Load Transfer Characteristics Research Articles

Pull-out tests and slope stability analyses of nailing systems comprising single and multi rebars with grouted cement

The pull-out capacities for soil nailing systems comprising of one single 29 mm diameter (type A) and four 16 mm diameter (type B) rebars with grouted cement were examined. A field test and numerical analysis for the type A and type B systems were carried out to investigate the pull-out capacities and the slope stability reinforcement efficiency in soil and rock slopes. The results of the pull-out tests show the mobilized shear force and load transfer characteristics with respect to soil depth. The load−displacement relationship was examined for both type A and type B systems. Slope stability analyses were carried out to study the relationships between soil and nail reinforcement and bending stiffness as well as combined axial tension and shear forces. Factors of safety were calculated in relation to the number of nails and their outside diameters. Both soil and rock slopes were included in this evaluation.

Photoelastic stress analysis of external versus internal implant-abutment connections

Common complications of implant restorations are abutment screw loosening and screw fracture. The geometry of the implant-abutment connection may affect stresses generated from loading, and these stresses may have a role in screw loosening or fracture. This study compared the load transfer characteristics of a complete-arch restoration supported by 4 implants with external and internal implant-abutment connections. Loads were applied to the prostheses in 3 positions. Two-dimensional photoelastic models were used to simulate bone. Two types of implants (ReplaceSelect Internal-Interface Tapered Implants and ReplaceSelect External-Interface Tapered Implants) were placed in the photoelastic models. Complete-arch metal frameworks were fabricated on the abutments. Artificial teeth were arranged on the framework, and the prosthesis was screwed onto the abutments. The specimens were analyzed at 2 levels (implant-abutment level and apical to the implant level) with 3 loading conditions (4-point load; 2-point anterior load; and 2-point lateral load). The numbers of fringe orders were recorded and compared. With the 4-point load, no stress differences occurred between the external-implant abutment connection and internal-implant abutment connection at the connection level and at the apical level. With the 2-point anterior load, the internal-implant abutment connection resulted in lower stresses at the connection level both in the loaded and non-loaded areas. With the 2-point lateral load, the internal-implant abutment connection resulted in lower stresses at the connection level at the non-loaded area. When loaded off-center, the internal-implant abutment connection produced less stress when compared with the external-implant abutment connection.

Prediction of penetration rate of sheet pile installed in sand by vibratory pile driver

A few full scale field tests were conducted on instrumented steel sheet piles under vibro-driving to find out the characteristics of the dynamic behavior of a sheet pile. These sheet piles were tested for situations with and without clutch friction. Parameters of the proposed vibratory pile driving model were correlated with the blow count (N-value) of the standard penetration test obtained from the test site. By comparing the peak amplitude of the section forces at the sheet pile heads for situations with and without clutch friction, it was found that the peak section forces for a sheet pile with clutch friction were greater than those without clutch friction and also that the distribution of the clutch friction was not constant with penetration depth. The assumption of sheet pile rigidity, which is essential for the proposed vibratory pile driving model, was shown to be justifiable from the test results. The efficiency ratio, which is defined as the ratio between the amplitude of the actual driving force and the theoretical driving force, was derived for all considered depths, and the average value of the efficiency ratios was 0.18. A computer program for the predicting the penetration rate of a sheet pile was developed by incorporating the modified Ramberg-Osgood model, which simulates the dynamic load transfer characteristics of a sheet pile. Both the predicted load transfer characteristics and the predicted penetration rates of a sheet pile agreed well with the measured values obtained from field tests.

