Types Of Stiffeners Research Articles

Seismic performance of TOBs bolted endplate connection to concrete-filled square steel tube with damaged hole threads repaired by using spiral wire inserts

Thread-anchored One-side Bolts bolted Endplate Connections to Concrete-Filled Square Steel Tube (TOBEC-CFSSTs) have a great potential in steel structures for its excellent behavior and ease of construction, but the hole threads of the column wall are easily damaged on account of non-standard operations of workers in the installation process. Thereupon, this paper proposes a novel thread repairing method, i.e. Spiral wire inserts, to repair the damaged hole threads, which ensures the safety of TOBEC-CFSSTs. Tests on seven specimens were conducted to investigate the seismic behavior of the hole threads-repaired connections with inner stiffeners under cyclic loading. The experimental parameters contained the inner stiffener type, the thread anchored length, the anchorage detail of bolt and the endplate thickness. The performance of the connections with repaired threaded holes were analyzed and compared in terms of failure modes, strength and rigidity, the ductility and the energy dissipation capacity. It was found that the connections using spiral wire inserts to repair the hole threads can exhibit a comparable mechanical property to that with intact hole thread. Besides, the presence of the epoxy adhesive in bolted endplate connections made the assembly of components more flexible without considering the concrete cast sequence, which revealed that the TOBEC-CFSSTs with repaired threaded holes would present extensive application prospects in prefabricated or built-up modular steel buildings. • Spiral wire inserts were used to repair threaded holes for Thread-fixed One-side bolts (TOBs). • TOBs bolted Endplate Connections under cyclic loads were tested. • Moderate strengthening component can enhance ductility and energy dissipation capacity. • Effects of concrete cast sequence on connection seismic behavior were presented.

Seismic performance of TFOSBs bolted endplate connection to CFSST with repaired threaded holes

This paper evaluates the seismic behavior of short thread-fixed one-sided bolts (TFOSBs) bolted connection of an I-section beam to concrete-filled square steel tube (CFSST) with repaired threaded holes by enlarging threaded holes through cyclic tests. The parameters investigated were endplate thickness, inner stiffener type, thread anchored length and bolt installation sequence. The test results are presented in terms of strength, rigidity, ductility and energy dissipation capacity. Based on the experimental results: 1) the failure modes of the connections with repaired threaded holes by enlarging threaded holes were similar to the failure modes of the connections having intact hole threads; 2) the connections with repaired threaded holes exhibited 1.8% ∼ 23.8% higher ductility and 3.9% ∼ 46.6% higher energy dissipation capacity compared with the connections having intact hole threads, and the ultimate bearing capacity of those two types of joints were comparable; and 3) the bolt installation sequence has a negligible influence on the failure modes and seismic behavior of connections with repaired threaded holes. In addition, the existing calculation methods of yield moment capacity for TFOSBs bolted endplate connections under various failure modes were still suitable for connections with repaired threaded holes, and the theoretical values and test results were well-matched with errors no greater than 15%.

Computing steel frame analysis of behavior semi-rigid connection

Semi-rigid connections are very economical compared to other connections because they can prevent the frame from breaking immediately due to brittleness without endangering the entire structure. Steel frame construction is one of the types of construction described in the building codes for simple seismic buildings. The research on the use of this semi-rigid connection uses one of the computer software that uses the finite element method, namely ANSYS ED.9, by taking validation models from experimental and manual calculation analysis and using 35 research models with different loads, positions and number of bolts and types of portal bracing. The ability to survive on the gantry due to side loads is dominated by the number and position of the bolts and the type of gantry stiffener used, this is evident from the different models, with the rise ratio in each model ranging from 0.7852 to 2.5900 and in ranges of softening compared to clamped stiffeners, which experience a decrease in stress, with the same ratio.

