Frame Joints Research Articles

Shear capacity model for reinforced concrete joints

Studies on the behavior of reinforced concrete joints of frames in seismic areas have been conducted in recent decades especially, and principally following the most recent seismic events, during which the crisis of nodal panels has been recorded more frequently. For the same reason, technical guidelines have paid specific attention to the construction details of joints. The models for calculating the capacity of joints have been designed primarily for cases where beams do not converge on all sides. These joints are rightly considered to be more critical because they benefit less from confinement effects. On the other hand, experimental tests are conducted on nodal panels loaded in the plane and, also because of experimental difficulties, most full-scale tests are conducted on panels in which only one beam converges. These panels represent the least confined joints but, at the same time, they are less loaded than joints in which two beams converge. When the loads transmitted by the beams are particularly high (e.g., two strongly reinforced beams), design relationships provide large quantities of reinforcement that cause some difficulties in the construction phase. To overcome this issue partially, some guidelines suggest less severe checks if a lower dissipative capacity of the structure is needed. Nevertheless, joint failure is a fragile mechanism that should be avoided because it considerably affects the ductility of a structure.This paper presents a model of joint shear capacity based on a traditional mechanical approach (i.e., Mohr’s circles), which explicitly considers the presence of single or double beams in the plane of the nodal panel. Using the average value of the material strengths, the model was validated with a database of almost 300 tests on nodal panels that had failed due to shear. The predictions have a reasonable scatter compared to the typical variability of the mechanical strength of concrete and the variability of the construction details with which the panels have been made, which reflects the variability with which the joints are made in common practice. When used with the design values of the material strengths, the model predicts the capacity of nodal panels subject to cyclic action with a level of caution sufficiently similar for cases with one beam and two beams. Therefore, its application allows a significant reduction of the amount of reinforcement for joints in which beams converge on all sides, compared to several models given in the literature.

Analytical Study Regarding the Seismic Response of a Moment-Resisting (MR) Reinforced Concrete (RC) Frame System with Reduced Cross Sections of the RC Beams

In the last few decades, a series of earthquakes were recorded which pointed out several deficiencies regarding the ductile seismic response of MR RC frame structures. Thus, the research problem centres around the failure mechanisms registered by the structures, which differ from the general notions of seismic response commonly found in current design standards and norms regarding seismic actions. In these conditions, in the present paper—by using comparative methods—the analytical validation of the solution of plastic hinge concentration and seismic energy dissipation in the marginal beam areas is proposed. Therefore, the RC beam sections were reduced (weakened) in the marginal areas which exhibit a plastic deformation potential, as well as in the corner areas of concrete slabs with vertical rectangular holes. The significant outcomes of this research imply the partial “guiding” of plastic hinges in the zones adjacent to beam ends. Furthermore, a reduction of both the negative effects of horizontal rigidization of the beams and the cracking and plastic deformation effects of beam-column frame joints was observed. With these technical implications, a complex mechanism of plastic deformation of MR RC frame models is registered in which all lateral elements (including RC columns) participate in the dissipation of seismic energy, without the occurrence of the “weak storey” mechanism for any of the analytical RC frame models. Furthermore, it is possible to observe the partial formation of the global plastic mechanism “Strong Columns—Weak Beams” (SCWB) for some of the structural models. Finally, the analytically studied innovative element regarding the improvement of the seismic response of pure MR RC frame structures is successfully validated.

Design and numerical analysis of steel frame joints with replaceable buckling-restrained links

This paper proposes a steel frame joint with a replaceable buckling-restrained link to prevent the buckling of joint plates and enhance the seismic performance. The calculation formulas of the yield load and initial stiffness are derived to determine a theoretical skeleton curve. A design method for the joints is proposed to determine the design parameters of the core plate area and length, ear and end plate thicknesses, and restraining plate thicknesses, based on the design conditions of the designed joint yield load and core plate strain limited values, plate deformation limited values, and restraining ratios, respectively. The derived formulas and design method are verified by analyzing the results of a cyclic loading test and 37 parametric numerical models calibrated with the test results. The results show that the theoretical skeleton curve is in good agreement with the test and numerical results, and the performances of the joints designed using the proposed method are close to the design conditions, implying the satisfactory performance of the design theory. The influences of the design parameters on the joint are well reflected by the parametric analysis

