Shear Failure Research Articles

Riveting damage behavior and mechanical performance investigation of CFRP/CFRP thin-walled single-lap blind riveted joints

Riveting has a wide range of advantages in improving the performance of composite connections, however, it is highly likely to cause damage to the composite structure. Therefore, an experimental study was conducted to assess the damage behaviors of the carbon fiber reinforced polymer (CFRP)/CFRP blind riveted joint. Mechanical performance of joints was also evaluated experimentally. Furthermore, failure modes were exhaustively discussed. The influences of the rivet shank length on both the riveting damage and the mechanical performance were also investigated. The results demonstrated that: the surface bearing damage occurred on the first ply and was mainly caused by the pressure of forming the riveted head along the rivet shank axial. Serious damage occurred in the upper plies near the riveted head due to the radius expansion of the rivet shank. The damage modes were affected by the angles of the fiber laying direction and the rivet shank. The grooved blind riveting formed a localized protruding area around the periphery of the holes and caused less riveting damage. The failure modes of the tensile specimens were all shear failure, and the failure modes of the pull-off specimens were characterized by laminate fracture around the rivet holes, which subsequently led to rivet pull-off failure. It is worth emphasizing that the pull-off damage load and failure load of grooved blind riveted specimens were higher than those of general blind riveted specimens, while the grooved blind riveting reduced the tensile resistance.

Investigation of scale effects of rock bridges based on Multi-Physical field monitoring

The presence of rock bridges is crucial for ensuring the stability of rock slopes. However, evaluating the mechanical properties of rock bridges solely based on the joint persistence coefficient (K) raises doubts due to potential variations in the scales of rock bridges within a rock mass with a constant K value. In this study, direct shear tests with different scales were carried out on sandstone specimens. Acoustic Emission (AE) and Digital Image Correlation (DIC) techniques were utilized to monitor the damage procession of the specimens. The evolution process of the specimen was divided into stages and three threshold points were determined based on AE parameters. As the scale decreased, the Joint Roughness Coefficient (JRC) increased, the tensile failure increased, and the shear failure decreased. As the normal stress increased, the JRC with the same scale decreased, the tensile failure decreased, and the shear failure increased. The change of fracture mechanism was the primary reason for the strength deterioration with decreasing scales. The decrease of the scale was not conducive to the failure prediction. By improving the rock bridge failure potential (RBP) index, the proposed RBPn index could appropriately characterize scale effects under different normal stresses.

Evaluation of CO2 Leakage Potential through Fault Instability in CO2 Geological Sequestration by Coupled THMC Modelling

A faulted saline aquifer system was simulated in a coupled thermal-hydraulic-mechanical-chemical (THMC) framework to examine the potential breaching of the caprock seal from long-term CO2 sequestration. The pH of the brines steadily dropped from 7.5 to 4.7 due to the continuous injection of scCO2 (supercritical CO2), which was caused by the rapid dissolution of calcite in the reservoir and associated fault zones, alongside alterations in the concentrations of primary and secondary minerals within the formation. The increase in pore pressure with the continuous injection of scCO2 triggered fault reactivation at 6y with the resultant leakage of CO2 along the fault. This builds CO2 saturation inside the fault at 7y to six-fold higher than pre-slip. Continuing shear reactivation and creation of reactive surface area following the initial CO2 leakage accelerates dissolution/precipitation reactions, in turn further increasing porosity and permeability of the reservoir and fault. In particular, the permeability and porosity in the fault zone were increased by only 2% and 6%, respectively – staunched by competitive feedbacks in dissolution countered by precipitation that are individually much larger. Comparison of mineral concentrations adjacent to the fault before-and-after instability revealed that the development of shear failure also promotes the transport of reactivated minerals into the fault zone. Among them, feldspar changes most significantly in later stages, dominated by dissolution with the volume fraction decreasing by 80% and increasing the aqueous concentration of K+ by approximately an order of magnitude. However, secondary minerals counter this dissolution through precipitation with the volume fraction of kaolinite increasing by an order of magnitude compared with the original fraction. Finally, the evolution of the fault sealing coefficient (FS) demonstrates that the porosity and permeability exert a pivotal influence in controlling the self-sealing behavior in the basal of the fault, while the upper fault layer exhibits self-enhancing response. A notable observation is that changes in mineral ion concentrations in fault zones could be applied as a significant diagnostic signal to monitor fault stability and the potential for progress of self-sealing behavior.

