Safety Factor Of Structure Research Articles

Evolution of structural safety for tunnel arch crown linings under the coupled influence of void and insufficient thickness

The existence of voids behind tunnel linings constitutes a recognized inherent defect in tunnel engineering. Void and insufficient thickness can significantly compromise structural safety, especially at the tunnel arch crown. In this study, we employed similar model tests and numerical analysis methods to examine how the coupling of voids and insufficient thickness affects the structural performance of arch crown linings. Key findings reveal that the coupling of arch crown voids and insufficient thickness causes notable shifts in displacement patterns and internal force distribution. The displacement pattern of the arch shifts from the inner side to the outer side of the tunnel, resulting in the concrete stress state on the inner side of the arch crown changing to compression. Spatial distribution characteristics of voids and insufficient thickness defects were analyzed to assess their impact on structural degradation, with quantitative analysis using the safety factor index. Geometric parameters of voids and insufficient thickness (longitudinal length, thickness, circumferential range) were chosen based on analysis under various conditions to predict the structural safety factor using a Wide Neural Network regression model with 98 % accuracy. This method offers a new approach for rapidly predicting the safety status of lining structures. These findings are crucial for comprehending the effects of arch crown voids and insufficient thickness defects and for devising effective strategies to address tunnel lining defects.

Aeroelastic Influence of Blade-Shaft Coupling in a 1 1/2-Stage Axial Compressor

Abstract The design process of turbomachinery, is often constraint by aeroelastic phenomena. The design choices are limited by possible structural failure, which can be caused by high vibration amplitudes. In particular, damping has an important impact on these phenomena. In the absence of friction, damping is mainly created by aerodynamics. In this paper, additional damping created by the shaft will be investigated. This becomes relevant when blade vibrations with nodal diameters 1 and -1 couple structurally with shaft vibrations. To investigate the blade-shaft coupling, a simulation process is set up based on a full structural dynamic model of the blisk-shaft assembly and a harmonic balance CFD model to account for the aeroelastic effects. In addition, mistuning identification is performed based on an experimental modal analysis at standstill. All results are incorporated into a structural reduced order model that calculates the vibrational behavior of the blading. These results are compared to damping determined during operation using an acoustic excitation system and measured forced frequency responses. The numerical results agree well with the experimental results, i.e. within the measurement uncertainty. Furthermore, the blade-shaft coupling results in significant changes of the eigenfrequencies and damping. As a consequence, damping increases by up to twelve times due to the coupling. This reduces amplitudes by a factor of nine for the mistuned blade responses. Consequently, higher structural safety factors can be achieved by taking the blade-shaft coupling into account so that the remaining potentials in the aerodynamic design could be better exploited.

Fatigue damage tolerance of CFRP/Al adhesive joints with thermal effects

In order to promote application of adhesive connection in primary load-bearing structures for engineering practice, tolerance of fatigue damage signifies a critical parameter in line with the guidance of FAA AC 20-107B. This study aims to investigate this issue from four aspects, namely, statistics of fatigue cracks, residual performance, critical point for fatigue damage tolerance, and degradation of adhesive property. To carry out a dedicated study, the carbon fiber reinforced polymer and aluminum (CFRP/Al) adhesive joint specimens with different degrees of fatigue damage were considered by monitoring real-time variation of stiffness in the course of pre-fatigue loading. The residual strengths at different temperatures and related degradation mechanisms were explored through the experimental tests and numerical analysis. The study suggests the 92% normalized stiffness to be a critical point, at which the structural safety factor is 2.5. It is found that a safety factor of 1.5 may not be sufficient for the structure under fatigue condition as the joint is fairly susceptible in the structure. This study unveiled that a reliable management for residual fatigue performance can be achieved. It is anticipated to provide an effective guide for damage-tolerant design, reliable safety monitoring, and punctual repair of damaged adhesive structure.

