Iraj H. P. Mamaghani

Analysis of Masonry Bridges: Discrete Finite Element Method

Masonry bridges are composed of a finite number of distinct interacting blocks that have a length scale relatively comparable to the structure of interest. Therefore, they are ideal candidates for modeling as discrete systems instead of modeling as continuum systems. The discrete finite element method (DFEM) developed by the author to model discontinuum media consisting of blocks of arbitrary shapes is adopted in the static and dynamic analyses of masonry bridges. The developed DFEM is based on the principles of the FEM that incorporate contact elements. DFEM considers blocks as subdomains and represents them by solid elements. Contact elements, which are far superior to joint or interface elements, are used to model the block interactions, such as sliding or separation. In this study, the DFEM is briefly reviewed. Through some typical illustrative examples, the applicability of the DFEM to analysis of masonry arch bridges is examined and discussed. It is shown that the DFEM has the potential to become a useful tool for researchers and practicing engineers in designing, analyzing, and studying behavior of masonry bridges under static and dynamic loading.

Evaluation of Penetrating Sealers for Reinforced Concrete Bridge Decks

An evaluation of sealers based on eight sets of laboratory tests was done. Five concrete sealer treatments were studied: D335, DCS, SS, R7, and CT40. These sealers were evaluated for three groups of concrete mixes: normal, fly ash, and old concrete. There were also control specimens that did not use any type of sealer for comparison purposes. The test data were used to determine which sealer and concrete mix combination was the most adequate in improving resistance to the deterioration of concrete properties.

Seismic Design and Ductility Evaluation of Thin-Walled Steel Bridge Piers of Box Sections

This paper deals with seismic design and ductility evaluation of thin-walled steel bridge piers of box sections supporting highway bridge superstructures. The basic characteristics of the thin-walled steel box section structures are noted. A seismic design method for ultimate strength and ductility evaluation of thin-walled steel bridge piers of box sections 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 to both the design of new, and the retrofitting of existing, thin-walled steel bridge piers of box sections. The effects of some important parameters, such as width-to-thickness ratio, column slenderness ratio, and residual stress, on the ultimate strength and ductility of thin-walled steel bridge piers of box sections are presented and discussed.

Discrete Finite Element Method Application for Analysis of Unreinforced-Masonry Underground Structures

Unreinforced-masonry underground structures are composed of a finite number of distinct interacting blocks that have length scales relatively comparable with the underground openings of interest. Therefore, these structures are ideal candidates for modeling as discrete systems instead of as continuous systems. The discrete finite element method (DFEM) developed by the author to model discontinuous media consisting of blocks of arbitrary shapes was adopted for the static analysis of unreinforced masonry underground structures. The developed DFEM was based on the principles of the finite element method incorporating contact elements. The DFEM considers blocks as subdomains and represents them by solid elements. Contact elements, which are far superior to joint or interface elements, are used to model block interactions such as sliding or separation. In this study, the DFEM is briefly reviewed; then, through some illustrative examples, the applicability of the DFEM to the analysis of unreinforced-masonry underground structures is examined and discussed. It is shown that the DFEM provides an efficient tool for researchers and practical engineers in designing, analyzing, and studying the behavior of unreinforced masonry underground structures under static loading.

INELASTIC BEHAVIOR OF STRUCTURAL STEELS UNDER CYCLIC BIAXIAL NONPROPORTIONAL LOADING

This paper deals with the cyclic behavior of structural steels under biaxial nonproportional compression and torsion. The experimentally observed biaxial cyclic behavior of steels subjected to combined nonproportional compression and torsion is examined and discussed. Some important cyclic behavior of steels within the yield plateau and strain-hardening region, such as reduction of the elastic range, the decrease of the yield plateau, cyclic strain hardening, fading and nonfading memory under biaxial nonproportional loading are presented. The rate of nonproportionality of loading on cyclic behavior is evaluated.

Cyclic Elastoplastic Analysis and Stability Evaluation of Steel Braces of Hollow Section

This paper deals with the cyclic elastoplastic analysis and stability evaluation of steel braces of hollow sections subjected to axial tension and compression. The inelastic cyclic performance of cold-formed steel braces of circular and box hollow sections is examined through finite element analysis using the commercial computer program ABAQUS. First some of the most important parameters considered in the practical design and ductility evaluation of steel braces of tubular hollow sections are presented. Then the details of finite element modeling and numerical analysis are described. Later the accuracy of the analytical model employed in the analysis is substantiated by comparing the analytical results with the available test data in the literature. Finally the effects of some important structural and material parameters on cyclic inelastic behavior of steel braces are discussed and evaluated. INTRODUCTION Steel braced frames are one of the most commonly used structural systems because of their structural efficiency in providing significant lateral strength and stiffness. The steel braces contribute to seismic energy dissipation by deforming inelastically during an earthquake. The use of this type of construction indeed avoids the brittle fracture found in beam-to-column connections in moment resisting steel frames that occurred in the Northridge earthquake in 1994 and the Kobe earthquake in 1995 (ASCE 2000, IGNTSDSS 1996). However, careful design of steel braced frames is necessary to avoid possible catastrophic failure by brace rupture in the event of a severe seismic loading. The current capacity design procedure adopted in most seismic design steel specifications (AISC 1997, CAN-CSAS16.1 1989), for concentrically braced frames requires yielding in the braces as primary members, whereas the secondary members of the frame should remain elastic and hence carry forces induced by the yielding members. The transition from current perspective seismic codes to performance-based design specifications requires accurate predictions of inelastic limit states up to structural collapse. The cyclic behavior of steel brace members is complex due to the influence of various parameters such as, material nonlinearity, structural nonlinearity, boundary condition, and loading history. The material nonlinearity includes structural steel characteristics such as, residual stresses, yield plateau, strain hardening and Bauschinger effect. The structural