Slenderness Ratio Research Articles

Bending fatigue performance of high-strength seven-wire monostrand

Large-amplitude cable vibrations are remarkably common in cable-stayed bridges subjected to wind and mechanical loading due to low inherent damping of these structures. Although the high slenderness ratio of cables means that bending moments are not normally significant over their free length, local effects near the cable anchorage induce non-negligible bending stress variation under dynamic loading, which could lead to fatigue failure of stay cables. In modern parallel strand stay cables, the fatigue performance depends on the fatigue properties of the individual seven-wire monostrands which together make up the cable. We introduce a new bending fatigue testing device for seven-wire monostrand which can control the fatigue loading in the axial and transverse directions of the cable independently. The fatigue endurance of monostrand with guide deviators is significantly longer than without guide deviators present, especially for smaller bending fatigue amplitudes. We found that bending fatigue life of monostrand is also reduced by increased constant or dynamic axial stress, but over-tensioning of the monostrand (e.g. during construction) had no consistently adverse effect on fatigue life. For monostrand loaded in severe bending, fatigue occurs due to the bending stress variation caused by the combination of bending moments and axial forces at the extreme edges of the monostrand cross-section, rather than due to relative movement and fretting between adjacent wires within the monostrand.

Mechanical Behaviour Slenderness Ratio of 13 Solid Wall Panels Under Uniformly Distributed Load

Recently, there has been a lot of research in the concrete industry on a sustainable approach using concrete waste as a substitute for natural aggregates. The reason for this is that the quantities of construction and demolition waste generated today pose a significant threat to the environment but can be used as a useful concrete material in the construction industry. The aim of this study is therefore to investigate the mechanical behaviour of solid concrete wall panels containing recycled concrete aggregates as a partial substitute for natural fine aggregates. Mortar cubes and wall panels with dimensions of 50 mm x 50 mm x 50 mm and 1000 mm x 300 mm x 75 mm, respectively, were produced. The wall panels were made from a 1:4 concrete mix consisting of 50% recycled concrete and 5% perlite (to reduce the weight of the concrete, and improve its workability), and 1% superplastizer, while the control wall was made with 100% natural fines. The wall panels were subjected to a compression test under uniformly distributed load. The cube samples were tested at 28 days of age. Mortar cubes with RCA achieved the highest compressive strength of 16.27 MPa compared to the control sample. The control wall panel has a higher ultimate load of 147.51 kN compared to the sample that contains RCA and perlite, which has an ultimate load of 128.68 kN. By 2030, our country needs to achieve sustainable management and efficient use of natural resources. By recycling this solid waste through separating, cleaning and crushing the concrete waste into small particles so that it can be used as a building material to replace sand. This shows that recycled concrete aggregate can be a potential material for making wall panels.

Experimental and theoretical investigations on out-of-plane buckling of circular aluminum arches with web openings under a central concentrated load

Perforated arches with cellular openings are widely used as roof beams in various buildings due to the functional and appearance requirements of architecture. Perforated arches under a central concentrated load may suffer from out-of-plane buckling when the load reaches to a critical value. This paper presents the analytical solution based on the energy method to predict the critical load of perforated arches under a central concentrated load. Experimental tests and finite element analyses are also carried out for perforated circular aluminum arch specimens to validate the present analytical solution. Good agreement between the analytical, experimental, and numerical results is demonstrated. The present results show that the size of web openings and the slenderness of the arch could affect the out-of-plane buckling behavior of perforated arches significantly. The arch with larger web perforations or larger slenderness ratio has the lower critical load of out-of-plane buckling.

