Joint Shear Stress Research Articles

Nonlinear data-driven zero-thickness joint element for concrete dam shear keys

Shear keys have been designed into the contraction joints of many concrete gravity dams to provide interlocking and shear transfer between adjacent monoliths. Their shear transferring capacity is usually estimated as the friction and cohesion that can be mobilized across a 2D plane located at the base of the keys. Once the shear stress in the contraction joint exceeds its estimated shear capacity, the shear keys are typically considered failed, and the joint may subsequently only transfer shear through concrete-concrete friction. This behaviour is often simulated in practice by placing tiebreak contact formulations along contraction joints. However, the nonlinear response and potential residual strength of the keys are usually ignored. In this paper, a novel nonlinear zero-thickness joint element named Macro Shear Key Joint Element (MSKJE) is proposed to simulate the response of a detailed shear key while capturing its nonlinear behaviour. A detailed geometrical numerical model of shear keys using a concrete Continuous Surface Cap Model (CSCM) is first validated against experimental data. Then, a parametric analysis of the number of keys in the joint, confinement pressure, initial opening and lateral boundary condition is performed using the validated detailed shear key numerical models. The stress-displacement responses obtained from the parametric analysis are used to calibrate the proposed MSKJE. At the local shear key scale, the MSKJE models present a very similar stress-displacement response compared to the detailed geometrical key models in terms of stiffness, maximum shear capacity, residual strength and nonlinear softening. At the global dam scale, the MSKJE presents a somewhat similar behaviour to the conventional tiebreak formulations. However, the advantages of the MSKJE over the tiebreak contact include its capability to simulate the nonlinear softening of shear keys, and residual sliding displacement, and, once calibrated, it is not necessary to estimate the shear keys capacity a priori.

Finite element analysis to predict the cyclic performance of GFRP-RC exterior joints with diagonal bars

This paper presents a finite element modeling (FEM) approach to predict the cyclic response of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) exterior beam-column joints with different joint details. Four GFRP-RC exterior beam-column joints detailed with U or L-shaped anchorages at the end of the longitudinal bars of the beam, horizontal stirrups and additional diagonal bars (Z or U-shaped) at the joint region were modeled and analyzed under reversed cyclic loading. The FEM cyclic behavior in terms of load-drift ratio, cracking patterns, joint shear stress and strain evolutions were compared with the experimental behaviors. The FEM predicted load-drift ratio response, cracking patterns and dissipated energy showed good correlations with the experimental results. A parametric study was conducted to evaluate the influence of compressive strength of concrete, column axial load ratio and size of the additional diagonal bar on the performance of the GFRP-RC joints. It was found that an increase in the column axial load significantly degraded the performance in terms of strength, maximum joint shear stress and ductility of the GFRP-RC joints. Also, GFRP-RC joints with additional U-bars were able to resist higher joint shear stress and drift ratio than GFRP-RC joints with additional Z-bars, respectively.

Numerical study on shear strength of GFRP-RC T-Joints

This paper presents the numerical modeling and behavior of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) exterior beam-column joints (T-joints) under cyclic loading. The numerical modeling was implemented on four tested RC T-joints (two steel-RC and two GFRP-RC) in the finite element software ATENA. The numerical model was verified against the results of previous experimental studies. The validated numerical model was used to investigate the effects of the flexural reinforcement ratio of the beam, the compressive strength of concrete, axial load on the column, joint aspect ratio, joint confined area by lateral beams, and joint configurations on the shear strength and load–displacement envelope curves of the GFRP-RC T-joints. The numerical study results indicated that increasing the flexural reinforcement ratio of the beam by up to 1.77% increased the strength and stiffness of the GFRP-RC T-joints. The GFRP-RC T-joints were able to resist joint shear stress by up to 0.85fc′, and higher joint aspect ratios led to premature failure of the GFRP-RC T-joints. The GFRP-RC T-joint with 54% joint confined area by lateral beam attained 33% higher strength than the unconfined (no lateral beam) GFRP-RC T-joint.

Influence of Welding Parameters of Resistance Spot Welding on Joining Aluminum with Copper

The resistance spot welding (RSW) method was used to join aluminum alloy AA 1050 and copper alloy UNS C50100 sheets. Mechanical properties of the joints were examined. The influence of welding process parameters on tensile shear force of the joints was discussed. The design of experiments (DOE) method was used to analyze the influence of welding parameters on the mechanical properties of the joints. Three RSW parameters were used: welding current, squeeze time, and welding time. The results showed that the joint shear stress increased with increasing the welding current until a value of 12000 Amp. Then the shear stress decreased. The tensile shear stress increased with increasing the welding and squeeze time. As a consequence, it can be possible to weld copper with aluminum by RSW.

