•The proposed methodology could take the amplification ratio, strength, service life and isolation capacity into consideration at the same time.•Moreover, the parameterized models which have been ...established and deduced can make the rapid design of amplifiers possible.•In fact, this capacity provides a new way of achieving precision driving and micro-vibration isolation just by using the drive system without additional isolation equipment.•A different optimization strategy is proposed and implemented.
Flexure-hinged displacement amplifiers play an important part in ultra-precision engineering due to their advantages of no friction, no backlash, compactness, high resolution and so on. In fact, the flexure-hinged displacement amplifier is initially proposed for addressing the travel shortcoming of piezoelectric or magnetostrictive actuators. However, some new challenges such as micro-vibration isolation and long service life, etc., arouse attentions especially when working in the harsh environment. Therefore, a new methodology for designing amplifier which could handle such issues is proposed and discussed in this paper. The focus of this study is on the design, theory analysis, and optimization of amplifiers, not only with the purpose of providing a larger displacement output, but also achieving micro-vibration isolation in desired frequency band. First, a generalized model for flexure hinges, the largest principal tensile stress and fatigue safety factor are formulated mathematically under combined tension and bending loads. Then the applied loads acting on each flexure hinge is calculated according to pseudo-rigid-body model. The equivalent dynamic model is established by Lagrange method. Whereafter, the procedure of the methodology is summarized and a different optimization strategy is implemented. Finally, a prototype is fabricated and tested. The experiments and simulation results confirm that the amplifier can achieve the desired amplification ratio and passive vibration isolation, which validate the effectiveness of this methodology.
Abstract
Engineering codes, design standards and analytical criteria for hydraulic structures are the final determinative specifications for designing and constructing a water resources project. As ...such, they are the authoritative and legally accepted standards for project design and construction. Engineering codes and standards are developed to optimize public safety and performance by focusing on structural reliability, which includes a wide range of extreme conditions that encompass most contemporary climate uncertainties, and which are likely to overlap some portion of future climate non-stationary conditions. Current practices of risk-based planning and design standards have evolved incrementally, responding to each catastrophic natural disaster, whether it is geotechnical, floods, droughts or hurricanes. Design standards and building codes encompass an accumulation of changes that progressively reflect changing climate conditions, most notably because they focus on climate extremes. Design standards and embedded ‘safety factors’ that are based on extremes are likely to encompass a good deal of an anticipated non-stationary climate regime and its associated uncertainties. Modern risk analysis methods and risk-based standards, codes and methods comprise an important part of a progressive autonomous adaptation to climate change. They represent an essential component of ‘no regrets’ climate adaptation.
AbstractThe strength of thin-walled stainless steel columns has been investigated extensively over the last few years. The present paper presents the results of an extensive computational study of ...the buckling strength of lipped–channel section columns made of austenitic, duplex, and ferritic grades. The numerically computed strengths together with the available experimental data collected in the literature are compared to the current European and Australian/New Zealand standard (AS/NZS) codified predictions over the whole slenderness range. Minor and major axis buckling as well as flexural-torsional buckling are considered. A reliability assessment in the sense of both standards is then performed. The safety factor γm and resistance factor ϕc are computed per family of stainless steel. In conclusion, we advise the use of different European buckling column curves rather than the one currently adopted in the code and to make a distinction between the families of stainless steel. Besides, seeing the very good agreement found against the AS/NZS guidance, we propose that the factor η, currently being a linear expression in the European standard, be replaced by the AS/NZS expression with the proposed parameters for each stainless steel family.
In the seismic design of underground subway station structures, the influence of side diaphragm walls as safety factor is not considered. In general, the role of the diaphragm wall has not been ...adequately investigated. In this study, an advanced finite element analysis model was developed to simulate the dynamic interactions among the soil, underground diaphragm walls, and subway station by considering different connection modes for the diaphragm wall and sidewall and the effect of the initial static stress. The influences of the diaphragm wall and its connection to the sidewall of the underground subway station were analyzed and compared. The results show that the existence of diaphragm wall will strengthen the lateral stiffness and reduce the lateral deformation of underground subway station, however, in some cases, it is not entirely for preventing a seismic damage in the underground subway station; Rather, a slipping connection between the diaphragm wall and side wall exacerbates the earthquake damage in the middle column of the underground structure under a strong ground motion input. However, a tied connection between the diaphragm wall and sidewall improves the seismic responses of the underground subway station.
