Structural Safety Analysis Research Articles

Inspection and structural assessment of traditional timber floors: a practical systematization

PurposeThis paper addresses the evaluation of traditional wooden floors, based on (1) visual strength grading (VSG) techniques adopted for ancient wooden structures; (2) a new approach to biological damage and (3) structural safety analysis. This assessment includes complex concepts. Therefore, the study presents a highly needed practical tool to help technicians make a preliminary assessment whereby many of the timber elements in our heritage can be saved from removal.Design/methodology/approachA simple and effective procedure was developed for each step. An inspection and diagnosis datasheet was drawn up, and the structural analysis presented by the Eurocodes was summarized. This methodology was then applied in a case study to demonstrate the complete procedure. During the assessment of this sort of structures, the drilling technique was a relevant method utilized as it provided essential and clear information about the beams' conservation.FindingsThe case study results indicate that 70% of the beams of the analysed structure exceed strict minimum performance criteria. This shows that other similar buildings can have their wooden elements saved from demolition, which is not the current regular refurbishment approach.Originality/valueThe current reality shows that the technicians' lack of capacity for a pragmatic assessment of the timber members’ structural capacity promotes their disinterest in them. To avoid that, this text presents a process for evaluating wooden floors using a simple and clear approach. This will prevent the demolition of wooden elements and instead encourage their preservation.

Analysis of Dynamic Response and Ultimate Strength for Box Girder under Bending Moment

The box girder can be seen as a kind of simplified ship structure that can withstand a vertical bending moment. Dynamic loads play an important role in structural safety analysis, such as ship bow slamming during harsh sea conditions. In this paper, the dynamic elastic–plastic response and ultimate strength of a box girder under a bending moment are analyzed. A box girder with the same cross-section scantlings and span length as the Nishihara experiment is selected as the analysis object. Based on the model experiment results, the non-linear FE analysis method is validated to capture the ultimate strength of a box girder under bending moment. Then, six box girders were designed to study the critical influence factors on the dynamic ultimate moment, including the model length, plate thickness, mass density and load excitation period. On the basis of structural dynamic response, an evaluation criterion of dynamic limit state for the box girder under a bending moment is proposed in this paper. Compared with the static ultimate moment, the change in the dynamic ultimate moment is discussed in detail to obtain the general principal method for dynamic strength analysis. The conclusions in this paper can provide guidance for dynamic ultimate strength evaluation.

An Application of Relative Entropy in Structural Safety Analysis of Elastoplastic Beam under Fire Conditions

The main aim of this work is to propose a new algorithm of reliability assessment for steel civil engineering structures subjected to fire temperatures. This new algorithm is based upon the relative probabilistic entropy concept elaborated by Bhattacharyya, and this probabilistic distance is sought in-between extreme and admissible deformations of some structural beam subjected to higher temperatures. Similar to the First Order Reliability Method, this approach uses the first two probabilistic characteristics of the structural response, when structural output may be modelled with the use of Gaussian distribution. The probabilistic structural response is found here using hybrid computational technique–the Finite Element Method system ABAQUS with its fully coupled thermo-elastic analysis with 3D solid elements and probabilistic modules implemented in the computer algebra system MAPLE. The probabilistic response is determined via a triple stochastic analysis, which is based on the classical Monte-Carlo simulation, iterative generalized stochastic perturbation technique, and also using semi-analytical probabilistic calculus. Final determination of the relative entropy in the Serviceability Limit State of the given structure and its comparison with the results obtained using the FORM analysis enables to calibrate this new technique to numerical values proposed in the engineering designing codes. Hence, a more accurate probabilistic method may use some experimental-based admissible values included in the existing design of legal provisions.

