Load-bearing Mechanism Research Articles

Analysis on failure mechanism of CFRP double-tap interference-fit joint

Composite interference-fit joints have attracted much attention because they can effectively reduce the stress concentration around the holes during loading. In this paper, the load-bearing mechanism and strength of a typical double-lap structure under static load are studied through experiment and finite element method. In order to eliminate the influence of bending moment and other factors, a special fixture was designed to study the damage failure mechanism of CFRP interference fit joint under pure tension. The finite element model of CFRP interference fit double lap structure considering both intralaminar and interlaminar damages was established with ABAQUS user subroutine and cohesive element. The damage propagation mechanism during loading process is revealed and the ultimate bearing strength is predicted by comparing the results of experiment and finite element model.

Modelling Triaxial Tests on Fibre-Reinforced Sands with Different Fibre Orientations Using the Discrete Element Method

Fibre-reinforced soil has been widely applied as a composite fill material in geotechnical engineering. In this study, triaxial tests of fibre-reinforced specimens with different fibre orientations were performed employing the discrete element method. The approach enables an investigation of some significant micromechanical properties, including the contact orientation distribution, coordination number, particle displacement field, and contact sliding fraction. From the discrete element method (DEM) perspective, fibre orientation affects the contact force distributions and the load-bearing mechanism for this mixture system. More horizontal fibre particles participate in supporting the strong force chains compared with the vertical and random fibres. Fibre orientation also affects the pattern of displacement fields, which shows that horizontal fibres can limit the formation of localised shear bands. Horizontal fibres also cause the largest increase in the normal contact force acting on the fibre-sand interface and the coordination number of the sand-fibre contact type, which leads to an increase of sliding friction between fibres and the sand matrix. The majority of horizontal fibres could also produce tension during triaxial compression, leading to a more effective reinforcement. The results from this study could contribute to improving our knowledge of mechanical behaviours of sand-fibre composites.

An analytical model on compressive arch action capacity of 3D beam-column sub-assemblages under failure of one or two adjacent interior columns

Compressive arch action (CAA) is a desired load-bearing mechanism to mitigate the progressive collapse risk of commonly designed reinforced concrete (RC) frames. Thus, there have been number of studies concentrated on the behavior of in-plane beam-column sub-assemblages under a single column removal scenario. However, the effect of possible multicolumn loss scenarios due to severe vehicular impact or terrorist attacks has been neglected in the previous CAA calculation models. This paper develops analytical models to estimate CAA capacity of 3D beam-column sub-assemblages under failure of one or two adjacent interior columns. Due to shortage of relevant data, the proposed formulas are validated through comparisons with the numerical results of a full-scale sub-assemblage. Evaluating the response of sub-assemblages extracted from sample buildings with various frame span lengths, it is shown that the failure of two adjacent interior columns along shorter spans of the floor is more likely to reduce CAA capacity than loss along longer spans. The contributions of the bridging beams over removed columns to arch action capacity are also compared.

Investigation on variables affecting bond strength between FRP reinforcing bar and concrete by modified hinged beam tests

The bond strength between FRP reinforcement and concrete significantly affects the load bearing capacity and deformation ability of an FRP reinforced concrete member subjected to bending. There are numerous parameters affecting this bond. In the past, however, studies of FRP rebar-concrete bond strength have considered only one or more of the basalt, glass and carbon FRP reinforcement types, and generally only one or a limited number of surface properties. Since all variables affecting this bond were not set forth, experiments were not conducted on the basis of keeping other test variables constant to examine the effect of a single parameter. In this study, in order to conduct a proper experimental study on concrete-FRP bond by isolating a single parameter in the related tests, 90 hinged beam tests were carried out under transverse loading. The effects of reinforcement fiber type (basalt, glass, carbon), reinforcement surface property (ribbed, wrapped, wounded, sand coated), distance between rebars, bottom and side concrete cover, reinforcement diameter, reinforcement embedment length, presence of stirrups, concrete compressive strength on FRP -concrete bond strength were investigated. Experiments conducted within the scope of this study showed that the effects of concrete compressive strength and concrete cover (bottom and side) on this bond are limited. Moreover, the bond strength values of rebars with mechanical interlocking load-bearing mechanism were found to be higher than the respective values of the ones with friction mechanism. Finally, an increase in the modulus of elasticity of FRP resulted in an increase in bond strength and the presence of stirrups in the beams reduced the bond strength.