•The influence of side diaphragm walls is considered as a safety factor.•Numerical simulation on the seismic behavior of the underground structure.•The diaphragm walls can effectively reduce the seismic deformation of structure.
It is important to investigate the uncertainty of failure assessment models for safety management and reliability calculations of pipelines containing cracks. In this paper, firstly, we predict the ...burst pressure of 250 experiments with 9 different failure assessment models and obtain the prediction accuracy (PA) based on the measured test data. Secondly, the PA of different models is analyzed according to the new model prediction performance evaluation system, which includes distributional location characteristics (rough accuracy, risk, robustness and conservativeness) and stability (dispersion, correlation and multi-peakedness). Finally, the critical safety factors are determined for different models to control reliability based on the best-fit distribution. The results show that for distribution location characteristics, CorLAS is the most accurate; the R6-2A-I (R6-Option 2A, global solution based on the Tresca criteria, 2016), API-Ⅱ (API RP 579-Level 2, 2016), R6-2A-III (R6-Option2A, local solution, 2016) and SINTAP-I (SINTAP-Level 1, 1999) are robust; CorLAS and R6-2A-II (R6-Option 2A, global solution based on the von Mises criteria, 2016) are risky, and GB-Ⅱ (GB/T-Conventional Assessment, 2019) and BS7910-Ⅰ (BS 7910-Option 1, 2019) are very conservative. The order of their stability is: ① R6-2A-III; ② R6-2A-I, R6-2A-II, API-Ⅱ and SINTAP-I; ③ GB-Ⅱ and BS7910-Ⅰ; ④ Battelle; ⑤ CorLAS. GB-Ⅱ, BS7910-Ⅰ, Battelle and CorLAS are dispersed. The correlation between PA and pc is weak and negligible for all models. The best-fit distributions are lognormal for R6 and SINTAP and GMM for the others. Finally, the use of all models is recommended by considering the critical safety factors.
•The most often used models for the integrity assessment of pipelines are investigated by means of mathematical test methods concerning their prediction accuracy.•Recommendations for the application of such assessment tools are deduced from the analysis.•The new model prediction performance evaluation system is constructed, which includes distributional location characteristics (rough accuracy, risk, robustness and conservativeness) and stability (dispersion, correlation and multi-peakedness).•Not only the common unimodal distributions but also the Gaussian mixture model are used to determine the optimal distribution of prediction accuracy. Based on the optimal distribution, the critical safety factors for different models are calculated.
In this study, a masonry panel under a high compressive stress to strength ratio is considered. The panel is modeled as a composite structure by considering a repeated unit cell of mortar and brick. ...Load redistributions due to creep in mortar and brick as composite materials are accounted for. A step-by-step in-time analysis is performed to calculate the load redistribution in the composite masonry. Time-dependent system reliability analysis of the masonry panel is performed by defining the component and system limit state functions at each time step. While the reliability index of ductile materials depends on the load level in each part of masonry, the reliability index of brittle materials depends only on the overall load. By proposing the reliability index of quasi-brittle materials being between these two reliability index bounds, the reliability index of quasi-brittle materials depends on both the load level in each part and the overall load. Using the proposed reliability index of quasi-brittle materials, partial safety factors for masonry panel design considering creep and damage are calibrated based on the Hasofer and Lind method. A design example using the proposed partial safety factor is presented.