Seismic performance of RC-ECC composite frame by eliminating shear reinforcement in beam-column joint: Shake table tests

The inherent vulnerability of beam-column joints to seismic loading and steel congestion are two major research problems connected with beam-column joints of moment-resisting frames. The experimental study presented herein addresses these research questions and seeks to solve them by using Polyvinyl Alcohol based Engineered Cementitious Composite (PVA-ECC) in beam-column joints without transverse shear reinforcement. The study included the manufacture and shake table testing of two 1:3 reduced scale one bay two-story moment-resisting frame models using simulated earthquake motions. To evaluate the performance of ECC beam-column joints without shear reinforcement, two frame models, one with and the other without shear reinforcement in the beam-column joints, were prepared and tested. The acceleration time history record of the 1994 Northridge Earthquake USA was used for the excitation of specimens at different levels to produce progressive damage up to the near collapse state. The observed damage mechanism of tested models was recorded, and the response parameters, including floor displacement and acceleration, were measured. The measured data was processed to develop a lateral force-displacement envelope curve for the supposed prototype frames and calculate their seismic design factors (ductility, overstrength, and response modification). Comparison of the seismic performance parameters of the two prototype frames reveal that the ECC beam/column joint without shear ties performed marginally inferior to the ECC beam-column joints having shear ties but it still achieved a 75% larger R-factor compared with the code specified value.

Elasto-dynamic performance evaluation of a 6-DOF hybrid polishing robot based on kinematic modeling and CAE technology

By taking a 6-DOF hybrid polishing robot as an example, this paper presents a generalized methodology for elasto-dynamic analysis of hybrid robots in an easy, accurate and rapid manner. The approach can be implemented by three steps: (1) creating an inverse kinematic model for calculating the configuration parameters of the body-fixed frame of each substructure and the coordinates of the joint frames with respect to the reference frame of the fixed platform; (2) building a parameterized Finite Element (FE) model at the home pose by using the modal reduction techniques and Parametric Design Languages (PDL) embedded in the CAE system; (3) driving the FE model to specified poses using the calculated configuration parameters of substructures and coordinates of joint frames in the batch mode, and evaluating the elasto-dynamic performance of the robot over its entire workspace. The merit of this approach lies in that parallel or hybrid robots having different topologies can be modeled without complex mathematical derivation and operation, allowing the lower-order dynamic performance to be rapidly predicted with sufficient accuracy.

Mechanical Performance and Failure Mode Research on the Braced Frame Joint of Tower Cranes in High-Rise Building Construction

The collapsing number of tower cranes has increased with the development of the building industry. The safety of tower cranes has the potential to improve practices of building and outcomes in construction. The mechanical performance and failure mode of braced frame joints are analyzed in this research. Firstly, a mechanical model of a braced frame joint (BFJ) is established, and the experiment is designed. The destruction process and failure mode are researched by experiment. Then finite element model is established by ABAQUS. Moreover, working conditions with different concrete strength grades (CSG) and tension direction are researched. The results prove that braced frame joint cracks seriously with ultimate bearing capacity, simultaneously, the pre-embedded steel component (PESC) is pulled out. The failure mode is tensile and bending failure of BFJ in the test. The ultimate bearing capacity of failure is controlled by concrete strength grades. The tensile strength increases with the CSG, and the ultimate capacity of BFJ improves equally. The brittle fracture characteristic is more obvious in the ultimate state. The failure mode changes from crushing failure to tensile and bending failure with increasing tension angle. The research results could provide a better understanding of the working mechanism and performance evaluation of the BFJ of the tower crane.

