Load Transfer Mechanism Research Articles

Experimental investigation on retrofitting effects of circular steel rod damper systems on non-seismic detailed reinforced concrete frames

Existing non-seismically detailed low-rise reinforced concrete (RC) buildings are vulnerable to seismic attacks due to their insufficient seismic details including the spacing of transverse reinforcements and splice length at column critical regions. In order to mitigate those deficiencies, various retrofit strategies using externally-bonded reinforcing materials and adding external braced frames have been suggested, and adopted on the construction fields. Although various retrofit methods have been verified their retrofitting effects, there have been architectural concerns and difficulties in providing appropriate connections between supplemental structural systems and existing RC frames. One of the methods applying supplemental energy dissipating devices, this study introduces an externally retrofit method using circular steel rod dampers (CSRDs) which are installed between the existing RC frame and the external sub-frame. The existing RC frame have relatively long natural period and large displacement demand while the external sub-frame has short natural period and small displacement demand. Such relative displacement between two frames is a main mechanism acting the CSRDs. When the interaction of two frames occurs in the CSRD due to the seismic load, the load-transfer mechanism ensures stable hysteretic behaviors of the CSRD even during extreme earthquakes. To verify retrofitting effects of CSRD systems on non-seismically detailed RC frames, this study carried out component-level tests of CSRD systems and their hysteretic characteristics are investigated, especially in terms of their fatigue resistance. Then, full-scale cyclic tests are carried out with non-seismic detailed RC frames with and without CSRD systems in order to confirm the effectiveness of the introduced external retrofit method.

Numerical analysis of soil arching effect in piles-reinforced airport foundation

The soil arching effect is the key mechanism for load transfer in pile-supported reinforced road (runway) foundations. To investigate the formation and evolution process of soil arching effect in the whole process of embankment filling and soft soil foundation consolidation, a three-dimensional hydro-mechanical coupled numerical model of pre-fabricated high-strength concrete (PHC) pile-reinforced soft soil runway foundation was established based on the foundation treatment project in Pudong Airport. The laws of variation of soil settlement, pore water pressure and pile soil stress were analysed, and the influence of pile spacing was considered. These data from both numerical simulation and field test indicate the soil arching effect in the foundation reinforced by PHC piles and preliminarily reveal the evolution of soil arching in the process of embankment filling and soft soil foundation consolidation. The preliminary results encourage the authors to continue this research to investigate the evolution of soil arching under aircraft dynamic loads through adding a more suitable constitutive model or subroutine in this numerical model.

Axial Load Transfer Mechanism in Fully Grouted Rock Bolting System: A Systematic Review

The main objective of implementing primary ground-controlling methods, such as applying rock bolting systems, is to increase the strength of surrounding rock mass. Among all rock bolting systems, fully grouted rock bolting systems are the most popular and reliable retaining systems due to their simplicity, availability of materials, ease of installation in the field, and cost-effectiveness. While these types of rock bolts experience both axial and shear forces, understanding their response to axial loads remains complex and dependent on several factors. Extensive research has addressed the overall behaviour of the fully grouted rock bolting system, but a systematic review of the axial load transfer mechanism and its impact on overall performance is lacking. This study addresses this gap by employing a bibliometric analysis of 77 peer-reviewed publications to explore the current state of knowledge regarding the axial load transfer mechanism in fully grouted rock bolting systems. The analysis identifies influential journals, publishers, researchers, highly cited articles, and emerging keywords within this field. Furthermore, it reveals three key parameters significantly impacting the axial behaviour: (a) rock mass and boundary conditions, (b) mechanical behaviours of the grouts, and (c) the geometry and surface profile of the rock bolt. These parameters are subsequently discussed in detail, highlighting their influence on the axial performance of the system. Finally, this article concludes by suggesting promising directions for future research.

