Bearing Capacity Degradation Research Articles

Seismic Performance of Precast Concrete Bridge Piers with Built-In Steel Tube Connection Key

Investigating the seismic behavior of precast concrete bridge piers is crucial in the design process due to the complex stress distribution in the connecting components. To demonstrate the seismic behavior of precast concrete bridge piers with hybrid joint connections, three bridge piers were designed with a scaling ratio of 1:8 and then tested under low cyclic loading conditions. The tests involved varying shapes of steel tube connection keys as parameters. This study involved examining failure modes and crack development, as well as analyzing the hysteretic performance, deformation capacity, energy dissipation, and stiffness degradation of the specimens. Furthermore, a finite element model was developed using ABAQUS, and the validity of the modeling approach suggested in this study was confirmed through tests. The results indicate that the precast piers exhibit reduced concrete damage at the joints. The enhanced strength of the joints is attributed to the incorporation of steel tube connection keys. The circular steel tube connection key integrated into the precast bridge pier offers a superior bearing capacity, energy dissipation, and stiffness degradation compared to the cross-shaped steel tube connection key. The presence of the built-in circular steel tube connection key in the precast bridge pier suggests that it complies with the seismic structural measures and is consistent with the design principle of “strong joint and weak member”.

Low-cycle fatigue behaviour of concrete-filled double skin steel tubular (CFDST) members for wind turbine towers

Wind energy has the advantages of being clean and renewable. Wind turbine towers endure horizontal cyclic loads that could influence the performance of entire structure. To clarify the low-cycle fatigue behaviour of concrete-filled double skin steel tubular (CFDST) members, a total of 16 specimens were experimented. The hollow, slenderness, and axial compression ratios are specifically designed to clarify the effects on performance under constant amplitude loading and hysteretic loading conditions. The typical failure modes under both loading conditions and the relationship between loop strain, loop bearing capacity, loop energy dissipation, cycle number, and various degradation indices were analysed. Studies indicate that the failure mode under low-cycle fatigue loading is mainly local deformation, which includes transverse fracture occurring at the region between the steel tube and ribbed stiffener, the crushing concrete. Fatigue specimens with different amplitudes exhibit varying shapes of hysteresis responses. Higher amplitudes could enhance damage and significantly reduce fatigue life. Increasing the hollow and axial compression ratios boosts the energy dissipation capacity, and decreasing the slenderness ratio enhances the lateral resistance. A 2 % constant amplitude preload intensifies the degradation of bearing capacity and energy dissipation under subsequent constant amplitude loading.

Behaviour of a Cold-Formed Steel Shear Wall with Centre-Corrugated Steel Sheathing under Cyclic Loading

A cold-formed steel shear wall with centre-corrugated steel sheathing (CCSS-CFS shear wall) was innovatively developed to meet the requirement of earthquake resistance for multi-rise CFS structures in regions at high seismic risk. This wall exhibits superior seismic performance in comparison with the conventional CFS shear wall. Five full-size specimens were tested under cyclic loading to evaluate their failure mode, shear strength, lateral stiffness, ductility, energy dissipation, as well as degradation of bearing capacity and stiffness. Additionally, the effects of CFS frame structure forms, screw spacing, and corrugated steel sheet thicknesses on the behaviour and failure mechanism of shear walls were analysed. The seismic performance objectives corresponding to intact, slight, moderate, and severe damage were also determined. The results revealed that the main failure modes of shear walls were plastic buckling of corrugated steel sheathing and local buckling of the end composite stud. Optimising configurations such as setting up stiffening plates on the end composite stud, installing transverse braces, and increasing screw spacing between composite studs and sheathing significantly improved their behaviour. The strength of corrugated steel sheathing after plastic buckling should be taken into consideration for the lateral design of the CCSS-CFS shear wall. A calculation method was also proposed in order to determine the elastic global buckling shear strength of the CCSS-CFS shear wall – which exhibited high accuracy. Finally, nominal shear strength, a resistance factor, and a safety factor were recommended.