Seismic Performance Analysis of Fabricated Concrete Beam-Column Joints Based on Intelligent Finite Element Analysis

In order to improve the seismic performance analysis effect of prefabricated concrete beam-column joints, this article uses intelligent finite element analysis technology to analyze the seismic performance of prefabricated concrete beam-column joints. Moreover, this article conducts in-depth research on the shear bearing capacity of the plastic hinge area so as to improve the accuracy of the calculation of the shear bearing capacity of the plastic hinge area. In addition, this article conducts finite element analysis of integral frame joints, uses finite element software to carry out numerical simulation of frame joints, and compares and analyzes the experimental results in the literature. Further, this article proposes an improvement of a prefabricated frame joint, performs finite element analysis on it, and compares and analyzes the numerical simulation results of concrete joints. The analysis results show that the finite element analysis model proposed in this article has high accuracy in the seismic performance analysis of prefabricated concrete beam-column joints, which meets the actual needs of the seismic performance analysis of modern prefabricated concrete beam-column joints.

Experimental research of seismic performance of buckling-restrained braced frame with ductile connections

The connection joints of Buckling-Restrained Braced Frames are critical to the performance of structures. The maximum ductility and cumulative ductility of Buckling-Restrained Braces are sufficiently large, and the ductility of beam-column connection of steel frame should be matched with that of the BRB component, then the structure would exhibit good global performance. The pseudo-static test of a 1/3 scale 2-story 1-span buckling-restrained braced frame (BRBF) system consisting of the reduced beam section (RBS) connections were conducted. The performance of BRBF with reduced beam section (RBS) connections was analyzed, and the deformation capacity of ductile connection was studied. The RBS sections on the beam ends effectively protect the beam-column connections of BRBF, and better deformation capacity can be achieved to provide large ductility up to 4.75. For BRBFs using new connection, the maximum roof drifts before the failure were governed by the rotational capacity of the beam-column connections and the stability performance of the BRBs. The global ductility of structures is highly relevant to the local ductility of beam-column connections and BRBs. The yielding sequence of structural components followed as BRBs, ductile connections and structural members, which is the reasonable plastic development of the structure for seismic design. The test BRBF underwent a big amount of fully-reversed hysteretic curves without strength or stiffness degradation during the significant drift demands imposed by the subsequent quasi-static cyclic test, which possessed good global ductility and energy dissipation capacity.

Seismic performance of self-centering beam-column joints reinforced with superelastic shape memory alloy bars and engineering cementitious composites materials

This paper presents a preliminary experimental investigation of a self-centering beam-column joint reinforced with superelastic Ni-Ti SMA bars and ECC materials. As an alternative to the longitudinal bars in the beam plastic hinge, SMA is used to reduce the residual deformations and dissipate energy, whereas the ECC materials used in the critical region of the joints can improve the ductility of the structural member. Five 1/2 scale frame joints were designed and manufactured. The failure phenomenon, bearing capacity, energy dissipation capacity, displacement ductility, residual deformation, and self-centering performance of the joints were comparatively analyzed through a low cyclic loading experiment. A finite element model of SMA-ECC joints was established, and the influence of the SMA and ECC on the seismic behavior of the joints was investigated. The study results show that SMA bars can dramatically enhance their self-centering capability, enabling self-retrofitting damage. The ECC material is helpful for optimizing the development of the plastic hinge at the end of the beam and improving the ductility and energy dissipation capacity of the structure. The SMA-ECC composite materials exhibit good supplement to significantly improve the ductility, energy dissipation, and self-centering capabilities and delay the stiffness degradation of the structure under extreme events.

The impact on nudge acceptability judgements of framing and consultation of the targeted population

AbstractThe aim of this article is to better understand how judgements about nudge acceptability are formed and whether they can be manipulated. We conducted a randomized experiment withN= 171 participants to test whether acceptability judgements could be (1) more favourable when the decision to implement the nudges was made following a consultation with the targeted population and (2) influenced by the joint framing of the nudge's purpose and effectiveness (in terms of an increase in desirable behaviour versus decrease in undesirable behaviour). We tested these hypotheses on various nudge scenarios and obtained mixed results that do not clearly support our hypotheses for all nudge scenarios. A surprising result that calls for further work is that by mentioning that a nudge had been implemented through a consultation with the targeted population its acceptability could be lowered.

