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The failure of rock in cold regions due to repeated freeze–thaw (F-T) cycles and periodic load-induced fatigue damage presents a significant challenge. This study investigates the evolution of the multi-scale structure of fractured granite under combined freeze–thaw (F-T) cycles and periodic loading and develops a constitutive damage model. The results indicate that after F-T cycles, network cracks develop around pre-existing cracks, accompanied by block-like spalling. After applying the fatigue load, the nuclear magnetic resonance (NMR) T2 spectrum shifts to the right, significantly increasing the amplitude of the third peak. The freeze–thaw process induces a "liquid–solid" phase transition, weakening the original pore structure of the rocks and leading to meso-damage accumulation. The pores in fractured granite progressively enlarge and interconnect, reducing the rock's load-bearing capacity and fatigue resistance. The combined effects of F-T cycles and periodic loading induce particle movement and alter fracture modes within the rock, subsequently affecting its macro-damage characteristics. The theoretical curves of the constitutive model align with the experimental data. The findings can serve as a theoretical reference for preventing and controlling engineering disasters in fractured rock masses in cold regions. [ABSTRACT FROM AUTHOR]

To investigate the degree of stability deterioration in toppling dangerous rock mass under different action times, firstly, the vibration load generated by train travel in a single action and its decay law were studied, and the theoretical relational equation of rock strength deterioration under the action of vibration loading was obtained by analyzing the increase in half axle expansion of micro fissures inside the rock. Secondly, the freezing stress of the microfissures was determined according to the rock freezing and swelling theory, and the theoretical relational equation of rock strength deterioration under the action of freeze-thaw cycles was obtained by integrating the rock confinement and moisture migration conditions of the fissures wall. The stability coefficient of the toppling dangerous rock mass exhibited a rapid and then slow decreasing trend with increasing number of actions, which was non-linearly negatively correlated with the train running speed and the initial porosity of the rock, and non-linearly positively correlated with the freezing temperature. Controlling the freezing temperature and initial porosity of rock can significantly reduce the degree of deterioration in the stability of dangerous rock mass. [ABSTRACT FROM AUTHOR]

In order to study the deterioration law of compressive strength of fly ash mixed concrete, fly ash mixed concrete specimens were prepared with crushed stone, cement, fly ash, medium sand and tap water as raw materials. Under the action of carbonization and dry wet cycle, the strength deterioration test of the specimen was carried out by using the universal pressure testing machine. The test results show that when the content of fly ash does not exceed 30% (including 30% ), the compressive strength of the specimen does not deteriorate. When the content of fly ash exceeds 30%, the more the content of fly ash, the greater the deterioration of compressive strength. The compressive strength of each specimen increased with the extension of age. Increasing the content of fly ash will improve the deterioration of splitting tensile strength. Prolonging the age will slow down the deterioration rate of splitting tensile strength. Increasing the content of water binder ratio leads to the improvement of splitting tensile and compressive strength deterioration of the specimen. Under carbonization, the compressive and splitting tensile strength of the specimen are improved. When the carbonization time is 13 days, the compressive and splitting tensile strength of the specimen reach the peak value. Under the action of dry wet cycle, the compressive and splitting tensile strength of the specimen will deteriorate. When the content of fly ash is 30%, the average compressive and splitting tensile strength of the specimen is relatively high. [ABSTRACT FROM AUTHOR]

Particle impact drilling (PID) is a promising technology to enhance the rate of penetration in hard and abrasive formations. The changes to physical and mechanical properties near the crater of a full-size tight sandstone sample after successive impacts of a steel-particle water jet are investigated by different scales of rock physics measurements to estimate the range of the damage zone. Similar measurements are also carried out on a sample from the same formation without steel-particle water jet as a reference. The results indicate that: (i) there is a damage zone around the crater with induced cracks and pore collapse caused by the impact stress wave produced by the steel-particle water jet. The dimensionless depth of the damage zone from the crater's surface is about 0.69 times the jet diameter (d0). Within the damage zone, the dense compaction zone is just near the crater surface within a dimensionless distance of about (0.02–0.06) d0, where the porosity and the permeability slightly decrease, and show significant strength decrease. (ii) The changes of the porosity and the P- and S-wave velocities after steel-particle water jet at core scale are neglectable. Compared to the reference sample, the permeability at the lateral of the crater is (4.52–30.90) times higher, while the permeability beneath the bottom of the crater is 79% lower. The uniaxial compressional strength (UCS) decreases by 15.6%–65.7%. (iii) The indentation hardness after particle jetting shows a significant decrease. The macro-indentation hardness decreases from 1.92 GPa to 1.30 GPa at core scale. Within the damage zone, the hardness and the Young's modulus calculated from nanoindentation tests decrease with the increase of the distance to the crater's surface. This work as a case study provides new experimental evidence of the evolution of rock damage by the impact stress of the steel-particle water jet. Highlights: The dimensionless depth of the damage zone from the crater's surface is about 0.69 times jet diameter. Permeability is (4.52–30.90) times higher at the laterals of the crater. Macro-indentation hardness and UCS decrease significantly in the damage zone. Nanoindentation hardness decreases with its distance to the crater's surface. [ABSTRACT FROM AUTHOR]

Granite residual soil (GRS) exhibits favorable engineering properties in its natural state. However, a hot and rainy climate, combined with vibrations generated during mechanical construction, can cause a notable decrease in its strength. In this study, the evolution of stress–strain curves and strength parameters (cohesion c and internal friction angle φ), unconfined compression strength (UCS) under drying and wetting(DW) cycles and vibration were investigated by means of direct shear test and UCS test. Furthermore, modified formulas for calculating shear strength and UCS under DW cycles and vibration were proposed, and their accuracy was verified. The results are as follows: The stress–strain curve of shear strength exhibits strain-hardening characteristics, and the shear compressibility of the sample increases with the number of DW cycles and vibration time. However, the stress–strain curve of UCS shows strain-softening properties, and the peak strength shifts forward with the number of DW cycles and vibrations. With the increase in the number of DW cycles and the vibration time, c shows a non-linear degradation, with a maximum degradation of 58.6%. φ fluctuates and increases due to the densification effect of DW cycles, but the influence of vibration on φ decreases with the increase in the number of DW cycles. UCS rapidly decreases and gradually stabilizes after DW cycles and vibration, with a maximum degradation of 81.1%. This study can serve as a reference for the stability analysis of GRS pits subjected to long-term influences of hot and rainy climates and mechanical vibration, providing valuable insights for future research. [ABSTRACT FROM AUTHOR]

