Conventional Joint Research Articles

Casting and installation of segmental precast quadratic concrete driven geothermal energy piles

Geothermal energy pile foundations are used both for structural purposes and to provide sustainable, clean, and cost-effective ground energy for heating and cooling buildings [1]. The majority of energy piles are cast-in-place concrete piles, which require extensive and expensive drilling during construction. A better alternative is to use precast concrete segmental driven energy piles, which can be cast in large quantities with high-quality assurance at a concrete factory, after which they are transported and installed into the ground [2]. This study aims to present a novel method of casting and installing segmental energy piles that utilize an innovative steel joint [3] for connecting the precast concrete segments on-site. In addition to structural integrity, the steel joint provides the possibility of a leak-proof coupling and continuity for heat-exchanging pipes embedded in concrete segments. The precast-driven pile foundations are made of high-strength concrete with a 14-day compressive strength of almost 80 MPa and have a quadratic shape with a maximum length of 12 m and a square width of 270 mm or 350 mm. In the 270-mm piles, a single U-loop can be used, while in the 350-mm piles, two U-loops can be used as presented in Figure 1. The heat-exchanging pipes are coupled inside the sidewall channels of the steel joint which are shielded using a steel cover plate, riveted to the joint. At the tip of the bottom segment of the piles, there is a strong steel rock shoe with a hardened steel point that allows the piles to penetrate the bedrock [4]. At a construction site, the joint and pipes can be connected quickly without any welding or electric equipment that expedites the installation work and obsoletes the health and safety risk associated with electricity. Utilizing the precast energy piles presented in this study increases the quality, and speed of installation while decreasing the overall cost of the project compared to cast-in-place energy piles. To prove the proper performance of the piles under real construction conditions, structural integrity tests and hydraulic pressure tests were performed according to BS EN 12794:2005 [5] and ASTM F2164–21 [6], and the results are briefly presented and discussed in the present study. Structural integrity tests consisted of impact tests in which 1000 blows imposing a minimum stress level of 28 MPa were applied on the pile segments connected using the new driven energy pile joint. During the impact tests, the pile structure and the joints remained undamaged. After the impact tests, the pipes were pressurized up to 100 psi (690 kPa) and no leakage or pressure drop was observed. Then the pile segments were cut according to the standard into shorter segments and subsequent bending tests were performed to measure the bending capacity. The bending tests show that the driven energy pile joints have a similar bending capacity as conventional normal joints. The results of this study show that segmental precast concrete energy piles using the new steel driven energy pile joints, are a perfect alternative for cast-in-place energy piles, which can provide sufficient structural and bearing capacity and can be used both for heating and cooling buildings.

Enhancing Microstructural, Textural, and Mechanical Properties of Al-Ti Dissimilar Joints via Static Shoulder Friction Stir Welding

Abstract The present study explores the application of static shoulder friction stir welding (SSFSW) to address the challenges of poor mechanical properties in conventional Al-Ti dissimilar friction stir joints, which arise due to significant material mixing and the formation of thick intermetallic layers. The results show that SSFSW inhibited material mixing and the mutual diffusion of Al and Ti were suppressed due to lower heat input. Mutual interdiffusion of Al and Ti was directed by an exothermic chemical reaction, forming an Al5Ti2 – Al3Ti sequence due to sluggish diffusion of Al in Ti at a temperature of 512°C achieved in this study. The microstructure at stir zone (SZ) comprised equiaxed grains with Ti particles acting as dispersoids for nucleation, whereas the presence of large Ti blocks at SZ of Conventional FSW (CFSW) resisted plastic deformation, resulting in non-homogeneous concentration of dislocations near its interface. A significant decrease in grain size at all the critical zones of weldment was due to rearrangement of dislocations through slip-and-climb mechanism, as evidenced by the occurrence of dynamic recrystallization. Emergence of γ-fiber and basal fiber texture increased the tensile strength of SSFSW to 289 MPa, which is about 11.2% higher than CFSW, with joint efficiency of about 88%. The study also analysed the contribution of various strengthening mechanisms to the yield strength improvement of SSFSW weldments in detail of SSFSW weldments in detail, and the results showed that grain boundary strengthening contributed the most to strength improvement in SSFSW.