Shear resistance of multi-cell special-shaped CFST column to H-section steel beam joint

This paper studies the shear behavior of frame joint between multi-cell special-shaped concrete-filled steel tubular (CFST) column and H-section steel beam based on experimental research. The shear failure mode and hysteretic behavior of the joint were investigated from the experiment. A finite element (FE) model for multi-cell cruciform CFST column to H-section steel beam joint was conducted to study the influences of the following parameters on joint shear resistance: the axial compression ratio of column, aspect ratio of the joint, thickness of steel tube in joint panel zone, and the concrete compressive strength. Stress analysis on the steel tube and the concrete of each cell in joint panel zone was conducted by using the FE model to clarify the load transfer path and shear mechanism. Furthermore, a mechanical model for the joint shear resistance was developed, in which the contributions from the steel tube and concrete in different cells were considered. Based on the shear mechanical model, a calculation method for joint shear resistance is also proposed to facilitate the practical applications and verified by the experimental and numerical results.

Seismic analysis of a frame structure equipped with displacement-amplified torsional dampers

The angular displacement of the beam-column joints of the frame structure is small under earthquake action, and the seismic mitigation effect of ordinary dampers placed at the joints is not obvious. The displacement-amplified torsional damper (DATD) is one that can be directly installed at the joint and has a displacement-amplifying function. Finite element numerical simulation on the mechanical properties of DATD was carried out in this paper. The theoretical mechanical model of DATD was derived, and the trilinear mechanical model and the modified Bouc-Wen model were used to describe the mechanical characteristics of DATD, respectively. Numerical simulation and theoretical analysis results agreed well with the experimental results. Then, the ETABS software was adopted to analyze and compare the dynamic responses of ordinary frame and frame equipped with DATAs under frequent and rare earthquakes. Results showed that compared with the uncontrolled structure, the inter-story angular displacement, top-story displacement and internal force at the frame joints of the controlled structure equipped with DATDs remarkably decrease, and the effect of energy dissipating and vibration control is obvious. DATD significantly delays the structural damage at the joints while dissipating the input earthquake energy and reducing the structure’s dynamic responses.

Experimental and Numerical Analysis of the Behavior of Beam–Column Connections with Reinforced Side Plates

This paper describes an experimental and numerical study of the hysteretic behavior of side-reinforced joints of a steel frame manufactured from Q345B steel and welded using an E5015 electrode. The objectives of this study were to observe the mechanical behavior of side-plate reinforced joints under cyclic loads; identify their plastic hinge, skeleton curve, stiffness degradation, ductility, and energy dissipation capacity; and provide useful test data for future damage analysis of steel frames with side-plate reinforced beam–column connections. Two specimens were designed, and both were tested under cyclic loads. The test setup consisted of one beam at the end and a column connected by three groove welds. The cyclic loads were applied to the beam’s free end, and the sizes of the beams and the columns of the two specimens were held constant because the only element studied in the present work was the side-plate reinforcement. In this paper, the responses of these two joints are discussed in terms of their experimentally and numerically obtained failure modes, hysteretic curves, plastic hinge, skeleton curve, stiffness degradation, ductility, and energy dissipation capacity. The results show that the steel frame’s side-plate reinforced joints, compared with normal joints, have smaller plastic hinge displacement and deformation, and higher bearing capacity. Furthermore, if designed according to code, all these welded joints perform satisfactorily.

Analysis and Evaluation on the Harmfulness of Sports Dance Based on Intelligent Computing

With the rapid development of motion analysis and editing technology, more and more animation technologies based on real human motion analysis are widely used in games, medicine, film and television, sports, and other fields. The role of this technology in the teaching system of sports dance arrangement cannot be ignored. This paper studies the application of intelligent algorithm in injury analysis of sports dance choreography and puts forward a smooth and natural motion editing method which is more in line with the characteristics of human motion. The square spherical surface intelligent algorithm is used to naturally transition the rotation posture of each frame of human joint, and the action modification of computer-aided dance choreography system is more in line with the real action of human body. Simulation results show that interframe data can be used for the same type of dance. Different types of dance arrangement can adopt the method of inserting a new framework between the two dance movements, so as to finally meet the needs of sports dance coaches and students to observe their own dance movements in an all-round way, so as to facilitate the arrangement and modification of sports dance movement design. It provides a certain reference for the application and development of virtual technology in the field of sports and greatly improves the current situation of sports dance teaching equipment. Through animation simulation technology, we can effectively avoid the injury caused by dangerous movements, provide a way of observation and improvement for coaches’ dance teaching, and effectively improve the training effect. Compared with traditional dance choreography methods, the intelligent algorithm in this study can make the animation display of sports dance more coherent and realistic and effectively solve the needs of current events observation and modification in sports dance choreography. It can produce complex movements with simple movements and help teachers arrange and teach sports dance. Avoid the accidental injury caused by the limitation of time and space in traditional teaching and realize the modernization and intelligence of physical education teaching.

