Design Safety Factors Research Articles

Effects of new nonlinear curvature models and non-local elasticity on buckling investigation of FG tapered nano-beams locating on elastic foundations

New nonlinear curvature models are proposed to show their effects on the compressive critical buckling load on functionally graded (FG) tapered nano-beams locating on elastic foundations in the presence of non-local elasticity. Fourth and fifth orders finite difference methods (bvp4c and bvp5c) are applied on the governing differential equation which is a highly non-linear, due to curvature and has variable coefficients, due to properties. Dimensional analyses have been applied on the governing system together with the problem conditions to produce their dimensionless forms. For different considered parameters, the critical buckling load is computed using the eigenvalue theorem. The effects of nonlinear curvature, variable Young modulus, variable moment inertia and foundation parameters are studied and displayed in tables and figures. The stability and convergence of the present solution are tested using more than one strategy as: comparison with available results, comparison between bvp4c and bvp5c with different mesh intervals and tolerances of truncation errors. These comparisons show that, the new curvature model affects the critical buckling with different ratios depending on variability of properties and foundation parameters. The new results show that the nonlinear curvature model reduces the critical buckling load in comparison with the classical linear model, which, leads to decreasing in factor of safety in design of structures. The new results show that the design of structures will be influenced with the new reduction of the compressive critical buckling load, since it may affect the factor of safety in design of structures. The new results can lead, generally, to more reduction of critical buckling load for large or small input parameters and it will affect other critical values such that frequencies. The introduced Tables and Figures of the present problem with comparisons of previously exact, analytical and numerical works establish the higher accuracy and stability of current findings using bvp4c or bvp5c with preferable of the later. This study is related to some practical applications such as aeronautical and structural engineering.

Analysis on slope stability by anchorage based on soil creep with flood effect

In order to analyze the adverse effect of flood affection on slope stability, the analytical expressions of buoyancy force and capillary force, hydrodynamic pressure and impact force, and scour erosion were proposed based on the aging characteristics of soil shear strength and limit equilibrium theory. According to the load combination and flood action, shear failure occurs preferentially at the foot of slope. Then, the plastic zone continues to extend upward to produce traction landslide disaster mode. Furthermore, the power function relation between shear strength index and time was established. The nonlinear accelerated creep model was also obtained. At the same time, the safety factor formula for flood loading effect slope aging stability, the time-varying characteristic value of anchor force and the compensation value of anchor force were also obtained and used to research sliding mechanism. In addition, the numerical calculation example shows that the slope safety factor decreases by more than 20 % considering the effect of flood ascending scour and impact, and the compensation value of anchorage force increases obviously with time increasing. Simultaneously, the change rate of compensation value of anchorage force increases nonlinearly with the increase of design safety factor.

Probabilistic failure envelopes of tripod bucket-supported offshore wind turbines in spatially variable clay based on a novel continuous method

Marine geologic conditions play key roles in offshore geotechnical preliminary design and construction decisions. Tripod bucket foundations are considered promising geotechnical foundations for offshore engineering. Their bearing characteristics are often determined based on tripod foundation system failure modes in uniform clay without considering spatially variable soil properties. Therefore, this study investigates the combined bearing capacity of tripod bucket foundations in spatially variable clay based on comprehensive finite element analysis with Monte Carlo simulation (MCS) using a novel simplified modified swipe (SMS) method considering the effects of bucket spacing and foundation skirt length. The SMS method can directly represent the ultimate combined bearing capacity of the whole space efficiently and accurately. The results show that a reduced bucket spacing or increased skirt length changes the failure mode of the foundation from independent caisson failure to global failure. Moreover, the spatial variation in soil leads to an asymmetric failure mode, which is more remarkable for foundations with small bucket group effects. An independent safety factor design approach is adopted to represent failure envelopes with different recurrence probabilities, which should be cost-effective, especially for foundations sensitive to soil variability. Finally, an application based on a convex polynomial optimization strategy for representing failure envelopes is demonstrated.

