Anchor Bolts Research Articles

Centrifugal test on the mechanical characteristics of existing prestressed anchor bolts in highway widening

To study the stress characteristics of existing prestressed bolts and slope stability during secondary excavation in a slope reconstruction and expansion project, five slope centrifugal tests were conducted. Tests focused on prestressed bolt-reinforced bedding slope with anchoring angles of 10°, 20°, 30°, 45°, and 60° during the excavation phase. The test results showed that the horizontal displacement at slope top increased slightly during the excavation of rock and soil masses in the upper slope part, while during the excavation of slope foot, such displacement increased rapidly. The bolt axial force in the anchorage section decreased along the anchoring depth. The peak axial force in the free section decreased significantly with the progress of excavation, and the axial force distribution in the free section presented a monotonically decreasing pattern. The anchoring angle significantly impacted the attenuation amplitude of axial forces in the anchorage section, while having insignificant effect on the distribution of axial forces. With the increase of anchoring angle, the cumulative horizontal displacement at slope top first decreased and then increased, while the earth pressure in slope first increased and then decreased, suggesting the presence of an optimal anchoring angle for the prestressed bolt.It is suggested that graded excavation should be adopted for the secondary excavation of slope engineering. Moreover, it is recommended to appropriately reduce the rate of excavation when working on the top and foot of the slope. Additionally, the design of the anchoring angle should consider various factors, including slope slope, rock formation, and the dip angle of the weak surface.

Study of a New Type of Large-Diameter Multi-Disc Soil Anchor and Its Bearing Characteristics and Creep Property

This paper presents a new type of large-diameter multi-disc soil anchor and its cavity-forming tool. The large-diameter multi-disc soil anchor is obtained by adopting a toothed chain, centrifuging holes to form cavities, forming multiple cavities, placing a steel strand with centering support, injecting cement mortar, and curing. In order to study the uplift bearing characteristics and creep property of the large-diameter multi-plate soil anchor, the equal-diameter soil anchor was taken as the control group. The ultimate pull-out bearing capacity, vertical displacement, axial force, anchor plate bearing load, and side friction resistance were simulated and analyzed by FLAC3D 5.0 64-bit software, and the creep property test of the anchor bolt was carried out. The results show that under the same conditions, the ultimate pulling capacity of the large-diameter multi-disc soil anchor is 125% higher than that of the same-diameter soil anchor. The vertical displacement of the large-diameter multi-disc soil anchor decreases by 51.74% compared with that of the equal-diameter soil anchor when the ultimate uplift capacity is reached. The side friction resistance of the large-diameter multi-disc soil anchor is small and its growth rate is slow. When the ultimate pulling capacity is reached, the load sharing of the anchor disc accounts for 76.54% of the total load applied. The creep rate of the large-diameter multi-plate soil anchor bolt is 0.91 mm, and the creep rate of the equal-diameter soil anchor bolt is 1.69 mm. By fitting the data, it is found that the large-diameter multi-disc soil anchor provides a method to increase the anchorage force of the soil anchor, and the research on its bearing characteristics and creep property provides a theoretical basis for the application of the soil anchor.

Feasibility Study of Capacitor-Based Smart Washer Sensor Systems for Highway Sign, Luminaire/Light, and Traffic Signal Structures

This paper aims to provide an improvement on the current inspection methods for anchor bolts used in highway sign, luminaire/light, and traffic signal (SLTS) support structures to reduce the risk of structural failure as well as human labor costs. A feasibility study on a capacitance-based smart washer system was conducted. The capacitor-based sensor system design combined with customized polylactic acid three-dimensional printed attachments was proposed and tested. Laboratory tests on multiple sets of sensors were performed through initial testing and tightening–loosening testing; results have shown that the performance of the sensor system follows the working principle of the capacitor and, with a less than 5% error tolerance, a capacitance–pretension relationship was developed in the laboratory. Then the sensor system was installed at a sign structure specimen for long-term evaluation; the 12-month consecutive monitoring results show that the sensor system was able to perform steadily with a proper waterproof cover applied. The change of the capacitance was found at ±5% of the reference value, and torques were applied to verify the measurement results from the sensor system, indicating that the minor capacitance change was caused by a change of temperature. The results have proven the feasibility of this capacitor-based smart washer system that detects the pretension change inside the anchor bolts and performs steadily in a controlled on-site environment with a high durability. In summary, this study provides the possibility of improving the monitoring methods for anchor bolts in highway SLTS structures.