Stability Analysis of Gravity Dam using Matlab Programming

Gravity dams are critical structures in civil engineering, designed to withstand the immense forces exerted by water pressure and gravity. Ensuring their stability is paramount to prevent catastrophic failures that could result in significant economic and environmental consequences. This study presents a comprehensive stability analysis of a gravity dam using MATLAB programming. The analysis focuses on evaluating the structural integrity and safety factors of the dam under various loading conditions, including hydrostatic pressure and seismic forces. MATLAB's computational capabilities are utilized to perform rigorous numerical simulations, incorporating finite element analysis (FEA) and stability criteria assessments. Key aspects of the stability analysis include the determination of critical failure modes such as sliding, overturning, and base pressure distribution. Through MATLAB programming, the study explores different dam geometries and material properties to assess their influence on overall stability. Furthermore, sensitivity analyses are conducted to investigate the impact of uncertainties in input parameters on the dam's stability margins. This provides insights into potential weak points and allows for optimization of design parameters to enhance dam safety.

Subregional Differentiated Safety Factors Design Based on Nonprobabilistic Structural Reliability

The structural safety factor is an essential parameter in aircraft design, representing the ratio of the design load to the operating load. Traditional design methods rely on subjective determination of safety factor values based on experience, lacking objectivity in quantifying uncertainty. However, with advancements in aircraft design technology and increasing competition in the commercial space market, new-generation hypersonic aircraft with complex load environments require a more optimal approach. Applying a uniform safety factor to each component within subregions of the aircraft leads to overly conservative results and impacts flight performance. To address this limitation, a design scheme that incorporates subregional, differentiated safety factors is necessary. This approach allows for better material utilization and ensures compliance with safety requirements. This paper utilizes reliability-based design optimization theory to consider uncertainty in structural systems. It establishes a mapping relationship between structural reliability and differentiated safety factors, providing safety under uncertainty while guaranteeing weight reduction. Additionally, this paper develops a subregional, differentiated safety factors distribution program to determine the safety factors of different subregions of the structure. Consequently, a refined subregional differentiated safety factors scheme that balances safety and economy is derived.

A framework to demonstrate the utility and safety of the observational method

AbstractUnderground engineering projects are often characterised by significant uncertainties, leading to complex decision‐making when selecting appropriate design methods. Traditional approaches, such as the observational method (OM), have been widely used but rarely explicitly account for the integration of risk, costs, construction timeframes and engineering judgement. Successfully reaching a consensus to implement the OM on tunnelling projects can be challenging and requires ensuring stakeholders understand how the method impacts structural safety. Fostering such understanding can be an arduous process. A risk‐based decision framework is introduced using expected utility theory to aid the decision to choose the OM, or not. The framework integrates risk, cost, construction timelines and engineering judgement within an economic decision model using a probabilistic approach. It is tested on a Sydney, Australia case study. A Monte Carlo model analysis examines contingency actions and structural failure probability when applying the OM. The case study highlights the significance of considering indirect costs in complex decisions and harnesses experienced professionals’ insights for a comprehensive risk and cost assessment. We conclude that merging probabilistic‐based design with OM enhances the ability to demonstrate structural safety and economic factors within a unified model.

PERENCANAAN ULANG STRUKTUR GEDUNG LIMA LANTAI ASRAMA HAJI SEMARANG

Due to the increasing number of Hajj pilgrims, the need for accommodating them has also risen. Therefore, a redesign is necessary to enhance the capacity of accommodating the pilgrims. The Analysis and Structural Planning of the Hajj Dormitory Semarang using ETABS software in compliance with the Indonesian National Standard (SNI). The redesign of the Hajj dormitory aims to augment the housing capacity for prospective Hajj pilgrims. The Revised Structural Planning for the Five-Story Hajj Dormitory Building Semarang aims to analyze and redesign the structure of the dormitory. This involves utilizing concrete quality of 24.9 MPa for the upper structure and 30 MPa for the lower structure, with main reinforcement using 420 MPa, while secondary reinforcement uses 280 MPa. The structural analysis approach involves inputting geometric data, loads, and material characteristics, including desired concrete and steel qualities, into the ETABS software. The analysis adheres to the SNI guidelines governing building loads, seismic resilience, and other structural safety factors. The analysis results provide insight into the structural response spectrum, with a mass participation of UX 99.98% and UY 99.19%. Control Base Shear Vdynamic > Vstatic, with Eq Dx > Eq Sx and Eq Dy > Eq Sy, is 8623.266 > 8563.3067 and 7928.0409 > 7722.4166. The maximum story displacement due to dynamic seismic motion in the X and Y directions is 14.33 mm and 15.95 mm. Meanwhile, the story drift with an Inelastic Drift value less than 61.5 mm for safety building permissible deviation. The largest permissible deviations obtained for the X and Y directions are 18.816 mm and 20.554 mm.

