers, in addition to increasing the bearing capacity and ductility of the specimens. The improved LCSS segment connection is more reliable and increases the strengthening efficiency. The influence of self-stress on the bearing capacity of the specimens is cubic and the influence of the filled concrete strength on the bearing capacity of the specimens is nonlinear. The calculation formula for predicting the bearing capacity of axially compressed columns possesses good applicability and can be used as a reference for practical engineering.

The excellent performance of the CFRP-concrete bonding interface is a key to ensure the reliability and effectiveness of the rehabilitation in concrete structures with external fiber reinforced polymer (FRP). Meanwhile, the epoxy primer, which bonded the FRP plate and the concrete substrate, is significantly affected by the aggressive environment. In this paper, two kinds of experiments which associated with the CFRP-concrete specimens and the epoxy primer after corroding in a wet-dry cycles environment were conducted. It shows that the immersion area of the epoxy primer has a significant influence on the properties of the moisture absorption, and that would lead to a degradation in the mechanical properties of the CFRP-concrete interface. Simultaneously, the failure modes of the CFRP-concrete interface presented a transformation from the epoxy/concrete interaction layer to the epoxy primer layer along with the increase of aging duration. To further depict the degraded bond behavior, a time-dependent bond-slip model considering the degradation of epoxy primer was proposed, and the interface fracture energy was utilized to quantify the degree of the deterioration. By comparing with the value of interface fracture energy, it was figured out that the normal bond-slip model (Popovics model) is not enough for the safety of the concrete structures rehabilitated with external CFRP, and the proposed time-dependent bond-slip model is more accurate in evaluating the time-dependent mechanical properties of concrete structures suffering in an aggressive environment.

This article proposes an improved multi-scale principal component analysis approach to recover the structural dynamic response in the time domain from data measured by performance-deteriorated sens...

Anti-washout underwater concrete (AWC) is widely used in nondrainage strengthening, however, there still exist some problems with it, such as high strength loss and poor interfacial bond in practical engineering application. Based on the study of self-stressed concrete (SSC), a research on the mix ratio for the C30 self-stressed anti-washout underwater concrete (SSAWC) was carried out in this paper in hope of solving the above problems, specifically, by adding an expansive agent to the AWC. The parameters, such as strength, fluidity, anti-dispersity, and expansibility, were picked as target indices in determination of the mix ratio. The orthogonal test design and range analysis were used to determine the reasonable mix ratio and study the influence of various parameters on the performance of SSAWC. The experimental program conducted includes a series of strength, fluidity, anti-dispersity, and expansibility tests on 18 groups of specimens. The results show that C30 SSAWC has an excellent performance using the optimal mix ratio. Compared with AWC, the expansibility and self-stress of the SSAWC can be easily observed, and the compressive strength ratio of the SSAWC casted in water to that casted in air is much bigger. This implies that SSAWC is applicable to the nondrainage strengthening.

In a steel-concrete composite beam (hereafter referred to as a composite beam), partial interaction between the concrete slab and the steel beam results in an appreciable increase in the beam deflections relative to full interaction behavior. Moreover, the distribution type of the shear connectors has a great impact on the degree of the composite action between the two components of the beam. To reveal the effect of shear connector layout in the performance of composite beams, on the basis of a developed one-dimensional composite beam element validated by the closed-form precision solutions and experimental results, this paper optimizes the layout of shear connectors in composite beams with partial interaction by adopting a stepwise uniform distribution of shear connectors to approximate the triangular distribution of the shear connector density without increasing the total number of shear connectors. Based on a comparison of all the different types of stepped rectangles distribution, this paper finally suggests the 3-stepped rectangles distribution of shear connectors as a reasonable and applicable optimal method.

This paper reports the numerical simulation of earthquake-damaged circular columns repaired with the combination of near-surface-mounted (NSM) basalt fiber reinforced polymer (BFRP) bars with external BFRP sheets jacketing at quasi-static loading. The numerical modeling was carried out with the nonlinear OpenSees software platform by using the BeamWithHinges element. In the simulations, the effect of the previous earthquake damage on the behavior of the repaired columns was taken into account, and a simple and effective material damage-accumulation model is proposed to modify the constitutive of materials in the unrepaired regions of the repaired columns. The developed numerical models were validated by comparing their quasi-static findings with those obtained from a previous experimental program, and a good agreement can be observed. Furthermore, the efficiency of the repair technique used in tests is evaluated via the developed numerical model.

To reduce the risk in the integrity and safety of concrete composite structures (CCS), a monitoring approach was developed by using piezoelectric-based smart aggregates (SAs) and an evaluation method with the damage extent (Dc) of crack was proposed based on the energy attenuation of stress wave. A two-phase monitoring approach was presented firstly, and then two experiments and a numerical simulation were carried out to validate the approach proposed. More specifically, a push-out experiment was conducted with the active sensing approach on the laminated interface, and the results show that with the increase of loading, the signal energy attenuation index (DI) increases continuously. At the phase of damage initiation, there exists an alternative impact by the crack length and crack depth, and almost no slippage appeared on concrete prisms; subsequently, the crack width holds the dominant position in the phase of crack evolution, and the slippage rises rapidly; lastly, the components of composite structures completely debond at the failure phase. In addition, based on a combination of artificial cracks experiment and numerical simulation analysis, the debonding and damage behavior of the laminated interface were figured out. A correlation equation of damage extent and energy attenuation index was derived. The results show that the proposed damage index can effectively detect the existence and severity of crack on the concrete laminated interface. This indicates that the approach proposed is applicable to monitor the occurrence and evolution of crack damage and predict crack extent on the laminated interface.