Sensitivity of fatigue reliability in wind turbines: effects of design turbulence and the Wöhler exponent

Abstract. Fatigue assessment of wind turbines involves three main sources of uncertainty: material resistance, load, and the damage accumulation model. Many studies focus on increasing the accuracy of fatigue load assessment to improve the fatigue reliability. Probabilistic modeling of the wind's turbulence standard deviation is an example of an approach used for this purpose. Editions 3 and 4 of the IEC standard for the design of wind energy generation systems (IEC 61400-1) suggest different probability distributions as alternatives for the representative turbulence in the normal turbulence model (NTM) of edition 1. There are debates on whether the suggested distributions provide conservative reliability levels, as the established design safety factors are calibrated based on the representative turbulence approach. The current study addresses the debate by comparing annual reliability based on different scenarios of NTM using a probabilistic approach. More importantly, it elaborates on the relative importance of load assessment accuracy in defining the fatigue reliability. Using the DTU 10 MW reference wind turbine and the first-order reliability method (FORM), we study the changes in the annual reliability level and its sensitivity to the three main random inputs. We perform the study considering the blade root flapwise and the tower base fore–aft moments, assuming different fatigue exponents in each load channel. The results show that integration over distributions of turbulence in each mean wind speed results in less conservative annual reliability levels than representative turbulence. The difference in the reliability levels varies according to turbulence distribution and the fatigue exponent. In the case of the tower base, the difference in the annual reliability index after 20 years can be up to 50 %. However, the model and material uncertainty have much higher effects on the reliability levels compared to load uncertainty. Knowledge about such differences in the reliability levels due to the choice of turbulence distribution is especially important, as it impacts the extent of lifetime extension through reliability reassessments.

Bearing capacity of strip footings seated on unreinforced and reinforced granular layers over random homogeneous and isotropic spatially variable undrained soft clay

The bearing capacity of a footing seated directly on a soft clay foundation with constant undrained shear strength is the classical Prandtl geotechnical problem. However, a footing seated directly on an undrained clay soil is an unlikely arrangement in practice. Rather, a granular layer is used as a working platform for the construction of the footing and to dissipate the footing loads over a wider area of the clay foundation surface. This paper revisits the footing problem for the case of a footing seated directly on the clay foundation, and seated on an unreinforced and geosynthetic reinforced granular layer overlying the clay foundation. Both deterministic and stochastic numerical modelling of the bearing capacity problem using the program FLAC 2D were carried out. The relationship between the design factor of safety and probabilistic margins of safety is explored for clay foundations with random homogenous and isotropic spatially variable undrained shear strength with mean strengths from 5 to 25 kPa (very soft to soft clay). For practical target probabilistic margins of safety against exceeding a design bearing capacity, the random homogenous soil condition is shown to be the most critical case for design.

An Analysis of the Structural Properties of 3D Printed Square Blocks Prepared using Sustainable Thermoplastic Polyurethane (TPU) Material

For a wide range of utilization, 3D printing is a swiftly developing technology that demands meticulous evaluation of materials, production speed, and resolution. Significant outcomes have been obtained from the application of 3D technology in Cultural Heritage (CH) protection, the valorisation process, communication, and asset incorporation; this is especially true of interdisciplinary initiatives including manufacturing engineering, computer-generated records, and CH accessibility. The primary factors influencing the layout and choosing materials for additive manufacturing are applicability and fabrication technique. A wide range of materials, comprising ceramics and metals, hydro-gels, thermoplastic substances and combinations of these substances, can be used. This study investigates the design and fatigue analysis of a 3D-printed square block made of thermoplastic polyurethane (TPU) under various test conditions, including static structural analysis for compression, fatigue analysis and total deformation within the block layer. The uniform stress distribution was also discussed in detail, as well as the design life and safety factors of the block under fatigue conditions, with its natural frequencies observed in experimental results adjusted the printing parameters for and maintained the process to ensure the best output quality. Post-publication steps included detailed analysis and mechanical testing to verify mechanical properties and dimensional accuracy.