Aircraft Joints: the Interaction between Corrosion Protection and Structural Performance

Aircraft joints feature prominently in aircraft structural degradation. Fatigue cracking and corrosion damage can reduce joint strength and degrade service life. Corrosion management can include use of paints and sealants and, increasingly, the application of Corrosion Inhibiting Compounds (CICs) which retard corrosion, by penetrating into crevices and cracks, and displacing water. A combination of coatings and CIC use can provide effective corrosion protection, but both interact - in different ways - with structural performance and overall system durability. This paper discusses the interaction between these two corrosion protection measures and fatigue performance of joints. The first issue relates to a reduction in the fatigue life of mechanically-fastened joints after application of CICs (or other lubricants) The lubricating properties of the CICs reduce the friction at the faying surface, which may change the load transfer characteristics of the joint. The paper discusses results from a test program assessing the fatigue life and failure mode of riveted lap joints; the results show a marked reduction in fatigue life for joints containing CICs, and the paper discusses the changes which may be responsible for the reduction. The second issue discussed is the degradation of protective coatings in service. Joints are key locations for coating cracking and failure, since areas such as sheet ends and fastener heads, where displacements are concentrated, will produce concentrated strain in coatings. So far, however, the potential influence of aircraft loading on coating degradation prognostics has received little attention. The paper discusses the role of joint displacement in service as a factor contributing to early degradation of aircraft coatings, and argues that this local strain effect, and indeed structural loading history, needs to be considered in predicting and assessing rates of coating degradation. It describes initial analyses of displacements in aircraft joints, to identify the levels of coating strain and the roles and relative contributions of the various deflections in the joints. The results indicate the potential for very large strains in coatings.

Intravertebral neotrabecularization as an expression of focal load transfer by a keel-design lumbar total disc arthroplasty

The aim of this study is to direct attention to the specific load transfer characteristics of keel-design total disc arthroplasty (TDA) implants that may be underreported. A variety of implants for lumbar TDA are available on the market. One of the main differences between the design types of lumbar TDA implants is whether they use a keel or small spikes/ridges in order to achieve primary stability. The consequences of such design features on load transfer have not been adequately discussed. We report and discuss a case in which new intravertebral bone trabecula have appeared after double-level implantation of a keel-based TDA. We think that the mid- and long-term follow-up radiographs of patients after TDA with keel-design implants should be examined for the presence or absence of such changes. Should our case turn out to be not a singular occurrence, this might have an impact on the design of future TDA implants.

The interaction between corrosion management and structural integrity of aging aircraft

ABSTRACTAircraft joints feature prominently in aircraft structural degradation; fatigue cracking and corrosion damage are major issues, which can reduce joint strength and degrade service life. Protecting the structure against corrosion usually involves use of highly developed protective coatings – paints and sealants – and, increasingly, the application of corrosion inhibiting compounds (CICs) which retard corrosion principally by penetrating into crevices and cracks, and displacing water. A combination of coatings and CIC use can provide effective corrosion protection, but both interact – in different ways – with joint structural performance and overall system durability. This paper discusses the interaction between these two corrosion protection measures and fatigue performance of joints. The first issue relates to the extent to which application of CICs (or other lubricants) can cause a reduction in the fatigue life of mechanically fastened joints. The CICs are lubricants which will reduce the friction at the faying surface of the joint, and change the load transfer characteristics of the joint. This paper discusses results from a test program assessing the fatigue life and failure mode of simple riveted lap joints; the results show a distinct reduction in fatigue life for joints containing CICs, and the paper discusses the changes thought to be responsible for the reduction. The second issue discussed is the degradation of protective coatings in service. Joints are key locations for coating cracking and failure, because areas such as sheet ends and fastener heads, where displacements are concentrated, may produce concentrated strain in coatings. So far, however, the potential influence of aircraft loading on coating degradation prognostics has received little attention. This paper discusses the role of joint displacement in service as a factor contributing to degradation in aircraft coatings at joints, and argues that this local strain effect, and indeed structural loading history, needs to be considered in predicting and assessing rates of coating degradation. It describes analyses of displacements in aircraft joints, to identify the levels of strain and to identify the roles and relative contributions of the various deflections in the joints. The results indicate the potential for very large strains in coatings.

A Topology Optimization Method in Fuselage Flutter Model Design

Airplane flutter scale model should maintain the load transfer characteristics of the original structure. It is a structural inverse problem for proper natural frequencies as well as structural simplification. This inverse problem could be solved by topology optimization. So based on bi-direction evolutionary structural optimization (BESO) method, a topology method for designing fuselage flutter model is presented. Facing porous and irregular shape often appears in topology optimization, a regular shaped grid frame structure consisted of the finite elements is discussed, including its internal mapping relationship and boundary conditions. The ratio criterion for structural modification is raised in this structural topology optimization using frequency sensitivity. Finally, this topology optimization method is applied to cylindrical fuselage flutter model design, result shown that the proposed approach is feasible to achieve given natural frequencies, maintains the character of inner frame structure completely, and the similarity between optimized structure and original structure is achieved.