Crack evolution mechanism of stratified rock mass under different strength ratios and soft layer thickness: Insights from DEM modeling

Research on stratified rock masses, which are common geological formations, has primarily focused on their mechanical properties, while studies on crack evolution and microscopic damage mechanisms remain limited. This study addresses this gap by investigating the combined effects of strength ratios and soft layer thicknesses on the microcrack evolution mechanism of stratified rocks using the discrete element method (DEM). Through FISH language programming in the particle flow code (PFC), this study reveals the acoustic emission (AE) characteristics, crack initiation and propagation, damage degree, and final failure characteristics. The key findings are: (1) Higher strength ratios between the hard and soft components of stratified rocks make specimens more sensitive to increases in soft layer thickness. (2) Three types of AE events were identified: continuous active, intermittent active, and silent. (3) Cracks initiate at the interface between components and propagate along the interface into the rock matrix. The strength ratios determine the crack propagation path and the damage extent of the components. (4) The failure of stratified rocks is primarily controlled by the soft component. Crack connections typically form vertical and sub-vertical tensile failure planes in the hard component, and a shear failure surface with a “V”-shaped intersection in the soft component.

Damage monitoring on inter-lamination of GFRP via the resistance change of the MWCNT@GF sensor

The paper aimed to investigate the performance of multi-walled carbon nanotube-coated GF (MWCNT@GF) sensors on interlayer shear damage monitoring and sensing capability of glass fiber-reinforced polymers (GFRPs) based on the resistance change under short beam shear (SBS) load. The MWCNT@GF sensor, manufactured by physical vapor deposition (PVD), was embedded into the neutral layer of laminates to form an in-situ sensing network in different directions and positions. “The MWCNT@GF sensor, manufactured by physical vapor deposition (PVD), was embedded into the neutral layer of laminates to form an in-situ sensing network.” “With the help of Keithley 2700 programmable electrometer and the 3D-digital image correlation(3D-DIC), monotonic and cyclic tests were carried out.” The monotonic test found that the off-axis sensor is more sensitive to shear failure than the on-axis sensor because of its lower shear strength. In addition, the qualitative relationship between shear damage and relative resistance was established by selecting crucial moments. In the cyclical test, the relative resistance of off-axis sensors presented a cyclic mode under cyclic load. Furthermore, the relative resistance under the first 20 cyclic loads was similar to that under monotonic loads. “Furthermore, the relative resistance under the first 20 cyclic loads was similar to that under monotonic loads, which shows that the sensor has superior sensing ability. Finally, the quantitative relation between shear damage and relative resistance was established.” “That means MWCNT@GF sensors can be used to reasonably evaluate the damage state and further evaluate the service performance, reliability and remaining life of the structure.”

Influence of steam curing on cyclic triaxial characteristics of recycled aggregate concrete: Experimental analysis and DEM simulation

The engineering application of steam-cured recycled aggregate concrete (often in a cyclic triaxial stress state) can not only improve the recycling efficiency of resources, but also accelerate the construction progress. In this paper, we adopt a combination of laboratory experiments, theoretical analysis and numerical simulation to study the cyclic triaxial characteristics of recycled aggregate concrete (RAC) under different curing regimes (20℃, 40℃, 60℃ and 80℃). The results indicate that as the steam curing temperature increases, the internal damage caused by high temperature continues to intensify, and the cyclic triaxial failure mode of RAC transitions from shear failure to compression failure, and its peak strength, dynamic elastic modulus, and dilatancy angle all show a downward trend. A linear prediction model is established based on the strong correlation between peak strength and steam curing temperature. As the loading cycles increase, the dynamic elastic modulus and dilatancy angle of RAC show exponential and linear downward trends respectively, and the decline rate increases with the increase of steam curing temperature, and the prediction models for dynamic elastic modulus and dilatancy angle are established based on quantitative relationships between variables. On the basis of experimental analysis results, a cyclic triaxial DEM model considering real recycled aggregates is established by introducing steam-cured damage indexes into the mesoscopic parameters, and its applicability in predicting cyclic triaxial mechanical properties of RAC under different curing regimes is verified. The research outcomes can save a lot of test cost and time consumption for developing steam-cured concrete with better performance, and have important theoretical guidance and practical significance for the wide application of steam-cured concrete.