Nonlinear buckling analysis of FGM plates stiffened by different FGM stiffener types

In this paper, the nonlinear buckling behavior of functionally graded material (FGM) plates subjected to an axial compression is analytically investigated. Assuming that the plates are stiffened by FGM rectangular, I- and T-stiffeners. The formulations are established by using the classical plate theory considering the geometrical nonlinearities of von Karman. The Lekhnitskii’s smeared stiffener technique is developed for different types of FGM stiffeners. The Galerkin method is utilized to obtain the nonlinear algebraically equation system, then, solve it to determine the explicit expressions of critical buckling loads and postbuckling load–deflection curves of plates. Numerical examples validate the effects of different types of FGM stiffeners, material and geometrical parameters on nonlinear behavior of plates.

Nonlinear buckling analysis of FGM plates stiffened by different FGM stiffener types

In this paper, the nonlinear buckling behavior of functionally graded material (FGM) plates subjected to an axial compression is analytically investigated. Assuming that the plates are stiffened by FGM rectangular, I- and T-stiffeners. The formulations are established by using the classical plate theory considering the geometrical nonlinearities of von Karman. The Lekhnitskii’s smeared stiffener technique is developed for different types of FGM stiffeners. The Galerkin method is utilized to obtain the nonlinear algebraically equation system, then, solve it to determine the explicit expressions of critical buckling loads and postbuckling load–deflection curves of plates. Numerical examples validate the effects of different types of FGM stiffeners, material and geometrical parameters on nonlinear behavior of plates.

Nonlinear buckling analysis of FGM plates stiffened by different FGM stiffener types

In this paper, the nonlinear buckling behavior of functionally graded material (FGM) plates subjected to an axial compression is analytically investigated. Assuming that the plates are stiffened by FGM rectangular, I- and T-stiffeners. The formulations are established by using the classical plate theory considering the geometrical nonlinearities of von Karman. The Lekhnitskii’s smeared stiffener technique is developed for different types of FGM stiffeners. The Galerkin method is utilized to obtain the nonlinear algebraically equation system, then, solve it to determine the explicit expressions of critical buckling loads and postbuckling load–deflection curves of plates. Numerical examples validate the effects of different types of FGM stiffeners, material and geometrical parameters on nonlinear behavior of plates.

Seismic behavior of TOBs bolted endplate connection to strengthened CFST column

When using the Thread-anchored One-side Bolts (TOBs) which are a type of one-side bolts anchored through the tube wall hole threads instead of the nuts, the conventional Concrete Filled square Steel Tube (CFST) with the limited wall thickness fails to provide the sufficient thread anchored length to resist the tensile force of TOBs. Meanwhile, the joint region of the relatively thin tube wall is prone to deform outward to a large degree, which is crucial to the safety of the whole structure. To solve the above issues, in this work an experimental investigation on TOBs bolted Endplate Connection to strengthened CFST (TOBEC-CFST) under cyclic loads is conducted by putting a stiffener inside the CFST. Six specimens were designed to study the effects of following parameters: (a) stiffener type (the inner polygonal tube stiffener or the cross-H section stiffener); (b) thread anchored length (18 mm and 24 mm); and (c) bolt diameter (M16, M20 and M22). The experimental results revealed that the hole thread fracture can be avoided by increasing the stiffener flange thickness to extend the hole thread length and the inner stiffener can improve the behavior of the panel zone of the connection. Compared to the inner polygonal tube stiffener, the cross-H section stiffener can effectively enhance the overall integrity of the connection because of the presence of the web transferring force directly to the opposite tube wall, contributing to a higher bearing capacity and energy dissipation capacity of the joints. Increasing the bolt diameter can improve the bearing capacity and energy dissipation capacity of TOBEC-CFSTs, but the degree of the improvement does not increase linearly with bolt diameter. Based on test results, to enhance the overall mechanical behavior of TOBEC-CFSTs in seismic zones, the cross-H section stiffener is recommended provided for sufficient thread length.