Flexural behavior of precast UHPC beam with prestressed bolted hybrid joint

Ultra-high performance concrete (UHPC) is suitable for precast and assembled bridges due to its unique characteristics. Therefore, an efficient, safe, and durable joint connection that fits between the precast UHPC beam segments is of crucial importance. In existing conventional prestressed joints, a potential safety hazard exists because steel strands corrode under long-term detrimental environmental conditions. To address this issue, a prestressed bolted hybrid joint was proposed in this study. Eight precast UHPC beams with different types of joints were constructed. Experimental tests were conducted to examine the flexural behavior and load-bearing mechanism of the prestressed bolted hybrid joint, prestressed joint, and bolted joint. The flexural capacity, characteristic loading values, deformation characteristics, and the failure modes of the three types of joints were investigated and the influences of the bolts and epoxy resin adhesive on the flexural capacity of the joints were also discussed. The test results showed that the failure of the hybrid joint was characterized by the local crushing of the UHPC at the top compression zone together with shearing off of some of the bolts. The flexural capacity of the hybrid joint was significantly improved and was 46.8–60.3% higher than that of the conventional prestressed joint. The overall flexural capacity of the hybrid joint can be divided into two parts, the contributions of the prestressed UHPC joint and bolted connection. The epoxy resin adhesive had little effect on the slip resistance of the bolted joint; however, its bonding effect increased the cracking moment and flexural capacity of the joint by 16.5–29% and 11.5–21.8%, respectively. Besides, due to the strengthening effect of the bolted steel plates and the prestressing, the overall stiffness of the UHPC beam with the hybrid joint was significantly higher than that of the prestressed joint and the bolted joint after joint opening. Based on the test results, a computational method was proposed for calculating the slip moment, joint-opening moment, and ultimate flexural capacity of the prestressed bolted hybrid joint and the prestressed joint, and the feasibility of the hybrid joint was verified.

Preparation of chemically etched surface texture and its friction characteristics in sheet forming

The surface texture of die can reduce friction, and the reasonable texture type can also form oil film on the die surface to save the use of lubricant. In this paper, a method of preparing surface texture on the die by chemical etching is proposed. This paper mainly studies the law of preparation of surface texture by chemical etching and the effect of chemically etched surface texture on die friction. In the experiments, the surface of samples of Cr12 were treated by chemical etching to obtain several groups of surface texture, and the morphology of the chemically etched surface was observed by laser confocal microscope to obtain the characteristics of the surface. Then, four gradients of surface texture with different etching time are selected according to the three-dimensional parameters to obtain the frictional property of samples with chemically etched surface texture using the home-made friction testing machine. Finally, the mechanical rheological model is used to analyze the lubrication state and load-bearing mechanism to prove the results. The results show that the chemically etched surface texture was composed of asperities and pits. The characteristics of surface texture with different etching time show a certain pattern, and the surface of the die had certain hydrophilicity. In addition, the chemically etched surface texture can effectively reduce the friction coefficient between the die and the plate under high load condition (nominal pressure ≥ 32MPa), with an average reduction of 35.6%, a maximum reduction of 49.5% (nominal pressure = 72 MPa, arithmetical mean height of the scale limited surface Sn=1.3.And the analysis results show that the friction coefficient is mainly determined by the area ratio of closed oil pit which was obtained using the image processing technology of MATLAB to verification experiment results. The calculation data and the experiment results are consistent which proves the conclusion.