Axial Compression Behavior of Elliptical Concrete-Filled Steel Tube Composite Short Columns with Encased Steel Considering Spherical-Cap Gap

This study explored the axial compression behavior of elliptical concrete-filled steel tubes with encased steel considering spherical-cap gap (GSECFST) composite short columns. We designed 25 composite column specimens by varying the steel tube yield strength (fty), steel skeleton yield strength (fsy), concrete cubic compression strength (fcu), steel tube thickness (t), steel skeleton sectional area (As), the long and short half-axis ratio (a/b), the gap ratio (Xsg), and the slenderness ratio (λ). Based on the nonlinear constitutive models of the materials and the nonlinear contact effect among materials, the ABAQUS 6.20 finite element software established the refined finite element models of these composite short columns. Also, the rationality of the finite element modeling with a spherical-cap gap was verified by comparing it with the existing experimental results. The influence regularity of various parameters on the load (N)-displacement (Δ) curves, bearing capacity, initial stiffness, and ductility of the composite short columns was obtained. In addition, the failure modes, N-Δ process, sectional strain distribution, and gap feature index of the constraint partition model for GSECFST axial compression short columns were revealed. The results showed a weakened interaction between the elliptical steel tube and concrete. Also, the axial compression bearing capacity, initial stiffness, and core concrete ductility were reduced because of the spherical-cap gap. As fty, fsy, fc, and Asy increased, the axial bearing capacity, initial stiffness, and ductility of GSECFST composite short columns improved significantly but decreased with increasing of a/b, Xsg, and λ. When the gap ratio of the spherical crown was less than 4%, the outer steel tubes in the mid-span area of the GSECFST composite short columns buckled in the direction of the elliptical short axis under axial compression, and the concrete expanded outward and crushed. The failures were similar to those of the specimens without the spherical-cap gap. Based on the sectional constraint partition model, we propose the calculation formula of axial compression bearing capacity for GSECFST composite short columns. Consequently, this study is a reference for the elastic-plastic analysis of frame systems with similar composite columns.

Anatomy based papermaking potential of some woody plants under different ecological conditions

The increasing use of wood in the forest industry and reduction of forest resources have prompted the paper industry to look for new materials. To this end, this study examined the biometric coefficients of the seven woody stems grown in different regions and investigated suitability for papermaking as an alternative to the use of wood. Wood samples of each species were collected from two different regions in Türkiye: the Kozan region, which has a Mediterranean climate, and the Yuvacık region, which has a mostly oceanic climate. The species included in the study were Phillyrea latifolia (mock privet), Arbutus andrachne (greek strawberry tree), Erica arborea (tree heath), Spartium junceum (spanish broom), Laurus nobilis (bay tree), Pistacia turpentine (cyprus turpentine tree), and Rhus coriaria (elm-leaved sumac). All fibers were classified as short. The longest fiber was observed for Spartium junceum (spanish broom) in Kozan. The fiber diameter was highest for Arbutus andrachne (greek strawberry tree) from Kozan, followed by Rhus coriaria (elm-leaved sumac) from Yuvacık and Laurus nobilis (bay tree) from Kozan. The fiber dimensions and the relationship between them were statistically analyzed. These included the slenderness ratio, flexibility coefficient, Runkel ratio, rigidity coefficient, Luce’s shape factor, F-factor, and Muhlsteph ratio. Although differences in fiber properties were detected between the two regions, it was determined that these were not enough to affect the desired properties for paper production. It was concluded that the fibers could be used in pulp, paperboard, and corrugated board production when mixed with long fibers.

Rounded corner thicken strut re-entrant auxetic honeycomb: Analytical and numerical modeling

An analytical model is formulated for 2-D periodic negative honeycomb thicken strut re-entrant lattice structures and a modified rounded corner negative honeycomb structure that shows negative Poisson’s ratios (NPR). Analytical modeling is done using Castigliano’s second theorem, where each beam is modeled using Timoshenko beam theory, considering bending, stretching, and transverse shearing. Elastic modulus and Poisson’s ratio have been formulated for both structures in the form of non-dimensional geometrical characteristics, such as length ratios, angles of re-entrant arms, shear correction factor, and the material’s Young’s modulus and Poisson’s ratios. Numerical simulations conducted in ABAQUS-CAE explicit solver validate the analytical model. The effect of the non-dimensional parameters on the qualities of the developed structure is demonstrated. It is observed that the structures with a low curvature ratio have a high fluctuation of Poisson’s ratio and Elastic constant when plotted against the other parameters. The slenderness ratio has little impact on Poisson’s ratio but significantly influences elastic modulus. It is shown that various needs can be satisfied by customizing the Poisson’s ratios and elastic constant of both forms of lattice construction over an extensive range by carefully choosing the geometrical parameters and material.