Numerical Study on Elastic Parameter Identification of Large-Span Steel Truss Structures Based on Strain Test Data

Large-span steel trusses are widely used in public buildings such as large-span factory buildings, exhibition halls, gymnasiums, and bridges because of their fast construction speed and easy industrial manufacturing. Due to construction errors and environmental factors, the material properties may change during their service life, and it is an important prerequisite for the structural safety assessment to identify the true material parameters of the structure. Among the many parameters, the elastic modulus is one that has the greatest impact on the accuracy of structural safety analysis. In this paper, a mathematical analysis model of elastic modulus identification was constructed, based on the strain test data and the improved gradient regularization method. The relationship between the strain test data and elastic moduli was established. A common finite element program based on the method was developed to identify the elastic modulus. A series of numerical simulations was carried out on a 53-element steel truss model to study the availability and numerical stability of the method. The effects of different initial values, numbers of strain tests, and locations of the strain test as well as the number of unknown parameters on the identification results were studied. The results showed that the proposed method had very high accuracy and computational efficiency. For the case of 53 unknown parameters without considering the test error, the identification accuracy could reach a 1 × 10−10 order of magnitude after only several iterations. This paper provides an effective solution to obtain the actual values of the elastic modulus of steel truss structures in practical engineering.

Novel Nonprobabilistic Bayesian Uncertainty Quantification Method for Structures with Interval Parameters

Structural reliability analysis is a crucial task in structural safety analysis. Owing to insufficient data information, traditional probabilistic methods do not accurately quantify input or output variables and the resultant assessment of structural reliability. Considering the development of engineering technology, a quantitative model of uncertainty based on improbability method is urgently needed. Herein, a novel nonprobabilistic Bayesian-inference-based interval uncertainty quantification model is developed with a user-specified credibility level. On the contrary, limited samples are introduced to update the bounds of the interval, and the conservativeness is decreased compared to the traditional unbiased interval estimation based on uniform distribution. Moreover, it can provide more conservative quantification than the extreme values-based interval model. Consequently, two examples are implemented to demonstrate the feasibility and effectiveness of the proposed model.

Use of polar coordinates for improving the measurement of resistant cross-sections of existing timber elements combining laser scanner and drilling resistance tests

Historic timber structures typically have elements with irregular cross-sections often with decayed segments, making of extreme importance to have proper methods to obtain the resistant cross-section. Knowing as accurately as possible the measurements of the resistant section of these beams is fundamental for the structural safety analysis. Small changes on the size and geometry of the resistant cross-section may be fundamental in an intervention decision process. In this work an algorithm was created that allows to obtain the geometry of the resistant section of existing timber beams by use of data obtained by laser scanning of the external apparent sections combined with drilling resistance tests. The algorithm is based on polar coordinates and proved to obtain more reliable resistant cross-sections than those obtained solely by common practice using drilling resistant tests. The developed algorithm was calibrated with a laboratory beam and subsequently applied and validated in a case study.

Seismic Safety Design and Analysis of Hydraulic Sluice Chamber Structure Based on Finite Element Method

One of the important links in the safety evaluation of sluices is the aseismic safety examination. In order to ensure the daily safe operation of sluices, it is necessary to conduct a normalized aseismic safety examination of sluices, and it is also necessary to study the aseismic safety examination of return sluices. Based on the application of ADINA finite element analysis software, a three-dimensional finite element model of the gate chamber structure is established, and the seismic response of the gate chamber structure is calculated and analyzed by the mode decomposition response spectrum method. The seismic safety of the gate chamber structure is evaluated comprehensively. The results show that 2.00 MPa of tension stress is generated at the junction of the pier and the gate. According to the structural mechanical method, the maximum tensile stress that can be endured is 4.41 MPa, which meets the safety requirements. There is a large tension stress zone between the elevator floor and some parts of the elevator, which far exceeds the standard tension strength value of the concrete moving shaft. Considering the safety, corresponding aseismic reinforcement measures should be taken. The structure of the gate chamber is nonslip and stable, and the safety factor is larger than the standard value of the Gate Design Specification (SL265-2016), which meets the safety requirements. The aseismic safety of the gate chamber structure meets the requirements of the “Standard for Seismic Design of Water Conservancy Buildings” (GB5127-2018), but it has safety defects and the aseismic grade is B.