Dynamic Response Parameter Analysis of Steel Frame Joints under Blast Loading

A finite element model of steel frame joints is established using finite element analysis software ANSYS/LS-DYNA. The ideal triangular impact load is used to numerically analyze the dynamic response of steel frame welded joints under blast loading, the main factors affecting this response, and the failure modes of three types of joints, so as to provide reference for the antiexplosive design of steel frame joints. The results show that steel frame joints vibrate violently in the explosive blast direction. Due to the strain rate effect, the strength of steel increases, the material enters the plastic strengthening stage, and there is a certain residual displacement. In addition, displacement and stress caused by blast action in the joint area are large, and the flange shear failure of the beam and column is prone to occur in the joint. Increasing the flange width of the beam and the column cannot improve the antiexplosive performance of the joints, while increasing their thickness can. Furthermore, bolted and welded joints have the highest stiffness and best antiexplosion performance, followed by welded joints, while the antiexplosion performance of bolted joints was the worst.

Novel design equation on minimum column depth for interior beam-column joints in special moment frames with large-diameter high-strength rebar

Recently, large-diameter high-strength rebar have been used for the longitudinal reinforcements of beams that penetrate interior beam-column joints, to improve in-situ constructability. The seismic performance of reinforced concrete (RC) interior beam-column joints is decreased by the yield of the rebar, bond failure, and rebar slip. Existing standards of RC special moment frames (SMFs) limit the minimum column depth to control the bond stress of the longitudinal reinforcements penetrating the interior beam-column joint. However, the standard criteria, which is an empirical equation derived in the 1980s based on experiments using mild steel with small-diameter, do not accurately represent the minimum column depth for joints with large-diameter high-strength rebar. This study proposes a new design equation basis on the analytical formulation that determines the minimum column depth of the interior beam-column joint in the SMF with large-diameter high-strength rebar. The proposed design equation considered the effect of large-diameter high-strength rebar on the design of the minimum column depth by formulating the bond strength with respect to the diameter and strength of the rebar from the moment equilibrium condition based on the diagonal strut action. The proposed design equation was verified based on a database of 48 interior beam-column joints and compared with the existing standard criteria. The comparative analysis results confirmed that the proposed design equation presents the minimum column depth for the interior beam-column joint using large-diameter high-strength rebar more accurately than the existing standard criteria. In addition, the proposed equation is expected to address the design feasibilities required to secure the structural safety of the interior beam-column joint in the SMF using large-diameter high-strength rebar and the seismic performance of the structure.

Failure analysis of composite F-joint structures under tensile loading: Experimental and numerical study

This paper presents an investigation on the failure process of two different types of composite frame joints (F-joints), one is connected by high-lock bolts (FH) and the other reinforced by high-lock bolts and adhesive (FHA). The mechanical behavior of F-joints subjected to out-of-plane tension load is analyzed by experiment and numerical simulation. Test results show significant differences in the damage process, failure modes and strain distribution between FH and FHA. The strength of FHA increases nearly 13% compared to FH. Three-dimensional finite element models considering failure criterion and damage evolution are developed and implemented in the commercial code Abaqus/Standard through a user-defined subroutine UMAT. Cohesive zone model is used to simulate the adhesive layer damage of FHA. Simulating failure load and the damage process match the experimental data. The information on the failure mechanism and final failure load of composite F-joints is useful for the optimal design of such joints.