Experimental test setup design for ultimate limit state evaluation of ductile wrapped composite KK‐joints

AbstractComplex circular hollow section double KK‐joints are widely used in, e.g. offshore wind turbine jackets. As an alternative to conventional welded joints of the CHS multi‐membered structures, wrapped composite joints have shown superior structural performance in previous pilot tests. Experimentally characterizing the joint behaviour under uniplanar loading can be complicated, because of the ductile failure mechanisms of wrapped composite joints and second‐order bending moments. This paper presents the design of a test frame in combination with a conventional tensile 2.5 MN test rig. Ductile joint failure, joint imperfections and second‐order effects are considered in the design. Structural finite element software SOFiSTiK is used to analyse the effects of wrapped joint behaviour and imperfections on the test system and interaction of joint, frame and loading rig behaviours. Non‐linear joint behaviour and misalignments of the braces increased the second‐order effects significantly. Mitigation strategies have been explored to reduce additional bending moments in the KK‐joint. A complete test setup is proposed to perform static experiments on double KK‐joints in uniplanar axial loading conditions.

Experimental investigation of wrapped composite X‐joints under uniaxial and multi‐axial loading conditions

AbstractCircular hollow section (CHS) multi‐membered structures, such as off‐shore wind turbine jackets and floating wind structures, face significant challenges under multiaxial loads. Wrapped composite joints have emerged as a promising alternative to conventional welded joints, offering superior structural and fatigue performance in previous pilot tests. This paper presents an experimental study on the failure mechanisms and load‐bearing capacity of wrapped composite joints under multi‐axial monotonic loading, using the Hexapod a six‐degree‐of‐freedom testing machine. The research question addressed in this study is to investigate the effectiveness of wrapped composite joints in resisting multi‐axial loads, and to understand the underlying failure modes. The experimental results demonstrate that the joints exhibit excellent resistance to uniaxial tension, uniaxial bending, and multi‐axial tension + bending loading, with failure modes including interfacial debonding, delamination, composite fracture, and steel yielding. Digital Image Correlation (DIC) and embedded optical fibers were used to monitor surface and interface strain. These findings suggest that wrapped composite joints offer significant resistance to multi‐axial loading.

Size effects on the structural behaviour of wrapped composite CHS joints

AbstractRecent pilot studies have shown the superior performance of wrapped composite joints as an alternative to conventional welded joints for circular hollow sections (CHS). Considering the large dimensions of CHS joints for field application and potential size effects from testing the structure on reduced scales, geometrical size effects need to be investigated. This work presents an experimental analysis and FE results of wrapped composite joints with three different scale sizes. The size effects on the uniaxial tensile behaviour of specimens were investigated in monotonic loading. The size effects on the structural behaviour of wrapped composite joints were evaluated regarding the performance in ultimate limit states. The outcome of this research supports the structural analysis and modelling of wrapped composite joints with upscaled sizes.

Hip rotation obtained via conventional and functional knee joint axis calibration in the context of femoral derotation osteotomy

Hip rotation obtained via conventional and functional knee joint axis calibration in the context of femoral derotation osteotomy

Proposal and experimental verification of additive manufactured beam‐column connection designed by topological optimization

AbstractThe aim of this research is to provide an alternative for the conventional design of beam‐to‐column connections in building structures. The new design is performed by means of Structural Topological Optimization and executed by means of additive manufacturing with steel.Regarding the methodology, the joint that would be manufactured by conventional methods (i.e. welded and bolted plates) is modelled by means of finite elements in the first place. Its behavior is obtained, as well as the boundary conditions and the loads to be applied to the part that is going to be optimized. Subsequently, a solid part is defined and optimized by means of the optimization module TOSCA. Then, the complete joint is simulated with the optimized connection, and the behavior and the weight of the material used are compared with those of the conventional joint. Some modifications are made to improve some aspects of the design.Afterwards, the optimized joint is printed with steel S316L, the connection is assembled with the columns and beams, and it is tested. The experimental results are analyzed to be able to make the necessary adjustments both in the connection and in the design methodology.