An investigation of relationships between statistical dispersion of crankshaft’s fatigue properties and initial damage

Premature failure due to fatigue would occasionally happen even in a well-designed crankshaft. The microstructural nonuniformity (including micro-defects) plays an essential role in the premature failure due to fatigue, which can lead to the scatter of strength and fatigue life properties. In this paper, the statistical distribution of initial damage corresponding to microstructural nonuniformity has been introduced to uniformly characterize scattering behaviors of tensile strength, fatigue life and impact energy in sampling tests of crankshafts. The goal of this study is to investigate quantitative relationships between the dispersion of initial damage and scattering behaviors of the above sampling tests, so that dispersion properties of a crankshaft can be determined only by relatively simple experiments. By impact sampling tests and several single-throw crankshaft fatigue tests, probability density functions of initial damage have been determined for two crankshafts provided by different manufacturers. It is found that the fatigue reliability of a crankshaft depends on its actual dispersion properties. For a crankshaft with large dispersion of initial damage, the safety factor in the fatigue strength design should be sufficiently large to prevent its premature failure due to fatigue, rather than the one directly recommended in the design manual.

Piling Data-Driven Framework for Optimized Pile Structures Based on Minimizing the Expected Total Cost

The use of data in the construction industry is growing rapidly. However, projects that do not have multiple stages, such as pile foundation and cantilever wall construction, are difficult to reinforce based on the data of observation. It cannot be said that the design–build construction process is optimized by piling data and active learning. In this paper, a new data-driven framework is proposed so that it can be used even for construction under single-stage conditions. The proposed method adopts a lower safety factor (SF) in the preliminary design than that in the conventional methods, and checks the performance after the building using piling data. Countermeasures are conducted to satisfy the target reliability, if necessary. Focusing on the expected total cost, the parametric studies reveal that the proposed method can reduce the expected total cost under specific conditions, such as lower countermeasure cost, higher failure cost, and higher relative costs of safety measures. Furthermore, our method exhibits robustness, as even with low initial safety factors, the expected total cost does not become excessively larger compared to the conventional methods. The findings highlight the potential benefits of piling data for optimizing construction projects under single-stage conditions.

ANALISIS DESIGN CHASSIS ALAT ANGKUT BUAH SAWIT KAPASITAS 500 KG DENGAN METODE ELEMEN HINGGA

Currently, the area of oil palm plantations in Indonesia is increasing. However, the condition of oil palm plantations generally has very minimal infrastructure. Therefore, a means of transporting palm fruit is needed that can move in plantation areas that have minimal infrastructure and have the ability to turn with a small turning radius. Chassis is the most important component in every vehicle. Chassis is a component used to support the load, vehicle body, engine, and driver. The development of technology in the field of engineering requires the chassis design of a vehicle to be light but strong. Therefore, this study aims to analyze the strength and safety factor of the chassis using the Finite Element Method. The software used in this analysis is SolidWorks 2018. By doing this analysis, the safety factors in the chassis design will be known. In this design, the magnitude of the factor of safety must be more than two. 3D modeling and material data are required to run the simulation of strength and factor of safety analysis. The material that will be used in the design of this chassis is ASTM A36 steel. From this research, it is expected that the chassis can withstand a maximum load of 500 kg and a maximum driver of 100 kg. From this research, it is expected that the chassis can withstand a maximum load of 500 kg and a maximum driver of 100 kg. From the simulation results using the SolidWorks 2018 software, it can be seen that the safety factor results when accelerating are 3, braking are 3.4 and when turning are 4.2. So it can be concluded that the chassis design is certainly safe.

Eurocode-compliant system safety factor for advanced design of hollow section Warren trusses

Eurocode allows for the design of structural systems by advanced analysis, i.e. by Geometrically and Materially Nonlinear Imperfection Analysis (GMNIA). In GMNIA, the entire structural system is designed by carrying out a nonlinear finite element analysis and by comparing the load proportionality factor obtained from the analysis to the predetermined system safety factor. This study determines the required Eurocode-compliant GMNIA system safety factor for the ultimate limit state design of Warren-type roof trusses. The system safety factor is determined based on system-level reliability studies conducted for 15 trusses. The investigated trusses are made of cold-formed rectangular hollow sections having a nominal yield strength of 700 MPa. The determined system safety factor is then applied for comparison calculations, in which three trusses are designed both by GMNIA and the conventional EN 1993-1-1 method. This comparison reveals a need for an accurate modelling method of hollow section connections in GMNIA. Furthermore, the comparison shows that GMNIA can offer reduced material consumption compared to the conventional method even in roof trusses, in which load redistribution capabilities are very limited. This reduction is achieved due to capability of GMNIA to accurately capture the buckling capacities of continuous top chords, whereas the conventional method must rely on conservative approximations of buckling lengths.