The failure of rock in cold regions due to repeated freeze–thaw (F-T) cycles and periodic load-induced fatigue damage presents a significant challenge. This study investigates the evolution of the multi-scale structure of fractured granite under combined freeze–thaw (F-T) cycles and periodic loading and develops a constitutive damage model. The results indicate that after F-T cycles, network cracks develop around pre-existing cracks, accompanied by block-like spalling. After applying the fatigue load, the nuclear magnetic resonance (NMR) T2 spectrum shifts to the right, significantly increasing the amplitude of the third peak. The freeze–thaw process induces a “liquid–solid” phase transition, weakening the original pore structure of the rocks and leading to meso-damage accumulation. The pores in fractured granite progressively enlarge and interconnect, reducing the rock’s load-bearing capacity and fatigue resistance. The combined effects of F-T cycles and periodic loading induce particle movement and alter fracture modes within the rock, subsequently affecting its macro-damage characteristics. The theoretical curves of the constitutive model align with the experimental data. The findings can serve as a theoretical reference for preventing and controlling engineering disasters in fractured rock masses in cold regions.

The particle size distribution of gangue is an important factor affecting the strength of backfill body. To uncover the strength deterioration law and energy dissipation characteristics of cemented backfill with different gangue particle sizes, the uniaxial compressive strength mechanical tests were carried out by scanning electron microscopy analysis combined with rock mechanics test system and acoustic emission monitoring equipment. The deformation failure mode, mechanical characteristics, acoustic emission response characteristics and energy dissipation characteristics of backfill samples with different particle size distribution under uniaxial compression were studied. The results shown that: The particle size distribution of gangue material is very important to the performance of backfill body. The compressive strength of the backfill sample with medium particle size was the largest. As the particle size of the gangue increases, the acoustic emission response degree of the backfill firstly increases followed by a subsequent decrease. The acoustic emission ringing count and energy rate reach the peak when the backfill was destroyed. Building upon the principle of energy dissipation and release, the defined energy dissipation ratio was used as the strength deterioration index of the backfill body. The energy dissipation ratio of fine grain size, medium grain size and coarse grain size filling was 19.64%, 7.85% and 12.93%, respectively. When the failure mode of the backfill shifts from tensile failure to shear failure, the energy dissipation ratio decreases from 19.64% to 7.85%. The storage capacity of elastic strain energy in the backfill gradually increases, and the strength degradation degree of backfill gradually decreases.

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cemented paste backfill (CPB) has been a practical approach for mining waste management, underground goaf treatment, and green mining. Strength deterioration because of high sulfide content (SC) is a severe challenge for sulfide-rich CPB. To investigate the influence of rice straw (RS) on the strength of sulfide-rich CPB, RS was utilized as an inhibitor of strength deterioration. RS dosage (RSD), RS length (RSL), and sulfide content (SC) were chosen as the factors, and two stages of the experiment were carried out. It was found that high SC produced pores, cracks, and loose microstructure of CPB, resulting in the strength deterioration of sulfide-rich CPB. The 90-day uniaxial compressive strength (90 d-UCS) was the maximum of the UCS of sulfide-rich CPB. The hydration products and microstructural characteristics observed by XRD and scanning electron microscopy (SEM) illustrated that RS has the effect of bridging and water retention. Accordingly, adding RS improved the long-term strength of sulfide-rich CPB. The optimal RSD, RSL, and SC for 90 d-UCS of sulfide-rich CPB were obtained through the response surface methodology approach. The optimal conditions within the experimental range of this study for maximum 90 d-UCS of CPB with high SC (17 wt%) were RSD of 0.032 wt% and RSL of 0.28 cm, producing a 90 d-UCS of 5.14 MPa.

In heavy oil recovery, calcium aluminate cement (CAC) is in the working environment of "low-temperature hardening and ultrahigh temperature service." However, the formation of C 3 AH 6 under low temperatures results in a decrease in strength and reduce the cementing quality. In this study, titanium extraction slag (TES) was used to inhibit CAC strength deterioration. TES, characterized by a high Ti content, presents challenges in terms of utilization and poses significant ecological risks owing to its large accumulation. Cementite hydration with 0%, 20%, 30%, and 40% TES relative to CAC was examined at 30 °C for 28 d. The high C 3 AH 6 content of the pure CAC increased the strength deterioration, pore size, and cementite carbonation. With 20% TES, a dilution effect was observed without strength improvement. Furthermore, 30% TES generated layered double hydroxides and converted C–S–H into C–A–S–H, thereby increasing compressive strength. By-products were generated with 40% TES, which inhibited the strength development while generating C–A–S–H to maintain the compressive strength. Therefore, TES can inhibit the strength decline of CAC, and the byproducts of the LDH structure can improve corrosion resistance. [ABSTRACT FROM AUTHOR]

The strength of karst fillings is vital for the safety of tunnels in large-filled karst areas. Karst fillings in areas with seasonal rainfall often experience dry–wet cycle environments, which have a deteriorating effect on their strength and threaten the safety of underground projects such as tunnels. In this study, direct shear tests of dry samples (samples with the moisture content of w 1 ) and wet samples (samples with saturated moisture content) at different dry densities ( ρ d ), the number of dry–wet cycles (n ), and the lower-bound moisture content of dry–wet cycles ( w 1 ) were performed to analyze the deterioration rule of c and φ of karst fillings. The causes of the strength deterioration of karst fillings were explained based on scanning electron microscopy tests. The deterioration rate was fitted using an exponential function, and a karst filling strength deterioration model (KFDM) was developed that integrated three influencing factors. The KFDM was used through FLAC3D to predict the deformation and safety coefficient of tunnels under dry–wet cycles. The following results were obtained: (1) dry–wet cycles had a significant degrading effect on c and φ , and ρ d and w 1 had an important influence on the degradation; (2) the KFDM accurately predicted the c and φ values of karst fillings after dry–wet cycles; and (3) the tunnel deformation and safety coefficient exhibited cyclic changes during dry–wet cycles. The deformation increased gradually at increasing n , and the safety factor increased in the opposite direction. These results provide insights into the prediction of the deformation and safety coefficient of tunnels in large-filled karst areas and can aid in developing long-term maintenance strategies to ensure safety. [ABSTRACT FROM AUTHOR]