Microstructure, mechanical properties and interaction mechanism of seawater sea-sand engineered cementitious composite (SS-ECC) with Glass Fiber Reinforced Polymer (GFRP) bar

With increasing demand for sustainable and long-lasting materials, seawater sea-sand engineered cementitious composite (SS-ECC) has emerged as a promising alternative to conventional concrete in near-ocean construction projects. Glass fiber reinforced polymer (GFRP) bar with excellent corrosion resistance is an ideal choice for these applications. This study evaluated the bond performance of GFRP bars embedded in normal-strength ECC with polyvinyl alcohol (PVA) fibers and high-strength ECC with polyethylene (PE) fibers through pull-out tests. Additionally, tests were conducted on GFRP bars in pristine ECC made with freshwater and river sand for comparison. Further investigation explored the structural properties and uncovered load transfer mechanisms. Results indicated that saline content facilitated early cement hydration of normal-strength ECC, resulting in finer pore structure (10.5% lower porosity and 12.5% lower sorptivity), slightly enhanced compressive performance (1.2% higher compressive strength and 8.3% higher elastic modulus), denser microstructure at GFRP-ECC interface (13.7% lower porous transition zone thickness, 19.2% narrower transition zone and 19.7% higher Ca/Si ratio), and superior bond performance (28.3% higher bond strength and 22.6% higher fracture energy). Conversely, saline content imposed a limited impact on the mechanical properties of high-strength ECC, primarily attributed to the ultra-fine microstructure and early strength characteristics exhibited by the silica fume (SF)-based cementitious binder.

Bearing capacity of monopile-bucket composite foundation in sand-over-clay under V-H-M combined static loads

With the rapid development of offshore wind power energy, the requirements for the bearing capacity of offshore wind turbines have been obviously stricter. In response to this subject, an innovative monopile-bucket composite foundation consisting of an embedded pile and a suction bucket is proposed in recent years, and the bearing mechanism of this new type of composite foundation in double-layer soils has not been investigated comprehensively. To explore the bearing capacity and failure mechanism of this composite foundation embedded in sand-over-clay under V-H-M combined static loads, a series of the 1-g model tests are firstly conducted in this paper. Then, the experimental tests under different common loading conditions are validated with 3D finite element analysis. Finally, parametric analysis has been performed to investigate the behaviors of the composite foundation considering different foundation configurations (geometric dimensions, soil properties, loading pattern, etc.). In detail, the load transfer mechanism between single pile and suction bucket are also discussed. Therefore, the composite foundation is demonstrated that has great potential in bearing performance compared to the traditional monopile and suction bucket. This work may pave the way for the guidelines of engineering design and applications of monopile-bucket composite foundation in marine environment.

Optimizing toughness and cost-effectiveness in one-part geopolymers via fiber reinforcement: A comprehensive investigation of PVA, PE, and glass fibers

This study explores developing and characterizing a one-part geopolymer, an innovative and sustainable construction material. The effects of incorporating polyvinyl alcohol (PVA), polyethylene (PE), and glass fibers (GF) on the toughness of slag and fly ash-based one-part geopolymer mortars were investigated through compressive, three-point flexural, and four-point bending tests. The findings demonstrate that fiber incorporation reduces fluidity and compressive strength due to increased porosity, lower elastic modulus of fibers, and weak interfacial bonding. However, fibers significantly enhance damage resistance and toughness via crack bridging and load transfer mechanisms. Formulations with 2 % PVA fibers and combinations of 1 % PVA with 1 % PE fibers and 1 % PVA mixed with 0.5 % PE and 0.5 % GF demonstrate excellent toughness. Notably, the latter two fiber blends achieve 14 % and 10 % cost reductions, respectively, compared to using only PVA fibers, making them economically viable for large-scale applications. Scanning electron microscopy and X-ray diffraction provided insights into the toughening mechanisms, including crack bridging, fiber pull-out, and enhanced stress distribution within the geopolymer matrix. Digital image correlation techniques further elucidated the fibers' role in improving the post-cracking behavior and structural resilience under load.