Influence of mechanical anchors on bond performance of fiber fabric-steel joints

This study proposes an experimental model for anchor reinforcement and conducts uniaxial static tensile tests. The influence of anchor reinforcement on the failure mode of specimens is revealed. This includes the effects of bond length, number of layers, and types of fiber fabric under anchor reinforcement on the ultimate bearing capacity and bond-slip curve. The results demonstrate that anchors can effectively increase the ultimate bearing capacity of the test specimens. There are differences in bond-slip behavior between the anchors near the free end and the joint end. Higher stresses are experienced near the joint end. The use of anchor reinforcement can significantly enhance the load-bearing capacity of multi-layer carbon fiber specimens. Increasing the number of anchors and reducing the distance between the anchor and the joint end can further improve the stiffness of the specimens. A finite element model is established using ANSYS, which agrees well with the experimental results and parameterized analysis results reveal a linear increase in load-bearing capacity and stiffness with higher anchor bolt preload, achieving an 84.42 % increase at 11kN. Increased preload enhances friction at the carbon fiber-steel interface, reducing deformation. Similarly, expanding anchor width from 9 mm to 39 mm improves load-bearing capacity by 54.28 %, with larger anchors significantly boosting stiffness and bonding performance, which can be used to predict the mechanical properties of fiber fabric-steel reinforced by anchors.

Experimental Study of the Influence of Supplementary Reinforcement on Tensile Breakout Capacity of Headed Anchors in Nuclear Power Plant Equipment Foundations

Anchor bolts are often used in nuclear power plants to connect equipment and equipment foundations. Under a severe earthquake, tensile breakout failure is prone to occur in the anchor bolts. As the total amount of installed machines rises, the inertial forces transferred to the anchor bolts under seismic loads also increase significantly. Therefore, the capacity is no longer satisfied by concrete alone, and specialized supplementary reinforcement needs to be installed around the bolts. The study analyzed the tensile behavior of anchor bolts in foundations with supplementary reinforcement experimentally. A total of 16 single-headed anchors in RC foundations with various diameters, yield strengths, and forms of supplementary reinforcement were tested under monotonic tensile loading. The results show that supplemental tie bars and supplemental U-shaped bars, respectively, rely on the bond with the concrete and their own tensile strength to increase the tensile breakout capacity. Furthermore, based on the failure mechanism, a new model considering the terms of concrete resistance and reinforcement resistance for the tensile breakout capacity of headed anchors around with supplementary reinforcement was proposed. Compared with the strut–tie model by EN 1992-4:2018, the predicted results of the model proposed by this study are relatively consistent with the experimental results, while the results by EN 1992-4:2018 are overly conservative.

The Behavior of Post-installed Rebar Connectors in Steel Frame Retrofitted Concrete Structures Under Combined Shear and Tension

To investigate the response of post-installed rebar connectors in steel frame retrofitted concrete structures under combined shear and tension, seven shear-and-tensile tests were conducted. The bearing capacity, stiffness, and hysteresis behavior of the connectors were investigated during the tests. Both Monotonic and cyclic load regimes were applied in the loading process. The results show that with the increase of the loading angle, the deformation capacity, the yield force, ultimate tensile force, and tensile stiffness of the specimen decrease, while the maximum shear force and shear stiffness of the specimen increase. The bearing capacity, stiffness, and energy dissipation performance of the specimen under a monotonic load is greater than that under the coupled shear-and-pull load. The bearing capacity, stiffness, hysteresis curve, and failure status of the specimens are not affected by different loading regimes. At the end, the design formula of anchor bolt for this type of connectors from the design code of China, United States, and Japan were compared. Formulas to calculate the shear strength under combined shear and tension is developed.

