Bar Mode Research Articles

Bond behavior and modeling of steel-FRP composite bars in engineered cementitious composites

The combination of the steel-FRP composite bar (SFCB) and engineered cementitious composite (ECC) holds favorable applications in terms of durable resilient structures. However, a clear understanding of the interfacial bond performance of this novel combination is currently lacking. Therefore, the bond behavior and mechanism of the SFCB-ECC interface were investigated through direct pullout tests. A total of 48 cube specimens were fabricated, with the test variables including bar type, bar diameter, embedment length, and matrix type. The experimental results indicated that the bond failure mode of SFCBs and FRP bars differed from that of deformed steel bars, attributed to the damage of resin-rich ribs in relatively high-strength ECC. The bond-slip curves revealed both the fundamental differences and similarities among steel bars, SFCBs, and FRP bars. The Poisson effect and shear lag effect increased with a decrease in bar stiffness and an increase in diameter. The combined impact of the interaction between the bar stiffness and diameter resulted in varying bond strengths for steel bars, SFCBs, and GFRP bars, despite their similar surface geometries. A theoretical model for the bond strength at the SFCB-ECC interface was derived using the thick-walled cylinder principle and subsequently validated with test data. Finally, a unified empirical model framework for predicting the bond strength of various bar-matrix combinations was proposed based on the theoretical model. The accuracy of this method was evaluated using a collected database.

Fracture of four semi-regular lattices regulated by T-stress in modified boundary layer models

The development of additive manufacturing technology has promoted the rise of various lattice metamaterials, and evaluating their fracture properties is critical for both application and safety. Here, by conducting finite element simulations on four types of elastic-brittle semi-regular lattices (kagome, snub-trihexagonal, elongated-triangular, and snub-square), we indicate that the fracture toughness of lattice metamaterials is not solely determined by the crack-tip singular term, i.e., the critical stress intensity factor, but is also influenced by the non-singular T-stress term. T-stress regulates fracture toughness by modulating geometrical distortions and force-carrying modes of lattice bars around the crack front. This regulation effect depends on the lattice topology and becomes weaker under mixed-mode loading. As the relative density of lattices decreases, T-stress can force elastic buckling of bars around the crack front, which may deteriorate the fracture toughness. Additionally, positive T-stress tends to promote the crack deflection and negative T-stress tends to inhibit. Our results offer new insights into the structure-property relationships in the presence of T-stress, which may contribute to design the geometry of micro/nano-lattice metamaterials.

Morphological Evolution of Disk Galaxies and Their Concentration, Asymmetry, and Clumpiness (CAS) Properties in Simulations across Toomre’s Q Parameter

We investigate the morphological and structural evolution of disk galaxies in simulations for a wide range of Toomre’s Q parameters. In addition to the inspection of conventional bar modes, we compute the concentration, asymmetry, and clumpiness (CAS) parameters to enlarge the understanding of the galaxy evolution. These parameters are widely employed to analyze the light distribution of the observed galaxies, but the adaptation to numerical simulations is not much considered. While the bar formation takes place in a considerable range of Q around 1, barred galaxies originating from Q > 1 and Q < 1 disks yield CAS values that differ significantly. Disks starting with Q < 1 develop clumps due to local gravitational instabilities along with the bar, and these clumps play a central role in enhancing the CAS values. This process is absent in the Q > 1 counterparts in which the evolution is dominated by linearly unstable two-armed modes that lead to lower CAS values. Likewise, unbarred galaxies that are obtainable from disks with Q far below and far above 1 exhibit greatly different CAS magnitudes. It turns out that the CAS parameters can serve as indicators of the initial kinematical state and the evolution history of a disk of any morphology. In addition, we find an alternative mechanism of the formation of the lopsided barred galaxy when Q ≲ 1. Bars that evolve in the midst of the clumps can spontaneously become lopsided at the end.

