To-thickness Ratio Research Articles

A novel slit damper configuration to enhance ductility and seismic behavior of concentrically braced frames

Steel slit dampers are the specific type of metallic yielding dampers used for the structural passive control. They are constructed by introducing a series of openings or slits in a steel plate to control the seismic behavior of structures. These dampers absorb energy through shear yielding, flexural yielding, or a combination of both. In this paper, a new form of steel slit damper is introduced and examined. The novel damper, called the Zipper-shaped Slit Damper (ZSD), is composed of two nested boxes connected through high-strength bolts. There are several steel strips in an external box and L-shaped profiles to prevent out-of-plane buckling, maximize flexural capacity, and ensure optimal lateral force distribution. Additionally, L-shaped profiles are welded to the ends of the steel strips. To assess the structural capacity and seismic behavior, ZSD is modeled in three dimensions using ABAQUS finite element software. The model is first validated against experimental results and then subjected to cyclic nonlinear static analysis, comprising 15 models with different width-to-thickness and height-to-width ratios of steel strips. The failure index (FI), based on equivalent plastic strain, is employed to predict the moment of failure. The results obtained from the FI were analyzed, and the analysis was limited until the moment of the first failure. On average, the novel damper demonstrated improved durability with an increase in the height-to-width ratio, resulting in enhanced ductility up to 8.75. Additionally, within each width -to-thickness ratio group, a 0.5 unit increase in this ratio corresponded to a reduction of approximately 10 % in energy dissipation efficiency. The equivalent viscous damping in the models averaged 42 %. The analysis indicated that all models exhibited stable hysteresis cycles and had high ductility and energy dissipation. Also, considering the obtained results, it can be concluded that the ZSD, due to its replaceable components, ease of construction, and easy installation, can be utilized in concentrically braced frames. Mechanical models, as well as stiffness and force relationships for design and implementation in braced frames, are presented. The findings provide valuable insights for the utilization of this innovative damper in seismic-resistant structural systems.

Design of Class 4 hollow structural section compression members

This paper presents a study on the CSA S16:19, AISC 360-16, and EN 1993-1-1 approaches to determine the nominal capacity (Cn) of Class 4 hollow structural section compression members. Class 3 limits and effective width (be) equations are compared, and the effect of member slenderness (KL/r), width-(or diameter-)to-thickness ratio, and height-to-width (or aspect) ratio on the relative Cn predictions are evaluated. For Class 4 rectangular hollow sections, CSA S16:19 is shown to under-predict Cn by up to 34% relative to AISC 360-16. A more economical, yet still safe, method to calculate be (and hence, Cn) is proposed. For Class 4 circular hollow sections, a new method to calculate Cn utilizing the “effective area method” is proposed. This new method removes the need for having an “effective yield stress method” in CSA S16 Clause 13.3.4.

Numerical investigation on shear strength of tapered perfect end web panels

Plate girders are used as an alternative in construction when hot rolled I-shaped beams show poor strength or do not meet design requirements. Under high bending moments and shear forces, it is more efficient to use tapered plate girders. Current design codes lack specific design rules to estimate shear strength of plate girders with tapered web. The aim of this research is to investigate the elastic buckling and ultimate shear strengths of tapered end web panels in plate girders. More than two hundred detailed finite element models of plate girders with tapered end web panels are constructed and analyzed to cover a wide range of geometric parameters including: aspect ratio of end web panel, depth–to-thickness ratio of end web plate, inertia of intermediate stiffeners, and angle of tapering. Upon validation of the numerical solution, numerical results are used to establish a mathematical expression for the ultimate shear strength of prismatic and tapered end web panels. Design requirements of intermediate stiffeners are also proposed to achieve >95% of shear strength of web when stiffened with infinitely rigid stiffeners.

Static response of sandwich plates with FG core and piezoelectric faces under thermo-electro-mechanical loads and resting on elastic foundations

This study presents an analysis of the static bending of a sandwich plate composed of a functionally graded (FG) core and face sheets manufactured of piezoelectric material. The sandwich plate is resting on Pasternak's elastic foundations and subjected to sinusoidal thermo-electro-mechanical loads. Four-unknown shear deformation theory is utilized to define the displacement components. The equilibrium equations are established using the virtual work principle and solved by following Navier's solution method. The influences of applied voltage, thermal expansion coefficients, volume fraction exponent, elastic foundations parameters, side to-thickness ratio, and aspect ratio have been discussed. The current formulation is supported by comparisons with the published results.