Static Testing of Pile-Base Post-Grouting Piles of the Suramadu Bridge

Abstract Pile-base post-grouting is a method in which solidifiable cement slurry is injected into the base of the pile through grouting pipes after the strength of the concrete reaches a certain value to strengthen the loose sediment at the hole base and the soil around the pile. The roles of grouting are to eliminate the influence of the technological defects of bored piles, to recover the bearing capacities of strata, and to improve the bearing capacities of piles. Pile-base post-grouting piles technology and Osterberg Cell load testing were applied to some test piles of the Suramadu Bridge. Based on test results of the bearing capacity, side frictional resistance, and base resistance of piles before and after grouting, post-grouting was found to have an obvious role in improving the quality, bearing capacity, and load transfer characteristics of the piles. An equation for calculating post-grouting piles under specific grouting conditions was obtained based on the statistical analysis of more than 50 test piles. The ranges of the improvement coefficients of side frictional and pile-base resistance for different soils are given. Key technologies and parameters of post-grouting are also suggested. The results of this research can be applied to designing bridge pile foundations, which may tap the bearing potential of the piles and result in notable economic benefits.

Optimizing load transfer in multiwall nanotubes through interwall coupling: Theory and simulation

An analytical model is developed to determine the length scales over which load is transferred from outer to inner walls of multiwall carbon nanotubes (MWCNTs) as a function of the amount of bonding between walls. The model predicts that the characteristic length for load transfer scales as ℓ∼tE/μ¯, where t is the CNT wall spacing, E is the effective wall Young’s modulus, and μ¯ is the average interwall shear modulus due to interwall coupling. Molecular dynamics simulations for MWCNTs with up to six walls, and with interwall coupling achieved by interwall sp3 bonding at various densities, provide data against which the model is tested. For interwall bonding having a uniform axial distribution, the analytic and simulation models agree well, showing that continuum mechanics concepts apply down to the atomic scale in this problem. The simulation models show, however, that load transfer is sensitive to natural statistical fluctuations in the spatial distribution of the interwall bonding between pairs of walls, and such fluctuations generally increase the net load transfer length needed to fully load an MWCNT. Optimal load transfer is achieved when bonding is uniformly distributed axially, and all interwall regions have the same shear stiffness, implying a linear decrease in the number of interwall bonds with distance from the outer wall. Optimal load transfer into an n-wall MWCNT is shown to occur over a length of ∼1.5nℓ. The model can be used to design MWCNTs for structural materials, and to interpret load transfer characteristics deduced from experiments on individual MWCNTs.

Point bearing stiffness and strength of socketted drilled shafts in Korean rocks

The load distribution and deformation of rock-socketted drilled shafts subjected to axial loads were evaluated via a load-transfer approach to quantify the point bearing load transfer characteristics of rock-socketted drilled shafts based on Hoek-cell triaxial compressive tests and a three-dimensional numerical analysis with varying rock strengths and rock mass conditions. It was found that the ultimate unit point resistance ( q max ) was influenced by rock mass discontinuities; moreover, the initial tangent of the point bearing load transfer curve ( G i ) was highly dependent on the rock mass modulus and pile diameter. Thus, a point bearing load transfer function for drilled shafts socketted into rock is proposed. Through comparison with the results of field loading tests, it was found that the point load transfer function proposed in the present study is in good agreement with the general trend observed by field loading tests.

Load Transfer Characteristics of Aggregate Interlocking in Concrete Pavement

This paper presents a finite-element model of a jointed concrete pavement with aggregate interlocking load transfer system. Interlocking mechanism has been modeled by a set of discrete springs. A new parameter “modulus of interlocking joint ( Kj ) ” has been introduced to represent the load transfer characteristics of the interlocked joint. Guidelines have been proposed for the selection of the modulus of interlocking joint as a function of aggregate size and joint opening. Stiffness values for the linear springs can be selected using the modulus value Kj . The numerical model, with the joint spring stiffness values selected from the present guidelines, has been validated with experimental results available in literature.

