M. Saiid Saiidi

Exploratory Study of Seismic Response of Concrete Columns with Shape Memory Alloys Reinforcement

Superelastic shape memory alloys (SMAs) are unique materials that have the ability to undergo large deformation, but can recover deformations fully upon load removal. The primary objective of this study was to investigate if this characteristic of SMAs can be harnessed to reduce residual displacement of concrete columns that are reinforced with SMA bars in the plastic hinge area. Another target was to evaluate seismic performance and damage in a SMA-reinforced column that is repaired using engineered cementitious composites (ECC). Two quarter-scale spiral reinforced concrete (RC) columns with SMA longitudinal reinforcement in the plastic hinge area were tested on a shaketable. The data showed that SMA- reinforced columns were able to recover nearly all of post-yield deformation and that the use of ECC reduced the concrete damage substantially, thus requiring minimal repair even after a strong earthquake. A new hysteresis model for SMA-reinforced members led to close correlation with the measured displacement histories for both test specimens.

Cyclic Response of Concrete Bridge Columns Using Superelastic Nitinol and Bendable Concrete

This study investigates the effectiveness of reinforced concrete bridge columns with superelastic shape memory alloy (SMA) reinforcement and engineered cementitious composites (ECC) in plastic hinges in reducing permanent residual column displacements and damage due to earthquakes. Three circular column models incorporating innovative materials in the plastic hinge zone were tested under slow cyclic loading to failure. The first model, round steel conventional concrete (RSC), used conventional concrete and steel reinforcement in the plastic hinge. The other two models incorporated SMA longitudinal reinforcement: one (round Nitinol conventional concrete (RNC)) and the other (round Nitinol engineering cementitious composites (RNE)). The average ratio of residual to maximum displacement in RNE was one-sixth of that of RSC and one-half of that of RNC, indicating substantial benefits of using the combination of SMA and ECC. RNE experienced the least damage and the highest drift capacity among the three columns. The residual drift in RNC was also small, but the damage was significant. Results from analytical studies using a computer program showed good correlation with the experimental data.

Large scale testing of nitinol shape memory alloy devices for retrofitting of bridges

A large scale testing program was conducted to determine the effects of shape memory alloy (SMA) restrainer cables on the seismic performance of in-span hinges of a representative multiple-frame concrete box girder bridge subjected to earthquake excitations. Another objective of the study was to compare the performance of SMA restrainers to that of traditional steel restrainers as restraining devices for reducing hinge displacement and the likelihood of collapse during earthquakes. The results of the tests show that SMA restrainers performed very well as restraining devices. The forces in the SMA and steel restrainers were comparable. However, the SMA restrainer cables had minimal residual strain after repeated loading and exhibited the ability to undergo many cycles with little strength and stiffness degradation. In addition, the hysteretic damping that was observed in the larger ground accelerations demonstrated the ability of the materials to dissipate energy. An analytical study was conducted to assess the anticipated seismic response of the test setup and evaluate the accuracy of the analytical model. The results of the analytical simulation illustrate that the analytical model was able to match the responses from the experimental tests, including peak stresses, strains, forces, and hinge openings.

SEISMIC PERFORMANCE OF RECTANGULAR BRIDGE COLUMNS WITH MODERATE CONFINEMENT

This study is part of a project to develop detailing guidelines for reinforced concrete bridge columns and walls in areas of low to moderate seismicity. The work presented examines the ductility and behavior of rectangular reinforced concrete columns with moderate confinement. Four half-scaled rectangular bridge columns were built and tested. The transverse reinforcement ratios provided in the strong direction of the column specimens corresponded to 46% and 60% of the minimum lateral reinforcement required by the American Association of State Highway and Transportation Officials for seismic detailing. Each specimen was tested under constant axial load while subjected to quasistatic cyclic lateral loading in the column strong direction. The axial load indexes were 10% and 25%. The specimens exhibited displacement ductilities ranging between 5 and 7. Based on analytical and experimental results, an equation for designing the confinement steel for target ductility is presented.