Synergistic reinforcement of Cu/Ti3SiC2/C laminated-like composites with the bimodal and highly oriented graphite flake and graphene nanoplatelets

This study describes the preparation of bimodal reinforced Cu/Ti3SiC2/C laminated-like composites using flake powder metallurgy and vacuum hot-press sintering process. The objective was to accurately modulate the formation of oriented reinforcement network in two-dimensional carbon materials. The powders used in the five designed composites were flake Cu powder (45–60 μm), Ti3SiC2 (1–5 μm), graphite flakes (GFs, 120 μm) and graphene nanoplatelets (GNPs, 15 μm). Among them, the proportions of Ti3SiC2 (10 wt %) and GFs (3 wt %) remained unchanged, GNPs accounted for 0 wt %, 0.5 wt %, 1.0 wt %, and 1.5 wt %, and Cu powder accounted for a decreasing proportion. Formation mechanisms of GFs and GNPs in oriented networks were quantitatively analyzed using the alignment model. Additionally, the related strengthening and failure mechanisms were investigated. According to the study, the bimodal laminated-like Cu/Ti3SiC2/C composites with 0.5 wt% GNPs added showed the best overall performance. Specifically, it exhibited a hardness of 125.7 HV, tensile strength of 276.3 MPa, thermal conductivity of 207.8 W m−1 K−1, and electrical conductivity of 23.6 MS/m. The network enhanced by the two-dimensional carbon material achieves efficient and orderly load transfer and dissipation mechanisms, optimizing stress distribution and enhancing fracture resistance, resulting in improved mechanical properties. In addition, the formation of the oriented reinforcement network optimizes the orientation arrangement of the reinforcing particles, which somewhat mitigates the scattering of thermoelectric carriers by structural defects in the composites, and the enlarged mean free-range improves the migration efficiency of electrons and phonons. Therefore, the erection of bimodal laminated-like structure achieves the goal of optimizing the properties of the composites.

Shear performance and failure mechanism of socket CFST column-beam connection with UHPC grouting

Prefabrication assembly technology has been widely recognized due to its rapid construction, minimal environmental impact, and superior quality of precast components. The reliability and construction convenience of the connection joints of precast components are particularly important. In this paper, a novel Ultra High-Performance Concrete (UHPC)-filled concrete-filled steel tube (CFST) socket connection (UCSC) was proposed for the column-beam connection. To explore the shear behavior and shear load transfer mechanism of UCSC joints, four direct shear experiments were conducted in terms of different parameters (socket depth, presence of studs). Meanwhile, ABAQUS was used to perform a systematic parametric analysis (socket length, embedded length, outer diameter of CFST, thickness of steel tube). The results indicated that the shear performance of UCSC joints was significantly influenced by both the socket depth and the outer diameter of CFST. The proposed finite element model (FEM) can predict the load-displacement relationships of UCSC joints with a maximum peak load error of 2.3 %. Combining the experimental results and numerical results, a simplified calculation model was formulated to accurately estimate the shear bearing capacity of UCSC joints, and was verified by numerical and experimental results with a maximum error of 8.6 %. The research results have practical implications for the preliminary design of UCSC joints to avoid non-ideal failure mode.

Shear behavior of the fully prefabricated liftable connection for modular steel construction

Modular steel construction (MSC) is a novel structural system comprising of stacked modular units. It represents a type of green building with broad market prospects, which is aligned with industrialization and intellectualization trends. The shear behavior of the inter-module connection significantly impacts the lateral force resistance behavior of the MSC, which directly determines the load bearing capacity of the MSC. However, there are few studies on the shear behavior of the inter-module connection. A fully prefabricated liftable connection (FPLC) for MSC was proposed. The damage mechanism and design method of the FPLC under shear force were systematically investigated. Monotonic shear tests were conducted on six full-scale FPLC specimens. The failure mode, strain distribution, and load-bearing capacity of the FPLC under shear force were discussed. Subsequently, a refined finite element model (FEM) of the FPLC was established using the universal finite element analysis (FEA) software ABAQUS. The accuracy of the developed FEM was validated by comparing the experimental and numerical results. In addition, the development of the internal forces of the long stay bolts of the specimens was discussed to reveal the load-transfer mechanism of the FPLC. Finally, a series of prediction equations for the ultimate load-bearing capacity of the FPLC under a shear force were derived. The reliability of the proposed formulas was validated by comparing the theoretical and experimental results. The present research work will provide a comprehensive understanding of the shear behavior of the FPLC and corresponding design method, which is beneficial for the promotion of the MSC; limitations and future work are also briefly presented.