Static behavior of large-diameter stiffened steel tubes for wind turbine towers under combined compression-bending-torsion load

Thin-walled steel tubes have been widely used in wind turbine towers. These towers are commonly subjected to combined compression-bending-torsion loads; thus, the steel tubes are prone to local buckling. Installing stiffeners has proven an effective method to improve the local stability of the thin-walled members. This paper presents an experimental and analytical study of thin-walled steel tubes strengthened by longitudinal stiffeners. Six specimens with different types of stiffeners and various diameter-thickness ratios were tested under a combined compression-bending-torsion load. The failure modes, load–displacement relationships, ultimate strength, and deformability were revealed. The validated finite element model was used to analyze the structural mechanisms of the stiffened steel tubes. The results show that stiffeners can substantially alleviate the local buckling of steel tubes, significantly improving their ultimate strength and plastic deformability. In addition, T-type stiffeners perform better than I-type stiffeners. The ultimate strength of the specimens is preliminarily evaluated using the methods recommended in existing design guidelines. The calculated ultimate strength of the unstiffened specimens shows a good agreement with the test results, whereas the ultimate strength of the stiffened specimens is underestimated.

Structural behaviour of post-earthquake steel plate shear wall repaired by non-welded oblique stiffeners

A two-stage experimental study was conducted to investigate the structural behaviour of two single-span two-storey steel plate shear wall (SPSW) specimens repaired by non-welded oblique stiffeners. In stage Ⅰ, both SPSW specimens were subjected to a quasi-static load to simulate the damage under an earthquake attack. Afterwards, the infill panels in one SPSW specimen were repaired and stiffened by non-welded oblique stiffeners (i.e., specimen OR-SPSW). The damaged SPSW specimens with or without repair were subjected to cyclic load to evaluate the effectiveness of the repair method in stage II. The seismic performance of two SPSW specimens was compared in terms of initial stiffness, bearing capacity, energy dissipation capacity and out-of-plane deformation of infill panels. Test results indicate that the residual out-of-plane deformations of infill panels were effectively restrained after the installation of oblique channel steel. The bearing capacity of specimen OR-SPSW was 11.06% higher than that without repair. In addition, the finite element analysis was performed to further investigate the seismic performance of the SPSW structures repaired by various types of stiffeners, including oblique multi ribs, orthogonal and oblique channel steel. The simulation results indicate that using the three types of stiffeners is able to restore the seismic behaviour of SPSW structures, while using the oblique multi-rib stiffeners is the most effective method in restraining the out-of-plane deformation of infill panels and increasing the bearing capacity. However, the orthogonal channel steel stiffener can contribute to little enhancement of the structural bearing capacity. Besides, the bearing capacity of the SPSW structure repaired by the oblique multi-rib stiffeners was 14.29% higher than that with the oblique channel steel stiffeners.

Bond stress-slip relationship in concrete-filled square stainless steel tubes

The application of stainless steel tubes in concrete-filled steel tube systems can significantly improve their corrosion resistance in comparison with those that employ carbon steel tubes. In this paper, a series of push-out tests were carried out to investigate the bond stress-slip behavior between stainless steel tubes and concrete. A total of 14 concrete-filled square stainless steel tube specimens were tested, covering two cross-sectional width-thickness ratios (B/t = 30 and 50), two concrete strength (fcu = 44 and 76 MPa), three rib stiffener types (ordinary, saw-shaped and perfobond leister) and two stainless steel grades (austenitic and duplex). The test results indicate that B/t, fcu and stainless steel grade have noticeable influences on the ultimate bond stress (τu) in concrete-filled square stainless steel tube and the addition of rib stiffeners significantly improves the bond behavior. The bond mechanism at different stages of loading and the effect of various parameters on τu are discussed. Based on the test results, an idealized bond stress-slip strain (τ-εS) curve was proposed, where good agreement between the test and the proposed model has been achieved.

Performance Analysis of Castellated Steel I-Beam using FRP Stiffeners

Abstract: Castellated beams are now widely used for a variety of structural applications. Castellated beams are the ones which have perforations in their web part. However, these perforations increase stress concentration around the openings, and also get subjected to web post-buckling. To reduce these post-buckling failures and increase the load-carrying capacity, the castellated steel I-beams are provided with different types of stiffeners at various locations. In this paper, the behaviour of a hexagonal castellated steel I-beam (ISMB) under point loading is investigated using carbon fibre polymer (CFRP) strips as stiffeners. Two different types of CFRP strip stiffeners are provided in the transverse direction and around the openings of the castellated beam. The finite element analysis of these stiffeners has been carried out by using ABAQUS software. The results show that the use of CFRP stiffeners for castellated beams enhances load-carrying capacity up to 20% and reduces the deflection by 12% as compared to the control castellated beam. The use of transverse CFRP stiffener reduces the web buckling failure and increases the load carrying capacity effectively as compared to the stiffeners used along the openings. As a result, it is preferable to use transverse stiffeners instead of the stiffeners used along of the openings. Keywords: Abacus software, Castellated beam, CFRP, Openings, Transverse stiffeners

