Reinforcement Shape Research Articles

Agent based modeling to optimize workflow of robotic steel and concrete 3D printers

Abstract At a time when construction projects are increasing in complexity and costs are constantly rising, 3D concrete printing have emerged as a revolutionary technology in construction. However, reinforcing 3D printed concrete elements has posed technical issues in research and practice. This paper introduces a methodology for 3D printing nonstandard steel rebar shapes together with 3D concrete printing. The new process can revolutionize the construction industry's approach to reinforced concrete design, as it provides a high degree of flexibility in both concrete and steel free-form creation, which is a key difference from traditional methods that only utilize standard steel reinforcement shapes. In addition, the proposed method will provide an even higher degree of automation in the concrete 3D printing construction process. An agent based model using Any Logic© was developed to simulate and optimize the printing of retaining and shear walls for a floor in a reinforced concrete building. Results show the optimization ratios of steel printing heads to concrete printing heads using the current technology and promise significant reductions in time and cost while providing a cleaner, safer, more automated, and an unbounded construction process. Findings from this research call for an in-depth investigation of the capabilities of steel 3D printing and its utilization in construction. It also highlights the importance of considering the application of new construction tools that would cope with the rapid growth of computational capabilities, and their adoption in design practices.

Local bearing capacity of concrete under the combined action of pressure force and bond stress

To evaluate the effect of the bond stress on the local bearing capacity, an experimental study was conducted on 30 concrete specimens using pull-out tests. The experimental results indicated that there are three types of local compression failure modes in specimens, and the failure modes essentially depend on the shell structure and the wedge action. There was an increase in the local bearing capacity of the concrete in accordance with an increase in the concrete strength and the loaded area. The net area of loaded area was recalculated by a quantitative calculation method of the removal area, and the method was established based on the reinforcement shape and the characteristics of concrete. In this experiment, the ratio of the expanded area to the original area ranged from 1.56 to 1.82. A correction coefficient was required to ensure a high accuracy which was fitted using the ratio embedment length to the bar diameter and the ratio bar diameter to the concrete cover as parameters. Finally, a calculation method of the local bearing capacity of concrete under the bond stress was developed, which can provide new insights into the standard revision and engineering application.

Effects of arrangement and shape of MWCNT and GNP reinforcements on nanocomposite mechanical properties

In this investigation, multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets were used to prepare two-phase and hybrid epoxy-based nanocomposites. Tensile and compressive mechanical pro...

Design of Reinforcement in Nano- and Microcomposites.

The application of numerical homogenization and optimization in the design of micro- and nanocomposite reinforcement is presented. The influence of boundary conditions, form of a representative volume element, shape and distribution of reinforcement are distinguished as having the crucial influence on a design of the reinforcement. The paper also shows that, in the optimization problems, the distributions of any design variables can be expressed by n-dimensional curves. It applies not only to the tasks of optimizing the shape of the edge of the structure or its mid-surface but also dimensional optimization or topology/material optimization. It is shown that the design of reinforcement may be conducted in different ways and 2D approaches may be expanding to 3D cases.

Numerical Assessment of Slab–Column Connection Additionally Reinforced with Steel and CFRP Bars

This paper investigates behavior of reinforced concrete (RC) slab–column connection additionally reinforced with punching-shear steel or carbon fiber reinforced polymer (CFRP) bars. Such connection is commonly used in RC flat slab system. However, the absence of supporting beam results in three-dimensional shear stresses with higher hogging moment acting over RC columns which may present internal inclined cracks gradually propagating toward compressive zone leading to sudden brittle punching-shear failure. This research proposes using of steel/CFRP bars intersecting the expected inclined cracks to provide better contribution to punching-shear carrying capacity and obtain ductile failure mode. Nonlinear three-dimensional finite element (FE) analysis was created and validated through simulating the behavior of experimental specimens (with or without steel/CFRP punching-shear reinforcement) tested under static loading to failure. Moreover, further validation was conducted against previous experimental work. Such FE model was employed for parametric study on three groups of slab–column connections with variable parameters: bar type (steel/CFRP), shape and position of additional punching-shear reinforcement. Slab–column connections with additional punching-shear reinforcements showed enhanced performance in terms of higher cracking load, higher pre-cracking elastic stiffness, higher ultimate deflection reflecting ductile failure mode and higher strength.

Effect of crack position and loading conditions on SIF in SiC particles reinforced Al composite

In this paper the effect of reinforcement crack position and loading conditions (in mode I) on the stress intensity factors of the Al/SiCp metal matrix composite was examined using a finite element method. A simple cubic cell model with square reinforcement shapes was developed to investigate its effect on the mechanical properties of the MMC. The finite element technique was used to calculate the stress intensity factors KI and KII for crack in the matrix and in particle. The particle and matrix materials were modelled in linear elastic conditions. The obtained results show the important role on the stress intensity factors played by the relative elastic properties of the particle and matrix. The results also show that the loading conditions and inter-distance between two particles with two interfacial cracks has an important effect on the KI and KII stress intensity factors.