Finite Element Analysis on the Behavior of Solidified Soil Embankments on Piled Foundations under Dynamic Traffic Loads

Most research conducted so far has primarily focused on pile-supported gravel embankments. The ability of solidified soil used as an embankment filling material has been verified, and a clear view on the performance of solidified soil embankments on piled foundations is rather limited. The three-dimensional unit cell models of pile-supported embankments are conducted to investigate the performance of solidified soil embankments in comparison to gravel embankments under static and dynamic loads. Then, a systematic parametric analysis is performed to investigate the effects of various factors, including the cohesion and friction of solidified soil, the velocity and wheel load of vehicles, the pile spacing, the height of embankments. The results show that, compared with the results of gravel embankments, the heights of the outer soil arch plane in solidified soil embankments reduces under static and dynamic loads, and the piles bear more load. In addition, the total settlements of solidified soil embankments decrease with increasing cohesions, and there is an economical cohesion of 25 kPa. The vehicle wheel load, pile spacing, and the height of embankment significantly influence the load transfer mechanism and total settlement of solidified soil embankment, while the friction angles and velocities have little effect on the total settlements and vertical stress. The relationship between the soil arch height and various parameters in solidified soil embankments is established by multiple regression analysis. This investigation highlights the advantage of solidified soil in reducing total settlement and provides an insightful understanding of the load transfer mechanism of solidified soil embankment on piled foundation.

Laboratory Tests of Large-Scale Block Models on the Load Transfer and Failure Mechanisms of Rock Masses Subjected to Anchor Loading

This paper presents a laboratory testing rig designed to investigate the failure mechanisms and load transfer of rock masses under rock anchor loading. The study revealed that joint patterns significantly affect the strength and capacity of the rock mass, with existing design approaches based on apex angles of 90∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document} or 60∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document} found to be potentially overly conservative. Joint orientation and spacing should be included in the anchor design to obtain a more precise design criterion. In all the studied patterns, increasing the horizontal and vertical stress increased the block models’ capacity, and load arching did not occur in the model with an unfavourable joint orientation. This study also revealed that the failure surface followed the joints in all tests and that the block model capacity was significantly higher than estimated with the design principle based on the weight of the overlying rock. The findings of this work have important implications for designing rock anchoring systems in mining and civil engineering demonstrate that joint orientation and block size significantly affect the rock mass capacity. This study confirms the need to consider the influence of in situ stresses on rock mass capacity when designing of rock anchors. Overall, this work guides the development of more precise design criteria for rock anchors, contributing to more efficient and effective rock engineering practices.

Experimental and numerical studies on the displacement and load-transfer mechanism of pile-caisson composite structure

The pile-caisson composite structure (PCCS) is an innovative underground anchorage foundation used to support large-span suspension bridges. This paper presents the displacement and the load transfer mechanism of the PCCS. The bearing responses of each individual pile in the PCCS were analyzed employing the finite element method, which was verified by the model test results. The peak bending moments borne by pile P11 and pile P53 in the PCCS exhibit the most significant disparity, with a difference that can reach up to 133.97%. Moreover, a parametric study utilizing numerical simulations indicates that augmenting the pile diameter and length, while reducing the pile spacing, can mitigate the displacements of the PCCS. However, there is an upper limit (i.e. S = 3.5d) for the pile spacing beyond which marginal benefits could be obtained. The findings of this study can provide guidance for the design and construction of the PCCS.

