Design Safety Factors Research Articles

Analyses of embedded piles reinforced landslides using strength reduction finite element method

Embedded stabilising piles for landslide reinforcement were proposed as a viable alternative to conventional full-length piles. Embedded piles are shorter than full-length piles, while still providing a sufficient factor of safety (FS) to landslides; however, the cost of embedded piles may be significantly less than full-length piles due to the smaller bending moment demand. The concept of effective length was introduced. A strength reduction finite-element model was developed for the analyses of embedded anti-slide pile-reinforced landslides. A method for searching for the optimum effective length and estimating lateral loads on piles was developed. A conceptual landslide reinforced with a single embedded pile was adopted to exercise the proposed method. Results showed that the FS increased with the pile length at the plastic limit failure state, the maximum bending moment of the pile increased significantly with the pile length. However, for a given design safety factor (target FS), the lateral load acting on the embedded pile was similar to that of the full-length pile. Finally, the proposed method was applied to stabilise a massive landslide using 18 embedded piles; field monitoring data implied that the performance of the reinforced landslide is acceptable.

Consideration on Effect of Excessive Load on Structural Safety and Introduction of Partial Safety Factors in Structure Design of Concrete Gravity Dams

Consideration on Effect of Excessive Load on Structural Safety and Introduction of Partial Safety Factors in Structure Design of Concrete Gravity Dams

Large Structures Monitoring Using Unmanned Aerial Vehicles

Structural health monitoring offers significant benefits in reducing whole of life costs of infrastructure ownership, and improves the reliability and availability of high value assets. There are significant works towards applying structural health monitoring (SHM) to aircraft, maritime and civil structures. Numerous techniques have been developed to facilitate the monitoring of the structural components and the different classes of defects expected. One of the distinct advantages of SHM is the ability to monitor hard-to-inspect areas of an operating structural component. There is another attractive feature of SHM; incorporating SHM into new design offers a perspective into concept of “safety in design”. The integrated sensing system can be used initially to verify the design safety factors used when the structure is first commissioned and subsequently for integrity assessment purposes. In both purposes, the challenge remains with sensor placement, and the durability and reliability of the sensing elements located on the structure. Recent advances in non-contact measurement techniques have overcome some of these limitations. In most of these works, the inspection region is limited due to the constraints associated with the hardware requirement. This paper will discuss the use of displacement measurements using remotely piloted aerial vehicles (RPV) for the condition assessment of a large membrane floating cover that is approximately 170 m x 420 m. It is envisaged that the health monitoring of the membrane can be assisted by the periodic monitoring and assessment of the deformation of the large membrane cover. The collation of the profile of the membrane over time will provide important information for the structural integrity assessment of the floating cover.

설계법에 따른 풍화토 지반 얕은기초의 안전여유 비교

본 논문에서는 기존의 허용응력설계법(ASD)과 신뢰성해석에 기반을 둔 하중저항계수설계법(LRFD)과 유로코드의 부분안전계수설계법(PSFD)을 사용하여 풍화토지반 얕은기초의 전단파괴에 대한 지지력과 안전여유 산정결과에 대하여 비교 분석하였다. 얕은기초의 지지력에 영향을 주는 지반정수의 불확실성을 정량화하기 위하여 시공 및 설계용 평판재하시험 자료를 수집하고 확률 통계 분석을 통하여 극한지지력의 저항편향계수와 변동계수를 조사하였다. 국내 현장의 얕은기초 대표 단면 예에 대한 신뢰성해석(FORM)을 통하여 신뢰도지수를 구하고 지반정수의 확률변수가 전단파괴에 미치는 영향을 조사하기 위하여 확률변수의 민감도 분석을 하였다. ASD설계법, ASD설계법의 안전율에 대응하는 목표신뢰도 지수의 LRFD설계법, PSFD설계법을 사용하여 얕은기초 대표단면의 안정성 검토를 실시하여 산정된 각 설계법의 안전여유에 대하여 비교 검토를 실시하였다. In this paper bearing capacity and safety margin of shallow foundation on weathered soil ground against shear failure by using current design method of allowable stress design (ASD), load resistance factor design (LRFD) based on reliability analysis and partial safety factor design (PSFD) in Eurocode were estimated and compared to each other. Results of the plate loading test used in construction and design were collected and analysis of probability statistics on soil parameters affecting the bearing capacity of shallow foundation was performed to quantify the uncertainty of them and to investigate the resistance bias factor and covalence of ultimate bearing capacity. For the typical sections of shallow foundation in domestic field as examples, reliability index was obtained by reliability analysis (FORM) and the sensitivity analysis on soil parameters of probability variables was performed to investigate the effect of probability variable on shear failure. From stability analysis for these sections by ASD, LRFD with the target reiability index corresponding to the safety factor used in ASD and PSDF, safety margins were estimated respectively and compared.