Seismic vulnerability of reinforced concrete knee joints under reversed cyclic loading

Reinforced concrete beam–column knee joints are generally located at the roof level of moment-resisting frame structures. Knee joints undergo significantly different closing and opening actions under seismic excitations. The complex and vulnerable behaviour of knee joints makes them considerably different from conventional exterior and interior joints. To understand this complexity, three full-scale knee joint specimens were subjected to varying closing and opening joint shear stresses produced from the variation of relative closing and opening moment capacities. Peak opening-to-closing joint shear stress ratios of 0·5, 0·6 and 0·8 were achieved for the three specimens. In addition, the effect of anchorage of longitudinal and joint transverse reinforcement was studied in terms of the enhancement of peak joint closing and opening shear stresses. This paper presents a detailed discussion on the effect of closing and opening actions on the overall joint performance of knee joints subjected to reversed cyclic loading.

Study on effect of dynamic load on rail joint bar by finite element method (FEM)

ABSTRACT The effects of vertical dynamic wheel loading and bolt conditions on rail-end joint bar by using the finite element method (FEM) in terms of vertical displacement, principal and shear stress are investigated. Preliminary results of dynamic load show that variation of either tight/loose-bolted joint bar has the response of rail-end joint varies, the joint bar vertical displacement, principal and shear stresses on the joint bar also vary. The test results show that contact force at the wheel-rail joint bar interface would not change monotonically with the variable train speed and the shear stresses calculated at joint bar significantly lower than the principal stress and stresses of the joint bar for a given speed. The tightly bolted joint bar is strongly recommended because of its high stiffness causing smaller deflection and smaller principal and shear stress on the joint bar can reduce initiation of failure around the joint.

Seismic performance of exterior reinforced concrete beam-column joint with corroded reinforcement

Corrosive environment adversely affects the durability of existing reinforced concrete (RC) structures as well as its performance under seismic loading. In this paper, the seismic behaviour of corroded reinforced concrete (RC) exterior joint was experimentally evaluated. Eight similar RC exterior joints with various corrosion level of reinforcements were tested under two levels of representative column axial force ratio. Lateral loading resisting, ductility, energy dissipation and stiffness of corroded specimens were examined and compared with uncorroded control specimens. Joint shear stress and the development length of beam longitudinal reinforcement were investigated and compared with available design code. In addition, the joint internal force flow of corroded joint was investigated analytically based on modified strut-and-tie model (STM). Experimental results indicate that corrosion of reinforcements have significant adverse effect on the strength and lateral drift capacity of the joints as well as other mechanical properties. Based on the STM model and parametric study, it is further found that the effect of corrosion level on joint stress level is more significant at higher axial force ratio. In addition, an axial force ratio above 0.2 is detrimental to the joint.

Effect of NOCOLOK® flux dry-off temperature on mechanical properties of brazed joint for automotive aluminum-based heat exchangers

The drying temperature of the flux at a normal atmosphere has a crucial role in brazing quality in automotive aluminum-based heat exchangers. Throughout this research, NOCOLOK® flux consists of two phases of K2AlF5.H2O and KAlF4 with a melting point around 580 °C was used. A flux slurry was applied on the base metal and dried at 220, 300 and 380 °C in air. The mechanical assessment revealed that when flux dried at 300 °C, the joint withstand maximum shear stress of 44 MPa with complete bonding. At 220 °C and 380 °C, joint shear stresses are 34 MPa, 30 MPa respectively. 380 °C dry-off temperature under nitrogen gas improved shear strength to 39 MPa. Taking dry-off temperature as 300 °C the number of defective heat exchangers was reduced from 3.2% to 0.6% every week.

