A Study on the Crack Propagation Process in Concrete Structures Using Energy Method

2012 ◽  
Vol 204-208 ◽  
pp. 3151-3155
Author(s):  
Shao Wei Hu ◽  
Zheng Xiang Mi ◽  
Jun Lu
Keyword(s):  
Energy Dissipation ◽  
General Equation ◽  
Mechanical Performance ◽  
Process Zone ◽  
Unit Length ◽  
Crack Depth ◽  
Concrete Structures ◽  
Actual Structure ◽  
Three Point Bending ◽  
Crack Propagation Process

The mechanical performance of concrete structures closely relates to the propagation of cracks. Depth studying energy dissipation of concrete in fracture process zone not only contributes to comprehensive understanding fracture failure mechanism of concrete, but also has significant in detecting and forecasting the cracks in actual structure. In view of this, a general equation for calculating at any time’s mean energy dissipation per unit length was given. After that, we further simplified and deduced the general equation and got a simple, practical and high accuracy numerical solution, with which Gauss integration method was used. At last, the specific steps of calculating mean energy dissipation were given by taking 10 three-point bending beams of different crack-depth ratios for an example. Compared with test dates, we found that calculated results are in good agreement with the test dates. According to results, influence of crack-depth ratio on the fracture energy was also discussed.

Static and dynamic response of sandwich beams with lattice and pantographic cores

2021 ◽  
pp. 109963622110338
Author(s):  
Yury Solyaev ◽  
Arseniy Babaytsev ◽  
Anastasia Ustenko ◽  
Andrey Ripetskiy ◽  
Alexander Volkov
Keyword(s):  
Mechanical Performance ◽  
Lattice Structure ◽  
Unit Length ◽  
Experimental Tests ◽  
Plane Geometry ◽  
Sandwich Beams ◽  
Static Tests ◽  
Three Point Bending ◽  
The Core ◽  
The Impact

Mechanical performance of 3d-printed polyamide sandwich beams with different type of the lattice cores is investigated. Four variants of the beams are considered, which differ in the type of connections between the elements in the lattice structure of the core. We consider the pantographic-type lattices formed by the two families of inclined beams placed with small offset and connected by stiff joints (variant 1), by hinges (variant 2) and made without joints (variant 3). The fourth type of the core has the standard plane geometry formed by the intersected beams lying in the same plane (variant 4). Experimental tests were performed for the localized indentation loading according to the three-point bending scheme with small span-to-thickness ratio. From the experiments we found that the plane geometry of variant 4 has the highest rigidity and the highest load bearing capacity in the static tests. However, other three variants of the pantographic-type cores (1–3) demonstrate the better performance under the impact loading. The impact strength of such structures are in 3.5–5 times higher than those one of variant 4 with almost the same mass per unit length. This result is validated by using numerical simulations and explained by the decrease of the stress concentration and the stress state triaxiality and also by the delocalization effects that arise in the pantographic-type cores.

Effect of Crack-Depth Ratio on Double-K Fracture Parameter of Reinforced Concrete

2012 ◽  
Vol 226-228 ◽  
pp. 937-941 ◽  
Author(s):  
Shao Wei Hu ◽  
Zheng Xiang Mi ◽  
Jun Lu
Keyword(s):  
Fracture Toughness ◽  
Reinforced Concrete ◽  
Crack Propagation ◽  
Crack Depth ◽  
Fracture Parameter ◽  
Propagation Process ◽  
Three Point Bending ◽  
Depth Ratio ◽  
Crack Propagation Process ◽  
Crack Depth Ratio

In order to study the influence of the crack-depth ratio on reinforced concrete fracture parameters and the resistance of the reinforcing bar to crack propagation in concrete, the fracture tests were carried on by using four groups three-point bending specimens with initial crack-depth ratios of 0.2, 0.3, 0.4 and 0.5 in this paper. An analytical model was presented to calculate fracture toughness of reinforced concrete by analyzing crack propagation process of the three-point bending beams. The formula of calculating effective crack length of reinforced concrete was established. The research results show that the double-K criterion can be used for describing crack propagation process of reinforced concrete by introducing fracture toughness, which is suitable for reinforced concrete. Initiation fracture toughness and unstable fracture toughness of reinforced concrete slowly increase with the increase of crack-depth ratio, which is different from the properties of ordinary concrete. The reinforced can improve the ductility of concrete obviously and inhibit the rate of crack propagation well.

scholarly journals Experimental Study on Mechanical and Sensing Properties of Smart Composite Prestressed Tendon

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2087 ◽  
Author(s):  
Danhui Dan ◽  
Pengfei Jia ◽  
Guoqiang Li ◽  
Po Niu
Keyword(s):  
Stress State ◽  
Carbon Fibers ◽  
Prestressed Concrete ◽  
Mechanical Performance ◽  
Experimental Studies ◽  
Concrete Structures ◽  
Tension Force ◽  
Smart Composite ◽  
Steel Wires ◽  
Sensing Performance

