Numerical Study on Concrete Pumping Behavior via Local Flow Simulation with Discrete Element Method

The use of self-consolidating concrete and advanced pumping system enables efficient construction of super high-rise buildings; however, risks such as clogging or even bursting of pipeline still exist. To better understand the fresh concrete pumping mechanisms in detail, the discrete element method is employed in this paper for the numerical simulation of local pumping problems. By modeling the coarse aggregates as rigid clumps and appropriately defining the contact models, the concrete flow in representative pipeline units is well revealed. Important factors related to the pipe geometry, aggregate geometry and pumping condition were considered during a series of parametric studies. Based on the simulation results, their impact on the local pumping performance is summarized. The present work demonstrates that the discrete element simulation offers a useful way to evaluate the influence of various parameters on the pumpability of fresh concrete

Adaptive Crack Modeling with Interface Solid Elements for Plain and Fiber Reinforced Concrete Structures

The effective analysis of the nonlinear behavior of cement-based engineering structures not only demands physically-reliable models, but also computationally-efficient algorithms. Based on a continuum interface element formulation that is suitable to capture complex cracking phenomena in concrete materials and structures, an adaptive mesh processing technique is proposed for computational simulations of plain and fiber-reinforced concrete structures to progressively disintegrate the initial finite element mesh and to add degenerated solid elements into the interfacial gaps. In comparison with the implementation where the entire mesh is processed prior to the computation, the proposed adaptive cracking model allows simulating the failure behavior of plain and fiber-reinforced concrete structures with remarkably reduced computational expense

Study on Optimization of Working Performance of Ultra High Performance Concrete

The water binder ratio is a key parameter in the mix design of ultra-high performance concrete. Aiming at the high sensitivity of ultra-high performance concrete to water consumption, the influence of water consumption on the performance of ultra-high performance concrete was studied in a narrow range. The compatibility ratio of raw materials of ultra-high performance concrete can be adjusted, but the space is small, so we try to improve the fluidity of concrete by physical and chemical means. The experimental results show that the fluidity of concrete increases slightly with the addition of glass beads, but the flexural properties of the concrete are adversely affected. With the addition of viscosity reducer, the workbility of concrete increases, but the compressive strength decreases

Multilevel modeling of fiber-reinforced concrete and application to numerical simulations of tunnel lining segments

Für faserverstärkte Betonstrukturen wird ein numerisches Mehrebenen-Modell entwickelt, mit dem die Einflüsse verschiedener Entwurfsparameter, ausgehend von der Ebene der Einzelfaser bis zur Bauteilebene, untersucht werden können. Das Mehrebenen-Modell besteht auf der untersten Ebene aus einem analytischen Modell für die Beschreibung des Auszugsverhaltens von Stahlfasern mit und ohne Endhaken und beliebigen Faserorientierungen. Daraus werden Rissüberbrückungsmodelle insbesondere für anisotrope Faserorientierungen abgeleitet. Für numerische Strukturanalysen von Faserbetonbauteilen wird das Rissüberbrückungsmodell in eine Interface-Element-Formulierung auf Basis der Finite-Elemente-Methode überführt. Auf Basis dieses Mehrebenen-Ansatzes wird das Tragverhalten von Faserbetontübbings simuliert und das Rissverhalten unter Biege- und Längsbeanspruchungen, insbesondere durch die hydraulischen Vortriebspressen, numerisch analysiert

Study on Workability Compensation Laws of Concrete with Different Strength Grades

This paper, by adopting the reverse mixing compensation technique of the admixtures, deals with the rules of how the secondary compensation mechanism of admixtures affects the recovery of concrete workability under conditions with different strength grades and different mix ratio designs, reveals the mechanism of how to adjust and control the concrete workability, and sets up the workability compensation law equation of C30-C60 concrete mixture based on average fit curve

Autonomous navigation and collision prediction of port channel based on computer vision and lidar

