Stiffener Arrangements Research Articles

Collision-Damage Analysis of a Floating Offshore Wind Turbine Considering Ship-Collision Risk

As the number of offshore wind-power installations increases, collision accidents with vessels occur more frequently. This study investigates the risk of collision damage with operating vessels that may occur during the operation of an offshore wind turbine. The floater used in the collision study is a 15 MW UMaine VolturnUS-S (semi-submersible type), and the colliding ships are selected as multi-purpose vessels, service operation vessels, or anchor-handling tug ships based on their operational purpose. Collision analysis is performed using ABAQUS and substantiation is performed via a drop impact test. The collision analyses are conducted by varying the ship velocity, displacement, collision angle, and ship shape. By applying this numerical model, the extent of damage and deformation of the collision area is confirmed. The analysis results show that a vessel with a bulbous bow can cause flooding, depending on the collision conditions. For damage caused by collision, various collision angles must be considered based on the internal stiffener arrangement. Additionally, the floater can be flooded with relatively small collision energy when the colliding vessel has a bulbous bow.

Mechanical analysis and interior stiffeners arrangement discussion of a specific ship side collision situation

Collision between ships of different sizes may result in a situation where a vessel with a higher deck height impacts another vessel with a lower deck height. In such case, the absence of bearing structure above the lower-draft struck ship's deck means that the bow of the high-draft striking ship transfers pressure to both the deck and side plates of the struck ship during collision. According to this situation, the numerical simulation of small scale compartment impacted by a higher-draft ship bow was carried out. Based on the analysis of the numerical results, the main impact area of the small scale compartment was simplified into a typical L-shaped plate-frame structure to facilitate the experiment. A small scale quasi-static experiment was implemented and the force-displacement curve and energy absorption data of the L-shaped structure penetrated by a rigid approximate bow indenter were obtained. Moreover, material tensile tests provided parameters for numerical simulation and the deformation process of the structure was analyzed. Based on that, several L-shaped structure cases with different stiffeners of height and position were calculated in LS-DYNA. Failure process, structural energy absorption and efficiency were summarized and the excellent structural characteristics for this ship side collision situation were obtained.

Experimental and numerical studies on cyclic behavior of stiffened corrugated steel plate shear walls with different corrugation orientations

AbstractCorrugated steel plate shear walls (CSPSWs) can be applied to high‐rise building structures to serve as lateral load‐bearing and energy‐dissipating members. Arranging stiffeners on corrugated steel plates shows substantial potential to further improve the seismic performance of ordinary CSPSWs. This study experimentally and numerically investigated the hysteretic behavior of unstiffened and stiffened CSPSWs. Cyclic quasi‐static tests were conducted on four, 1/2‐scale, two‐story, single‐bay specimens with different corrugation orientations, including two specimens with unstiffened corrugated steel plates and two specimens installed with stiffened corrugated steel plates equipped with two pairs of stiffeners. According to the hysteretic curves of different specimens, the effects of corrugation orientations and arrangement of stiffeners were revealed in terms of the skeleton curves, energy‐dissipating capacity, and stiffness degradation. Then, finite element (FE) models, which were applied to gain a deeper understanding of the experimental results, were established, and validated against the test results. This study demonstrated that the arrangement of stiffeners was effective in improving the seismic performance of CSPSWs regarding the ultimate shear strength and energy‐dissipating capacity, while the influence of corrugation orientations on the performance of the specimens involved in this study could be ignored.

A Two-Stage Optimisation of Ship Hull Structure Combining Fractional Factorial Design Technique and NSGA-II Algorithm