Safety Analysis and Experimental Research on the Key Structure of FPSO Pressure Vessel Under the Complex Sea States

Abstract Pressure vessel is the key device of the floating production storage and offloading (FPSO) oil and gas processing module. The internal crude oil generates an impact load on the inner wall under the action of the ship rolling motion, resulting in a stress concentration or even cracking on the head, which seriously threatens the safety of offshore oil mining and FPSO workers. Take No. 118 FPSO pressure vessel as an example, the researches are carried out by considering the actual sea states in the South China Sea. The ship motion response equations are established; a dynamic evaluation study is carried out on the safety evaluation and analysis of the key structure of the pressure vessel based on fluent numerical simulation calculations, the results show that the key structure of the pressure vessel safety, and its stress value is positively correlated with sea state level and filling coefficient. The pressure vessel scale model experiment was carried out with an electric six degrees-of-freedom experimental platform, and the change rule of the measured point test was basically consistent with the simulation value, and the numerical error was only 11.804%, which verified the accuracy of the simulation model. The research results provide guidance for FPSO pressure vessel structure design and preventative maintenance, and the test method provides reference for FPSO pressure vessel simulation test and structure design.

A new method for structural safety and reliability analysis of offshore wind turbines

With the motivation to overcome the shortcomings of the Rosenblatt inverse-first-order reliability environmental contour method (IFORM), in this study, the use of bivariate kernel density estimation with smoothed cross-validation bandwidth selection method is proposed for generating more accurate environmental contour lines. The environmental contour lines at a chosen offshore site obtained by using the proposed new method were compared with those obtained by using the Rosenblatt IFORM, and the accuracy and effectiveness of the proposed new method have been fully and clearly substantiated. Next, the 50 year extreme structural dynamic responses of a monopile-supported 5 MW offshore wind turbine installed at this chosen offshore site based on the proposed new method and the Rosenblatt IFORM were calculated. Analysing the calculated results, it can be found that the 50 year extreme fore−aft shear force value based on the 50 year extreme sea state obtained using the proposed new method is 78.9% larger than the corresponding value obtained based on the Rosenblatt IFORM. The calculation results in this paper were further systematically analysed and compared, and the necessity and importance of using more realistic environmental contour lines (such as those generated using the proposed new method) have been finally highlighted.

Investigation on Pore Structure and Permeability of Concrete–Rock Interfacial Transition Zones Based on Fractal Theory

The concrete–rock interfacial transition zone (ITZ) is generally considered the weak layer in hydraulic engineering, for it is more permeable than the intact concrete or rocks. The water permeability of the ITZ is a critical parameter concerned with structural safety and durability. However, the permeability and pore structure of the ITZ has not been investigated previously, and the mathematical model of ITZ permeability has not been established. This study performed multi-scale experiments on the concrete–rock ITZ with various rock types (limestone, granite, and sandstone). A series of quantitative and qualitative analysis techniques, including NMR, SEM-EDS, and XRD, characterize the ITZ pore structures. The controlled constant flow method was used to determine the permeability of the concrete, rock, and ITZ. The mathematical model of ITZ permeability was proposed using the fractal theory. The consistency between the experimental data and the proposed model indicates the reliability of this study. The results of the experiment show that ITZ permeability is between 4.08 × 10−18 m2 and 5.74 × 10−18 m2. The results of the experiment and the proposed model could determine ITZ permeability in hydraulic structure safety and durability analysis.

