Load Of Tubes Research Articles

Behavior of CFRP-strengthened short spiral welded tubes under axial load

Spiral welded tubes (SWTs) are formed by rolling steel plates at a certain angle and welding the resulting abutting edges. They are extensively utilized because of their large diameter ranges, high production efficiency, and low production cost. Thin-walled spiral welded tubes with large diameter-to-thickness ratios are susceptible to local buckling under compressive load, and their performance can be affected by corrosive environments. Therefore, this paper proposed the use of carbon fiber-reinforced polymer (CFRP) to strengthen tubes by external bonding. There are limited studies on the axial compression behavior of CFRP strengthened spiral welded tubes, particularly studies that consider the initial imperfections and residual stresses in spiral welded tubes. To bridge this gap, this paper first investigated the distributions of initial imperfections and residual stresses in spiral welded tubes, finding that both are significantly influenced by distinct forming and welding manufacturing processes. Subsequently, axial compression tests were carried out on four unstrengthened specimens and twelve CFRP-reinforced specimens to investigate the compressive behavior by considering the diameter-to-thickness ratio, the length of the steel tubes, and CFRP layer orientation. The experimental results indicate that CFRP strengthening delays local buckling, and significantly enhances the yield load, ultimate load, and initial stiffness of spiral welded tubes, achieving a maximum increase of the yield load up to 69.11 % and the ultimate load up to 61.99 %, while its impact on the ductility index remains uncertain and is influenced by variables such as the diameter-to-thickness ratio of the tubes and the CFRP layer orientation. Finally, a comparison of the ultimate loads of the specimens by tests and design codes was conducted.

Coupled AC2-CFD simulations for a high-pressure core melt accident scenario

Abstract Even though very unlikely to occur, severe accident scenarios in nuclear power plants have to be analyzed. During high-pressure core meltdown scenarios in a pressurized water reactor the primary circuit should fail first. Previous analyses found that a free convection flow within the vertical steam generator (SG) tubes with a simultaneous stratified gas counterflow in the hot legs could arise. This phenomenon leads to higher thermal loads on individual SG tubes which might then fail leading to a containment bypass and the release of radioactive material into the environment. Lumped parameter system codes used for safety analyses do not provide the models necessary to simulate phenomena like mixing in three-dimensional flows and could not consider local turbulence effects. Computational fluid dynamic (CFD) codes provide such capabilities but are much more computationally expensive. Coupling of a system code with a CFD code can therefore be used to simulate such phenomena. The advantages of both approaches can be maximized by splitting up the simulation domain between the codes, depending on the expected flow conditions. The system code AC2 coupled with the CFD code OpenFOAM was used to simulate part of the severe accident transient. Free convection in the hot leg and the U-tubes of the vertical SG was observed in case of high-pressure severe accident sequences. The thermal load of individual SG tubes has been estimated from the results. These loads can be used as inputs for structural-mechanical analyses to estimate which part of the primary circuit would fail first.

Experimental investigation on the axial compression behaviour of perforated glass fibre reinforced plastic medium-length tubes

This paper aims to investigate the axial compression behaviour of perforated glass fibre reinforced plastic (GFRP) circular tubes. A total of 12 GFRP medium-length tubes with and without circular holes were tested under axial compression. The influence of hole size and hole quantity on the failure mode and mechanical behaviour of perforated GFRP tubes were carefully evaluated. The overall buckling failure and material strength failure, mainly determined by the hole size, were observed in the axial compression tests. The critical load and axial stiffness of the perforated tubes decreased further with the increase of hole sizes and quantities, compared to those of the intact GFRP tubes. To reveal the damage mechanism of perforated GFRP tubes, three-dimensional digital image correlation (3D-DIC) technique was used to analyse the evolution of full-field strain around the hole. It was demonstrated that the damage mechanisms of the overall buckling failure and material strength failure were respectively compression-shear destruction and tension-shear destruction in the high strain concentration regions around the hole. Finally, design-oriented equations were proposed to predict the critical load and axial stiffness of perforated GFRP tubes under axial compression, and 95% confidence interval was used for interval estimation. The proposed equations were in good agreement with the test results. In addition, the prediction results of axial stiffness are generally more accurate than that of critical load.

