Ultimate Load Conditions Research Articles

3D printed strain-hardening cementitious composites (3DP-SHCC) reticulated shell roof inspired by the water spider

Inspired by the diving bell of the water spider, this paper designs and fabricates nature-inspired 3D printed strain-hardening cementitious composites (3DP-SHCC) reticulated shell roofs. The compression performance and energy absorption capabilities of 24 specimens with eight different strut angles are evaluated through a combined experimental and simulation approach. The results demonstrate that all specimens exhibit excellent ductility and structural integrity under ultimate load conditions. The 45–45 and 60–60 specimens exhibit the highest energy absorption and efficiency, respectively, while 60–90 specimens exhibit the best ductility. Compared with traditional lightweight concrete structures, reticulated shells have lower average structural density, higher specific energy absorption, and ductility index values. A building with a proposed nature-inspired 3DP-SHCC reticulated shell roof is constructed to verify buildability, demonstrating reduced construction time and enhanced automation. This paper offers valuable insights for highly automated construction projects, especially in extreme environments.

Study of the tensile mechanical properties and failure mechanisms of CFRP screwed joints

Removable joint technology is commonly used in composite laminates for various load-bearing structures. However, existing research primarily focuses on bolted joints, there is relatively limited research on screwed joints in composite materials. This study investigates the influence of connected layer thickness and hole diameter on the tensile behavior of threaded joints in carbon fiber-reinforced polymer (CFRP) laminates. After fabricating different CFRP screwed joint specimens, tensile tests were conducted. The digital image correlation (DIC) technique captured the deformation process. The experiment results indicate a significant increase in load-bearing capacity with the increase in diameter. For instance, joints with an 8 mm diameter exhibited a load-bearing capacity of 10.82 kN. The increase in the connected layer thickness correspondingly enhanced the load-bearing capacity of the joint. The joint with a thickness of 7 mm had the highest load-bearing capacity of 8.83 kN. Besides, with the increase in the thickness of the connected layer, the failure mode transitioned from shear failure in the connected layer to screw pull-out. The tilt angle of the screw during the pull-out process also decreases with the increase in the connected layer thickness. Strain and out-of-plane displacement measurements under ultimate load conditions verify these observations.

Bond behavior of CFRP reinforcement systems with concrete under static and fatigue loading

In this research, the single lap shear tests were used to investigate the bond behavior of carbon fiber reinforced polymer (CFRP) sheets bonded to concrete blocks under static and fatigue loads. The magnitude of the fatigue load was considered as a parameter that varied from a minimum load of 10% of Pu to a maximum load of 60%, 70% and 80% of the ultimate static load. For both loading scenarios, the applied load versus slips curves and the profiles of the interface zone strain were presented. In addition, comparisons, and analyses of the failure mode of samples subjected to static and fatigue loading are presented. The experimental results demonstrate that the loading level has a significant impact on the failure mode, fatigue life and stiffness degradation of CFRP-concrete joints during the fatigue loading.Finally, a prediction model for the fatigue life of the CFRP-concrete joint was developed as part of this investigation.

Research on Anchorage Performance of the Foundation Ring for Wind Turbines.

The foundation ring (FR) is a steel component embedded within the concrete of a wind turbine foundation, playing a pivotal role in connecting the wind turbine tower to the foundation structure. In this paper, the FR-foundation connection is equivalent to the exposed foundation and the shallow foundation by analyzing the anchorage characteristics of the foundation ring. Based on the ABAQUS concrete damaged plasticity model, full-scale modeling of the wind turbine foundation is carried out. The influence of embedment depth, ring radius and base flange width of the foundation ring on moment capacity is simulated. Based on the observed stress distributions under ultimate loads, analytical expressions were proposed to estimate the variation law of anchorage load-bearing capacity in the ultimate load state. Compared with the numerical simulation, the average errors under different influencing factors are 8.2%, 9.6% and 10.8%, respectively. The results indicate that the base flange provided the majority of the moment capacity, though the contribution of the sidewall increased to 25-50% that of the base flange in later stages.