High mechanical properties of CNTs/Al composites achieved by second phase refinement and reinforcement dispersion via hot extrusion

The carbon nanotubes (CNTs) reinforced 2A70 alloy by the coating of ZrO2 (ZrO2@CNTs/2A70) are processed by a hot extrusion process. The microstructure and mechanical properties of ZrO2@CNTs/2A70 composites were investigated in this study. The results show that the second phase of the composites is broken and uniformly dispersed under the action of shear force and the second phase as well as the ZrO2@CNTs reinforcement is uniformly distributed along the extrusion direction. The hot extrusion process eliminates the cast defects and improves the reinforcing phase's dispersion and the material's mechanical properties are significantly improved. At the extrusion ratio of 25, the composites exhibited notable enhancements in their mechanical properties, as evidenced by a significant increase in hardness, yield strength (YS), ultimate tensile strength (UTS), and elongation (EL), with respective values of 141.7 HV, 237.4 MPa, 309.7 MPa and 13.9%. These values were higher than those obtained from cast composites by 17.5%, 20.0%, 20.9% and 152.7%, respectively. The fracture characteristics of the composite are mainly ductile fractures. Besides, the extruded composites are strengthened mainly by grain refinement and load transfer mechanism.

Experimental and numerical studies of mechanical performance of an assembled friction type structural underpinning joint

This paper proposed an assembled underpinning joint (UPJ) based on the interfacial friction action between the underpinned concrete member and the underpinning steel beams (UPSBs). To investigate the mechanical performance and failure modes of the proposed UPJ, 20 specimens with different concrete strengths were fabricated and tested with varied preloading levels. Experimental results showed that the proposed UPJs could effectively transfer the vertical loads in the concrete columns through the friction action and all specimens failed due to the slip between the underpinned concrete column and the UPSBs. The failure loads of the specimens were in a positively linear relationship with the preloading levels and an interfacial friction coefficient of 0.46 was found. Numerical models were also created to further examine the detailed structural behaviours of each components in the UPJs, which confirmed that, the UPSBs were subjected to a composite action mainly combining both bending and torsion. The frictional stresses between the UPSBs and the concrete column were concentrated in the regions of the web of UPSBs near flanges and stiffeners. The load transfer mechanisms of the proposed UPJs under complex loading conditions were clarified. The damages, occurred at the corners of concrete columns due to high stress and strain concentrations, should be alleviated or prevented by protective measures in practice.

Numerical study of geosynthetic-reinforced soils above voids – validation on centrifuge tests

ABSTRACT Understanding the load transfer and deformation mechanisms within geosynthetic-reinforced embankment overlying voids is fundamental for improving the current design methods. Based on geotechnical centrifuge tests, the numerical study highlights the cavity opening procedures within reinforced systems. Two procedures were studied: the increasing-diameter and gradual movement ones. For the gradual opening process, a cubic function is found to be well-suited, while a combination of cubic and quadratic functions is more appropriate for a progressive opening process. The study sheds light on the understanding of the load distribution over the cavity expansion. The soil arch formation occurs when the height reaches 2.5 times the sinkhole width. A triangular shape is found to be suitable for describing a progressive opening process, while an inverse triangular shape is more appropriate for a gradual opening process. Appropriate functions are utilized to fit the deformed geometry of the soil surface and of the deflected geosynthetics.

An enhanced understanding of the lateral response of large-diameter monopile: Development of a new P-y curve

The present design practices of laterally loaded monopiles tends to discretize the pile into a series of beam elements and connect each element to uncoupled non-linear springs, or P-y curves, to represent soil reactions. The prevailing design codes tend to support the use of a universal P-y curve irrespective of pile configuration, flexural rigidity, and soil rigidity index. However, accumulating evidence suggests otherwise, underscoring the imperative to revise formulas, especially for large diameter rigid monopiles. This study conducts a thorough examination of load transfer and failure mechanisms in large diameter monopiles subjected to monotonic lateral loading in clayey soil. A refined formula is proposed to estimate ultimate net soil resistance, rectifying deficiencies in prevailing design codes prone to underestimation. Findings reveal significant influence of soil rigidity index on the P-y curve of rigid monopiles. Consequently, endeavours are undertaken to develop a new P-y formulation integrating the pivotal role of soil rigidity index. The newly devised P-y curve is anticipated to propel advancements in the design of large diameter monopiles, pivotal in offshore renewable energy exploitation.