Effect of reinforcement shape on fracture behaviour of SiC/Al composites with network architecture

Experimental results on metal-matrix composites (MMCs) with inhomogeneous reinforcement distribution confirmed the enhancement of the mechanical properties. Here three-dimensional network architecture, formed by particle- and rod-shaped SiC, was modeled and the effect of network structure on the strength and fracture was numerically investigated. The present specific network structural design enhances the 10 vol% SiC/Al composite, leading to a higher elastic modulus and yield stress in SiCrod/Al and SiCp/Al composite. The enhanced strength is attributed to the high load-transfer efficiency in the network composites: SiC walls parallel to the load direction carries a stress of 750–1000 MPa in SiCp/Al network composite, which is close to stress level of perpendicular SiC wall in SiCrod/Al network composite, and are higher than that in homogeneous composite (500 MPa). In SiCp/Al network composite, the main crack initiates in perpendicular SiC wall and then deflects to the matrix alloy, while the main crack initiates by rods fracture and propagates through perpendicular SiC walls in the SiCrod/Al network composite. The main crack is generated much earlier in SiCp/6061Al than in SiCrod/Al composites.

On the limiting grain sizes in carbon nanotube nanocomposites

Despite their continuing popularity over the past two decades, the influence of carbon nanotubes on grain growth is not understood clearly and often a Zener analysis is applied erroneously. The role of second phase particle drag on grain boundaries and the Zener limiting grain size behavior is well documented for spherical particles. Surprisingly, no such reports of limiting grain size in carbon nanotube composites are available in the literature, which may be related potentially to issues with poor dispersion. Systematic grain growth studies in well dispersed multiwall carbon nanotube reinforced alumina composites show for the first time a limiting grain growth behavior. The drag force exerted by cylindrical nanotubes on grain boundaries was calculated and compared with spherical particles. Due to nanometric dimensions, radial flexibility and the unique tendency of nanotubes to be present only at the grain boundaries, a Zener analysis is inapplicable for analyzing grain growth in these composites. Therefore, a simple geometrical analytical model was developed that rationalizes the experimentally observed limiting grain growth behavior. The influence of grain size distributions on the limiting grain size was determined, showing that the limiting grain size is reduced with an increase in the standard deviation. The geometric grain boundary coverage model proposed here can be used as a guideline for tailoring microstructures based on size, shape and volume fraction of nanometric carbon-based reinforcements, for exploring interesting properties including superplasticity.

Finite element analysis of cast-in-situ RC frame corner joints under quasi-static and cyclic loading

DOI: 10.7764/RDLC.18.3.579 Many types of computer software are currently available for the numerical modeling of monolithic RC structures; however, the accuracy of the numerical models created with the programs can only be acceptable by using a well-developed modeling method. We present the behavior of monolithic RC frame corners and beam to column joints for quasi-static and cyclic lateral loads, using numerical models created by our modeling method. Several laboratory experiments have already been carried out to investigate the failure of the joints and the behavior of these unique connections. In this paper, we made three-dimensional nonlinear FE body models with different reinforcement shapes, based on actual laboratory tests. We present the behavior of the joints in case of monotonic increasing quasi-static and cyclic changing loads. The results of laboratory experiments found in the literature and finite element calculations are compared and the conclusions that can be drawn from them are summarized within this article.

Effect of Cu-Zn coated steel fibers on high temperature resistance of reactive powder concrete

Even though many studies have reported about the impacts of shape, length and distribution of steel fiber reinforcement on global concrete properties, there is a lack of information about the influence of coating type of steel fibers on high temperature resistance of concrete. This paper describes the effect of Cu-Zn coated steel fibers on selected properties of reactive powder concrete (RPC) after exposure to elevated temperatures. The initial corrosion of zinc in Cu-Zn surface layer is found to be already activated by the alkaline environment of the fresh concrete. The RPC samples reinforced with Cu-Zn coated steel fibers are heated to 600 °C and 1000 °C, and the influence of thermal load on microstructure, basic physical, mechanical, thermal and durability properties is analyzed. Based on the obtained results, it can be concluded that the maximal temperature to maintain effectiveness of the RPC reinforced with Cu-Zn steel fibers is 600 °C.

