Iraj Mamaghani

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Iraj H.P. Mamaghani, D. Eng., P.Eng. is an assistant professor in the Department of Civil Engineering at the University of North Dakota. His primary research is in the analytical and numerical aspects of solid mechanics. Specific interests include material modeling and metal plasticity under cyclic loading, metal finite element method, Seismic design of structures, mechanics of materials, and numerical analysis of extreme loading events. He authored 3 book chapters and >200 journal/conference papers. Dr. Mamaghani teaches structural steel design, structural mechanics, advanced steel design, and structural stability.

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Seismic design and ductility issues in concrete-filled steel tubular structures

Seismic Retrofit and Ductility Enhancement of Thin-Walled Steel Tubular Bridge Piers

Transportation Research Board 92nd Annual MeetingTransportation Research Board, 2013

This paper deals with the seismic retrofit and ductility enhancement of thin-walled steel tubular... more This paper deals with the seismic retrofit and ductility enhancement of thin-walled steel tubular bridge piers. The basic characteristics of the thin-walled steel tubular bridge piers are noted and the importance of various retrofit techniques in improving strength and ductility capacity of such structures is explained. A seismic design method for ultimate strength and ductility evaluation of the new and retrofitted, thin-walled, steel tubular bridge pier is presented. The application of the method is demonstrated by comparing the computed strength and ductility of some bridge piers with test results. The method is applicable for both the design of new and retrofitting of existing thin-walled steel tubular bridge piers. The effects of some important parameters such as width-to-thickness ratio, column slenderness ratio, height of infill concrete, residual stress, arrangement of additional longitudinal stiffeners and inclusion of energy absorption segment on the ultimate strength and ductility of thin-walled steel tubular bridge piers are presented and discussed.

Seismic design of partially concrete-filled steel tubular columns with enhanced ductility

This paper deals with the seismic design of partially concrete-filled steel box bridge piers. A s... more This paper deals with the seismic design of partially concrete-filled steel box bridge piers. A seismic design method for ultimate strength and ductility evaluation of hollow and concrete-filled thin-walled steel box beam-columns is developed. The method involves an elastoplastic pushover analysis and definition of failure criterion taking into account local buckling and the effects of residual stresses. The application of the method is demonstrated by comparing the computed strength and ductility of some cantilever beam-columns with test results. The interaction between the effects of residual stresses and some important parameters, such as width-to-thickness ratio, column slenderness ratio and height of infill concrete, on the ultimate strength and ductility of thin-walled steel box beam-columns are presented and discussed.

Seismic Design and Ductility Evaluation of Partial Concrete-Filled Steel Bridge Piers

Transportation Research Board 86th Annual MeetingTransportation Research Board, 2007

This paper deals with seismic design and ductility evaluation of partially concrete-filled steel ... more This paper deals with seismic design and ductility evaluation of partially concrete-filled steel bridge piers supporting highway bridge superstructures. The basic characteristics of the thin-walled steel tubular structures are noted and the importance of partially concrete fill in improving strength and ductility capacity of such structures is explained. A seismic design method for ultimate strength and ductility evaluation of concrete-filled, thin-walled, steel tubular bridge piers is presented. The application of the method is demonstrated by comparing the computed strength and ductility of some bridge piers with test results. The method is applicable for both the design of new, and retrofitting of existing, thin-walled steel tubular bridge piers. The effects of some important parameters, such as width-to-thickness ratio, column slenderness ratio, height of infill concrete and residual stress, on the ultimate strength and ductility of thin-walled steel tubular bridge piers, are presented and discussed.