Structural Evaluation of Torsional Rigidity of New FRP–Aluminum Space Truss Bridge with Rigid Transverse Braces

A unique fiber-reinforced polymer (FRP)–aluminum spatial truss structure with upper I-type, transverse beam braces was developed for deployable bridging, yielding the operational advantages of bestraddled erection bridges. Experimental testing and numerical simulation were performed to evaluate the torsional rigidity of a fabricated cantilever, full-scale experimental structure. The predictions obtained based on a computational finite element model were strongly consistent with the experimental results. Moreover, a numerical decomposition and reconstruction procedure was employed to understand the load-bearing mechanism of the structure. The results demonstrated that the improved transverse braces possessed adequate capacity for providing sufficient rigidity and lateral stability to the complete twin-treadway structure under torsion. The torsional center of the improved structure was located at the axis of symmetry of the twin-treadway bridge deck. The representative torsional rigidity of the twin-treadway module was approximately 87.5 kN·m2/degree. Compared to the original construction, the improved structure exhibited only minor discrepancies regarding the torsional rigidity, and consistent characteristics in terms of the load-bearing mechanism. The torsional rigidity of the improved twin-treadway structure was primarily generated by the vertical bending rigidities of its two parallel single treadways through the rigid transverse braces. This significant finding specifically pertains to the unique twin-treadway hybrid bridge. The results presented in this work are expected to provide valuable insights, which could, in turn, lead to further the development of similar lightweight structural systems.

Strength design of concrete-infilled double steel corrugated-plate walls under uniform compressions

Concrete-infilled double steel corrugated-plate walls (CDSCWs) are composed of two steel corrugated-plates (SCPs) which are connected through bolts, and concrete filled the spacing formed between the two SCPs. Two vertical boundary elements are installed additionally at both sides of CDSCWs. On the one hand, the corrugated configuration of SCPs has great improvement on the load-bearing efficiency of CDSCWs; on the other hand, much higher bearing capacities and better seismic performance for CDSCWs are provided owing to the interactions among SCPs, bolts and infilled-concrete. This paper investigates the load-bearing mechanism and strength design formulae of CDSCWs under compressions. Since SCPs are prone to local buckling failure between two rows of bolts under the conditions of large vertical bolt spacing and small thickness of SCPs, this paper mainly focuses on the load-bearing mechanism of SCPs in CDSCWs under uniform compressions. The unilateral constraint on SCPs provided from infilled-concrete and the restraining effect on the flexural deformation of SCPs owing to bolts are considered. At first, series of finite element (FE) eigenvalue buckling analyses are conducted to study the elastic buckling behavior of SCPs subjected to uniform compressions. On the basis of Euler's formula, the formulae for predicting the elastic buckling stresses and corresponding normalized slenderness ratios λs of SCPs are achieved respectively. The instability performance of SCPs under uniform compressions is then investigated through FE nonlinear analyses, and accordingly the stability coefficient φs is attained. The corresponding φs−λs curve is therefore established in order to calculate the ultimate bearing capacities of SCPs. In addition, the cooperative performance of material strengths between SCPs and concrete is analyzed numerically when CDSCWs reach their compressive ultimate strength. With this consideration, the design method for predicting the cross-sectional strength of CDSCWs under compressions is proposed. Moreover, a CDSCW specimen with I-section is tested under a compressive load. Its cross-sectional strength is investigated experimentally. The results of the experiment coincide with those of numerical simulation, this verifying the safety and validity of the design method for cross-sectional strength design of CDSCWs.

Investigation of Bonding Behavior of FRP and Steel Bars in Self-Compacting Concrete Structures Using Acoustic Emission Method.

