Free Flange Research Articles

Experimental Investigation of the Failure Scenario of Various Connection Types between Thin-Walled Beam and Sandwich Panel.

The paper presents failure scenarios for various types of connections between a thin-walled beam and a sandwich panel. In addition to standard connections used in civil engineering applications, that is, self-drilling fasteners for sandwich panels, the study examined the use of bolts, blind rivets, and double-sided acrylic tape applied linearly and pointwise. The connections were subjected to the horizontal load applied with constant eccentricity with respect to the plane of the connection surface. This load arrangement simulates the behaviour of a free flange of the thin-walled beam in bending while lateral-torsional buckling occurs. In this way, the research covers the determination of the lateral stiffness of the thin-walled beam-free flange, while the other flange is connected to the sandwich panel using various connection systems.

Finite Element Analysis of Overlapped Z-Purlins Restrained by Sheeting

Cold-formed steel Z-purlins with overlapping at the intermediate supports ensures the continuity of the bending moment. A continuous beam with two equal spans of 6 m is investigated under gravity loading using the finite element method. The numerical model includes the beneficial interaction between the Z-purlins and the trapezoidal sheeting. Finite element results show that the screw spacing and sheeting thickness has a limited influence on the resistance of the member. The effect of the overlapping length and detailing of the connection is studied through a parametric study. Six overlaps varying from 100mm to 1200mm (1.6% to 20% of one span) capture the change of the failure mode from the overlap edge to the support region of the purlin. The connection detailing is studied considering multiple bolt/screw patterns. The detailing and length of the overlap connection has a major influence on the moment distribution and consequently on the failure mode. The detailed finite element analysis shows that assuming the beam connection as continuous in 1D beam models lead to an unrealistic bending moment distribution and failure mode. Connecting the bottom flange using screws improves the overall load carrying capacity of the beam especially for short overlap lengths. The increase in resistance is attributed to the restraining effect on the free flange which fails due to distortional buckling.

Effective Width of the Free Flange of the Ship’s Wide Beam with an Axis Bend

Effective Width of the Free Flange of the Ship’s Wide Beam with an Axis Bend

Determining the elastic-plastic effective width of the free flange of a hull girder with the breaking of a wall

This paper reports the dependences that have been derived to determine the effective width of a free flange in a dangerous cross-section of the wide-flange hull girder with the breaking of the wall/edges/axis at elastic-plastic deformation depending on the applied load for a perfectly plastic material without strengthening. Currently, there are no systematic dependences to determine the effective width of the free flange of girders of this type, except for certain cases. The technique is suitable for use for both purely elastic and elastic-plastic deformation. To calculate the stressed-strained state (SSS), a finite-element method (FEM) was used to solve the three-dimensional problem from the elasticity and plasticity theory. It has been shown that the node is exposed to simple loading. The reported results were derived within the framework of the deformation theory of plasticity. The largest ratio of external load to the boundary of fluidity is 0.9. The estimation scheme takes into consideration the most unfavorable working conditions of the examined node when the safest data are acquired. The dependences were built for the theoretical coefficient of concentration in a dangerous cross-section, which is used in the proposed procedure to determine the moment of transition from the elastic stage of deformation to elastic-plastic. When determining the effective width, the complex work of the flange and its deplanation was taken into consideration by defining the SSS components in the median plane. The feasibility of the idea of designing the SSS components on the inclined plane of a free flange has been proven. In this case, there is practically a (quasi) flat stressed state, suitable for the application of classical methods to determine the effective width. The proposed technique simplifies the calculations of the strength of the examined girder.

Web–flange distortional buckling of partially restrained CFS beams under uplift loading

Cold-formed steel members are usually used as purlins in buildings to support roof cladding and thus they can be treated as beams restrained fully or partially in the lateral and torsional directions. However, when these beams are subjected to wind suction loading, their free flange is in compression, which may cause web–flange distortional buckling (WFDB). This paper presents an analytical study on the WFDB of zed-section purlins when subjected to uplift bending. A simplified model is proposed to describe the WFDB of partially restrained purlins, from which the formula for calculating the critical stress of the WFDB is derived. The present model is validated by the results obtained from the finite strip analysis.