Practical Tool for the Design and Cost Optimization of Permeable Pavements in the Planning Stage of Stormwater Management

To address issues created by increased stormwater runoff, there is growing interest in sustainable tools such as permeable pavement (PP), which is a green infrastructure (GI) practice. This paper outlines the development and application of a design tool called the “cost optimization tool for permeable pavements (COTPP).” This tool aims to help states, municipalities, and consultants design PPs using reliable hydrological and structural pavement design methods. The COTPP uses a cost optimization algorithm similar to a heuristic search that helps identify which combination of PPs, conventional pavement, and other GIs provides the most economic value. A sensitivity analysis was conducted using the tool, which consisted of designing the three main types of PP using varying design inputs and comparing the COTPP’s results to results from an existing design tool or guidelines. The average percent differences between the COTPP’s results and that of other methods were below 10% for the structural designs and around 15% for the hydrological designs. The differences were caused by the use of a safety factor in the hydrological design and other adjustments to design methods. It was concluded that the tool is reliable and can be confidently used by designers. The tool was then used for a representative case study site (PP parking lot) in which the actual design and cost estimates of on-site components were known. The COTPP was able to identify other design alternatives that helped reduce the actual construction cost of the existing parking lot from $305,918 to as low as $238,790.

A study on the probabilistic safety assessment of the truss structure designed by the LRFD code

The probabilistic analyses provide a more rational approach for the safety assessment of structures since they consider the uncertainties in the calculations. Consequently, the design specifications of engineering structures are gradually transformed from the allowable stress design to the reliability-based specifications such as load and resistance factors design (LRFD) or partial safety factor design. The partial safety factors and the load andresistance factors provided in the reliability-based design codes are successfully determined from probabilistic frameworks. However, these specifications are classified into semi-probabilistic-based codes because no probabilistic analysis is required in the design practice. Thus, the actual reliability index of the design solutions maynot be as close to the target value as expected. This study employs the fully probabilistic analysis as an additional analysis to examine the reliability index of an LRFD-based design of the truss structure. A planar truss,which is designed following the semi-probabilistic code, is thoroughly examined. Several feasible sections are first designed using the LRFD code. Then, the actual reliability indexes of truss structures are evaluated to check if they meet the target reliability index specified in the reliability-based design codes. The tension and compression members concerning the strength limit state and the maximum deflection presenting for service ability are investigated as representative performances. The results of the probabilistic analyses indicate thatthe reliability indexes for the strength limit state are higher than the target value stipulated in the LRFD code. Compared to the tension members, more redundancy in terms of reliability index is observed for compression elements, although they are both designed at the limit state. Moreover, the reliability index obtained for theserviceability limit state is strongly dependent on the component (i.e., floor or roof) where the truss is utilized.

Slope geometry optimization considering groundwater drawdown scenarios at an open-pit phosphate mine, southeastern Brazil