The intricate nature of ships and floating structures presents a significant challenge for ship designers when determining suitable structural dimensions for maritime applications. This study addresses a critical research gap by focusing on a three-cargo hold model for a multipurpose cargo ship. The complex composition of these structures, including stiffening plates, deck plates, bottom plates, frames, and bulkheads, necessitates thorough structural analysis to facilitate effective and cost-efficient design evaluation. To address this challenge, the research utilises FEMAP-integrated NX NASTRAN software (2021.2) to assess hull girder stress. Furthermore, a novel approach is introduced, integrating the Design of Experiments (DOE) principles within Minitab 21.4.1 software to identify critical parameters affecting hull girder stress and production costs. This method determined the top five key parameters influencing hull girder stress: Hatch coaming plate, Hatch coaming top plate, Main deck plate, Shear strake plate, and Bottom plate, while also highlighting key parameters that impact production costs: the inner bottom plate, Inner side shell plate, Bottom plate, Web frame spacing, and Side shell plate. Ship design optimisation is then carried out by incorporating regression equations from Minitab software into the Non-dominated Sorting Genetic Algorithm II (NSGA-II), which is managed using Python software (PyCharm Community Editon 2020.3.1). This optimisation process yields a significant 10% reduction in both ship weight and production costs compared to the previous design, achieved through prudent adjustments in plate thickness, web frame positioning, and stiffener arrangement. The optimally designed midship section undergoes rigorous validation to ensure conformity with industry standards and classification society regulations. Necessary adjustments to inner bottom plates and double bottom side girders are made to meet these stringent requirements. This research offers a comprehensive framework for the structural optimisation of ship hulls, potentially enhancing safety, sustainability, and competitiveness within the maritime engineering industry.

Lateral performance of cold-formed steel framed shear walls using slitted sheathing with stiffeners

Cold-formed steel (CFS) framed shear walls with steel sheathing are promising lateral-force-resisting members of mid-rise buildings in seismic regions. Previous studies have demonstrated that steel sheathed CFS framed shear walls have high shear capacity but some shortcomings, such as the low ductility caused by the premature damage of the frame and the shear buckling of the sheathing. This paper presents an experimental study on a novel type of CFS framed shear wall with slitted steel sheathing (CFS-SSWs), which uses longitudinal slits to change the failure mode of the sheathing so that the ductility of the wall can be improved; Meanwhile, stiffeners are utilized to enhance the out-of-plane stability of the slitted sheathing and the integrity of the wall. Six full-scale CFS-SSW specimens were tested under monotonic and cyclic lateral loading. Three types of stiffening approaches (Type I, Type II and Type III) were adopted for the walls. Test results were analysed to investigate lateral performances of walls under different stiffener arrangements, including failure modes, load-displacement hysteresis curves, backbone curves, stiffness and strength degradation, and energy dissipation capacity. The measured strengths of the walls in the tests were assessed using theoretical indexes. It is found that peak loads and energy dissipation capacity of stiffened walls are noticeably higher than those of the unstiffened wall. Type II and Type III are effective stiffening approaches that could mitigate the buckling of the slitted sheathing and enable the links between the slits to reach the full plastic strength. By connecting the stiffeners and studs through stiffener connectors, Type III has the most significant enhancement on the stiffness, strength and ductility of the wall.

Flexural capacity and local buckling half-wavelength of high strength steel tubular beams under moment gradients: An experimental study

An experimental investigation into the effect of moment gradients on the flexural behaviour of hot-rolled high strength steel square hollow section (SHS) beams is presented in this paper. In total, 20 beam specimens in steel grades S690 and S770, and with cross-sections spanning from Class 2 to Class 4 based on the Eurocode 3 slenderness limits, were tested under three- and four-point bending. In the three-point bending tests, the beam spans were varied to achieve a range of moment gradients; the influence of different stiffening arrangements at the loading point was also considered. Local geometric imperfections were measured by means of 3D laser-scanning prior to testing and digital image correlation (DIC) was adopted to monitor the displacement and strain fields at critical regions and to assess the local buckling half-wavelengths of the test specimens for which a consistent measurement approach was proposed. The measured local buckling half-wavelengths were compared against the elastic local buckling half-wavelengths calculated using the finite strip method. It was observed that while the measured local buckling half-wavelengths remained approximately constant up to first yield, a significant reduction in half-wavelength was observed with increasing moment due to the non-uniform spread of plasticity. The comparisons also revealed that the local buckling half-wavelengths reduced with both the presence of moment gradients and intermediate stiffeners, with a new parameter proposed to quantify the local moment gradient. It was shown from the tests that the specimens subjected to moment gradients, despite the presence of shear, exhibited higher ultimate moment capacities (up to 10.5% for stiffened specimens and 3.4% for unstiffened specimens) than those subjected to uniform moments. This is attributed to the delay in the local buckling of the critical cross-section of beams under moment gradients due to the restraint provided by the less heavily stressed adjacent cross-sections.

