Concrete - filled steel tube columns - tests compared with Eurocode 4

This paper summarises the data from 1819 tests on concrete-filled steel tube columns and compares their failure load with the prediction of Eurocode 4. The full data is given on the website http://web.ukonline.co.uk/asccs2 . The comparison with Eurocode 4 is discussed and shows that Eurocode 4 can be used with confidence and generally gives good agreement with test results, the average Test/EC4 ratio for all tests being 1.11. The Eurocode 4 limitations on concrete strength could be safely extended to concrete with a cylinder strength of 75 N/mm2 for circular sections and 60 N/mm2 for rectangular sections

Behavior of biaxially loaded concrete-encased composite columns

The theory of nonlinear behavior of biaxially loaded short and slender composite columns is used to study the load-deformation and moment-curvature of four pin-ended composite column specimens tested under axial compressive load and biaxial bending moments in a single curvature. The accuracy of the test results is verified by comparison with analytical results obtained by a method of analysis that includes the nonlinear material properties of concrete and steel and covers the ascending and descending branches of the linear segmented column specimen. A computational method is presented to model the analytical behavior of the biaxially loaded composite column. Its validity is verified by the comparisons with other analytical methods, and the results of experimental tests from four different authors. A generalized interaction equation for the analysis and design of composite columns is presented. Its validity is verified by comparing the results of existing design examples and some test results with the results obtained from the equation. A comparative review of the available design methods currently being used in the United States is presented. Their major differences, compatibilities and inconsistences are highlighted and discussed. Finally some design recommendations are proposed for the analysis and design of biaxially loaded concrete-encased composite columns

The effect of preloading on the strength of jacketed R/C columns

The influence of core preloading on the strength of jacketed reinforced concrete (R/C) columns is analytically investigated. A recently proposed method for arbitrary composite section analysis in biaxial bending and axial load is extended to include preloading actions. A parametric evaluation of the preloading effect using quantitative indices is performed, considering the variability of several parameters such as section geometry, amount of reinforcement, and various axial and moment preloading levels. Results are presented in the form of 3D failure surfaces and moment-curvature curves. Specific cases where the preloading effect is more pronounced are finally highlighted

Advancement in FRP composites using three-dimensional stitched fabrics and enhancement in FRP bridge deck component properties.

Use of FRP composites in construction industry has been growing rapidly. However, currently all composite products are manufactured with one and/or two dimensional fibers and fabrics (1-D or 2-D). A shortcoming thick composite (\u3e 0.75 in.) made of 1-D or 2-D fabrics is its dramatic reduction in strength, i.e., up to 50% of thin (\u3c0.5 in.) composites. This can be attributed to shear lag leading to ply-by-ply failure; in addition, premature failure of matrix and fibers or the interface failure is very common in thick composites. Therefore, the motivation of the present work is to fabricate and test composites with 3-D stitched fabrics, which overcome the limitations in composites made of 1-D or 2-D fabrics. In this study, composites were fabricated using 3-D stitched fabrics with different: (1) fiber architecture; (2) stitch density; (3) stitch material; and (4) manufacturing process. Strength and stiffness of composites with 3-D stitched fabrics (at coupon level) under tension, bending and shear loads were experimentally established and theoretically evaluated. Structural properties of composites made of 3-D stitched fabrics were compared with the structural properties of composites made of unidirectional fibers and 2-D stitched fabrics. Composites made of 3-D stitched fabrics were found to have enhanced strength and stiffness (about 30%). The existing FRP bridge deck component (first generation) was modified with respect to weight, fiber architecture and manufacturing process leading to the development of the second generation FRP bridge deck component. In the second generation FRP bridge deck component, the self-weight was reduced by about 11% without sacrificing strength and stiffness. The global stiffness of second generation FRP bridge deck component was evaluated experimentally (3 point bending test) and theoretically by Approximate Classical Lamination Theory. The ultimate stress of second generation FRP bridge deck component (30.8 ksi) was three times more than that of first generation FRP bridge deck component (10.3 ksi). The stiffness of second generation FRP bridge deck component was found to be 8.28E+08 lbs-in2/foot width while the stiffness of first generation FRP bridge deck component was found to be 8.44E+08 lbs- in2/foot. Trail second generation FRP bridge deck module has to be tested under fatigue loads

Behaviour of Corroded Oil and Gas Pipes Rehabilitated with BFRP Wrap

Corrosion in oil and gas pipelines is a major integrity problem for pipeline operators. Throughout their lifespan, pipelines experience a variety of loads including internal pressure, external pressure, bending, and axial loads. These load combinations along with corrosion defect make the pipes vulnerable to failure. Traditional corrosion repair techniques require hot work and can be very expensive. In recent years, researchers have been exploring the possibility of using new techniques and materials to repair defective sections of pipelines. Carbon and glass fibre-reinforced polymers have been proven to enhance the burst strength of corroded pipes. However, few studies were found in the literature that investigated the effectiveness of using composites to restore the bending performance of the corroded pipes. Basalt is a natural rock and hence, a green material and abundant in nature. Basalt fibre is produced from Basalt rock. The mechanical properties of basalt fibre are better than glass, while it is much cheaper than carbon. Although it has been effectively used to repair several structural elements, however, no research was found to use BFRP composite to repair corroded pipelines. The purpose of this research is to experimentally and numerically investigate the feasibility and effectiveness of using BFRP composite wrap on restoring the behaviour of the pressurized corroded pipes while subject to bending load. The experimental study was conducted in two phases: Phase A and phase B. Seven full-scale laboratory experiments were tested in phase A and five full-scale specimens were tested in phase B. Several finite element model-based parametric studies were performed using ABAQUS software. Based on experimental and numerical results, it was found that biaxial BFRP composite can effectively rehabilitate and restore the bending capacity of the corroded pipes and prevent wrinkle formation