Abstract This study aims to enhance the safety and efficiency of port navigation by reducing ship collision accidents, minimizing environmental risks, and optimizing waterways to increase port throughput. Initially, a three-dimensional map of the port’s waterway, including data on water depth, rocks, and obstacles, is generated through laser radar scanning. Visual perception technology is adopted to process and identify the data for environmental awareness. Single Shot MultiBox Detector (SSD) is utilized to position ships and obstacles, while point cloud data create a comprehensive three-dimensional map. In order to improve the optimal navigation approach of the Rapidly-Exploring Random Tree (RRT), an artificial potential field method is employed. Additionally, the collision prediction model utilizes K-Means clustering to enhance the Faster R-CNN algorithm for predicting the paths of other ships and obstacles. The results indicate that the RRT enhanced by the artificial potential field method reduces the average path length (from 500 to 430 m), average time consumption (from 30 to 22 s), and maximum collision risk (from 15 to 8%). Moreover, the accuracy, recall rate, and F1 score of the K-Means + Faster R-CNN collision prediction model reach 92%, 88%, and 90%, respectively, outperforming other models. Overall, these findings underscore the substantial advantages of the proposed enhanced algorithm in autonomous navigation and collision prediction in port waterways

MULTISCALE MODELING OF FRC COMPOSITES

Abstract. We propose a multiscale model for FRC composites that is a combination of semianalytical and computational sub-models specified at multiple scales. At the scale of the single fiber, a semi-analytical model is developed that characterizes the microslip behavior at the interface between the matrix and the fiber in terms of the overall composite stresses. The influence of fiber bundles on microcrack bridging and arrest is taken into account within the framework of the linear elastic fracture mechanics. Upscaling to the macroscopic level is achieved by using continuum micromechanics. We show that the macroscopic deformation of the FRC composite is governed by a 'TERZHAGI' like effective stress. Selected numerical experiments provide insight into the role of the interface property, resulting on the macroscopic level -in a brittle, softening behaviour in case of weak bond and a rather ductile, hardening behavior in case of a relatively strong interface bond that is completely described by simple microslip laws. For the finite element analyses of failure behavior at the structural level, the so-called 'interface solid element' (ISE) is used to represent the cracking process. The softening behavior of ISE is governed by the crack bridging law obtained above. The implicit-explicit integration scheme is implemented to enhance the robustness of computation. Selected numerical examples demonstrate that the crack pattern as well as the structural responses under tension-dominant stress conditions can be well simulated 1 INTRODUCTIO

Construction of Discrete Element Constitutive Relationship and Simulation of Fracture Performance of Quasi-Brittle Materials

In order to solve the problem that the built-in parallel bond model in the discrete element software cannot adequately simulate the post-peak fracture behavior of quasi-brittle materials, a linear cohesive model was established. First, two particles are used to simulate the interface constitutive behavior in different modes. The results show that the new model can better simulate the behavior of Mode-I fracture, Mode-II fracture, and Mixed-mode fracture. Then, the influence of micro-parameters on the newly constructed constitutive model is analyzed, which provides a basis for the determination of micro-parameter values. Finally, the proposed softening model is applied to a three-point bending test of mortar, and the fracture behavior obtained is compared to the acoustic emission results. The simulation results also show that the constitutive model we built can be used to simulate the fracture behavior of quasi-brittle materials such as mortar and concrete

Adaptive crack modeling with interface solid elements for plain and fiber reinforced concrete structures

The effective analysis of the nonlinear behavior of cement-based engineering structures not only demands physically-reliable models, but also computationally-efficient algorithms. Based on a continuum interface element formulation that is suitable to capture complex cracking phenomena in concrete materials and structures, an adaptive mesh processing technique is proposed for computational simulations of plain and fiber-reinforced concrete structures to progressively disintegrate the initial finite element mesh and to add degenerated solid elements into the interfacial gaps. In comparison with the implementation where the entire mesh is processed prior to the computation, the proposed adaptive cracking model allows simulating the failure behavior of plain and fiber-reinforced concrete structures with remarkably reduced computational expense