Experimental study on seismic behavior of RCS joints with asymmetric friction connections and slabs

This paper introduces a new reinforced concrete column-steel beam (RCS) joint that employs asymmetric frictional connections (AFC) to improve energy dissipation and moment transfer, reducing stress concentrations within the joint’s core. Two RCS joint specimens with AFC and floor slabs were designed and tested under quasi-static loading to analyze the impact of bolt preload on seismic performance. The experimental results demonstrate that RCS joints with AFC and slabs exhibit favorable seismic behavior in terms of bearing capacity, energy dissipation, and stiffness degradation. Increasing bolt preload enhances the bearing capacity, stiffness, and energy dissipation capacity of the joints. The failure occurred at the steel beam splice connections, while only minor micro-cracks appeared in the reinforced concrete column when the joint's bearing capacity dropped below 80% of the peak load. Displacement at the column top was primarily influenced by steel beam and column deformation, with minimal contribution from joint core deformation. The use of AFC effectively reduced deformation in the joint core area, meeting seismic design code requirements for “strong columns-weak beams.”

Experimental Study on the Seismic Performance of Insulated Single-Sided Composite Shear Walls under Different Shear Spans and Axial Compression Ratios

The new insulated single-sided composite shear wall (NISCSW) composition involves setting a precast wall panel on one side and an insulation panel on the other side, with a middle cavity for casting concrete. To investigate the seismic performance of NISCSW under different shear spans and axial compression ratios, eight specimens are made, including six composite and two cast-in-place walls. The shear span ratio is controlled at 1.2 and 1.9, and the axial compression ratio is controlled at 0.1, 0.3, and 0.4. The specimens are subjected to quasistatic tests to analyze failure modes, hysteresis characteristics, stiffness degradation, displacement ductility, and energy dissipation capacity and to compare the seismic performance of the composite and cast-in-place walls. Results show that for each composite specimen, under the same axial compression ratio, the large shear span ratio specimen has a lower ultimate bearing capacity and faster stiffness degradation but better ductility and postyield energy dissipation capacity. Under the same shear span ratio, the high axial compression ratio specimen had a higher ultimate bearing capacity, slightly worse ductility, and similar stiffness degradation and energy dissipation capacity compared to other specimens. Compared with the cast-in-place specimen with the same axial compression ratio, the composite specimen failure mode and hysteresis characteristics are similar, and the ductility and energy dissipation capacity are comparable to the cast-in-place shear wall specimen, indicating that NISCSW has similar seismic performance to the cast-in-place shear wall under conditions of a large shear span ratio and high axial compression ratio. Based on the test results, the program ABAQUS is used to simulate the specimens. Compared with the test results, the simulated specimen failure mode is consistent with the test results, and the hysteresis and skeleton curves are consistent with the test curve, indicating that the model is correct, reliable, and can be verified with test results.

Experimental and theoretical investigation on the impact dynamic response of CFDST-K joints under different structure-related parameters

K-joints have been commonly used in steel structures benefiting from excellent connection performance. In this study, a combined experimental and nonlinear analysis was performed on CFDST-K joints to investigate the displacement, strain evolution, bearing capacity degradation, impact force, and energy absorption capacity in detail with different structure-related parameters such as hollow rate and steel tube thickness. The finite element model was developed and validated by experimental results. Results indicated that the CFDST-K joint can effectively enhance impact resistance with a more reasonable energy distribution. To improve the anti-impact property, the optimal hollow rate is 0.63 and the diameter-to-thickness ratio of the outer tube should be less than 30. Meanwhile, the inner tube thickness had little effect on impact resistance under low-impact energy. Finally, simplified calculation methods for the deformation and impact force were derived based on a parametric study on the dynamic response by discussing the influence of the impact energy, hollow rate, diameter-to-thickness ratio, and axial compression ratio. The findings can serve as a foundation for the development of more reliable CFDST-K joints for steel structures.