Сегментно-пальцевая косилка для скашивания естественных и сеяных трав в условиях малых форм хозяйствования

Segment-finger mowers are used mainly in forage harvesting. To improve their qualitative and operational indicators it is necessary to study the trajectory of movement, speed and acceleration of the mower knife under variable terrain conditions. For this purpose, the authors studied the influence of change of the non-axial value on qualitative and energy indicators of the mower’s cutter bar. They also determined parameters and operating modes of the mower knife with the axial knife drive mechanism. According to the results of experimental studies, it was established that while copying the field relief, the cutter bar changes the angle of inclination relative to the horizon within the limits of ±15 degrees. In this case, the non-axial value varies between 0.281 and 0.492 m with a step of one degree. The change of the non-axial value entails the change of the stroke, speed, and acceleration of the knife. Using the analytical method of kinematic study of crank mechanisms according to Artobolevsky’s procedure and performing calculations in the Excel software kit, the authors have obtained graphical relationships between the knife stroke and speed depending on the angular position of the cutter bar with the interval of 0, 5, 10, and 15. A change in the location of the cutter bar up to 15 degrees causes unequal speeds of the forward and reverse knife strokes, increasing it from 76.2 to 89 mm, which increases the energy consumption for the knife drive up to 17%. Another disadvantage of the non-axial crank mechanism of the knife drive is its dynamic unbalance, which is only partially smoothed with a counterweight. To eliminate the drawbacks, the authors have developed an experimental mower with axial arrangement of the crank mechanism on the finger bar of the cutter bar. The new design makes it possible to activate the transport position of the finger bar in the working mode of the cutter bar when bypassing such obstacles as bushes, trees, or rough bumps.

Bond-Slip Behaviors Between BFRP Bar and Ecological High Ductility Concrete Using the Beam Test

To better understand the design parameters of bridge deck link slab made by basalt fiber reinforced polymer (BFRP) bar and ecological high ductility concrete (Eco-HDC), the bond behaviors of BFRP bar embedded in Eco-HDC using beam test based on RILEM standard were studied. The beam specimens had variable factors namely diameter of BFRP bar, embedment length and cover thickness. The results indicate that most beam specimens display a failure mode of BFRP bar pulled out with specimen splitting. Besides, with the increase of diameter and embedment length, the bond strength decreases. While as the cover thickness increases, the bond strength and first bond stress show an increasing trend. The free end slip increases as the embedment length or cover thickness increases. In addition, the strain at loaded end is larger than that at free end as the load increases. Moreover, the formulas of bond strength and peak slip are proposed based on the test data of specimens. At last, embedment length and cover thickness of BFRP bar in the bridge deck link slab are recommended.

Novel two-stage superelastic SMA bars with enhanced ductility and graded pseudo-yielding for seismic applications

This study proposed a novel design concept of two-stage superelastic shape memory alloy (SMA) elements to achieve graded pseudo-yielding and enhanced ductility that are suitable for multi-level seismic design. This design concept utilizes the natural stiffness hardening of superelastic SMA after martensite finish stress to activate two transformation stress plateaus (i.e., graded pseudo-yielding points) of two-stage SMA elements. Consequently, the small- and large-diameter parts can be activated under small and rare earthquakes, respectively. This study discussed the design concept, experimental tests, and numerical simulations of two-stage SMA bars with two different diameters. The cyclic behaviour and failure modes of the two-stage SMA bar observed in the tests successfully validated the expected merits. The ductility of the tested two-stage SMA bar increased by 50% compared with that of a normal one-stage SMA bar. Meanwhile, the self-centring (SC) capacity was not compromised when parts of the bar were in the martensite phase during the graded pseudo-yielding. The two-stage SMA bar showed desirable cyclic performance during the whole loading process. Finally, a finite element model was established based on the testing results to facilitate parametric and comparative studies. The two-stage SMA bar showed obvious graded pseudo-yielding behaviour, larger ductility, and greater post-pseudo-yielding stiffness, which can potentially benefit seismic applications.

Experimental Research on the Bond Performance between SMAF-ECC Composites and Steel Bar.