Effects of Stiffener Type on Fatigue Resistance of Steel-UHPC Composite Bridge Decks

Recent research showed that ultrahigh-performance concrete (UHPC) and orthotropic steel bridge decks could be integrated to form steel-UHPC composite sections offering superior load-carrying capacity and fatigue resistance. This study investigates the effects of longitudinal stiffener types on the fatigue resistance of steel-UHPC composite sections. Three types of longitudinal stiffeners were compared, including U-ribs, bulb flat ribs, and plate ribs. Finite element analysis and full-scale fatigue tests were performed to investigate the load-carrying capacity and fatigue resistance of the composite bridge decks with different stiffeners. Besides, the proposed steel-UHPC composite bridge decks were compared with conventional orthotropic steel decks. The results show that steel box girders with bulb flat rib composite deck have reasonable fatigue resistance, construction efficiency, and economic benefits. This study is expected to promote the design and evaluation of economic steel-UHPC composite bridge decks to achieve higher mechanical performance and long-term durability.

Experimental and numerical study of fire performance of L-shaped concrete-filled steel tubular columns under eccentric compression

Six special-shaped columns composed of concrete-filled steel tubes (CFST) were designed and tested based on the ISO-834 temperature curve to access their fire performance under eccentric loads. Key test variables include the types of stiffener, load eccentricity, as well as load angle, and the failure modes, temperature distribution, and deformation of specimens were analyzed. The test outcomes indicate that the L-shaped CFST columns’ fire resistance declines as the load eccentricity rises, but its decrease amplitude narrows under a relatively high eccentricity. Besides, the impact exerted by the load angle on the columns’ fire resistance is also significant. A Finite Element Analysis (FEA) method was carried out afterward and compared with the test outcomes. Moreover, an extensive parametric analysis containing 2008 FEA models was developed to study the impact of major parameters on the L-shaped CFST columns’ fire resistance, namely load ratio (n), slenderness ratio (λ), column limb width (B), column limb depth-to-width ratio (D/B), load eccentricity ratio (e/r0), steel ratio (αs), steel strength (fy), concrete strength (fck), and load angle (θ). The analysis results imply that the parameter of load ratio (n) remarkably affects the columns’ fire resistance, while the other parameters exert a certain impact on the fire resistance when n < 0.5. Given the test and analysis, a simplified calculation approach for the fire resistance of L-shaped CFST columns is designed.

Parametric investigation of vibration of stiffened structural steel plates using finite element analysis and grey relational analysis

Thin plates with arbitrary shapes and stiffeners find wide usage in construction, aerospace, marine, etc. industries. In the present work a parametric investigation of thin structural steel plates has been carried out. The design parameters considered were the subtended angle and aspect ratio of plates to account for the different shapes of plates used for various applications. Another design parameter that was considered is the stiffener and its different orientation. The impact of varying parameters on the first five modal frequencies and in turn the stiffness was considered as the response. Finite element method (FEM) coupled with Taguchi’s L16 orthogonal array and grey relational analysis was used to maximize the first five natural frequencies simultaneously. The thin plate was subjected to modal analysis when all its sides are in simply supported boundary condition. The optimum combination of design variables predicted by grey relational analysis is a thin plate with 80° subtended angle, 1.75:1 aspect ratio and crossed stiffener orientation for simultaneous maximization of the frequencies. Analysis of variance revealed highest contribution of stiffener type which affects the first 5 natural frequencies simultaneously.