A fully coupled regularized mortar‐type finite element approach for embedding one‐dimensional fibers into three‐dimensional fluid flow

SummaryThe present article proposes a partitioned Dirichlet‐Neumann algorithm, that allows to address unique challenges arising from a novel mixed‐dimensional coupling of very slender fibers embedded in fluid flow using a regularized mortar‐type finite element discretization. The fibers are modeled via one‐dimensional (1D) partial differential equations based on geometrically exact nonlinear beam theory, while the flow is described by the three‐dimensional (3D) incompressible Navier‐Stokes equations. The arising truly mixed‐dimensional 1D‐3D coupling scheme constitutes a novel approximate model and numerical strategy, that naturally necessitates specifically tailored solution schemes to ensure an accurate and efficient computational treatment. In particular, we present a strongly coupled partitioned solution algorithm based on a Quasi‐Newton method for applications involving fibers with high slenderness ratios that usually present a challenge with regard to the well‐known added mass effect. The influence of all employed algorithmic and numerical parameters, namely the applied acceleration technique, the employed constraint regularization parameter as well as shape functions, on efficiency and results of the solution procedure is studied through appropriate examples. Finally, the convergence of the two‐way coupled mixed‐dimensional problem solution under uniform mesh refinement is demonstrated, a comparison to a 3D reference solution is performed, and the method's capabilities in capturing flow phenomena at large geometric scale separation is illustrated by the example of a submersed vegetation canopy.

In-plane nonlinear buckling analysis and design method of concrete-filled steel tubular catenary arches

The prevalence of concrete-filled steel tubular (CFST) catenary arches, renowned for the optimal load-bearing efficiency, has shown a marked increase over the past decades. To date, extensive research has been conducted into the nonlinear buckling behaviors and elastic-plastic strength of circular and parabolic CFST arches, grounded on the assumption that the curvature of the arch axis remains a specific constant. However, for CFST catenary arches, this assumption is not appropriate, given the substantial variation in curvature along the arch rib, and the influence of the arch axis is not adequately addressed in the existing design codes. Therefore, in this paper, a more precise strain expression is employed to conduct the nonlinear buckling analysis on CFST catenary arches. The analytic solutions for both symmetric snap-through buckling and anti-symmetric bifurcation buckling loads are obtained. In addition, a validated finite element (FE) model is adopted to investigate the influence of key parameters, including the slenderness ratio, the arch-axis coefficient, the rise-to-span ratio, and the steel ratio, on the in-plane stability bearing capacity of CFST catenary arches subjected to axial compression. Moreover, the obtained numerical results are utilized for comparison with the prediction results calculated by the existing design codes for CFST or steel arches. The comparison results indicate that the existing design codes have tended to overestimate the in-plane strength of CFST catenary arches, mainly due to the ignorance of the influence of pre-buckling deformation. Thus, based on the nonlinear buckling analysis results, a revised lower-bound design formula for predicting the in-plane stability bearing capacity of CFST catenary arches under axial compression is proposed, considering the influence of the rise-to-span ratio and the steel ratio.

Free vibration and buckling analysis of functionally graded beams using the DMCDM

In this paper, the Dual Mesh Control Domain Method (DMCDM) is used to carry out the free vibration and buckling analysis of two-constituent Functionally Graded Beams (FGBs) with through-thickness material variation. The material composition (modulus and density) is varied continuously through the beam thickness according to a power-law. The Euler-Bernoulli beam model consisting of the displacements and bending moment as the primary nodal degrees of freedom (i.e., mixed model) and the Timoshenko beam model with the displacement degrees of freedom (i.e., displacement model) are formulated as eigenvalue problems using the DMCDM. The numerical examples presented consider typical beam boundary conditions and various power-law exponents and slenderness ratios. The accuracy of this method is demonstrated by comparing the numerical results with those available in the literature.

