Estimation Of Ultimate Strength Research Articles

Progressive collapse analysis and ultimate strength estimation of continuous stiffened panel under longitudinal extreme cyclic load and lateral pressure

Stiffened panel is a fundamental member of hull structures which is designed to withstand multiple loads such as revered cyclic load and lateral pressure. At present the ultimate strength of stiffened panel is conventionally determined by the monotonic compression criterion, ignoring the real progressive collapse of ship in rough sea conditions. To provide useful insights for improving the ship design, the present study focuses on dealing with the structural collapse characteristics and ultimate strength estimation of continuous stiffened panel under combined longitudinal extreme cyclic load and lateral pressure. A large number of nonlinear finite element analyses (FEA) are conducted to identify the influences of various factors on the failure mode and ultimate strength including the slenderness ratio of local panel, stiffener type, size and number, sequence and amplitude of the cyclic load, cycle number and lateral pressure. It is found that the ultimate limit state behaviours are governed by the coupling effects of several influential parameters. Based on artificial neural networks (ANN), a prediction model with high accuracy is proposed to evaluate the ultimate strength in different cycles.

Finite element model updating with quantified uncertainties using point cloud data

AbstractWhile finite element (FE) modeling is widely used for ultimate strength assessments of structural systems, incorporating complex distortions and imperfections into FE models remains a challenge. Conventional methods typically rely on assumptions about the periodicity of distortions through spectral or modal methods. However, these approaches are not viable under the many realistic scenarios where these assumptions are invalid. Research efforts have consistently demonstrated the ability of point cloud data, generated through laser scanning or photogrammetry-based methods, to accurately capture structural deformations at the millimeter scale. This enables the updating of numerical models to capture the exact structural configuration and initial imperfections without the need for unrealistic assumptions. This research article investigates the use of point cloud data for updating the initial distortions in a FE model of a stiffened ship deck panel, for the purposes of ultimate strength estimation. The presented approach has the additional benefit of being able to explicitly account for measurement uncertainty in the analysis. Calculations using the updated FE models are compared against ground truth test data as well as FE models updated using standard spectral methods. The results demonstrate strength estimation that is comparable to existing approaches, with the additional advantages of uncertainty quantification and applicability to a wider range of application scenarios.

Experimental and Numerical Small Punch Tests of the 14Cr ODS Ferritic Steel

Abstract Nowadays, various small specimen test techniques have gained wide popularity and appreciation among researchers as they offer undoubtful benefits in terms of structural material characterisation. This paper focuses on small punch tests (SPTs) performed on small-sized disc specimens to assess the mechanical properties of 14Cr oxide dispersion strengthened (ODS) steel. A numerical model was established to support experimental data and gain deeper insight into complex strain states developing in a deformed specimen. Modern evaluation procedures were discussed for obtaining mechanical properties from the small punch force-deflection response and were compared with the literature. Applicability and universality of those relations at different test conditions were also studied. It appeared that different ball diameters used had negligible influence on yield point but strongly affected ultimate strength estimation. It was found that friction belongs to decisive factors determining strain distribution in samples, as dry conditions increase the peak strain and move its location farther from the punch pole.

Study on ultimate strength estimation of intermittently welded stiffened plates under uniaxial compression

In this paper, a simplified method for estimating the ultimate strength of intermittently welded stiffened plates under uniaxial compression is developed. Its plate and stiffener of a stiffened plate are considered as individual beam-columns. The whole span of an intermittently welded stiffened plate is divided into welded and non-welded segments. For modeling the behavior of the intermittently welded stiffened plate, the differential equations which describe the bending of the beam-columns in welded and non-welded segments are considered. Based on the model, the Euler limit load of the intermittently welded stiffened plate is calculated. The intermittently welded stiffened plate is changed into a continuously welded one with the equivalent Euler limit load. The Paik's empirical formulation is used to estimate the ultimate strength of the changed continuously welded stiffened plate under uniaxial compression. The results are in good agreement with the FEA results by Khedmati et al.