Key Component Capture and Safety Intelligent Analysis of Beam String Structure Based on Digital Twins

In the construction process of beam string structures, the environmental effect and corresponding mechanical properties of the structure are complex. The problem of the misjudgment of structural safety performance caused by the uncertainty of a structural mechanical parameter analysis under various factors needs to be solved. In this study, a method for capturing key components and an intelligent safety analysis of beam string structures based on digital twins (DTs) was proposed. Combined with the characteristics of DTs mapping feedback, a component capture and security analysis framework was formed. Driven by twin framework, multi-source data for structural safety analysis were obtained and the parameter association mechanism established. Considering the space-time evolution and the interaction between the virtual and real elements of the construction process, a multidimensional model was established. Driven by the Dempster–Shafer (D–S) evidence theory, the fusion of structural mechanics parameters was carried out. The safety of the structure was analyzed intelligently by capturing key structural components, thereby providing a basis for the safety maintenance of the structure. The integration of DTs modeling and multi-source data improves the accuracy and intelligence of structural construction safety analysis. In the analysis process, capturing the key components of the structure is the core step. Taking the construction process of a string supported beam roof (symmetrical structure) in a convention and exhibition center as an example, the outlined research method was applied. Based on DTs and D–S evidence theory, the variation degree of mechanical parameters of various components under temperature was determined. By comprehensively investigating the changes of various mechanical parameters, the key components of the structure were captured. Thus, the intelligent analysis of structural safety was realized. The comparison of data verified that the intelligent method can effectively analyze the safety performance of the structure.

Structural performance degradation identification of offshore wind turbines based on variational mode decomposition with a Grey Wolf Optimizer algorithm

The performance degradation assessment of offshore wind turbine (OWT) structures plays a crucial role in ensuring the safe operation of the structures. This paper presents a method for assessing the performance degradation of OWT structures based on an optimized variational mode decomposition (VMD) algorithm. The method introduces the technique of multisensor data fusion and the Grey Wolf Optimizer (GWO) algorithm to optimize the setting of VMD parameters and then enables the assessment of the structural performance degradation of offshore wind turbines by extracting the structural performance degradation signature of the structure from noise-reduction data. To demonstrate the correctness and advantages of the method in this paper, a 4-degree-of-freedom (4-DOF) system under the action of white noise is used. Numerical calculations show that the developed method can accurately identify the 5%, 10%, 15% or 20% reduction in the structural stiffness and the coefficient of variance of the optimal structure is decreased to 3.6% of the initial design. To further investigate the performance of the proposed strategy, physical tests of the offshore wind monopile structure are conducted. As the loss of the overall structural performance is simulated by removing different numbers of bolts from the connected device, it is demonstrated that the proposed method can effectively assess the structural performance. Finally, field measurements are carried out on a monopile OWT located near Rudong County, Jiangsu Province, in the Yellow Sea of China. The impact of typhoons on the performance of the structure is effectively assessed by analyzing measurement data before and three days after the typhoon In-Fa through the wind farm, the potential application of the method in the structural safety assessment and analysis of OWTs is validated.

Ice load prediction of a podded propulsor under the dynamic azimuthing condition

In the process of cutting an ice layer by dynamic azimuthing of a podded propulsor, the unsteady and high pulsation characteristics of the ice load may compromise the safety and structural strength of podded propulsors. In this study, the failure criterion of simulated materials for the ice-breaking problem and the ice load calculation method were derived based on the peridynamics and the idea of panel division. The contact judgment method between the propeller and ice under the dynamic azimuthing condition of the podded propulsor was proposed. A numerical calculation model of the milling action of the ice–podded propulsor was established, and a numerical simulation of the ice–propeller milling process under the dynamic azimuthing conditions of the podded propulsor was realized. Moreover, numerical simulations under different ice layer moving velocities, propeller rotational speeds, podded propulsor azimuthing rates, and azimuth angles were carried out, and the ice layer breaking phenomenon and the variation characteristics of the propeller ice load under the dynamic azimuthing condition of the podded propulsor were obtained. The research results can guide technical support for the load evaluation, structural safety analysis, mechanism research of load components, and the selection of polar navigation steering strategies for ice-class podded propulsors.