Rapid repair and retrofitting is increasingly urgent and significant for the earthquake-damaged columns. To restore the flexural strength, and also attempt to restore stiffness and deformation capacity of damaged columns, this paper proposes a repair technique using near-surface-mounted (NMS) basalt fiber reinforced polymer (BFRP) bars and BFRP sheets jacketing, and then four one-fourth scale earthquake-damaged reinforced concrete circular bridge columns repaired by the proposed technique are retested under the similar cyclic lateral load as the corresponding original columns. The repaired columns are compared with the original columns in the seismic behavior finally, and the results have shown that the flexural capacity of the repaired columns was restored and even enhanced; furthermore, the stiffness and the displacement capacity of repaired columns were restored to an extent that can meet the needs of a temporary repair and allow emergency service use after an earthquake. This implies that the repair technique is effective in restoring the flexural performance of the damaged circular bridge columns.

Circular steel tube members with the absence of anticorrosive protection or coating failure are prone to uniform corrosion, which threatens the reliability and safety of members in the atmospheric environment. To fully study the mechanical behavior of uniformly corroded circular steel tubes, compression test and theoretical analysis were conducted, and two methods considering section reduction and material degradation, respectively, were adopted for the calculation of ultimate load carrying capacities of specimens. The results indicate that uniform corrosion did not change the failure modes of specimens, and all of them belonged to global buckling failure. The load carrying capacities and stiffness of specimens decreased with the increase of corrosion ratio, and the degree of reduction was greater than that of material degradation, showing a linear relationship with the corrosion rate. Under the same corrosion ratio, the specimens with larger eccentricity represented more obvious load carrying capacity and stiffness degradation. The load carrying capacities predicted by both methods were in good agreement with the test results and had a certain safety margin. The conservative degree of calculation results from three specifications followed a descending order of ANSI/AISC 360-16, GB 50017-2017, and EN 1993-1-1. Under the same corrosion ratio, the load carrying capacity variation of specimens between one-sided corrosion and two-sided corrosion was less than 3%.

This paper proposes a novel index, the extreme value of the largest principal component scores of the generalized likelihood ratio based on the statistical process control chart, to develop...

Distributed deformation based on Fiber Bragg Grating sensors or other kinds of strain sensors can be used to evaluate safety in operating periods of bridges. However, most of the published researches about distributed deformation monitoring are focused on solid rectangular beam rather than box girder—a kind of typical hollow beam widely employed in actual bridges. Considering that the entire deformation of a single-cell box girder contains not only bending deflection but also two additional deformations respectively caused by shear lag and shearing action, this paper again revises the improved conjugated beam method (ICBM) based on the LFBG sensors to satisfy the requirements for monitoring two mentioned additional deformations. The best choice for the LFBG sensor placement in box gilder is also proposed in this paper due to strain fluctuation on flange caused by shear lag effect. Results from numerical simulations show that most of the theoretical monitoring errors of the revised ICBM are 0.3%~1.5%, and the maximum error is 2.4%. A loading experiment for a single-cell box gilder monitored by LFBG sensors show that most of the practical monitoring errors are 6%~8%, and the maximum error is 11%.

To protect the China ancient cultural heritage and ancient buildings, this paper proposed an ultimate life prediction method that is suitable for the Chinese ancient wooden buildings. An ancient building installed a structural health monitoring (SHM) system was an example of practical engineering to validate the proposed method. In the practical engineering, the SHM system was briefly introduced firstly, afterwards a finite element model was developed and updated by the monitoring data, and the life of the building was analyzed and predicted. The results show that the proposed damage prognosis and life prediction method is applicable and efficient.

This paper develops a novel two-node linear composite beam element for the steel–concrete composite beam with elastic shear connection. The element stiffness matrix takes into account the effects of interface slip and shear deformation. Both simply supported- and continuous composite beams are used to validate the proposed element, and a comparison is made between the proposed element and other methods. The impact of cross sectional shear deformation on deflection is also discussed. The results show that the novel element is capable of effectively and accurately calculating the deflection and slip, and is applicable to slender composite beams or deep ones.

A vibration signal acquisition system was designed based virtual instrument technology. The process and principle design of structure vibration signal acquisition system based on LabVIEW software and CompactRIO hardware were discussed in detail. Finally, system test was conducted by a three story steel frame structure. And the test results were compared with traditional instruments system. The experiment showed that the data acquisition system of structure vibration signal which based on CompactRIO is precise and reliable in measurement results, and can realize multi channel synchronous data acquisition, storage, and support the real-time online data filtering and spectrum analysis and so on.Compared with the traditional platforms, the system proposed in the paper has short development cycle, low cost, user-defined functions, rugged, portable and other advantages. It can be widely used in complex and special building environment, so it will have a broad application prospect in the field of SHM.