Thermomechanical Analysis of Conformally Coated QFNs for High-Reliability Applications

The use of quad flat no-leads (QFNs) in high-reliability applications is receiving increased interest. To address concerns of harsh working environments, conformal coatings are used to protect the components and associated printed circuit board (PCB). However, using conformal coatings can pose a reliability risk for the components on the PCB. This paper details an investigation into the effect of conformal coatings on the reliability of QFN second-level solder interconnections. Five QFN package types and two types of conformal coatings were investigated. In the experiments, a large population of QFN assemblies coated with conformal coatings were subjected to a thermal cycling test condition. These components, designed with daisy-chain connections, were monitored during the thermal cycling tests, and the exact time for failure to occur for each component was recorded and analyzed. Detailed finite-element models for the tested QFN assemblies were developed; the inelastic strain energy density was used as the damage indicator to evaluate the impact of conformal coating on the solder joint reliability. Modeling results reveal that the conformal coating plays an intricate role in QFN solder joint reliability. The presence of conformal coating results in a reduction in the shear stress in the solder joint and plays a positive role in solder reliability. However, it also induces more stress in the solder joint in the out-of-plane direction and plays a negative role. These two mechanisms are competing, and their relative magnitude will determine the overall effect of conformal coating on solder joint reliability.

Relationship between shoulder forces, shoulder joint shear stress, and throwing velocity during baseball pitching

It is well accepted that the anterior shoulder joint force generated in baseball pitching is a risk factor for throwing-related injuries. However, the exact mechanism that causes shoulder joint force is still unclear. This study aimed to clarify the mechanism underlying generation of shoulder shear stress, and gain knowledge about proper throwing mechanics that can minimise joint stress and maximise performance. To this end, the throwing motions of 16 male collegiate baseball pitchers were measured using a three-dimensional motion capture system. Subsequently, induced-joint force analysis and induced-segmental velocity analysis, developed in this study, were used to decompose the shoulder joint force and fingertip velocity of the throwing upper extremity into causal muscular and interactive torque components. Induced-joint force analysis showed that the muscular torque–induced component to the maximum anterior shoulder joint force accounts for more than 100%, and the shoulder horizontal adduction torque is the greatest contributor among all joints. Induced-segmental velocity analysis found that the centrifugal force effect was the largest contributor, at 42.3% of the maximum fingertip velocity. The current findings imply that effectively exploiting centrifugal force for throwing arm acceleration is the key factor for achieving proper throwing that maximises ball speed and minimises shoulder joint load.

Effect of joint shear stress on seismic behaviour of interior GFRP-RC beam-column joints

Four full-scale specimens were constructed and tested under reversal cyclic loading to study the seismic performance of interior GFRP-RC beam-column joints. The main test parameters were joint shear stress ratio and type of reinforcement (steel or GFRP). The performance of the specimens was evaluated in terms of hysteresis diagrams, mode of failure, strains in the reinforcement and energy dissipations. Test results indicated that the linear nature of GFRP materials resulted in lower residual damage in GFRP-RC beam-column joints compared to the corresponding steel-RC counterparts. Moreover, GFRP-RC joints withstood multiple cyclic loadings up to 8% drift ratio without exhibiting brittle failure.

Strengthening of seismically deficient exterior beam-column connections using embedded steel bars

Several techniques for improving performance of reinforced concrete (RC) beam-column (BC) connections have been developed in last two decades, but these techniques have been criticized for being labourintensive and susceptible to premature de-bonding. To overcome these shortcomings, a novel technique utilising embedded steel bars has been developed in this study for strengthening seismically deficient RC BC connections. This technique involves drilling holes within the joint core. After the drilled holes are cleaned, they are partially filled with epoxy. Finally, steel bars are inserted in the epoxy-filled holes. Two exterior BC connections were constructed and loaded under displacement-controlled cyclic loading. The first specimen was a control specimen designed in accordance with the pre-1970s building codes to represent BC connections requiring strengthening. The second specimen was strengthened with eight 8 mm steel bars embedded within the concrete core in the joint area and epoxied to maintain the bond between the concrete and the steel bars. The strengthened specimen had superior performance compared to that of the control specimen in terms of joint shear stress, normalised principal tensile stress demand and stiffness degradation. The results show that shear stress of the joint was enhanced by about 8% whereas the enhancement in the principal tensile stress demand was 24% compared to that of the control specimen. The results showed that the proposed technique is capable in upgrading the seismic performance of seismically deficient RC BC connections.

