Beam Joints Research Articles

Numerical simulation of damaged RC half-joint beams: towards appraisal and retrofitting

Concrete half-joint beams (HJB) are characterised by local reductions in the overall beam depth at the support and are ideal for structural connections. However, the beam joint region is vulnerable to deterioration and design/detailing shortcomings. Non-linear numerical modelling of the behaviour of a series of impaired reinforced concrete HJBs was conducted in this study. The major defects considered were unavailability of diagonal bars/U bars, shear reinforcement inadequacy and reinforcement corrosion. The numerical simulations captured global and local behaviours of the beams. The load capacity prediction discrepancy was in an impressive range of −16.7% to +1.5%, in contrast to the predictions of the commonly used strut-and-tie model in the range of −39.2% to 16.9%. Subsequently, an experimental study was established using finite-element modelling to explore the retrofitting potential of defective HJBs using the deep embedment (DE) technique. The strength enhancement was almost 30% and the internal load paths and the failure mode of the defective beam were favourably altered with the post-installation of the retrofitting element. The DE technique was thus identified as an ideal option for the retrofitting of impaired HJBs.

Seismic shear behavior of new high-strength reinforced concrete column and steel beam (New RCS) joints

New high-strength reinforced concrete column and steel beam (New RCS) joints were developed in this research. Two-way, through-beam New RCS joint details with beams concentrically or eccentrically connected to the joint were proposed. The beam in one direction was continuous through the joint (continuous beam). The beam in the other direction was connected to the continuous beam by complete joint penetration (CJP) groove welds. Five-spiral reinforcement was used for joint transverse reinforcement. A method to calculate the amount of five-spiral reinforcement was proposed considering the confinement effect from the face-bearing plates (FBPs). Doubler plates were used to strengthen the eccentric beam flanges with predrilled holes to allow the passage of column longitudinal reinforcement. A method was proposed for the design of the doubler plates. Large-scale New RCS joint specimens designed to fail in joint shear were tested. Test results showed that the proposed joint details and design methods effectively avoided failure in undesirable locations. All the specimens failed in joint shear but still reached high drift ratios. The eccentric joint specimens (IDEHS and ISEHS) exhibited peak joint shears higher than the concentric beam specimen (IHS). The 1994 ASCE and 2015 ASCE shear strength models produced conservative predictions of the peak joint shear and the joint shear at 0.5% joint shear deformation for all the specimens. The predictions by the 2015 ASCE method were more reasonable with less scatter than the 1994 ASCE method because the former recognizes the shear strength contribution from the outer joint panel even without the use of shear keys and allows a longer steel web in shear strength calculation.

Design features of modular buildings

The paper is devoted to modular buildings as а current topic of modern construction. A significant number of studies on this topic have appeared both in Russia and abroad in last years. It is necessary to classify modular buildings and highlight their design features to systematize the research. The main distinguishing feature of modular construction is the erection of a structure from volumetric modular blocks manufactured at the factory, each of which must also fully meet the requirements of functional, technical, economic feasibility and architectural expressiveness. Steel or wood is a common materials for modular constructions. Steel modular buildings have become more widespread due to their greater bearing capacity, so the paper provides a classification of modular buildings with a steel structure. Modular buildings are classified according to the following features: structural system of the building (arrangement and load transmission from one module to other); framework of modules (bearing structures of individual modules); nodal connections. There is two types of nodal connections: intermodular (joints of modules to each other) and intramodular (joints of beams and columns inside the module). Based on a review of literature sources and an analysis of advantages and disadvantages, the most common structural solutions for modular buildings in the Russian Federation were identified: buildings from stacked modules with support columns, intermodular joints on welding and welded intramodular joints. However, this provision does not limit research on modular buildings of other design solutions.

