• Steel and Composite Structures
• /
• v.25 no.5
• /
• pp.545-556
• /
• 2017

The tubed steel reinforced concrete (SRC) column is a composite column in which the outer steel tube is mainly used to provide confinement on the core concrete. This paper presents experimental and analytical studies on the behavior of circular tubed SRC (TSRC) columns subjected to axial compression. Eight circular TSRC columns were tested to investigate the effects of length-to-diameter ratio (L/D) of the specimens, diameter-to-thickness ratio (D/t) of the steel tubes, and use of stud shear connectors on the steel sections. Elastic-plastic analysis on the steel tubes was used to investigate the mechanism of confinement on the core concrete. The test results indicated that the tube confinement increased the strength and deformation capacity for both short and slender columns, and the effects on strength were more pronounced for short columns. A nonlinear finite element (FE) model was developed using ABAQUS, in which the nonlinear material behavior and initial geometric imperfection were included. Good agreement was achieved between the predicted results using the FE model and the test results. The test and FE results were compared with the predicted strengths calculated by Eurocode 4 and the AISC Standard. Based on the analytical results, a new design method for this composite column was proposed.

• Steel and Composite Structures
• /
• v.34 no.6
• /
• pp.783-794
• /
• 2020

Steel-concrete-steel sandwich composite wall is composed of two external steel plates and infilled concrete core. Internal mechanical connectors are used to enhance the composite action between the two materials. In this paper, the compressive behavior of a novel sandwich composite wall was studied. The steel trusses were applied to connect the steel plates to the concrete core. Three short specimens with different truss spacings were tested under compressive loading. The boundary columns were not included. It was found that the failure of walls started from the buckling of steel plates and followed by the crushing of concrete. Global instability was not observed. It was also observed that the truss spacing has great influence on ultimate strength, buckling stress, ductility, strength index, lateral deflection, and strain distribution. Three modern codes were introduced to calculate the capacity of walls. The comparisons between test results and code predictions show that AISC 360 provides significant underestimations while Eurocode 4 and CECS 159 offer overestimated predictions.

• Earthquakes and Structures
• /
• v.19 no.5
• /
• pp.315-329
• /
• 2020

Through bolt connections in Concrete Filled Steel Tubes (CFSTs) has been proved to be good in terms of seismic performance and constructability. Stiffened extended end plate connection with full through type bolt helps to avoid field weld altogether, and hence to improve the quality of joints. An experimental study was conducted on the hysteretic performance of square interior beam-column connections using flat extended end plates with through bolt. The study focuses on the effect of the bond between the tie rod and the core concrete on the cyclic performance of the joint. The study also quantifies how much the interior joint is getting strengthened due to the confinement effect induced by bi-directional bolting, which is widely used in 3D moment resisting frames. For a better understanding of the mechanism and for the prediction of shear capacity of the panel zone, a mathematical model was generated. The various parameters included in the model are the influence of axial load, amount of prestress induced by bolt tightening, anchorage, and the concrete strut action. The study investigates the strength, stiffness, ductility, and energy dissipation characteristics. The results indicate that the seismic resistance is at par with American Institute of Steel Construction (AISC) seismic recommendations. The bidirectional bolting and bond effect have got remarkable influence on the performance of joints.

• Structural Engineering and Mechanics
• /
• v.65 no.3
• /
• pp.349-357
• /
• 2018

An extensive research was undertaken to study the vibration serviceability of a long-span and light-weight floor subjected to human loading experimentally and numerically. Specifically, heel-drop test was first conducted to capture the floor's natural frequencies and damping ratios, followed by jumping and running tests to obtain the acceleration responses. In addition, numerical simulations considering walking excitation were performed to further evaluate the vibration performance of a multi-panel floor under different loading cases and walking rates. The floor is found to have a high frequency (11.67 Hz) and a low damping ratio (2.32%). The comparison of the test results with the published data from the 1997 AISC Design Guide 11 indicates that the floor exhibits satisfactory vibration perceptibility overall. The study results show that the peak acceleration is affected by the walking path, walking rate, and adjacent structure. A simpler loading case may be considered in design in place of a more complex one.

• Steel and Composite Structures
• /
• v.35 no.3
• /
• pp.353-370
• /
• 2020

This paper describes a new type of replaceable fuse for moment resisting frames. Column-tree connections with beam splice connections are frequently preferred in the moment resisting frames since they eliminate field welding and provide good quality. In the column-tree connections, a part of the beam is welded to the column in the shop and the rest of the beam is bolted with the splice connection in the field. In this study, a replaceable reduced beam section (R-RBS) connection is proposed in order to eliminate welding process and facilitate assembly at the site. In the proposed R-RBS connection, one end is connected by a beam splice connection to the beam and the other end is connected by a bolted end-plate connection to the column. More importantly is that the proposed R-RBS connection allows the replacement of the damaged R-RBS easily right after an earthquake. Pursuant to this goal, experimental and numerical studies have been undertaken to investigate the performance of the R-RBS connection. An experimental study on the RBS connection was used to substantiate the numerical model using ABAQUS, a commercially available finite element software. Additionally, five different finite element models were developed to conduct a parametric study. The results of the analysis were compared in terms of the moment and energy absorption capacities, PEEQ, rupture and tri-axiality indexes. The design process as well as the optimum dimensions of the R-RBS connections are presented. It was also demonstrated that the proposed R-RBS connection satisfies AISC criteria based on the nonlinear finite element analysis results.

