Flash flood is one of the most common natural hazards affecting many mountainous areas. Previous studies explored flash flood susceptibility models; however, there is still a lack of case studies in ...the transport sector. This paper aimed to develop advanced hybrid machine learning (ML) algorithms for flash flood susceptibility modeling and mapping using data from the road network National Highway 6 in Hoa Binh province, Vietnam. A single ML model of reduced error pruning trees (REPT) and four hybrid ML models of Decorate-REPT, AdaBoostM1-REPT, Bagging-REPT, and MultiBoostAB-REPT were applied to develop flash flood susceptibility maps. Field surveys were conducted about the flash flood locations on the 115-km route length of the National Highway 6 in 2017, 2018, and 2019 flood events. This study used 88 flash flood locations and 14 flood conditioning factors to construct and validate the proposed models. Statistical metrics, including sensitivity, specificity, accuracy, root mean square error, and area under the receiver operating characteristic curve, were applied to evaluate the models’ performance and accuracy. The DCREPT model showed the best performance (AUC = 0.988) among the training models and had the highest prediction accuracy (AUC = 0.991) among the testing models. We found that 12,572 ha (Decorate-REPT), 9564 ha (AdaBoostM1-REPT), 11,954 ha (Bagging-REPT), 14,432 ha (MultiBoostAB-REPT), and 17,660 ha (REPT) of the 3-km buffer area of the highway are in the high- and very high-flash-flood-susceptibility areas. The proposed methodology could be potentially generalized to other transportation routes in mountainous areas to generate flash flood susceptibility prediction maps.
Due to their low intrinsic damping, stay cables in cable-stayed bridges are vulnerable to dynamic excitation. The cables have often been exhibiting undesirable and excessive vibrations, which result ...in increasing maintenance frequency and disruption to normal operations of the entire bridges. Mitigation of undesired cable vibration can be achieved by attaching a traditionally mechanical damper near the anchorage. Although utilizing this type of damper demonstrates vibrating diminishment in cables, the approach is not the most effective method due to geometric constraints. Tuned Mass Damper (TMD) has been used to overcome the deficiency of the traditional mechanical damper since it can be mounted anywhere along a cable. This paper proposes a new type of damper called the Tuned Mass - High Damping Rubber (TM-HDR) damper for increasing damping ratio of the cable. Oscillation parameters of cable with an attached TM-HDR damper are investigated in detail using an analytical formulation of the complex eigenvalue problem. As a result, optimal parameters of the damper can be evaluated and selected in order to reduce vibrations of cable. In addition, this paper demonstrates the effects of TM-HDR damper by using an example.
Abstract
Flood-induced scours near the pier foundation are an adverse phenomenon that may cause the collapse of bridges. However, in the seismic design of bridges, the scour impact is commonly ...ignored when evaluating the seismic response. This study aims to quantify the effect of flood-induced scours on nonlinear static and dynamic behaviors of typical reinforced concrete bridges. For this regard, three-dimensional finite element models of two- and three-span bridges with a multi-cell box girder, circular column bent, and extended pile-shaft foundation are first developed, where the column bent is modeled considering the material and geometry nonlinearity. The interaction between the soil and structure is also accounted for by using soil spring models. By considering different scour depths, the modal, static pushover, and dynamic time-history analyses of the bridges in both directions are investigated. It is observed from the modal analysis that the fundamental periods of the bridges increase with the increase of scour depth. In addition, the results in terms of the column drift ratio show that scour may increase the seismic damage to the bridges, which transfers damage from the column bent to the pile-shaft foundation. The findings of this study exhibit the significant effect of the scour on the seismic damage of reinforced concrete bridges; therefore, it is recommended that this phenomenon should be considered in the bridge seismic design.