To extend understanding of the bonding behavior of fiber reinforced polymer (FRP) and steel bars in self-compacting concrete (SCC), an experimental series consisting of 36 direct pull-out tests monitored by acoustic emission (AE) were performed in this paper. The test variables involved rebar type, bar diameter, embedded length, and polypropylene (PP) fiber volume content. For each test, the pull-out force and free end slip were continuously measured and compared with the corresponding AE signals. It was found that the proposed AE method was effective in detecting the debonding process between the FRP/steel bars and the hosting concrete. The AE signal strength exhibited a good correlation with the actual bond stress-slip relationship measured in each specimen. Based on the AE location technique, the invisible non-uniform distribution of bonding stress along the bar was further revealed, the initial location of damage and the debonding process were captured. Additionally, the contribution of bar-to-concrete load-bearing mechanism (chemical adhesion, friction, and mechanical interlocking) to sustain the pull-out force was effectively clarified by studying the collected signals in the frequency domain of AE methods. The experimental results demonstrate that the proposed AE method has potential to detect the debonding damage of FRP/steel bar reinforced SCC structures accurately.

Experimental study of tensile properties and deformation evolutions of 2D and 2.5D woven SiO2f/SiO2 composites using single-camera stereo-digital image correlation

SiO2f/SiO2 composites have become a promising candidate material for thermal protection systems due to its unique combination of various properties such as low density, high thermal shock resistance, favorable electrical insulating properties and enhanced mechanical properties. The increasing interests in these materials lead to a pressing requirement on comprehensively understanding their mechanical behaviors and load bearing mechanisms under external loads. The present work focuses on experimental study and comparison of the mechanical properties and deformation evolutions of 2D and 2.5D woven SiO2f/SiO2 composites using single-camera stereo-digital image correlation (stereo-DIC) technique. Based on the full-field displacements and strains retrieved by single-camera stereo-DIC, the mechanical properties of 2D and 2.5D woven SiO2f/SiO2 composites can be determined. It is found that 2D woven SiO2f/SiO2 composites present a lower yield strength and elastic modulus than 2.5D SiO2f/SiO2 composites. Also, remarkable differences in full-field displacement and strain distributions of the 2D and 2.5D SiO2f/SiO2 composites are observed, indicating a strong influence of the weave architecture on the deformation evolution and load bearing mechanism of SiO2f/SiO2 composites. Finally, the failure mechanisms of these two composites are discussed.

Performance evaluation of semi-flexible permeable pavements under cyclic loads

ABSTRACTTraditional permeable pavements are constructed with rigid aggregates and have low load-bearing capacity. The crack development due to loads and unpredicted ground movements reduces their service life. The widespread cracks on the surface of conventional asphalt accelerate the pavement structure deterioration and reduce the overall service life. In this research, the end-of-life tyre products shredded to tyre-derived aggregates (TDAs) were utilised along with crushed rock (CR) in different fractions of a porous structure to enhance the flexibility of permeable pavement whilst maintaining the minimum load-bearing capacity for use in footpath and low-volume roads. The transitional behaviour from a semi-rigid structure owing to the rigidity of CR aggregates to a more flexible structure for mixtures at higher TDA content was investigated. The impact of rigid-rigid and flexible-rigid inter-particular contacts at low and high stress levels is investigated. The plastic and recoverable deformations of the flexible-rigid blends under monotonic and repeated loadings are compared. Also, the impact of polyurethane binder content on improving the mixtures flexural strength is investigated. The lightly bonded flexible-rigid mixtures are a viable replacements for traditional porous pavements to improve the load-bearing mechanism and increase the flexibility of pavement.

Analysis of the shape effect on the axial performance of a waveform micropile by centrifuge model tests

A new type of micropile, the waveform micropile, has been developed to provide improved load-bearing capacity compared with that of a conventional micropile. The waveform micropile has a wave-shaped grout with a partially enlarged shear key formed by the jet grouting method on the cylindrical shaft of the micropile. Previous research has determined that the waveform micropile can be installed faster than the conventional micropile and that the bearing capacity increases as the wave-shaped grout provides additional shaft resistance between the ground and the grout. In this study, a series of centrifuge model tests were conducted on the waveform micropile model with various wave-shaped grouts to analyze the relationship between the arrangement of the shear key and the load-bearing mechanism of the waveform micropile. The load–settlement relationship and the load-transfer mechanism were analyzed based on the test results of six test micropiles, including three waveform micropiles with a single shear key at various depths, one waveform micropile with a multiple shear key along the pile depth, and two micropiles with only a cylindrical shape. The test results showed that the ultimate bearing capacity of the waveform micropile was over two times greater than that of the conventional micropile. The rate of increase in the bearing capacities of each waveform micropile differed with the shape of the shear key. Furthermore, the characteristics of the load-sharing ratio due to the shaft resistance and end bearing varied depending on the shape of the waveform micropiles.