The reciprocating shear mechanical properties and strength deterioration mechanisms of rockfill materials are of great research significance for high-fill slope stability analysis. To study the shear strength characteristics of argillaceous siltstone rockfill materials with different fabric characteristics under reciprocating shear loading, we analyzed the shear strength, hysteresis loop area, damping ratio, shear strength parameter, and shear stiffness of coarse-grained soils with different coarse grain contents using a coarse-grained soil direct shear testing machine capable of reciprocating shear and revealed their strength deterioration mechanism. The test results show that the shear strength of argillaceous siltstone rockfill materials is significantly affected by the coarse grain content and the number of reciprocating shears. Specifically, the shear strength increases with the coarse grain content and decreases with the number of reciprocating shears. The hysteresis loop area is positively correlated with the coarse grain content and negatively correlated with the number of reciprocating shears. The damping ratio is not related to the coarse grain content but tends to decrease with the number of reciprocating shears. Soil cohesion and the internal friction angle increase with the coarse grain content and decrease with the number of reciprocating shears. The soil failure shear stiffness is linearly correlated with the coarse grain content, and the normalized shear stiffness is logarithmically related to the number of reciprocating shears. According to these relationships, an empirical formula for the shear stiffness of argillaceous siltstone rockfill materials under different coarse grain contents and different numbers of reciprocating shears can be established to provide a basis for analyzing rockfill stability. [ABSTRACT FROM AUTHOR]

The vertical component of ground motions can affect the seismic performance of reinforced concrete (RC) piers as significant as its horizontal counterpart. However, real‐time testing for RC piers subjected to both horizontal and vertical ground motions has been scarcely conducted due to the difficulty in multi‐axial control of actuators. In this study, the seismic response of a bridge RC pier was investigated by conducting real‐time hybrid simulation (RTHS), where the RC pier was physically tested in the laboratory and the bridge superstructure was numerically modeled. The test setup that can synchronously apply both horizontal and vertical ground motions was constructed by using three dynamic actuators and a flexible loading beam (FLB). The lateral response of the RC pier was investigated by varying the intensities for vertical ground motions, while the same intensity for horizontal ground motion is used. It was found that the axial force from the dead load of superstructure can significantly affect the initial stiffness, strength, and post‐yield response of the RC pier. For the selected earthquake ground motions, however, the intensity of vertical ground motion did not make a substantial difference in the lateral response, although there was a notable difference in the fracture pattern. [ABSTRACT FROM AUTHOR]

Pulse hydraulic fracturing is an effective fracturing stimulation technology, which can reduce rock breakdown pressure and improve fracturing effects. Under pulse hydraulic loading, fatigue damage occurs in the rock, and the rock strength gradually deteriorates. However, the characteristics of rock strength deterioration and rock fracture mechanisms under different pulse hydraulic pressures are not clear, and the fracture model induced by strength deterioration has not been well established. In this study, strength deterioration tests are carried out under different pulse hydraulic pressures, and tensile strength deterioration curves are obtained. We introduce the strength deterioration curve in the continuous discontinuous element method (CDEM) to establish the fracture damage deterioration model of rocks, and implement crack propagation using the improved cohesion zone model. The validity of the fracture damage deterioration model is verified by comparison with the test results. During pulse hydraulic loading, the hydraulic pressure of pulse loading can influence fatigue tensile strength and hydraulic fracture propagation behaviors. With the decrease of pulse loading stress ratio, the fatigue tensile strength gradually decreases, resulting in more fractures in the specimen. Under different pulse loading stress ratios, with the increase of pulse loading numbers, the damage tensile strength of the specimen decreases gradually. When the pulse loading stress ratio is low, the degree of damage to the tensile strength decreases significantly, which easily induces rock failure and increases the fracturing effect. Highlights: A fracture damage deterioration model is proposed for rock failure under pulse hydraulic fracturing. The rock strength deterioration characteristics and rock failure mechanisms under different pulse hydraulic pressures are investigated. The fracture damage deterioration model is introduced in the CDEM to simulate the rock failure under pulse hydraulic fracturing. By simulating hydraulic fracture propagation behaviors under different pulse loading conditions, the rock failure mechanism is revealed. [ABSTRACT FROM AUTHOR]

Hydrodynamic-driven bedding rock landslides are the focus of research in the field of landslide geological hazards due to their large number, frequent disasters, and excessive harm. However, the understanding of the initiation mechanism of landslides is still insufficient, and the accurate prediction of landslides still faces great challenges. Because of this, this paper takes moderate-dip angle bedding rock landslides with weak interlayers as the research object and conducts a series of landslide model tests under the action of hydrodynamics by constructing an ideal single-layer landslide physical model. On this basis, the macroscopic deformation evolution process of the landslide and the erosion degradation characteristics of the slide zone soil is analyzed in depth. The results show that the failure of bedding rock landslides is associated with the slip surface roughness and dip angle and can go through four stages: the initial deformation stage, uniform deformation stage, accelerated deformation stage, and failure stage.The seepage erosion in the sliding zone causes the loss of aggregates, which reduces the shear strength and causes the slope to slide. Simultaneously, the compression-shear action and the deformation of the overlying slope also adversely affect erosion strength.Based on the variation law of soil cohesion in the sliding zone with hydraulic gradient and erosion time, a seepage-driven evolution model of soil cohesion in the sliding zone is proposed, which can describe the degradation process of soil cohesion in the sliding zone well. The existence of sliding surface roughness not only significantly affects the deterioration law of the sliding zone, but also changes the failure modes of different regions of the sliding zone. By considering the influence of the roughness on the failure modes of different areas of the sliding zone, the multi-effect correlation analysis of dynamic water is carried out, and the mechanical model of the landslide is established, which realizes the effective evaluation of the dynamic stability of the landslide. The research achievements in this study can provide a theoretical reference for predicting and preventing actual hydrodynamic-driven bedding rock landslides.

