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American Society for Testing and Materials

Developments and advanced applications of concrete-filled steel tubular (CFST) structures: Members

In practice, concrete-filled steel tubes (CFST) are often subjected to torsion. To date, such a problem however has not been addressed satisfactorily by design codes. The present study is thus an attempt to study the torsional behaviours of concrete-filled thin-walled steel tubes. ABAQUS software is used in this paper for the finite element analysis (FEA) of CFST subjected to pure torsion. A comparison of results calculated using this modelling shows good agreement with test results. The FEA modelling was used to investigate the influence of important parameters that determine the ultimate torsional strength of the composite sections. The parametric studies provide information for the development of formulae to calculate the ultimate torsional strength, as well as the torsional moment versus torsional strain curves of the composite sections.

Performance of concrete-filled thin-walled steel tubes under pure torsion

A simple, yet effective, analytical model is proposed for the representation of near-field strong ground motions. The model adequately describes the impulsive character of near-fault ground motions both qualitatively and quantitatively. In addition, it can be used to analytically reproduce empirical observations that are based on available near-source records. The input parameters of the model have an unambiguous physical meaning. The proposed analytical model has been calibrated using a large number of actual near-field ground-motion records. It successfully simulates the entire set of available near-fault displacement, velocity, and (in many cases) acceleration time histories, as well as the corresponding deformation, velocity, and acceleration response spectra. Furthermore, a very simplified methodology for generating realistic synthetic ground motions that are adequate for engineering analysis and design is outlined and applied. Finally, it should be noted that the analytical model (along with the scaling laws of its parameters) proposed in the present work has the potential to facilitate the study of the elastic and inelastic response of conventional, nonconventional (e.g., base-isolated), and special structures (e.g., suspension bridges, fluid-storage tanks) subjected to near-source seismic excitations as a function of the model input parameters and thus, ultimately, as a function of earthquake size.

A Mathematical Representation of Near-Fault Ground Motions

Reliable collapse assessment of structural systems under earthquake loading requires analytical models that are able to capture component deterioration in strength and stiffness. For calibration and validation of these models, a large set of experimental data is needed. This paper discusses the development of a database of experimental data of steel components and the use of this database for quantification of important parameters that affect the cyclic moment-rotation relationship at plastic hinge regions in beams. On the basis of information deduced from the steel component database, empirical relationships for modeling of precapping plastic rotation, postcapping rotation, and cyclic deterioration for beams with reduced beam section (RBS) and other-than-RBS beams are proposed. Quantitative information is also provided for modeling of the effective yield strength, postyield strength ratio, residual strength, and ductile tearing of steel components subjected to cyclic loading.

https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%29ST.1943-541X.0000376

Deterioration Modeling of Steel Components in Support of Collapse Prediction of Steel Moment Frames under Earthquake Loading

This paper studies composite action in concrete filled tubes (CFT) that have dimensions and proportions like those used in U.S. practice. CFT applications in buildings and the importance of bond stress and interface conditions to behavior are noted, past research is summarized, and the combined results are analyzed. An experimental study is described and evaluated. It is shown that shrinkage can be very detrimental to bond stress capacity, and the importance of shrinkage depends upon the characteristics of the concrete, the diameter of the tube, and the surface condition at the inside of the tube. The bond capacity is smaller with large diameter tubes and large d/t ratios. The bond capacity is interrelated with slip at the steel concrete interface. An exponential distribution of bond stress is expected prior to slip, and a more uniform distribution occurs after slip. An equation that estimates the bond stress capacity is developed, and this leads to design recommendations at different performance levels.

Composite Action in Concrete Filled Tubes

Steel concentrically braced frames are generally designed to resist lateral force by means of truss action. Design consider- ations for columns in these frames are therefore governed by the column axial force while column bending moment demands are generally ignored. However, if the columns cannot carry moments, then dynamic inelastic time-history analyses show that a soft-story mechanism is likely to occur causing large concentrated deformations in only one story. Such large concentrations of damage are not generally seen in real frames since columns are generally continuous and they possess some flexural stiffness and strength. This paper develops relationships for column stiffness and drift concentration within a frame based on pushover and dynamic analyses. It is shown that continuous seismic and gravity columns in a structure significantly decrease the possibility of large drift concentrations. An assessment method and example to determine the required column stiffness necessary to limit the concentration of story drift is provided.

Effect of column stiffness on braced frame seismic behavior

A unique, practical structural steel system that possesses many advantages in the seismic design of structures is described The system employs diagonal bracing with large eccentricity between the brace-beam connection and the beam column joint The eccentricity provides a ductile fuse that yields in shear and prevents brace buckling Static and dynamic analyses indicates that this system can perform well during earthquakes, because it combines the stiffness of a braced frame with the excellent energy dissipation of a moment-resisting frame One-third-scale experiments showed that the system behaves as predicted in the analyses It dissipates large amounts of energy while maintaining a very stiff structure, and it offers many potential applications in the seismic design of structures

Eccentrically Braced Steel Frames for Earthquakes

Current design practices use a strength-based design approach to design gusset plate connections in special concentrically braced frames (SCBFs), in which the expected tensile and compressive capacities of the brace are used to design the gusset plate and the weld used to connect the brace to the frame. To achieve brace end rotation, the gusset plate is sized using a linear offset rule, and large, uneconomical gusset plate connections may result. A research program was undertaken to improve the economy and performance of gusset plate connections. A new approach is proposed in which the gusset plate design is based on a balanced design approach in which the yield mechanisms of the brace are balanced with the yield mechanisms of the connection and the failure modes of the system to achieve a target yielding hierarchy and suppress unwanted failure modes. Full-scale one-story, one-bay frames were designed and tested to investigate the seismic performance of current and proposed design methods. In the test program, variations in balance factors between the brace, gusset plate, and weld were considered to study the proposed method, to evaluate possible yield mechanisms and failure modes, and to obtain the desired yielding hierarchy. Comparison of the observed and measured performance of each specimen is made and specific design expressions to improve the seismic engineering of SCBF systems are proposed.

Improved Seismic Performance of Gusset Plate Connections

https://www.tpbin.com/Uploads/Subjects/e1cfb3a0-2ed9-496f-97a7-d29f0a1de5cd.pdf

Charles W. Roeder

Papers

Composite Action in Concrete Filled Tubes

Effect of column stiffness on braced frame seismic behavior

Eccentrically Braced Steel Frames for Earthquakes

Improved Seismic Performance of Gusset Plate Connections

Improved analytical model for special concentrically braced frames