Evaluation of the mean crushing load of perforated circular tubes undergoing progressive collapse

Perforations have been successfully employed for reducing the initial collapse load of tubes undergoing axial collapse. Most of the available literature evaluates the reduction in the initial collapse load through either experiments or numerical simulations. Theoretical models for calculating the mean crushing load are available for tubes without any perforations. In this study, the theoretical model proposed by Abramowicz and Jones is adapted to calculate the mean crushing force of circular tubes, having multiple perforations, undergoing collapse in the concertina mode as a function of the number of perforations, their size, and radius to wall thickness ratio of the cylinder. The mean load predictions from the model compared well with results from finite element (FE) simulations with a maximum deviation of 10%. The FE results indicated that the peak load during initial collapse is correlated well with the mean crushing load. Therefore, the presented model can be used for obtaining an indirect initial estimate of the effect of number of perforations and their size in reducing the initial collapse load.

Research on Wind Load Characteristics on the Surface of a Towering Precast Television Tower with a Grid Structure Based on Large Eddy Simulation

Local wind pressures on tiny rods of complex grid structures are difficult to obtain through wind tunnel tests due to their small sizes after scaling down, resulting in a lack of data support in wind load calculations for similar structures. However, local wind pressures on tiny rods can be obtained through numerical wind tunnel simulation using full-sized models. In order to investigate the wind pressure distribution of a grid structure and the influence of grid structures on the wind load of core tubes, three different television tower models are established based on an engineering example for large eddy simulations. A turbulence inlet generator (NSRFG) is adopted in the simulations while reproducing a portion of the wind tunnel test section including the mean and fluctuating pressures for validation. The results indicate that the mean wind pressures on the intersection of rods in the windward zone of the grid structure are higher than those on adjacent rods. Distinct reductions in the mean and fluctuating wind pressure of the grid structure are found in different zones. Moreover, resultant wind load forces and bending moments in the X and Y direction of the grid structure generally exceed 70% of the total wind loads. Based on simulation results, extreme net wind pressures of the grid structure and shape coefficients of enclosed regular octagonal cross-section buildings with the grid structure are provided for reference.

Novel Fuzzy-Based Optimization Approaches for the Prediction of Ultimate Axial Load of Circular Concrete-Filled Steel Tubes

An accurate estimation of the axial compression capacity of the concrete-filled steel tubular (CFST) column is crucial for ensuring the safety of structures containing them and preventing related failures. In this article, two novel hybrid fuzzy systems (FS) were used to create a new framework for estimating the axial compression capacity of circular CCFST columns. In the hybrid models, differential evolution (DE) and firefly algorithm (FFA) techniques are employed in order to obtain the optimal membership functions of the base FS model. To train the models with the new hybrid techniques, i.e., FS-DE and FS-FFA, a substantial library of 410 experimental tests was compiled from openly available literature sources. The new model’s robustness and accuracy was assessed using a variety of statistical criteria both for model development and for model validation. The novel FS-FFA and FS-DE models were able to improve the prediction capacity of the base model by 9.68% and 6.58%, respectively. Furthermore, the proposed models exhibited considerably improved performance compared to existing design code methodologies. These models can be utilized for solving similar problems in structural engineering and concrete technology with an enhanced level of accuracy.

Effects of variability in experimental database on machine-learning-based prediction of ultimate load of circular concrete-filled steel tubes

This study investigates the performance and robustness of regression machine-learning models in the presence of variability in the experimental database. The main objective of this work is to predict the ultimate load of circular concrete-filled steel tubes. The simulations were designed by combining size of the learning dataset, random realizations and prediction models. The variability (i.e. probability density function of each variable) is propagated to the output response through the regression machine-learning models. Results show that such variability must be considered when training and testing regression machine-learning models. The performance and robustness of the prediction models are presented and discussed. Based on the most robust and efficient model, a prediction equation is proposed for practical use. After conducting a comparison investigation, the performance of the proposed equation is found superior to one of current models. Finally, the proposed equation is implemented in Excel and appended to this paper.