Study on Large Deformation Characteristics and Secondary Lining Supporting Time of Tunnels in Carbonaceous Schist Stratum under High Geo-Stress

The deformation characteristics and the timing for secondary lining support in high geo-stress soft rock tunnels have drawn significant attention. In carbonaceous shale formations, tunnel construction deformations are very pronounced under construction disturbances due to the development of joints, dense fractures, and poor interlayer bonding. With the Xishuangbanna tunnel as our research backdrop, this study meticulously analyzed the deformation patterns and characteristics inherent to high geo-stress tunnels constructed within carbonaceous schist formations. Employing a comprehensive approach involving full displacement analysis and on-site construction mechanics testing, we utilized the displacement release rate and structural safety factors as key indicators to determine the secondary lining supporting time. Employing this innovative approach, we successfully identified the ideal junctures for implementing secondary lining support in tunnels excavated through high geo-stress carbonaceous schist. The research findings indicate that the primary damage modes in high geo-stress carbonaceous schist tunnels are initial support failure and extensive early support deformation. These vulnerabilities are primarily attributed to weak and fragmented strata, elevated ground stress levels, and inadequate support strength. During the early stages of tunnel construction, substantial deformations are observed, exhibiting high rates of change. Horizontal convergence, notably, significantly surpasses the settlement at the tunnel’s crown. When employing the three-bench method for construction, the deformation occurring before the excavation of the middle bench contributes the most to the total deformation monitored, whereas the deformation generated after the excavation of the inverted arch constitutes a minor proportion. The tunnel’s crown and invert experience tension while the secondary lining undergoes compression. The internal forces are most significant at the tunnel’s hance and knee, with the left tunnel knee being the weakest section of the secondary lining. The findings of our study are poised to guide the design and execution of tunnels constructed within high geo-stress carbonaceous schist formations.

Safety Analysis of Secondary Lining of Yulinzi Tunnel Based on Field Monitoring

In order to assess the safety of the secondary lining in water-rich Loess Tunnel, this study relies on the Yulinzi Tunnel project to continuously monitor the stress of the steel reinforcement in the secondary lining and analyze the temporal variation of the steel strain. Based on this data, the temporal variation and distribution characteristics of the internal forces of the structure were obtained through section force calculation. The safety factor of the secondary lining structure was evaluated by calculating the safety factor of the structure. It was found that the variation of the safety factor with time conforms to the exponential function, and the fitting results of different measurement points were good. This could be used to predict the future safety factor of the tunnel and evaluate its long-term safety, which has practical guidance significance for actual engineering projects. In addition, the long-term stress and structural deformation characteristics of the tunnel were obtained through numerical simulation.

Titanium Wind Tunnel Balance Leveraging Additive Manufacturing

Titanium force transducers have among the highest strength–to–Young’s modulus ratios of common transducer materials. This can be leveraged to increase the sensitivity of the transducer relative to other materials or to increase the structural safety factor of the transducer for a given sensitivity. It is surprising then that no titanium wind tunnel balances have been reported in the literature or produced by NASA. With the increasing maturation of additive manufacturing technology, this work explores additively manufacturing a titanium wind tunnel balance. Additive manufacturing of the balance was completed in less than 1 week. Then, several secondary finishing and machining operations were performed to finalize the balance geometry, and it was strain gaged and calibrated. Calibration results confirm that the titanium balance has approximately 68% higher output compared to a steel balance of identical geometry and applied load. Based on the calibration results, hysteresis, pure error, and accuracy of the titanium balance are reported. These performance characteristics are comparable to conventionally manufactured state-of-the-art steel balances.