Experimental study on seismic behavior of a novel RC slab- SC wall joint based on UHPC and rebar – steel plate lap splices

Steel plate concrete shear walls (SC walls) have been widely used in practical projects because of great mechanical properties. For the application in nuclear power plant containment, the joint of specially shaped reinforced concrete slab and SC walls is difficult to design and construct. By using ultra-high performance concrete (UHPC), a new type of joint with the non-contact lapping method is proposed in this paper, which has advantages of simple construction, superior performance, suitable cost, and wide application range. Five RC-UHPC slab-shear wall joints were designed and tested under reciprocating load to study the effects of structures of lapping steel plate, shear-resisting methods, and interfacial reinforcing methods on the mechanical properties of the joints. The test results showed that the joints adopting the new structures were damaged for the flexural failure of the concrete area, with no damage to the joint zone, while the other specimens failed in the shear failure of the joint zone. It can be demonstrated that the ribs formed by bars and studs on the lapping steel plates are effective measures for non-contact force transferring, and interfacial reinforcing bars can improve the strength of the interface between concrete and UHPC. The force transferring efficiency of the new joints was close to or more than 90%, which indicates that the proposed joint structures can effectively realize the non-contact lapping force transferring. The design formulas and suggestions are proposed based on the analysis of the mechanism of new structures.

Experimental and Numerical Analyses of Shear Failure Mechanisms of Rock Bolt Surrounded by Bedded Rock

Experimental and Numerical Analyses of Shear Failure Mechanisms of Rock Bolt Surrounded by Bedded Rock

Effect of repeated temperature cycles on thermal expansion coefficient and elastic moduli of high porosity chalks

This paper describes the impact of repeated temperature cycles on elastic mechanical parameters of chalk. The experiments were performed at both hydrostatic and deviatoric stress geometries at an axial stress 70% of stress at failure. Thus, shear failure tests are reported. Geomechanical stability during cooling was evaluated at constant axial stress, while the side stress was reduced to counteract thermal contraction at uniaxial strain conditions. The study was motivated by the fact that chalk reservoirs are exposed to cooling due to intermittent water injection during hydrocarbon extraction and are future prospects for CO2 storage. Detrimental effects on rock-mechanical stiffness and strengths were anticipated because temperature cycles are known to degrade calcite cemented sedimentary rocks and marble. This study documents how temperature cycles influence elasticity and thermal expansion coefficient of two chalks with different degree of calcite cementation. The more indurated and less porous Kansas chalk, and the less indurated and more porous Belgian Mons chalk.Following temperature cycling, elastic bulk modulus measured under hydrostatic conditions decreased for the softer Mons chalk, while no significant effect was found for the stiffer Kansas chalk. For both chalks, Young´s modulus measured under deviatoric stress, showed no effect of temperature cycling. At hydrostatic stresses, the thermal expansion coefficient of the Kansas chalk was found to decrease with increasing number of temperature cycles, while a less clear, but similar trend was seen for the Mons chalk samples. The thermal-elastic coupling coefficient, needed to evaluate effective stresses during cooling, was measured before and after the repeated temperature changes.