Accurately simulating the nonlinear response of reinforced concrete (RC) columns under cyclic loading is crucial in performance-based seismic design for building structures, especially regarding strength degradation. This paper presents the description, calibration and simulation of the hysteretic model for RC columns based on effective hysteretic energy dissipation with positive and negative directions. During the analysis of previous experimental data, the relationship between hysteresis energy dissipation, maximum displacement, and the effects of positive and negative loading directions on strength degradation has been summarized. The proposed method for determining the yield strength of the hysteresis loop is based on the farthest point method. Calibration of the hysteretic models' existing RC columns' experimental data demonstrates that the proposed model can simulate the main characteristics that influence deterioration. [ABSTRACT FROM AUTHOR]

Granite residual soil (GRS) exhibits favorable engineering properties in its natural state. However, a hot and rainy climate, combined with vibrations generated during mechanical construction, can cause a notable decrease in its strength. In this study, the evolution of stress–strain curves and strength parameters (cohesion c and internal friction angle φ), unconfined compression strength (UCS) under drying and wetting(DW) cycles and vibration were investigated by means of direct shear test and UCS test. Furthermore, modified formulas for calculating shear strength and UCS under DW cycles and vibration were proposed, and their accuracy was verified. The results are as follows: The stress–strain curve of shear strength exhibits strain-hardening characteristics, and the shear compressibility of the sample increases with the number of DW cycles and vibration time. However, the stress–strain curve of UCS shows strain-softening properties, and the peak strength shifts forward with the number of DW cycles and vibrations. With the increase in the number of DW cycles and the vibration time, c shows a non-linear degradation, with a maximum degradation of 58.6%. φ fluctuates and increases due to the densification effect of DW cycles, but the influence of vibration on φ decreases with the increase in the number of DW cycles. UCS rapidly decreases and gradually stabilizes after DW cycles and vibration, with a maximum degradation of 81.1%. This study can serve as a reference for the stability analysis of GRS pits subjected to long-term influences of hot and rainy climates and mechanical vibration, providing valuable insights for future research.

Multiple freeze–thaw cycle tests were conducted on sandstone samples. The sandstone samples were examined using X-ray diffraction (XRD) and nuclear magnetic resonance (NMR). The mineral content, porosity distribution, T2 (transverse relaxation time) spectral distribution, spectral area, and nuclear magnetic resonance imaging (MRI) data for sandstone samples were obtained, and the distribution and variation of the sample pores were analyzed. Uniaxial compression tests were performed on samples that had undergone 0, 20, 40, and 80 freeze‒thaw cycles, and the effects of freeze‒thaw cycles on the mass, compressive strength, and elastic modulus of the sample were analyzed. The damage evolution and strength degradation characteristics of sandstone after freeze‒thaw cycles were studied. As the number of freeze‒thaw cycles increases, mineral particle flaking and cracking appear on the rock surface, the uniaxial compressive strength and elastic modulus of rock samples decrease, and the typical stress–strain curve compaction stage corresponding to the deformation increases. According to the NMR T2 distribution, the pore size of rock samples increases after 80 freeze‒thaw cycles, especially that of medium-sized and small-sized pores. Meanwhile, the internal damage to the rock mass is a gradual process of cumulative fatigue damage caused by freezing and thawing, and the microscopic damage evolution law during freeze‒thaw cycles was revealed using MRI. Based on plasticity theory and damage fracture mechanics theory, the sandstone damage propagation criterion under freeze‒thaw-loading action was deduced, and a sandstone freeze‒thaw damage degradation model was established. [ABSTRACT FROM AUTHOR]

The reciprocating shear mechanical properties and strength deterioration mechanisms of rockfill materials are of great research significance for high-fill slope stability analysis. To study the shear strength characteristics of argillaceous siltstone rockfill materials with different fabric characteristics under reciprocating shear loading, we analyzed the shear strength, hysteresis loop area, damping ratio, shear strength parameter, and shear stiffness of coarse-grained soils with different coarse grain contents using a coarse-grained soil direct shear testing machine capable of reciprocating shear and revealed their strength deterioration mechanism. The test results show that the shear strength of argillaceous siltstone rockfill materials is significantly affected by the coarse grain content and the number of reciprocating shears. Specifically, the shear strength increases with the coarse grain content and decreases with the number of reciprocating shears. The hysteresis loop area is positively correlated with the coarse grain content and negatively correlated with the number of reciprocating shears. The damping ratio is not related to the coarse grain content but tends to decrease with the number of reciprocating shears. Soil cohesion and the internal friction angle increase with the coarse grain content and decrease with the number of reciprocating shears. The soil failure shear stiffness is linearly correlated with the coarse grain content, and the normalized shear stiffness is logarithmically related to the number of reciprocating shears. According to these relationships, an empirical formula for the shear stiffness of argillaceous siltstone rockfill materials under different coarse grain contents and different numbers of reciprocating shears can be established to provide a basis for analyzing rockfill stability.

Accurately simulating the nonlinear response of reinforced concrete (RC) columns under cyclic loading is crucial in performance-based seismic design for building structures, especially regarding strength degradation. This paper presents the description, calibration and simulation of the hysteretic model for RC columns based on effective hysteretic energy dissipation with positive and negative directions. During the analysis of previous experimental data, the relationship between hysteresis energy dissipation, maximum displacement, and the effects of positive and negative loading directions on strength degradation has been summarized. The proposed method for determining the yield strength of the hysteresis loop is based on the farthest point method. Calibration of the hysteretic models’ existing RC columns’ experimental data demonstrates that the proposed model can simulate the main characteristics that influence deterioration.

To simulate the dynamic traffic loads imposed on the concrete during service, a piece of self-designed dynamic loading equipment was used to study the strength deterioration pattern of basalt fiber reinforced concrete (BFRC) under fatigue loading at 0.5 and 0.7 stress levels. Subsequently, crack images of the fracture surface and interior were obtained with a high-pixel camera and SEM, respectively, from which the fractal dimension of the cracks was finally obtained by processing and calculating with MATLAB, Image-Pro Plus, and Fractalfox software. The results showed that, at 0.5 and 0.7 stress levels, the flexural strengths of both BFRC and the reference concrete gradually decreased with increasing number of load actions, but the higher stress caused a faster decrease. Significantly, the flexural strength of BFRC consistently dropped more slowly than that of the reference concrete. The reduction rate of flexural strength of basalt fiber reinforced concrete was reduced by 2.26% and 5.28% compared with the reference group after 200,000 times at 0.5 and 0.7 stress levels, respectively. The maximum crack length, average crack width and crack area density of fiber concrete decreased by 8.81%, 10.69% and 42.29%, respectively, after 200,000 cycles of dynamic fatigue loading at low-stress level compared to the reference concrete. Fatigue loading with high-stress level accelerates the rate of structural deterioration within the concrete, but basalt fibers improve the fatigue performance of concrete by synergistically stressing it with concrete, changing the direction of crack development and extending the crack expansion path. The flexural strength at low-stress level is significantly negatively correlated with the average crack width, while the flexural strength at high-stress level is significantly correlated with the fractal dimension of cracks, crack area density and average crack width.