FULL-SCALE MEASUREMENTS OF WELDING-INDUCED INITIAL DEFLECTIONS AND RESIDUAL STRESSES IN STEEL-STIFFENED PLATE STRUCTURES

Plated structures such as ships and offshore structures are constructed using welding techniques that attach support members (or stiffeners) to the plating. During this process, initial imperfections develop in the form of initial deformations (deflections or distortions) and residual stresses. These initial imperfections significantly affect the buckling and ultimate strength of these structures. Therefore, to assess the strength of welded plate structures, it is very important to predict the magnitude and pattern of welding-induced initial imperfections and their effects on buckling and ultimate strength. To determine the reliability of the prediction methods, it is desirable to validate the theoretical or numerical predictions of welding-induced initial imperfections through comparison with full-scale actual measurements. However, full-scale measurement databases are lacking, as they are costly to obtain. This study contributes to the development of a full-scale measurement database of welding-induced initial imperfections in steel-stiffened plate structures. The target structures are parts of real (full-scale) deckhouses in very large crude oil carrier class floating, production, storage and offloading unit structures. For parametric study purposes, four test structures by varying plate thickness are measured while the stiffener types and weld bead length are fixed. Modern technologies for measuring initial deformations and residual stresses are applied. The details of the measurement methods are documented for the use of other researchers and practicing engineers who welding-induced initial imperfections.

Güçlendirilmiş Dört Folyo Kesitli Al6061 Tüplerinin Eksenel ve Eğik Darbe Koşulları Altında Çarpışma Dayanıklılık Performansı

This study presents the crashworthiness performance of Al6061 tubes with stiffened quatrefoil sections under axial and oblique impact conditions. Influences of different types of stiffeners through the depth of tubes in the design of a quatrefoil sectional crash absorber structure are investigated, numerically. Four types of stiffener patterns are considered under oblique impact angles of 0º, 10º, 20º, and 30º measured from the horizontal axis. Force-displacement characteristics, deformation patterns, and crashworthiness indexes of the tested tubes are given to decide optimal crash absorber configuration. The numerical tube models are placed between two rigid plates and an axial impact speed of 1m/s is considered in the numerical study. Al6061 series aluminum alloy is used as a tube material with a multi-linear material model assuming strain-rate independent properties. It is found that the crashworthiness performance is very sensitive to impact angle and Q-S-4 type stiffeners can be proposed for a better tube design.

Güçlendirilmiş Dört Folyo Kesitli Al6061 Tüplerinin Eksenel ve Eğik Darbe Koşulları Altında Çarpışma Dayanıklılık Performansı

This study presents the crashworthiness performance of Al6061 tubes with stiffened quatrefoil sections under axial and oblique impact conditions. Influences of different types of stiffeners through the depth of tubes in the design of a quatrefoil sectional crash absorber structure are investigated, numerically. Four types of stiffener patterns are considered under oblique impact angles of 0º, 10º, 20º, and 30º measured from the horizontal axis. Force-displacement characteristics, deformation patterns, and crashworthiness indexes of the tested tubes are given to decide optimal crash absorber configuration. The numerical tube models are placed between two rigid plates and an axial impact speed of 1m/s is considered in the numerical study. Al6061 series aluminum alloy is used as a tube material with a multi-linear material model assuming strain-rate independent properties. It is found that the crashworthiness performance is very sensitive to impact angle and Q-S-4 type stiffeners can be proposed for a better tube design.

Autologous rib cartilage as implanted stiffener of phalloplasty: comparing three different methods

