No / Concrete filled steel tube (CFST) columns are becoming increasingly popular due to the advantages they offered. They are not only considered aesthetically pleasing but can also offer significant improvement in axial capacity without increases in crosssectional area being required. Elliptical steel hollow sections represent a recent and rare addition to the range of cross-sections available to structural engineers, however, despite widespread interest in their application, a lack of verified design guidance is inhibiting uptake. The use of elliptical steel hollow section with concrete infill is new and innovative, not only provides the advantage mentioned above, but also on the basis of both architectural appeal and structural efficiency. The aim of this paper is to investigate the behaviour of the elliptical CFSTs under axial loading. A total of 12 specimens were tested with wall thicknesses of 4 mm, 5 mm, 6.3 mm and concrete core strength of 30 MPa. This paper reported on the behaviour of concrete filled elliptical hollow sections under axial load. The effect of the wall thickness of the steel section, the bond between steel and concrete and the concrete confinement are presented.

I Sverige kan VKR (varmformade konstruktionsrör) vara 15-23 % dyrare än KKR (kallformade konstruktions­rör) av samma tvärsnittsstorlek. Trots detta lägre pris på KKR har det upp­skattats att i Svensk stål­byggnation används endast 5 % KKR, av det totala användandet av VKR och KKR. I detta examensarbete har det först undersökts vilka skillnader i egenskaper som finns mellan VKR och KKR. Därefter beräknas prisdifferensen mellan de två profiltyperna när de utsätts för en centrisk tryckkraft under likadana förhållanden. Målet är att ta reda på vilket som är det mest ekonomiskt lönsamma alternativet i valet mellan VKR och KKR. Tryckkraftskapaciteten med hänsyn till knäckning för alla profilstorlekar i Tibnor konstruktions­tabeller har beräknats för varje möjlig kombination av tio olika längder mellan 1 till 10 m, tio olika laster mellan 100 till 1000 kN och två olika upplagsförhållanden, ledad i båda ändarna eller fast inspänd i båda ändarna. De KKR‑ respektive VKR-profiler med lägst pris, som håller för lasten, har jämförts och prisdifferensen mellan dessa redovisas genom att ange hur många procent dyrare, eller billigare, VKR är i jämförelse med KKR. I 80 % av mätningarna vid ledad infästning i båda ändarna blev KKR det mest ekonomiskt lönsamma alternativet. Samma siffra blev 86 % för fast inspänd i båda ändarna. Den genomsnittliga pris­differensen hamnade på 10-11 % med ett spridningsmått på 8-12 %. Detta leder till slutsatsen att ett användande av enbart KKR kan resultera i be­sparingar på ca 10‑11 % i stålkostnader, jämfört med att enbart använda VKR. Utifrån pris­differensernas variation dras därefter slutsatsen att det inte finns några tendenser på att VKR eller KKR är mer lönsam än den andra inom något specifikt längd- eller lastintervall. Rekommendationen är att i första hand optimera och använda den profiltyp som är mest lönsam för rådande förhållanden. Om en optimering inte är möjlig blir istället rekommendationen att använda KKR. / In Sweden, hot formed rectangular hollow sections (HFRHS) can be 15-23 % more expensive than cold formed rectangular hollow sections (CFRHS) of the same section size. Although the price on CFRHS is lower, estimations reveals that   - from the total use of HFRHS and CFRHS in Swedish steel buildings - CFRHS is only utilized by less than 5 % compared to 95 % HFRHS. This study began by examining the differences between these two types of steel. The price difference between the two processed metal types was then calculated when both of them were subjected to a centric compressive force under the same conditions. The purpose was to compare prices and find out which one is the most economically feasible, offering a more profitable choice between HFRHS or CFRHS. The design buckling resistance of all the section sizes in Tibnor kon­­struktions­tabeller was calculated for every possible combination out of ten different lengths between 1 m and 10 m, ten different loadings between 100 kN and 1000 kN and two different support conditions being pinned at both ends and fixed at both ends. The sections sizes of CFRHS and HFRHS that withstood the loading and held the lowest prices were compared by calculating the price difference as per­centage increment or decrement between the two types of hollow sections. In 80 % of the cases, when pinned at both ends, CFRHS showed to be the most economically feasible alternative. When fixed at both ends the same number was 86 %. The average price difference was 10-11 %, showing an absolute deviation of approximately 8‑12 %. These findings conclude that using only CFRHS can result in savings of 10‑11 % from reduced costs of steel, compared to only using HFRHS. From the observed variation of the price differences another conclusion is drawn that there aren’t any tendencies showing HFRHS or CFRHS to be more economically feasible than the other in a specific interval of length or loading. The recommendation is to optimize and use the type of steel that is the most economically feasible under the current circumstances. If an optimization isn’t possible then the recommendation is to use CFRHS.

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No / This paper presents the behaviour and design of axially loaded concrete filled stainless steel circular and square hollow sections. The experimental investigation was Conducted using different concrete cube strengths varied from 30 to 100 MPa. The column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with existing design methods for composite carbon steel sections-Eurocode 4 and ACI. It was found that existing design guidance for carbon steel may generally be safely applied to concrete filled stainless steel tubes. though it tends to be over-conservative. A continuous strength method is proposed and it is found to provide the most accurate and consistent prediction of the axial capacity of the composite concrete filled stainless steel hollow sections due largely to the more precise assessment of the contribution of the stainless steel tube to the composite resistance.