Gravity estimation of groundwater mass balance of sandy aquifers in the land subsidence-hit region of Yunlin County, Taiwan

Land subsidence will decrease the safety factor of bridges and structures. Many highways and railways constructed decades ago are experiencing damage due to continual land subsidence in several alluvial fans of Taiwan. Groundwater over-pumping for industrial and agricultural uses leads to severe (>3 cm/year) land subsidence in the middle to distal Choushui River Alluvial Fan (CRAF), the largest alluvial fan in Taiwan. The Taiwan High Speed Rail passes through CRAF and land subsidence is now a major concern. Replenishing groundwater with artificial recharge lakes is a potential solution to mitigate land subsidence impacts. Using gravimetry, we examined two undetermined regional unconfined aquifers (RUAs) in the land subsidence-hit region that could host potential artificial recharge lakes to replenish groundwater. We established seven absolute gravity sites and measured time-lapsed gravity values in Yunlin in southern CRAF in 2021, including five sites in the subsidence-hit region and over two unconfined aquifers in the proximal fan. A consistent pattern of residual gravity changes associated with water storage changes at all the gravity sites confirms the recharge potential of the two RUAs in the land subsidence-hit region. Here we estimated groundwater storage changes by residual gravity changes around gravity sites without using prior hydrology information such as groundwater levels and storage coefficients. Of all the gravity sites in the land subsidence-hit region, the most significant March-to-September residual gravity change (26.6 μgal) and vertical displacement (−4.2 cm) were observed at Siutan elementary school (STES). The estimated groundwater storage change around STES is significantly large to increase the water balance in Yunlin, despite the site's severe land subsidence in 2021. We used electrical resistivity imaging (ERI) to aid the identification of the RUA near STES and discussed a potential joint gravimetry-ERI study of the RUAs for subsidence-mitigation engineering works such as constructions of recharge lakes.

Nonlinear Creep Amplification Factor Considering Damage Evolution of Concrete under Compression.

Creep affects the long-term deformation of concrete structures. Nonlinear creep further overestimates the safety factor of structures and affects the safety service performance. The coupling of creep and a damage model considering the rate effect is conducive to accurate prediction of nonlinear creep, but the iterative process of strain makes the calculation method more complex. The purpose of this study is to propose a nonlinear creep explicit method that considers the damage evolution of concrete under compression. Two groups of axial compression members with compressive stresses of 0.2 fc and 0.4 fc were made. Considering the law of concrete damage evolution under uniaxial compression, coupled with elastic creep and damage incremental strain, the lower limit of the medium stress level that gives rise to nonlinear creep is analyzed. The concrete nonlinear creep amplification coefficient with a loading age of 28 days and loading duration of 360 days is studied with consideration for the uncertainty of relative humidity and the theoretical thickness of the component. On this basis, the explicit calculation formula of the nonlinear creep amplification coefficient related to the concrete axial compressive strength and stress level is given. The results indicate that the nonlinear creep amplification coefficient increases nonlinearly with an increase in the stress level, and, when the compressive stress level ratio is higher than 0.6, the nonlinear creep amplification coefficient increases significantly; when the stress level is determined, the creep amplification coefficient decreases gradually with an increase in the compressive strength of the concrete. It is suggested that a stress level range of 0.35~0.75 should be used for the study of a nonlinear creep amplification factor under the medium stress state.

Study on Structural Health Monitoring and Damage Detection in the Field of Civil Engineering

Structural health monitoring and damage detection can help people avoid emergency casualties and take preventive measures, and it is very important in practical application. After consulting authoritative information, the structural health often affected by the surrounding environmental safety factors and structural safety factors. This paper begins with the harm of the inadequate building safety and the factors affecting building safety. To detect structural health problems and avoid many kinds of disasters, three monitoring methods have been mentioned, two new building safety detection methods and a damage detection scheme, called wireless sensor network subsystem, global navigation satellite system technology, and ultrasonic flaw detection technology. The principles of three methods are mainly expounded, and their advantages and disadvantages are analyzed, by putting forward suggestions for future research prospects and giving some practical examples. Finally, it is concluded that wireless sensor network method is simple to achieve but the monitoring data is single; GNSS system has high precision but cannot be widely used; And ultrasonic flaw detection technology can detect steel damage single efficiency.