Rapid evaluation method for compressive performance degradation of welded hollow spherical joints based on random corrosion distribution

The use of welded hollow spherical joints (WHSJs) is widespread in spatial structures. However, steel is susceptible to corrosion during operation, which can lead to a decrease in the mechanical performance of the joints and ultimately affect the overall safety of the structure. This study focuses on assessing the compressive performance degradation of WHSJs after corrosion. A sophisticated finite element model of corroded joints was developed using the life and death element method. System parameter analysis and sensitivity analysis were conducted, utilizing parameters such as the diameter-to-thickness ratio, axial corrosion ratio, circular corrosion ratio, corrosion depth, envelope ratio, and sphere diameter ratio. Considering the factors mentioned above, a grid-based method was proposed to rapidly evaluate the compressive bearing capacity degradation of corroded joints: When the corrosion area has an irregular and randomly distributed shape, this method can quickly assess the performance degradation of joints by combining "regular corrosion areas that just envelop random corrosion areas" with a "correction factor that considers the degree of random corrosion distribution". This method provides a methodological foundation and technical guidance for evaluating the safety performance of WHSJs and similar joints after corrosion.

Reinforced ECC-UHPC-SCC composite modular framed shear wall systems under lateral cyclic loading

The shear strength and deformability of high performance reinforced composite framed shear wall systems made of Engineered Cementitious Composite (ECC), Ultra-High-Performance Concrete (UHPC) and Self-Consolidating Concrete (SCC) subjected to lateral cyclic shear loading to failure were investigated. A total of seven framed shear wall specimens were constructed using combinations of ECC or SCC wall, SCC frame and ECC or UHPC frame joints. The performance of such novel modular forms of walling systems were compared based on experimental results in terms of cracking, failure mode, hysteretic shear load-deformation response, shear load capacity, ductility, bearing capacity degradation, stiffness degradation, dissipated energy, viscous damping capacity, induced wall shear stresses and strain development characteristics. ECC walling system exhibited better structural performance compared to their SCC counterparts showing up to 40% higher load capacity forming significantly higher number of closely spaced diagonal cracks with up to 72% lower crack shear stress, 14% to 21% higher ductility, up to 2 times higher energy dissipation capacity and lower rate of stiffness/bearing capacity degradation through both hysteretic and damping actions. The incorporation of ECC and ECC or UHPC joint in frame significantly improved shear strength capacity of infill wall and overall framed shear wall system. ECC incorporated framed shear walls even with frames made of SCC and UHPC joints also exhibited superior performance. This study confirmed the superior performance of ECC material for the construction of reinforced framed shear wall with boundary frame made of ECC/SCC/UHPC combinations for better seismic resistance.

Degradation of Seismic Performance of Thin Steel Plate Shear Walls in Earthquakes

Steel plate shear walls (SPSWs) are widely used in earthquake-prone areas, and they usually undergo multiple earthquakes throughout their service lives. The performances of SPSWs under a single shot of an earthquake have been widely studied, although the secondary seismic performance of earthquake-damaged structures remains unclear. Damage to an SPSW structure during an earthquake is difficult to evaluate. In this study, the degradation of the seismic performance of SPSWs during earthquakes was investigated. A test specimen was subjected to a two-stage quasistatic load. The plastic development and failure modes of SPSW specimens were investigated. The degradation of bearing capacity, stiffness, and energy dissipation performance was analyzed. On the basis of the experimental investigation, finite-element models introducing the ductile damage criterion and the cyclic constitutive model of steel were established. The degradation of the seismic performance of SPSWs under secondary earthquakes was studied. The results indicate that the stiffness of the SPSWs degrades more significantly than the bearing capacity. The larger the height-to-thickness ratio of the embedded plate, the more obvious the decrease in the bearing capacity, and the smaller the decrease in stiffness. With the increase in the maximum lateral displacement reached by the structure in an earthquake, and as the pinch phenomenon of the hysteresis curve of the SPSW becomes more serious, the energy dissipation capacity shows a uniform downward trend.