<p> Trusses and Vierendeel girders are usually built from a single chord HSS "Hollow Structural Sections", but the largest HSS size as produced in Canada may limit its use for longer span applications. Therefore, the possibility of using double chord sections to enable the use of HSS for longer span trusses without the need for manufacturing new larger sections, presented itself. </p> <p> A new concept utilizing double chord square hollow sections in welded K-joints of Warren trusses is described. The experimental results of 29 tests are reported, including four connections types — standard, channel, bolted and back-to-back. The latter type comprised of gapped, overlapped and gapped with connecting stiffener plates. </p> <p> The results indicate that the standard type is an excellent joint in both strength and stiffness. The channel type is generally susceptible to twisting. It was found adequate only when a significant increase in chord thickness (≃ 50%) was employed. The bolted connection appears to hold promise when on-site assembly of large trusses is necessary. Its performance was further improved by connecting the chords with small tie bars. The back-to-back type needed to be reinforced or fully overlapped to develop full branch member strength. </p> <p> The double chord system of connection reveals itself to be much superior in strength to an equivalent single chord joint. </p> <p> The effects of eccentricity, branch member to chord angle, and chord preloading were investigated. Interaction formulae are presented for the standard and channel type joints which suffered from a chord failure at the connection. </p> <p> Results of four T-type connections using the double chord concept are also reported and were recently published in the ASCE (8). </p> / Thesis / Doctor of Philosophy (PhD)

The purpose of this research is to examine the behaviour of elliptical concrete-filled steel tubular stub columns under a combination of axial force and bending moment. Most of the research carried out to date involving concrete-filled steel sections has focussed on circular and rectangular tubes, with each shape exhibiting distinct behaviour. The degree of concrete confinement provided by the hollow section wall has been studied under pure compression but remains ambiguous for combined compressive and bending loads, with no current design provision for this loading combination. To explore the structural behaviour, laboratory tests were carried out using eight stub columns of two different tube wall thicknesses and applying axial compression under various eccentricities. Moment-rotation relationships were produced for each specimen to establish the influence of cross-section dimension and axis of bending on overall response. Full 3D finite element models were developed, comparing the effect of different material constitutive models, until good agreement was found. Finally, analytical interaction curves were generated assuming plastic behaviour and compared with the experimental and finite element results. Ground work provided from these tests paves the way for the development of future design guidelines on the member level.

This paper presents the details of an experimental investigation on the behaviour of axially loaded concrete-filled stainless steel elliptical hollow sections. The experimental investigation was conducted using normal and high strength concrete of 30 and 100 MPa. The current study is based on stub column tests and is therefore limited to cross-section capacity. Based on the equations proposed by the authors on concrete-filled stainless steel circular columns, a new set of equations for the stainless steel concrete-filled elliptical hollow sections were proposed. From the limited data currently available, the equation provides an accurate and consistent prediction of the axial capacity of the composite concrete-filled stainless steel elliptical hollow sections.

no / The behaviour of circular concrete-filled steel tubes (CFT) with various concrete strengths under axial load is presented. The effects of steel tube thickness, the bond strength between the concrete and the steel tube, and the confinement of concrete are examined. Measured column strengths are compared with the values predicted by Eurocode 4, Australian Standards and American Codes. 15 specimens were tested with 30, 60 and 100 N/mm2 concrete strength, with a D/t ratio from 22.9 to 30.5. All the columns were 114 mm in diameter and 300 mm in length. The effect due to concrete shrinkage is critical for high-strength concrete and negligible for normal strength concrete. All three codes predicted lower values than that measured during the experiments. Eurocode 4 gives the best estimation for both CFT with normal and high-strength concrete.

Although branch plate connections with circular hollow section (CHS) members are simple to fabricate and cost-effective, they are generally very flexible under low load application resulting in the limit states design resistance being governed by an imposed deformation limit. Restricting the ultimate capacity of a branch plate connection by a deformation limit results in the inherent strength of the CHS member being under-utilized, highlighting the need to develop connection stiffening methods. Two methods to stiffen branch plate-to-CHS connections are examined: a through plate connection and a grout-filled CHS branch plate connection. Further, the current design guidelines of various plate-to-CHS connection types are reexamined including the effect of chord axial stress and chord length on connection behaviour. Finally, the behaviour of connections with non-orthogonal or skew plate orientation, which has not previously been examined, was studied in depth.The behaviour of these uniplanar connection types under quasi-static axial loading was studied through 16 large-scale laboratory experiments and 682 numerical finite element analyses, as well as an extensive review of all previous international experimental and numerical findings. The extensive study formed the basis for a complete set of proposed design guidelines and provided insight into plate-to-CHS connection behaviour. For all plate-to-CHS connection types, the plate thickness is shown to effect connection capacity, though previously this was thought not to have significant impact on connection behaviour. The existing ideology of using the same design recommendations for tension- and compression-loaded connections, which was developed from compression results, under-utilizes an inherent increase in capacity provided by a connection primarily loaded in tension. As such, the recommended design guidelines split the two load senses into separate expressions that reflect the difference in behaviour. Stiffened through plate connection behaviour was determined to be the summation of branch plate behaviour in compression and tension, leading to a significant increase in capacity and identical behaviour regardless of branch load sense. The skewed branch plate connection behaviour was found to relate directly to the established behaviour of longitudinal and transverse plate connections. A design function was developed that interpolates the capacities of intermediate angles by using the proposed design recommendations of the two extreme connection types. Finally, the examination of chord axial stress and chord length for plate-to-CHS connections yielded results similar to previous international studies on CHS-to-CHS connections. The effect of chord length, however, has wide-reaching implications as to how experimental and numerical FE research programs are developed.