Topology optimization of truss structures considering local buckling stability

This paper proposes the double-layer optimization algorithm to solve the truss topology problem with bar local buckling constraints. With this algorithm, the constraints on the local buckling are treated as linear functions of the optimized variables, which ensures efficient computation. In addition, two practical algorithms are proposed to solve the problems of the existence of transient hinges and the difficulty in matching the bar sections with standard sections. In addition, the topology optimization plug-in, named Topaz, is developed in this paper in the Rhino-Grasshopper parametric modeling platform to facilitate rapid model building. Finally, numerical examples show that the optimization results satisfy the requirements of strength, local buckling, and slenderness ratio of the bar, which demonstrates the effectiveness of the proposed algorithm.

Experimental investigation on axial compression behaviour of cold-formed thick-walled steel tubes

This paper presents an experimental and numerical investigation on the stability behaviour of cold-formed thick-walled steel tubes. Axial compression tests were conducted on 15 steel tubes with square and rectangle cross-sections to investigate their structural behaviours. The primary test parameters were slenderness and width-to-thickness ratios. Material properties, failure modes, load-deflection curves, and load-strain curves of the specimens are discussed. Furthermore, a numerical simulation was conducted to further investigate the effects of the slenderness ratio, width-to-thickness ratio, and initial geometric imperfection on the axial compression behaviour of cold-formed thick-walled tubes. Based on the experimental and numerical results, the applicability of the design codes, GB50018–2002, AISI S100–16, and EN 1993-1-1 was assessed. Results revealed that all three codes predicted the yield strength well after considering the cold-formed effect. With an increase in the slenderness ratio, GB50018–2002 and AISI S100–16 yielded increasingly unsafe predictions for overall stability, whereas EN 1993-1-1 yielded safe predictions. Finally, a modified design method for the overall buckling resistance of cold-formed thick-walled rectangular tubes under axial compression was proposed based on EN 1993-1-1 and verified using test and FEM results.

Numerical investigation of the influence of transverse welds on the strength of aluminum alloy I - shaped members – beams

The weldability of high strength aluminum alloys is an important consideration when designing aluminum structures. While these alloys do suffer significant strength loss in the weld heat affected zone (HAZ), available design codes are often overly conservative in their guidelines regarding the design of welded aluminum members. This paper presents a numerical investigation of the effect of reduced strength in the HAZ adjacent to a transverse weld in simply-supported aluminum alloy beams subject to concentrated end moments. Nonlinear finite element (FE) models were developed, validated, and applied in a parametric study of non-welded and transversely welded 6061-T6 flexural members with an I-shaped cross section. The FE model included initial geometric imperfections and material nonlinearities in both the HAZ and the base material. The parametric study examined 400 unique beam cases defined by the combination of four factors, including slenderness ratio or unbraced length, weld location along the beam span, post-yield material stiffness model, and loading case or resulting moment gradient. The FE results were subsequently compared with capacities predicted by the Aluminum Association’s Specification for Aluminum Structures, with proposed modifications to SAS also provided. A similar study on columns is presented in a companion paper within this issue.

Ultimate strength of hybrid repaired offshore pipelines with various slenderness ratio subjected to through-thickness pitting corrosion under axial compressive loading