On the hydrodynamic responses of a multi-column TLP floating offshore wind turbine model

The offshore floating wind turbine system is a key piece of equipment for harvesting wind energy from the ocean field. However, the structural safety analysis and design of such equipment largely require a suitable platform to accurately obtain the dynamic characteristics. In the present study, an attempt was made to investigate the dynamic responses of the proposed 5-MW WindStar multi-column tension-leg-platform (TLP) system under different ocean environment conditions. Typical motion responses of the WindStar system, including the surge and pitch, and a series of measurements obtained from wave basin tests, such as nacelle acceleration and tendon tension, were compared with those of simulated results from the FAST code under four hydrodynamic load conditions. Additionally, the second-order wave load was incorporated with the first-order wave load, so as to allow for accurate evaluation of the high-frequency response of the floating offshore wind turbine (FOWT). Further, the effect of high-order wave loads on the high-frequency responses of the TLP FOWT was elucidated. The second-order frequency wave load was found to be a significant factor in determining the motion responses of the WindStar TLP system, and the results from FAST were found to agree well with those of the experiment. The coupled method of experiments and numerical analysis can be effectively used to understand the high-frequency dynamic responses of TLP FOWT systems, such as the WindStar TLP.

Structural Safety Analysis of Cantilever External Shading Components of Buildings under Extreme Wind Environment

The high intensity of solar radiation and long sunshine time in the Turpan area lead to the necessity of sunshade construction. Sunshade components can effectively block direct solar radiation and the secondary heating of buildings. Through the analysis of the importance and sensitivity of sunshade components, it was found that the importance of sunshade components accounts for the largest proportion of multi-parameters, and the sensitivity of sunshade components accounts for about 60% of the total. At the same time, the change in sunshade length has an important influence on the proportion of air conditioning energy consumption and space comfort when the sunshade length reached the 0.6 m–0.8 m range. The energy consumption curve of air conditioning no longer decreased and tended to be horizontal, which showed that a sunshade could effectively reduce the energy consumption of air conditioning, while the PMV comfort curve gradually increased and tended to be horizontal, indicating that a sunshade could effectively improve indoor comfort; therefore, a sunshade could reduce direct solar radiation, reduce the energy consumption of air conditioning and improve indoor thermal comfort. In view of the extremely harsh climate characteristics of Turpan, although Turpan needs to carry out shading design, as a typical wind-sensitive component, the structural safety of the visor under the action of an extreme wind environment is the primary focus of designers. The design requires wind loads as control loads. Based on the ANSYS Workbench platform, this study used the fluid–structure coupling technology to calculate and solve for the wind load stress and strain of a horizontal sunshade and a vertical sunshade in a cantilevered external sunshade of different buildings orientations. In this study, by solving for the maximum principal stress and maximum principal elastic strain under 10 working conditions, the results showed that the maximum principal stress of the sun visor under all working conditions was 0.39 MPa, which is much smaller than the tensile strength of C25 concrete. The calculated maximum principal elastic strain of the sun visor was 0.12 × 10−4, which is much smaller than the maximum strain value of concrete. Therefore, the wind load under this research condition had no great influence on the structural safety of the concrete sunshade, which proves the structural feasibility of the building sunshade member in the Turpan area, and provides a reference for the future practical engineering of cantilever members in the Turpan area.

Intelligent Prediction of Prestressed Steel Structure Construction Safety Based on BP Neural Network

In the construction process of a prestressed steel structure, it is a point of research interest to obtain the safety state of the structure according to the design parameters and working conditions of the structure. The intelligent prediction of structural construction safety provides the basis for safety control. This study proposes an intelligent prediction method of structural construction safety based on a back propagation (BP) neural network. Firstly, the correlation mechanism of structural construction safety performance parameters is established, which involves structural design parameters and mechanical parameters. According to the basic principle of a BP neural network, the relationship between design parameters and mechanical parameters is captured. The virtual model of a structure construction process is established based on digital twins (DTs). The DTs and BP neural network are combined to form a structural safety intelligent prediction framework and theoretical method, setting working conditions in a twin model to obtain mechanical parameters. Mechanical parameters are intelligently predicted by design parameters in neural networks. The safety performance of structure construction is evaluated according to mechanical parameters. Finally, the intelligent prediction method is applied to the construction process of string beam. Based on DTs and BP neural network, the intelligent analysis of structural construction safety is carried out. This provides a reliable basis for safety control. The feasibility of this research method is verified by comparing the predicted results of the theoretical method with the measured data on site.