Influences of number of geosynthetic reinforcement layers on soil arching under cyclic loading

Geosynthetic-reinforced pile supported (GRPS) embankments have been widely used in highways and railways on soft subsoil. During the operation period, these embankments are often subjected to cyclic loading, such as traffic loading. Considering that soil arching is a key load transfer mechanism in these embankments, the development of soil arching under cyclic loading is vital important to operational safety of these embankments. Conventional trapdoor system cannot represent actual conditions of soil arching in GRPS embankments because it have a forcibly-moved trapdoor and cannot simulate load-induced subsoil settlement. Hence, this paper used a self-moving trapdoor supported by compression springs that moved up and down dependent on its overburden pressure. To investigate influences of number of geosynthetic reinforcement layers on soil arching under cyclic loading, two self-moving trapdoor tests were conducted, including a single layer and two layers, where the total reinforcement stiffness were approximately same. The trapdoor test results show that the inclusion of two reinforcement layers with a fill layer of a certain height in between reduced surface settlement of the fill and tensile forces of reinforcement, as compared with a single reinforcement layer. It also enhanced soil arching effect and improved the stability of soil arching under cyclic loading.

Study on Dynamic Mechanical Properties of Sandwich Beam with Stepwise Gradient Polymethacrylimide (PMI) Foam Core under Low-Velocity Impact.

Different PMI foam materials of 52, 110, and 200 kg/m3 were used to design stepwise gradient cores to improve the impact resistance of the sandwich beam. The stepwise gradient core consists of three layers arranged in positive gradient, negative gradient, and sandwich-core (e.g., 200/52/200). These sandwich beams were subjected to the impact of a steel projectile under impact momentum of 10 to 20 kg·m/s, corresponding to impact energy in the range of 12.5 to 50 J. During the test, the impact force was recorded by an accelerometer, and the different failure modes were also obtained. Subsequently, the influence of the layer arrangement on the energy absorption and load transfer mechanism between the different layers was analyzed. The results showed that the top layer with a large density can improve the impact force, but the middle/bottom layer with a low density promoted specific energy absorption. Thus, based on these two points, the negative gradient core (200/110/52) had an excellent specific energy absorption because it can transfer and expand the area to bear the load layer by layer, which improved the energy absorption in each layer. Combined with the failure modes, the load transfer and deformation mechanisms between the layers were also discussed. The present work provided a valuable method to design an efficient lightweight sandwich structure in the protection field.

Study on load transfer mechanisms and impact on adjacent railway subgrade within loess regions

Clarifying load transfer mechanism and the influence of the widening of a newly-built railway is the premise for the construction of adjacent project in loess region. This paper uses monitoring datas obtained from three sections in different stages to analyze the distribution laws of load exert on piles and soil between piles, investigates the variation laws of filling height on the earth pressure at different excavation steps and elucidates the influence of the filling height of newly built subgrade on the existing subgrade. In addition, a fitting formula y = a(1-e-bx) + cx is proposed to describe the relationship between the ratio of the additional displacement to the filling height, which is applicable for similar projects.

Influence of obesity on load-transfer mechanism, contact mechanics, and longevity of cemented acetabular cup

ObjectiveThis investigation aimed to assess the impact of obesity on the load-transfer mechanism, longevity, and contact mechanics of cemented acetabular cups. MethodsThree obesity scenarios were considered: obese case-I (100–110 kg), obese case-II (120–130 kg), and obese case-III (140–150 kg). Utilising six finite element models, the effects of different bodyweights on load transfer, contact mechanics, and cup longevity during normal walking conditions were assessed. Muscle forces and hip joint reaction forces were adjusted and linearly calibrated based on obesity cases. ResultsElevated stresses in cortical and cancellous bones, as well as the cement mantle, were observed in obese cases, suggesting a heightened risk of loosening and failure of the cemented fixation of the acetabular cup. Additionally, increased contact pressure and micromotion between articulating surfaces were noted in obese individuals, with a gradual escalation from obese case-I to obese case-III. ConclusionsThese findings highlight the significant negative impact of obesity on the performance of cemented acetabular cups, emphasizing the importance of considering bodyweight variations in the design and assessment of orthopaedic implants for optimal functionality and durability.