Seismic Upgrading of Exterior Reinforced Concrete Frame with Small Column and Joint Area Using Externally Attached Steel Column

Abstract This paper presents cyclic load test of five exterior reinforced concrete frames. All the specimens represent a substandard single-span, low-rise reinforced concrete frame building which behaves a weak column-strong beam mechanism under a strong seismic loading. The first three exterior frames M1, M2 and M3 were designed for the joint shear critical to investigate the effect of joint reinforcement. They are similar except the joint reinforcement detailing. The fourth specimen M4 was an exterior frame with a very small column member. The fifth specimen U5 was the seismic upgrade of M4 specimen using externally attached steel column. From the first three tests, the increase in shear capacity due to the reinforcement provided in the beam-column joint was negligible when the column size was small leading to high joint shear stress. The shear capacity of the specimens was agreed well with the calculation formula provided by ACI318 (ACI, 2008) ignoring the contribution from the reinforcement. The upgraded frame markedly indicated the increased capacity of 2.02 times of the strength of M4 specimen. However, the ductility of the upgraded frame was decreased. It was the result from that the failure mode of the specimen was shifted from the joint failure to the column damage at the section next to the end of the attached steel column.

Seismic Behavior of Exterior GFRP-RC Beam–Column Connections: Analytical Study

Four full-scale specimens were constructed and tested under reversal cyclic loading to study the seismic behavior of exterior glass fiber-reinforced polymer (GFRP)-reinforced concrete (RC) beam-column joints with lateral beams. The test variables were joint shear stress (0.85, 1.0, and 1.1 times the square root of the concrete compressive strength) and type of reinforcement (steel or GFRP). Test results indicated that well-designed exterior GFRP-RC beam-column joints confined with lateral beams exhibit linear behavior with minimum residual damage up to 5% drift ratio. A specialized software was used to construct a finite elements model, capable of simulating hysteresis behavior of reinforced concrete beam-column joints under seismic loading by taking into account the nonlinear behavior of concrete, confinement provided by the internal reinforcement, and the effect of cracks and bond-slip relationship between reinforcing bars and surrounding concrete. The model was used to investigate the effect of joint shear stress, size of lateral beams, reinforcement material, column axial load, and geometrical configuration on the joints’ behavior.

Nonlinear shear behavior of rock joints using a linearized implementation of the Barton–Bandis model

Experiments on rock joint behaviors have shown that joint surface roughness is mobilized under shearing, inducing dilation and resulting in nonlinear joint shear strength and shear stress vs. shear displacement behaviors. The Barton–Bandis (BB) joint model provides the most realistic prediction for the nonlinear shear behavior of rock joints. The BB model accounts for asperity roughness and strength through the joint roughness coefficient (JRC) and joint wall compressive strength (JCS) parameters. Nevertheless, many computer codes for rock engineering analysis still use the constant shear strength parameters from the linear Mohr–Coulomb (M−C) model, which is only appropriate for smooth and non-dilatant joints. This limitation prevents fractured rock models from capturing the nonlinearity of joint shear behavior. To bridge the BB and the M−C models, this paper aims to provide a linearized implementation of the BB model using a tangential technique to obtain the equivalent M−C parameters that can satisfy the nonlinear shear behavior of rock joints. These equivalent parameters, namely the equivalent peak cohesion, friction angle, and dilation angle, are then converted into their mobilized forms to account for the mobilization and degradation of JRC under shearing. The conversion is done by expressing JRC in the equivalent peak parameters as functions of joint shear displacement using proposed hyperbolic and logarithmic functions at the pre- and post-peak regions of shear displacement, respectively. Likewise, the pre- and post-peak joint shear stiffnesses are derived so that a complete shear stress-shear displacement relationship can be established. Verifications of the linearized implementation of the BB model show that the shear stress-shear displacement curves, the dilation behavior, and the shear strength envelopes of rock joints are consistent with available experimental and numerical results.

Exterior RC wide beam-column connections: Effect of beam width ratio on seismic behaviour

Abstract Design recommendations stipulated in international standards for seismic design of reinforced concrete (RC) wide beam-column connections are based on limited experimental studies. To supplement the existing information, an experimental study was conducted that focused on the effect of beam width to column width ratio (or beam width ratio) on the seismic behaviour of exterior beam-column connections. Four specimens were designed, constructed and tested under reversed cyclic loading conditions. The primary test variables were the beam width ratio and the joint shear stress ratio ( γ d ). The specimens were designed in conformance with ACI 318-14 and ACI 352R-02. They had beam width ratios of 1, 1.5, 2 and 2.5 and γ d , of 0.74, 1.12, 1.63, and 2.03. According to ACI 352R-02, the γ d value should be lower than γ n = 1.25 for joints confined on three faces. The results indicated that specimens with beam width ratios of 1 and 1.5 and γ d of 0.74 and 1.12 were capable of supporting the complete formation of beam plastic hinges with no major cracks in the joint region. In contrast, specimens with beam width ratios of 2 and 2.5 and γ d of 1.63 and 2.03 exhibited significant damage at the joint core. Torsional failure of the spandrel beam was also observed in specimen with beam width ratio of 2.5.