Seismic behavior of prefabricated frame with special‐shaped concrete‐filled steel tubular columns and H‐shaped steel beams

AbstractTo realize the prefabricated structure of special‐shaped concrete‐filled steel tubular (CFST) column frame and enhance the level of indoor room utilization, this paper proposed a novel prefabricated frame with special‐shaped CFST columns and H‐shape steel beams connection with side plate. To investigate seismic behavior of this prefabricated frame structure, a 2‐story and 2‐bay CFST frame specimen was fabricated and tested under reversed cyclic loading. The failure mode, hysteresis behavior, degradation of lateral stiffness and bearing capacity, ductility and energy dissipation were analyzed. Experiment results indicated that failure mode presented strong columns and weak beams. Hysteresis curve of frame showed fully shuttle‐shaped. The mean story drift angle was 1/36 at ultimate stage. Equivalent viscous damping coefficient was 0.038–0.464. The bearing capacity degradation was relatively gentle, but the overall stiffness degradation was more obvious. It suggested that the frame had proper seismic and energy dissipation property. After the test, the seismic property of test frame was further investigated through the numerical simulation approach. The failure mode and skeleton curve obtained from the simulation were nearly consistent with test results, indicating that numerical analysis results were precise and with high reference meaning.

Compression behavior of CFST columns under combined influence of gap and freeze-thaw

Owing to factors related to construction quality and environment, concrete-filled steel tube (CFST) structures that have been in use for many years in regions experiencing seasonal freeze–thaw cycles are susceptible to the combined effects of a spherical-cap gap and freeze–thaw cycling. Therefore, in this study, a combination of experiments and the finite element method is used to investigate the effects of these two factors on the axial compression behavior of CFST stub columns. The experimental results show that the main failure mode of the specimen is local buckling at the end or the middle and inward depression of the steel tube on the existing gap side. The degradation of mechanical parameters, such as the ultimate bearing capacity and ductility of the specimens, gradually increased with increasing gap ratio and number of freeze–thaw cycles. In the numerical simulation section, the change in the stress response to freeze–thaw cycling on the gap side is analysed. The impact of the constraint effect coefficient on the ultimate bearing capacity degradation of the specimens is also investigated. Finally, a formula for calculating the ultimate capacity of CFST stub columns affected by the two factors is proposed, and the formula for calculating the ultimate bearing capacity in the code is improved. The results of this study can provide a reference for durability prediction and structural safety evaluation of CFST structures with a spherical-cap gap in cold regions.

Study on the shear resistance of CFS walls with built-up side columns

This study experimentally and numerically investigated the shear resistance of cold-formed steel (CFS) walls with built-up side columns. Horizontal monotonic and reversed cyclic loading tests were performed on four full-scale CFS walls. The influence of aspect ratio on the shear resistance of the walls was investigated in terms of load-displacement curves, skeleton curves, energy dissipation, stiffness degradation, and cyclic bearing capacity degradation. The shear capacity, stiffness, and energy dissipation capacity of CFS walls with built-up side columns (CFSWs) were effectively improved with decreasing aspect ratio. In addition, finite element models of the wall specimens were established using ABAQUS and validated against the test results. A parametric study with twelve finite element models was also conducted to examine further the effect of essential parameters, including the aspect ratio, stiffeners, and thickness, on the lateral behavior of CFSWs.

Investigating the bearing performance of the foundation under the combined effects of flood scouring and soaking

Bearing capacity degradation of foundations under the impact of the flood is one of the major reasons responsible for the collapse and damage to the rural buildings, posing a serious threat to the local village societies. Based on a case study of a rural building foundation had been destroyed by flooding. This paper investigated the deterioration process of rural building foundations under the combined effect of dynamic scouring and static soaking caused by flooding. Using the two-dimensional shallow water equation, erosion depth was calculated for different flood velocities. Then, the bearing capacity degradation under the combined scouring-soaking effect was analyzed using the finite element method. Finally, investigating the influence of inflow direction and building group masking on the foundation's bearing capacity. The results indicate that under the combined effect, the bearing capacity of village building foundations decreases by 47.88%, with scouring slightly more impactful than soaking. Inflow angle has minimal effect on bearing performance, while the masking effect of the building group provides better protection for the foundation of rear buildings.