Analysis and optimization of pre-stressed modal features of ship anchor support parts

In order to solve the problems of excessive weight and unreasonable structure of anchor machine parts caused by traditional design methods, a lightweight optimization method was proposed based on pre-stressed modal analysis. The design variables were determined, and the parameterized model was established by using ANSYS Workbench. Under ultimate load conditions, the strength of wall frame board and lower box bodies was simulated and calculated. Through modal analysis, the discretized natural frequencies under different design variables could be obtained. The multi-objective genetic algorithm and sequence quadratic programming were respectively used to calculate the lightweight analysis model. The results showed that the weight of the supporting components in ship anchor can be reduced by more than 5 % without reducing strength and equivalent stiffness.

Study on predicting rolling contact fatigue of pitch bearing raceway in offshore wind turbine

Pitch bearing is the critical component that are widely used to ensure the operation of offshore wind turbine blades and enable efficient capture of wind energy. Uncertain environmental factors and extreme load conditions can induce early fatigue failure in pitch bearings, and lead to major accidents such as blade detachment. In this study, a damage coupling fatigue simulation model, considering residual stress (RS) and surface hardness effect, was constructed following the continuum damage mechanics (CDM) to investigate the rolling contact fatigue (RCF) of pitch bearing under ultimate loading conditions. Different ultimate loading conditions were calculated on an integrated load simulation platform established using Python script. The damage-coupled elastoplastic constitutive equation and damage-controlling equations considering RS and surface hardness were derived and programmed in the material user subroutine UMAT. The effects of ultimate loading conditions, RS, and surface hardness on RCF were studied. Results show that increasing the surface hardness or increasing the compressive RS enhances the anti-fatigue performance of pitch bearing.

Mechanical Properties and Loading Simulation of Unidirectional Laminated Slabs Made from Recycled Concrete with Manufactured Sand

To align with the trend of the development of prefabricated buildings, this study aimed to produce unidirectional laminated slabs by using recycled concrete with manufactured sand (RCM). Additionally, performance evaluation and loading simulation analyses were conducted on these unidirectional laminated slabs. The experimental results indicate that the mechanical characteristics of RCM closely approximate those of recycled aggregate concrete (RAC), and they are all higher than the design value. Under ultimate loading conditions, the mid-span deflection of laminated slabs fabricated with RCM surpasses its RAC counterpart by 5.9%, indicating a pronounced proximity in flexural performance between RCM and RAC laminated slabs. Concurrently, ABAQUS finite element software was used to compare and simulate the performance of the unidirectional laminated slabs. The difference between the deflection generated by the actual applied ultimate load and the deflection generated by the simulated ultimate load is about 7.1%, and the simulation results are very close to the experimental results. Based on the experimental results, the practical application of RCM unidirectional laminated slabs has high value in the field of construction engineering.

Tensile strength analysis of sandwich composite-to-metal joints based on experimental investigation and progressive failure method

In this study, the tensile strength characteristics of the hybrid sandwich composite-to-metal specimen consisting of two steel I-beams and a T-shaped sandwich composite structure were studied. The tensile strength of the sandwich hybrid joints under design load and ultimate load has been tested. The progressive failure model is established according to the modified Shokrieh-Hashin criterion. The interface cohesive zone model is applied to reveal the damage development of the bonding layer. The stresses, strains, ultimate strength, and main damage modes of the hybrid joint under design load and ultimate load conditions are simulated and the predicted results are compared with those from tests. The experimental and numerical results show that the strain, the trend of load-displacement curves and the damage modes are in good agreement. The strength of matrix is the main factor limiting ultimate strength. Therefore, the influences of the overlapping width and thickness on ultimate bearing capacity were analyzed to obtain the optimized structural strength of the sandwich composite-to-metal bolted joints.

Study on the Ultimate Load Failure Mechanism and Structural Optimization Design of Insulators.