Axial load capacity and failure mechanism of flange and ring joints of process piping system

This paper investigates the capacity and failure mechanism of flange and ring joints of a process piping system under axial load using integrated experimental study and finite element analysis (FEA). The experimental results show that the stiffness and strength of the joints are lower than those of the pipes connected by the joints. The flange joint has greater initial stiffness and ultimate capacity than the ring joint, while has smaller ultimate deformation capacity than the ring joint. Under axial tensile load, the flange joint fails by thread shear failure, while the ring joint fails by the pullout of the convex ring from the free flange. Finite element models of the joints are created using the software program ABAQUS for FEA to further understand the experimental results and evaluate the capacity and failure mechanism of the joints. Finally, a simplified method is proposed to calculate the tensile stiffness and capacity of the joints, and design requirements are advised to keep the joints in good sealing performance under tensile loads

Оптимизационное проектирование замковых соединений из эластомера

This paper discusses the development of small boats made of polymeric composites in combination with metal skeleton based on detachable elastic connections. Lock material was polyethylene with hyperelastic properties of an elastomer. Static calculation is performed as per the finite-element method in plane formulation taking into account contact, geometric and physical non-linearity, as well as implementing a step-wise procedure. Design calculation is performed as per the research method approximating the sub-task (quadratic programming). The paper presents calculations for the process of inserting/extracting a rigid bar with round free flange to/from the lock, with determination of maximum responses, strains and stresses of the insert. Variation of geometric parameters yielded a design variant with minimum load on the insert and the same strength properties as the initial design. The study also yielded the analytical design methodology for elastic detachable connections that combines the solutions to non-linear contact problem and the optimization problem.

RESEARCH OF EFFECTS OF DEFECTS ON STABILITY FAILURES OF SEMI-MONOCOQUE STIFFENERS

This article presents further results of the research of effects of model defects on the local buckling of compressed stiffeners in nonlinear finite element (FE) analyses. The main outcomes are confirmation of trends for 10 sets of profile dimensions, final validations of various sets of FE simulations, and designs of practical types of defects with appropriate ratio values. A single node defect and then complex types of defects with alternating distributions of node shifts along one edge, two free flange edges, one flange surface and both flange surfaces are analyzed in this research project. First parts of this paper describe designed FE models with defects, their effects on simulation results, colored graphic visualizations with stress scales and determinations of the sudden failure of stability in the local mode. Then, particular results of FE analyses are validated by a comparison with the results of analytical methods of stability failure. Final detail comparisons of analytical and FE simulation results with data of experimental tests confirm predicted critical buckling forces. The validation of results and design parameters together with the knowledge of effects of model defects on buckling behaviors allows more accurate simulations of internal stiffeners of thin-walled semi-monocoque structures.

Effect of fully restrained beam-to-column connection on the progressive collapse strength of steel moment frames

The beam-to-column connection has been identified as a key element for steel frame structures to maintain the structural integrity during progressive collapse phenomenon. In the current study, in order to assess the effects of beam-to-column connection type on the progressive collapse strength of steel moment frames, the progressive collapse behavior of a steel intermediate moment frame structure was evaluated with 10 different types of fully restrained connections. The progressive collapse strength of these buildings against sudden removal of a column was separately studied using nonlinear static alternate path method presented in Unified Facility Criteria progressive collapse guideline. To consider the nonlinear effects in the structural modeling, plastic hinges for beam and column members and connections were defined and modeled according to the ASCE 41 standard. The results of the progressive collapse analyses indicated that if the plastic hinges of connections are separately defined in addition to the plastic hinges of beams and columns, the structure will have lower progressive collapse strength, and the calculated dynamic increase factor will grow. Among the studied types of connections, the free flange connection had the best performance and the highest strength against progressive collapse.

Optimization of initial blank shape for flexible micro deep drawing of square parts

Micro flexible tool-assisted sheet metal forming is one of the forming techniques that have increasingly attracted extensive attention of researchers. Due to its simplicity, low overall production cost, feasibility of prototyping, this forming process seems appropriate for producing micro components. This work presents an evaluation study on using flexible deep drawing process to produce micro stainless steel 304 square cups. The influence of initial foil thickness and blank shape are investigated in details. An optimization of blank shape is implemented to provide micro square products with net-shape and flange free. The finite element simulations are achieved using the commercial code Abaqus/Standard. The results showed that the initial foil thickness affects the thinning and thickening values of the formed cup wall. As well as, the optimization method is feasible to indicate the optimum initial blank shape for producing free flange- micro square parts.