Motion recognition using deep convolutional neural network for Kinect-based NAO teleoperation

AbstractThe capabilities of teleoperated robots can be enhanced with the ability to recognise and reproduce human-like behaviour. The proposed framework presents motion recognition for a Kinect-based NAO teleoperation. It allows the NAO robot to recognise the human motions and act as a human motion imitator. A stable whole-body imitation is still a challenging issue because of the difficulty in dynamic balancing of centre of mass (CoM). In this paper, a novel adaptive balancing technique for NAO (ABTN) is proposed to control the whole body in single as well as double supporting phases. It targets dynamic balancing of the humanoid robot by solving forward kinematics and applying a weighted average of mass with the CoMs of individual links with respect to the previous joint frames, which provides us with the dynamic CoM of the whole body. Our novel approach uses this dynamic CoM and calculates joint angles using proposed pitch and roll control algorithm to keep the dynamic CoM inside the stable region. Additionally, the NAO robot is capable of recognising human motions using the proposed 7-layer one-dimensional convolutional neural network (1D-CNN). To solve the problem of variable length of time sequences, Zero padding is introduced with 1D-CNN. It attains a recognition accuracy of 95% as compared to the hidden Markov model and neural network. The experimental results demonstrate that the developed teleoperation framework is robust and serves as potential support for the development and application of teleoperated robots.

The Seismic Performance of New Self-Centering Beam-Column Joints of Conventional Island Main Buildings in Nuclear Power Plants

In order to improve the deformation energy consumption and self-centering ability of reinforced concrete (RC) frame beam-column joints for main buildings of conventional islands in nuclear power plants, a new type of self-centering joint equipped with super-elastic shape memory alloy (SMA) bars and a steel plate as kernel components in the core area of the joint is proposed in this study. Four 1/5-scale frame joints were designed and manufactured, including two contrast joints (a normal reinforced concrete joint and a concrete joint that replaces steel bars with SMA bars) and two new model joints with different SMA reinforcement ratios. Subsequently, the residual deformation, energy dissipation capacity, stiffness degradation and self-centering performance of the novel frame joints were studied through a low-frequency cyclic loading test. Finally, based on the OpenSees finite element software platform, an effective numerical model of the new joint was established and verified. On this basis, varying two main parameters, the SMA reinforcement ratio and the axial compression ratio, a simulation was systematically conducted to demonstrate the effectiveness of the proposed joint in seismic performance. The results show that replacing ordinary steel bars in the beam with SMA bars not only greatly reduces the bearing capacity and stiffness of the joint, but also makes the failure mode of the joint brittle. The construction of a new type of joint with consideration of the SMA reinforcement and the steel plate can improve the bearing capacity, delay the stiffness degradation and improve the ductility and self-centering capability of the joints. Within a certain range, increasing the ratio of the SMA bars can further improve the ultimate bearing capacity and energy dissipation capacity of the new joint. Increasing or decreasing the axial compression ratio of column ends has little effect on the overall seismic performance of new joints.

Seismic damage and evaluation analysis of joints in enhanced-performance recycled aggregate concrete frame

Through the low cycle loading test of three full-scale enhanced- performance recycled aggregate concrete frame joints, the damage evolution and accumulation are analyzed according to the traditional ductile damage model (single parameter) and the improved Park-Ang damage model (double parameters): when the characteristic displacement of each specimen equals 20 mm, the specimen has been damaged, but the calculated results are negative according to ductile damage model; when the characteristic displacement exceeds 100 mm, the calculated results of the improved Park-Ang damage model show that all the specimens have been completely destroyed and cannot continue to bear load, but the actual results of the specimens still show certain bearing capacity and energy dissipation capacity. Therefore, it is necessary to modify the aforementioned damage model to make it suitable for enhanced-performance recycled aggregate concrete structures. Based on the foregoing test results, the fiber coefficient a, displacement coefficient α, and correction coefficient of energy coefficient k were proposed and fitted for the improved Park-Ang damage model. In addition, a corresponding modified Park-Ang damage model was established. Finally, using the proposed damage model, the error analysis of damage index was carried out with the example of HF-RAC2. The results show that the average error is within 6%, so the proposed two-parameter damage model can be applied to the analysis of seismic damage assessment of EC-RAC frame joints.