Soft computing-based estimation of ultimate axial load of rectangular concrete-filled steel tubes

In this study, we estimate the ultimate load of rectangular concrete-filled steel tubes (CFST) by developing a novel hybrid predictive model (ANN-BCMO) which is a combination of balancing composite motion optimization (BCMO) - a very new optimization technique and artificial neural network (ANN). For this aim, an experimental database consisting of 422 datasets is used for the development and validation of the ANN-BCMO model. Variables in the database are related with the geometrical characteristics of the structural members, and the mechanical properties of the constituent materials (steel and concrete). Validation of the hybrid ANN-BCMO model is carried out by applying standard statistical criteria such as root mean square error (RMSE), coefficient of determination (R2), and mean absolute error (MAE). In addition, the selection of appropriate values for parameters of the hybrid ANN-BCMO is conducted and its robustness is evaluated and compared with the conventional ANN techniques. The results reveal that the new hybrid ANN-BCMO model is a promising tool for prediction of the ultimate load of rectangular CFST, and prove the effective role of BCMO as a powerful algorithm in optimizing and improving the capability of the ANN predictor.

Effect of Helical Winding Angle on External Pressure based Buckling of Partially Filled Thin Composite Cylindrical Shells

Effect of helical winding angle on buckling load of thin composite tubes is investigated in this work. Experiments are conducted on both empty and partially filled S2 glass tubes to estimate contribution of strength to the tubes by the filler material. Chosen filler material mechanically simulates behavior of typical solid propellant used in aerospace application. FE analysis with non-linear effect correlates well with the experimental data. Three series of experiments are conducted to quantify effect of helical winding angle and increase in volumetric loading fraction(VLF). Results confirm appreciable improvement in strength of filled tubes for higher VLF. For the chosen pattern of winding, lower winding angle provides more strength to the tubes against external pressure buckling. 

Quasi-Static Crushing of Aluminum Foam-Filled Thin-Walled Aluminum Tubes

The effect of aluminum foams with different cell structure on the quasi-static compression behavior and energy absorption of aluminum tubular structures was investigated. For comparison, empty tubes and aluminum foams with different cell structure were also tested, respectively. The results indicated that the value of crushing peak load of aluminum foam-filled tubes increases from 57.88% (1.94mm cell size) to 89.33% (1.22mm cell size) respectively compared with 2.83mm cell size. Splitting deformation of foam filling was found to effect in increasing the extra contact between the foam filling and the tube during progressive crushing, which increases the lateral compressive forces on the tubes. The energy absorption of aluminum foams filled aluminum tubes was also improved significantly due to the change of cell structure.

Energy absorption analysis for tapered multi-cell tubes improved by foams: Theoretical development and numerical simulation

In this paper, Energy absorption characteristics of tapered multi-cell tubes improved by foams are studied. For the energy absorption process, a theoretical formulation is developed to represent the mean crush load of the foam-filled tubes considering a combination of mean crush loads due to non-filled tube, the foam-filler, and a frictional resistance between them (interaction effects). The formulation is based on the assumptions including equivalent segmented non-tapered single-cell tubes as well as a parallel resisting force of the contributors (non-filled tubes, foam-filler, and interaction effects). Moreover, an extensive numerical analysis on the crushing of the foam-filled tapered multi-cell tubes, with a taper angle ranging from 0 to 7 degrees, a wall thickness ranging from 0.25 to 3 mm, and a cell number ranging from 11 to 10 × 10, is conducted to evaluate the effects of side wall tapering, cross section’s division into multiple cells and wall thickness enlargement on the crashworthiness characteristics. Analyses indicate that there are significant enhancements in the energy absorption behavior of the foam-filled tubes with respect to the non-filled ones. As a special case, the force-displacement results obtained in the numerical simulation are verified against those experimentally observed and reported in the literature for a foam-filled non-tapered single-cell tube.

Structural Behavior of Steel Tube and Coupler Scaffolds with Stability Strengthening Details

The multi-span steel tube and coupler scaffold is one of the main temporary structural forms in building and bridge construction. Given the insufficient research on their bearing capacity and design method, steel tube and coupler scaffolds have frequently collapsed in recent years and have caused serious casualties and economic losses. Through six prototype tests and a numerical analysis, this study investigated the effect of stability strengthening measures, such as vertical X-bracing, horizontal X-bracing, surrounding non-loading area, and lateral wall-tied constraints, on the ultimate bearing capacity and failure mode of multi-span steel tube and coupler scaffolds under a uniformly distributed line load of upper horizontal tubes. Using the finite element numerical analysis verified by the test data, the influence of height-width ratio, structure height, story height, spacing of vertical tubes, X-bracing layout, lateral wall-tied constraints, and surrounding non-loading area on the ultimate bearing capacity of multi-span steel tube and coupler scaffolds was analyzed. Design methods for multi-span steel tube and coupler scaffolds under a uniformly distributed line load of upper horizontal tubes were proposed based on the results of the prototype test and finite element numerical analysis. The reasonability of the design method was verified by the test data and finite element analysis results.