Deep spinning of sheet metals

Spinning of sheet metals into cylindrical cups is an important sheet metal forming process for its advantages of flexible tooling and very small forming loads. The most challenging aspect in this process is its low formability due to wrinkling formation in the free flange. In this work, a new deep spinning process with roller set aided with blank-holder of constant clearance is proposed aiming to suppress the wrinkling formation in the deformation zone. Experimental work on annealed and hard aluminum sheet metals is carried out to assess the new process. The proposed spinning process has shown rapid increase in the formability of the sheet metals as the roller feed increases. On the other hand, significant increase in the roller feed worsens the formability of sheet metals in conventional spinning. The Limiting Spinning Ratios, LSRs; or the blank to mandrel diameters ratios, have increased from 1.75 using the conventional spinning to 2.40 using the deep spinning with annealed aluminum sheets in one pass. Also, the LSRs have increased from 1.67 using the conventional spinning to 2.24 using the deep spinning with hard aluminum sheets in one pass. New failure modes of flange jamming and wall fracture have been presented and discussed. In addition, the formability limitations, thickness strains, and spun cup form features at different process parameters are experimentally investigated and discussed. Further, a finite element model for the new process is presented and verified showing the limitation of the available shell elements offered by ANSYS Mechanical APDL in modeling the new process.

Stabilisation of continuous Z-purlins by sandwich panels: Full scale experimental approach

The sandwich panel roof supported by continuously connected thin-walled cold-formed Z-purlins with overlapping over intermediate supports is a practical case of very frequent use. Among the two possible directions of investigation mentioned in the code when studying torsional/distortional instability of Z-purlins (i.e. rotational stiffness and linear stiffness) the authors have chosen to look at the notional linear spring placed at the free flange of the purlin. The linear spring is defined by EN 1993-1-3 Annex A5, as an equivalent or alternative to the stabilizing rotational spring generated by the continuous connection of the sandwich panels to purlin upper flange. This type of approach, on authors' opinion, has the advantage to include into the experimental phase, the real imperfections, and support conditions characteristic to such roof systems, having a very important impact on purlin stability behaviour. A description of the proposed full scale arrangement and experimental conditions, plus values of obtained results are given in the paper.

Extending the Direct Strength Method for Cold-Formed Steel Design to Through-Fastened Simple Span Girts and Purlins with Laterally Unbraced Compression Flanges

AbstractA direct-strength method (DSM) prediction approach is introduced and validated for metal building wall and roof systems that are constructed with steel panels through-fastened with screws to girts or purlins. The focus is capacity prediction for simple spans under wind uplift or suction; however, the DSM framework is generally formulated to accommodate gravity loads, continuous spans, standing-seam roofs, and insulated roof and wall systems in the future. System flexural capacity is calculated with the usual DSM approach; global buckling, local-global buckling interaction, and distortional buckling strengths are determined with a finite-strip Eigen-buckling analysis, including a rotational spring that simulates restraint provided by the through-fastened steel panel. The DSM flexural capacity is then reduced with a code-friendly equation consistent with existing standard provisions to account for the additional stress at the intersection of the web and free flange that occurs as the girt or purlin ...

Cyclic Testing of Welded Free Flange Type and Welded Flange Plate Type Weak-Axis Steel Moment Connections

Moment resisting frames are most frequently used in seismic design systems for steel buildings. Following the Northridge and Kobe earthquakes there have been many studies examining the strong axis steel moment connections. In particular, these efforts have been supported by the government in the US. In Korea on the other hand, researches on the seismic behaviours of weak-axis moment connections are difficult to fine even though these connection details have been frequently used as seismic details of local MRF. As a result, the objective of this research is to provide information on the seismic behaviours of welded free flange type(FF) and welded flange plate type(WFP) weak-axis steel moment connections that were quoted by the FEMA. For this purpose, an experimental program was designed and performed with 2 types of weak-axis steel moment connections. From the test results, both FF and WFP type connections revealed to have more than 3% story drift capacity, which satisfy the required performance for OMF systems.