Safety analysis and prediction of a marine structure is a very important field which has received attention from many scientists. Prof. R. Ajit Shenoi has made significant contributions in investigating various issues in this field. In this invited paper of recollection nature, a philosophical attitude is taken to re-examine some fundamental issues about the safety of marine structures with a purpose to identify the key issues to be solved in the future. It is intended to help young generations of scientists how to focus on more important problems related to the safety of marine structures. [ABSTRACT FROM AUTHOR]

River silt deposited by water in coastal areas is unsuitable for engineering construction. Thus, the in situ stabilization treatment of river silt as the bearing layer has been an important research area in geotechnical engineering. The strength degradation behavior and mechanism of stabilized river silt reinforced with cement and alginate fibers (AFCS) in different engineering environments are crucial for engineering applications. Therefore, freeze-thaw (F-T) cycle tests, wetting-drying (W-D) cycle tests, water immersion tests and seawater erosion tests were conducted to explore the strength attenuation of stabilized river silt reinforced with the same cement content (9% by wet weight) and different fiber contents (0%, 0.3%, 0.6% and 0.9% by weight of wet soil) and fiber lengths (3 mm, 6 mm and 9 mm). The reinforcement and damage mechanism of AFCS was analyzed by scanning electron microscopy (SEM) imaging. The results indicate that the strength of AFCS was improved from 84% to 180% at 15 F-T cycle tests, and the strength of AFCS was improved by 26% and 40% at 30 W-D cycles, which showed better stability and excellent characteristics owing to the hygroscopic characteristics of alginate fiber arousing the release of calcium and magnesium ions within the alginate. Also, the strength attenuation of AFCS was reduced with the increase in the length and content of alginate fibers. Further, the strength of specimens in the freshwater environment was higher than that in the seawater environment at the same fiber content, and the softening coefficient of AFCS in the freshwater environment was above 0.85, indicating that the AFCS had good water stability. The optimal fiber content was found to be 0.6% based on the unconfined compressive strength (UCS) reduction in specimens cured in seawater and a freshwater environment. And the strength of AFCS was improved by about 10% compared with that of cement-stabilized soil (CS) in a seawater environment. A stable spatial network structure inside the soil was formed, in which the reinforcing effect of fibers was affected by mechanical connection, friction and interfacial bonding. However, noticeable cracks developed in the immersed and F-T specimens. These microscopic characteristics contributed to decreased mechanical properties for AFCS. The results of this research provide a reference for the engineering application of AFCS.

The strength deterioration of compacted loess caused by drying–wetting cycles is influenced by various factors. In this paper, the influence of dry density (ρ), drying–wetting amplitude (A), and lower bounds of drying–wetting cycles (wl) on strength deterioration of compacted loess due to drying–wetting cycles was studied through triaxial tests and environmental scanning electron microscope (ESEM). By fitting a hyperbolic function to the deterioration data, the influence of ρ, A, and wl on the maximum deterioration rate and the development speed of the deterioration of strength parameters were quantitatively analyzed. Accordingly, a compacted loess deterioration model (CLDM) that comprehensively considers the influencing factors was established. Finally, based on Python, the CLDM was applied to finite element software ABAQUS, and the stability of a loess fill slope after exposure to drying–wetting cycles was analyzed. Analysis results show that the CLDM is capable of simulating the effect of drying–wetting cycles on the stability of fill slopes. [ABSTRACT FROM AUTHOR]

The strength deterioration of soil-rock mixtures (SRM) subjected to freeze–thaw (F–T) cycles leads to instability and failure of upper engineering structures in cold regions. However, the mutual feedback response mechanism pertaining to the changes of pore and strength in SRM under F–T cycles are rarely addressed. Nuclear magnetic resonance and triaxial tests were carried out to study the pore structure characteristics and strength response patterns of samples. A correlation model of SRM porosity and strength deterioration was first proposed under F–T cycles, and the model rationality was verified by test data. The results demonstrated that the pore connectivity and porosity increased throughout the F–T process, with the T 2 spectral distribution curves exhibiting three peaks. Among these peaks, the main peaks underwent slight changes, while the secondary and micro peaks presented significant changes. Before 3 F–T cycles, the pore distribution evolved to small pores uniformly, followed with the large pores increasing and the micropores disappearing. With increasing of F–T times, the strength and cohesion of SRM experienced a drastic decline, while the internal friction angle demonstrated a slight decrease accompanied by fluctuations. Based on the analysis of test results, a correlation model regarding the porosity and strength deterioration was proposed through the relationship between the micro-structure evolution and the macro–mechanical response during F–T cycles. Furthermore, intrinsic mechanism of SRM strength deterioration under F–T cycles was revealed by considering the pore structure characteristics. The results can provide theoretical insights for the analysis of F–T disaster mechanism and prevention of SRM in cold regions. • The macro and micro characteristics of SRM during F–T cycles are obtained. • Qualitative and quantitative analysis of pore structures are performed based on NMR. • The changes in pore connectivity of samples under F–T cycles are evaluated with MnCl 2 solution. • A correlation model of SRM porosity and strength deterioration are first proposed. • The feed-response mechanism between pore and strength in SRM under F–T cycles are revealed. [ABSTRACT FROM AUTHOR]

The fractal characterisation of stress and acoustic emission (AE) of coal and rock failure may provide quantitative guidance for analysing the stability of rock mass during excavation engineering. The correlation between stress and AE data was calculated using fractal theory methods and Grassberger-Procaccia (G-P) algorithms to evaluate the damage and degree of flaw in coal and rock materials under multilevel dynamic loading (MDL). First, the mechanical properties of the testing device were developed to obtain synchronous data regarding the stress and AEs of coal and rock specimens under MDL. Second, strength deterioration behaviour and the Felicity effect during coal and rock failure are compared under different levels of dynamic loading. The results show that cumulative dynamic loading are less than the uniaxial compression strength of coal and rock. The Felicity effect is notable, and Felicity ratios decrease to 1 with increased loading velocity. Finally, stresses and AE signals are considered as the data mining specimens of correlation dimensions based on the G-P algorithm. Fractal characteristics on stress and AE coupling properties become more notable as the correlated dimensions become larger. However, the Felicity effect is less prominent, reflecting a lesser degree of damage and flaws in coal and rock materials. Therefore, this study suggests a data mining method for the correlation dimension to be applied in an in-situ monitoring system for rock mass excavation engineering. [ABSTRACT FROM AUTHOR]