Strengthening of reinforced concrete beams with insufficient lapped splice length of reinforcing bars

The insufficient lapped splice length of reinforcing bars due to the design or construction errors reduces both the flexural strength and ductility of Reinforced Concrete (RC) beams. The defected RC beams need to be strengthened to allow structures to be ductile and robust in their design life. This paper reports experimental and numerical investigations into the flexural behavior of RC beams having insufficient lapped splice length of reinforcing bars strengthened by various techniques. Eleven RC beams have been tested to examine the effects of strengthening techniques and anchorage lengths of the strengthening materials on the performance of the beams. The test program and results are described on RC beam specimens strengthened by using the externally bonded stainless-steel (EBSS) sheets, the near surface mounted (NSM) steel bars, and the external prestressing system. Finite Element (FE) models are developed using ABAQUS to simulate the responses of strengthened RC beams in which the lapped splice length of reinforcement is inadequate. A parametric study is conducted using the validated FE models to examine the effects of the length of EBSS sheets and steel anchor bolts at the ends on structural behavior. An analytical model is proposed for calculating the ultimate capacity of beams strengthened by NSM technique. Experimental results reveal that the proposed strengthening methods can significantly improve both the cracking and ultimate loads of the defected beams. The application of the external prestressing method results in the largest increase in the cracking and ultimate loads of the defected beams calculated as 222 % and 213 %, respectively compared to the defected control beam. The ultimate load of the defected beam strengthened with EBSS sheet, NSM steel bars, and prestressing system with a length of 100D increases by 50 %, 109 %, and 182 %, respectively. It is shown that the developed FE models can accurately predict the behavior of strengthened beams having inadequate lapped splice length of reinforcing bars. The parametric study demonstrates that strengthening the entire clear span of the beam B-ESS-65D with EBSS sheet increases its ultimate load by 207 %. The failure mode of strengthened beams is ductile bending without debonding. The proposed analytical model is shown to yield accurate calculations of the ultimate loads of strengthened RC beams.

Influence of bolt preload of anchors on bond-slip behavior of fiber fabric-steel interface

Bond-slip behavior is a common failure mode in steel structures reinforced with fiber fabric. Premature debonding of the fiber fabric significantly impacts the effectiveness of steel structure reinforcement. In this study, a gripping anchor is proposed to enhance the reliability of the interface between fiber fabric and steel plates. Experimental investigations were conducted to analyze the influence of anchor bolt preload on the double shear joint between fiber fabric and steel plates. 41 specimens were prepared and tested to explore the effects of parameters such as bolt preload, anchor position, number and type of fiber fabric layers, and bond length on load-bearing capacity. Comparative analyses were conducted on failure modes, ultimate loads, and stress-strain distributions of the specimens. Experimental results indicate that the position of the anchor has a minimal impact on the ultimate bearing capacity of the specimen. However, anchors positioned closer to the joint end exhibit lower ductility upon failure. A novel predictive model was developed to characterize the bond-slip behavior of preload applied to carbon fiber fabric and steel plates. The theoretical model of the ultimate bearing capacity in the yield stage fits well with the experimental results of specimens with three layers of carbon fiber fabric, with a difference range of 0.34 % to 14.97 % compared to actual results. This indicates that the model has high accuracy in predicting stress-strain and bearing capacity.

Effects of degraded durability on the long-term stability of in-service slopes with reinforced concreted support structures

Engineering slope stability issues typically exhibit the impact of deteriorating durability on the susceptibility of slopes to failure. A thorough investigation was essential to explore theoretical and experimental aspects of slope durability degradation and its implications on long-term stability. Hence, a durability model was developed to accommodate slope stabilization using reinforced concrete (RC) support structures. This model was grounded in classical durability principles for RC structures. Subsequently, a model test was conducted to compare the responses of a standard slope model with a weakened counterpart subjected to environmental impacts. According to the proposed methodology for slope durability and stability, a case study involving future durability and stability predictions was performed. It was found that the theoretical solutions for the carbonation or neutralization (CN) velocity, depth, and penetration time agreed well with model test results. The slope surface displacements of the weakened slope with deteriorating coefficients between 0.6 and 0.9 were 4 to 8 times those of the standard slope, demonstrating significant degradation in stability. The case study indicated a steady reduction in the safety factor, at a rate of 2.3 to 2.4‰ per year throughout the slope’s service life. Finite-element-based predictions also suggested the potential for corrosion of slope anchor bolts within 20 years and breakage within 30 years, at an average rate of 7.5‰ per year in the ultimate bearing capacity. These findings highlight the need for timely maintenance and reinforcement interventions to ensure the long-term durability of operational slopes.