Study on the tensile performance degradation of bolt-ball joints after bolt-thread corrosion

Bolt-ball joints, which have been used in corrosive environments for a long time, are prone to corrosion problems, particularly in the contact area between the bolt and the ball, posing a threat to the overall structural safety. This paper established a refined finite element model of bolt-ball joints that considers the effects of bolt-thread corrosion and corrosion products using an integrated simulation method of 3D corrosion evolution and mechanical properties of steel building components. The reliability of the simulation method was verified through several tensile tests. Subsequently, the stress distribution and load-displacement curves of M20, M24, and M27 joints with varying degrees of corrosion were analyzed after tension. The results indicate that when the corrosion mass loss rate is less than 80%, the tensile failure mode of the joint is bolt rod yielding. However, when the mass loss rate of the thread reaches 80%, the failure mode is ball thread yielding. For joints with the same thread mass loss rate and section area, the bearing capacity degradation increases as the bolt diameter increases. Additionally, for joints with different cross-sectional areas of threads, the bearing capacity degradation rate is higher when the cross-sectional area of the thread is smaller. Finally, a degradation formula for the tensile bearing capacity, taking into account the corrosion mass loss rate and bolt diameter, was proposed through regression analysis. This formula serves as a technical reference for the safety evaluation of corroded bolt-ball joints and similar joints.

Comprehensive analysis of structural and thermal performance for the concrete and steel joints used in the assembled building

The structure joints and connection type of buildings play a decisive role in their safety and reliability. Therefore, most studies have focused on the structural performance, ignoring their thermal performance. Three common assembled concrete joints and four steel joints usually used in the assembled building were selected to study their bearing capacity, seismic performance and stiffness degradation. In addition, the temperature and relative humidity distribution of six types of envelopes were evaluated within a year and the effect of different envelope options on the linear thermal transmittance of each joint was investigated. The results show that the best structural performance of concrete joints and steel joints are the grouting sleeve joint and the cantilever section bolt connection respectively. The seismic performance of steel joints is generally stronger. Furthermore, for every 25 mm increase in AAC thickness, the overall linear thermal transmittance of the component increases by 0.02–0.04 W·m−1·K−1. On balance, the grouting sleeve joint is the optimal concrete joint in terms of both structural and thermal performance, but better damp proofing measures are necessary outside of it. Moreover, the cantilever section bolt connection is the optimal steel joint and requires better insulation measures. Interestingly, the building envelope construction of “75 mm autoclaved aerated concrete + 90 mm mineral wool + 75 mm autoclaved aerated concrete” is the best choice for matching joints.

Experimental and numerical research on the static behavior of locally corroded OSBD

Corrosion can accelerate the deterioration of the mechanical properties of orthotropic steel bridge decks (OSBDs), seriously affecting the service safety of steel bridges. In this paper, thirty Q345C steel and four OSBD specimens with various corrosion levels are designed to investigate the effect of corrosion on the static behavior of OSBDs. Then, corrosion damage and its influence on mechanical properties are explored by static loading experiments. The constitutive model for Q345C steel is built considering the impact of corrosion. Finally, a numerical analysis considering geometric initial defects is employed to compare the effect of corrosion location on bearing capacity degradation. It is observed from the tested results that the corrosion led to the failure mode of Q345C steel changing from plastic failure to brittle failure. The ultimate bearing capacity of specimens with a local corrosion rate of 7.92%, 12.05%, and 16.24% decreased by 11.08%, 14.45%, and 17.82%, respectively. Corrosion leads to stress concentration in the top plate area, causing local instability of the structure. The degradation degree of the bearing capacity of the top plate is greater than that of the U-rib corrosion corresponding to the same corrosion conditions.

Assessment of chemo-mechanical degradation of concrete sewer pipes through an integrated experimental approach

The chemo-mechanical degradation of unreinforced concrete sewer pipes applied in domestic service locations is assessed through a systematic, integrated experimental approach, considering 18 new and 35 used sewer pipes. The characteristics and environmental conditions of the sewer pipes are reported, and data obtained from surface condition classification, residual alkalinity tests and XRD analyses are combined to identify the type and degree of chemical attack of the used sewer pipes. Concrete material properties are determined by material tests on sewer pipe samples, providing quantitative insight into the age dependency of the Young’s modulus, compressive strength, tensile strength and mode I toughness. All relatively old pipes (installed in the 1920s and 1950s) show substantial chemical attack by biogenic sulphide corrosion (at the inner side of the pipe) and carbonation (at the outer side of the pipe). The time development of the corresponding corrosion depths on average follows a linear trend, whereby the corrosion rate for biogenic sulphide corrosion is about a factor of 1.3 larger than for carbonation. Due to these chemical processes, the mechanical properties of concrete may significantly depend on the age of the sewer pipe. In particular, the average compressive strength and average tensile strength decrease approximately linearly with the age of the pipe, in correspondence with relative reductions of, respectively, a factor of 1.7 and 1.5 over a period of almost 100 years. The values and time-dependent trends found for the concrete properties and corrosion depths of sewer pipes can serve as input for practical analyses and advanced numerical simulations on their bearing capacity and time-dependent degradation. The experimental results also emphasize the importance of regularly assessing the amount of chemical degradation of (especially older) in-situ sewer pipes, by determining the (decrease in) effective wall thickness via core sampling and laser profiling.