The post-breakage response of laminated heat-treated glass under in plane and out of plane loading

Abstract Any reliable use of glass for structural purposes cannot neglect that its breakage may be provoked by imponderable events, like impacts at critical spots or thermal shocks. Laminated glass, composed by glass plies sandwiching polymeric interlayer sheets, is used in architectural application thanks to its safe post-glass breakage response. When glass breaks, the interlayer retains the glass shards, and the cracked element maintain a certain residual load-bearing capacity, strongly influenced by the tension stiffening of the polymer due to the adhesion with the glass shards, which depends upon the size of the shards and of the debonded zones. Here, we review the most recent experimental results on the post-glass breakage response of laminated heat-treated glass elements, providing charts for the evaluation of such a stiffening effect. Based on this, simple formulas to analyze and interpret the experimental findings under both in-plane and out-of plane bending are proposed, providing analogies with the bending of bimodulus materials and the load-bearing mechanism of reinforced concrete, respectively.

Mechanical behaviour and load bearing mechanism of high porosity permeable pavements utilizing recycled tire aggregates

The benefits of Permeable Paving Systems (PPS) in minimizing surface water run-off which in turn reduces the imposed pressure on stormwater collection systems at the time of flash flooding have been recently remarked profoundly. In addition, the PPS have additional advantages such as filtering the pollutants for downstream water collection systems and accommodating transformation of nutrients and water to the surrounding vegetation. Inclusion of end-of-life tire products in the mixture of PPS can adjust the flexibility of the final product. Tire aggregates will potentially enhance the final product performance in areas where the ground movement or intrusion of roots can cause damage to conventional rigid pavement systems. The effect of addition of waste tire and rubber aggregates to solid granular material have been investigated in the past; however, their focus have been mainly on creating highly compacted mixtures. In contrast; in this study; mixtures of soft (end-of-life tire aggregates) and rigid aggregates (crushed rock) with a relatively high porosity was tested to evaluate their suitability for construction of permeable pavements which require high porosity. The flexibility of mixtures and their stress dependant behaviour was investigated based on the volumetric fraction of soft aggregates in the blend. The transitional soft-rigid behaviour of the mixture can be utilized to mitigate the unexpected deformation induced on the pavement. The compressive behaviour of highly permeable mixtures under ko loading and deviatoric shear provides an insight on the formation of force chains in the mixtures between the rigid particles. In addition, monitoring the compressive behaviour of rigid-soft aggregates under ko loading explains soft aggregates cushioning impact on improving the compressibility and shear behaviour of the mixture.

Seismic performance of new-type box steel bridge piers with embedded energy-dissipating shell plates under tri-directional seismic coupling action

Accurate numerical models are necessary to evaluate the seismic performance and load-bearing mechanism of new-type box steel bridge piers with embedded energy-dissipating shell plates under tri-directional seismic coupling action. Numerical simulations of seismic performance under six types of tri-directional seismic coupling action was conducted. The effects of this stress on the seismic performance of the new-type steel bridge piers was evaluated through analysis of damage mode, hysteresis curve, skeleton curve, stiffness and strength degradation characteristic, and energy-dissipating capacity. This study also compared the numerical analysis with experimental results in order to validate the accuracy of the proposed finite element model. Based on this model, the range of relevant parameters expanded and 88 numerical specimens were analysed for seismic performance, producing further information about the influence of thickness and curvature of the embedded shell plate, spacing of transverse stiffening ribs of the shell, axial compression ratio, and slenderness ratio. Results showed that tri-directional seismic coupling action significantly affects the specimen’s deformation capacity; the embedded shell plate effectively improves the piers’ load-carrying and deformation capacity; and the thickness of the embedded shell plate, width-to-thickness ratio of the wall plate, axial compression ratio, and slenderness ratio significantly affect the seismic performance of the new-type steel bridge piers. To promote the ease of seismic design of new-type box steel bridge piers, this study used theoretical analysis and numerical simulation to calculate equations for the minimum height of the energy-dissipating zone of the bottom embedded shell plate. Finally, formulas were also established to calculate the relevant stability bearing capacity and displacement ductility factor of the new-type steel bridge piers under tri-directional seismic coupling action in order to improve their seismic design.