The design of open-pit mines should balance safety and economy. However, safe geotechnical conditions generally involve redesigning the geometry of slopes and groundwater drawdown, significantly increasing the costs of mining operations. The use of numerical models to simulate groundwater drawdown and slope stability can be an alternative to assess cost–benefit trade-offs for decision-making. This study documents a mining plan using groundwater drawdown scenarios that illustrate how geotechnical, economic, and environmental indicators can be combined to obtain optimum slope geometry for open-pit mining. The optimization approach analyzed different scenarios of groundwater drawdown for the final pit of a phosphate mine to improve the pit slopes stability. The groundwater simulation scenarios included the combination of deep horizontal drains and pumping wells. Stability analyses using the limit equilibrium method were used to obtain the bench, inter-ramp, and overall factors of safety of different representative sections. The factors of safety obtained, the drawdown costs and the water table elevation of each section were selected as indicators for obtaining the optimal drawdown scenario using a multi-objective tool. The groundwater control system obtained with 11 horizontal drains and 1 pumping well was considered the most adequate from the geotechnical and economic perspectives. Slope geometry optimization obtained with this drawdown scenario led to adequate inter-ramp and overall safety factors for the final pit design, reducing the barren-to-ore ratio to 0.38, much less than the present ratio (≈ 3). The results are important for optimizing the slope geometry of open-pit mines and can be replicated in other regions.

Designing of Aircraft Reinforced Carbon- Composite Torsion Boxes

At the initial design stage, there is a problem of determining the thicknesses of the load-bearing elements of an aircraft structure made of composite materials. The paper presents the intelligent design of the composite caisson structural strength. Intelligent design is based on the finite element method. The task of optimization used the objective function of minimum mass and setting some constraints including no types of buckling al-lowed. In optimization, the parameter is the thickness of the element, which changes in the process of minimizing the objective function for elements made of PCM by an amount equal to the thickness of the package. The results show the strength margins of spar webs and rib webs of the caisson of vertical empennage torsion box satisfy the safety factor design.

Experimental and numerical research on opening size effect of novel short fiber reinforced composite laminates

This study investigates the opening size effect of a novel short fiber reinforced quasi-isotropic composite laminate with unidirectionally arrayed chopped strands (UACS) under tensile load by approaches of simulations and experiments. The layup of [45/0/-45/90]s was used to fabricate novel carbon fiber laminates with various central hole diameter from 4 mm to 10 mm. Low notch sensitivity and strength reduction rate were observed in UACS open-hole laminates. It was found that when the width diameter ratio (d/w) of UACS laminate with open-hole is less than 20%, 80% of the original strength can be maintained, which can greatly reduce the design safety factor. Compared with continuous fiber laminates, high increase rate of strength reduction rate was induced by bi-angled slits with the increasing of open hole diameter. The strain distribution around the hole was affected significantly by bi-angled slits, which also inhibited the initiation and propagation of delamination effectively. The strain concentration factor of UACS laminates increases with the increasing open hole diameter. The damage progression of notched and unnotched UACS laminates were analyzed by simulation method, which are consistent well with experimental results.

Rancang Bangun Rangka dan Penggerak Mesin FDM Berbasis Arduino Tipe XZ-Head

FDM is an AM method that is currently being developed due to the flexibility of the object geometry that can be formed. This study aims to design the frame and drive of the XZ Head type FDM engine. Stress simulation was carried out to determine the safety factor in the frameXZ design. Lead screw parameters in the form of torque, shear stress, axial stress, and critical load were calculated to determine the torque requirement of the driving motor. The value of the linear axis of the stepper motor was calibrated to determine the dimensions of the printed output. Based on the simulation, the dynamic and static stresses on the XZ frame were 1.9 MPa and 2 MPa. The yield strength was 55 MPa with a safety factor of 28. The results of the calculation of the lead screw torque (TR) and (TL) were 18.27 N.mm and 6.60 N.mm. The calculated nominal shear stress of the screw () was 0.43 N/mm2, the axial loading stress () was -0.62 N/mm2, and the critical load (Wcr) was 9986.41 N. The difference in dimensions of the measurement results in the X and Z planes was 0.22 and 0.17 mm larger than the target dimensions of 20 mm.