• Journal of Korean Society of Steel Construction
• /
• v.12 no.4 s.47
• /
• pp.437-443
• /
• 2000

In order to clarify the behavior of beam-to-concrete filled steel tube column under cyclic loading condition, experimental studies were carried out on shear connections. Test parameters of this study are the width-to-thickness ratio and the effect on beams with or without slab and diaphragm. Test results show that the moment-rotation relationships of connections without slab are in the range of AISC regulation of pinned connections and the rotation capacity of connection is dependent upon the width-to-thickness ratio of the column.

• Computers and Concrete
• /
• v.25 no.1
• /
• pp.1-14
• /
• 2020

This study presents applications of the multivariate adaptive regression splines (MARS) method for predicting the ultimate loading carrying capacity (N_u) of rectangular concrete-filled steel tubular (CFST) columns subjected to eccentric loading. A database containing 141 experimental data was collected from available literature to develop the MARS model with a total of seven variables that covered various geometrical and material properties including the width of rectangular steel tube (B), the depth of rectangular steel tube (H), the wall thickness of steel tube (t), the length of column (L), cylinder compressive strength of concrete (f'_c), yield strength of steel (f_y), and the load eccentricity (e). The proposed model is a combination of the MARS algorithm and the grid search cross-validation technique (abbreviated here as GS-MARS) in order to determine MARS' parameters. A new explicit formulation was derived from MARS for the mentioned input variables. The GS-MARS estimation accuracy was compared with four available mathematical methods presented in the current design codes, including AISC, ACI-318, AS, and Eurocode 4. The results in terms of criteria indices indicated that the MARS model was much better than the available formulae.

• Structural Engineering and Mechanics
• /
• v.66 no.2
• /
• pp.173-183
• /
• 2018

This paper proposes a developed optimization model for steel frames with semi-rigid beam-to-column connections and fixed bases using teaching-learning-based optimization (TLBO) and genetic algorithm (GA) techniques. This method uses rotational deformations of frame members ends as an optimization variable to simultaneously obtain the optimum cross-sections and the most suitable beam-to-column connection type. The total cost of members plus connections cost of the frame are minimized. Frye and Morris (1975) polynomial model is used for modeling nonlinearity of semi-rigid connections, and the $P-{\Delta}$ effect and geometric nonlinearity are considered through a stepped analysis process. The stress and displacement constraints of AISC-LRFD (2016) specifications, along with size fitting constraints, are considered in the design procedure. The developed model is applied to three benchmark steel frames, and the results are compared with previous literature results. The comparisons show that developed model using both LTBO and GA achieves better results than previous approaches in the literature.

• Steel and Composite Structures
• /
• v.19 no.5
• /
• pp.1185-1201
• /
• 2015

The aim of this experimental research is to investigate the conformity of the four-bolt unstiffened moment end-plate connections consisting of European steel sections which do not meet the limitations specified for beam flange width and overall beam depth in ANSI/AISC 358-10 to the requirements of seismic application. However, the connections are satisfactory with the limitations required by Turkish Earthquake Code. For this purpose, four test specimens were designed and cyclic load was applied to three specimens while one was tested under monotonic loading to provide data for the calibration of the analytical models. The moment-rotation hysteresis loops and the failure modes for all test specimens are presented. A full three-dimensional finite element model is also developed for each test specimen for use to predict their behavior and to provide a tool for generating subsequent extensive parametric studies. The test results show that all specimens performed well in terms of rotation capacity and strength. Finite element models are found to be capable of approximating the cyclic behavior of the extended end-plate connection specimens.

• Steel and Composite Structures
• /
• v.19 no.6
• /
• pp.1581-1598
• /
• 2015

A concentric braced steel frame is a very efficient structural system because it requires relatively smaller amount of materials to resist lateral forces. However, primarily developed as a structural system to resist wind loads based on an assumption that the structure behaves elastically, a concentric braced frame possibly experiences the deterioration in energy dissipation after brace buckling and the brittle failure of braces and connections when earthquake loads cause inelastic behavior. Consequently, plastic deformation is concentrated in the floor where brace buckling occurs first, which can lead to the rupture of the structure. This study suggests reinforcing H-shaped braces with non-welded cold-formed stiffeners to restrain flexure and buckling and resist tensile force and compressive force equally. Weak-axis reinforcing members (2 pieces) developed from those suggested in previous studies (4 pieces) were used to reinforce the H-shaped braces in an inverted V-type braced frame. Monotonic loading tests, finite element analysis and cyclic loading tests were carried out to evaluate the structural performance of the reinforced braces and frames. The reinforced braces satisfied the AISC requirement. The reinforcement suggested in this study is expected to prevent the rupture of beams caused by the unbalanced resistance of the braces.