Among all factors affecting the stability of soil slopes, the effects of seepage, and especially drawdown, have long been a topic of study. This paper proposed a novel method for predicting the ...phreatic surface of three-dimensional (3D) slopes. Based on the solved phreatic surface, the normal stress expression of the slip surface under seepage force was deduced. A strict overall analysis method that combines the seepage force to analyze the stability of the bank slopes with reservoir drawdown was proposed. The credibility of the proposed method was verified by calculating different conditions set by a classic slope model. Finally, the change rules of the phreatic surface and the safety evolution with reservoir drawdown of a practical slope in the Three Gorges reservoir area were studied. The results demonstrated that the safety factor of the slope first decreases and then increases with reservoir drawdown and the most unfavorable water level is at the lower 1/3–1/4 of the total height of the slope.
Abstract
The activity of the Opak Fault on May 27
th
, 2006, caused a strong earthquake of M
w
6.3, then known as the Yogyakarta Earthquake. Previous studies have shown that several damages during ...the earthquake were caused by liquefaction. This paper aims to determine potential liquefaction hazards at toll road construction in Klaten Regency, within less than 10 km of the Opak Fault. The liquefaction potential was analyzed from Standard Penetration data using the simplified procedure to determine the safety factor and Liquefaction Potential Index by Iwasaki et al. (1981). In addition, vertical displacement caused by liquefied soil was calculated using the equation developed by Yoshimine et al. (2006). Based on the analysis of the liquefaction potential of 10 boreholes, the results showed that liquefaction occurs at 6 boreholes, with a high to a very high level of liquefaction potential index with a maximum horizontal acceleration of at least 0.46g. The extensive ground surface damage potentially occurs at 2 boreholes, with the vertical settlement of 32.55 cm and 47.02 cm, which occur at the nearest site distance to Opak Fault.
The construction sector is recognized as one of the most dangerous industries in the world. The situation is worsening in Iraq, as a result of a lack of attention to safety in the building industry ...and the poor implementation of safety programs. This research aims to identify the critical safety factors (CSFs) of safety program implementation in the Iraqi construction industry. The CSFs were first identified from a review of literature before being verified by construction practitioners, using semi-structured interviews. A questionnaire, based on the verified CSFs, was distributed to construction practitioners in Iraq. Exploratory factor analysis (EFA) was used to analyze the quantitative data, and the results show that the CSFs can be categorized into four constructs: worker involvement, safety prevention and control system, safety arrangement, and management commitment. Following that, partial least square structural equation modelling (PLS-SEM) was executed to establish the connection between safety program implementation and overall project success. The result confirms that safety program implementation has a significant, positive impact on project success. This article contributes to knowledge and practice by identifying the CSFs for implementing safety programs in the Iraqi construction industry. The successful implementation of a safety program not only improves safety performance, but also helps to meet other project goals.
Stress shielding secondary to bone resorption is one of the main causes of aseptic loosening, which limits the lifespan of the hip prostheses and increases the rates of revision surgery. This study ...proposes a low stiffness polyether–ether–ketone (PEEK) hip prostheses, produced by fused deposition modelling to minimize the stress difference after the hip replacement. The stress shielding effect and the potential bone resorption of the PEEK implant was investigated through both experimental tests and FE simulation. A generic Ti6Al4V implant was incorporated in this study to allow fair comparison as control group. Attributed to the low stiffness, the proposed PEEK implant showed a more natural stress distribution, less stress shielding (by 104%), and loss in bone mass (by 72%) compared with the Ti6Al4V implant. The stiffness of the Ti6Al4V and the PEEK implant were measured through compression tests to be 2.76 kN/mm and 0.276 kN/mm. The factor of safety for the PEEK implant in both static and dynamic loading scenarios were obtained through simulation. Most of the regions in the PEEK implant were tested to be safe (FoS larger than 1) in terms of representing daily activities (2300 N), while the medial neck and distal restriction point of the implant attracts large von Mises stress 82 MPa and 76 MPa, respectively, and, thus, may possibly fail during intensive activities by yield and fatigue. Overall, considering the reduction in stress shielding and bone resorption in cortical bone, PEEK could be a promising material for the patient–specific femoral implants.
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