Shear behavior of FRP-UHPC composite beams enhanced by FRP shear key: Experimental study and theoretical analysis

To investigate the shear behavior of FRP (fiber reinforced polymers)-UHPC (ultra-high performance concrete) composite beams, four-point bending tests were conducted on seven FRP-UHPC specimens and two FRP-NSC (normal strength concrete) specimens, having different width and depth of concrete flange as well as FRP shear key (FSK) spacing. The slip between FRP profiles and concrete flange was controlled by employing FSK and epoxy resin bonded hybrid connection. The failure pattern, load-deflection/strain curves, and sliding response of composite beams were analyzed to study the influence of concrete type, FSK spacing, width and thickness of concrete slab. The results indicate that FRP-UHPC composite beams exhibited shear failure, while FRP-NSC composite beams experienced bending-shear failure. The composite beams demonstrated shear-lag effect, which became more pronounced with the increasing of the concrete slab width. The use of UHPC, reducing FSK spacing, and increasing the size of cross-section of concrete flange can effectively enhance the shear performance and reduce interface sliding. Formulae were developed to predict the shear capacity and deflection, considering shear deformation. The results predicted by the formulae developed match well with the experimental results.

Provides Efficient Shear Bond Strength and Durability Between Lithium Disilicate Glass-ceramic and Resin Cement: A Potential Alternative to the Conventional Hydrofluoric Acid Protocal

Objectives: This study investigated the effects of two surface treatment protocols on the shear bond strength, bond durability, and failure mode at the interface between lithium disilicate glass-ceramic and resin cement. The protocols compared were a self-etching ceramic primer and the conventional hydrofluoric acid (HF) etching followed by silane. Methods: Fifty lithium disilicate specimens were randomly divided into five surface treatment groups (n=10 each). A control group received no treatment. The remaining 4groups included: 5% HF etch with Monobond Plus thermocycled and non-thermocycled, Monobond Etch & Prime (MEP), thermocycled and non-thermocycled. Microshear bond strength (microSBS) was assessed before and after thermocycling to evaluate bond durability. Failure modes (adhesive, mixed, cohesive in resin/ceramic) were recorded under a stereomicroscope. Results: Both surface treatment protocols exhibited comparable microSBS for both pre- and post-thermocycling results. Moreover, bone durability obtained from the two treatment protocols seemed to be comparable. Most groups displayed adhesive/mixed failures. Notably, the self-etching ceramic primer group showed cohesive failure in half of the specimens initially, persisting in 20% after thermal aging. Conclusions: Compared with the conventional HF protocol, the self-etching ceramic primer protocol provided similar microSBS and bond durability between lithium disilicate glass-ceramic and resin cement. The data suggest a self-etching ceramic primer is a viable option for the conventional HF protocol in bonding to glass-ceramic, minimizing the HF hazard and simplifying the clinical procedure.

Study on the influence of anchor plate parameters on the bearing characteristics of the new large-diameter multi-plate soil anchor and creep property of anchor.

The existing mechanical and grouting anchors mostly use the expansion shell method to form a cavity on the borehole wall, and the cement slurry is poured to form multiple enlarged head plates, but the operation is more difficult and the diameter of the formed plate is smaller. In this paper, a new type of large-diameter multi-plate soil anchor and its reaming cavity forming tool are proposed, which can make the operation easier and form a large-diameter enlarged head plate. In order to study the influence of the diameter of anchor plate, the number of anchor plates and the spacing of anchor plates on the vertical uplift capacity of the large-diameter multi-plate soil anchor, 25 sets of comparative models were established for simulation analysis. The finite difference method of FLAC3D software is used to simulate the model. It is found that when the length of the anchor is 6m and the diameter of the anchor rod body is 150mm, the optimal diameter of the anchor plate of the large diameter multi-plate soil anchor is 590mm, the optimal number of anchor plates is 6, and the optimal anchor plate spacing is 800mm, which means the action range of the anchor plate on the lower soil is about 5 times the diameter of the bolt. When the number of anchor plates is too small or the spacing between anchor plates is too large, the structural advantages of large-diameter multi-plate soil anchor cannot be fully utilized, resulting in a decrease in the ultimate uplift capacity. When the number of anchor plates is too large or the spacing between anchor plates is too small, the stress superposition effect occurs in the soil, and the through shear failure occurs, which leads to the decline of the ultimate uplift capacity. Under the condition that the number of anchor plates and the spacing of anchor plates are fixed, the larger the diameter of the anchor plate is, the larger the ultimate pull-out capacity of the large-diameter multi-plate soil anchor is, the smaller the vertical failure displacement of the anchor head is, but the increase of the uplift capacity is gradually reduced. The creep rate of the new large-diameter multi-plate soil anchor bolt is 0.91mm, and the creep rate of equal-diameter soil anchor bolt is 1.69mm. It is verified that the new large-diameter multi-plate soil anchor can be effectively applied to various projects.

