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This paper investigated a novel hybrid precast pier system that utilized ultrahigh-performance concrete (UHPC). The pier combines features of emulative and nonemulative (of cast-in-place c...

Self-centering, precast, post-tensioned concrete, bridge columns can provide low-damage under earthquake loading and accelerated bridge construction. These columns can also be designed so that shear-slip occurs between precast segments to provide energy dissipation. This paper, first, presents experimental results of large-scale testing of pier specimens that can self-center and undergo shear-slip under cyclic lateral loading. In these tests, segment interface properties, which control shear-slip, changed as the silicone layer placed between each segment degraded during testing. Specimens with fresh silicone had more energy dissipation, lower stiffness, and higher residual displacements compared with the ones with degraded silicone. A hysteretic model is created to predict the global load-displacement behavior of piers under lateral loading by superimposing self-centering and shear-slip responses. Shear-slip measurements under both quasi-static and rapid cyclic tests were used to characterize the interface frictional properties to be used in hysteretic modeling. Friction coefficients of segment interfaces were also investigated under varying accumulative displacement, normal force, and shear-slip velocity. The proposed hysteretic model is validated using the experimental results. A parametric study was performed using the established hysteretic model to investigate the influence of friction properties of interface materials and initial post-tension forces on the seismic response. The results show that interface materials with lower friction coefficient will lead to enhanced energy dissipation, lower stiffness, and smaller self-centering capability. Selecting lower initial post-tension force decreases the stiffness. Finally, incorporating the hysteretic model in the Capacity-Demand-Diagram method, seismic response of piers with varying properties was predicted. The increase in friction coefficient and initial post-tension force consistently increases the maximum base shear demand. Increasing initial post-tension force decreases the peak displacement in most cases. Increasing friction coefficient can either increase or decrease the peak displacement.

As is known to all, Generative Antagonism Network (GAN) plays an important role in the field of image generation and classification. However, there are some shortcomings in it, one of which is that the generator and discriminator cannot converge to the real data at the same time. Therefore, Triple-GAN is proposed. Compared with GAN, it is composed of three parts: classifier, generator and discriminator, which guarantees that the data distribution of generator and classifier can converge to the real distribution. Yet, there are still some traditional limitations in the field of activation function and gradient descent such as gradient disappearance and gradient explosion. Thus, this paper adopts the new activation function Mish, the gradient ascending method and the gradient descending method instead of the original activation function and the gradient ascending algorithm. When a certain sparsity prevents the gradient from exploding and disappearing, the smooth curve of negative input value near the origin makes up for the defect of inactivation of neurons flowing into large gradient,and thus achieving better activation efficiency and greatly improving the efficiency of deep learning.

Generative adversarial network is an important generation model in the fields of big data, machine learning and deep learning. For semi-supervised learning, the improved generative adversarial network plays an important role in image generation and classification. Triple-GAN is the best one among them, which consists of classifier generator and discriminator, and it guarantees that the data distribution of generator and classifier can converge to the real distribution. However, the activation function and the gradient descent method of the original generative adversarial network have not been changed, and still have traditional limitations, which are prone to gradient disappearance and gradient explosion. Therefore, this paper adopts the new activation function Xwish and the fractional gradient step descent method with fixed memory step gradient descent method instead of the original activation function and the gradient descent method. It makes up for the disadvantages of inactivation caused by neuron flowing into large gradient while preventing gradient explosion and gradient disappearance with certain sparsity and introduces adaptive parameters to achieve better activation efficiency, which greatly improves the efficiency of deep learning.

On May 5, 2019, a truck-tractor-trailer loaded with six coils of steel crashed into a pier column of the Dongguofenli Bridge located on the Yongjin Highway in Shengzhou, China, resulting in severe damage to the impacted pier column. Prior studies on heavy truck collision with bridge piers mainly based on finite element (FE) simulations. However, none of them examined the behavior of bridges under a real vehicle-bridge collision accident. To fill in this gap, this paper aims to reproduce the Dongguofenli Bridge vehicle collision accident and scrutinize the causes of the observed bridge damages. This is achieved by using the high-resolution simulation models for both the impacted bridge structures and the colliding heavy truck. The typical heavy truck model widely used in previous studies was employed and validated based on the experimental data. Four different methods were examined to reasonably capture the soil-pile interaction behavior during vehicle collisions. Important lessons were learned from the FE simulation that reproduced this accident: 1) the characteristics of the cargo (i.e., cargo type and cargo’s fixing method) play an important role in determining the response of the bridge and 2) the damage that occurred to the bridge pier is most likely attributed to the direct impact between the bridge and the cargo (steel coils) that slipped off the truck. The analysis results also revealed that using the state-of-practice method for defining the impact force may lead to an unconservative bridge design for vehicle impact resistance. The applicability of the bridge design provisions related to vehicle impact design was also examined and the code-prescribed vehicle collision load was found to be inadequate to produce the damages that are observed in either the high-resolution simulation results or the real collision accident.