The adhesion of aluminium inserts in epoxy composites: The role of surface pre-treatment

Aluminium inserts are frequently embedded within the composite sandwich structures used in modern sports cars. Since the inserts are used for attaching safety-critical components to the structure, the adhesion between the metal and composite needs to be strong and durable. The bond is achieved through an epoxy resin system. However, when the resin includes an internal mould release agent (IMR) to facilitate the demoulding process of the structure, the adhesion between the inserts and the composite structure can be compromised. In addition, inserts can be exposed to high treatment temperatures. As such, to ensure that high adhesion performance can still be achieved, an appropriate surface treatment should be applied on the inserts.In this paper, four commercially available surface treatments for aluminium inserts were assessed using single lap joint (SLJ) and double cantilever beam (DCB) tests. Moreover, to investigate the influence of the IMR and the high-temperature process on the joint properties, four sample manufacturing methods were used to prepare the SLJ samples: without IMR and without high-temperature process (Method 1), with IMR (Method 2), with high-temperature process (Method 3) and with both IMR and high-temperature process (Method 4). The DCB samples were only prepared using Method 4. The locus of failure for the SLJ samples prepared with Method 4 was evaluated by using X-ray photoelectron spectroscopy (XPS) and optical microscopy. It was found that a silane-based primer was sensitive to the use of both the IMR and high temperature (31% drop in the lap joint strength when both applied). A cataphoretic electrocoat was also investigated and only deteriorated when exposed to high temperature (up to 40% decrease in the lap joint strength). An epoxy-based primer did not show a significant sensitivity to the IMR, however, when exposed to high-temperatures, the joint became even stronger (up to 15% increase in the lap joint strength).

Machine Learning-Based Vision-Aided Beam Selection for mmWave Multiuser MISO System

In this letter, we propose a machine learning-based vision-aided beam selection (ML-VBS) for millimeter-wave indoor multi-user communications. The proposed scheme is aimed at addressing the beam selection overhead with narrow beams in a multi-user scenario. The proposed scheme relies on a base station (BS) equipped with a single camera to observe the scene and estimates the angles to the multiple users. Given the estimated angle information and the limited number of radio frequency chains at the BS, two serial deep neural network structures are employed for joint user and beam selection subject to a minimum rate constraint. The numerical evaluation shows that the proposed ML-VBS scheme achieves a good performance in terms of the multi-user angle estimation, achievable sum rate and low computational complexity compared to conventional beam selection techniques.

Numerical and analytical studies of flexural behaviour of prestressed UHPC joints

This study numerically and analytically investigates flexural behaviour of precast ultrahigh performance concrete (UHPC) segments connected by post-tensioned prestressing strands with or without epoxy on keyed joint surfaces. The analytical formulas are proposed for calculation of joint opening load and ultimate flexural capacity, and a numerical model is established to investigate flexural behaviour of the jointed beam. The joint surfaces without epoxy are simulated by a pair of contact elements with a friction coefficient of 0.6. For the joint surfaces with epoxy, besides the contact elements, a spring element is defined for consideration of the epoxy and an optimized force–displacement relationship is first proposed and input for the spring property. The previous test data and data from one intact beam with low reinforcement ratio tested in the present study are used for validation of the analytical and numerical calculations. The numerical results agree well with the test results in terms of load-midspan deflection, load-joint opening displacement as well as failure modes. Based on the validated numerical model, the effect of number of prestressing strands and beam depth on the flexural behaviour of the prestressed jointed beam is investigated. This study will promote prestressed UHPC joints’ application in practical engineering.

Global optimization of excitation directions for scavenging energy based on a cross-jointed L-shape multidirectional piezoelectric energy harvester

Energy harvesting technology can collect energy from environmental vibrations, but it is still challenging because the vibration from an environment is random and the directions vary. In this study, a novel cross-coupled L-shaped vibration piezoelectric energy harvester (CL-VPEH) was proposed to collect energy from different environmental vibration directions. This CL-VPEH consists of a vertical beam and a horizontal beam joint crosswise with two laminated piezoelectric layers. Finite element analysis was performed to study the voltage output and resonant frequency. A simplified lumped mass model of CL-VPEH under excitation from an arbitrary direction was built to describe its working principle and multi-directional energy-harvesting ability. The experimental results demonstrate that the CL-VPEH shows good agreement with the numerical and analytical solutions. The experimental results validate the CL-VPEH’s multidirectional energy harvesting ability. Using the lumped mass model, the performance of the CL-VPEH under every single-direction excitation is investigated. A weak power output area is found with a frequency range of 10 Hz − 25 Hz, which should be avoided in future applications of this kind of multiple-directional excitation energy harvesting.