It is typically difficult for engineers to detect the tension force of prestressed tendons in concrete structures. In this study, a smart bar is fabricated by embedding a Fiber Bragg Grating (FBG) in conjunction with its communication fiber into a composite bar surrounded by carbon fibers. Subsequently, a smart composite cable is twisted by using six outer steel wires and the smart bar. Given the embedded FBG, the proposed composite cable simultaneously provides two functions, namely withstanding tension force and self-sensing the stress state. It can be potentially used as an alternative to a prestressing reinforcement tendon for prestressed concrete (PC), and thereby provide a solution to detecting the stress state of the prestressing reinforcement tendons during construction and operation. In the study, both the mechanical properties and sensing performance of the proposed composite cable are investigated by experimental studies under different force standing conditions. These conditions are similar to those of ordinary prestressed tendons of a real PC components in service or in a construction stage. The results indicate that the proposed smart composite cable under the action of ultra-high pretension stress exhibits reliable mechanical performance and sensing performance, and can be used as a prestressed tendon in prestressed concrete structures.

The Comparison of Self-Compacting Rock-Filled Concrete with Large-Size Natural and Recycled Aggregate

2014 ◽  
Vol 513-517 ◽  
pp. 20-23
Author(s):  
Hai Chao Wang ◽  
Xue Hua Wang ◽  
Xue Hui An
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Fracture Energy ◽  
Fracture Mechanism ◽  
Recycled Aggregate ◽  
Propagation Process ◽  
Fracture Characteristics ◽  
Three Point Bending ◽  
Large Size ◽  
Crack Propagation Process

The different fracture characteristics of self-compacting rock-filled concrete with large-size natural and recycled aggregate are analyzed by three-point bending experiment. According to the analysis of the crack propagation process, the fracture mechanism differences of self-compacting rock-filled concrete with large-size natural and recycled aggregate are discussed. The further analysis of the differences of fracture toughness, fracture energy, and are gain

Designing Composites for Graceful Failure

2020 ◽  
Author(s):  
Amany Micheal ◽  
Yehia Bahei-El-Din ◽  
Mahmoud E. Abd El-Latief
Keyword(s):  
Mechanical Properties ◽  
Energy Dissipation ◽  
Composite Laminates ◽  
Ultimate Load ◽  
Low Cost ◽  
Cost Effective ◽  
Carbon Composite ◽  
Three Point Bending ◽  
Glass Carbon ◽  
Effective Product

Abstract When inevitable, failure in composite laminates is preferred to occur gracefully to avoid loss of property and possibly life. While the inherent inhomogeneity leads to slow dissipation of damage-related energy, overall failure is fiber-dominated and occurs in a rather brittle manner. Multidirectional plies usually give a more ductile response. Additionally, stiffness and strength as well as cost are important factors to consider in designing composite laminates. It is hence desirable to optimize for high mechanical properties and low cost while keeping graceful failure. Designing composite laminates with hybrid systems and layups, which permit gradual damage energy dissipation, are two ways proposed in this work to optimize for mechanical properties while avoiding catastrophic failure. In the hybrid system design, combining the less expensive glass reinforced plies with carbon reinforced plies offers a cost-effective product, marginal mechanical properties change and ductile profile upon failure. Hybrid glass/carbon composite laminates subjected to three-point bending showed strain to failure which is double that measured for carbon composite specimens, without affecting the ultimate load. Energy dissipation mechanisms were also created by building laminates which were intentionally made discontinuous by introducing cuts in the fibers of the interior plies. This created a longer path for damage before cutting through the next ply resulting in double failure strain with marginal reduction in load. The effect of fiber discontinuity in terms of spacing and distribution are among the factors considered.

scholarly journals Seismic Damage Model of Bridge Piers Subjected to Biaxial Loading Considering the Impact of Energy Dissipation

2019 ◽  
Vol 9 (7) ◽  
pp. 1481 ◽  
Author(s):  
Shangshun Lin ◽  
Zhanghua Xia ◽  
Jian Xia
Keyword(s):  
Energy Dissipation ◽  
Structural Damage ◽  
Biaxial Loading ◽  
Mechanical Performance ◽  
Damage Model ◽  
Damage Index ◽  
Seismic Damage ◽  
Bridge Piers ◽  
Dissipated Energy ◽  
The Impact