Offshore pipelines are susceptible to various types of corrosions where pitting corrosion is generally considered the most severe. This study aims to study the effect of ratio of Carbon Fiber Reinforced Polymer to Glass Fiber Reinforced Polymer and wrapping patterns on the repair performance of composite repair system for offshore pipelines subjected to pitting corrosion. Four sets of samples with different slenderness ratios are subjected to axial compression, where the peak loads are recorded as the performance indicator of different repair schemes. Based on the experimental results, the average repair index, which is the ratio of repaired strength to intact strength, increases from 1.06 to 1.40 as the ratio of CFRP to GFRP increases. However, 1G3C repair schemes experience brittle failure while other repair schemes show different extents of ductility upon failure. Longitudinal wrapping pattern achieves the average repair index of 1.19 while Alternate and Horizontal yields the average repair index of 1.18 and 1.15 respectively. Furthermore, Longitudinal wrapping pattern exhibits the highest rigidity followed by Alternate and Horizontal. A higher slenderness ratio can contribute to a lower repair index where the cross-sectional properties have a more prominent effect compared to sample length. The theoretical results calculated based on equations provided in ASME PCC-2 show good agreement with the experimental results as there is only a percentage difference of 5.5% between them.

Trussed concrete-filled steel tubular hybrid structures subjected to axial compression: Performance and design calculation

This paper presents a study on the axial compression performance of trussed concrete-filled steel tubular (CFST) hybrid structures. A total of 26 specimens were tested, including 15 circular and 11 square cross-sectional specimens. The effects of cross-sectional types, yield strength of steel of CFST chord, web types, number of chords, and equivalent slenderness ratio were investigated to clarify the mechanical behavior of trussed structure. The analyses of the full-range response, the typical failure mode, and the distribution of the transverse deflection and strain of the structures were carried out. A finite element analysis (FEA) modelling of trussed CFST structure was established and validated against the experimental results. Through the numerical simulation, the analysis of the internal force and stress was conducted, and the hybrid effect between the web and CFST chord was revealed. Based on parameter analysis, the design calculation was proposed, and the trussed CFST hybrid structure was equivalent to a single CFST to calculate its load-bearing capacity by introducing equivalent slenderness ratio proposed.

Scour Effect on the Lateral Bearing Behaviour of Monopiles Considering Different Slenderness Ratios

Scour leads to the loss of soil around monopile foundations for offshore wind turbines, which affects their structural safety. In this paper, the effect of scour on the lateral behaviour of monopiles was extensively investigated using finite element analysis, and calibration and comparison were undertaken using centrifuge tests. Piles with three slenderness ratios, i.e., 3, 5 and 8, were studied by keeping the diameter constant and varying the embedment length. Three scour types (local narrow, local wide and global) and four scour depths (0.5D, 1D, 1.5D and 2D; D signifies the pile diameter) were considered in this investigation. The results indicate that the lateral resistance of the pile is the greatest in the case of local narrow scour, followed by that in the cases of local wide scour and global scour. When the scour depth is larger than 1D, the influence of the scour type on the pile lateral bearing behaviour is insignificant. The influence of the scour type and scour depth on the pile lateral bearing behaviour is broadly similar for piles with slenderness ratios of 3, 5 and 8. However, the piles featured with smaller embedment lengths show a larger decrease rate in their lateral capacity, which means the effect of scour should cause more concern on small slenderness ratio monopiles.

Axial compressive behavior of high-strength steel-UHPC-clad steel composite walls

This paper proposed a novel high-strength steel-UHPC-clad steel composite wall (HS-UHPC-CS composite wall) and investigated its axial compressive behavior through experimental and numerical methods. A total of 18 axial compressive tests and finite element (FE) analyses, including parametric studies of 120 cases, were conducted. It was shown that the stud spacing-to-plate thickness ratio and the normalized slenderness ratio notably affected the strength and local buckling, while their influence on the initial stiffness was minor. The strength and initial stiffness were improved, while the ductility was compromised by the presence of ultra-high-performance concrete (UHPC). Steel fiber was critical to the HS-UHPC-CS composite wall, while the lack of steel fiber could trigger premature brittle failure. The influence of the strength of concrete was higher compared to steel plate. The critical buckling stress of the steel plate was calculated using Euler's buckling formula for the clad steel plate of the HS-UHPC-CS composite wall. The results were compared with the ordinary composite wall database. In addition, strength from test results, FE results, and the database were compared were compared with strength calculated by design provisions. It was found that the calculated strength was close but not safe. It was recommended that different concrete contribution coefficients should be applied for HS-UHPC-CS composite walls with different normalized slenderness ratios.