Estimation of ultimate strength of ring-stiffened cylindrical shells under external pressure with local shell buckling or torsional buckling of stiffeners

This study discusses the ultimate strength and collapse behavior of ring-stiffened cylindrical shells under external pressure with local shell buckling or torsional buckling of stiffeners. In past studies, the effect of initial deflection shape on the ultimate strength has not been completely elucidated. Additionally, a clarification of the collapse behavior and theoretical formulation based on it has not yet been reached. Therefore, in this study, the influence of the initial deflection shape is investigated using eigenmodes obtained from the elastic buckling eigenvalue analysis and the hungry-horse mode described by a simple equation. Then, the ultimate strength analyses of 432 models of ring-stiffened cylindrical shells with various dimensions are carried out using the nonlinear finite element method. From the analysis, the collapse modes are classified into five categories, namely, the shell buckling (SB) collapse (localized mode SB-1 and uniform deformation mode SB-2), the torsional buckling (TB) collapse (localized mode TB-1 and uniform deformation mode TB-2), and the combined shell-torsional buckling collapse. A new slenderness ratio is proposed using the formula for strength when the circumferential stress reaches yield stress, and the formula for the elastic buckling strength developed previously by the authors. Then, theoretical formulas for the ultimate strength are developed using the slenderness ratio, which can rationally estimate the strength.

A Proposed Soft Computing Model for Ultimate Strength Estimation of FRP-Confined Concrete Cylinders

In this paper, the feed-forward backpropagation neural network (FFBPNN) is used to propose a new formulation for predicting the compressive strength of fiber-reinforced polymer (FRP)-confined concrete cylinders. A set of experimental data has been considered in the analysis. The data include information about the dimensions of the concrete cylinders (diameter, length) and the total thickness of FRP layers, unconfined ultimate concrete strength, ultimate confinement pressure, ultimate tensile strength of the FRP laminates and the ultimate concrete strength of the concrete cylinders. The confined ultimate concrete strength is considered as the output data, while other parameters are considered as the input data. These parameters are mostly used in existing FRP-confined concrete models. Soft computing techniques are used to estimate the compressive strength of FRP-confined concrete cylinders. Finally, a new formulation is proposed. The results of the proposed formula are compared to the existing methods. To verify the proposed method, results are compared with other methods. The results show that the described method can forecast the compressive strength of FRP-confined concrete cylinders with high precision in comparison with the existing formulas. Moreover, the mean percentage of error for the proposed method is very low (3.49%). Furthermore, the proposed formula can estimate the ultimate compressive capacity of FRP-confined concrete cylinders with a different type of FRP and arbitrary thickness in the initial design of practical projects.

Semi-analytical simulation of plastic collapse mechanism of cracked continuous unstiffened plates used in ship structure under in-plane longitudinal compression

The present study is undertaken based on a nonlinear finite element study carried out by the same authors for estimation of ultimate strength of cracked continuous unstiffened plates used in ship structures under in-plane longitudinal compression. Investigations show that in addition to the magnitude of ultimate strength, the deflection shape and plastic collapse mechanism will also change completely. Results show that deflection in the cracked half wave increases more rapidly than other half waves. Consequently generated half waves in a cracked plate will not have identical length and amplitude. This implies that the conventional plastic collapse mechanism cannot be used to predict the behavior of cracked plates in the post ultimate strength region. A new plastic collapse mechanism based on the FEM results is suggested and the principle of virtual work is used to derive the axial stress-deflection relation of the plate. However, due to inequality of the length and amplitude of generated half waves, the axial stress-deflection relation cannot be directly derived from the principle of virtual work. Therefore, in order to solve the virtual work equation, some auxiliary relations between the involved parameters are required. Auxiliary equations are derived using regression analysis based on FEM results. Finally, a semi-analytical formulation is derived to estimate post ultimate strength behavior of cracked plates. It is shown that the proposed semi-analytical formulation can predict both magnitude and slope of the stress-deflection curves with better accuracy compared to the conventional plastic collapse mechanism. The formulation can be used within the defined ranges of simulated crack lengths, slenderness and aspect ratios.