The large degradation of the mechanical performance of hollow reinforced concrete (RC) bridge piers subjected to multi-dimensional earthquakes has not been thoroughly assessed. This paper aims to improve the existing seismic damage model to assess the seismic properties of tall, hollow RC piers subjected to pseudo-static, biaxial loading. Cyclic bilateral loading tests on fourteen 1/14-scale pier specimens with different slenderness ratios, axial load ratios, and transverse reinforcement ratios were carried out to investigate the damage propagation and the cumulative dissipated energy with displacement loads. By considering the influence of energy dissipation on structural damage, a new damage model (M-Usami model) was developed to assess the damage characteristics of hollow RC piers. The results present four consecutive damage stages during the loading process: (a) cracking on concrete surface, (b) yielding of longitudinal reinforcements; (c) spalling of concrete, and (d) collapsing of pier after the concrete crushed and the longitudinal bars ruptured due to the flexural failure. The damage level caused by the seismic waves can be reduced by designing specimens with a good seismic energy dissipation capacity. The theoretical damage index values calculated by the M-Usami model agreed well with the experimental observations. The developed M-Usami model can provide insights into the approaches to assessing the seismic damage of hollow RC piers subjected to bilateral seismic excitations.

scholarly journals Experimental Evaluation of Hysteretic Behavior of Rhombic Steel Plate Dampers

2014 ◽  
Vol 6 ◽  
pp. 185629 ◽  
Author(s):  
Qiang Han ◽  
Junfeng Jia ◽  
Zigang Xu ◽  
Yulei Bai ◽  
Nianhua Song
Keyword(s):  
Energy Dissipation ◽  
Yield Strength ◽  
Mild Steel ◽  
Steel Plate ◽  
Mechanical Performance ◽  
Hysteretic Behavior ◽  
Loading Test ◽  
Hysteretic Energy ◽  
Steel Material ◽  
Energy Dissipation Capacity

Rhombic mild-steel plate damper (also named rhombic added damping and Stiffness (RADAS)) is a newly proposed and developed bending energy dissipation damper in recent years, and its mechanical properties, seismic behavior, and engineering application still need further investigations. In order to determine the basic mechanical performance of RADAS, fundamental material properties tests of three types of mild-steel specimen including domestically developed mild-steel material with low yield strength were carried out. Then, a quasistatic loading test was performed to evaluate the mechanical performance and hysteretic energy dissipation capacity of these rhombic mild-steel dampers manufactured by aforementioned three types of steel materials. Test results show that yield strength of domestically developed low yield strength steel (LYS) is remarkably lower than that of regular mild steel and its ultimate strain is also 1/3 larger than that of regular mild steel, indicating that the low yield strength steel has a favorable plastic deformation capability. The rhombic mild-steel plate damper with low yield strength steel material possesses smaller yield force and superior hysteretic energy dissipation capacity; thus they can be used to reduce engineering structural vibration and damage during strong earthquakes.

Investigation of Parameter Spaces for Topology Optimization With Three-Dimensional Orientation Fields for Multi-Axis Additive Manufacturing

2020 ◽  
Vol 143 (5) ◽  
Author(s):  
Joseph R. Kubalak ◽  
Alfred L. Wicks ◽  
Christopher B. Williams
Keyword(s):  
Topology Optimization ◽  
Additive Manufacturing ◽  
Design Space ◽  
Mechanical Performance ◽  
Unit Length ◽  
Three Dimensions ◽  
Layer By Layer ◽  
Material Distribution ◽  
Orientation Fields ◽  
Material Orientation

Abstract The layer-by-layer deposition process used in material extrusion (ME) additive manufacturing results in inter- and intra-layer bonds that reduce the mechanical performance of printed parts. Multi-axis (MA) ME techniques have shown potential for mitigating this issue by enabling tailored deposition directions based on loading conditions in three dimensions (3D). Planning deposition paths leveraging this capability remains a challenge, as an intelligent method for assigning these directions does not exist. Existing literature has introduced topology optimization (TO) methods that assign material orientations to discrete regions of a part by simultaneously optimizing material distribution and orientation. These methods are insufficient for MA–ME, as the process offers additional freedom in varying material orientation that is not accounted for in the orientation parameterizations used in those methods. Additionally, optimizing orientation design spaces is challenging due to their non-convexity, and this issue is amplified with increased flexibility; the chosen orientation parameterization heavily impacts the algorithm’s performance. Therefore, the authors (i) present a TO method to simultaneously optimize material distribution and orientation with considerations for 3D material orientation variation and (ii) establish a suitable parameterization of the orientation design space. Three parameterizations are explored in this work: Euler angles, explicit quaternions, and natural quaternions. The parameterizations are compared using two benchmark minimum compliance problems, a 2.5D Messerschmitt–Bölkow–Blohm beam and a 3D Wheel, and a multi-loaded structure undergoing (i) pure tension and (ii) three-point bending. For the Wheel, the presented algorithm demonstrated a 38% improvement in compliance over an algorithm that only allowed planar orientation variation. Additionally, natural quaternions maintain the well-shaped design space of explicit quaternions without the need for unit length constraints, which lowers computational costs. Finally, the authors present a path toward integrating optimized geometries and material orientation fields resulting from the presented algorithm with MA–ME processes.

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