Influence of Scour Protection on the Vertical Bearing Behaviour of Monopiles in Sand

Extensive studies have been performed on the effectiveness of scour protection against scour erosion progression. But there is little research to date evaluating the effect of scour protection on vertical resistance behaviour of monopile foundations. This paper investigates the influence of scour protection on the vertical loading behaviour of monopiles installed in sand using centrifuge tests and finite element analysis (FEA). Four scour protection widths (1D, 2D, 3D, 4D; where D is the pile diameter) and three scour protection thicknesses (1 m, 2 m, 3 m) were modelled on a pile with a slenderness ratio (L/D) of five. In the FEA, the scour protection mechanism was modelled using two strategies, namely the ‘stress method’ by applying stress and the ‘material method’ by applying virtual material on the seabed surface around the pile. Outcomes between these two strategies were compared, and the contact coefficient δ used in the ‘material method’ for describing the contact effectiveness of the overlaying scour protection material with the pile structure was introduced, providing a more scientific and accurate calculation reference for engineering applications. The results indicated that the vertical capacity of monopiles could be increased by 5% to 23% by adopting the scour protection measure, depending on the scour protection width and scour protection thickness.

Seismic behavior of polypropylene fiber reinforced rubber concrete-filled circular steel tubular columns

In this study, the seismic behavior of polypropylene fiber reinforced rubber concrete-filled circular steel tubular columns subjected to low cyclic loading was investigated. The effects of varying rubber content, slenderness ratio, axial compression ratio, and steel content on specimen damage were analyzed. Digital Image Correlation (DIC) and Acoustic Emission (AE) instruments were utilized to monitor the full-field strain on the surface of the specimens and the generation and development of internal concrete cracks. A fiber modeling method was developed for calculating the compression bending bearing capacity of the columns. The results indicated a uniform failure pattern, primarily located at the column base. Adding rubber powder decreased the bearing capacity of the specimen, yet enhanced their energy dissipation capacity and ductility. Higher axial compression ratio led to early failure in the steel tube, with the slenderness ratio significantly affecting seismic performance. The calculation methods according to GB 50936–2014 (CECS 254–2012) and DL T5085–1999 showed higher accuracy than other codes, with average values of 0.558 and 0.576, and standard deviations of 0.067 and 0.089, respectively. The variation coefficient for the calculation method in GB 50936–2014(CECS 254–2012) was 12.02%, lower than that of DL T5085–1999. The proposed fiber modeling method demonstrated superior calculation accuracy, with an average value of 0.957, a standard deviation of 0.032, and a variation coefficient of 3.29%.

Dynamic response of a large-diameter end-bearing pile in permafrost

Vertically dynamic model of a large-diameter pile in frozen soil is established, in which the frozen soil is described to a saturated frozen porous media, and the large diameter end-bearing pile is simplified to a one-dimensional rod considering the influence of the transverse inertia effect. Analytical solutions of the longitudinal coupling vibration between the end-bearing pile and the frozen soil are obtained using Helmholtz decomposition and variable separation methods in the frequency domain. By comparing the dynamic responses of the longitudinal vibration of the large diameter end-bearing pile with the traditionally one-dimensional pile, as well as the impedance factor of the frozen soil layer induced by the pile vibration, these demonstrate the influence of the transverse inertia effect on the high frequency vibration of large diameter pile is significant, and the influence on the pile with a smaller slenderness ratio is larger. The temperature and the Poisson’s ratio also have significant effects on the vertical vibration of large diameter piles in frozen soil, which cannot be ignored in the analysis.

Strengthening Reinforced Concrete Rectangular Columns with Various Slenderness Ratios by Fiber Reinforced Polymer (FRP)

Strengthening Reinforced Concrete Rectangular Columns with Various Slenderness Ratios by Fiber Reinforced Polymer (FRP)