Exterior reinforced concrete beam column joint subjected to monotonic loading

The joints between beams and columns are crucial zones in a reinforced concrete moment resisting frame. The behaviour of such joints greatly influences the strength and ductility of the overall frame. In this research, analysis of three-dimensional numerical models of exterior reinforced concrete beam-column joints under monotonic loading was performed using the finite element ABAQUS package. Concrete and reinforcing steel material nonlinearities, as well as bond characteristics between reinforcing bars and surrounding concrete were considered in the analysis. A parametric study involving thirty joint models was conducted to examine the influence of concrete strength, column axial load, joint stirrups and shape of the beam top reinforcement on the beam tip load and displacement capacities. The concrete dimensions and reinforcement of the studied models were chosen to ensure the occurrence of joint failure. The study showed that the beam tip ultimate load significantly increased as the concrete strength, column axial load and joint stirrups were increased. Joints with L-shaped beam top reinforcing bars exhibited similar performance to those with U-shaped bars. The use of straight bars for beam top reinforcement significantly reduced the beam tip ultimate load.

Simulating Intermediate Crack Debonding on RC Beams Strengthened with Hybrid Methods

Abstract The externally bonded (EB) and the near-surface mounted (NSM) are two well-known methods for strengthening reinforced concrete (RC) beams. Both methods are unfortunately prone to fail prematurely through debonding when the amount of strengthening reinforcement provided is high. In response to this, a hybrid method that combines the EB and NSM method was introduced. The method allows the amount of reinforcement needed for EB and NSM methods to be reduced; this, in theory, should lower the interfacial stresses, thus reducing the possibility of debonding failures. While debonding failure can be prevented, certain amounts of debonding would still occur through the interfacial crack (IC) debonding mechanism which can affect the strength and stiffness of hybrid strengthened beams even if it does not directly cause failure. This paper presents a method to simulate IC debonding of hybrid strengthened beams using the moment-rotation approach. The proposed method allows a better prediction of maximum load and stiffness of the beams. The method is also less dependent on empirical formulations compared to the commonly used moment-curvature approach; this allows the method to be applicable to all material and shape of hybrid strengthening reinforcement, assuming correct material models are used. The proposed method was then used to perform parametric studies; among the important findings is the length of IC debonding tend to increase when FRP sheet with higher elastic modulus is used, thus negating most of the benefit from the higher modulus.

Residual stress generation in metal matrix composites after cooling

ABSTRACTEffects of reinforcements’ shapes, sizes and contents on (a) von-Mises stress along a horizontal line in MMCs, (b) directions and distributions of principal stresses inside particles, matrix and interface, and (c) distribution of thermal residual stress in MMCs were analysed in this investigation. It was found that the matrix–particle interfaces experience a sudden change of von-Mises stress which depends on the reinforcement shape. The smoothest change of stress occurred in triangle particle-reinforced MMCs. However, the highest stress was concentrated at the corners of the triangular particles. The directions of stress vectors depend on the shape of the particles. The extent of the von-Mises stress increases with the increase in reinforcement content and a decrease in particles size at constant content.

Uniaxial behavior of circular ultra-high-performance fiber-reinforced concrete columns confined by spiral reinforcement

This paper presents results from the uniaxial tests of six large-scale ultra-high-performance fiber-reinforced concrete (UHPFRC) circular columns confined by spirals. The UHPFRC used in this study had 1.5% of hybrid micro-steel fibers (1.0% of 19.5 mm fibers and 0.5% of 16.3 mm fibers) in the mixture and had compressive strengths varying from 163 to 181 MPa. The effects of the volumetric ratio of spiral reinforcement, compressive strength of concrete, and presence of hybrid micro-steel fibers on the axial load responses, including post-peak deformability, were investigated. In addition, the ductility level reached by circular UHPFRC columns designed according to the minimum spiral reinforcement of current design provisions of the CSA A23.3-14 Standard and the ACI 318-14 Code were evaluated to investigate the applicability of these equations to UHPFRC columns. Test results showed that the combined effect of the minimum spiral reinforcement and steel fibers resulted in sufficient post-peak ductility of the UHPFRC columns. To investigate the efficiency of the shape of the confinement reinforcement, the test results of the circular UHPFRC columns confined by spirals were compared with those from equivalent-sized square UHPFRC columns confined by hoops. The test results demonstrate the superior performance of circular spirals for developing the ductile behavior of UHPFRC columns than the same volumetric ratio of rectilinear hoops. A design recommendation for spiral reinforcement that ensures the ductile behavior of UHPFRC columns in moderate seismic regions is proposed.

Dislocation-based strengthening mechanisms in metal-matrix nanocomposites: a molecular dynamics study of the influence of reinforcement shape in the Al-Si system

We use molecular dynamics simulations to study the interaction of dislocations with reinforcements of various shape during nanoindentation of Al/Si metal-matrix nanocomposites. Three different geometries of the Si reinforcement are considered: a spherical particle, a cylindrical fiber, and a plate. We show that plate reinforcements may absorb dislocations and emit them back into the matrix with altered glide direction, both strengthening and toughening the composite, in agreement to experiment. This mechanism does not work for spherical reinforcements, since the curved interface does not allow for dislocation emission; the case of fibers is intermediate. It is concluded that the shape of the reinforcement plays a dominant role in dislocation-based strengthening mechanisms in metal-matrix nanocomposites.