Analysis of Reinforced Concrete and Composite Columns With and Without Steel Fibers

Analysis of eccentrically loaded plain and steel fiber high strength reinforced concrete and concrete-encased composite columns is presented. In the analysis procedure, the experimental nonlinear stress−strain relations are used for plain and steel fiber concrete material. The concrete compression zone of the section is divided into segmental subdivisions parallel to the neutral axis. The compression stress resultants of the concrete material and structural steel have been calculated in the centre of each segment. In the presented study, a computer program has been developed based on the proposed procedure for the prediction of ultimate strength analysis of eccentrically loaded steel fiber high strength reinforced concrete and composite columns. The main parameters of this study are the concrete compressive strength, load eccentricity, steel yield stress, slenderness effect and steel fiber content. The results show that adding steel fibers into high strength concrete significantly improves the ductility and deformability of reinforced concrete and composite columns under biaxial bending and axial load

Application study of filamentary composites in a commercial jet aircraft fuselage

A study of applications of filamentary composite materials to aircraft fuselage structure was performed. General design criteria were established and material studies conducted using the 727-200 forebody as the primary structural component. Three design approaches to the use of composites were investigated: uniaxial reinforcement of metal structure, uniaxial and biaxial reinforcement of metal structure, and an all-composite design. Materials application studies for all three concepts were conducted on fuselage shell panels, keel beam, floor beams, floor panels, body frames, fail-safe straps, and window frames. Cost benefit studies were conducted and developmental program costs estimated. On the basis of weight savings, cost effectiveness, developmental program costs, and potential for early application on commercial aircraft, the unaxial design is recommended for a 5-year flight service evaluation program

Normal-strength and high-strength concrete columns under cyclic axial load and biaxial moment

The technique of using Carbon Fiber Reinforced Polymer (CFRP) materials to repair and strengthen various concrete members has become popular in the structural retrofitting field as an effective way to enhance the strength and ductility of concrete members due to its superior mechanical properties. In this study a method was introduced to study the behavior of concrete columns with and without CFRP jackets under constant axial load and variable lateral load. The lateral load was applied monotonically and cyclically. To predict the behavior of concrete columns under monotonic and cyclic compressive loadings, a computer code was developed to produce the moment-curvature diagram for concrete sections. The moment-curvature diagram was then input in SAP2000 to study the behavior of reinforced concrete columns. The result of this analysis was found to correlate with experimental data well. The behavior of high-strength concrete (HSC) columns having various properties and subjected to a variety of loading conditions has been the topic of considerable investigation. Of particular significance in this area is the behavior of HSC columns under cyclic compressive load with bidirectional eccentricity. For the experimental investigation, tests of six square slender HSC columns were conducted under stroke control to achieve both ascending and descending branches of the load-deformation curves. Analysis of HSC columns subjected to cyclic axial compression with bidirectional eccentricity was approached from the standpoint of a three-dimensional problem. A computer program based on the extended finite segment method and accounting for geometrical nonlinearity has been proposed here to predict the load-deflection curves of HSC columns under cyclical loading. The HSC stress-strain relationship obtained by parametric study and experimental investigation into the behavior of concrete under cyclical load history has been incorporated into the numerical procedure. The presented computer analysis results have been compared with the experimental data, and a satisfactory agreement was attained for both the ascending and descending branches of the load-deformation curves

Restrained composite columns

This Thesis describes the development of an analysis for inelastic columns, with cross-sections composed of one or more materials, loaded with axial load and biaxial moments. The column can have both rotational and directional restraints at its ends. The analysis has been programmed for a computer and subsequently tested against published results for steel columns, reinforced concrete columns, and concrete-encased steel composite columns and shown to give good agreement. A test rig with an axial load capacity of 2MN and capable of testing full-scale columns of any practical length has been designed and built. Columns with elastic and elastic-plastic rotational restraints or, pin-ends or any combination can be tested and column end-moments of up to 50 kNm can be applied through the beams. One important feature of the test rig is sets of crossed knife-edges, which give both major and minor axis rotational freedom and thus allow accurate positioning of the axial load. Eight elastically restrained concrete-encased steel composite no-sway columns have been tested, three with biaxial restraints and loadings, using the rig. The results from the tests have been compared with predictions using the computer program and agreement between the observed and predicted results for ultimate loads, deflections, and end-moments is good. The behaviour of column lengths within rigid-Jointed no-sway frames with both plastically and elastically designed beams has been studied. For the case of a column with elastic restraints design proposals have been checked and shown to be conservative. When the beams are designed plastically it is recommended that a conservative approach should be adopted until further research has been carried out into this topic