Konstantinos A. Skalomenos

Experimental Behavior of Concrete-Filled Steel Tube Columns Using Ultrahigh-Strength Steel

Concrete-filled steel tube (CFT) columns offer significant advantages over columns made of either steel or concrete alone, such as large energy dissipation and increased strength and stiffness. To further improve the seismic performance of these columns, an experimental investigation was conducted into CFT columns using ultrahigh-strength steel. More specifically, seven square and circular specimens made with high-strength and conventional steel were subjected to constant compressive axial load and cyclic flexural load protocols with two and 20 cycles imposed at each drift level. Based on the test results, the influence on the CFT’s cyclic behavior of the high-strength steel, crosssectional shape, axial load, and number of cycles in lateral loading history was studied. In comparison with the conventional steel specimens, larger elastic deformation, higher strength, and delay of local buckling were observed in the high-strength steel specimens, while compared with the circular specimens, the square specimens sustained larger drift angles without fracture of their steel tubes because of the development and progress of serious local buckling. Furthermore, a simple analytical model based on the concept of the superposed strength method was proposed. The accuracy of this model was confirmed with the experimental results.

Development of a Steel Brace with Intentional Eccentricity and Experimental Validation

AbstractConventional buckling braces are the most commonly used steel bracing systems but are characterized by intense local midlength buckling that leads to unstable energy dissipation and finally...

Gusset Plate Connections for Naturally Buckling Braces

AbstractA naturally buckling brace (NBB) is a steel brace that consists of a high-strength and low-yielding steel channel arranged in parallel with eccentricity acting along the brace length. To en...

Inelastic behavior of circular concrete-filled steel tubes: monotonic versus cyclic response

In this paper, a computational procedure for determining the response of circular concrete-filled steel tube (CFT) columns to monotonic loading is developed. Firstly, the basis of the proposed method is established by creating accurate three-dimensional nonlinear finite element models of these columns, which are validated by comparing their response results with those of experimental tests that are available in the literature. Then, these models are used for an extensive parametric study that determines the response to monotonic lateral loads of 192 circular CFT specimens with fairly broad values of diameter-to-thickness ratios, yield stress of steel tube, compressive strength of concrete core and axial load levels. On the basis of this response databank, empirical expressions are developed to estimate the force–displacement behavior of circular CFT columns under monotonic loading with simple yet reliable manner. The validity of these empirical expressions is verified by comparing their results with those of experimental tests. It is found that the proposed expressions can effectively describe the force–displacement behavior and capacity of circular CFT columns under monotonic loading conditions. These expressions are also used in pushover analysis of a simple frame consisting of steel beams and CFT columns in order to demonstrate their applicability and usefulness in simple practical problems. Finally, the proposed method, of determining the response of composite structures to monotonic lateral loading is compared with nonlinear time-history response analysis of these structures and useful conclusions are provided.

On-Line Testing of Steel Brace Connections Using Non-Linear Substructuring and Force-Displacement Combined Control

The present paper suggests an on-line hybrid test environment for evaluating the seismic performance of steel bracing connections. The test method combines substructuring techniques and finite element analysis. The behavior of the brace member is simulated by the finite element analysis program ABAQUS, while the bracing end connections are physically tested. Two actuators are used to simulate the physical continuity between the analytical and experimental substructures by controlling axial load and out-of-plane rotation. A MATLAB user subroutine is created as the interface between the main control program and ABAQUS to impose the target rotation and axial force to the connection quasi-statically. A gusset plate connection designed to behave as a pin connection is tested and its efficiency to accommodate inelastic rotations up to a 4.0% story drift is evaluated. The test method is reasonable and smooth operation is achieved. The test system ensures pragmatic loading and boundary conditions to the brace connections, which are tested in full interaction with the brace member until failure. The maximum strength and rotation capacity of the connection can be clarified under actual cyclic inelastic rotations and varying axial loads derived from the inelastic behavior of the brace member.

An Empirical Methodology for Seismic Damage Control of CFT-MRFs

An empirical methodology to evaluate damage by the use of two damage indicators for 2D steel/concrete composite structures is proposed. This methodology has been established with aid of the results of an extensive parametric study regarding the non-linear behaviour of 48 steel/concrete composite frames subjected to 100 far-fault records. A large number of inelastic dynamic analyses are conducted by increasing the earthquake motions to lead the frames to several levels of non-linear response. The results of the analyses show that the characteristics of the structure and the ground motions affect damage of the structures. The results are post-processed by the use of statistical methods to generate expressions, which show the effect of the abovementioned parameters and give an evaluation of the damage indicators utilised here. In particular, given the characteristics of the frames and the record, someone can compute the maximum damage found in beams and columns. Finally, one example serves to show the use of the developed formulae and demonstrates their validity.

Seismic Analysis and Design of Composite Steel/Concrete Building Structures Involving Concrete-Filled Steel Tubular Columns

Composite construction in steel and concrete offers significant advantages over the conventional one based exclusively on either steel or concrete. This paper provides a comprehensive overview of the state of research in analysis and design of composite steel/concrete building structures involving concrete-filled steel tubular (CFT) columns and steel beams. Experimental and analytical/numerical research on the seismic behavior and simulation of CFT columns and composite framed structures under strong ground motions are all considered with emphasis on recent works of the authors. The paper also discusses seismic analysis/assessment methodologies and performance-based seismic design (PBSD) methods that enable engineers to produce composite structures with deformation and damage control.

Simple formulae for damage estimation of composite steel/concrete moment resisting frames

Simple empirical expressions to estimate maximum seismic damage on the basis of three well known damage indices for planar regular steel/concrete composite moment resisting frames are presented. They are based on the results of extensive parametric studies concerning the inelastic response of a large number of frames to a large number of ordinary far-field type ground motions. Thousands of nonlinear dynamic analyses are performed by scaling the seismic records to different intensities in order to drive the structures to different levels of inelastic deformation. The statistical analysis of the created response databank indicates that the number of stories, beam strength ratio, material strength and the ground motion characteristics affect structural damage. Nonlinear regression analysis is employed in order to derive simple formulae, which offer a direct estimation of the damage indices used in this study. More specifically, given the characteristics of the structure and the ground motion, one can calculate the maximum damage observed in column bases and beams. Finally, one example serves to illustrate the use of the proposed expressions and demonstrates their efficiency and accuracy.