Development and testing of demountable RC column-to-steel beam connections under cyclic loading

In order to achieve the disassembling and recycling of the structure members, three novel demountable Reinforced Concrete column to Steel beam (RCS) joints are developed in this work. By conducting the cyclic loading test and the FEM simulation, the seismic performances of three demountable RCS joints and one reference non-detachable joints are numerically and experimentally investigated. The three demountable RCS joints present larger lateral capacity and better energy absorption than the non-detachable joints. The FEM models are validated by the experimental data and can successfully predict the hysteresis responses and failure modes of the demountable RCS joints. With the help of the validated FEM model, parametric studies are conducted as well. As illustrated by the numerical result, the beam length has a marginal influence on the seismic performance of the three demountable RCS joints, while increasing the longitudinal and transverse ratios can dramatically improve the lateral capacity of the three demountable RCS joints.

Seismic performance of CFST column to steel beam joint with outer annular stiffener

This paper investigates an experimental study on CFST (concrete-filled steel tubular) column to H-shaped steel beam joints with outer annular stiffener. Five joint specimens (three T-shaped joints and two cruciform joints) were carried out under cyclic loading tests. The main experimental parameters included column width-thickness ratio (D/t = 30 or 38), and axial load ratio (n = 0.4 or 0.6). The strength, stiffness, ductility, and energy dissipation capacity were compared and analyzed based on the experimental results. The results showed that small column width-thickness ratio could effectively improve the elastic stiffness and ultimate bearing capacity of tested specimens. Two failure modes, column local buckling of T-shaped joint and beam weld cracking of cruciform joint, were observed during the test.

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.

Monitoring the crack length of adhesively bonded carbon-fiber-reinforced polymer by using aligned graphene

In this study, the lengths of cracks in composite joints bonded with epoxy were monitored by evaluating the electrical resistance. Samples of double cantilever beam joints bonded with epoxy-containing aligned graphene were subjected to Mode I fracture tests. During sample fabrication, 0.15 wt% graphene was included in the epoxy and then aligned under an electrical field. The presence of aligned graphene resulted in the formation of an electrically conductive medium between composite adherents. During the fracture tests, the variation in resistance with the crack length was recorded; the resistance of the adhesively bonded joint increased with the crack length. The experimental results for the relationship between the resistance and crack length agree well with theoretical predictions. The functionalized epoxy exhibited homogeneous electrical conductivity, which indicated that the aligned graphene was uniformly dispersed in the epoxy. Thus, epoxy functionalized with aligned graphene can be used to detect the lengths of cracks within composite joints.

Joint beam selection and power allocation in cognitive collocated MIMO radar for potential guidance application under oppressive jamming

The collocated multiple-input and multiple-output (MIMO) radar can track multiple targets simultanesouly under the simultaneous multi-beam (SM) working mode. In this case, each transmit beam is focused to illuminate the region of interest (ROI), and then a focused beam is formed at the receiver for higher resolution. A joint beam selection and power allocation (JBSPA) strategy for potential guidance application under oppressive jamming is developed in this mode. On account of the posterior Cramér-Rao lower bound (PCRLB) offering a quantitative measurement for target tracking accuracy, the PCRLB is derived and utilized as the optimization criterion. The optimization model is formulated with the aim of improving the effective tracking target quantity and the sum of the PCRLBs of the effective tracking targets (ETTs). By exploiting the local search based on the benefit-cost ratio (BCR), the previous JBSPA problem is converted into a convex problem, and then transformed into a semidefinite programming (SDP) problem to solve it. Numerical results demonstrate the superior performance of the proposed strategy in improving the multiple target tracking (MTT) performance.

Joint User Grouping and Beam Selection for Beamspace mmWave Multi-User MIMO System

Lens antenna arrays based beamspace millimeter-wave multi-user massive MIMO (B-MIMO) can significantly improve energy efficiency without significant loss of spectral efficiency (SE), which is considered as a highly expected technology for future wireless communication networks. Motivated by the requirement of reducing SE loss by efficient user grouping (UG) and beam selection (BS), a joint user grouping and beam selection algorithm is studied. Specifically, a local search based BS algorithm is proposed by proving the convexity of the BS problem after relaxing the constraints. Moreover, a deep learning based UG algorithm is proposed by equivalently transforming the UG problem into a classification problem. The results of theoretical analysis and numerical simulation show that the proposed algorithms can be more closely with the performance of the exhaustive search algorithm and the complexity is lower than that of the traditional algorithms.