Interlaminar Shear Properties of Bamboo Composite for Structural Applications

Interlaminar shear strength in bamboo composite (BC) is mainly provided by epoxy resin as the matrix in BC. This may greatly change due to humidity. This study aims at evaluating the shear strength of BC by testing and developing probabilistic relationships. The interlaminar shear strength of bamboo composite (BC) in different moisture conditions was tested according to ASTM D2344. The results show that the maximum shear stress does not generally occur at the centroid of samples, which could be associated with imperfections in BC layers. An extreme value theory-based model is suggested to evaluate the probability of shear failure in BC samples. The shear capacity decreased from 20.4 MPa to 14 MPa as the humidity increased from 60% to 90%. A summary of findings is as follows: It was found that under transient moisture conditions, local failure is likely to happen before the first significant crack occurs. Local failure is suggested to be considered in the design for serviceability. Stress drop caused by the local failure could exceed 10% of total shear strength and, therefore, should be regarded as a serviceability design. The probabilistic model developed in this study could be used for developing structural design safety factors.

Intelligent Analysis for Safety-Influencing Factors of Prestressed Steel Structures Based on Digital Twins and Random Forest

The structure of a prestressed steel structure is complex, which can result in insufficient control accuracy and the low efficiency of the structural safety. The traditional analysis method only obtains the mechanical parameters of the structure and it cannot obtain the key factors that affect the structural safety. In order to improve the intelligence level of the structural safety performance analysis, this study proposes an intelligent analysis for the safety-influencing factors of prestressed steel structures that is based on digital twins (DTs) and random forest (RF). Firstly, the high-precision twin modeling is carried out by the weighted average method. The design parameters and the mechanical parameters of the structure are extracted in real time in the twin model, and the parameters are classified by the RF. The fusion mechanism of the DTs and RF is formed, and the intelligent analysis model of the structural safety factors is established. Driven by the analysis model, the correlation mechanism between the design parameters and the mechanical parameters is formed. The safety state of the structure is judged by the mechanical parameters, and the key design parameters that affect the various mechanical parameters are analyzed. Through the integration of the design parameters and mechanical parameters, the intelligent analysis process of the safety-influencing factors of prestressed steel structures is formed. Finally, an intelligent analysis of the importance of the safety-influencing factors is carried out with the string-supported beam structure as the test object. Driven by the integration of DTs and RF, the key design parameters that affect the various mechanical parameters are accurately obtained, which provides a basis for the intelligent control of the structural safety.

Damping characteristics of the architectural coated fabric and its influence on the vibration response of membrane structures

The influence of material damping is ignored in the current membrane structure design. Based on the damping characteristics of coated fabric obtained by the dynamic mechanical analyzer, the applicability of classical Maxwell model, generalized Maxwell model, three-parameter liquid model, fractional derivative Maxwell model, and fractional derivative Kelvin model to describe the viscoelastic properties of coated fabric were discussed. The free-falling body excitation vibration test of plane tensioned membrane structure is carried out and the dynamic response of plane membrane structure under impact load was studied. The reasonable viscoelastic damping constitutive model is obtained through a systematic comparison of the existing models then implemented in Abaqus software and subsequently validated with the data obtained from the vibration test. Taking saddle-shaped and umbrella-shaped membrane structures as research objectives, the dynamic response of membrane structures under dynamic wind load considering material damping performance is discussed. The results show that the damping property of the coated fabric significantly affects the dynamic characteristics of the membrane structure. Due to the existence of material damping, the modal frequency of the overall structure is greater than the result of the elastic model. The reduction factor of maximum vertical displacement can reach 67.14%, and the reduction factor of maximum principal stress can reach 68.93%, which makes the structural design safety factor high.