Simplified Gravity Load Collapse Dynamic Analysis of Old-Type Reinforced Concrete Frames

The results of shaking table tests from previous studies on a one-story, two-bay reinforced concrete frame—exhibiting both shear and axial failures—were compared with nonlinear dynamic analyses using simplified models intended to evaluate the collapse potential of older reinforced concrete structures. To replicate the nonlinear behavior of columns, whether shear-critical or primarily flexure-dominant, a one-component beam model was applied. This model features a linear elastic element connected in series to a rigid plastic, linearly hardening spring at each end, representing a concentrated plasticity component. To account for strength degradation through path-dependent plasticity, a negative slope model as degradation was implemented, linking points at both shear and axial failure. The shear failure points were determined through pushover analysis of shear-critical columns using Phaethon software. Although the simplified model provided a reasonable approximation of the overall frame response and lateral strength degradation, especially in terms of drift, its reduced computational demands led to some discrepancies between the calculated and measured shear forces and drifts during certain segments of the time-history response.

Failure mechanisms of coarse-grained sandstone under pure mode I/II loading: insights from energy evolution and acoustic emission

ABSTRACT Tensile and shear failure are the main damage modes of rocks in geotechnical engineering. To investigate the energy evolution and failure characteristics of coarse-grained sandstone during pure mode I/II loading, loading-unloading tests were performed on cracked straight-through Brazilian discs (CSTBD) with different unloading levels (i), and its acoustic emission (AE) signals and microstructure were monitored. The results show that the AE signals of the CSTBD are negligible before the peak load (Mode I), or appear when the axial load exceeds a stress threshold and then increases significantly before the peak load (Mode II), and the Kaiser effect was observed in the second loading stage. The specimens’ input, elastic and dissipative energies varied quadratically with i. The elastic energy is always greater than the dissipative energy (Mode I), whereas the dissipative energy exceeds the elastic energy at i < 0.5 (Mode II). The crack propagation paths start from the crack tip and extend rapidly and straightly (Mode I) or slowly in the form of wing crack (Mode II) to the loading point. The microstructures of the specimens are mainly intergranular fracture (mode I) and transgranular fracture (mode II). The results provide references for studying energy evolution and failure mechanisms of rocks under mixed modes I+II/I+III loading.

Influence of Compressive Strength and Steel-Tube Thickness on Axial Compression Performance of Ultra-High-Performance Concrete-Filled Stainless-Steel Tube Columns Containing Coarse Aggregates

With the increasing use of concrete-filled steel tubular (CFST) structures, exposed steel tubes are highly susceptible to corrosion, posing potential safety hazards. This study innovatively proposes the use of stainless-steel tubes instead of traditional carbon-steel ones and introduces coarse aggregates into ultra-high-performance concrete (UHPC), forming a coarse aggregate-incorporated ultra-high-performance concrete-filled stainless-steel tube (CA-UFSST). The inclusion of coarse aggregates not only compensates for the shortcomings of UHPC but also enhances the overall mechanical performance of the composite structure. Twenty sets of specimens were designed to analyze the influence of four parameters, including the coarse aggregate content, compressive strength, stainless-steel-tube thickness, and stainless-steel type on the axial compression performance of UHPC. The experimental results indicate that the failure mode of UHPC is related to the confinement ratio. As the confinement ratio increases, the failure mode transitions from shear failure to bulging failure. The addition of coarse aggregates enhances the stiffness of the specimens. Furthermore, this paper discusses the applicability of six current codes in predicting the bearing capacity of CA-UFSST and finds that the European code exhibits the best prediction performance. However, as the confinement ratio increases, the prediction accuracy becomes notably insufficient. Therefore, it is necessary to establish a more accurate calculation model for the axial compression bearing capacity.