Combining Engineered Cementitious Composites (ECC) with shape memory alloy (SMA) fibers can form SMA fiber reinforced ECC (SMAF-ECC) that has excellent deformation recovery and energy dissipation capabilities. Substituting some of the tensioned concrete with this new composite material, along with steel bars, is expected to significantly improve the seismic energy dissipation and self-recovery capabilities of traditional reinforced concrete components. However, a reliable bond between steel bars and SMAF-ECC is critical to ensure their synergistic performance. In this paper, the failure mode and bond strength of steel bars and SMAF-ECC were studied through direct tensile tests, and the influence factors such as steel bar diameter, bond length, and SMAF volume fraction were analyzed. A bond-slip constitutive model for steel bars and SMAF-ECC was proposed. The results show that the failure mode of the tensile test specimens is mainly steel bar pull-out failure; the incorporation of SMAF significantly enhances the bond strength between the steel bar and matrix; increasing the steel bar diameter and bond length both lead to a decrease in bond strength while increasing the SMAF volume fraction can significantly increase the bond strength. Among them, the specimen with a steel bar diameter of 12 mm, bond length of 70 mm, and SMAF volume fraction of 0.5% has the largest increase in bond strength, reaching 52.96%. The proposed improved bond-slip constitutive model is in good agreement with the bond-slip curve obtained in the experiments, with a determination coefficient of 0.99. The research results of this paper provide an important theoretical basis for promoting the engineering application of SMAF-ECC materials.

Study on Bond Anchorage Behavior of Small-Diameter Rebar Planting under Medium and Low Cycle Fatigue Loads

In this paper, we describe how, through the combination of field testing and finite element simulation, the bonding and anchoring performance of small-diameter rebar under the action of medium and low cycle fatigue load was studied and the corresponding conclusions were obtained: ① Through the test, the performance parameters of the 6 mm and 8 mm rebar planting specimens were obtained after the rebar was subjected to 10,000, 50,000 and 100,000 times of medium and low cycle fatigue loading at depths of 10d, 15d and 20d. The analysis shows that the medium and low cycle fatigue load has a significant effect on the elastic ultimate load, elastic ultimate slip and ultimate slip of the small-diameter rebar planting specimens. With the increase in fatigue loading times, the elastic ultimate load of the rebar specimen decreased continuously, and the elastic ultimate slip and ultimate slip showed an increasing trend. By increasing the anchor depth, the influence of fatigue load on the anchoring performance parameters of the rebar planting specimen can be reduced. Under the influence of the upper ultimate condition of 100,000 times of fatigue loading, the ultimate load and failure mode of the planted bars basically did not change compared with the control specimens without fatigue loading. ② Based on the performance parameters of the rebar planting specimens obtained from the field test, the bond–slip constitutive relationship of the adhesive–rebar interface of the small-diameter rebar planting under the medium and low cycle fatigue load is analyzed and proposed. The F-U relationship of the spring element under the fatigue load is defined to simulate the bond–slip behavior of the adhesive–rebar interface. The finite element simulation results are in good agreement with the field test results. ③ Through a large number of finite element numerical simulation results, the elastic ultimate load calculation formulas of 6 mm and 8 mm diameter rebar planting specimens under medium and low cycle fatigue loads are obtained.