Study on energy dissipation performance of low-yield-point steel shear panel dampers

To investigate the energy dissipation performance of low-yield-point steel shear panel dampers (LSSPD), the eleven full-scale LSSPD specimens were designed and tested. By conducting quasi-static cyclic tests and numerical simulations, the influence of shear plate aspect ratios, flange plate thickness, numbers and layout of stiffeners on the failure modes for energy dissipation performance of LSSPD have been investigated. The results indicate that: The energy-dissipating capacity of the damper is positively correlated with the shear plate's cross-sectional area. Increasing the flange plate thickness can improve the bearing capacity and energy dissipation of LSSPD, but with a limit. The stiffeners can enhance the ultimate bearing capacity of the damper. A single stiffener in both horizontal and vertical directions effectively controls the out-of-plane buckling deformation of the shear plate. It achieves a damper with a full hysteretic curve and a high energy dissipation capacity. However, the arrangement of stiffeners on different sides will decrease the ultimate bearing capacity of the damper. Through finite element supplementary analysis, it is recommended to select the shear plate aspect ratio between 20 and 41, and the flange restraint coefficient βf should not be <10 for damper design. Meanwhile, limiting the stiffener restraint coefficient βs within 45 is recommended to achieve better energy dissipation performance for low-yield-point dampers.

Bio-inspired study of stiffener arrangement in composite stiffened panels using a Voronoi diagram as an indicator

Taking a biomimetic approach, this study introduces the use of a Voronoi diagram as an indicator of stiffener arrangement in stiffened composite panels. The locations of generator points that determine the shape of the Voronoi diagram are optimized for buckling problems under compression and shear load. An original optimization algorithm that combines the genetic algorithm and the finite element method is developed and implemented. The Voronoi diagram can also be used as an indicator for conventional, periodical stiffener shapes such as grid, lattice, honeycomb, and isogrid. We conducted parametric studies for periodical stiffener shapes, and demonstrated that these shapes can be designed using Voronoi diagrams. The results revealed that the optimized panel has a higher buckling load than that of conventional panels, and this methodology is effective for designing biomimetic stiffened CFRP panel structures.

Numerical analysis on the mechanical response of grouted connection for pile-bucket foundation

As a new foundation type for offshore wind turbine (OWT), pile-bucket foundation, which consists of a monopile and a bucket foundation, has good prospect in engineering application and has received wide attention. However, most of the current research ignored the function of grouted connection (GC) and assumed that the pile and bucket were rigidly connected, which may lead to unrealistic estimation of the loading response of pile-bucket foundation. In this study, Finite Element Analysis (FEA) is conducted to study the influence of grout connection on the bearing characteristics of pile-bucket foundation, with a special focus on the mechanical response of the grout connection itself. The concrete damage plasticity (CDP) model is used to simulate the mechanical response of the grout material. After validation of the numerical model, twelve simulations are conducted by changing the grout thickness, grout length and stiffener arrangements. Though the variance of grout thickness and grout length has little impact on the load-displacement curves of the pile-bucket foundation, the optimal grout thickness and grout length could be determined according to the development of contact pressure, stress and damage of the grout connection. On the other hand, the employment of stiffener leads to notable stress concentration and fluctuation, however, it also improves the overall capacity of the pile-bucket foundation and effectively controls the damage of the grouted connection. The numerical result is expected to provide some reference value for the structural design of grouted connection for pile-bucket foundation.