Performance‐based durability design, carbonation, part 3: PSF approach and a proposal for the revision of deemed‐to‐satisfy rules

AbstractA performance‐based safety factor durability design format is proposed and developed with respect to carbonation of concrete. Deemed‐to‐satisfy rules based on a partial safety factor design approach are developed for the carbonation of concrete. This design format follows the design procedure proposed in EN 1990 [1]. For the design format, the limit state equation for the carbonation is introduced in its probabilistic and safety factor format. The PSF approach has been used to derive design charts. Values for minimum concrete cover depending on material resistance and exposure class are proposed for critical environmental conditions and a design service life of 50 years.

DEVELOPMENT OF STRUCTURES OF "LIGHT" PISTON FOR DIESEL ENGINES TYPE D100

The paper considers the option of replacing the composite piston serial type locomotive diesel 10D100 20 kg new - a mass of 13 kg. The results of optimization of the shape of the steel inside the top of the piston. It is shown that the calculated maximum temperature on the combustion chamber surface of the proposed design is somewhat lower than in batch, and safety factors in design strained areas not lower than serial. It is shown that the technical problems associated with the introduction of the proposed piston and its solutions.

A simplified approach for stability analysis of slopes reinforced with one row of embedded stabilizing piles

Embedded stabilizing piles are new anti-slide structures that are unlike traditional stabilizing piles. The pile heads are embedded at a certain depth below the surface of a slope. The piles do not need to support the thrust of the entire upslope sliding mass, and it is, therefore, possible to reduce the sliding thrust on the piles. The embedded depth of the pile heads is an important parameter to maximize the anti-sliding function. Based on an analysis of the stability mechanism of a reinforced landslide with one row of embedded stabilizing piles, a calculation method for the embedded depth of a pile head using limit equilibrium theory is proposed. The related calculation formula is derived in detail using the transfer coefficient method. The proposed method features a close correlation between the embedded depth of a pile head and the design factor of safety of a slope to be reinforced. Additionally, the method can quantitatively demonstrate the relationship that the factor of safety of the slope for the failure mode of the surpassing pile head decreases as the embedded depth of the pile head increases. For a given factor of safety, the range of the maximum bending moment, the maximum shear force on a pile and the lateral displacement at the pile head also can be approximately predicted. Several calculation examples that are closely related to practical engineering applications are examined to show the convenience and rationality of the proposed method. In addition, the theoretical analysis is compared with the results of the numerical simulation of an actual accumulation landslide control engineering project. The results further demonstrate that the proposed theoretical analysis method is reasonable and applicable.

Pseudo-dynamic analysis of seawall considering non-breaking wave force

This paper presents the stability determination of seawall, supporting submerged cohesion-less backfill under combined actions of earthquake and non-breaking wave forces. The pseudo-dynamic approach is adopted for the calculation of seawall stability using limit equilibrium method against sliding, overturning and bearing failure. Parametric study shows significant effects of B/H ratio, pore water pressure ratio, horizontal seismic acceleration coefficient, ratio of height of water on seaward side to the wall height, ratio of non-breaking wave height to height of water on seaward side, wall friction angle, ratio of height of water on landward side to the wall height on stability of seawall at both restrained and free water cases, against all failure modes. Present result is compared with results available in literature. The results are presented in non-dimensional forms and design charts are provided to calculate factor of safety for design of stability of seawall against different failures under earthquake forces combined with non-breaking wave forces.