NSM and hybrid techniques for retrofitting corroded RC beams using GFRP bars

This is an experimental study on the flexural performance of corroded reinforced concrete (RC) beams strengthened by three different methods using Glass Fibre Reinforced Polymer (GFRP) bars. Three methods of strengthening were used: the traditional method of replacing damaged concrete covers and installing GFRP bars, the near-surface mounted (NSM) method, and a hybrid method involving mechanical fasteners and the NSM method. In total, seventeen RC beams were constructed one of which was used as a control specimen, while the remaining sixteen were divided into four groups and were exposed to accelerated corrosion to reach a theoretical mass loss of 3.5 to 30% in tensile steels. Three groups of corroded beams were strengthened using the three methods mentioned, while the other group received no strengthening. Then, all the beams were tested under four-point loading to determine their load-deflection response, stiffness, ductility, failure mode, and strain of the GFRP bars. The results showed that the conventional strengthening method using GFRP bars was relatively efficient in restoring the load-bearing capability of corrosion-damaged beams. However, sufficient anchorage length for the GFRP bars was required to achieve high ductility. The NSM method effectively improved the load-bearing capacity of beams with low corrosion levels; however, increasing the corrosion level caused the strengthened beams to fail prematurely due to concrete cover separation. It was observed that the hybrid strengthening method improved the load-bearing capacity of corroded beams while maintaining their ductility by preventing premature failure due to concrete cover separation.

Study on durability of transverse shear properties for novel carbon/glass hybrid fiber‐reinforced polymer bars in simulated concrete environments

AbstractDurability on the transverse shear properties of hybrid fiber‐reinforced polymer (HFRP) bar may control the cross‐sectional load‐bearing capacity and failure mode of the HFRP bar reinforced concrete members due to its strength degradation with time. Herein, the degradation of novel carbon/glass (C/G)‐HFRP bars were accelerated in simulated concrete environments at 60°C to investigate the effects of fiber volume fraction and distribution pattern, matrix resin volume fraction, exposure environment, and period on their transverse shear properties. The results displayed that the transverse shear strength of the samples reduced by 15%, 20%, and 8% after exposure to the simulated ordinary concrete, seawater sea‐sand concrete environments, and tap water for 6 months, respectively. The inward diffusion of water molecules and free hydroxyl ions caused the hydrolysis of matrix resin, etching of glass fiber and debonding of fiber/matrix interface, which were the incentives of the degradation of C/G‐HFRP bars. The increase of matrix resin volume fraction and the application of a waterproof coating were recommended to alleviate the degradation of fibrous composites in concrete environments. Finally, two prediction models were proposed to determine the transverse shear strength of HFRP bar before and after exposure to different harsh environments, respectively. The comparisons indicated that the predicted values were coincided with the experimental results.

Effects of simulated seawater on static and fatigue performance of GFRP bar–concrete bond

Due to their excellent resistance to chloride ions, glass-fiber-reinforced polymer (GFRP) bars are employed to replace steel bars in seawater–sea-sand concrete (SWSSC). The performance of the concrete beams reinforced with GFRP bars depends on the bond between GFRP bars and SWSSC, which is significantly influenced by the marine environment and fatigue loading. Thus, the present study uses pullout tests to investigate the effects of simulated seawater on the static and fatigue properties of the GFRP bar–concrete bond. The impacts of the immersion time, environmental temperature, concrete type, and fatigue loading level are examined. The static interfacial bond strength and the corresponding slip of GFRP bar–SWSSC and GFRP bar–river-sand concrete (RSC) composites increase with the immersion time and the environmental temperature. Coupling the immersion environment and fatigue loading does not affect the failure mode of the GFRP bar–SWSSC and GFRP bar–RSC composites. Fatigue loading eliminates the defects in the interface between the GFRP bar and concrete, and the effects of eliminating the interfacial defects lessen with the immersion time and the environmental temperature. The fatigue load controls the performance degradation of the interfacial bond between the GFRP bar and concrete under coupling fatigue loading and immersion in simulated seawater. Meanwhile, there is no difference in the bond strength of the GFRP bar–RSC and GFRP bar–SWSSC composites under coupling fatigue loading and immersion in seawater. Nevertheless, the GFRP bar–SWSSC composite offers better static bond stiffness than the GFRP bar–RSC composite.