Shake Table Studies of Energy-Dissipating Segmental Bridge Columns

Five one-third scale segmental bridge columns with plastic hinges incorporating different advanced materials were designed and tested on one of the shake tables at the University of Nevada, Reno. The columns were subjected to the Sylmar Earthquake record with increasing amplitudes until failure. All the models were cantilever with longitudinal steel dowels connecting the base segment to the footing. Unbonded posttensioning was used to connect the segments and to minimize the residual displacements. Energy dissipation took place mostly through the yielding of the longitudinal bars in the base segment. Conventional RC was used in the plastic hinge of a reference column. In one of the models, a built in elastomeric pad integrated with the footing and a concrete segment constituted the plastic hinge. The other two columns incorporated engineered cementitious composite (ECC) and unidirectional carbon fiber reinforced polymer (CFRP) fabrics at the lower two segments. The effectiveness of repair with CFRP wraps was also studied by repairing and retesting the reference column. The test results showed that the proposed models with advanced materials are suitable for accelerated bridge construction in high seismic zones because of their fast construction, high energy dissipation, minimal damage in the plastic hinge zone, and minimal residual displacement.

Seismic Performance of Precast Columns with Mechanically Spliced Column-Footing Connections

This paper presents the results from a large-scale experimental study that was conducted at the University of Nevada in Reno, NV. Five half-scale bridge column models were constructed and tested under reversed slow cyclic loading. The study focused on developing four new moment connections at column-footing joints for accelerated bridge construction in regions of high seismicity. The new connections were employed in precast columns, each using mechanical splices to create connectivity with reinforcing bars in a cast-in-place footing. Two different mechanical splices were studied: an upset headed coupler and a grout-filled sleeve coupler. Along with the splice type, the location of couplers within the plastic hinge zone was also a test variable. All precast models were designed with the intent to emulate conventional cast-in-place construction and, thus, were compared with a conventional cast-in-place test model. Results indicate the behavior of these new connections was similar to that of conventional cast-in-place construction with respect to key response parameters, although the plastic hinge mechanism could be significantly affected by the couplers.

Shake-Table Studies of a Four-Span Bridge Model with Advanced Materials

As part of a major study on the seismic response of bridge systems with conventional and advanced details, a large-scale model of a 4-span bridge incorporating several innovative plastic hinges was recently tested on shake tables at the University of Nevada, Reno. The bridge model included six columns, each pair of which utilized a different unconventional detail at the bottom plastic hinges: shape memory alloys (SMAs), engineered cementitious composites (ECCs), elastomeric pads embedded into columns, and posttensioning tendons. The bridge model was subjected to two horizontal components of simulated earthquake records of the 1994 Northridge earthquake in California. More than 340 channels of data were collected. Test results showed the effectiveness of the innovative materials in reducing damage and permanent displacements. The damage was minimal in plastic hinges with SMA/ECC and those with built-in elastomeric pads. Conventional reinforced concrete plastic hinges were severely damaged because of spalling of concrete and rupture of longitudinal and transverse reinforcement.