Structural Safety Analysis of Electric Kickboard According to Shape of Connection Parts Using Finite Element Analysis

Structural Safety Analysis of Electric Kickboard According to Shape of Connection Parts Using Finite Element Analysis

Analysis of Structural Safety and Durability in Civil Engineering Design

Analysis of Structural Safety and Durability in Civil Engineering Design

Quantitative Inversion of Water-Inrush Incidents in Mountain Tunnel beneath a Karst Pit

Quantitative inversion of accidents is an important work of finding the cause of accidents and avoiding their recurrence. However, quantitative inversion of accidents is difficult due to the lack and limitation of accidents monitoring information. Focusing on water-inrush incidents of Jiguan Mountain tunnel, this paper proposes a set of workflows to find out the missing conditions and quantitative inversion of accidents by flow analysis and structural safety analysis on the basis of investigating the rain capacity and water outflow in water-inrush incidents. First, hydraulic boundary in water-inrush incidents is acquired by analyzing the relationship of catchment, infiltration, and accumulation of rainwater in karst pit using the flooding algorithm of ArcGIS and the topographic mapping of UAV photogrammetry. Second, the permeability coefficients of karst infiltration zone and tunnel surrounding rock are acquired by two-step decoupling and inverse analyzing the water inflow, flow rate, and interval time between rainfall and water inrush. Third, tunnel accidents of the overload of tunnel lining induced by the catchment and infiltration of karst pit under extreme rainfall conditions are numerically simulated by using FLAC. The results indicate that quantitative inversion of water-inrush incidents reveals the process and cause of accidents and provides the safety index of tunnel structure. Not only is the water-inrush incidents of karst tunnel controlled by hydrogeology conditions, but also the rainfall recharge should not be ignored.

RC 슬래브 교량 바닥판의 철근노출 및 부식에 대한 상태평가와 안전성 분석

본 논문은 국내 교량의 23.5 %를 차지하고 공용연수 30년 이상 된 교량의 55.2 %를 차지하는 RC 슬래브 교량에 대해서 바닥판 하부 표면손상에 의한 철근노출과 철근부식에 따른 상태평가 등급과 구조적 안전성을 분석하였다. 대상 RC 슬래브 교량은 실제 교량을 대상으로 설계도면을 참고하여 수치해석 모델을 구성하였다. 철근노출면적률과 부식률은 한국시설안전공단 정밀안전진단 세부지침의 상태평가 등급 기준을 참고하여 교량 바닥판 하부 인장철근 위치에서의 콘크리트 피복 탈락을 가정하여 총 35가지의 철근 부식 시나리오를 적용하였다. 각 시나리오별 해석 결과를 바탕으로 교량의 안전율과 내하율을 산정하여 안전성평가 및 철근노출면적률과 철근부식률에 대한 영향을 분석하였다. 안전율과 내하율은 철근노출면적률의 변화에는 영향이 거의 없었고, 철근부식률 증가에는 선형감소를 보였다. 선형추세선 분석을 통해 철근부식률이 4 %까지는 A등급, 10.77 %까지는 C등급, 16.74 %까지는 D등급, 그 이상일 때는 E등급으로 평가되었다. 노후화된 교량이 지속적으로 증가되고 있는 상황에서 육안조사에 의한 상태평가 결과와 철근부식에 따른 안전성평가 결과와의 비교 분석이 더욱 필요할 것으로 판단된다.