High temperature thermomechanical properties of a microcracked model refractory material: A silica-doped aluminium titanate

An aluminium titanate based (AT) material doped with silica was investigated as refractory model material in order to highlight its thermomechanical properties through various techniques of characterization operating at high temperature such as ultrasonic pulse echography technique operating in long bar mode, acoustic emission, dilatometry and tensile test measurements up to 1400 °C. Young's modulus (MoE) as a function of temperature evolves in the form of a large hysteresis loop with a maximum value of about 170 GPa due to the healing of diffuse microcracks during heating. A sharp decrease in MoE occurs on cooling at about 780 °C, corresponding to the re-opening of the microcracked network due to a high level of stress around AT grains. In addition, during cooling, the dilatometric analysis shows a quasi-linear shrinkage followed by a sudden non-linear expansion from 750 °C. The thermal expansion coefficient value determined between 1100 °C and 750 °C is about 8.8 10−6 °C−1. By recording the evolution of the cumulative number of hits as a function of temperature, the results of the acoustic emission clearly confirm the resurgence of microstructural defects at 780 °C. The incremental tensile loading test performed at 1400 °C shows a greater degree of nonlinearity suggesting a higher flexibility of the studied AT due to both the microcracks network and the low viscosity of intergranular glassy phase. Symmetric alternating loading tests have highlighted that the viscous contribution in the viscoelastic behaviour of such materials is increasing from 850 H °C to 1400 H °C as the viscosity of the silica-riched amorphous phase is decreasing. These results are very useful to understand the more sensitive parameters involved in the high thermal shock resistance of aluminium titanate.

The bar-resonator interaction in mallet percussion instruments: A multi-modal model and experimental validation

In some mallet percussion instruments, like vibraphones and marimbas, acoustical resonators are placed under the tuned bars to enhance acoustic radiation. Despite its wide use in commercial instruments, the vibro-acoustic interaction between the tuned bars and their acoustic resonators has not been studied extensively, and previous modeling attempts often neglect important aspects of the coupling dynamics. This work presents a physical model describing the two-way vibro-acoustic interaction between a vibrating beam and an acoustic resonator. The proposed formulation leads to a system composed of a set of mechanical oscillators coupled to a set of acoustical oscillators, representing bar and resonator modes, respectively. The simplicity of the proposed model provides an intuitive understanding of the physics occurring in real instruments and show how specific design parameters will affect their behavior. The dynamics of the system are analyzed through energy balance, time-domain simulations and eigenvalue analysis, revealing a number of interesting features and highlighting three dimensionless parameters: the ratio of frequencies and quality factors, as well as a coupling “strength” coefficient, dependent on the bar-resonator distance, the placement of the resonator along the bar length, bar and resonator mode shapes, amongst others. The proposed model is also shown to be a useful tool for the design of instruments optimized for multi-modal coupling, where several resonator modes are tuned to bar frequencies. Finally, experimental results are presented to validate various aspects of the proposed model and demonstrate its capacity to emulate real instruments, both qualitatively and quantitatively.

Nonsmooth modal analysis of a varying cross-sectional area bar in unilateral contact

Nonsmooth modes of vibration allow for identification of resonant behaviours and attendant vibratory frequencies in structures prone to unilateral contact conditions on the boundary. The prominent approach for finding nonsmooth modes of vibration entails finding continua of periodic solutions to the system in question. In this paper, nonsmooth modes of a one-dimensional bar of varying cross-sectional area prone to unilateral contact with a rigid obstacle are determined. While numerical and analytical techniques were previously proposed, they were limited to constant cross section bar and could not be applied on the varying area bar for which the classical d’Alembert solution no longer exists. In this article, nonsmooth modal analysis of the varying area bar is performed via a novel treatment of the Signorini conditions within the finite element framework: the nodal boundary method. The nodal boundary method solves the Signorini problem by switching between two sets of shape functions describing either (1) inactive contact motion (motion away from the rigid obstacle) or (2) active contact motion (bar in contact with the rigid obstacle). In the proposed nodal boundary method, the motion of the contacting node does not participate in the resulting governing Ordinary Differential Equation (ODE). Instead, its motion is prescribed by the boundary conditions and is dictated by the motion of internal nodes. The nodal boundary method results in a discontinuous ODE in the internal nodes which can be solved both analytically and via numerical techniques. Solutions obtained by the nodal boundary method exhibit several advantages over existing numerical techniques: no chattering at contact, no penetration of the rigid obstacle, and existence of periodic solutions. Specifically, these periodic solutions are readily detectable via the shooting method with sequential continuation. The nodal boundary method is used successfully for the nonsmooth modal analysis of different models of the varying area bar. Besides, application of the nodal boundary method for nonsmooth modal analysis of the uniform area cantilever bar in Dirichlet or Robin boundary conditions is also demonstrated for comparison with existing literature.