Experimental and numerical investigation on concrete filled steel tube columns reinforced with diagonal stiffeners under axial loading

In modern construction use of composite sections such as CFST columns was improved because of their numerous benefits in construction processes. However, some disadvantages like buckling of steel tube, poor corrosion and fire resistance necessitates the stiffening measures to be adopted. In this study, a novel stiffening scheme was proposed to use with unstiffened CFST column. The stiffening scheme is named as diagonal stiffeners which comprises diagonal stiffeners attached at diagonally opposite ends of steel tube. The stiffeners can be provided in three formats viz, binary, tertiary, and quaternary arrangement. In this paper the response of diagonal stiffeners CFST columns under axial compression was investigated through experimental program. The findings of the analysis were collected with regard to ultimate capacity, load vs strain response, and load vs deformation behavior. Further, to explore the performance of suggested stiffener arrangement, a FE model was developed in ABAQUS and validated through experimental findings. A parametric examination was conducted to evaluate the influence of diameter of stiffeners, number of stiffeners and its yield strength on the ultimate load capacity, load vs strain behavior, axial stress distribution in concrete, lateral deformation of column, and Poisson’s ratio of outer steel casing. Results of the analysis showed that CFST columns strengthened with proposed stiffening arrangements showed approximately 15–25 % higher ultimate load capacity than unstiffened CFST section. Also, using the diagonal stiffeners improved the pre-peak and post-peak behavior of column section. The local buckling of outer steel casing was eliminated and ductility of column section improved. It was deduced that stiffened CFST columns had better confining pressure on concrete infill and composite interaction between outer steel casing and infill concrete was enhanced. The prediction formula to anticipate axial load capacity was also established and can be employed to design of CFST with diagonal stiffeners.

Moment capacity of eaves brackets of cold-formed steel portal frames

The strength and stiffness of cold-formed steel portal frames are heavily related to the performance of their joints; these joints are normally formed through brackets, bolted to the webs of channels. Previous research in the literature has considered the strength of the apex bracket, and design equations proposed to predict its moment capacity. No similar research, however, has been undertaken for the eaves bracket. In the literature, the only design guidance found is a design chart, limited to eaves joints fully restrained against lateral torsional buckling, for use under a closing moment and an eaves bracket details having a stiffener along its hypotenuses. This paper describes a finite element study comprising 7,560 models, that addresses all these limitations. Unified equations are presented that can be used for the design of eaves brackets in practical partially restrained eaves joints, as found in New Zealand practice, both closing and opening moments, and different arrangements of stiffeners in the detail of the eaves bracket.

Comparison and design of stiffened rectangular concrete-filled steel tubular members

A stiffened rectangular concrete-filled steel tubular (CFST) member offers improved composite action over the unstiffened counterpart in terms of delaying local buckling of the rectangular steel tube and enhancing confinement to the infilled concrete, and thus various stiffening forms were proposed. Choosing an appropriate stiffener in practical design needs comprehensive understanding and comparison on the efficiency of various stiffeners. However, most studies focused on a single type of stiffener only, no guidance was provided on how to account for the benefits of stiffened rectangular CFST members in mainstream design specifications, and no unified calculation method for load capacity was formed. In this work, finite element models for stiffened rectangular CFST members were established and verified by test results. Then parametric analyses were conducted to compare the axial compressive and flexural behavior of rectangular CFST members with various types of stiffeners. The appropriate arrangement and detailing of stiffeners were proposed, and the diagonal ribs showed the best performance under the same material strength and steel consumption. Finally, mechanics-based models and unified calculation methods were proposed to calculate the axial compression and interaction strength, and were found to well predict the strength of stiffened and unstiffened CFST members. These results will further facilitate the use of stiffened rectangular CFST members in practical engineering projects.

Bandgap formation and low-frequency structural vibration suppression for stiffened plate-type metastructure with general boundary conditions