GBLinks: GNN-Based Beam Selection and Link Activation for Ultra-Dense D2D mmWave Networks

In this paper, we consider the problem of joint beam selection and link activation across a set of communication pairs to effectively control the interference between communication pairs via inactivating part communication pairs in ultra-dense device-to-device (D2D) mmWave communication networks. The resulting optimization problem is formulated as an integer programming problem that is nonconvex and NP-hard. Consequently, the global optimal solution, even the local optimal solution, cannot be generally obtained. To overcome this challenge, this paper resorts to design a deep learning architecture based on graph neural network to finish the joint beam selection and link activation, with taking the network topology information into account. Meanwhile, we present an unsupervised Lagrangian dual learning framework to train the parameters of the GBLinks model. Numerical results show that the proposed GBLinks model can converge to a stable point with the number of iterations increases, in terms of the weighted sum rate. Furthermore, the GBLinks model can reach near-optimal solutions through comparing with the exhaustive scheme in small-scale ultra-dense D2D mmWave communication networks and outperforms GreedyNoSched and the SCA-based method. It also shows that the GBLinks model can generalize to varying network densities and network coverage regions of ultra-dense D2D mmWave communication networks.

Experimental study on seismic behavior of the self-centering RCS joint with replaceable buckling restrained dampers

Reinforced concrete column and steel beam (RCS) joints are typically designed to ensure that plastic hinges develop at the end of the steel beams. The seismic energy is dissipated through the inelastic deformations of the steel beam. This design will result in difficult-to-repair damage and residual drifts. In this paper, a self-centering RCS joint with replaceable buckling restrained dampers and unbonded post-tensioning strands is proposed which can significantly eliminate residual drift under a strong earthquake. It dissipates seismic energy through replaceable buckling restrained dampers. It is easy to replace damaged dampers to ensure quick restoration of the capacity of the joint. Nine self-centering RCS joints were designed, constructed, and tested under cyclic loading. The experiments investigated the mechanical behavior, hysteretic curve, energy dissipation capability, self-centering capability, and replaceability of the self-centering RCS joints. The experimental results showed that the proposed joint experienced minimal residual drift and performed satisfactorily at the moment carrying capacity and energy dissipating capacity. Additionally, the specimens performed almost identically after the damaged dampers were replaced; thus, the effectiveness of damper replacement was verified.

Experimental research on wood beams strengthened with engineered bamboo laminates attached with self-tapping screws

An experimental study of the flexural performance of heavy timber beams strengthened using self-tapping screw-affixed engineered bamboo materials is presented. Twelve larch beams were tested under monotonic loading to failure; these were reinforced on their soffits with either laminated bamboo or bamboo scrimber plates. In lieu of adhesive bonding, self-tapping screws with different diameters, lengths and layouts were drilled in the bamboo plates and the beams to transfer bond forces across the interface. Flexure failure modes including wood crushing and wood fracture failure were observed for most beams. The ultimate failure mode of beams strengthened using bamboo plates was a combination of longitudinal splitting and transverse fracture of the plates. Through service level deflections, the strengthening bamboo plates improved the beam stiffness and showed no indication of relative slip along the wood-bamboo interface. At higher loads, and approaching ultimate capacity, the laminated bamboo tends to split, resulting in slip at the strengthening interface. The highly anisotropic laminated bamboo did not perform as well as the more orthotropic bamboo scrimber. The latter better resisted splitting. The mechanical jointed beam model was shown to provide a good estimate of strengthened beam moment capacity.

Long-Term Monitoring of Local Track Irregularity and Its Influence for Simply Supported Girder Bridge of HSR

By analyzing dynamic track geometric irregularity data of high-speed railway (HSR) with ballast track in China, there is a peak of [5, 11] m wavelength for the longitudinal level at the beam joint of simply supported girder bridges. The difference between the absolute value of track longitudinal level at the beam joint and that at the midspan is one to three mm. Under annual temperature cycle, the ballast at the beam joint loosens because of the bridge–track interaction, which results in the longitudinal level at the beam joint gets larger in winter and smaller in summer, that means the longitudinal level is negatively correlated with temperature, and at the same time, the development of the track longitudinal level and Track Quality Index (TQI) with the temperature are given. In addition, the vertical acceleration of axle box and bogie, and wheel–rail vertical force are larger when the train passes the beam joint than when it passes the midspan, which threatens running safety significantly. This article established a three-dimensional vehicle–track–bridge finite element model (FEM), thus the thresholds of track longitudinal level at the beam joint for simply supported girder bridge with ballast track in 250 km/h HSR were proposed, i.e., the maximum of dynamic track longitudinal level is 14 mm, and the maximum of static value is 11 mm. Once one of the two thresholds exceeds the corresponding limit, the train speed should be reduced to 160 km/h or below.