This study aims to enhance the productivity of high-voltage transmission line insulators and their operational safety by investigating their failure mechanisms under ultimate load conditions. Destructive tests were conducted on a specific type of insulator under ultimate load conditions. A high-speed camera was used to document the insulator's failure process and collect strain data from designated points. A simulation model of the insulator was established to predict the effects of ultimate loads. The simulation results identified a maximum first principal stress of 94.549 MPa in the porcelain shell, with stress distribution characteristics resembling a cantilever beam subjected to bending. This implied that the insulator failure occurred when the stress reached the bending strength of the porcelain shell. To validate the simulation's accuracy, bending and tensile strength tests were conducted on the ceramic materials constituting the insulator. The bending strength of the porcelain shell was 100.52 MPa, showing a 5.6% variation from the simulation results, which indicated the reliability of the simulation model. Finally, optimization designs on the design parameters P1 and P2 of the insulator were conducted. The results indicated that setting P1 to 8° and P2 to 90.062 mm decreased the first principal stress of the porcelain shell by 47.6% and Von Mises stress by 31.6% under ultimate load conditions, significantly enhancing the load-bearing capacity. This research contributed to improving the production yield and safety performance of insulators.

Investigation of Elastic Softening and Stiffening Effect of Aluminum Nitride Under Stress Loading by Born‐Lande Equation

As a core functional material in acoustic resonators and filters, the elasticity of aluminum nitride (AlN) piezoelectric thin film and its correlated intrinsic properties deserve priority attention. This paper presents an in‐depth investigation of elastic softening and stiffening effect induced by stress loading in AlN piezoelectric thin film. Based on the Born‐Lande equation, the physical mechanism of such new intrinsic elastic property is revealed and predicted quantitatively for the first time from the perspective of atomic interaction forces. It is found that a maximum 6.7% modulation range of elasticity coefficient can be achieved under ultimate stress loading conditions from (−2.5, −2.5) to (2.5, 2.5) GPa. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Performance Analysis of an Improved Gravity Anchor Bolt Expanded Foundation

With the continuous utilization of renewable energy, the number of onshore wind turbines is increasing. Small design improvements can save costs and facilitate the maintenance and repair of the wind turbine foundation. In this paper, an existing gravity expansion foundation with an anchor cage is improved. Our improvements further expand the space inside the foundation and reduce the length of the anchor bolt, which could reduce the costs and facilitate construction. To study the performance of the new foundation, a three-dimensional finite element model of the foundation–soil–anchor bolt was established via a finite element simulation. The damage evolution of the foundation was simulated with the concrete damage plasticity model (CDP). The separation ratio, foundation settlement, inclination ratio, reinforcement stress, foundation stress, and foundation damage of the new foundation under ultimate load conditions were analyzed. The influence of parameters h1 and b3 on the performance of the foundation was further studied. The finite element analysis results show that the tensile stress of concrete can be effectively reduced by appropriately increasing the corbel height and ring beam width of the foundation. The results also show that the improved wind turbine foundation force is reasonable and can meet the use of the actual project requirements on the level of finite element analysis.

Full-scale test and numerical simulation of three-ring staggered-joint shield segment reinforcement under ultimate load conditions

Using the self-developed multiring shield segment prototype test loading system, the three-ring staggered full-scale segments under ultimate loading are tested to investigate the mechanical characteristics of the segments before and after reinforcement. Then, a numerical simulation is carried out based on the MIDAS GTS NX to study the stiffness change before and after segment reinforcement. The test results show that the maximum bending moment at the waist of the reinforced segment moves down, and the maximum offset and bolt stress are greatly reduced. The maximum offset occurs at the waist and top of the reinforced segment, and joint 5 bears the maximum shear stress and principal stress, which decreased by 29.5% and 28.6%, respectively. Compared with the single-ring shield segment after reinforcement, the three-ring segment enters the plastic state earlier, and the overall stiffness of the segment is greatly improved, which can weaken the intermediate stage of plastic deformation and delay the process of the segment entering the plastic state. In addition, the stiffness of the unreinforced segment decreases sharply when its lateral convergence deformation is greater than 25.03 mm, but the stiffness of the reinforced segment is still in a stable state. The plastic deformation of the concrete starts from the bolt hole and goes along the bolt hole to the two ends of the bolt. Lateral expansion occurred, and the bolts of the reinforced segment did not break during the whole loading process.