Shear behavior of BFRP anchor-jointed rock mass considering inclination angle and pre-tension

In this study, the double-shear tests of anchor-jointed rock mass were carried out to investigate the mechanical behaviors of Basalt Fiber Reinforced Polymer (BFRP) anchor bolt in the joint surface. A total of 21 specimens were prepared and two main influence factors were considered: the inclination angle of the BFRP anchor bolt (0°, 5°, 10°, 15°) and the load level of pre-tension (36, 72, 108 kN). The parametric study and design recommendations for the shear capacity of the joint surface under the BFRP anchor bolt were carried out. The results showed that a larger inclination angle or pre-tension force can improve the shear capacity and reduce the relative dislocation at the joint surface. When the inclination angle was 15°, the ultimate bearing capacity was increased by 51 % compared with that when the inclination angle was 0°. When the pre-tension force was 108 kN, the ultimate bearing capacity was increased by 142 % compared with that without pre-tension force. The analytical study found that Ranjbarnia's formulations were reliable to calculate of the shear capacity at the joint surface. The predicted results showed good agreement with the experimental results, with the relative errors less than 5 % for all groups. Then, by using this analytical model, the design parameters of the BFRP anchor bolt were tentatively determined at demanded shear capacities of 200 kN and 350 kN, respectively.

Experimental study on mechanical aging properties of self‑swelling anchorage bolt under chemical corrosion

ABSTRACT Chemical corrosion is found to influence the strength of grouted rockbolt reinforcement in underground excavations leading to catastrophic. As such, in this paper, we investigated the impact of the chemical corrosion on the new self-swelling anchorage rockbolt, designed by us, during long-term corrosion processes and accelerated corrosion tests with different chemical solutions. The self-swelling anchorage rockbolt uses a self-swelling anchoring agent that hydrates and expands, providing high anchoring force. The impact of pure water, acidic, and salt solutions on the load-bearing capacity and deformability of self‑swelling anchorage bolts was analysed. Additionally, a microscopic XRD component analysis method was used to reveal the changes in microscopic composition of self‑swelling anchoring agents. It was found that after 180 days of accelerated corrosion, pure water and salt solutions had a small effect on the anchorage force of self‑swelling anchorage bolts, whereas the anchorage force of self‑swelling anchorage bolts decreased by 73.4% in an acidic solution with a PH of four. In addition, the deformation capacity of the bolt deteriorates with the time regardless of the chemical solutions. Combined with XRD micro-composition analysis, the effects of different solutions on the mechanical properties of self‑swelling anchorage bolts were as follows in descending order: PH = 4>6% NaSO4>6% NaCl>3% NaSO4 + 3% NaCl>water.

Flexural behaviour of shallow-embedded steel column bases

This paper investigated the flexural behaviour (the initial rotational stiffness and ultimate moment resistance, in particular) of the shallow-embedded column bases through experimental and numerical approaches. Three full-scale tests with different embedded depth ratios (i.e., 0.5, 1.0 and 1.5) were carried out, from which the moment-resisting mechanisms were identified and the effects of the embedded depth ratio on the initial stiffness, moment resistance and ductility were evaluated. The test results were further used to evaluate the accuracy of the available resistance and stiffness models for the shallow-embedded column bases. The resistance models codified in design codes GB 50017-2017 and AISC 341-16 are highly conservative, with an average prediction accuracy of 0.268 and 0.451, respectively; by contrast, the resistance models recently reported in the published articles show better accuracy. The stiffness models are fewer in number and are also inaccurate for the shallow-embedded column bases. Complementary finite-element models were developed and validated. Subsequently, systematic parametric finite-element analyses were performed to investigate the effects of axial force and shear force in the steel column, as well as those of the structural details such as the presence of base plate, arrangement of anchor bolts and width of concrete foundation. Shear force has an adverse effect on both the initial stiffness and moment resistance, and this effect becomes more significant with the increase in the embedded depth ratio; axial compression force leads to an increase in both the initial stiffness and moment resistance, which is more pronounced for embedded column bases with smaller η-values. Among all structural details, the presence of the base plate has the most notable influence on the flexural behaviour of the shallow-embedded column base, increasing both its initial stiffness and moment resistance; comparatively, the effects of the other structural details are minor or even could be ignored.