Comparative Analysis of the Efficiency of the Top Ten Conventional Joint Venture Life Insurance Companies in Indonesia in the Period Before and During the Covid-19 Pandemic Using the Data Envelopment Analysis Method

This study aims to capture the efficiency level of industry players in conventional joint venture life insurance companies in Indonesia before and during the Covid-19 pandemic. Efficiency is related to the level of success of an activity being assessed in terms of the ratio between amounts of the output generated and the input used to generate the outputs in the activity. Efficiency can be measured using the Data Envelopment Analysis (DEA) method, which is a non-parametric frontier approach that uses mathematical programming with 2 (two) assumptions, namely Constant Return to Scale (CRS) and Variable Return to Scale (VRS). The variables used are input and output variables, wherein the input variables include total debt, labor costs, claims expenses, investment composition of stocks, bonds, and securities issued by the government of the Republic of Indonesia (RI). The output variables used are premium income and investment returns. The type of data used is secondary data. The data collection technique used is library research. The objects used as samples were top 10 (ten) conventional joint venture life insurance companies in terms of revenues with the data obtained from the financial reports and annual reports of each company for the period between 2015 and 2021. The analysis show that investment portfolio performances derived from the company strategy acts as the main efficiency determinant in the industry.

Insights into Bending Stiffness Modeling of Elementary Flexure Hinges

Flexure hinges are widely used in mechanical devices, especially for micro- or even nano-scale applications, where conventional joints based on conjugate surfaces prove unsuitable. However, to achieve accurate motion of devices whose joints are flexure hinges, knowledge of stiffness models that correlate applied forces or bending moments with the resulting displacements is required. Nonlinear bending models are typically too complex and difficult to implement. Therefore, it is preferred to use linear models, which admit analytical solutions. The purpose of this paper is to show what is lost in terms of accuracy in reducing a nonlinear bending stiffness model associated with a flexure hinge when simplifications are made to obtain an analytical solution. An analysis of the simplification process leading to a linear stiffness model and its analytical solution is presented. From this study arises an increased awareness of flexure joints in terms of the accuracy obtained with their stiffness models, suggesting important information to the user in choosing the level of complexity required to model them in a specific application. A comparison between analytical and numerical results is provided in the form of maps and tables so as to make that choice as clear as possible.

Two-stage deep spectrum fusion for noise-robust end-to-end speech recognition

Recently, speech enhancement (SE) methods have achieved quite good performances. However, because of the speech distortion problem, the enhanced speech may lose significant information, which degrades the performance of automatic speech recognition (ASR). To address this problem, this paper proposes a two-stage deep spectrum fusion with the joint training framework for noise-robust end-to-end (E2E) ASR. It consists of a masking and mapping fusion (MMF) and a gated recurrent fusion (GRF). The MMF is used as the first stage and focuses on SE, which explores the complementarity of the enhancement methods of masking-based and mapping-based to alleviate the problem of speech distortion. The GRF is used as the second stage and aims to further retrieve the lost information by fusing the enhanced speech of MMF and the original input. We conduct extensive experiments on an open Mandarin speech corpus AISHELL-1 with two noise datasets named 100 Nonspeech and NOISEX-92. Experimental results indicate that our proposed method significantly improves the performance and the character error rate (CER) is relatively reduced by 17.36% compared with the conventional joint training method.

EFFECT OF CHORD PRELOADING AND BRACE INCLINATION ON AXIAL RESISTANCE OF FULL-WIDTH RHS X-JOINT

According to current representative design standards, the influence of brace angle on the axial resistance of rectangular hollow section (RHS) X-joints is assumed to be independent of the chord preloading state. To investigate the appropriateness of this assumption, extensive test-validated finite element (FE) analyses are performed on full-width RHS X-joints with varying brace angles and chord preloads. The analyses showed that an appreciable coupling effect between the brace angle and chord preload exists on the joint resistances. The most adverse coupling effect occurs under the condition of high brace inclination and large compressive chord preload, leading to the concern that the current design resistance formula may overestimate the ultimate joint strength. Consequently, a revised chord stress function is sought for inclined full-width RHS X-joints that accounts for the coupling effect between chord preload and brace angle. In the FE analyses, high strength steel joints are included as well as conventional mild steel joints. The chord stress effect in high strength steel joints is found to be more detrimental compared to geometrically identical mild steel joints, implying that the chord stress effect may be influenced by the class (slenderness) of the chord cross-section. Therefore, a proper limitation on the chord section slenderness, such as the Class 2 requirement in design codes, appears essential.