A broadband dual‐polarized antenna with irregular polygon patches and trapezoidal coupling plates

Microwave and Optical Technology Letters, Mar 28, 2020

In this article, a small broadband dual-polarized antenna is presented. The main structure consis... more In this article, a small broadband dual-polarized antenna is presented. The main structure consists of the four irregular polygon patches printed on the bottom layer of the substrate, two trapezoidal coupling plates printed on the top layer of the substrate, and a box-shaped reflector at the back of the substrate at resonance distance. Design principles are based on the rules of complementary antennas, cross dual-polarized antennas, and aperture antennas. The proposed antenna has technical specifications such as impedance bandwidth 48% (1.7-2.7 GHz) with lower than 15 dB return loss, port-to-port isolation about 32 dB, high pattern stability, and half-power beam width about 63 AE 9. The antenna measurement results confirm these. At the end, a comparison between the proposed antenna and the other antennas of this type is presented. The proposed antenna has smaller dimensions, high gain, high port isolation, and excellent pattern stability over the whole bandwidth. The proposed antenna can be used in the base transceiver stations (BTSs) and multi input-multi output (MIMO) systems.

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Cyclic elastoplastic finite element analysis and ductility evaluation of cold-formed thin-walled steel tubular columns

Journal of civil & environmental engineering, Nov 6, 2017

Cyclic Elastoplastic Large Displacement Analysis of Cold-formed Steel Box Columns under Combined Action of Axial and Bidirectional Lateral Loading

This paper deals with the cyclic elastoplastic large displacement analysis of cold-formed steel b... more This paper deals with the cyclic elastoplastic large displacement analysis of cold-formed steel box columns under combined action of axial and bidirectional lateral loading. Cold-formed steel box columns are very useful in highway bridge pier construction as they offer flexible space requirement and provide speedy construction. Behavior of cold-formed steel box columns under earthquake-induced loads is rather complicated as earthquakes occur in an oblique direction. However, modern seismic design philosophies have been based on the behavior of structures under independent actions of uni-directional loading in orthogonal directions. In this study, inelastic cyclic behavior of steel columns subjected to constant axial force together with simultaneous bi-directional cyclic lateral loads is investigated using an advanced finite element analyses procedure. Several types of linear and non-linear idealized loading patterns are employed to check the strength and ductility. The effects of important structural parameters

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Design and Analysis of Reinforced Expanded Polystyrene Styrofoam for Use Under Falling Rock Impact

Transportation Research Board 93rd Annual MeetingTransportation Research Board, 2014

The present paper is concerned with the design and analysis of reinforced expanded polystyrene St... more The present paper is concerned with the design and analysis of reinforced expanded polystyrene Styrofoam (R-EPS) to reduce the impact of falling rock. R-EPS is developed as an improved alternative buffer material to be placed on the roof of rock-sheds to absorb and distribute the energy of falling rocks. First, based on the experimental results, the effects of some important parameters on the buffer behavior and energy absorption capacity of the R-EPS are discussed and evaluated. These parameters include reinforcement, thickness of Styrofoam, and weight and height of the falling rock. Then a design method incorporating the design equations and design charts is proposed for the R-EPS and validated using the experimental data. Finally the practical application of the proposed method for design of R-EPS protection measures is presented and discussed.

Cyclic Behavior and Ductility Evaluation of Thin-walled Stiffened Steel Box Bridge Piers

Transportation Research Board 91st Annual MeetingTransportation Research Board, 2012

This paper deals with cyclic behavior and ductility evaluation of thin-walled stiffened steel box... more This paper deals with cyclic behavior and ductility evaluation of thin-walled stiffened steel box bridge piers subjected to cyclic lateral loading in the presence of constant axial load. The basic characteristics of steel box bridge piers are noted. The results of finite-element analyses on cyclic elastoplastic behavior of steel box bridge piers are presented. For comparison purposes, in the analysis three material models are employed for material nonlinearity to trace the inelastic cyclic behavior of steel: kinematic hardening, isotropic hardening, and elastic perfectly plastic. A method for evaluating ductility capacity of tubular columns modeling bridge piers is presented. The application of the method is demonstrated by comparing the computed strength and ductility of some cantilever bridge piers with the test results.