Safety and accuracy of stereoelectroencephalography for pediatric and young adult patients with prior craniotomy.

The authors assessed the safety and accuracy of stereoelectroencephalography (SEEG) electrode implantation in pediatric patients who had previously undergone craniotomy compared to those without prior cranial surgery. The authors performed a retrospective analysis of patients under 25 years of age with medically refractory epilepsy at a single institution who underwent SEEG electrode placement between March 2016 and July 2023. Surgical history and demographic characteristics were collected from the electronic medical records. The coordinates of the anchor bolts and their respective SEEG electrode contacts were manually annotated using postoperative head CT scans. Bolt coordinates were used to calculate the initiated electrode trajectory set by the bolt by using the least-squares method to define a line along the bolt, projected along the length of the electrode. The shortest distance from each electrode contact to this line was calculated to obtain the error measurement. Statistical analysis was conducted using the Kolmogorov-Smirnov test to compare the distribution of errors between groups, the Student t-test was used for continuous variables, and the chi-square/Fisher's exact test was used for categorical variables. Fifty-eight patients underwent a total of 60 SEEG placements and met the inclusion criteria. Eighteen had a history of prior craniotomy and 40 without prior surgery, indicating entirely native cranial bone. Mean age, sex, and mean number of electrodes implanted per surgery were similar between groups. For the electrode contact furthest from the bolt, a mean (IQR) deviation of 1.32 (0.73-2.53) mm was noted for the prior craniotomy group and 1.08 (0.65-1.55) mm for the native bone group (p < 0.0001). A greater number of outliers for the contact furthest from the bolt, defined as > 6 mm from the initiated electrode trajectory, was seen in the prior craniotomy group (p < 0.0001). The complication rate was low and not statistically different between groups. The authors' analysis draws attention to the effect of the intracranial biomechanical environment along the path of the electrode after traversing past the anchor bolt and found that prior craniotomy was associated with a higher number of contacts with a significant deviation from the initiated trajectory. Despite these deviations, we did not find a difference in the overall low complication rate in both groups. Therefore, the authors conclude that SEEG electrode placement is a safe option in pediatric patients even after prior craniotomy.

A Component Method for Full-Range Behaviour of Embedded Steel Column Bases

This paper introduces a component model for analysing embedded column bases to predict rotational stiffness, moment resistance, and the full-range moment–rotation response. The key components identified include the embedded column, concrete in compression on the column side, concrete in compression beneath the base plate, concrete in punching shear above the base plate, and anchor bolts. The embedded column is modelled as a Timoshenko beam, considering both shear and flexural deformations, while other components are represented by springs. Methods are provided for determining their uniaxial constitutive behaviour. A simplified iterative solution method is proposed, where the embedded column is further simplified into three rigid segments to specifically address shear and bending deformations. A corresponding simplified finite element model is developed for accurate numerical solutions. The validity of the component model is confirmed through comparisons with the results of existing tests and refined solid finite element analysis for H-steel column bases. The simplified iterative solution method effectively predicts strength but underestimates the stiffness of deeply embedded column bases. This is due to the trilinear deformation pattern simplification, which concentrates flexural deformation at the upper bearing stress resultant force point, leading to an overestimation of steel column rotation on the foundation surface.