P92 steel and inconel 617 alloy welds joint produced using ERNiCr-3 filler with GTAW process: Solidification mechanism, microstructure, mechanical properties and residual stresses

The objective of the current study was to analyse the microstructure, mechanical characteristics, and residual stresses of a dissimilar welded joint (DWJ) made of P92 steel and the Inconel alloy 617 (IN617) using the gas tungsten arc welding (GTAW) method. The ERNiCr-3 filler was selected to produce the conventional V groove (VG) and narrow V groove (NVG) butt joint. The filler deficient zones in the weldments, such as the filler deficient beach, i.e. unmixed zone (UZ), peninsula, and island, as well as the distinct heat-affected zone (HAZ), were visible near the interface of ERNiCr-3 filler weld and P92 steel due to the distinct differences in the chemical composition, microstructure, and mechanical properties between the filler and P92 base metal (BM). A very narrow partial melted zone (PMZ) and almost negligible UZ and HAZ were noticed at the interface of IN617 and ERNiCr-3 weld metal and it occurred mainly due to the similarity in microstructure and melting point. The austenitic microstructure of ERNiCr-3 filler weld was accompanied by precipitates enriched with Ti and Nb along with the inter-dendritic space. At room temperature, the mechanical properties of both the groove joints were evaluated, and the test results indicated that the welded joint satisfied the standard requirements for AUSC power plants' boiler applications. The tensile test results showed the failure from ERNiCr-3 filler weld with a tensile strength of 627 ± 2 MPa and 636 ± 3 MPa for VG and NVG welded joints, respectively. A poor weld metal impact toughness in comparison to the BMs was attributed to the presence of the brittle Ti(C, N) and Nb(C) particles in the interdendritic space. The impact toughness for the NVG weld joint was measured higher than for the VG weld joint. A significant hardness deviation was measured along the weldments that might be due to heterogeneous microstructure, i.e. UZ, HAZ, delta ferrite, and weld metal. To impart the ductility and temper the martensite in P92 HAZ, post-weld heat treatment (PWHT) was also performed, and a studied their effect on microstructure evolution across the weldments and mechanical properties. Groove design also showed a significant effect on residual stress variation. The work highlights the groove geometry, welding procedure, evolution of the microstructure along the weldments, mechanical characteristics, and residual stress variation of DWJ of P92 steel and IN617 alloy. In comparison to conventional VG joints, the NVG joints exhibited superior mechanical properties and lower residual stress values.

Progressive collapse behaviour of advanced precast reinforced concrete joints with headed bars and plastic hinge relocation

This study proposed three types of precast concrete (PC) wet joints, viz., using Headed bars (Type H) to replace hooked bars, placing an Additional bottom bar layer (Type A), or implementing plastic hinge relocation method with X-bent bars (Type X) in the beam-joint region. These detailing features could compensate for negative effects caused by geometric discontinuity at the joint interface and prevent pull-out failure, as observed in conventional PC joints with hooked bars. An experimental investigation based on four interior joints showed that based on the steel content in Type H joint, by increasing respective steel contents of 7% and 8% in Type A and Type X joints, structural resistance to collapse could be enhanced by 34% and 47%, respectively. A fourth specimen of Type A joint incorporated the slab. It was found that although the slab could slightly enhance flexural resistance, it also reduced the joint rotational capacity. Subsequently, component-based joint models (CBM) with a bond-slip model of headed bars were proposed for the three types of PC joints and validated against the test results with satisfactory accuracy. Based on the validated CBMs, parametric studies were conducted for different cases, such as exterior and penultimate joints, under a penultimate column removal scenario. It was found that if the exterior column was too weak, compressive arch action and catenary action could not be effectively triggered, and column failure governed joint behaviour. Hence, to mitigate progressive collapse, the exterior columns and joints must be required to possess a sufficient level of horizontal resistance and stiffness.