[Display omitted] • Studied CCS with incorporated PCM experimentally. • Porosity and crack increased with PCM addition. • PCM addition into concrete reduced its compressive strength. • Explored the mechanism of concrete strength deterioration from microscopic. In this study, a novel kind of phase-change cementitious composites with cloud concrete stone (CCS) as aggregate were prepared and studied. The CCS was synthesized with fly ash, slag, and other construction waste through water heat and autoclaving. The phase-change paraffin was absorbed into the CCS using the vacuum impregnation technique, and then the epoxy resin combined with cement powder was applied to the aggregate surface to prevent the leakage of phase-change materials (PCMs). The composite aggregate with phase change function was, thus, fabricated. A series of experiments were carried out to study and evaluate the molecular structure, physical phase, and phase transition temperature of encapsulated composite aggregate with the means of Fourier infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The PCM-cement composites were prepared by replacing coarse aggregates with the composite aggregate in proportions of 25%, 50%, 75%, and 100% in volume. To explore the strength degradation in view of the microscopic perspective, scanning electron microscopy (SEM), XRD, and Image-Pro-Plus (IPP) were used. The experimental results revealed that the effect of the micropores of CCS on the melting temperature of the phase-change aggregates (24.84 °C) is higher than that of the paraffin (22.91 °C). The mechanical experiments results demonstrated that the compressive strength and splitting strength losses in the PCM-cement composite with replacement ratios of 75% were 24% and 39%, respectively. The XRD results revealed that with the incorporation of PCM, the calcium silicate hydrate (C-S-H) in the hydration products decreased and the Ca/Si value in C-S-H decreased from 9.05 to 2.13, which is one of the reasons for the strength decline of the PCM-cement composites. The cracks in the interfacial transition zone between the aggregate and matrix became large with increasing admixture, and the pore characteristics gradually became more apparent. The strength of the PCM-cement composite decreased with the increase in the average porosity, pore size, and perimeter of the matrix material. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) columns with an annular cross-section are commonly utilized as supporting structural members in ocean engineering structures, and their structural performance deterioration is mainly caused by the corrosion of rebar in aggressive marine environment. This paper proposes an effective method to investigate the effects of rebar corrosion on the structural performance of the annular RC columns under various loading conditions. Firstly, the material degradation and residual structural strength models are proposed based on the analysis of the corrosion-induced deterioration of RC structures. Then, the general method for determining the load-bearing capacity is developed using the equivalent steel ring assumption. To improve computational efficiency and practical applicability, an effective method for assessing the residual load-bearing capacity is proposed by simplifying the calculations of rebar load-bearing capacity coefficients using the regression fitting approach. Finally, the effectiveness of the proposed simplified method is demonstrated with the relevant experimental data available. The results show the capacity deterioration rate is strongly related to the corrosion level and loading condition with the most severe degradation typically at the corrosion level of 5–10%, and the smaller and larger eccentric columns drop the capacities by about 28% and 41% at 10% corrosion level, respectively. • Investigating behaviour of corroded RC columns with an annular cross-section. • Developing a novel effective method for predicting residual load-bearing capacity. • New insight into how rebar corrosion affects structural strength of annual RC columns. • In-depth study on residual strength of corroded columns under various loading conditions. [ABSTRACT FROM AUTHOR]

Densely compacted loess on which many man-made infrastructures are built are often exposed to strong weathering processes such as repeated wetting-drying (WD) and freeze-thaw (FT) cycles. These weathering processes in arid and seasonally frozen ground regions result in loose structure and strength deterioration of loess soils, and they cause serious engineering problems and expensive maintenance costs of infrastructures built on densely compacted loess. In this study, specimens of densely compacted loess were exposed to different intensities of weathering processes under controlled laboratory environment to quantitatively assess their deterioration effects on geotechnical properties. According to the laboratory results, the wetting-drying weathering has a stronger impact on the geotechnical properties of densely compacted loess than the freezing-thawing weathering. The unconfined compressive strength, elastic modulus, and cohesion of the loess specimens decrease with increasing number of WD and FT cycles while the vertical compression strain and collapse deformation increase. The densely compacted and non-collapsible loess specimens exhibited collapsible again (secondary collapse) after 5 WD cycles. The deterioration mechanisms of densely compacted loess induced by wetting-drying and freezing-thawing weathering processes have been presented and were strongly recommended to be taken into account for the prediction of long-term stability and serviceability of man-made infrastructures built on densely compacted loess. [ABSTRACT FROM AUTHOR]

In the aggressive marine environment over a long-term service period, coastal bridges inevitably sustain corrosion-induced damage due to high sea salt and humidity. This paper investigates the strength reduction of coastal bridges, especially focusing on the effects of non-uniform corrosion along the height of bridge piers. First, the corrosion initiation time and the degradation of reinforcement and concrete are analyzed for bridge piers in marine environments. To investigate the various damage modes of the concrete cover, a discretization method with fiber cells is used for calculating time-dependent interaction diagrams of cross-sections of the bridge piers at the atmospheric zone and the splash and tidal zone under a combination of axial force and bending moment. Second, the shear strength of these aging structures is analyzed. Numerical simulation indicates that the strength of a concrete pier experiences dramatic reduction from corrosion initiation to the spalling of the concrete cover. Strength loss in the splash and tidal zone is more significant than in the atmospheric zone when structures’ service time is assumed to be the same. [ABSTRACT FROM AUTHOR]

This work presents the development of a hysteretic beam element in the context of the finite element method, that is suitable for the inelastic dynamic analysis of framed structures. The formulation proposed is able to capture the main characteristics of hysteresis in structural systems and mainly accounts for stiffness degradation, strength deterioration and pinching phenomena, as well as for non-symmetrical yielding that often characterizes their behavior. The proposed formulation is based on the decoupling of deformations into elastic and hysteretic parts by considering additional hysteretic degrees of freedom, i.e., the hysteretic curvatures and hysteretic axial deformations. The direct stiffness method is employed to establish global matrices and determine the mass and viscous damping, as well as the elastic stiffness and the hysteretic matrix of the structure that corresponds to the newly added hysteretic degrees of freedom. All the governing equations of the structure, namely the linear global equations of motion and the nonlinear evolution equations at elemental level that account for degradations and pinching, are solved simultaneously. This is accomplished by converting the system of equations into state space form and implementing a variable-order solver based on numerical differentiation formulas (NDFs) to determine the solution. Furthermore, hysteretic loops and degradation phenomena are easily controlled by modifying the model parameters at the element level enabling simulations of a more realistic response. Numerical results are presented and compared against experimental results and other finite element codes to validate the proposed formulation and verify its ability to simulate complex hysteretic behavior exhibiting cyclic degradations. [ABSTRACT FROM AUTHOR]