Cyclic Performance Evaluation of Hollow Structural Section (HSS) and Concrete-Filled Tube (CFT) Braces

Hollow structural sections (HSS) are widely used as braces because they have inherent axial, flexural, and torsional capacities. Delaying or preventing local buckling is accomplished by concrete infill in HSS braces to improve their cyclic response heavily relying upon three key parameters: (1) presence of concrete infill, (2) width (diameter)-to-thickness ratio, and (3) length-to-width (diameter) ratio impress the cyclic response of HSS braces. Nevertheless, it is not clear that based on which parameter, concrete infill can significantly enhance the peak compressive strength and energy dissipation capacity of HSS braces. This paper aims to investigate this concern while presenting a numerical study on the cyclic response of 120 HSS and Concrete-Filled Tubes (CFT) braces with various geometric characteristics. Square and circular cross-sections, 10, 12, 13.33, 20, 30, 33.33, and 50 width (diameter)-to-thickness ratios and 10, 15, 20, 25, 30, 37.5, 45, 50, 75, and 112.5 length-to-width (diameter) ratios are selected for the numerical investigation. Obtained results indicated that concrete infill can increase peak compressive and post-buckling strengths and energy dissipation capacity of HSS braces around 81%, 43%, and 73%, respectively. It was found that concrete infill and parameters of width (diameter)-to-thickness ratio and length-to-width (diameter) ratio influence the cyclic response of HSS braces differently. On the other hand, concrete infill noticeably enhances the peak compressive strength of HSS braces with larger values of width (diameter)-to-thickness ratio and energy dissipation capacity of such braces with lower values of length-to-width (diameter) ratio.

Investigation on modal behaviour of FGM annular plate under hygrothermal effect

This paper investigates modal characteristics of FGM annular plate under hygrothermal effect. The mechanical properties are supposed to have a continuous variation along the thickness of the plate. The power law or sigmoid law functions are used to govern the resultant mechanical properties. The MUMPS eigen solver which is exists in COMSOL Multiphysics® (version 5.2) software is employed to obtain the eigenfrequencies and corresponding mode shapes. The accuracy of the method is validated by comparing the results with the results published work for particular case. Effects of functionally graded index, radius- to-thickness ratio, and temperature and moisture changes on the natural frequencies are discussed in detail. An excessive stress due to drastic moisture and temperature gradients make the engineering structures susceptible to failure. Due to the fact that, continuously identified natural frequencies of vibration under temperature and moisture effect can provide unique information during both initial fabrication and service life of different mechanical structures. Hence, this study can be helpful directly or indirectly in development of highly efficient environmental sensors that are very necessary in a structural health monitoring perspective. It can be observed that the fundamental frequency decreases with increase in functionally graded index and the moisture content rise under the power law model whereas under sigmoid law model the frequencies remain almost constant with increase in functionally graded index.

Fracture ductility of hollow circular and square steel braces under cyclic loading

Steel braces of a concentrically braced frame (CBF) undergo inelastic cyclic axial deformations under earthquake loading to result in the hysteretic energy dissipation in a structure. However, the occurrence of low-cycle fatigue fracture of these braces significantly reduces the effectiveness of CBFs in dissipating the input seismic energy. Additionally, inaccurate quantification of fatigue fracture may lead to erroneous result interpretation of the collapse performance assessment of braced frames using numerical analysis tools. Hence, in this study both experimental and numerical studies have been carried out to accurately quantify the fracture ductility of braces of hollow circular (HCS) and square (HSS) sections under cyclic loading conditions. Experimental studies have been conducted for varying values of slenderness and width (or diameter)-to-thickness ratio of braces. Parametric study results from the validated simulation models have been used to verify the efficacy of the available empirical relations for the prediction of fracture ductility of HSS brace sections. Additionally, an expression for fracture ductility relating the slenderness ratio and diameter-to-thickness ratio has been proposed for HCS braces using the numerical model results. These expressions and numerical results have been compared with the past and present experimental results to highlight the efficiency of the available as well as the proposed empirical methods.