Modelling exterior unreinforced beam‐column joints in seismic analysis of non‐ductile RC frames

SummaryThe seismic response of non‐ductile reinforced concrete (RC) buildings can be affected by the behaviour of beam‐column joints involved in the failure mechanism, especially in typical existing buildings. Conventional modelling approaches consider only beam and column flexibility, although joints can provide a significant contribution also to the overall frame deformability. In this study, the attention is focused on exterior joints without transverse reinforcement, and a possible approach to their modelling in nonlinear seismic analysis of RC frames is proposed. First, experimental tests performed by the authors are briefly presented, and their results are discussed. Second, these tests, together with other tests with similar features from literature, are employed to calibrate the joint panel deformability contribution in order to reproduce numerically the experimental joint shear stress–strain behaviour under cyclic loading. After a validation phase of this proposal, a numerical investigation of the influence of joints on the seismic behaviour of a case study RC frame – designed for gravity loads only – is performed. The preliminary failure mode classification of the joints within the analysed frame is carried out. Structural models that (i) explicitly include nonlinear behaviour of beam‐column joints exhibiting shear or anchorage failure or (ii) model joints as elements with infinite strength and stiffness are built and their seismic performance are assessed and compared. A probabilistic assessment based on nonlinear dynamic simulations is performed by means of a scaling approach to evaluate the seismic response at different damage states accounting for uncertainties in ground‐motion records. Copyright © 2016 John Wiley & Sons, Ltd.

Seismic Performance of GFRP-RC Exterior Beam–Column Joints with Lateral Beams

Six full-scale specimens were constructed and tested under reversal cyclic loading to study the seismic behavior of exterior glass-fiber-reinforced-polymer (GFRP) reinforced concrete (RC) beam–column joints with lateral beams. Five specimens were completely reinforced with GFRP bars and stirrups and one was reinforced with conventional steel as a control specimen. The main test variables were reinforcing materials (GFRP and steel), presence of lateral beams, different joint shear stresses, and end anchorage of beam longitudinal bars (bent and headed-end bars). The specimens were subjected to increasing seismic drifts up to failure. Test results showed that GFRP-RC exterior beam–column joints confined with lateral beams can resist joint shear stress equal to 1.1 times the square root of the concrete compressive strength up to 6% drift ratio. In some cases, the specimens showed nonlinear behavior and nonbrittle failure, contrary to what it is expected from FRP-RC structures. Moreover, the anchorage method can change the mode of failure of GFRP-RC exterior beam–column joints.

Interaction of internal forces of interior beam-column joints of reinforced concrete frames under seismic action

This paper presents detailed analysis of the internal forces of interior beam-column joints of reinforced concrete (RC) frames under seismic action, identifies critical joint sections, proposes consistent definitions of average joint shear stress and average joint shear strain, derives formulas for calculating average joint shear and joint torque, and reports simplified analysis of the effects of joint shear and torque on the flexural strengths of critical joint sections. Numerical results of internal joint forces and flexural strengths of critical joint sections are presented for a pair of concentric and eccentric interior connections extracted from a seismically designed RC frame. The results indicate that effects of joint shear and torque may reduce the column-to-beam flexural strength ratios to below unity and lead to "joint-yielding mechanism" for seismically designed interior connections. The information presented in this paper aims to provide some new insight into the seismic behavior of interior beam-column joints and form a preliminary basis for analyzing the complicated interaction of internal joint forces.

Finite Element Analysis of Mono- and Bi-Adhesively Bonded Functionally Graded Adherend

The stress concentration at the end of bonded lap joints is a major concern in the design and application of adhesive joints, and, therefore, many research works have been carried out to reduce the stress level in the bond line. Most of the proposed methods focus on changing adhesive geometries or properties to achieve an optimized model. In this paper, the stress and strain distribution for adherend with functionally graded properties was analyzed to investigate the effect of the adherend material properties and the type of joint on the stress distribution within bond line. The effect of ceramic volume fraction of the functionally graded materials (FGMs) on the stress concentration has been studied. Also, bi-adhesive joint is used as an alternative stress reduction technique for the joint. Results show that using bi-adhesively joint technique together with high-ceramic volume fraction FGMs can significantly reduce the shear and peel stress in the lap joint.