Prediction of load transfer depth for cost-effective design of ground anchors using FBG sensors embedded tendon and numerical analysis

The load transfer depth of a ground anchor is the minimum length required to transfer the initial prestressing to the grout column through the bonded part. A thorough understanding of the mechanism of load transfer as well as accurate prediction of the load transfer depth are essential for designing an anchorage that has an adequate factor of safety and satisfies implicit economic criteria. In the current research, experimental and numerical studies were conducted to investigate the load transfer mechanism of ground anchors based on a series of laboratory and field load tests. Optical FBG sensors embedded in the central king cable of a seven-wire strand were successfully employed to monitor the changes in tensile force and its distribution along the tendons. Moreover, results from laboratory and in-situ pullout tests were compared with those from equivalent case studies simulated using the finite difference method in the FLAC 3D program. All the results obtained from the two proposed methods were remarkably consistent with respect to the load increments. They were similar not only in trend but also in magnitude and showed more consistency at higher pullout loading stages, especially the final loading stage. Furthermore, the estimated load transfer depth demonstrated a pronounced dependency on the surrounding ground condition, being shorter in hard ground conditions and longer in weaker ones. Finally, considering the safety factor and cost-effective design, the required bonded length of a ground anchor was formulated in terms of the load transfer depth.

Strategy for developing energy systems for remote communities: Insights to best practices and sustainability

Energy planners and policymakers have identified off-grid energy systems as an option for electrifying remote communities around the globe. Such systems could be fueled by either non-renewable or renewable energy resources, but because of the issue of climate change and the compelling need for environmental sustainability, the global community is strongly advocating the use of eco-friendly energy technologies. Renewable energy technologies are therefore deployed for clean energy production, especially in places where there are vast renewable energy resources. However, while there is high optimism about such technologies, there is a lack of knowledge and understanding of the strategies necessary to successfully develop them for off-grid communities. This invariably leads to poor, unreliable and unsustainable systems. This paper introduces enabling strategies for developing energy systems in remote communities, with the aim of achieving sustainability. The planning approaches attempt to integrate the necessary processes and stakeholders during the pre-design, detailed design, implementation and post-implementation stages, with reference to global engineering standards. We present a user-centered approach and also introduce design safety and load growth factors into the energy supply system sizing model for achieving reliable systems. Two different remote communities in Nigeria are used to test the proposed design approaches. The results demonstrate how the issue of a lack of knowledge could be addressed, thus, providing useful approaches for achieving widespread deployment of distributed energy generation projects for isolated communities around the world.

Comparative Studies on Calculation Methods of Shear Behavior of ReinforcedConcrete Beams of Chinese Modern Reinforced Concrete Buildings

In order to study the calculation methods of shear behavior of reinforced concrete beams of Chinese modern reinforced concrete buildings, this paper carried out tests on the concrete compressive strength of 12 Chinese modern concrete buildings, the mechanical properties of 66 rebars from different Chinese modern concrete buildings, and the concrete cover thickness of 9 Chinese modern concrete buildings, and the actual material properties and structural configurations have been obtained. Then, the comparison on calculation methods include the Chinese original calculation method, the Chinese present calculation method, the American present calculation method and the European present calculation method is studied with case analysis method. The results show that the Chinese original calculation method of shear behavior of reinforced concrete beams is based on the allowable stress calculation method, and the design safety factors are 3.55-4.00. The standard value of the compressive strength of concrete cubes is 8.48 MPa, the standard value of the concrete tensile strength is 1.20 MPa, the standard value of the yield strength of rectangular rebars is 229.56 MPa, and the standard value of the yield strength of round rebars is 276.82 MPa. The average value of the concrete cover thickness of beams and columns is 35.96 mm. In term of calculation area of hoop rebars of reinforced concrete beams, without considering earthquake loads, the Chinese original structural calculation method is safer than the Chinese present structural calculation method, but is more unsafe than the American present structural calculation method and the European present structural calculation method. The results can provide the support for structural safety assessments and repair designs of Chinese modern reinforced concrete buildings.