Numeric simulation of corroded steel bridge girder end region repairs

An extensive finite element (FE) modeling campaign focusing on different means of repairing corrosion-damage steel girder ends is presented. Significantly corroded end regions were repaired using three approaches: conventional bolted steel repair, encasement in ultra-high performance concrete (UHPC), and encasement in conventional reinforced concrete (RC). ABAQUS-based models were developed and validated based on a previously-reported experimental program (Mash et al. 2023). The modeling of the test specimens proved to be robust and captured observed behavior well. Once the test specimen modeling was “benchmarked” against the observed behavior, the models were expanded to archetypal plate girders to verify the validity of the repair methods. The models confirmed the validity of adopting AASHTO-prescribed equations for estimating residual capacity of damaged girder ends. The numerical analyses presented were able to capture tension field behavior and, therefore, illustrate the potential degree of conservativeness – under ultimate loading conditions – in actual repair designs in which relative stiff bearing stiffeners are used. Similarly, by encasing the web, the shear panel length is reduced and capacity may be increased. Based on the robustness of the models, the analyses presented in this work may be adopted as a benchmark for future studies.

Plastic design of sustainable steel earthquake resistant structures

Earthquakes induce ultimate load conditions in most earthquake resistant structures and often lead to complete failure and disposal. Seismic sustainability is a limit state condition with a view to revival, reuse, and environmental protection. In the present context, sustainable seismic design implies planning for controlled energy dissipation, sequential failures, collapse prevention, construction economy and post-earthquake realignment and repairs. However, regardless of savings and environmental improvements unless an earthquake resistant structure is designed for the purpose, it would be disposable with greater monetary loss and harm to the environment. It has been found that steel mixed multiple seismic systems are well-suited for sustainable seismic design. Mixed multiple structures are combinations of two or more low/controlled damage ductile structures, an articulated gravity frame, a collapse preventive, hybrid, rigid rocking core, and a phantom P-delta system acting together to form a repairable archetype. Each earthquake resistant system is equipped with replaceable energy dissipating and fail-safe devices. Such arrangements call for applications of Plastic Design and Performance Control principles, rather than conventional methods of approach. This in turn calls for development of modern design rules, technologies and details that govern the behavior of such systems equipped with replaceable energy dissipating devices. In the interim several observations that reduce the task of otherwise cumbersome analysis to simple rules of response have been introduced.

Experimental research on damage tolerance and air tightness of typical composite panels

The extensive use of composites in aircraft leads to the problem of damage tolerance after low-speed impact. It is necessary to consider not only the change of mechanical properties but also the change of work properties such as air tightness. In this paper, the damage morphology and air tightness of a typical composite stiffened panel subjected to low-speed impact were experimentally studied. The damage initiation and propagation and the change of air tightness after impact, static compression and compression fatigue were analyzed respectively. It is found from the test that after 120% ultimate load condition and 100,000 times constant amplitude fatigue load condition, the impact damage does not expand, and the air tightness is good and no obvious leakage is observed, indicating that the structural design meets the requirements of damage tolerance and air tightness.

The Response of Reinforced Concrete Composite Beams Reinforced with Pultruded GFRP to Repeated Loads

This paper investigates the experimental response of composite reinforced concrete with GFRP and steel I-sections under limited cycles of repeated load. The practical work included testing four beams. A reference beam, two composite beams with pultruded GFRP I-sections, and a composite beam with a steel I-beam were subjected to repeated loading. The repeated loading test started by loading gradually up to a maximum of 75% of the ultimate static failure load for five loading and unloading cycles. After that, the specimens were reloaded gradually until failure. All test specimens were tested under a three-point load. Experimental results showed that the ductility index increased for the composite beams relative to the reference specimen by 156.2% for a composite beam with GFRP with shear connectors, 148.6% for composite beams with GFRP without connectors, and 96% for the composite beam with a steel I-section.

Research on the Dynamic Response of Submerged Floating Tunnels to Wave Currents and Traffic Load

Submerged floating tunnel (SFTs) are typically subjected to complex external environmental and internal loads such as wave currents and traffic load. In this study, this problem is investigated through a finite element method able to account for fluid-structure interaction. The obtained results show that increasing the number of vehicles per unit length enhances the transverse vibrational displacements of the SFT cross sections. Under ultimate traffic load condition, one-way and two-way syntropic distributions can promote the dynamic responses of SFTs whereas two-way reverse distributions have the opposite effect.