Evaluation of the Biomechanical Characteristic of Tooth Supporting Structure under Occlusal Load

In this work the mechanical response of tooth supporting structure to the occlusal load was analyzed by means of finite element analysis. The attribution of the cementum-dentine junction (CDJ) and cementum to the stress distribution was investigated. Models of block-shape mandible included a premolar with/without cementum-dentine junction (CDJ) and cementums in the supporting structures were constructed. For each case, a load of 50 N was applied to the crown at a 45-degree angle to the long axis of the tooth. The present finite element analyses indicated that incorporation of CDJ and cementum resulted in decreases in the stress levels. These two tissues are important in absorbing and distributing stress thus they should be considered in analyzing the load transfer characteristics within the tooth supporting structure. In addition, this study proved that it is feasible to simplify the finite element model by employing the modified Young's modulus of PDL to realize the function of CDJ. Moreover, an attempt to correlate the results of the current study with the dental implant designing was made.

A Numerical Investigation on the Influence of Steel Fiber Shape and Interface Strength in Reinforced Concrete

Not all steel fiber reinforced concrete composites are equally effective in enhancing structural performance. Their mechanical behaviour strongly depends upon the reinforcement morphology as well as the properties of the interface lying between steel reinforcement and concrete matrix. Using bone-shaped short (BSS) steel fibers, instead of conventional straight short (CSS) steel fibers, to reinforce concrete has demonstrated their potential in improving toughness, ductility and energy absorbing capacity under impact significantly and simultaneously. Accomplishing a strong steel–concrete interface leads to a slight increase in composite strength but simultaneously to a significant decrease in its toughness. Due to the sensitivity of steel reinforced concrete performance on these complex geometric and material parameters, the development of a numerical tool capable of simulating accurately the composite mechanical behaviour and thus leading to optimized design solutions is desirable. The physical problem of the present work involves a typical concrete composite uniformly reinforced with steel fibers subjected to tensional loading. A micromechanical non-linear finite element formulation is utilized in order to predict the load transfer characteristics and the failure process. A linear material behaviour is assumed for the steel component; a non-linear multi-crack material response is used to describe concrete while a mix-mode bilinear behaviour is utilized for the interface providing separation of primary material phases. Numerical results are presented in terms of the global design parameters. The influence of the fiber end shape, the interface strength and the fiber volume fraction on the composite strength and toughness is addressed and consequently optimized design preferences arise.

Load Transfer Characteristics of Aggregate Interlocking in Concrete Pavement

This paper presents a finite-element model of a jointed concrete pavement with aggregate interlocking load transfer system. Interlocking mechanism has been modeled by a set of discrete springs. A new parameter “modulus of interlocking joint (Kj)” has been introduced to represent the load transfer characteristics of the interlocked joint. Guidelines have been proposed for the selection of the modulus of interlocking joint as a function of aggregate size and joint opening. Stiffness values for the linear springs can be selected using the modulus value Kj. The numerical model, with the joint spring stiffness values selected from the present guidelines, has been validated with experimental results available in literature.

Analytical Method for Load-Transfer Characteristics of Rock-Socketed Drilled Shafts

The load-settlement behavior of rock-socketed drilled shafts under axial loading is investigated by a load-transfer approach. Special attention is given to the shear load-transfer function and an analytical method for estimating load-transfer characteristics of rock-socketed drilled shafts. A nonlinear triple curve is employed to determine the shear load-transfer function of rock-socketed drilled shafts based on the constant normal stiffness direct shear tests and the Hoek-Brown failure criterion. An analytical method that takes into account the soil coupling effect was developed using a modified Mindlin’s point load solution. Through comparisons with field case studies, it is found that the proposed methodology in the present study is in good agreement with the general trend observed by in situ measurements and, thus, represents a significant improvement in the prediction of drilled shaft shear behavior.

