Saber Moradi

Feasibility study of utilizing superelastic shape memory alloy plates in steel beam–column connections for improved seismic performance

Steel moment-resisting frames are prone to extensive damage in seismically active zones. Large permanent deformations in structural members following strong earthquakes can be mitigated using smart materials such as shape memory alloys. In this article, three-dimensional finite element analyses are conducted to study the seismic performance of beam–column connections incorporating shape memory alloy plates. Eight beam–column connection subassemblies with shape memory alloy plates in the plastic hinge of beam were analyzed under cyclic loading. Based on the numerical results, the recentering properties of superelastic shape memory alloy plates were found to be effective in reducing the residual drifts of a flange plate beam–column connection, while displaying an excellent ductility. In addition, shape memory alloy plates could prevent the occurrence of local buckling and damage in structural members. The new self-centering connections could also exhibit a good energy dissipation capability.

Finite-Element Simulation of Posttensioned Steel Connections with Bolted Angles under Cyclic Loading

AbstractSteel beam-column connections with posttensioned (PT) elements are proven systems that can provide adequate stiffness, strength, and ductility, while eliminating permanent deformations in a moment-resisting frame subjected to seismic loading. In this study, detailed three-dimensional finite-element (FE) models of steel beam-column connections with PT strands are developed and analyzed under cyclic loading. Efforts are made to overcome challenges in performing the nonlinear FE analysis of large-scale PT connections, which involves gap opening and closing behavior as well as contact and sliding phenomena. Geometric and material nonlinearities, preloaded bolts and strands are also considered in the modeling. Through a verification study, the results from the FE models are validated against prior experiments on interior PT connections with top-and-seat angles. Parametric studies are also conducted to investigate the effects of three factors on the cyclic performance of PT connections. The factors inve...

Lateral Load–Drift Response and Limit States of Posttensioned Steel Beam-Column Connections: Parametric Study

AbstractThe objective of this study is to identify the significant parameters that influence the lateral load–drift response of steel posttensioned (PT) connections. In particular, the effects of v...

Simulation, response sensitivity, and optimization of post-tensioned steel beam-column connections

...........................................................................................................................ii PREFACE................................................................................................iii TABLE OF CONTENTS ........................................................................................................v LIST OF TABLES ................................................................................................................. ix LIST OF FIGURES ............................................................................................................... xi ACKNOWLEDGEMENTS ............................................................................................... xvii CHAPTER

Response surface analysis and optimization of controlled rocking steel braced frames

As an alternative to conventional seismic force resisting systems, controlled rocking steel braced frames (CRSBFs) can effectively eliminate permanent structural damage after earthquakes. Together with the rocking action in the braced frame, post-tensioning (PT) elements and fuse members are used to provide self-centering and energy dissipation, respectively. This study firstly aims to assess the influence of design parameters related to the fuse and PT materials on the seismic response of CRSBFs. These factors include the yield strength, initial stiffness, and strain hardening ratio of the fuse, the initial force and modulus of elasticity of the PT strands, and the gravity load on the rocking column. Additionally, different analysis cases are considered to include the effects of frame aspect ratio and earthquake intensity level. Nonlinear response history analyses are performed with factor combinations generated using a design of experiment methodology. The second goal of the study is focused on optimizing the seismic response of CRSBFs with respect to the influential factors identified in the sensitivity analyses. Using a response surface methodology and desirability approach, multiple-response optimization is applied to determine the design variable values needed to simultaneously minimize the maximum transient and residual roof drift ratio and peak floor acceleration. Among other results, it is found that the fuse strain hardening ratio and PT strand modulus of elasticity do not significantly influence the seismic response demands in CRSBFs. The results of the multi-response optimization demonstrate that the initial PT force is most useful for minimizing all three seismic response demand parameters.

Incremental Dynamic Analysis of Shape Memory Alloy Braced Steel Frames

Incremental Dynamic Analysis (IDA) is a technique to determine the overall seismic performance of structures under varied intensities of earthquakes. In this paper, the seismic performance of four-story steel braced frames equipped with superelastic Shape Memory Alloy (SMA) braces is assessed by performing IDA. The seismic response of SMA-braced frames was compared to that of corresponding Buckling-Restrained Braced Frames (BRBFs). Based on the results of this comparative study, the SMA-braced frames were generally effective in reducing maximum interstory drifts and permanent roof deformations. In addition, the SMA-braced frames demonstrated more uniform drift distribution over the height of the building. As the intensity of earthquake excitation increases, a higher response reduction can be expected for SMA-braced frames.