This paper investigated on the performance of slender concrete-filled carbon fiber-reinforced polymer (CFRP)–PVC tubular columns under axial compression. Four specimens with different slenderness ratios were firstly carried out to explore their performance and failure modes under axial compressive loads in laboratory. Secondly, a nonlinear finite element model (NFEM) was developed to analyze the relation between loads and deformation, and the analytical values were compared with the experimental results. After the efficiency of NFEM was verified, the parametric analyses varying the number of CFRP layer, concrete compressive strength and the slenderness ratio were conducted by the NFEM, and the ultimate bearing capacity formula as well as the relation model of the stability coefficient (φ) versus slenderness ratios (λ) were proposed. To validate the efficiency, ultimate bearing capacity was compared among the experimental results, NFEM analytical values and the prediction by the proposed formula. The results indicate that not only the developed NFEM can effectively depict the varying process of the loads and deformation in details, but also the proposed ultimate bearing capacity formula is reasonable and reliable in the fast prediction of the bearing capacity for slender concrete-filled CFRP–PVC tubular columns. It is beneficial to widely apply such new type composite columns in pile foundation or corrosion environments.

Through the finite element simulation to study the local stability of the circle-castellated beams, reasonable finite element model was established using finite element software and in-depth analysis of the local stability of the circle-castellated beams on the basis of the castellated beams shear performance test. The same span of the circle-castellated beams, deformation stability performance under two point loads simulation, got deformation form of castellated beams under different pitch of holes, opening ratio, stiffener thickness, depth-thickness ratio. The local stability properties of the same span of the circle-castellated beams are directly related to opening ratio and web depth-thickness ratio changes, which has little effect with the change of hole spacing, stiffener thickness. Using the appropriate opening ratio, web depth-thickness ratio plays an important role on improving the local stability of web under the shear force and the bending moment.

This paper presents an experimental method to investigate the attenuation performance of stress waves in concrete structures embedded in piezoelectric ceramics. To get the research objective, a series of test were hold. The relationship curve between the frequency and the attenuation coefficient was fit. The calculation method for propagation distances of stress waves with constant amplitudes and frequencies in the concrete medium was proposed. The research results show that the relationship curve of attenuation coefficient and frequency conform to the cubic polynomial function approximately. The attenuation performance for the concrete structure embedded into piezoelectric ceramics is relevant to the frequency, the amplitude and the medium character, and the frequency is the main factor. The research results of this paper can provide an effective evidence for correctly placing transducers.

This paper proposes a new structural novelty detection method in the case of vast measurement data having uncertainties. Considering the effects of measurement accuracy and environmental variations on measurement variance, precise analytical methods of adaptive confidence distance and measurement variance are presented on the basis of statistical theory, and thus an adaptive consensus data fusion algorithm has been firstly developed to deal with the large volume of data involving considerable uncertainties. The proposed adaptive fusion algorithm can adaptively choose sensors whose data will be subsequently fused. The algorithm is then incorporated with wavelet analysis for the purpose of structural novelty detection. Two numerical examples are carried out to validate the efficiency and adaptability of the proposed method. The obtained results have been compared with those from other existing methods, which demonstrate the high efficiency of the proposed method in data processing considering uncertainties and unsatisfied performance of some sensors, as well as its accuracy in structural novelty detection. The proposed method also shows some robustness to noise.

The objectives of this research were to investigate the structural behavior of slender steel reinforced concrete (Referred to as SRC)composite columns subjected to eccentric axial loading. The test consisted of 10 slender columns, with rectangular section160×180mm, and steel shape I10 encased in concrete. The stirrup spacing was 150 mm; its diameter was 6 mm. The diameter of longitudinal reinforcing bars was 10 mm. Details of the experimental investigations including description of the test columns, failure modes and mechanisms, strain characteristics, and load-deformation responses are discussed. Effects of concrete strength, slenderness of columns, and eccentricity of axial loads on the load-carrying capacity of slender column are then presented. Based on these results, a range of slenderness ratio and eccentric ratio of slender SRC column is proposed.

This paper presents an innovative bolt model suitable for the three dimensional finite element analysis (FEA) of the semirigid beam-to-column bolted connections. The model is particularly useful for the moment-rotation relationship of beam-tocolumn connections, especially in cases where the connectors such as endplates, angles, T-stubs, are not particularly thin. In this paper, the bolt tensile behavior is firstly discussed by using a refined finite element model, in which the complex geometries of both external and internal threads were modeled. Then, the bolt behavior predicted by the commonly used models was compared with that of the refined FEA to appraise the accuracy of these models. The comparison shows most of the models commonly used can not predict accurately the axial stiffness, carrying capacity and ductility of bolt simultaneously. Afterwards, an innovative bolt model was proposed and the model accorded with the refined FEA for single bolts. Finally, the proposed model was applied to analyze the moment-rotation behavior of several experimented and well documented connections with different configurations. The results indicate that the proposed model is feasible and efficient.