A minimal model of the bar-resonator vibroacoustic interaction in mallet percussion instruments

In some mallet percussion instruments, such as vibraphones and marimbas, tubular acoustic resonators are placed beneath the tuned bars to enhance acoustic radiation at their fundamental frequency. This work deals with the formulation of a minimal physical model describing the vibro-acoustic interaction occurring in these instruments. The fundamental bar mode is modelled as a disk-shaped oscillator and the resonator as a cylindrical acoustic waveguide, described in terms of its acoustic modes. The three-dimensional effects associated with sound radiation and the interaction between the two elements are calculated using a 2-D axisymmetric finite element (FE) model, whose numerical results are then fitted to dimensionless analytical expressions, which encapsulate the complex physics of the vibro-acoustic interaction in a simplified manner. This can pragmatically be used to formulate a lumped-parameter model of the coupled system. Illustrative numerical results are presented and qualitatively validated, demonstrating the ability of the proposed modelling approach to capture the essential features of the coupled dynamics occurring in real instruments.

The V-MVLE model for cyclic failure behavior simulation of planar RC members

As a widely used planar structural component, the reinforced concrete (RC) shear wall in service is usually subjected to axial, bending and shear loading, possessing high dissymmetry damage mechanics of concrete and failure mode of steel bars. To obtain a satisfactory level of simulation accuracy for the cyclic failure behavior of RC shear walls, progresses were made both in microscopic and macroscopic modeling method. In this study, a hybrid planar model based on vector form intrinsic finite element (VFIFE) and macroscopic multi-vertical line element (MVLE) was proposed, which combined the merits of detailed response of the microscopic model and high calculation efficiency of the macroscopic model. Owing to particle-based formulation along the path element, no assembling of a global stiffness matrix was required by the VFIFE method, which attributed the advantages in large deformation and reinforcement fracture behavior analysis for the proposed model during cyclic failure phase. Via the proposed hybrid model of MVLE, the RC shear walls with various parameters, involving axial compression ratios and height–weight​ ratios, were simulated to allow comparison between the experimental and analytical results in reversed cyclic tests, which demonstrated good agreement and satisfied calculation efficiency.

Investigation on in-plane mechanical behavior of joint connections for discrete connected new-type precast concrete diaphragms

This paper proposes three new types of connectors adopted in discrete connected new-type precast concrete diaphragms (DCNPD). An experimental investigation of innovated connectors under shear load was conducted to evaluate the failure mode, strain and bearing capacity of joint connections in DCNPD. Based on the experimental results, the hairpin connector (HPC) was selected for simulation verification and further analysis under combined loads to provide crucial information on bearing capacity, ductility, reduction rule, deformation and stiffness in order to reveal its working mechanism. The results indicate that three types of connectors can provide effective connection for slab joints. The ideal fracture failure mode of anchor bar or cover plate is realised in all joint connections. The shear capacity of HPC is weakened by simultaneous tension when it is under combined loads. With the increase of tension-to-shear force ratio, the ductility of HPC is improved, and the shear ductility is relatively better. The evaluation of yield displacement and bearing capacity, degradation law in strength, deformation and stiffness of HPC provides a theoretical basis for the development of joint connection and seismic design of DCNPD, which is vital for the application of DCNPD in precast concrete structures.