Performance of SRC column-RC beam joints under combined axial and cyclic lateral loadings

Strong column-weak beam behavior of a concrete structure with reinforced concrete (RC) beams and steel reinforced concrete (SRC) columns can only be ensured during a seismic event if the premature failure of beam-column joints could be avoided. The RC beam-SRC column joints, however, require special design and reinforcement detailing due to the presence of structural steel sections in the columns. Two different detailing schemes have been explored in this study for the exterior RC beam-SRC column joints. The key parameters varied in these detailing schemes are the anchorage length of beam longitudinal bars and the provision of transverse stiffeners in the structural steel sections. Three large-scale test joint specimens have been tested under the combined axial load and the varying lateral cyclic displacements. The crack propagation patterns, hysteresis behavior, moment-rotation characteristics, lateral stiffnesses, and joint shear-distortion behaviors of the composite specimens have been compared with the RC specimen to verify the suitability of the studied configurations. The experimental moment-rotation behavior of the test specimens has been compared with the theoretical moment-rotation curves derived using the current code provisions. Finally, the recommendations for the suitable configuration of the composite connection between the SRC column and RC beam have been proposed.

Energy and Delay Guaranteed Joint Beam and User Scheduling Policy in 5G CoMP Networks

Massive Multi-Input Multi-Output (MIMO) and Coordinated MultiPoint (CoMP) technologies in Cloud-RAN (C-RAN) architecture become inevitable trend due to the advent of next-generation mobile applications, which are traffic-intensive, such as ultra high definition (UHD) video. In this paper, we study a joint beam activation and user scheduling problem in a 5G cellular network with massive MIMO and CoMP utilizing orthogonal random beamforming technique. This paper aims to minimize total Remote Radio Heads’ (RRHs’) energy expenditure in a dynamic C-RAN architecture while ensuring finite service time for all user traffic arrivals in the communication coverage. We leverage Lyapunov drift-plus-penalty framework to transform an original long-term average problem into a series of per-slot modified problems. Since the provided per-slot problem is combinatorial and nonlinear optimization problem, we are inspired by a greedy algorithm to design energy and delay guaranteed joint beam activation and user scheduling policy, namely BEANS. We prove that the proposed BEANS ensures finite upper bounds of average RRH energy consumption and average queue backlogs for all traffic arrival rates within constant ratio of capacity region and all energy-delay tradeoff parameters. These proofs are the first attempt to theoretically demonstrate guarantees of energy and queue bounds in a framework consisting of possibly negative submodular objective function and non-matriod constraints. Finally, via extensive simulations, we compare the capacity region and energy-queue backlog tradeoff of BEANS with optimal and existing algorithms, and show that BEANS attains up to 65% of energy saving for the same average queue backlog compared to the algorithms which do not take traffic dynamics and energy consumption into considerations.

Millimeter-Wave NR-U and WiGig Coexistence: Joint User Grouping, Beam Coordination, and Power Control

Millimeter wave (mmWave) communication is a promising New Radio in Unlicensed (NR-U) technology to meet with the ever-increasing data rate and connectivity requirements in future wireless networks. However, the development of NR-U networks should consider the coexistence with the incumbent Wireless Gigabit (WiGig) networks. In this paper, we introduce a novel multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) based mmWave NR-U and WiGig coexistence network for uplink transmission. Our aim for the proposed coexistence network is to maximize the spectral efficiency while ensuring the strict NR-U delay requirement and the WiGig transmission performance in real time environments. A joint user grouping, hybrid beam coordination and power control strategy is proposed, which is formulated as a Lyapunov optimization based mixed-integer nonlinear programming (MINLP) with unit-modulus and nonconvex coupling constraints. Hence, we introduce a penalty dual decomposition (PDD) framework, which first transfers the formulated MINLP into a tractable augmented Lagrangian (AL) problem. Thereafter, we integrate both convex-concave procedure (CCCP) and inexact block coordinate update (BCU) methods to approximately decompose the AL problem into multiple nested convex subproblems, which can be iteratively solved under the PDD framework. Numerical results illustrate the performance improvement ability of the proposed strategy, as well as demonstrating the effectiveness to guarantee the NR-U traffic delay and WiGig network performance.