Behavior of thin walled steel tube confined concrete stub columns subjected to axial local compression

The behavior of thin walled steel tube confined concrete (STCC) stub columns subjected to axial local compression was experimentally investigated in this paper. A total of 46 specimens, including 36 STCC specimens and 10 plain concrete specimens, were tested. The main parameters varied in the tests are: (1) sectional types: circular and square; (2) local compression area ratio (concrete cross-sectional area to local compression area): from 1 to 25; (3) steel tube width (or diameter)-to-wall thickness ratio, B(or D)/ t, from 52.1 to 104.7. It was found that the ultimate bearing strength of the composite sections decreases with increase local compression area ratio. The confinement action of the steel tube to core concrete and the ultimate strength of the locally loaded STCC specimens decrease with increase in steel tube width (or diameter)-to-thickness ratio. It was also found that, generally, circular steel tubes have higher confinement to their concrete core than those of the tubes with square sections when the composite members are subjected to axially local compression.

繰返し載荷を受ける角形鋼柱の変形能力に及ぼす局部座屈の影響

This paper presents a numerical study on the effects of the width-to-thickness ratio, axial force ratio, and slenderness ratio on local buckling and strength deterioration of steel box columns subjected to cyclic loading. The maximum strength experienced during cyclic loading, and the strengths remaining after prescribed rotation angles are examined. The following observations are notable: 1) The maximum strength increases with a larger axial force ratio, but serious strength degradation is present due to local buckling; 2) The strength degradation is affected significantly by the width- to-thickness ratio, but the effect of the slenderness ratio is minor; 3) The width-to-thickness requirements stipulated in the present Japanese seismic design codes are not necessarily sufficient for columns sustain large cyclic loading up to 0.03rad in rotation.

Behavior of Eccentrically Loaded Concrete-Filled Steel Tubular Columns

Beam columns of concrete-filled steel tubular (CFT) columns are designed using a design formula established by the Architectural Institute of Japan (AIJ). However, the scope of the formula in the current AIJ standard is limited to ordinary material strengths, and a rational mathematical model which makes it possible to reproduce load-deformation behavior in CFT columns has not yet been established. The main objectives of this research were to investigate the effect of higher material strengths on the flexural behavior and to create mathematical models of the steel tube and filled concrete. Adequate study of the effects of the section shape, diameter (width)-to-thickness ratio, and the combination of strengths of the steel tube and filled concrete was included in the scope of this investigation. Based on the experimental results of 65 eccentric compression tests, an analytical model for the restoring force characteristics of the flexural behavior of CFT columns is proposed, and is found to reproduce experi...

Behavior of Concrete-Filled Steel Tube Beam Columns

The behavior of concrete-filled circular and square steel tubular (CFT) beam columns with a variety of material strengths was investigated experimentally. The main test parameters are steel strength (400, 590, and 780 MPa), diameter- (width-) to-thickness ratio of steel tube, and concrete strength (40 and 90 MPa). The interior beam-column models were tested under constant axial compression and cyclic horizontal load with incrementally increasing lateral deformation to clarify the effects of the test parameters on the behavior. The exterior beam-column models were laterally loaded under variable axial load, including axial tension. The behavior of square beam columns subjected to biaxial bending was also investigated. The test results show that higher strength and thicker steel tubes give better overall behavior of the beam column, while higher strength concrete has an adverse effect on the behavior. Furthermore, computer simulations for the hysteretic behavior of CFT beam-column specimens are presented here. The analytical results show excellent agreement with the test results except for a few cases.

被覆形鋼管コンクリート柱材における鋼管の幅厚比・径厚比の制限値

In AIJ design formula for composite steel tube and concrete structures, the limiting width (diameter)-to-thickness ratio of steel tube is relieved to 1.5 times that for a hollow tube. In this paper, it is investigated whether the limiting value for concrete-encased type section is appropriate or not. As the experimental parameters, shape of steel tube, section type and width (diameter)-to-thickness ratio are selected. Total thirty-four stub column specimens are tested under concentric load. From the view point of the maximum strength, current limiting width (diameter)-to-thickness ratio is practically appropriate.

Triangular Truss Joints Using Rectangular Tubes

This paper deals with the behavior and design of welded joints to the tension chord of triangular trusses, with two Warren-type web planes and a single tension chord, made of rectangular tubes (hollow structural sections or HSS). Experimental programs are outlined in which simplified double-T joints and triangular truss segments with double-K gap joints were tested. Parameters investigated include the gap size, the web-member-width–to-chord-width ratio, the chord-wall-width–to-thickness ratio, and the angle between web planes. The mechanics of deformations of the double-T and double-K joints are discussed in relation to yield line theory, and this theory is shown to give a good prediction of the experimental joint stiffnesses and strengths. Strength equations are proposed to cover tension chord gap joint behavior with respect to chord wall bending and a design example is outlined.