The Identification and Reservoir Architecture Characterization of Wandering Braided River in Nanpu 1-29 Area, Bohai Bay Basin

Nanpu 1-29 Area of Jidong Oilfield in China is currently in the stage of high water cut and low recovery degree. The remaining oil development and adjustment are difficult because of the complex reservoir heterogeneity and the lack of analysis of the reservoir architecture due to the unclear river type. This study first used sedimentary background, granularity, core, and sand body distribution to determine the river type and believed it belongs to the wandering braided river. Combined with core and logging data, four types of sedimentary architectural elements were found in the study area, namely, channel bar, braided channel, floodplain, and basalt. Based on the scale measurement of many similar modern wandering braided rivers, core data, and empirical formulas, the scales of the braided rivers were determined. The quantitative relationships among the scale of the braided river, the channel bar, and the braided channel were established. With this constraint, the reservoir architecture was anatomized. The results showed two filling types of the braided channels, including sandy filling and muddy filling. The combination patterns of the channel bars and the braided channels could be divided into three types, namely, superimposed, standalone, and contact, and the contact type was the primary type. On the whole, it showed the geometric morphological characteristics of the flat top convex at the bottom of the channel bar and the flat bottom convex at the top of the braided river channel. A careful measure of the architectural element was executed. The length of the single braided flow belts was 365.16-1349.72 m, and the width was 270.57-1160.54 m. The channel bar’s length was distributed 158.89-318.32 m, and the width was distributed 75.97-116.41 m. The braided river’s width was distributed 16.81-180.05 m. The length and width ratio of the channel bar was concentrated between 2 and 4, which manifested wide bar and narrow river channel mode. Finally, the static distribution model and dynamic response curve were compared to verify the correctness of the reservoir architecture characteristics to guide the subsequent development of the oilfield.

Research on the Intelligent Construction of the Rebar Project Based on BIM

Rebar engineering in the construction industry lacks effective technical means and has a high processing cost and high waste rate. Under the background of intelligent construction, the centralized processing mode of steel bars in prefabricated factories realizes the automatic processing of steel bars and improves the processing efficiency of steel bars. Using the C# programming language, combined with Revit secondary development technology, the automatic generation of the rebar model and the automatic export of rebar drawing are realized, which saves time for the designers to build the model. The calculation method of the cutting length of the steel bar is analyzed in this paper, which can be used as a reference for the subsequent optimization research of steel bar cutting. The assembly position information of the steel bar was introduced into an Excel table to help realize the automatic assembly of the steel bar cage and the intelligent construction of the steel bar. Combined with mixed reality technology, project personnel can interact with the reinforced BIM model through the mixed reality device Hololens2 to guide construction remotely.

Improvement of boring operations by means of mode coupling effect

Boring bars are inherently slender tools which are prone to show chatter problems due to their low dynamic stiffness and damping, being this problem their main limitation in productivity. The onset of chatter is mainly related to the dynamic stiffness of the bending mode of the boring bar when the length L to diameter D ratio is higher than 4. Tuned mass dampers (TMD) are effective technical solutions to increase the dynamic stiffness of large ratio boring bars. However, there are many applications where 4–6 L / D ratio tools are required, and the avoidance of chatter without the application of TMDs is interesting due to the high cost of damped tools. This work proposes the use of mode coupling effect to increase the damping and stabilise the machining process avoiding the use of any special device. This effect occurs when the frequency of one of the machine’s modes is similar to the frequency of the dominant mode of the boring bar. As a result, the shape of the critical mode of the boring bar is mixed with the mode originated in the machine, and the damping and stability will be higher than the one that is not subjected to any dynamic coupling. The main contribution of this work is the application of this concept to increase stability in boring operations. This objective has been achieved by optimising the tool length and material by means of a dynamic model based on Receptance Coupling Substructure Analysis (RCSA). The model combines an analytical model of the elastic body of the boring bar with the experimental characterisation of the effect of the rest of the machine. This way, the shape and materials of the boring bar can be optimised to create an increase of damping. The optimisation procedure has been experimentally validated resulting in an increase of cutting stability and demonstrating that not always a shorter bar supposes a higher stability.