BackgroundMaintaining the length, rigidity, and appearance of a reconstructed phallus in the long term has been challenging for phalloplasty and may depend on choosing the optimal implanted stiffener. The aim of this study was to determine the best type of stiffener for a reconstructed phallus regarding aesthetic and functional parameters. MethodsFrom 1987 to 2018, 376 individuals underwent phalloplasty at a single institution of which 81 met the following inclusion criteria: biological male gender, age between 18 and 60 years, radial forearm flap for tube-within-a-tube phalloplasty with rib cartilage and secondary glans sculpting and unimpaired urination preoperatively. Those were divided into three groups with regard to different types of autologous rib cartilage stiffener. A group with a cartilage strip, T-shaped cartilage, and mushroom-shaped cartilage group were evaluated regarding preserved length and aesthetic features of the phallus during a minimum period of 12 months. The rib cartilage length in the phallus was 10.5 cm in all groups. ResultsThe length of the phallus was 10.8 ± 0.5 cm in the cartilage strip group, 11.3 ± 0.3 cm in the T-shaped cartilage group and 11.3 ± 0.3 cm in the mushroom-shaped cartilage group at 1-year postoperatively. The aesthetic appearance score of mushroom-shaped cartilage group was 1.67 ± 0.48, significantly higher than the cartilage strip group (1.38 ± 0.50, p = 0.03) at 1 year after surgery. ConclusionsThe mushroom-shaped autologous rib cartilage group showed superior length preservation and aesthetic appearance and appeared as the best type of stiffener for one-phase phalloplasty.

Experimental investigation on monotonic bending behaviour of TSOBs bolted beam to hollow square section column connection with inner stiffener

In the reported research results on T-head Square-neck One-side Bolts (TSOBs) bolted Endplate Connection (TSOB-EC), the failure of TSOB pulling-out due to the punching shear failure of Hollow Square Section Column (HSSC) wall is typical, which should be avoided. Two types of inner stiffeners that have H-section and double channel section are used to improve the punching shear resistance of the HSSC wall. At the same time, the inner stiffeners are used as connection splices to connect the upper column and the lower. The effect of the length and plate thickness for the stiffener on the connection performance are also studied. A total of six TSOBECs with stiffeners were tested under monotonic bending moment. The test results show that the stiffeners can avoid the bolt pulling-out failure and improve the deformation capacity of TSOBEC. The yield bending moment and peak bending moment of TSOBEC can be increased by 8.1%∼31.8% and 11.6%∼21.7% by double channel stiffeners, respectively, and improved by 69.3%∼72.6% and 22.5%∼39.4% by H-steel stiffeners, respectively. The analytical models for predicting the bending moment capacity of TSOBEC with stiffeners are proposed and the prediction results are accurate with an error within 5%. In addition, extended H-steel stiffener is recommended for designing the strengthened TSOBEC, and the cross-section of the stiffener needs to be calculated by the proposed models to ensure that the H-steel stiffener and HSSC do not deform even if the joint fails.

A practical design formulation for perforated beams with openings strengthened with ring type stiffeners subject to Vierendeel actions

In this paper, the effect of ring type stiffeners on the Vierendeel mechanism of perforated beams with various opening shapes is investigated. Vierendeel mechanism causes beams to fail with four plastic hinges that occur in the vicinity of large and usually isolated web openings. The practical ring type stiffeners are used in this study to increase the mechanical strength of perforated beams. The effects of stiffener thickness and stiffener height are analyzed for different stiffener thickness to web opening diameter and stiffener height to web thickness ratios . A beam profile of UB457 × 152 × 52 and of steel grade S275 is employed. Finite element analysis is conducted with both geometric and material non-linearities to obtain the failure loads for different cases of perforated beams. Shear/moment interaction diagrams are also obtained so that they can be directly used by practicing engineers. Such interaction curves are plotted for various opening shapes with stiffeners to demonstrate the effect of stiffeners on the Vierendeel mechanism. Yield patterns of various beams with different web opening shapes and ring type stiffeners are also presented. Moreover, a design formulation is derived for direct use by engineers. This study has ultimately shown that, the stiffener's thickness and height has different shear and moment effects on the performance of perforated beams depending on the opening type and web opening diameter. • A non-linear FE study was carried out to understand the effect of ring type stiffeners. • A comprehensive parametric study is performed on perforated beams. • Shear and moment capacities as well as the Vierendeel mechanism for perforated beams with three different web opening shapes are investigated. • A Design recommendation scheme is provided for selecting a suitable shear ratio. • The bigger the stiffener thickness, the higher moment utilization ratio is achieved independent of the opening size and shape. • Independent of the web opening shape, it is more effective to use a ring type stiffener if the diameter to height ratio is high.