STABILITY PERFORMANCE OF INFLATABLE TUBE IMITATING CLANIS BILINEATA LARVA UNDER AXIAL PRESSURE

The body wall structure of Clanis bilineata larva exhibits strong stability. This characteristic prompted the development of a new inflatable tube to improve the stability under axial pressure. The C. bilineata larva was chosen to observe the connection between its body wall and nearby muscle tissues, as well as the distribution of these tissues, by using the tissue section technique. Using this method, an inflatable tube with reinforcing ribs was designed. Simulation using the finite element method and experimentation were employed to compare and analyze the stability of the inflatable tube with and without reinforcing ribs under different axial pressure levels. Results indicate that the ultimate load of both inflatable tubes increases linearly with increasing pressure. The difference between the slopes of the two lines is small. Under different axial pressure levels, the ultimate load of the inflatable tube with reinforcing ribs is about 1.34[Formula: see text]N higher than that without reinforcing ribs; the ultimate compression power increased by 31% to 68% compared with that without ribs. The simulation results are slightly larger than the experimental results, but the ultimate load value in the simulation exhibits the same trend as that in the experiment. Finally, the limit load and ultimate compression power are used as evaluation criteria to quantitatively analyze the stability performance of an inflatable tube with reinforcing ribs under axial pressure.

Compressive Crush Performance of Square Tubes Filled with Spheres of Closed-Cell Aluminum Foams

AbstractThis paper describes the compressive crush behaviour of spheres of closed-cell aluminium foams with different diameters (6, 8 and 10 mm) and square tubes filled with these spheres. The spheres of closed-cell aluminium foams are net spherical shape fabricated via powder metallurgy methods by heating foamable precursor materials in a mould. The square tubes were filled by pouring the spheres of closed-cell aluminium foams freely (without any bonding). The compressive crush performance of square tubes filled with spheres of closed-cell aluminum foams were compared to that of the empty tubes. The results show a significant influence of the spheres of closed-cell aluminium foam on the average crushing load of the square tubes. The energy absorption in the square tube filled with spheres of closed-cell aluminium foam with diameters of 10 mm is higher than in the other square tubes. The spheres of closed-cell aluminium foams led to improvement of the energy absorption capacity of empty tubes.

Nosing process of empty and foam-filled circular metal tubes on semispherical die by theoretical and experimental investigations

Abstract Nosing process of circular metal tubes in empty and polyurethane foam-filled conditions on a semispherical rigid die was analyzed by theoretical and experimental methods. A new theoretical model of plastic deformation of circular metal tubes was demonstrated during the nosing process on a rigid semispherical die. Based on the analytical model, some theoretical relations were calculated to estimate instantaneous forming load and dissipated energy of empty and foam-filled circular metal tubes versus axial displacement. Some circular brazen and aluminum tubes were prepared and shaped into semispherical nosed nozzles to verify the present theory. Comparison of theoretical predictions and the corresponding experimental measurements reveals that predicted load-displacement and dissipated energy-displacement diagrams by theoretical formulas have a good correlation with the corresponding experimental curves and it proves verity of the theory. Also, the present theory shows that dissipated energy and axial load of empty tubes depend on material type, wall thickness and diameter of the tubes and they are independent of tube initial length. Furthermore, the experimental results show that the presence of polyethylene Teflon-constraints increases ultimate axial displacement of the forming process.