個別有限要素法(DFEM)による不連続性岩盤のモデル解析 (小特集防災・環境シミュレーションの最前線)

地質と調査, 2005

Design and Analysis of High-Energy-Absorbing Rock Fence

Transportation research circular, Jun 1, 2017

Cyclic elastoplastic behavior of steel structures : theory and experiment

Department of Civil Engineering, Nagoya University eBooks, 1996

Cyclic elastoplastic analysis of steel tubular braces

Seismic Design of Partially Concrete-Filled Steel Box Bridge Piers

Transportation Research Board 93rd Annual MeetingTransportation Research Board, 2014

Design of reinforced expanded polystyrene styrofoam under falling rock impact

Application of Sealing Agents in Concrete Durability of Infrastructure Systems

Mr. Curt Dunn, and the entire staff of the Materials and Research Division of the North Dakota De... more Mr. Curt Dunn, and the entire staff of the Materials and Research Division of the North Dakota Department of Transportation (NDDOT) for providing financial, technical and logistical support to carry out this research. The authors would also like to thank Mr. Shane Johnson of Strata Concrete for providing aggregates for this project. The author's thanks to Mr. Curtis Nelson for providing Radcon Formula #7 sealer, Mr. Milton Anderson of DJA Consulatants Inc for providing Degussa Daga Deck Crack sealer, Mr. Mark Piriare supply of Degussa Corporation for providing Chem-Trete BSM-40VOC sealer, and Mr. Grish C. Dubey for providing Star Mcro-Deck sealer for tests on this project. The authors would like to thank Lafarge Dakota Inc of Grand Forks for donating Portland cement and Coal Creek fly ash for the tests. The authors express their thanks to the Euclid Chemical Company for providing concrete admixtures (air entraining and water reducer agents) for this project. Special thanks are extended to the author's students Mr. Luke Falken and Mr. Joseph Tonneson for helping in laboratory tests. The authors thank Mrs. Mary Jo Rasmussen, Administrative Secretary of the Civil Engineering Department, for her technical help and support throughout this research. Finally, the author hopes that NDDOT will maintain its research activities with UND and continue to fund CE department projects.

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Numerical Investigation on Buckling Response of Cylindrical Steel Storage Tanks Under Seismic Excitation

ce/papers

This paper presents the buckling response and vibration characteristic of the cylindrical steel l... more This paper presents the buckling response and vibration characteristic of the cylindrical steel liquid storage tanks filled with water when subjected to strong earthquake excitations. Finite element analysis (FEA) is performed by using ABAQUS software. The geometrically perfect tanks with different R/t and H/R ratios are considered for modal and linear seismic analysis. The modeling method, appropriate element type, and the necessary number of elements for numerical analysis are recommended. Field observations during past earthquakes and published experimental results are used to substantiate the accuracy of employed FEA. The accuracy of the current design guidelines is assessed based on the extensive parametric study. According to the results of the parametric study of the perfect tanks, the buckling strength decreases significantly as the radius‐to‐thickness ratio (R/t) increases. Furthermore, it decreases slightly as the height‐to‐diameter ratio (H/R) increases.

Strength and ductility evaluation of steel tubular columns under cyclic multiaxial loading

Proceedings of the 15th International Symposium on Tubular Structures, Rio de Janeiro, Brazil, 27-29 May 2015, 2015

Seismic performance evaluation of steel tubular columns under cyclic bidirectional loading

Tubular Structures XIII, 2010

Buckling Strength of Cold‐Formed Stiffened Thin‐Walled Steel Box Bridge Piers under Cyclic Loading

ce/papers

This paper presents numerical simulations on the behavior of thin‐walled steel tubular bridge pie... more This paper presents numerical simulations on the behavior of thin‐walled steel tubular bridge piers of box sections under cyclic lateral loading in the presence of constant axial compression loads, using three‐dimensional finite element analysis adopted in commercial computer software ABAQUS. The analysis and experimental results are compared to show how the adopted material models, such as elastic perfectly plastic (EPP), kinematic hardening (KH), and isotropic hardening (ISO) material models are effective and reliable for capacity prediction and cyclic behavior evaluation. The effects of cyclic lateral loading on the hysteresis behavior of the thin‐walled steel tubular bridge piers of box sections have been evaluated by analyzing the hysteresis curve, envelope curve, stiffness, and strength degradation characteristics, considering the interaction of local buckling and flexural buckling. In contrast to the ISO and EPP material models, the analysis results compare reasonably well wi...

Iraj Mamaghani

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