This paper describes the application of two artificial intelligence- (AI-) based methods to predict the 28-day compressive strength of fiber-reinforced high-strength self-compacting concrete ...(FRHSSCC) from its ingredients. A series of 131 data samples collected from various published literature sources were used for training, validation, and testing models. Various AI models were developed with different training algorithms and a number of nodes in the hidden layer to obtain the optimal model for the FRHSSCC data. It is shown that the performances of the artificial neural network (ANN) were better than that of the adaptive neurofuzzy inference system (ANFIS) model. Specifically, the overall coefficient of determination (R2) of the ANN and ANFIS models was 0.9742 and 0.9584, respectively. The sensitivity analysis was also conducted with the ANN model to investigate the effects of input parameters on the output. The results from the sensitivity analysis revealed that the compressive strength of FRHSSCC at 28 days was more sensitive with the changes of water by cement ratio (WCR) parameter and insensitive with varying amounts of fiber (VOF). Finally, it can be concluded that the application of artificial intelligence shows the great potential in the prediction of compressive strength of FRHSSCC.
This paper presents a fracture behavior modeling of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) slabs under contact blast loading using the finite element method. The UHPFRC is supposed ...to be brittle material and follow the Johnson-Holmquist-II(JH-2) model. The steel rebar is modeled using the elasto-plastic model. The Emulsion Explosive has been used and modeled by the SPH method. UHPFRC slabs with the dimensions 1000mm of length, 800mm of width and 120mm of thickness is considered. The steel fibers with a volume fraction of 2% is used. The UHPFRC material is fabricated in laboratory using the material available in Vietnam. The concrete crater and spall damage of UHPFRC slab under contact blast loading are considered. The numerical results are compared with experiment. These results allow to evaluate the resistance against blast load of UHPFRC fabricated in lab.
Vibration monitoring of tower-like structures is a major challenge in vibration-based structural health monitoring, which is commonly expensive and time-consuming. In this paper, a novel vibration ...frequency measurement system based on a classical pendulum and advanced optical instruments that provides rapid, high-precision vibration measurements is developed. This system is integrated by a laser-based pendulum with an ultrafast interface position detector to form a table-top vibrometer that can precisely monitor structural vibration frequencies. In which, the position of the laser beam spot on the position-sensitive detector produces a voltage signal that is continuously recorded as the pendulum oscillates around its equilibrium position. By a comparative study of vibration frequencies between shaking table tests on the proposed system and simulations, it can be concluded that the proposed measurement system is independent of friction on the rotation shaft and other resistances; this makes the system environmentally robust over the long-term use, and thus reduces significantly maintenance and labor costs, especially in the case of tower-like structures where the measurement point is difficult to human access.
Abstract
Failure-induced vibrations are a common phenomenon in many civil structures, and the characterization of their vibration frequencies is crucial for monitoring their structural health. This ...paper presents a new optics-based mechanical system that can monitor the vibrations of civil structures through the fluctuation of laser spot size using advanced image sensors. The principle behind this vibrometer combines mechanical oscillation and laser optics, and it provides information on vibration through the precise variation of spot size in a low-cost, low-risk, and high-speed manner. The system comprises simple components that are easily integrated into various civil structures. Therefore, this novel approach offers a promising method for effectively monitoring the health of civil structures.
Abstract
The use of ultra-high-performance concrete (UHPC) jackets as a seismic strengthening method for reinforced concrete structures has become increasingly prevalent. Specifically, these jackets ...are applied to plastic hinge regions of the structures to improve overall earthquake resistance. This study evaluates the effectiveness of UHPC jackets in strengthening reinforced concrete columns through fragility curves. The columns are modeled numerically, accounting for material nonlinearity, and various strengthening scenarios, including those without UHPC jackets and with UHPC jackets of different heights, are modeled and validated with cyclic loading tests. Subsequently, a case study of a two-column reinforced concrete bridge pier is examined. Time-history dynamics analyses are conducted on 140 ground motion records to develop probabilistic seismic demand models of the column with different strengthening designs. Fragility curves obtained using the cloud method indicate a significant impact of the strengthening method on the failure probability of the column. The research findings presented in this paper provide engineers with a basis for selecting appropriate UHPC jacket parameters, including thickness, height, and material strength in a rational manner.
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