Set-based parametric modeling, buckling and ultimate strength estimation of stiffened ship structures

There have been a great demand for a suitable and convenient method in the field of buckling analysis of stiffened ship structures, which is essential to structural safety assessment and is significantly time-consuming. Modeling, buckling behaviors and ultimate strength prediction of stiffened panels were investigated. The modeling specification including nonlinear finite element model and imperfections generation, and post-buckling analysis procedure of stiffened plates were demonstrated. And a software tool using set-based finite element method was developed and executed in the MSC. Marc environment. Different types of stiffen panels of marine structures have been employed to investigate the buckling behavior and assess the validity in the estimation of ultimate strength. A comparison between results of the generally accepted methods, experiments and the software tool developed was demonstrated. It is shown that the software tool can predict the ultimate capacity of stiffened panels with imperfections with a good accuracy.

Empirical formulations for estimation of ultimate strength of cracked continuous unstiffened plates used in ship structure under in-plane longitudinal compression

Nonlinear finite element method is used to investigate the ultimate strength of cracked continuous unstiffened plates under in-plane longitudinal compression. Various crack length, slenderness and aspect ratios of the plate are selected to assess their influence on the ultimate strength magnitude. Based on the results, an empirical formulation is developed to estimate ultimate compressive strength of the plates. The formulation implicitly includes effects of initial deflection and welding residual stress. A series of finite element analysis are carried out in order to create a data bank based on which regression analysis is used to derive the formulation. Obviously increase in crack length, decreases ultimate strength. It is assumed that ultimate strength varies linearly with change in the crack length. However, results show that rate of change of ultimate strength varies for different slenderness ratios. As the plate becomes more slender, rate of change of ultimate strength gets lower. Based on the results it can be said that ultimate strength of an intact plate plays an important role in estimation of ultimate strength of the cracked one. Additionally except for the crack length and slenderness ratio, it is seen that the behavior of plates with aspect ratio equal to one is different from other aspect ratios. Therefore a set of empirical formulae are also derived for ultimate strength of intact plates based on plate slenderness and aspect ratios. Predictions are then compared to those of finite element analysis and a simple formulation previously suggested by Paik et al. A very good agreement exists between the results and the formulation can be used to predict ultimate strength of cracked plates for wide ranges of crack lengths, slenderness and aspect ratios.

A semi-analytical investigation on geometric nonlinear and progressive damage behavior of relatively thick laminated plates under lateral pressure and end-shortening

Because of applications of composites in aircraft structures such as skin panels in the wings subjected to lift forces, ultimate strength estimation of these structures is of great importance. In order to more realistically simulate these structures, relatively thick composite plates are analyzed under both end-shortening and lateral pressure loadings using a new simplified and reliable approach. Ultimate strength, progressive damage and geometric nonlinear analyses of such laminates under these loading conditions have not been done yet. Therefore, in the present study, first order shear deformation plate theory is considered with the assumptions of large deflections to perform the geometrically nonlinear and progressive failure analysis of moderately thick composite plates. In order to simulate the lift loads, two different types of lateral pressure distribution have been assumed to be applied on the plates; uniform and sinusoidal lateral pressure loads. The initial failure loads are calculated by means of elastic stress analyses. In this investigation, Hashin failure criteria have been selected for predicting failures. To modify the material properties, two geometric models have been considered to estimate the degradation zone around the failure location; degrading the material in regions of the plies or degrading the entire plies. The load is then increased step by step and for each given load, the stresses are reevaluated to inspect for possible failure. This procedure is repeated for each load increment until the final failure occurs and then ultimate strength is determined. To verify the proposed formulation, obtained results are compared with those calculated by finite element analyses. Plates having a range of thicknesses and with different intensities of pressure load have been analyzed extensively.

Strength of steel and aluminium alloy ship plating under combined shear and compression/tension

The load shortening curves are essential to the estimation of ultimate strength of ship structures under longitudinal bending in the simplified progressive collapse method. Longitudinal bending is the dominant load on ships structures, but in cases where the ship is heading to oblique seas and/or there are large openings in the structure due to its design (i.e. containerships) or due to damage (i.e. grounding, collision, blast), torsional loads may also be important when calculating ultimate strength and further investigation is required. Torsional loads on ship structures generate shear stresses which are carried primarily on the ship’s plating, therefore the effect of shear on the in-plane load shortening behaviour of ship plating is thoroughly investigated in this paper. Initially, marine grade steel and aluminium alloy plates with different aspect ratio (1–4) and slenderness (1–5) are subjected only to shear loads. These results show that the plate aspect ratio does not significantly affect the progressive collapse behaviour of plates under shear, hence only square plates are investigated further. Steel and aluminium alloy square plates (5083-H116 and 6082-T6) with slenderness ratio 1–4 are subjected to shear, in-plane compression/tension and combined shear and compression/tension applying the same complex set of boundary conditions for all cases and using ABAQUS CAE. Finally, the generated interaction diagrams of shear and compressive/tensile loads provide essential information for the effect of shear on the progressive collapse of in-plane loaded plates allowing for the incorporation of torsion in the simplified progressive collapse method.