Multi-material forming using DP780 and CFRTP

Recently, carbon fiber reinforced thermo-plastic (CFRTP) has been used widely in a number of composite applications owing to the growing concerns about reducing energy consumption and protecting the environment. Various attempts have also been made to apply CFRTP to automotive parts in place of metal alloys because of the superior mechanical properties and being lightweight. Generally, CFRTP is applied to automotive parts with metal alloys because of the high material price. Therefore, research has been conducted on the multi-material forming process to reduce the process price. However, it is difficult to predict the formability of multi-materials and to design the shape of a CFRTP part because there is little research on the design and formability prediction of multi-materials. The aim of this study is to develop the B-pillar on automobile reinforced with CFRTP. Since the B-pillar is deformed simultaneously with CFRTP and DP780, the following study is required. First, a shape optimization analysis was performed to design the B-pillar reinforcement using CFRTP. The determined shape of the B-pillar reinforcement was used to determine the thickness of the product that satisfied the bending stiffness of the conventional product. Next, the friction coefficient at the interface between DP780 and CFRTP was measured for a multi-material forming analysis. The problems that occurred during forming process were analyzed through a multi-material forming analysis. Finally, the developed product was manufactured through the same method as in the analysis, and any problems were evaluated and analyzed.

Optimum design of reinforcement shapes around open-hole in laminate composite with Curvilinear fibers

Optimum design of reinforcement shapes around open-hole in laminate composite with Curvilinear fibers

Insight into the Effects of Reinforcement Shape on Achieving Continuous Martensite Transformation in Phase Transforming Matrix Composites

A continuous martensite transformation is indispensable for achieving large linear superelasticity and low modulus in phase transforming metal-based composites. However, determining how to accurately condition the residual martensite in a shape memory alloy matrix though the reinforcement shape to achieve continuous martensite transformation has been a challenge. Here, we take the finite element method to perform a comparative study of the effects of nanoinclusion shape on the interaction and martensite phase transformation in this new composite. Two typical samples are compared: one reinforced by metallic nanowires and the other by nanoparticles. We find that the residual martensite within the shape memory alloy matrix after a pretreatment can be tailored by the reinforcement shape. In particular, our results show that the shape memory alloy matrix can retain enough residual martensite phases to achieve continuous martensite transformation in the subsequent loading when the aspect ratio of nanoreinforcement is larger than 20. In contrast, the composites reinforced with spherical or low aspect ratio reinforcement show a typical nonlinear superelasticity as a result of a low stress transfer-induced discontinuous martensite transformation within the shape memory alloy matrix.

FSW of bimodal reinforced Al-based composites produced via spark plasma sintering

Abstract Metal-matrix composites produced via spark plasma sintering are characterized by enhanced mechanical and microstructural properties. Obviously, the material behavior is strongly related to the reinforcement properties, in particular the reinforcement shape. The present paper is aimed at showing the friction stir welding of Al-based composites reinforced with different percentages of nano (2%) and microsized (8%) alumina particles. The joints, microstructural and mechanical properties were evaluated as a function of the different processing parameters such as rotating and advancing speeds of the tool. The joint evolution was related to the heat input during welding. The welded material fracture behavior showed different types of rupture compared to the spark plasma sintered material.

10.14: Fire design method for eccentrically loaded concrete‐filled steel tubular columns based on interaction diagrams

ABSTRACTIn this paper, a simplified design method for evaluating the fire resistance of eccentrically loaded concrete filled steel tubular (CFST) columns is presented. The developed method is based on the results of an extensive parametric analysis conducted in the framework of the RFCS European Project FRISCC (Fire resistance of innovative and slender concrete filled tubular composite columns) and is currently being evaluated by the Working Group SC4.T4 for its approval as the method to replace the current Annex H in EN1994‐1‐2, which was proved in previous investigations to be unsafe for slender columns.The method presented in this paper is based on the provisions of Clause 6.7.3.6 of EN 1994‐1‐1 for room temperature design, using bending moment – axial force interaction curves specially built up for the fire situation. These interaction curves are obtained by considering several possible positions of the plastic neutral axis within the cross‐section, and determining the internal forces and moments from the plastic stress blocks, which results particularly challenging for CFST sections subjected to elevated temperatures, given the thermal gradient that occurs within the cross‐section. For simplifying this process, equivalent temperatures are proposed, which allow using a single uniform temperature for representing each part of the composite section. Appropriate coefficients are also proposed for evaluating the effective flexural stiffness for second‐order analysis at elevated temperatures. The influence of the cross‐section shape, load eccentricity and percentage of reinforcement is accounted for in the proposal.