Seismic shear and flexural performance of new RCS joints with W-FDP, W-FBP, and small hoops

New through-beam joint details were developed for New high-strength Reinforced Concrete and Steel beam (New RCS) special moment frames. The columns hadfy = 690 MPa andfc′ = 84 MPa. The new joint details enhanced the joint strength for the large force demand seen in high-rise buildings in regions of high seismicity and minimized the construction difficulty associated with conventional joint transverse reinforcement. The new joint details included Wide Flange Doubler Plates (W-FDPs), Wide Face Bearing Plates (W-FBPs), and small rectilinear hoops. Three large-scale beam-column joint specimens with the proposed design details were tested using lateral cyclic loading to examine their seismic shear and flexural performance. Test results showed that the W-FDPs were effective in preventing joint bearing failure. Using W-FDPs, FBPs, or W-FBPs, and small hoops effectively mobilized the joint shear strength. The 2015 ASCE model modified to consider the proposed details provided a conservative estimation of the joint shear strength of the specimen that failed in joint shear. Moreover, the model was successfully used to design specimens to prevent joint shear failure and to produce desired beam-hinging behavior that met the requirement of AISC 341 for beam-column connections of special moment frames. The beam eccentricity did not significantly affect the hysteretic behavior of the specimen up to the 4% drift ratio.

Joint modeling of action sequences and action time in computer-based interactive tasks.

Process data refers to data recorded in computer-based assessments that reflect the problem-solving processes of participants and provide greater insight into how they solve problems. Action time, namely the amount of time required to complete a state transition, is also included in such data along with actions. In this study, an action-level joint model of action sequences and action time is proposed, in which the sequential response model (SRM) is used as the measurement model for action sequences, and a new log-normal action time model is proposed as the measurement model for action time. The proposed model can be regarded as an extension of the SRM by incorporating action time within the joint-hierarchical modeling framework and as an extension of the conventional item-level joint models in process data analysis. Results of the empirical and simulation studies demonstrated that the model setup was justified, model parameters could be interpreted, parameter estimates were accurate, and taking into account participants' action time further was beneficial for obtaining a deep understanding of participants' behavioral patterns. Overall, the proposed action-level joint model provides an innovative modeling framework for analyzing process data in computer-based assessments from the latent variable modeling perspective.

A comparative study of microstructure and mechanical properties of conventional and synergistic double-sided FSW joints of 6061 zxaluminium alloy

In this study, synergistic double-sided friction stir welding (DS-FSW) is proposed to solve the problems of large deformation and the time-consuming of traditional DS-FSW. The microstructure, mechanical properties, and fracture paths of novel and conventional joints are studied under different welding parameters. Results show that defects in novel joints have been improved. However, the grain size in the stir zone of novel joints is larger than that of conventional joints. The microhardness map of the novel joint shows a more uniform distribution compared to that of the conventional joint. At a rotational speed of 1800 rpm and transverse speed of 1000 mm min−1, the distortion of the novel joint and conventional joint is 0.1 and 1 mm, respectively. The tensile force of novel joints is higher than that of conventional joints for the same welding parameters. The maximum tensile force of novel and conventional joints is 36.8 and 34.9 kN, respectively.

A S-wave Spectral Decomposition Hydrocarbon Detection Method Based on P-wave and S-wave Source and Its Application

S-wave source vector exploration is a promising technology in future seismic exploration. Conventional P-wave and S-wave joint inversion methods for hydrocarbon detection are limited in some aspects. First, P-wave and S-wave joint inversion is mainly based on the converted wave theory, but no theoretical support for S-wave generated by S-wave source. Second, the inversion method is complex and difficult to operate. Because P-wave and S-wave from S-wave source should accurately match with each other, without an effective approach, it has to follow the method of P-wave matching with converted wave, so it is not helpful to extensive application. This paper proposes a comprehensive s-wave spectral decomposition hydrocarbon detection method based on p-wave and s-wave source. First, the velocity ratio of P-wave to S-wave (Vp/Vs ratio) is derived to be equal to the frequency notch period ratio of P-wave to S-wave, and approximately equal to the dominant frequency ratio of P-wave to S-wave. Second, spectral decomposition is conducted at the target layer to obtain the tuning frequency spectra of P-wave and S-wave seismic data, respectively, and the dominant frequencies of P-wave and S-wave are automatically identified. Third, the Vp/Vs ratio and Poisson's ratio are calculated according to the dominant frequency ratio of P-wave to S-wave for final hydrocarbon detection. This method is independent on well data and accurate matching of P-wave with S-wave data, it is simple, quick and efficient. It’s widely applicable in any areas more or less explored. Application in an oilfield in western China has obtained effective results.