Shape and Mass Optimization of the Connecting Rod using Rigid Body Dynamics and Finite Element Method

Connecting rod is one of the major components in the automotive engine which transmits the reciprocating motion of the piston into the rotary motion of the crankshaft. The engine’s performance and efficiency are greatly influenced by the optimum design of the connecting rod. This numerical investigation ascertains the effect of shape and mass on the transient structural stability and integrity of the connecting rod. The solid model of the connecting rod is developed using PTC Creo. The kinematic movements between the joints and forces are assessed using the rigid body dynamics approach. The shape and mass of the connecting rod are optimized by using the shape finder tool of the finite element method using the outcomes of rigid body dynamics. The optimized connecting rod possesses better structural stability and comparable factor of safety as evaluated by comparing the transient structural deformation, localized and equivalent von-misses stress of the standard and shape optimized connecting rod.

위상최적화를 적용한 검사장비용 진공 그리퍼의 경량 설계

Owing to recent advances in additive manufacturing technology, design for additive manufacturing (DfAM) has been used to overcome design limitations due to constraints in traditional manufacturing processes. In this study, we applied DfAM technology to design lightweight and consolidated vacuum grippers for inspection equipment. We proposed a consolidated design to reduce manufacturing time and costs, which previously encompassed assembling eleven components. Topology optimization was used to reduce part weight while maintaining structural rigidity and safety, and two optimization models were designed: two-piece and one-piece models. Based on these optimized geometries, the internal vacuum paths were designed in a curved shape to enhance adsorption characteristics. Numerical simulations were conducted to evaluate the structural performance and flow characteristics of the initial design and the two optimization models. The pressure drop of the one-piece model, which was the best design, was reduced to 1/8 of the initial design and the structural safety factor was predicted to be 6.37. This final design was then additively manufactured by a digital light processing type 3D printer and the weight of the resulting parts was reduced from 12.94 to 2.08 g. Experimental observation found that the additively manufactured vacuum gripper showed enhanced absorption performance compared to the initial design.

Calibration of Partial Safety Factors of Sample Masonry Structures.

Technological progress in masonry structures has resulted in the creation of competitive solutions, which force the need for an ever deeper recognition of this type of structure. Masonry is a composite with heterogeneous strength properties. Therefore, the most appropriate way to accurately describe the behavior of the masonry structure under the influence of the working load are experimental research and their statistical and probabilistic analysis. This article presents a series of experimental tests carried out on real masonry structures. The results of the experiments were subjected to static evaluation, determining the most important parameter in the probabilistic analysis—the coefficient of variability of strength. The variability obtained in the experimental studies was used to determine the safety of the structure in the probabilistic method. Achieved values of coefficients of variation and safety coefficients proved to be satisfactory and adequate to the emerging technological progress in the production and embedding of masonry components.

Damage assessment of single-layer reticulated domes subjected to mainshock-aftershock sequences based on structural damage factor

Long-span infrastructures are usually taken over for public shelters, in which single-layer reticulated dome is a kind of popular structure. But there was less research for the damage assessment of single-layer reticulated domes subjected to mainshock-aftershock sequences. How to accurately assess the damage by mainshock and the stability redundancy for aftershock becomes an important problem. In order to explore the effects on the structural damage, this paper processes the dynamic time-history analyses for single-layer reticulated domes subjected to mainshock-aftershock sequences. The finite element model of Kiewitt8 single-layer spherical reticulated shell structure is established in ANSYS. Ten pairs of ground motion sequences in horizontal direction are generated with modulating amplitude to simulate the rare and extreme earthquakes. The results demonstrated that the structure even suffered from the extreme earthquake mainshock still has loading capacity and structural safety with the local plastic damage. But the effect on structural damage of aftershock ground motion with greater earthquake intensity cannot be ignored for single-layer reticulated domes. A structural damage assessment method is utilized with combining the damage factor by performing static stability analysis twice. It can effectively reflect the remaining loading capacity and structural safety factor for the practical seismic engineering applications.