Bonding strength of short carbon fiber reinforced PA6 composites ultrasonic welding joints

AbstractShort carbon fiber composites have high specific modulus, high specific strength and excellent formability, which are suitable for short‐term and environmentally friendly ultrasonic welding. In this study, ultrasonic welding experiments were conducted on short carbon fiber reinforced PA6 composites using a servo‐driven non‐metallic ultrasonic welder. The weld specimens were analyzed for spot weld morphologies, interfacial bonding strength, failure modes and compressive shear fracture to establish the correlation between weld energy and weld quality. The results indicate that when the welding energy is 450 J, the short carbon fibers are interlaced at the interface, which has a pinning effect, thereby enhancing the joint strength reaching 2990 N, and the welding efficiency reaches 46%. Besides, the compressive shear section is divided into regions. The proportion of heat and area in different compressive shear regions are quantitatively analyzed, and the calculation model of joint strength is proposed. Meanwhile, the correlation between welding energy and its correlation, as well as three different shear failure modes, is obtained. This work is helpful for the optimization of carbon fiber reinforced thermoplastic (CFRTP) ultrasonic welding process parameters and the evaluation of joint strength.Highlights A special fixture for ultrasonic welding was designed to optimize the welding energy process of ultrasonic welding CFRTP, and the properties of ultrasonic welded joints were analyzed. When the welding energy is 450 J, a high shear strength welded joint of 2990 N was successfully prepared. The shear fracture of the welded joint was successfully obtained by designing a special clamp for compression shearing. The welding area was qualitatively divided according to the temperature measurement results of the interface center. In addition, the heat and area ratio of different zones in the compression‐shearing area under different welding energy were quantitatively analyzed, and the calculation model of joint strength was proposed. At the same time, the welding energy and its correlation, as well as three different shear failure modes were obtained. The short fiber distribution characterization and pores effect on the joint's strength were analyzed. The appearance of porosity defects has a significant weakening effect on the welded joint.

Prediction of Strength and Failure Modes in Reinforced Concrete Beam–Column Joints using Ensemble Machine Learning Techniques

The beam-column joint is one of the important structural elements that control the structural behaviour during seismic excitation. Moreover, failure of any of these components may lead to the partial or overall collapse of the entire structure. In view of the safety concern, there is a need to evaluate the response properties, such as failure modes and ultimate shear capacity of the beam-column joints. Conventional methods to evaluate the shear capacity of beam-column joints are usually time-consuming. Therefore, in this study, an attempt has been made to evaluate the joint shear capacity and mode of failure of an exterior beam-column joint using ensembled machine learning (ML) approaches like Decision Tree, Random Forest, AdaBoost, CatBoost, and LightGBM. The present study highlights the potential use of the CatBoost model as a useful tool that can assist in predicting the shear strength and failure mode. The results of the study reveal that this model has performed well in predicting the load-carrying capacity and shear strength with high correlation coefficients of 0.9836 and 0.9978, respectively. Moreover, it has been observed that the prediction model provided by the CatBoost algorithm exhibits the highest accuracy for classification in the failure mode of beam-column joints.

Asymmetric deformation and failure behavior of roadway subjected to different principal stress based on biaxial tests