Load bearing and failure characteristics of perforated square CFRP tubes under axial crushing

Open holes or cutouts have been commonly used in composite structures for various engineering purposes. This paper aims to investigate the load bearing behavior and failure characteristics of the square weave carbon fiber reinforced plastic (CFRP) tubes with open holes subjected to axial compression. Effects of hole size, hole shape and hole distribution on failure modes and mechanical behaviors were evaluated experimentally and numerically. Different with the progressive crushing mode seen in the intact CFRP tubes, mid-height collapse and unstable local buckling were observed in the axial crushing tests. The peak load and specific energy absorption (SEA) of the perforated tubes decreased by around 3–22% and 26–57%, respectively, compared to those of the intact CFRP counterparts. It was found that the effect of hole size on failure strength in tubes was less sensitive than that in perforated composite laminates, but was relatively stronger than the perforation shape and distribution. The damage mechanisms were explored in-depth using strain gauge tests and finite element analysis, which showed a significant increase in shear stress around the holes prior to final failure.

A simplified prediction method for the local buckling load of cylindrical tubes

Local buckling is as important as column buckling, substantially, when a thin-walled tube is applied to a structural part for guaranteeing safety design. This paper newly proposes an analytic model for predicting local buckling since a conventional Plantema equation is not able to predict the local buckling load, accurately, due to perfectly plastic assumption in the tube material. The proposed analytic model adopts a plastic flow of tube material to take into consideration of strain hardening, sequentially, which has been validated with experimental and numerical buckling loads when applying a thin-walled cylindrical tube. Remarkably, it shows good agreement with numerical and experimental buckling load compared with the conventional Plantema equation.

Some considerations on instability of combined loaded thin-walled tubes with a crack

Instability of a thin-walled stainless steel tube with a crack-shaped defect under combined loading is studied in this paper. Furthermore, the effects of the tube length, crack orientation, and crack length on the buckling behavior of tubes are investigated. The behavior of tubes subjected to combined is analyzed by using the finite element method (by Abaqus software). For cracked tubes with a fixed thickness, the buckling load decreases as the tube length and the ratio of the tube length to its diameter increase. Moreover, the buckling load of cracked tubes under combined loading also decreases with increasing crack length.

Estimation of Collapse Load for Thin-Walled Rectangular Tubes Under Bending

In two recent papers, the authors investigated the bending collapse load of rectangular tubes consisting of a perfectly elastoplastic material. From these investigations, it is found that the collapse may also occur due to the buckling of web in a rectangular tube under bending, when the tube has a cross section with a large aspect ratio of web to flange b/a. In order to evaluate the collapse load of such tubes under bending, the effective width concept given by Rusch and Lindner for a plate compressed with stress gradient was used to calculate the postbuckling strength of the tube web. However, in the solution of Rusch and Lindner, the plate is supported at only one longitudinal edge with the other longitudinal edge being free. This boundary condition is obviously different from that of the tube web. This paper complements the previous work by addressing the postbuckling strength of the web under stress gradients. The postbuckling strength of the web under stress gradients is also calculated using the effective width concept given in AS/NZS 4600 standard and North American specification (NAS) for a plate compressed with stress gradient and supported at both two longitudinal edges. Moreover, the web slenderness also affects the condition for reaching cross-sectional fully plastic yielding when the web is wider. A new method is proposed to predict the maximum moment considering the effect of web slenderness on the cross-sectional fully plastic yielding. The validity of the collapse load estimation is checked by the results of FEM (finite element method) numerical analysis.

Behaviour of perforated GFRP tubes under axial compression

This study investigates the influences of various parameters on the behaviour of perforated Glass Fibre Reinforced Polymer (GFRP) tubes under axial compression. A total of 15 GFRP tubes with and without perforations were tested under axial compression. All the GFRP tubes were divided into two groups: 12 tubes with 89mm outer diameter and 6mm wall thickness and 3 tubes with 183mm outer diameter and 8mm wall thickness. The influences of hole diameter, vertical hole spacing, tube diameter, perforation pattern, transverse hole spacing, and hole reinforcement on the axial compressive behaviour of perforated GFRP tubes were experimentally investigated. Considerable decreases in the axial stiffness, axial critical load, and axial deformation capacity of perforated GFRP tubes have been observed. The hole diameter, tube diameter, perforation pattern, and transverse hole spacing significantly influence the axial compressive behaviour of perforated GFRP tubes. However, the influences of vertical hole spacing and hole reinforcement have been observed not significant. Design-oriented equations for the prediction of the axial stiffness, axial critical load and axial deformation capacity of perforated GFRP tubes under axial compression have been proposed. The proposed equations have been found to be in good agreement with experimental results and can be used for the reliable design of perforated GFRP tubes.