Traditional seismic design of framed structures uses a single constant value for the strength reduction factor. In this work, explicit expressions for different values of strength reduction factors for the first significant modes of steel moment resisting frames including strength deterioration and panel zone effects are developed. These factors are functions of modal periods and deformation/damage and are defined for four performance levels in a performance-based seismic design framework. The above factors are obtained through extensive parametric studies involving 20 steel frames and 100 far-field ground motions and following a two steps procedure: First an equivalent linear structure with the same mass and elastic stiffness of the original non-linear one is constructed based on equivalent modal damping ratios, which substitute the non-linearities; then use of these equivalent modal damping ratios in conjunction with modal damping reduction factors leads to modal strength reduction factors. Using these factors, one can obtain the seismic design base shear of a frame through response spectrum analysis. Thus, a more accurate and rational seismic design method is established. Numerical examples are presented to illustrate the method and demonstrate its advantages against conventional seismic design methods. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on seismic collapse capacity of high-rise concrete-filled steel tubular moment resisting frames (CFT-MRFs) under extreme ground motions that are beyond the design levels. The ground motions characterised as flat velocity spectral shape were selected to neglect record-to-record uncertainty induced by the changing of the natural periods of structures. A simple numerical approach was developed using fibre element with stiffness and strength degradation accounted in stress–strain models. Then, incremental dynamic analyses with various parameters were performed to evaluate the P-Delta and degradation effects on local and global collapse mechanisms. Results have shown that a drift concentration at the lower stories triggered the side-sway collapse mode that was dominated by the post-buckling strength degradation of CFT columns. The height of drift concentration indicates the range where the collapse mechanism was formed, and a drift concentration factor was proposed to estimate the extent of drift concentration. Last, a factor indicating the safety margin under collapse was computed based on the probability of earthquake occurrence. [ABSTRACT FROM PUBLISHER]

Fibers by themselves have a limited use in engineering applications since they cannot transmit loads from one to another; therefore, the matrix material plays an important role in the overall function of the fiber reinforced polymer (FRP) composites. This paper intends to study the long term strength of epoxy resins subject to accelerated hygrothermal conditions. Such tests are able to predict the weather durability performance of epoxy materials, which is particularly important for many FRP bonded concrete structures. Several sets of epoxy beam specimens have been constructed and exposed to various hygrothermal environments (25 °C, 100 °C, 180 °C and 0% or 100% relative humidity). Specimens were then evaluated at selected thermal cycles by three-point flexural tests. The flexural strength, mid-span deflection, and stiffness, as well as the mode of failure, have been examined in this study. [ABSTRACT FROM AUTHOR]

Current design approach for seismic isolated structures is to perform bounding analyses. These analyses provide an envelope for the response of the seismic isolated structure rather than focusing on the actual performance. In this study, the success of bounding analyses to estimate performance of a seismic isolated structure, in which the isolation is provided by means of lead rubber bearings (LRBs), is evaluated in a comparative manner. For this purpose, nonlinear response history analyses were performed under the effect of bidirectional ground motion excitations. In bounding analyses, non-deteriorating hysteretic representations were used to model the hysteretic behavior of LRBs. On the other hand, to estimate the actual performance of both the superstructure and isolator units, deteriorating hysteretic idealizations were employed. The deterioration in strength of LRBs was defined as a function of temperature rise in the lead core. The analyzed structure is an existing seismically isolated hospital building and analytically modeled in accordance with its reported design properties for both isolation units and superstructure. Results obtained from analyses where LRBs are idealized by both deteriorating and non-deteriorating hysteretic representations are used in the comparisons. The response quantities used in the comparisons are maximum isolator displacement, maximum isolator force, maximum absolute floor acceleration, and maximum relative story displacements. In an average sense, bounding analyses is found to provide conservative estimates for the selected response quantities and fulfills its intended purpose. However, it is revealed that there may be individual cases where bounding analyses fails to provide a safe envelope. [ABSTRACT FROM AUTHOR]

• Blast resistance of UHPC column pre- and post-fire hazard was studied. • Exposure to elevated temperature changed blast induced column failure mode. • Bond-slip behaviour had varying impact on the blast resistance. • Pressure-impulse diagrams were developed for fire damaged UHPC columns. Concrete structures may experience fire and blast during their service life as a result of accidental explosions or vehicular collisions. Both fire and blast can cause severe damage that threatens the structural safety. In the present study, reinforced concrete columns fabricated by ultra-high performance concrete (UHPC) are investigated under coupled fire and blast loads. Strength degradation and damage of UHPC and steel reinforcement after exposure to elevated temperature (up to 800 °C) were established based on the experimental data. In addition to the detrimental effect on individual material, bond-slip behaviour between the UHPC and reinforcement affected by the elevated temperature was considered. The findings revealed that material strength degradation and damage owing to elevated temperature significantly influenced the structural blast resistance, and the degraded bond-slip behaviour had varying impact on the structural response depending on the structural damage mode. Up to 10% mid-span displacement differences were noted in columns with/without the consideration of bond-slip behaviour. Different failure mechanisms pre- and post-fire damage were observed in the numerical simulations. To quickly assess blast induced damage on UHPC columns, Pressure-Impulse (P-I) diagrams of the UHPC columns before and after elevated temperature were established and empirical formulae were proposed to generate the P-I diagrams. [ABSTRACT FROM AUTHOR]

Existing high-rise steel moment resisting frames (SMRF) in Japan sustained severe damage under the background of Tohoku earthquake and face collapse risks if great ocean ridge earthquakes occur in the near future. This paper presents a numerical study on collapse analysis of existing high-rise SMRFs under long period ground motions over the design levels. A finite element model based on fiber discretized layers was employed to incorporate the deterioration effects in bending strength of beams and axial force-bending moment (N-M) interaction of columns. Parameters for the numerical model were validated by a series of component tests, and a shaking table test on a high-rise SMRF substructure. Simulation results shown reasonable accuracy for predicting the low-cycle fatigue of steel beams, post-local buckling of steel columns and side-sway collapse mode of high-rise SMRFs. Then, parametric analyses were conducted to evaluate the dominant factors controlling the collapse capacity of high-rise SMRFs with various story and degradation levels. It indicated that a beam-to-column strength deterioration factor (SDF) plays an important role on collapse behavior characterized by asymmetric sway deformation concentrated at lower stories. Finally, design recommendation in terms of critical buckling strength of columns is proposed to define the collapse capacity of critical columns in high-rise SMRFs. [ABSTRACT FROM AUTHOR]