Probabilistic Analyses of a Post-Grouted Anchor–Soil Bond Friction Performance Considering the Geological Origin and the SPT-N Tendency with Depth

This paper presents a probabilistic study of anchor–soil bond stress performance in a post-grouted anchor wall. The variability of geotechnical shear strength parameters will be described by a probability density function (PDF) and as a linear and squared shear strength function with depth based on widely available standard penetration test (SPT) data on two geologies (mudflows and residual soils). Monte Carlo simulation was carried out to evaluate the mean and standard deviation of ultimate anchor strength. The study allows the factor of safety (FS) to be determined to achieve a target probability of failure (pf). The first analyses consist of a probabilistic analysis without considering the shear strength varying with depth (SSVD), while the second one includes SSVD. Probabilistic analyses (without SSVD) show that a reduction of the pf depends only on the design FS. The probabilistic SSVD analyses showed that the N-value at the surface (N0), and the function gradient (ρ) had an important influence on the anchor pf. It is shown that the use of an overall FS can be considered as a high-risk design for soils with a high N0 variability and low ρ. Therefore, the target pf shows that the top anchors are the most critical, so higher FS values are required (FS > 2.5), especially for mudflow soils.

Study on the Development of Multi-Purpose Fire Engines through Vehicle Safety Factor Design

With the recent rapid economic growth, the construction of high-rise buildings such as new town apartment complexes, residential-commercial complexes, and office buildings has increased. This study thus attempted to develop a multi-purpose fire engine to enhance the response to a fire and rescue efforts in line with the steady increase in the demand for safety in high-rise buildings, through a design that combined techniques that focused on large ladders and a midsized 5-ton fire pump engine. A ladder function was added to the most widely used fire engine, with the design incorporating a maximum ladder height of 20 m for fire suppression and lifesaving. A basket was fitted to the end of the ladder to enable firefighters to safely perform these tasks, while the outrigger was designed to vertically descend to allow ladder work as long as vehicle entry is possible despite illegally parked cars. Based on the chassis of a commercial 5-ton fire engine as a type of conventional midsized pump engine, the result was a multi-purpose fire engine developed for special uses that require both fire pump and ladder functions. The multi-purpose fire engine was designed in consideration of safety factors for the direct rescue of people from buildings using a basket rated for a maximum load of 250 kg, through the application of a boom in addition to the common fire pump. It is expected that after their rapid arrival at the scene of a fire, such multi-purpose fire engines could be used for firefighting or lifesaving at relatively low 2-6-story buildings. It is anticipated that the present investigation and other relevant studies will allow the application of this novel design to various other vehicle types such as water tanks, chemical tanks, and rescue vehicles.

Feasibility study of flopper stoppers as a passive roll compensation system for offshore construction vessels

Heavy lift vessels are used to install offshore infrastructure. For floating vessels, roll responses can significantly limit their operability, especially for offshore sites where multimodal wave spectra are expected. This paper deals with a numerical study of a heavy lift vessel equipped with submerged flopper stopper (FS) templates suspended from the sides of the vessel. Dynamic analyses for various sizes and numbers of FS templates were conducted. A medium-size (28 m × 14 m) template can increase operational limits by shifting the roll’s natural frequency towards lower values and dampening the responses through drag forces. The operability can increase by about 500% when compared with a vessel without FS templates. A preliminary structural design of a critical beam shows an ultimate limit state design safety factor of 1.5 and fatigue damage of 0.32 for 20 years of service. The cost of construction per template is about $1.75 million (U.S. dollars); the total cost of 4 templates could be recovered in a single wind farm installation project. The system is shown to be feasible for construction vessels used in the execution of marine operations, especially heavy lifting.

Design-related reassessment of structures integrating Bayesian updating of model safety factors

In the semi-probabilistic approach of structural design, the partial safety factors are defined by considering some degree of uncertainties to actions and resistance, associated with the parameters’ stochastic nature. However, uncertainties for individual structures can be better examined by incorporating measurement data provided by sensors from an installed health monitoring scheme. In this context, the current study proposes an approach to revise the partial safety factor for existing structures on the action side, γE by integrating Bayesian model updating. A simple numerical example of a beam-like structure with artificially generated measurement data is used such that the influence of different sensor setups and data uncertainties on revising the safety factors can be investigated. It is revealed that the health monitoring system can reassess the current capacity reserve of the structure by updating the design safety factors, resulting in a better life cycle assessment of structures. The outcome is furthermore verified by analysing a real life small railway steel bridge ensuring the applicability of the proposed method to practical applications.