The magnitude and direction of stress will affect the failure of roadway. The impact of stress magnitude and direction on roadway failure was investigated using a rock failure system equipped with true triaxial loading, acoustic emission (AE), and digital image correlation (DIC) technologies. The system allowed for the simulation of rock sample failures under various three-dimensional stress conditions, while real-time monitoring was conducted using a high-precision microseismic system. By prefabricating rectangular holes at different angles in sandstone specimens, roadways under different stress effects in engineering can be simulated. Biaxial loading tests were then performed on these prefabricated sandstone cube specimens to observe external fracture characteristics and internal fracture information using acoustic emission equipment. The peak strength of samples with holes is approximately 38–56% of that of intact samples. In the early and middle loading stages, the strain on the surface is on the order of 10-3. In the later loading stage, the strain on the surface is on the order of 10-2. The findings indicate that roadway failure primarily involves local particle ejection, fragment spalling, large-scale particle ejection, plate crack buckling, and eventual failure. The ultimate failure mode varies based on stress deflection angles: with no included angle, the roadway exhibits a ’V’ shaped failure zone on both sides, predominantly experiencing tensile failure. At included angles of 30°, 45°, and 60° between stress and roadway axis, the roadway displays a “—” failure pattern along the diagonal, characterized by a combination of tension and shear failure. The extension angle of the“—” failure zone varies depending on the stress deflection angle. At a 90° included angle, the roadway shows a ’V’ shaped failure in the roof and floor, primarily undergoing tensile failure. Real-time monitoring of the strain field evolution around the roadway during failure using DIC method revealed valuable insights. AE events at different deflection angles reflect the progression of micro cracks in the specimen, showing a strong correlation with macro failure. The research outcomes elucidate the mechanisms behind various forms of roadway failure induced by stress deflection and shed light on the failure mechanism at different stress deflection angles.

Effects of openings on postbuckling behavior of large‐size composite C‐beam under bending‐shear coupling load

AbstractProper design and accurate mechanical assessment of composite C‐beam after opening are of great importance in structure engineering. This paper aims to experimentally and analytically investigate the postbuckling response of large‐size C‐beam with web opening under bending‐shear coupling load. New specimen with four different open shapes were designed and tested. Strain gauges and displacement measurements were applied to monitor its buckling behavior, strain field distribution and critical failure load. Four specimens with various openings were loaded until catastrophic failure occurred. Additionally, an analytical model was introduced to predict the residual strength of circular opening. The results indicate that while the presence of an opening significantly decreases the load carrying capacity, it has minimal effect on the bending stiffness. Compared with intact specimen, the initial delamination, buckling and ultimate strength of the circular opening decreases less than those of the rectangular opening. By altering the position of the rectangular opening, improvements can be made in terms of initial delamination resistance and buckling load; however, ultimate strength remains largely unaffected. Reinforcing the edge of an opening further reduces resistance to initial delamination but other two indicators are improved. Overall, from buckling to failure stages, post‐buckling bearing capacity after opening decreases by 40%. Moreover, the shear failure mode is observed during catastrophic failures. And the analysis method employed is relatively conservative.Highlights Ten large size composite C beams are conducted under coupling loads. Deformation, strain distribution and failure mode are presented. Influence of openings on postbuckling behavior of beam is analyzed. An analysis method is employed to predict the residual strength of beam. It could provide valuable insights for assisting in designing beam openings.

Flexural behavior of UHPC wet joints for precast bridge deck panels

Over the past decade or so, ultra-high performance concrete (UHPC) has been increasingly used for wet joints of bridge deck panels (BDPs) in bridge superstructures. To evaluate the flexural performance of UHPC wet joints for precast bridge deck panels, a total of seven BDPs were designed, including one monolithic cast-in-place bridge deck panel (MCIPBDP), one precast bridge deck panel (PBDP) with NC wet joints, and five precast bridge deck panels (PBDPs) with UHPC wet joints. The design parameters included reinforcement types (straight bars and U-bars), U-bar lap details (contact lap splice and non-contact lap splice), filling materials (UHPC and NC), and joint widths (150 mm, 200 mm, 250 mm, and 500 mm). Three-point bending tests were performed to evaluate the flexural performance based on the failure mode, load-deflection curve, cracking width in the wet joint region, and stiffness degradation. The experimental results showed that it is feasible to replace 500-mm-width NC wet joints with 200-mm-width UHPC wet joints for PBDPs with U-bars. UHPC wet joints, with a width of 250 mm, effectively prevented straight bars from slipping. As the width of UHPC wet joints decreased, the failure mode shifted from shear failure to bending failure. In addition, the cohesion-friction hybrid model was proposed to simulate the behavior of joint interfaces. The FE analysis results demonstrated that the FE model and modeling method have high accuracy and general applicability. Finally, the flexural capacity calculation formula was developed according to the strut-and-tie model. The theoretical calculation results were in good agreement with test results.