Ultimate capacity of large-span soil-steel structures

The ultimate limit states provided by current design codes and standards were based on full-scale field and laboratory tests performed on soil-steel structures (SSS) of spans less than 10.0 m. Recently, the spans of SSS have increased up to 32.4 m with the tendency to exceed this record. The ultimate capacity of SSS utilizing the deepest corrugation profile, i.e., 237 mm depth and 500 mm pitch, has not been yet investigated under earth and truck loading. The current study evaluates the ultimate capacity of the world’s largest-span SSS with 32.4 m span and 9.57 m rise, using three-dimensional (3D) nonlinear finite element simulation. The investigation covered both the maximum backfill height and ultimate truck loading conditions. The 3D finite element modelling technique under ultimate loading was validated by full-scale test measurements of 10.0 m span soil-steel structure subjected to tandem axle loading. The critical straining actions obtained from the steel structure at ultimate condition was used to evaluate the ultimate limit states provided by the Canadian Highway Bridge Design Code (CHBDC, 2019) and AASHTO (AASHTO LRFD, 2019). The results revealed that the ultimate capacity of the SSS was reached without conforming to all ultimate bounds provided by the current design codes. Finally, a limit state function was proposed to account for the structure instability that may occur to the steel structure under ultimate loading condition. The proposed function successfully predicted failure in the steel structure under all cases considered in the current analysis before failure occurred in the numerical results.

A topology optimization methodology for the offshore wind turbine jacket structure in the concept phase

This paper proposes a topology optimization methodology for offshore wind turbine (OWT) jacket structure design in the concept phase. First of all, modal analysis and load calculation of a 5 MW reference OWT are performed. On the basis of finite element analysis, the displacement and von Mises stress of multi-jacket support structures in various ultimate loading conditions are explored. Furthermore, structural topology optimization formulation aims to minimize a weighted normalized objective for the OWT jacket structure. Therefore, several optimum structures are obtained by adjusting weighting coefficients. For the coupling effect between the structure and applied load, load recalculation, displacement, and stress reanalysis are performed on the jacket structure based on the topological configuration under a specific weighting factor. Comparisons are made between the reference structure and optimized structure. Without the addition mass, the fundamental natural frequency of the optimized structure is marginally increased, but the maximum displacement and von Mises stress are drastically lowered, indicating that the optimized structure outperforms its reference counterpart. These findings conclusively demonstrate that the proposed TO technique for the design of OWT jacket structures is feasible and preferable.

Dynamic Response Analysis of a Novel Anti-Impact Pressure Balance Jack

Coal resources perform an important role in China’s energy structure. Hydraulic support is the main supporting equipment of fully mechanized mining face in coal mines. Because the hydraulic support frequently bears the impact pressure from the working face, it is very easy to cause failure of the balance jack. In order to solve the problem that the balance jack easily damaged by impact and improve the impact resistance of the hydraulic support, an improved fast response balance jack with multiple adaptive buffers was proposed in this paper. The energy dissipation characteristics of the balance jack were analyzed by establishing the mathematical model of the multiple buffering process of it. Based on ADAMS, the dynamic simulation model of the hydraulic support was constructed, and the mechanical response characteristics of the proposed balance jack and the traditional balance jack under different impact loads were compared and analyzed. By changing the equivalent stiffness of the novel balance jack system, the influence of different initial inflation pressure and length of the buffer cavity on the dynamic performance of the novel balance jack was discussed. The results show that compared with the traditional balance jack, the multi-adaptive response balance jack proposed in this paper can reduce the peak force of the hinge point by about 24.6% and the fluctuation frequency was also significantly reduced under the ultimate load condition at the front end of the top beam, which has better impact resistance. When the initial inflation pressure of the buffer cavity is 40~45 MPa and the initial length is less than 105 mm, a better buffer effect can be achieved. This study provides a new solution to solve the failure problem of the balance jack under the underground impact pressure and improve the safety and reliability of hydraulic support.