Effect of strength of steel sheets on peel tensile strength and failure mode of dissimilar joint of spot welds

Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. Peel tensile strength of spot welds tends to decrease as the steel sheet strength increases. Therefore, in order to further expand the application of AHSS, technology to prevent fracture of spot welds is required. In order to achieve that, it is necessary to understand the characteristics of spot-welded joints and clarify the controlling factors. However, most of the conventional joint strength evaluations have been conducted on the same kind material joints, and there are few systematic studies on the joint strength and fracture mode of dissimilar material joints that are often used in actual vehicles. Therefore, the purpose of this study is to obtain a guideline for grasping the characteristics of dissimilar joints in case of the plug failure. Using various joint shapes, we compared the peel tensile strength and failure position of the same kind material joints and the dissimilar material joints with the TS1500 MPa class hot-stamped steel sheet. As a result, it was found that the deformation behaviour of the test piece affects the joint strength and fracture position of the dissimilar material joints. Specifically, in dissimilar material joints, cross tension joints and double cup-shape tension joints tended to break on the TS1500 MPa class hot-stamped steel side. On the other hand, L-shape tension joints broke on the lower strength material side. From these results, it is considered important to understand their deformation behaviour in order to analyse and predict the fracture phenomenon of spot welds in actual vehicles and automotive parts.

Robust joint transmit and receive beamforming by sequential optimization for bistatic radar system

AbstractThe conventional joint transmit and receive beamforming algorithms maximise the output signal‐to‐interference‐plus‐noise ratio (SINR) by designing the weight coefficients simultaneously at the transmitter and receiver. However, their performance degrades significantly when the model mismatch exists. In this paper, the robust version of the joint transmit and receive beamforming method is considered in the context of the bistatic radar system. In particular, both the transmit array and the receive array suffer model mismatch. The designed beamformer aims to maximise its output SINR subjected to a robustness constraint by simultaneously designing the transmit beamforming vector and the receive beamforming vector. Two types of robustness constraints, namely the worst‐case constraint and the probability constraint, are considered in this paper. The proposed formulations are non‐convex, and the sub‐optimal solutions are obtained by a sequential optimization approach. In addition, a novel method to estimate the interference‐plus‐noise covariance matrices at the transmitter and receiver is proposed, which makes the proposed robust joint beamforming algorithms adapt to the variation of the surrounding environment. Numerical simulations verify the effectiveness of the proposed algorithms.

Mechanical behavior of additively and conventionally manufactured 316L stainless steel plates joined by gas metal arc welding

Combining several additive manufactured (AM) parts to larger parts by welding may be required due the limited building volume of powder bed AM methods. Laser powder bed fusion (LPBF) has a great potential because it enables the production of nearly full-density components through AM processes; however, additional residual stresses and production defects are induced by LPBF. These residual stresses affect the residual stress state of welded AM parts. In combination with the production related defects, both alter the mechanical and—in particular—the fatigue behavior of these welded joints. In this study, various tests are performed to characterize the butt joints of 316L AM steel plates made by gas metal arc welding. To this goal, joints are produced with weld seams parallel and vertical to the layer orientation of AM plates. The results are compared to joints of conventionally rolled steel plates produced with the same welding parameter. The residual stress states in initial (unloaded) condition and after cyclic loading were determined by X-ray diffraction techniques for AM and rolled plates. Complex residual stress states were determined at the welds made of AM steel plates compared to the welds made of rolled steel plates; however, the residual stress level in the heat affected zone of the butt-welded AM steel plates was similar to the welds made of hot-rolled steel plates. After cyclic loading with a high load level, high residual stress relaxations were observed in the parent materials. The fatigue design curve for butt joints from international standards is exceeded by all three test series, but the fatigue strength of the butt joints made by LBPF and hot rolling vary significantly. This is thought to be related to differences between the AM and conventional joints in microstructure, static strength, residual stress level, and small crack-like defects that partially interact with stress concentrations at the weld transition.