고강도 오스테나이트계 스테인리스강(STS201) 일면전단 볼트접합부의 최대내력평가

고강도 오스테나이트계 스테인리스강(STS201) 일면전단 볼트접합부의 최대내력평가

Computational framework for mimicking prototype failure testing of transmission line towers

Traditional analysis of transmission line tower structures gives good estimate of ultimate strength but deflection estimates are much less than actual deflections measured from tests. This is caused by additional deflections due to joint properties like bolt slip in splices and splice plate deformations. These two displacement contributing factors are difficult to include in analysis. Prototype tower testing in test beds, which provides design strength evaluation and actual deflections is expensive. This paper presents a simple analytical procedure which captures not only the ultimate load and associated deflections but also the additional deflections because of bolt slip in leg splices. The formulation incorporates a corotational updated Lagrangian procedure in finite element analysis framework. The additional deflections are integrated into a nonlinear analysis formulation used for reticulated structures which also considers member buckling and yielding. To demonstrate the applicability of the formulation, towers which were experimentally tested in test beds are studied and the results are compared with strength and deflection measurements. The formulation has been demonstrated to be a reasonable alternative to expensive proto type testing.

Estimation of ultimate strength in single shear bolted connections with aluminum alloys (6061-T6)

An experimental investigation for the structural behavior of single shear bolted connection fabricated with aluminum alloys (6061-T6) has been carried out by Kim et al. It is found that ultimate strengths caused by curling (out-of-plane deformation in the direction of plate thickness) were reduced for some specimens with long end distances parallel to the direction of loading. In this paper, finite element analysis model has been developed on the basis of existing experimental results and analysis results were compared with the test results in order to verify the validity of finite element analysis method for predicting the ultimate behaviors of bolted connections. Additional analyses with extended variables such as end distance and edge distance were performed. Strength reduction ratio by curling and the condition of curling occurrence were investigated. Moreover, ultimate strength of analysis result was compared with design strength by American Aluminum Association (AAA) and American Iron Steel Institute (AISI) design standards. Modified strength equations were suggested considering effective shear stress in block shear fracture and curling effect by bolt bearing action.

Contact friction included in the problem on rock failure under compression

The authors have developed the analytical method for estimating ultimate compression strength and plotting normal stress–axial strain curves using experimentally obtained indexes of rock properties—ultimate shearing strength and coefficients of internal and external friction. The values of the listed properties are readily found in mine experiments. The method is advantageous for simple and efficient acquisition of source data for stress–strain plots and estimation of ultimate strength of rocks immediately in mines.

Experimental investigation on strength and curling influence of bolted connections in thin-walled carbon steel

Experimental studies regarding the influence of curling on the ultimate strength of cold-formed stainless steel bolted connections have been carried out by Kim et al. Basic data and modified equations for predicting the structural behaviors considering strength reduction due to curling through the finite element analysis method have also been suggested by previous researchers.In this paper, single shear bolted connections fabricated with four bolts and thin-walled carbon steel commonly utilized in light-weight structural members were tested to investigate the fracture mechanism and curling influence on the ultimate strength. Main variables for test specimen are plate thicknesses and end distances parallel to the direction of loading. Curling (out-of-plane deformation in the direction of plate thickness) also occurred in thin-walled carbon steel bolted connections with a large end distance and thinner plate like previous cold-formed stainless steel connections. The curling occurrence reduced suddenly the ultimate strength of single shear carbon steel bolted connections and the influence pattern of curling on strength was affected according to the plate thickness and end distance. Current design specifications for block shear strength with the combination of tensile fracture and shear fracture are summarized and the ultimate strengths of test results are compared to the predicted design strengths. AISI (American Iron and Steel Institute) and EC3 (Eurocode 3) made conservative estimates of ultimate strength for thin-walled carbon steel bolted connections with no curling, whereas AIJ (Architectural Institute of Japan) and SSBA(Stainless Steel Building Association) manuals provided a good prediction for ultimate strength and fracture mode. Modified strength equations were recommended respectively for bolted connections with typical block shear fracture considering shear stress factor and severe curling accompanied by strength reduction.