Stress-strain state zoning model and novel large deformation classification method for squeezing tunnels

Accurately assessing the level of large deformation in squeezing tunnels is of great importance for the design of support structures. The current large deformations classification methods fail to account for the effect of support pressure on the relative deformation of surrounding rock. In this study, a theoretical model for the stress–strain state zoning of the surrounding rock in squeezing tunnels is established. A sensitivity analysis of the model parameters is conducted. The distribution law of the strength-stress ratio, relative deformation, and relative support pressure indices in 43 field monitoring squeezing tunnels are statistically analyzed. A novel large-deformation classification method based on the relative support pressure index is proposed and applied in case studies. The parameter sensitivity analysis shows that mechanical parameters of the surrounding rock significantly affect the deformation and the stress–strain state zoning of the surrounding rock. The stress–strain state zoning and deformation of the surrounding rock are also primarily dependent on the matching relationship between strength-stress ratio and support pressure. Statistical analyses indicate that there is a nonlinear negative correlation between the relative deformation of the surrounding rock and the strength-stress ratio, as well as the relative support pressure, which includes the steel arch relative support pressure index (SSPI) and the anchor bolt relative support pressure Index (ASPI). The key to controlling surrounding rock deformation lies in the rational matching of support pressure to the strength-stress ratio. In the novel large deformation classification method, three key indexes of strong stress ratio, relative deformation and relative support pressure are quantitatively included, and squeezing large deformation is divided into three levels. Moreover, the case study demonstrated that the novel large deformation classification method has significant guiding importance in verifying feasibility and optimizing support design schemes during both the design and construction phases.

The study of the blast resistance performance of underground cavern support structures under the effect of explosive ground loads

The use of support structures with good explosion resistance to support and reinforce underground projects has become a focus of concern for relevant units in order to ensure the safety of underground projects in explosive ground loads. The blast resistance of underground caverns and the influence of support parameters on blast resistance have been studied when lining and pre-stressing anchors are supported individually under dynamic and static coupling. Straight-walled arched caverns are chosen for this study because of their strong blast resistance. The influence of excavation unloading on the support structure was analyzed under the condition of a burial depth of 500 m. The study investigated the blast resistance of caves supported solely by singular concrete lining support and singular pre-stressed anchor bolt support. The research findings indicate that pre-stressed anchor bolts significantly limit the deformation capacity of surrounding rock while lining is more effective in restricting the vibration response of surrounding rock. The pre-stressed anchor bolts ensure operation within the strength range throughout the entire process with no alteration in load-bearing capacity. Increasing the thickness of the lining can reduce the vibration response of the cavern. Meanwhile, enhancing the pre-stressed anchor bolts within a certain range notably restricts the deformation response of the cavern. Therefore, the pre-stressed anchor bolts should be employed as the supporting structure to bear the excavation and unloading loads of the cavern.

Strengthening of reinforced concrete slabs using carbon fiber reinforced polymers rods and concrete jacket with a mechanical anchorage system

This study presented the development of a new method for strengthening of Reinforced Concrete (RC) slabs using Carbon Fiber Reinforced Polymer rods (CFRP) and an Ultra-High Performance Fiber Reinforcement Concrete (UHPFRC) external jacket with a Mechanical Anchorage System (MAS). The mechanical anchorage system includes two components: high-carbon steel plates and the Mechanical Expansion Anchorage Bolt System (MEABS), and it’s employed to prevent any premature de-bonding between the existing concrete surface and the externally strengthening layers (CFRP rods and UHPFRC jacket). The efficiency of the proposed strengthening method was evaluated through conducting an experimental test on a few fortified slabs by applying cyclic loads using a dynamic actuator. For this purpose, three distinct concrete slabs were tested to assess various design parameters, including a control slab, a strengthened slab with the UHPFRC jacket only, and a strengthened slab with CFRP bars at the bottom of the slab with an external UHPFRC jacket. The results of experimental tests reveal that the proposed strengthening system significantly enhanced the load capacity of the slab and prevented premature debonding failures between the old concrete of the slab and the new UHPFRC layer until the stage of slab failure. Accordingly, the new proposed strengthening system played a crucial role in enhancing the tension zone of the slabs and delaying the occurrence of diagonal crack loads. On the other hand, embedding CFRP bars within the UHPFRC jacket in the strengthened slab led to a notable enhancement of 82 % in the ultimate load capacity of the slab. The FE and analytical models were developed to predict the behavior of the specimens. The models' outcomes were in good agreement with the experimental data. Consequently, the new proposed strengthening system emerges as a reliable technique for enhancing the performance of reinforced concrete slabs, eliminating the risk of debonding between old and new parts.