Metastructures with unique mechanical properties have shown attractive potential application in vibration and noise reduction. Typically, most of the metastructures deal with the vibration bandgap properties of infinite structures without considering specific boundary condition and dynamic behaviors, which cannot be directly applied to the engineering structures. In this research, we design a Stiffened Plate-type Metastructure (SPM) composed of a plate with periodic stiffeners and cantilever beam-type resonators subjected to general boundary conditions for low-frequency vibration suppression. The effects of boundary conditions and the number and orientation of the stiffeners on Locally Resonant (LR) type bandgap properties in SPM are further investigated. An analytical modeling framework is developed to predict the bandgap formations and vibration behaviors of SPMs in finite-size configuration. The governing equations of the SPM reinforced by various arrangements of stiffeners are derived based on the first-order shear deformation theory and Hamilton’s principle, and a Fourier series combined with auxiliary functions is employed to satisfy the arbitrary boundary conditions. Finite element analysis and experimental investigations of vibration behaviors for the SPM are carried out to validate the accuracy and reliability of the present analytical model. For practical designs of the SPMs with specific boundary conditions, it is found that there exist optimal numbers of stiffeners and resonators which can produce the significant LR-type bandgap behaviors. Furthermore, various arrangements of stiffeners and resonators are explored for different boundary conditions by breaking the requirement of spatially periodicity. It is shown that for the designed SPM, the vibration modes of its host structure should be considered to widen the frequency range in which the resonators transfer and store energy, and hence improve the performance of low-frequency vibration suppression. The present work can provide a significant theoretical guidance for the engineering application of metamaterial stiffened structures.

Effect of Stiffeners on Mechanical Behavior of T-Stubs Based on Experiment and Numerical Simulations

T-stubs are important components in the application of the component method; hence it is crucial to clarify the T-stub mechanism for the analysis of the mechanical properties of steel joints. In this study, the mechanical behavior of T-stubs was assessed via 6 static tests and 18 finite element analysis models. The influences of flange thickness, bolt spacing, bolt diameter, and stiffener rib on initial stiffness, ultimate bearing capacity, and bolt force of T-stubs were analyzed. Furthermore, the development process and relations of the T-stub bolt force with and without stiffeners were analyzed. The results show that an effective stiffener arrangement can reduce the bending moment and prying force to a certain degree; however, offsetting the bending moment and prying force entirely is difficult. Furthermore, the influence of bending moment and prying force on the bearing capacity should be considered in the design.

Static Stress Analysis of Functionally Graded Cylindrical Stiffened Shells

In this paper, a study on bending performance of functionally graded (FGM) cylindrical shells under transverse mechanical load is presented. Computational and analytical tools are used to study the behavior of FGM cylindrical shells under bending. Analytical modeling is based on first order shear deformation theory (FOST) and a finite element computational tool ABAQUS is used to model the FGM cylindrical shell. Material properties are estimated by power law index. Results from computational tools for isotropic and FGM cylindrical shells with various boundary and loading conditions are validated with literature and present FOST. Stiffened FG cylindrical shells with cutouts are analyzed. The FGM circular cylindrical shells subjected to an internal pressure with various arrangements of stiffeners are also analyzed and von – Mises stresses are also studied.

Moving load response of ring-stiffened sandwich truncated conical shells with GPLRC face sheets and porous core

As a first attempt, the dynamic responses of sandwich truncated conical shells with graphene platelets reinforced composite (GPLRC) face sheets, porous core and circumferential stiffeners under asymmetric internal ring-shaped moving load are analyzed. The face sheets and porous core are reinforced by uniformly distributed and randomly oriented graphene platelets (GPLs). The spatially discretized equations of motion subjected to different boundary conditions are derived based on the first-order shear deformation theory (FSDT) using the Chebyshev–Ritz method. The admissible functions of the field variables are constructed using the trigonometric functions in the circumferential direction and the one-dimensional Chebyshev polynomials in conjunction with the suitable boundary functions in the meridional direction. The Newmark’s time integration scheme is employed to solve the resulting ordinary differential equations of motion. The robustness and accuracy of the method are demonstrated through the different examples. After that, the influences of core porosity, face sheets, GPLs parameters, shell geometric parameters, boundary conditions, and the arrangement, number and size of stiffeners on the results are explored. The results show that porosity, face sheets, the location, size and number of stiffeners play important roles on the dynamical response of the shells under investigation. Also, it is found that the critical load velocity decreases by increasing the porosity coefficients and increases by increasing the number of ring-stiffeners.