Empirical formulations for estimation of ultimate strength of continuous aluminium stiffened plates under combined transverse compression and lateral pressure

Empirical expressions are developed for predicting ultimate compressive strength of welded aluminium stiffened plates used in marine applications under combined transverse in-plane compression and different levels of lateral pressure. A database of the ultimate transverse strengths for aluminium stiffened plates numerically obtained by the authors is used for deriving formulations as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. Regression analysis is used in order to derive the empirical formulations. The formulae implicitly include the effects of the weld on the initial imperfections and the heat-affected zone.

Analyses of Steel Bridge Circular Columns using Fiber Model considering Local Buckling

One of the most concerned problems for analytical estimation of ultimate strength and ductility of steel bridge columns is the consideration of local buckling. Stress-strain curves with softening behavior to include local buckling in fiber model analysis method were proposed by several researchers. However, accuracy of those models is still relatively low. As a consequence, most steel bridge designs have been done using fiber model analysis method without consideration of local buckling. In order to improve the analytical response estimation of steel bridge columns, a fiber model analysis method considering local buckling is proposed in this study. In this method, multi-fiber elements were used to model the local buckling length to simulate local buckling deformation. The proposed method shows good results not only for estimating peak strength but also post-peak strength compared to previous experimental results. However, further research should be directed to improve the accuracy of the deformation modes.

Ultimate Strength Estimation of Ferritic Stainless Steel Single Shear Bolted Connections Fastened with Four Bolts

본 연구는 페라이트계 스테인리스강 일면전단 볼트접합부의 구조거동에 관한 기존실험연구를 바탕으로 유한요소해석법을 이용하여 접합부의 최대내력과 면외변형에 대해 조사하는 것을 목적으로 한다. 유한요소해석결과와 실험결과의 비교를 통해 접합부의 구조거동을 예측하는데 있어 해석의 타당성을 검증하였다. 면외변형에 의해 유발되는 접합부의 연단거리 조건을 조사하고 최대내력저하정도를 정량적으로 평가하였다. 또한, 변수해석을 통해 얻어진 해석결과의 최대내력과 현행기준식인 AISC, KBC2009, AIJ 및 AISI에 의해 예측된 내력과 비교하여 그 적용성을 검토하였다. The purpose of this study is to investigate the ultimate strength and curling influence using finite element analysis based on the previous test results of ferritic stainless steel bolted connections. Results obtained from finite element analysis (FEA) were compared with those of test results and the validity of numerical modeling was verified. The conditions of curing occurrence for edge/end distance were investigated and ultimate strength reduction ratio caused by curling was estimated quantitatively. Moreover, the ultimate behaviors such as fracture mode and ultimate strength by FEA were compared with those predicted by current design specifications such as AISC, KBC2009, AIJ and AISI.

Detail investigation on un-stiffened T/Y tubular joints behavior under axial compressive loads

This paper presents the failure pattern, ultimate static strength and detailed behavior of un-stiffened T and Y tubular joints under axial brace compressive loading using finite element method performed by ABAQUS software package. Properties of the un-stiffened tubular joints were extracted from the available experimental-based tubular joint database. Utilizing the Modified Riks Method in numerical analyses led to an accurate simulation of joint behavior and also helped to investigate its correct failure pattern. The modes of failure observed throughout the numerical analysis were local bending of the chord member, ovalization and plastic failure of the chord. The results obtained from the numerical modeling revealed the critical areas on the joint surface with respect to ovalization, deflections and stresses. Also, the ultimate strength predicted by the numerical analysis was compared and validated with available experiment results. Despite the fact that much research has been conducted on tubular joints which have mostly focused on the estimation of ultimate strength or stress concentration factors rather than detail study of joint behavior, the present detail investigation has provided a thorough understanding of joint behavior under axial compressive loads. Such an in-depth and detail tubular joint investigation has been rarely reported in the open literature.