Seismic Behaviour of Post-Tensioned Segmental Bridge Columns with Self-Centring System

Prefabricated bridge columns have shown increasing demands over the past few years due to their advantages compared to conventional bridge columns. The reason for this interest is due to their appropriate performance against severe earthquakes (EQs), where they remain functional and repairable with lower amount of cracks and damage. However, there is some uncertainty on application of these kinds of bridge columns in high seismic areas mainly due to lack of knowledge on their behaviour against severe earthquake loading. Therefore, comprehensive design guidelines which consider nonlinearity and energy dissipation and recentring capacity of the post-tensioning (PT) segmental columns are necessary. In this study, continuous steel bars are incorporated as starters through the segments and footing foundation in order to increase the seismic energy absorption of PT segmental columns. The influences of different parameters such as the force level criteria for post-tensioning, steel jacketing and mild steel ratio and column aspect ratio (AR) are important factors which have to be appropriately selected in various design procedures, such as displacement-based design, in order to achieve desirable stiffness, strength, equivalent viscous damping and lateral seismic demand. In this study, the cyclic loading and ground motion excitations were numerically performed in order to evaluate the bridge column seismic demands. Guidelines for performance-based design and displacement-based design are proposed

A numerical study on seismic response of self-centring precast segmental columns at different post-tensioning forces

Precast bridge columns have shown increasing demand over the past few years due to the advantages of such columns when compared against conventional bridge columns, particularly due to the fact that precast bridge columns can be constructed off site and erected in a short period of time. The present study analytically investigates the behaviour of self-centring precast segmental bridge columns under nonlinear-static and pseudo-dynamic loading at different prestressing strand levels. Self-centring segmental columns are composed of prefabricated reinforced concrete segments which are connected by central post-tensioning (PT) strands. The present study develops a three dimensional (3D) nonlinear finite element model for hybrid post-tensioned precast segmental bridge columns. The model is subjected to constant axial loading and lateral reverse cyclic loading. The lateral force displacement results of the analysed columns show good agreement with the experimental response of the columns. Bonded post-tensioned segmental columns at 25%, 40% and 70% prestressing strand stress levels are analysed and compared with an emulative monolithic conventional column. The columns with a higher initial prestressing strand levels show greater initial stiffness and strength but show higher stiffness reduction at large drifts. In the time-history analysis, the column samples are subjected to different earthquake records to investigate the effect post-tensioning force levels on their lateral seismic response in low and higher seismicity zones. The results indicate that, for low seismicity zones, post-tensioned segmental columns with a higher initial stress level deflect lower lateral peak displacement. However, in higher seismicity zones, applying a high initial stress level should be avoided for precast segmental self-centring columns with low energy dissipation capacity

Application of shape memory alloy bars in self-centring precast segmental columns as seismic resistance

The objective of this study is to investigate analytically the performance of self-centring precast segmental bridge columns with shape memory alloy (SMA) starter bars under nonlinear static and lateral seismic loading. For this purpose, a 3D finite element model for hybrid post-tensioned bridge column has been developed. The precast post-tensioned segmental bridge columns possessing a central tendon and adequate transverse confinement provided by the steel tube jacketing as self-centring bridge columns have an undesirable high lateral seismic demand due to their low energy dissipation. In order to eliminate this deficiency while keeping the residual displacement small, SMA starter bars are applied in this system. The effect of post-tensioning (PT) forces of the central strands and SMA bar size are investigated. The results indicate that in high seismicity zones, bridge columns with SMA bars at a higher level of PT forces have a superior performance against earthquake loading

A novel idea to increase the performance of a wheat flour cyclone separator: Controlling the reverse flow

In this study, as a novelty, the reverse flow effect on a wheat flour cyclone performance was evaluated. A computational fluid dynamics (CFD) simulation was realized using a Reynolds stress turbulence model. Also, particle–air interactions were modeled applying a discrete phase model. Besides the experimental measurement, the numerical simulation was conducted in a main (without reverse flow) and six various reverse flow levels (I = 0.0385 m3 s−1, II = 0.0396 m3 s−1, III = 0.0484 m3 s−1, IV = 0.0583 m3 s−1, V = 0.0704 m3 s−1, and VI = 0.0836 m3 s−1) by CFD. The validation between pressure drop in experimental data and numerical results revealed a good agreement with a maximum deviation of 8.2%. Cyclone performance including pressure drop and separation efficiency was assessed in the mentioned reverse flow levels. Moreover, velocity field, centrifugal force, and turbulence parameter were evaluated, comprehensively. It was found that the flour separation efficiency increased with enhancing the reverse flow level to IV = 0.0583 m3 s−1, but decreased with a sharp slope in the reverse levels of V = 0.0704 m3 s−1 and VI = 0.0836 m3 s−1

The Use of a Movable Vehicle in a Stationary Condition for Indirect Bridge Damage Detection Using Baseline-Free Methodology

The use of an instrumented scanning vehicle has become the center of focus for bridge health monitoring (BHM) due to its cost efficiency, mobility, and practicality. However, indirect BHM still faces challenges such as the effects of road roughness on vehicle response, which can be avoided when the vehicle is in a stationary condition. This paper proposes a baseline-free method to detect bridge damage using a stationary vehicle. The proposed method is implemented in three steps. First, the contact-point response (CPR) of the stationary vehicle is computed. Secondly, the CPR is decomposed into intrinsic mode functions (IMFs) using the variational mode decomposition (VMD) method. Finally, instantaneous amplitude (IA) of a high frequency IMF is computed. The peak represents the existence and location of the damage. A finite element model of a bridge with damage is created. The results show that the method can identify the damage location under different circumstances, such as a vehicle with and without damping, different speeds of the moving vehicle, different sizes of damage, and multiple damage. A higher speed was found to provide better visibility of damages. In addition, smaller damage was less visible than wider damage

The Use of a Movable Vehicle in a Stationary Condition for Indirect Bridge Damage Detection Using Baseline-Free Methodology

The use of an instrumented scanning vehicle has become the center of focus for bridge health monitoring (BHM) due to its cost efficiency, mobility, and practicality. However, indirect BHM still faces challenges such as the effects of road roughness on vehicle response, which can be avoided when the vehicle is in a stationary condition. This paper proposes a baseline-free method to detect bridge damage using a stationary vehicle. The proposed method is implemented in three steps. First, the contact-point response (CPR) of the stationary vehicle is computed. Secondly, the CPR is decomposed into intrinsic mode functions (IMFs) using the variational mode decomposition (VMD) method. Finally, instantaneous amplitude (IA) of a high frequency IMF is computed. The peak represents the existence and location of the damage. A finite element model of a bridge with damage is created. The results show that the method can identify the damage location under different circumstances, such as a vehicle with and without damping, different speeds of the moving vehicle, different sizes of damage, and multiple damage. A higher speed was found to provide better visibility of damages. In addition, smaller damage was less visible than wider damage