Numerical investigation of grooved gusset plate damper for using in cross-braced frames

The aim of the present study is to propose an innovative type of gusset plate damper, which can be employed to protect structures against severe earthquakes and improve the seismic behavior of concentrically cross-braced frames. The proposed device comprises of a gusset plate which is grooved such that it yields in time at several places and prevents any plastic action or buckling in the braces. It is called a grooved gusset plate damper (GGPD). The GGPD can be used as an energy dissipater when installed in cross-braced frames as it dissipates input energy through inelastic deformations at its steel strips. To predict the yield and ultimate capacity and elastic stiffness of the GGPD, theoretical derivations are conducted resulting in analytical equations of the system. Afterwards, finite element models of the system are analyzed using ABAQUS and its hysteretic behavior is investigated under cyclic loading. Effects of the length, width and thickness of the strips and arrangement of stiffeners, on the cyclic performance and energy dissipation of the GGPD are studied. It is concluded that the analytical formulas are in very good agreement with the numerical results. Moreover, the hysteretic curves of the system are full and stable and have a similar behavior in tension and compression without pinching. In addition, the proposed system is able to significantly dissipate the seismic energy and tolerate more than 4% story drift.

Seismic performance of stiffened steel box column with different corner stiffener arrangements: a numerical approach

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2021 Impact Factor: 0.682The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.Cover :Leatherback (a), green (b - adult &amp; f - hatchling), hawksbill (c) and olive ridley (d) turtles who nest in Sri Lankan beaches, green turtle crawl marks (e) and by-catch of sea turtles in fisheries (c &amp; d)Photo credits: SJ Perera (a &amp; c), WPN Perera (b &amp; e), K Ekaratne (d &amp; f)

Interaction of flange and web slenderness, overstrength factor and proposed stiffener arrangements for long links

This paper is aimed to investigate the interaction of flange and web slenderness ratio, overstrength factor and also to improve the behavior of long links. Pursuant to these goals, 150 numerical models of different long links were developed and exposed to cyclic loading protocol mandated by AISC 341. Link length ratio, flange and web slenderness and stiffener configurations are selected as parameters. The results revealed that the flange slenderness ratio can be relaxed to 0.38(E/Fy)0.5 for long links if the web slenderness ratio is <1.5 (E/Fy)0.5. The shear capacity of long links decreases as the link length ratio increases. The results of shear capacity showed the overstrength factor required by AISC 341 overestimates the shear capacity; therefore, two different equations to predict the overstrength factor for long links are proposed. The stiffener configuration recommended by AISC 341 limits the potential of long links. To mitigate this drawback, different stiffener configurations are proposed to empower the behavior of long links. Using additional one stiffener at each link ends can enhance shear strength, energy dissipation and plastic rotation capacities by 25%, 447% and 322%, respectively. When two additional stiffeners are introduced, these ratios modify to 29%, 479% and 332%. Moreover, rupture index values are utilized to verify proposed stiffener configurations further.

Theoretical modelling and design of metamaterial stiffened plate for vibration suppression and supersonic flutter

In the study, we propose a theoretical model of a metamaterial stiffened plate with multiple cantilever beam resonators (CBRs) for the vibration suppression and supersonic flutter analysis. Based on the first-order shear deformation theory and supersonic piston aerodynamic theory, the governing equations of metamaterial stiffened plate with various arrangements of stiffeners are derived through Hamilton principle. The vibration and supersonic flutter behaviors are carried out, which are validated well by comparing with the finite element results. It is shown that the multiple-resonant CBRs can be utilized to suppress the broadband vibration of multiple modes, and improve the aeroelastic behaviors of the metamaterial stiffened plate, since the existence of multiple CBRs can affect the coupled modes of the system flutter. In particular, the flutter boundary of the system can be significantly enhanced when the designed frequencies of CBRs are near the flutter frequency of the original aeroelastic system, which reveals the flutter suppression mechanism of the present metamaterial stiffened plate. The present work demonstrates that the proposed multiple-CBRs-stiffened-based design with excellent mechanical properties (including load-bearing capacity, broadband vibration suppression and aeroelastic stability) can provide some insights and potential application of metamaterial structures for vibration and flutter controls of the supersonic plate.