A continuous and smooth hysteretic model for shear-critical reinforced concrete (RC) columns was identified and calibrated based on an efficient stochastic search technique and an experimental database consisting of 30 shear-critical RC columns. The inelastic restoring force of shear-critical columns was described by the Bouc-Wen-Baber-Noori (BWBN) model to produce the requisite strength and stiffness degradation as well as pinching effect. Meanwhile, the backward Euler and Newton-Raphson schemes were adopted to determine the inelastic restoring force by solving the ordinary differential equations. Then a differential evolution (DE) algorithm was utilized to identify the control parameters of the BWBN hysteretic model based on an experimental database consisting of 30 shear-critical rectangular columns under cyclic loading. Finally, prediction equations for the BWBN model parameters were developed in terms of four structural physical parameters. The capability and accuracy of the calibrated hysteretic model were demonstrated by comparison with the available experimental data. [ABSTRACT FROM AUTHOR]

In concrete-filled steel tubular (CFST) beam-columns under cyclic loadings, local buckling of restrained steel tube, crushing and slipping of the confined concrete could have significant influences on strength and stiffness degradation. This paper presents a numerical model based on fiber element discretization for simulating the deterioration behaviour of both rectangular and circular CFST beam columns under axial load and cyclic loading. Uniaxial stress-strain relationships for steel and concrete in CFST beam columns are proposed by introducing unified parameters to control the extent of deterioration. Axial contraction caused by local buckling was accounted by defining an inelastic region that promises plasticity and strength degradation. The numerical model was validated by comparing the simulation results and the associated experimental results. The influences of diameter-to-thickness ratio, concrete and steel strength ranging from normal strength to high strength on the deterioration behavior of circular and rectangular CFST beam-columns were analyzed. Finally, through recognizing the limit state to trigger global strength degradation of a CFST frame, the developed numerical model is applicable for simulating global behavior of CFST frames under collapse-level deformations. [ABSTRACT FROM AUTHOR]

Fibers by themselves have a limited use in engineering applications since they cannot transmit loads from one to another; therefore, the matrix material plays an important role in the overall function of the fiber reinforced polymer (FRP) composites. This paper intends to study the long term strength of epoxy resins subject to accelerated hygrothermal conditions. Such tests are able to predict the weather durability performance of epoxy materials, which is particularly important for many FRP bonded concrete structures. Several sets of epoxy beam specimens have been constructed and exposed to various hygrothermal environments (25 °C, 100 °C, 180 °C and 0% or 100% relative humidity). Specimens were then evaluated at selected thermal cycles by three-point flexural tests. The flexural strength, mid-span deflection, and stiffness, as well as the mode of failure, have been examined in this study.

This study discusses strength deterioration during the curing process of fly ash geopolymer and the use of CaSO4·2H2O (gypsum) as a deterioration remedy when the ash was synthesized using a 10M NaOH and Na-silicate solution. The strength decline was mainly due to the widespread formation of nanometer-sized cracks that were related to excessive Na and Si concentrations at an early age. Use of 2 wt% CaSO4·2H2O resulted in the best measured strength by temporarily reducing Na and Si concentrations; Na was absorbed by SO42-, up to 11% in the matrix within one day, and formed Na2SO4 (thenardite), which gradually dissolved over time, slowly releasing Na ions. However, more than 4% gypsum suppressed overall strength development because too many Na ions were locked into Na2SO4 and could not participate in geopolymerization. The addition of gypsum impeded glass dissolution and even halted the process when more than 4% gypsum was used. [ABSTRACT FROM AUTHOR]

This paper investigates the cyclic behavior of deep wide-flange sections, used as columns in steel Special Moment Frames (SMFs), through detailed finite element (FE) analysis. A wide range of wide-flange sections is subjected to symmetric cyclic lateral loading combined with different levels of constant compressive axial load ratios representing the loading conditions of interior steel columns in SMFs. The FE simulations demonstrate that wide-flange beam-columns, with web and flange slenderness ratios near the current compactness limits of seismic design provisions (AISC 341-10), experience rapid cyclic deterioration in flexural strength under high axial load ratios. It is also found that deep wide-flange slender sections shorten axially to about 10 % of their length due to severe flange and web local buckling. Based on the FE simulations, for bottom story columns, where axial load ratios are in the range of 20-35 %, a reduction to about two thirds of the current compactness limit for highly ductile members would achieve a 4 % chord rotation while maintaining a flexural strength larger than 80 % of the expected plastic flexural strength of a steel column. The FE simulation results also suggest that the pre-capping rotation predicted by current modeling recommendations for steel components (PEER/ATC 72-1) is overestimated for sections with high web and flange slenderness ratios undergoing monotonic and/or cyclic lateral loading combined with high axial load levels. [ABSTRACT FROM AUTHOR]

SUMMARY A method of nonlinear seismic analysis for RC framed structures considering full-range factors, including stiffness and strength degradation, geometric nonlinearity, and structural member failure, is established based on the fundamental concept of the force analogy method. The strong material nonlinearity, large geometric deformation, and internal forces redistribution due to the member failure can be depicted by the proposed local plastic mechanisms, the rotation hinges at the member ends and the slide hinges assigned to the columns, of which the measurement relationships are moment versus plastic rotation and shear force versus shear plastic deformation, respectively. They are capable of evaluating the exact response of RC structures. Because only unchanging initial stiffness matrices are used through the whole computation process, the state-space formulation was used for solving the equations of motion. The advantages of the force analogy method, such as high efficiency and stability, are still retained. The exactness of the proposed local plastic mechanisms is verified against a group of tests data, and the application of the proposed procedure is performed to an RC framed structure to simulate the full-range nonlinear response by increasing the excitation step by step until failure of partial structural members appear. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights: [•] We apply two modifications to the Bouc–Wen type model by Sivaselvan and Reinhorn [3]. [•] The first corrects the loading history problem in the stiffness degradation rule. [•] The second is related to compatibility with plasticity postulates. [•] Numerical examples are presented for a sdof system demonstrating the modifications. [ABSTRACT FROM AUTHOR]