An Investigation of the Ground Motion Scaling Procedures for the Nonlinear Seismic Analyses of Concrete Gravity Dams

Seismic assessment of gravity dams is generally carried out using time history analyses. Scaling of the motions is commonly used; however, in contrast to buildings, the performance of scaling procedures at predicting the mean and reducing the dispersion in engineering demand parameters (EDPs) is not known. The main goal of this study is to assess the performance of different scaling procedures in predicting seismic demands on dams. The performance regarding the prediction of the damage and the required number of motions for effective analysis was investigated. The results show that techniques commonly used for moment frames should not readily be applied to these structures.     

Capacity Design of Coupled RC Walls

Capacity design aims to ensure controlled ductile response of structures when subjected to earthquakes. This article investigates the performance of existing capacity design equations for reinforced concrete coupled walls and then proposes a new simplified capacity design method based on state-of-the-art knowledge. The new method is verified through a case study in which a set of 15 coupled walls are subject to nonlinear time-history analyses. The article includes examination of the maximum shear force in individual walls in relation to the total maximum shear force in the coupled wall system, and subsequently provides recommendations for design.     

Performance of Degrading Reinforced Concrete Frame Systems Under the Tohoku and Christchurch Earthquake Sequences

Field investigations after the recent Tohoku and Christchurch earthquakes reported failure of structural systems due to multiple earthquakes. In most failure cases the reported damage was mainly due to dramatic loss of stiffness and strength of structural elements as a result of material deterioration due to repeated earthquake loading. This study aims to investigate the degrading behavior of reinforced concrete frame systems subjected to Tohoku and Christchurch earthquake sequences. Numerical models of RC frames that incorporate damage features are established and inelastic response history analyses are conducted. The results presented in this study indicate that multiple earthquake effects are significant.     

A Damage Index for the Seismic Analysis of Reinforced Concrete Members

This article proposes a damage index for the seismic analysis of Reinforced Concrete members using the hysteretic energy dissipated by a structural member and a drift ratio related to failure in the structure. The index was calibrated against observed damage in laboratory tests of 76 RC column units under various protocols. Values obtained in this calibration had acceptable agreement with the levels of damage observed in the test specimens. An analysis of the parameters involved in the definition of the proposed damage index shows the importance of displacement history in the drift ratio capacity of structures.     

Cyclic Response of Concrete Beams Reinforced by Plain Bars

There are many reinforced concrete structures throughout the world that have been built in the past decades that lack appropriate seismic details and reinforced by plain bars. To study the behavior of such buildings, seven beams have been tested under cyclic and monotonic load. The specimens include substandard specimens, with deficient seismic details and reinforced by plain bars, specimens designed in accordance with ACI-318-99 but reinforced by plain bars, and standard specimens reinforced by deformed bars. The tests indicate that the substandard specimens sustain relatively large slip of longitudinal bars, separation of specimen relative to foundation and sliding at large deformation phase, low initial stiffness ratio, limited lateral displacement capacity, and loss of nominal yield strength. The specimens reinforced by plain bars in accordance with ACI-318-99 perform almost similar to standard specimens with deformed bars, in terms of elastic stiffness and lateral displacement ductility; but, they sustain larger slip, and smaller yield strength. Failure of all specimens reinforced by plain bars is characterized by flexural cracks without visible shear failure. Residual shear strength of substandard specimens is modeled by dowel action of longitudinal bars to predict a lower limit for lateral strength of the specimens.     

Self-Centering Behavior of Unbonded,Post-Tensioned Precast Concrete Shear Walls

Self-centering ability of unbonded post-tensioned precast concrete shear walls has been attributed to the presence of post-tensioning force. However, the experimental results presented in this paper indicate that the post-tensioning force may completely die out during cyclic loading while the walls are able to retain their superior self-centering characteristic. Moreover, the analytical study presented in this article indicates that with proper configuration of end-anchorages for post-tensioned tendons, self-centering of post-tensioned walls can be achieved even when the post-tensioning force vanishes. This study also investigates the effects of tendon layout, tendon end-anchorage configuration, and external vertical load on the self-centering ability of unbonded precast concrete shear walls subjected to earthquake loading.     

Direct Displacement-Based Design of Buildings with Different Seismic Isolation Systems

A displacement-based design (DBD) procedure for buildings equipped with different seismic isolation systems is proposed. It has been derived from the Direct Dispaced-Based Design (DDBD) method recently developed by Priestley et al. [2007] Priestley, M. J. N., Calvi, G. M. and Kowalsky, M. J. 2007. Displacement-Based Seismic Design of Structures, Pavia, , Italy: IUSS Press.  [Google Scholar]. The key aspect of the proposed procedure is the definition of a target displacement profile for the structure. It is assigned by the designer to achieve given performance levels, expressed in terms of maximum displacement of the isolation system and maximum interstory drift. The proposed design procedure has been developed for four different idealized force-displacement relationships, which can describe the cyclic response of a wide variety of isolation systems, including: (i) Lead-Rubber Bearings (LRB); (ii) High-Damping Rubber Bearings (HDRB); (iii) Friction Pendulum Systems (FPS); and (iv) Combinations of lubricated Flat Sliding Bearings (FSB) with different re-centering and/or energy dissipating auxiliary devices. In this article, the background and implementation of the design procedure is presented first. It is followed by the results of validation studies based on nonlinear time-history analyses on different design configurations of base isolated buildings.     

Importance of Degrading Behavior for Seismic Performance Evaluation of Simple Structural Systems

This study focuses on effect of degradation characteristics on seismic performance of simple structural systems. Equivalent single degree of freedom systems are used for which the structural characteristics are taken from existing reinforced concrete (RC) frame buildings. Simulation of degrading behavior is achieved by considering actual experimental data. To obtain the seismic response of degrading structural systems, two different approaches are used: inelastic spectral analysis and fragility analysis. According to the results obtained from both approaches, degrading behavior is dominant for mid-rise RC frame buildings as it significantly amplifies seismic demand. Hence, in performance-based assessment approaches, analytical modeling of such degrading structures should be carried out carefully.     

Seismic Fragility Evaluation of RC Frame Structures Retrofitted with Controlled Concrete Rocking Column and Damping Technique

Acceleration response of simple yielding structure is proportional to its own weight, but it is limited by yield strength. Thus, using rocking columns that reduces global yield strength, a limited acceleration is achieved. However, the displacement becomes large due to lower strength and higher inelasticity, but it can be controlled by adding damping. Performing fragility analyses, the seismic response of R/C frame structures with rocking columns and viscous dampers is investigated. Near field MCEER ground motions are considered. The analyses show that the story accelerations are reduced by using rocking columns, while the story displacements are controlled by using viscous dampers.     

Real-time Seismic Damage Detection of Concrete Shear Walls Using Artificial Neural Networks

Concrete shear walls are widely employed in buildings as a main resistance system against lateral loads. Early identification of seismic damage to concrete shear walls is vital for deciding post-earthquake occupancy in these structures. In this article, a method based on artificial neural networks for real-time identification of seismic damage to concrete shear walls was proposed. Inter-story drifts and plastic hinge rotation of concrete walls were used as the inputs and outputs of a MLP neural network. Modal Pushover Analysis was employed to prepare well-distributed data sets for training the neural network. The proposed method was applied to a five-story concrete shear wall building. The results from the network were compared with those obtained from Nonlinear Time History Analysis. It was observed that the trained neural network successfully detected damage to concrete shear walls and accurately estimated the severity of seismic-induced damage.