Influence of Size and Load-Bearing Mechanism of Piles on Seismic Performance of Buildings Considering Soil–Pile–Structure Interaction

Influence of Size and Load-Bearing Mechanism of Piles on Seismic Performance of Buildings Considering Soil–Pile–Structure Interaction

Investigation of Optimization of Load-bearing Mechanism in Passive Support Wear Reducing Lumbar Load

Investigation of Optimization of Load-bearing Mechanism in Passive Support Wear Reducing Lumbar Load

Shear bearing of cross-plate joints between diaphragm wall panels – II: numerical analysis and prediction formula

In this, the second part of two companion papers, three-dimensional finite-element modelling of the shear load tests is presented and the shear bearing behaviour of the cross-plate joints is predicted. The isotropic damage plasticity model is adopted to model the non-linear behaviour of concrete and the interface, and the quasi-static load test process is approximately simulated with an explicit technique employing an artificial timestep to decrease the kinetic energy. The numerical analysis method is verified using the experimental results presented in the first part of the two companion papers, and the shear behaviour and shear bearing capacity of the cross-plate joints are evaluated numerically. The numerical results and parametric study reveal the load-bearing mechanism and failure modes of the joints. By introducing a correction coefficient considering the effect of the hole ratio in the longitudinal plate and based on the analytical expression for the ultimate shear load of perfobond connectors, a new and modified prediction formula for the shear bearing capacity of cross-plate joints is proposed. The close correlation of the prediction formula with the numerical and experimental results demonstrates that the proposed formula is reliable for predicting the ultimate shear load of cross-plate joints.

Fabrication of a bulk GdN nanoparticles-reinforced Mg-Gd matrix nanocomposite with phenomenal mechanical properties

A novel bulk Mg-Gd matrix nanocomposite reinforced with GdN nanoparticles has been successfully fabricated utilizing an advanced powder metallurgy route within in-situ reactions during sintering process. The as-prepared nanocomposite with nanocrystalline (NC) or ultrafine-grained (UFG) matrix and homogeneously dispersed nanoparticles exhibits phenomenal mechanical properties: ultimate tensile strength (UTS) of 521MPa, yield strength (YS) of 506MPa and tensile elongation (El) of 2.8%. The drastic improvement of the strength in comparison with that of conventional magnesium alloys is ascribed to fine grain strengthening of NC/UFG matrix, dispersion strengthening and load bearing mechanism of the GdN nanoparticles and β (Mg5Gd) or β′ (Mg3Gd) precipitates.

Effects of micropore structure on hydration degree and mechanical properties of concrete in later curing age

The hydration degree and compressive mechanical properties of concrete are evaluated in relation to microstructure composition at three curing ages. The analysis focuses on hydration and compressive load-bearing mechanism at the microstructural level. A concrete micromechanism that allows explicit parameters of pore distribution and pore diameter is investigated. Variations of concrete microstructure are measured and analysed over a range of curing ages. Results show that (1) different curing periods have significant effects on the hydration degrees and microstructure of concrete, (2) variations of hydration degrees are the basic reason of changes of pore structure and (3) type of porosity and pore diameter affects mechanical properties of concrete. Microstructure-behaviour relations are established to determine hydration degree and compressive mechanical properties, and facilitate microlevel studies on concrete properties for target-specific applications.