Effect of calcium leaching on the characteristics of chloride physical adsorption and chemical binding of cement-based materials

Chloride corrosion is an important reason for the degradation of bearing capacity of reinforced concrete structures. When chloride ions transport from external environment into concrete, a part of ions will be bound by the cement matrix through the behaviors of chemical binding and physical adsorption. In this paper, the cement paste samples (R0, R5 and R15) with different degrees of calcium leaching are prepared to investigate the chloride binding capacity, by performing the experiment of chloride isothermal adsorption and desorption. In the experiment, the R0, R5 and R15 are immersed into NaCl-CH composite solutions with different chloride concentrations (Cf-Cl). The change of total binding chloride ion (TBCI), physically adsorbed chloride ion (PACI) and chemically bound chloride ion (CBCI) concentrations in the samples with Cf-Cl is obtained. Then, the linear and nonlinear adsorption laws are adopt to fit the experimental data of chloride concentrations, and the most appropriate adsorption laws are determined separately for the behaviors of TBCI, PACI and CBCI. Finally, the equations for chloride binding capacity of R0, R5 and R15 are obtained, which can be used to analyze the capacity of TBCI, PACI and CBCI of cement-based materials subjected to calcium leaching.

Seismic Performance of SFRC Shear Walls with Window Opening and the Substitution Effect for Steel Bars

Shear walls are important vertical and lateral bearing element in structures. While shear walls with openings are fragile due to stress concentration and the quasi-brittle behavior of concrete in tension. Therefore, additional strengthening rebars are required for the shear walls with openings. However, it aggravates the problem of dense reinforcement which increases the steel cage manufacturing and concrete compaction problem and still lacks countermeasures against concrete damage and cracking. To reduce the rebar demand and improve the damage tolerance of squat reinforced concrete (RC) shear walls with openings, an optimized steel-fiber-reinforced concrete (SFRC) was adopted to understand the seismic performance by cyclical loading test. The tested specimens included a plain RC shear wall without strengthening bar around the opening (for comparison), an SFRC shear wall, and an SFRC shear wall with a reduced distributed steel bar. This paper mainly studies the effect of using SFRC to improve the seismic performance of the open shear wall and to replace the reinforcement around the opening and the shear reinforcement. The hysteresis curves, skeleton curves, stiffness degradation, bearing capacity degradation and energy dissipation of the specimens were analyzed. The results show that the failure can be delayed and relieved, the deformation capacity and energy dissipation can considerably improve, and rebars can be partially replaced by using SFRC.

Seismic Performance of Precast Short-Limb Shear Wall with the Bundled Connection at Different Axial Compression Ratios.

In order to investigate the seismic performance of a precast shear wall with a new bundled connection under a high axial compressive ratio, three full-scale precast short-limb shear walls and one full-scale cast-in-place short-limb shear wall were manufactured and loaded under cycling loading. The results show that the precast short-limb shear wall with a new bundled connection has a similar damage mode and crack evolution to the cast-in-place shear wall. Under the same axial compression ratio, the bearing capacity, ductility coefficient, stiffness, and energy dissipation capacity of the precast short-limb shear wall were better, and its seismic performance is related to the axial compression ratio, with the increase of the axial compression ratio. The embedded bellows can limit the cracking of the wall but have little effect on the bearing capacity and stiffness degradation performance. Furthermore, the bond between the vertical steel bars extending into the preformed holes and grouting materials was demonstrated to be reliable, thus ensuring the integrity of the precast specimens.