Seismic Design and Assessment of Bridges

Preface Contributors 1 Introduction Andreas J. Kappos 2 Modelling of Bridges for Inelastic Analysis M. Saiid Saiidi, Antonio Arede, Donatello Cardone, Pedro Delgado, Mauro Dolce, Matej Fischinger, Tatjana Isakovic, Stavroula Pantazopoulou, Gokhan Pekcan, Rui Pinho, and Anastasios Sextos 2.1 Introduction 2.2 Superstructure (Deck) 2.2.1 Deck Types, Sectional Layouts and Properties 2.2.2 The Role of Deck Modelling in Seismic Assessment 2.2.3 Effects of Skew and Curvature in Plan 2.2.4 Verification of Deck Deformation Demands 2.3 Bearings and Shear Keys 2.3.1 Modelling of Bearings 2.3.2 Mechanical Bearings (Steel Bearings) 2.3.3 Modern Bearing Types 2.3.4 Modelling of Shear Keys 2.4 Isolation and Energy Dissipation Devices 2.5 Piers 2.5.1 Modelling for Seismic Response of Columns in Reinforced Concrete Bridges 2.5.2 Finite Length Plastic Hinge Model 2.5.3 Distributed Flexibility Based Element Model 2.5.4 Two and Three-Dimensional FEM Discretizations 2.5.5 Example 1 on Fiber Model Application 2.5.6 Example 2 on Fiber Model Application 2.5.7 Analytical Modelling of Hollow Box Columns 2.6 Modelling of dynamic interaction between piers, foundation and soil 2.6.1 Pseudo-static Winkler approach 2.6.2 Linear Soil-Foundation-Bridge Interaction Analysis in the Time Domain 2.6.3 Nonlinear Soil-Foundation-Bridge Interaction Analysis in the Time Domain 2.7 Modelling of Abutment-Embankment-Superstructure Interaction 2.7.1 Simple P-y Relationships for Modelling Embankment-abutment Systems 2.7.2 Typical Bridges Studied 2.7.3 Modelling of the Abutment-Foundation-Backfill-Embankment Systems 2.7.4 Proposed P-y Relationships for Typical Abutment-Embankment Systems and Comparison with Caltrans Guidelines 3 Methods for Inelastic Analysis of Bridges M. Nuray Aydinoglu, Matej Fischinger, Tatjana Isakovic, Andreas J. Kappos, and Rui Pinho 3.1 Introduction 3.2 Nonlinear Response History Analysis (NRHA) procedure 3.3 Nonlinear analysis procedures based on pushover analysis 3.3.1 General 3.3.2 Historical vs. contemporary implementation of pushover analysis 3.4 Single-mode pushover analysis procedures 3.4.1 Single-mode pushover analysis procedure with invariant load patterns: The N2 Method 3.4.2 Single-mode pushover analysis procedure with adaptive load or displacement patterns 3.5 Multi-mode pushover analysis procedures 3.5.1 Multi-mode procedure based on independent modal pushover analyses with invariant load patterns: The MPA (Modal Pushover Analysis) Method 3.5.2 Simultaneous multi-mode pushover procedure with modal adaptive displacement patterns: The Incremental Response Spectrum Analysis (IRSA) Method 3.5.3 Multi-mode procedures based on single-run pushover analysis with modal combined adaptive load or displacement patterns 4 Case studies and comparative evaluation of methods Tatjana Isakovic, Antonio Arede, Donatello Cardone, Pedro Delgado, Matej Fischinger, Andreas J. Kappos, Nelson Vila Pouca, Rui Pinho, and Anastasios Sextos 4.1 Introduction 4.2 Basic parameters that influence the applicability of pushover methods 4.3 Case studies - comparison of alternative methods 4.3.1 Case study 1: Single-mode and multimodal pushover, and dynamic response history, analyses of bridges 4.3.2 Case study 2: Pushover and dynamic response history analyses of bridges 4.3.3 Case study 3: Comparison of four different NSPs in the assessment of continuous span bridges 4.3.4 Case study 4: Performance-based seismic assessment of simply supported deck bridges 4.4 Experimental evaluation of analytical methods 4.4.1 Applicability of analytical methods to the seismic analysis of RC bridge, experimentally tested on three shake tables 4.4.2 Numerical studies of RC bridge, supported by hollow box columns, which was tested pseudo-dynamically 5 Conclusions and Recommendations Andreas J. Kappos and Tatjana Isakovic Index

Reinforcing NiTi Superelastic SMA for Concrete Structures

AbstractSuperelastic (SE) shape memory alloy (SMA) is an advanced material that may be used as an alternative to conventional reinforcing steel in civil engineering structures to control residual deformations. The most common SE SMA type is an alloy of nickel and titanium (NiTi), which has been used in medical instruments and aerospace industries. A state-of-the-art review was conducted and factors that affect stress-strain behavior of SE SMA were identified. Subsequently, a simple constitutive stress-strain model was adopted from the literature, and mechanical properties for SE SMA that are of interest to structural engineering were defined. A procedure was proposed to extract mechanical properties of reinforcing SE SMA from test data obtained according to a standard test, and the range for each property was determined. Comprehensive seismic analyses of a bridge column were carried out to determine the effect of each mechanical property on the moment-curvature and force-displacement relationships. Then, ...

Shake-Table Studies of a Four-Span Reinforced Concrete Bridge

AbstractShake-table response of a 33.6-m-long (110-ft-long), four-span, RC bridge model with a continuous posttensioned superstructure supported on three, two-column bents was studied under horizontal bidirectional coherent simulated earthquakes. The pier heights varied, introducing a slight asymmetry about the centerline of the bridge model. The superstructure ends were supported on seat-type abutments that were connected to hydraulic actuators simulating abutment movements. The skew angle was zero. The bridge model was subjected to successive motions simulating a modified version of a record from the 1994 Northridge Earthquake. Results showed that damage was concentrated in plastic hinge regions of the columns and that the pier caps and the superstructure remained essentially elastic. The shortest pier failed, but this pier continued to carry vertical loads, and the bridge did not collapse. Despite the lack of skew, the superstructure-abutment interaction led to large in-plane rotations that caused sign...