Seismic fragility assessment using structural dynamic analysis remains challenging for complex systems due to the high computational demand, such as the sea-crossing cable-stayed bridges. The paper aims to overcome this difficulty by developing an efficient seismic fragility analysis framework based on endurance time method (ETM). To demonstrate the framework for developing fragility curves, an example sea-crossing cable-stayed bridge is used as a case study. The ETM framework is validated by comparing the calculated fragility curves with those calculated by IDA framework. It is shown that the ETM is capable of significantly reducing computational effort without compromising the accuracy of fragility analysis results. The validated framework is then used to discuss the seismic fragility of sea-crossing cable-stayed bridges under scour and earthquakes. The influence of the time duration of endurance time acceleration functions (ETAFs) on the structural fragility is discussed. The influence of the time duration of ETAFs on the component fragility varies across different components, but the system fragility increases with the increasing time duration on the whole. Scour can produce either beneficial or adverse effects on the component and system seismic fragilities depending on the scour depth.

A novel exposed column base (ECB) connection, featuring composite yield mechanism (i.e., a combination of anchor rod and base plate yielding), has been recently proposed in Japan for optimum seismic performance. This paper focused on investigating the effects of using composite yield mechanism on damage mitigation for ECB connections. In doing so, four two-thirds scale specimens, with different base connection configurations, were tested under combined flexure and axial load. Their performances were assessed and compared in terms of damage evolution, moment-rotation relationship and energy dissipation. The experimental results showed that for ECB connection with composite yield mechanism, both anchor rod and base plate will actively contribute to the moment resistance and energy dissipation. This can successfully postpone the interior anchor rod yielding and fracture, compared to the ECB connection with anchor rod yield mechanism. Meanwhile, the strain demands on exterior plate can be also released compared to the ECB connection with base plate yield mechanism. The relative contributions from anchor rod and base plate of ECB connection with composite yield mechanism can be controlled by changing the exterior plate thickness. In addition, an analytical method was proposed to predict the yield and ultimate moment strength for the Composite Yield ECB connection based on the principle of virtual work. The difference between predicted and measured moment strength is within 15%, showing the validity of the proposed method for moment strength prediction.

Bridges crossing navigable waterways have a high risk for vessel collision hazard, and are meanwhile experiencing significant ‘aging’ hazard due to the surrounding aggressive environments. These bridges must be designed to be resilient to both episodic (vessel collision) and chronic (structural deterioration) hazards. To achieve this goal, this paper will develop a novel fragility assessment framework for reinforced concrete (RC) bridges under vessel collision with the corrosion-induced structural deterioration being considered. The cornerstone of this fragility assessment framework is the computational model with the capability of accurately predicting vessel impact response and corrosion-induced deterioration measures. In doing so, detailed finite element (FE) modeling approaches, including reinforcement bond-slip effects, are firstly developed and validated by the experimental results. The effects of corrosion are characterized by a series of deterioration measures that can be implemented into FE models. These FE modeling approaches were utilized to model the baseline bridge. Three different exposure periods (i.e., 0, 50, and 100 years) and two types of vessel (barge and ship) are considered. Driven by the response data generated by the FE model, a surrogate model is developed to feature both accurate vessel-impact response estimates and negligible computation cost. This surrogate model is then employed to create fragility curves using Monte Carlo methods. Fragility analysis results have indicated the significant role played by corrosion in increasing the vulnerability of RC bridges under vessel collision throughout the lifetime of the baseline bridge. The probability of bridge collapse rises by almost 100% near the end of the bridge’s life. Significant differences were found for the damage evolution of the deteriorated bridge under barge impacts and ship impacts. Particular critical impact speeds were observed in the barge-impact response, but not during ship collisions.

Unbonded posttension strands are used between anchorages to provide restoring forces to self-centering structures. In this research, monotonic and quasi-static cyclic tests were performed o...

Cadmium (Cd) in coal, fly ash, slag, atmospheric deposition, soils and sediments collected from Tianjin, northern China, were measured to provide baseline information and determine possible Cd sources and potential risk. The concentrations of Cd in coal, fly ash and atmospheric deposition were much higher than the soil background values. Fallout from coal-fired thermal power plants, heating boilers and industrial furnaces has increased the Cd concentration in soils and sediments in Tianjin. The concentrations of Cd in soils of suburban areas were significantly higher than in rural areas, suggesting that coal burning in Tianjin may have an important impact on the local physical environment. Cd from coal combustion is readily mobilized in soils. It is soluble and can form aqueous complexes and permeate river sediments. The high proportion of mobile Cd affects the migration of Cd in soils and sediments, which may pose an environmental threat in Tianjin due to the exposure to Cd and Cd compounds via the food chain. This study may provide a window for understanding and tracing sources of Cd in the local environment and the risk associated with Cd bioaccessibility.