Stability Analysis and Charts for Borrowed Soil in Ecological Slope Engineering

The mechanical stability of man-made mixed slurry sprayed on a sloped surface, i.e., borrowed soil, in ecological slope engineering is examined in this study. Through indoor simulation tests, the failure mode of the soil without seepage and with surface seepage is found to be a translational sliding surface parallel to the original sloped surface. An infinite slope case is assumed on the basis of the obtained failure mode, and stability analysis of the soil is performed. A general equation is then formulated for the instability thickness of the borrowed soil under the actions of earthquake loading and seepage. The stability charts for the borrowed soil are produced after the parameters of the equation are defined. The charts are basically the same in form as Taylor’s stability charts. The charts are proved valid by indoor simulation tests. With the charts, the instability thickness of the borrowed soil can be designed with a given design safety factor, and the safety factor of the borrowed soil in ecological slope engineering can be deduced.

Kinematical Limit Analysis for a Slope Reinforced with One Row of Stabilizing Piles

Stabilizing piles are commonly used to improve slope stability. The load that a pile should sustain and the associated slip surface under a prescribed factor of safety are two critical design parameters in practice. Based on the kinematically admissible failure mechanism, a limit analysis approach is introduced, which considers two potential slip surfaces that individually lie in the upslope and downslope of the piles. The explicit formulas for the upslope thrust force and downslope resistance on a pile are derived, which enables the calculation of the maximum load on a pile and the corresponding critical slip surfaces using a computer program. The maximum load and critical slip surfaces under a design factor of safety are mainly affected by soil properties and five other parameters: location of the pile row, dip angle of the slope face, action point and dip angle of the force, and improvement coefficient of the slope stability. The relevant quantitative calculation can be performed using the proposed method. Moreover, the possible failure with the upslope soil surpassing the pile top under a specified design factor of safety is significantly illustrated in the paper, which is helpful in the rational determination of the location of the pile row.

Mathematical Consideration on Safety Factors in Structure Design of Concrete Gravity Dams

Mathematical Consideration on Safety Factors in Structure Design of Concrete Gravity Dams

The effect of some uncertainties associated to the environmental contour lines definition on the extreme response of an FPSO under hurricane conditions

The environmental contour concept, in conjunction with the Inverse First Order Reliability Method, is often used to determine the extreme response of marine structural systems. This technique is a powerful option to determine the extreme response associated to a probability of exceedance without the need to perform a long-term analysis, where a large number of short-term simulations are needed. However, there are significant uncertainties involved in its determination, such as the uncertainties related with the probabilistic model used for the environmental variables, as well as the ones related with the threshold selection when the peaks over threshold (POT) method is applied. This paper shows the results of a comparative analysis of the extreme tension of the most loaded mooring line of an FPSO subjected to environmental conditions in deep water, derived from environmental contour lines which were defined with different probabilistic models to represent the significant wave height and different criteria to establish the threshold for the POT methodology. The results showed that the probabilistic model has an important effect on the extreme response of the FPSO and this epistemic uncertainty should be accounted for in the calibration of the design safety factors.