Finite Element Analysis and Optimization of the Rotational Stiffness of Semi-Rigid Base Connection under Simultaneous Moment and Tension

The base connection is flexible, not fully pinned/fixed, implying a nonlinear moment–rotation relationship. This deviates from a linear response, where rotation is not directly proportional to the applied moment. Numerical investigations using the commercial software ABAQUS were conducted to analyze the steel base plate connections. The finite element (FE) models were verified against previous experimental results. Moreover, numerical findings of a comprehensive parametric investigation were conducted. The studied connections were examined with different configurations, including variations in the diameter, spacing, and number of the anchor bolts; the thickness of the base plate; and the applied axial force. The current study aims to use numerical results combined with the whale optimization algorithm (WOA) and classical genetic algorithm (GA) to derive a formulation for the moment–rotation (M-θr) relationship. The distinctive aspect of this formulation is that it aims to simulate the nonlinear rotational behavior exhibited by flexible base connections under combined moment and tension loads, while also considering various parameters such as bolt number/diameter and plate thickness. The findings indicate that the WOA is capable of obtaining an optimal equation for accurately simulating the M-Ɵr relationship. This underscores the ability of the WOA to effectively address the complexity of the problem and provide a reliable equation for predicting the rotational behavior of such connections. Consequently, the WOA method can be utilized to calculate the rotational stiffness at H/150, offering valuable support for engineering design processes.

Experimental and Numerical Study on the Anchoring Mechanism of an Anchor Bolt Considering its Lateral Restraint Effect

Experimental and Numerical Study on the Anchoring Mechanism of an Anchor Bolt Considering its Lateral Restraint Effect

Seismic Damage Analysis of Zamora Bridge in Ecuador

The Zamora Bridge, located in the Zamora-Chinchipe Province in the southeastern part of Ecuador, on the Pacific Rim seismic belt, serves as the sole river-crossing channel from the Mirador Copper Mine area to the exterior. Constructed and opened for traffic in 2013, this bridge is designed as a low-pier continuous girder bridge, featuring a three-span prestressed concrete continuous box girder for the main beam, with a span arrangement of 45.5+140+45.5 meters, and utilizes basin-type rubber bearings throughout. On May 6, 2019, and November 28, 2021, the Zamora Bridge experienced two significant seismic events. The initial seismic damage investigation revealed that the piers and foundation maintained their load-bearing capacity largely intact; the basin-type rubber bearings predominantly suffered shear failure and displacement, losing their horizontal limit capacity. Additionally, abutment blocks sheared, padstones cracked locally, and the main girder exhibited residual displacement. Following the first earthquake, repair work was undertaken based on the damage results, switching to friction pendulum seismic isolation bearings to enhance the seismic resilience of bridge. The subsequent seismic damage assessment indicated the overall stable condition of the bridge, with no observable damage, deformation, or settling to the main structure, thus maintaining basic traffic functionality. However, shear and deformation occurred to the bolts and pins fixing the direction of the friction pendulum isolation bearings, along with residual displacements after the activation of the seismic isolation function, and cracks developed in the abutment padstones and mortar layers. To delve into the performance and damage probability of vulnerable components of low-pier continuous girder bridges under various seismic intensities, numerical models of the Zamora Bridge equipped with basin rubber bearings and friction pendulum bearings were separately established using OpenSees finite element software. An analysis of the bearings' longitudinal seismic susceptibility was conducted by integrating the demand-capacity ratio and IDA method. The findings indicate that bearings, padstones, and anchor bolts are the vulnerable components necessitating reinforcement for such bridges. Compared to the basin rubber bearings, friction pendulum bearings significantly reduce the probability of bearing damage and demonstrate an excellent seismic isolation effect.