Modeling of through-thickness stress state in adhesive joints connecting pultruded FRP bridge decks and steel girders

The through-thickness performance of adhesive joints connecting pultruded FRP bridge decks and steel girders subjected to loading in the transverse bridge direction was investigated. Deck-to-girder adhesive joints can be assumed as being loaded by uplift forces only (and not by additional bending moments) if the adhesive layer has a minimal thickness of approximately 10 mm. If possible, however, steel web stiffeners should not be connected to the upper flange in order to allow free flange rotation. The tensile stress distribution in the adhesive joint is non-uniform with high stress concentrations below the FRP webs of the cellular deck and above the steel girder web. Alternately inclined deck webs cause significantly higher stresses below the vertical webs. An analytical model allowing the calculation of a representative approximation of the complex uplift stress state in the joint is proposed and validated by numerical and experimental results. Based on this model, a design method for adhesive joints connecting FRP decks and steel main girders can be established.

Design of Cold-Formed Steel Purlins Attached to Roof Sheeting Based on Eurocode 3: Effect of Gravity Load

In the design of cold-formed steel purlins based on Eurocode 3, the lateral bending moment in the free flange of the purlin, when in tension, is assumed to be zero due to flange curling and second order effects. To investigate the validity of this design assumption, non-linear analytical and finite element models for analyzing how the gravity load affects the maximum mid-span stresses in cold-formed steel purlins attached to the roof sheeting are presented in this paper. The second-order effect of tensile stresses induced by the gravity load in the free flange of purlins is investigated by emphasizing on Z and C sections. The results obtained from the two models are compared with Eurocode 3, and they are included in this article. It is observed that for shorter purlin span lengths the design assumption underestimates the maximum mid-span stresses.

An experimental and numerical study on omega stringer debonding

Omega stringers offer interesting structural capabilities and are expected on future aircraft fuselages. In postbuckling mode, the final failure of these structures may occur by stringer debonding between stringer flanges and the skin of the fuselage. In this study, it is demonstrated that the use of fracture mechanics allows to predict skin/omega stringer separation under multiple load cases. Three different load cases and experiments are presented allowing a debonding to start at different locations: at free flange edges or at the inner radius of the omega. Firstly, a skin/stringer configuration subjected to three point bending following the longitudinal axis of the stringer was tested. For this configuration, a numerical study was made and shows the influence of a refined mesh taking into account resin fillets. Secondly, new specimens were obtained by cutting into slices the longitudinal specimen. Those specimens were subjected to four points bending. It has been shown that the upper rolls position of the test jig could modify the debonding location. Numerical models have allowed to determine accurately the debonding location and the associated load level. For some specimens, resin fillets were removed from the flange tips and their effect were assessed numerically and experimentally.

A plastic collapse method for evaluating rotation capacity of full-restrained steel moment connections

An analytical method to model failure of steel beam plastic hinges due to local buckling and low-cycle fatigue is proposed herein. This method is based on the plastic collapse mechanism approach and a yield-line plastic hinge (YLPH) model whose geometry is based on buckled shapes of beam plastic hinges observed in experiments. Two limit states, strength degradation failure induced by local buckling and low-cycle fatigue fracture, are considered. The proposed YLPH model was developed for FEMA-350 WUF-W, RBS and Free Flange connections and validated in comparisons to experimental data. This model can be used to estimate the seismic rotation capacity of fully restrained beam-column connections in special steel moment-resisting frames under both monotonic and cyclic loading conditions.

Experimental Performance of Link-to-Column Connections in Eccentrically Braced Frames

A total of 12 large-scale link-column specimens were tested to study the cyclic loading performance of link-to-column connections in eccentrically braced frames. Four different link-to-column connection types with varying configuration and welding details were tested. Each of the four connection types was tested with three different link lengths to consider a wide range of force and deformation environments at the link-to-column connection. The specimens representing the pre-Northridge practice failed after developing only half of the inelastic link rotation required in U.S. building codes. Additional connection types were tested that implemented improved welding practices, as well as specimens that implement design and detailing modifications. This included connections that used the free flange concept and connections that eliminated the weld access holes. The experimental program and key test results are presented in this paper.

A new genus and species of congrid eel (Teleostei: Anguilliformes: Congridae) from Western Australia

A new genus and species of congrid eel, Castleichthys auritus, is described from a single specimen collected from 396 m off northwestern Australia. It belongs to the subfamily Congrinae and is characterized by a slender and flexible tail, a free flange on the upper lip, no plicae or other ornamentation on skin of head, large eye, uniserial maxillary and mandibular teeth, and conspicuous black pectoral fins. The vertebral formula is 15-36-128.