Rate dependent plastic deformation analysis of creeping short fiber composites using the virtual fiber method in the non-reinforced regions

In this research paper, analysis of time-dependent plastic deformation in non-reinforced regions of creeping short fiber composites is carried out under axial tensile stress using the virtual fiber method. As an important application of the present method, shuttles and spaceships, turbine blades and discs are usually subjected to the creep effects. So, analysis of the creep phenomenon is necessary and important in various industries. The nature of the stress distributions is investigated using the equilibrium and constitutive equations, compatibility relations, and incompressibility condition with various boundary conditions, and geometric relations. Analytical and finite element methods are used to predict the stress distributions in the steady state creep of the short fiber composites. Also, the creep analysis (nodal solution) is done by FEM to predict the possible creep rupture, in which, debonding at the interface of the matrix and fiber may happen due to the maximum tensile axial stress values at the interface. In addition to similarities of the present method and experimental results [34], a good agreement of the stress distributions between the present analytical solutions and the FEM results is found. As a result, the short fiber composites with large non-reinforced regions in the axial direction are proper because it increases the factor of safety for design.

Numerical study of the structural behaviour of impacted composite laminates subjected to compression load

Composite materials allow all the benefits which a high specific strength involves, in a design process their application involves many critical problems. Currently, these problems, such as environmental conditions, notch sensitivity, damaging under low velocity impacts, are taken into account by means of the application of conservative design safety factors regarding the ultimate tensile strength. In order to try to reduce these safety factors, this work aimed to study and to understand the impact damage growing mechanisms due to compression loads. To this purpose, compression tests have been experimentally performed on composite panels, which have been previously subjected to low velocity impact phenomena, considering impact energies of 6 J, 10 J and 13 J respectively. Moreover, numerical model able to simulate Low Velocity Impacts (LVI) and Compression After Impacts (CAI) onto CFRP panels is proposed. A single explicit finite element analysis has been carried out by using the Abaqus® finite element code; the need to build a numerical model, which allows simulation in only one analysis both LVI and CAI steps, depends on the difficulty to import the impact damage distribution into a separate compression analysis. In fact, in only one analysis the compression step can occur directly onto the impacted plate, which allows to consider the effective impact damage distribution as the starting configuration for quasi static analysis under operating loads.

Calibration of partial safety factors for offshore foundation design

The foundation of an offshore installation is designed to resist the static and dynamic loads it is subjected to during its lifetime. The design codes specify combinations of load factor on the static load, load factor on the dynamic load, and resistance factor on the soil resistance, with reference to the 'characteristic' loads acting on the foundation and the 'characteristic' foundation capacity. In principle, the designer aims at achieving a target annual failure probability. Whether or not the load and resistance factors specified in the design codes actually achieve a target annual probability of failure depends on the type of installation, the load characteristics, the soil characteristics, the analysis method(s) and the relative importance of static and dynamic loads. The paper calculates the load and resistance factors required for a target annual failure probability of 1 × 10−4. The calculated load and resistance factors are then compared with the values required by three offshore design guidelines and codes: API LRFD (2003), ISO 19902 (2007) and NORSOK (2004).

Pearl River Huangpu Southern Channel Bridge, China

The Pearl River Huangpu Southern Channel Bridge is a steel box girder suspension bridge with a main span of 1108 m. This paper presents the final design, global static and dynamic analysis, and construction of the southern channel bridge, including the anchorage foundation and block, pylon foundation and shaft, main cable, cable band, main cable saddle, splay saddle and steel box girder. The design loads and safety factors of the main cable in Chinese codes are compared with those in Eurocodes.

The Structural Analysis of a Mini Hydroelectric System

In recent decades, renewable energy has been one of the major theme for researchers around the globe. In this research, one of the main objective is to verify on the structural reliability of the Mini Hydroelectric device. At first, the Engineering Design Process has been utilised in order to run the overall project efficiently, beginning from the conceptual stage until data analysis. As a result, the preliminary design has been accomplished within one year duration; with the support of 3D CAD design tool (Catia). Based from the simulation result, majority of the stress concentrates around the area between shaft and insert hole portion. The product (especially the inner parts) also able to withstand until 2 bar of water pressure, achieving minimum design safety factor of 1.3. Overall, the simulation result is always severe compared to theoretical calculation. This highlights the importance of using FEA simulation software such as ANSYS Workbench in validating the structural analysis result. In near future, by focusing on improving the performance of critical parts and areas; more opportunities especially in terms of design optimization is positively viewed.