Load Transfer Characteristics of Dowel Bar System in Jointed Concrete Pavement

In a jointed concrete pavement, the dowel bar system and the aggregate interlock are two mechanisms for transferring wheel loads from one panel to the adjacent panel. The aggregate interlocking load transfer mechanism is effective for narrow joints while the dowel bar system works well for both narrow and wider joints. This paper examines the effects of different parameters on load transfer efficiency of a joint with the help of a three-dimensional finite-element model for the analysis of a dowel-jointed concrete pavement. The model was compared using experimental data available in the literature. The group action of the dowel bar system was also examined and useful relationships have been developed for estimation of the relative load shared by the individual dowel bars. These relationships will be useful in the design and evaluation of dowel jointed concrete pavements.

Load transfer characteristics of unilateral distal extension removable partial dentures with polyacetal resin supporting components

To photoelastically examine load transfer by unilateral distal extension removable partial dentures with supporting and retentive components made of the lower stiffness polyacetal resins. A mandibular photoelastic model, with edentulous space distal to the right second premolar and missing the left first molar, was constructed to determine the load transmission characteristics of a unilateral distal extension base removable partial denture. Individual simulants were used for tooth structure, periodontal ligament, and alveolar bone. Three designs were fabricated: a major connector and clasps made from polyacetal resin, a metal framework as the major connector with polyacetal resin clasp and denture base, and a traditional metal framework I-bar removable partial denture. Simulated posterior bilateral and unilateral occlusal loads were applied to the removable partial dentures. Under bilateral and left side unilateral loading, the highest stress was observed adjacent to the left side posterior teeth with the polyacetal removable partial denture. The lowest stress was seen with the traditional metal framework. Unilateral loads on the right edentulous region produced similar distributed stress under the denture base with all three designs but a somewhat higher intensity with the polyacetal framework. The polyacetal resin removable partial denture concentrated the highest stresses to the abutment and the bone. The traditional metal framework I-bar removable partial denture most equitably distributed force. The hybrid design that combined a metal framework and polyacetal clasp and denture base may be a viable alternative when aesthetics are of primary concern.

Shear Load Transfer Characteristics of Drilled Shafts Socketed in Rocks

This paper presents a shear load transfer function and an analytical method for estimating the load transfer characteristics of rock-socketed drilled shafts subjected to axial loads. A shear load transfer (f–w) function of rock-socketed drilled shafts is proposed based on the constant normal stiffness (CNS) direct shear tests. It is presented in terms of the borehole roughness and the geological strength index (GSI) so that the structural discontinuities and the surface conditions of the rock mass can be considered. An analytical method that takes into account the coupled soil resistance effects is proposed using a modified Mindlin’s point load solution. Through comparisons with load test results, the proposed methodology is in good agreement with the general trend observed in in situ measurements and represents an improvement in the prediction of the shear behavior of rock-socketed drilled shafts.

Evaluation of Load Transfer and Strut Strength of Deep Beams with Short Longitudinal Bar Anchorages

This paper examines the behavior of struts and nodes in deep beams fabricated using short longitudinal bar anchorages. Laboratory tests were conducted of 12 deep beams in which the longitudinal reinforcement was anchored into the support using short straight bar anchorages. The shortest anchorage lengths provided were below 50% of those required by ACI 318-08 Chapter 12 provisions. Four different specimen groups were constructed using three different shear span-depth ratios (a/d) and two longitudinal bar sizes. Most of the beams failed by strut crushing after yielding of the main longitudinal reinforcement at midspan. Only those specimens with the shortest anchorage length in each group developed concrete splitting failures along the anchorage region. The effect of a/d and anchorage length on strut strength and load transfer mechanism observed in the tests is presented and discussed. Test results indicate that a significant portion of the applied shear force may be transferred through truss action even in beams with low a/d. Short anchorage length affected the load transfer characteristics of the deep beams. These findings can be used in better understanding the merits of different strut-and-tie models for design of deep beams.

Evaluation of load transfer characteristics of a dynamic stabilization device on disc loading under compression

In the current study, finite element analyses were conducted to examine the biomechanical capability of a newly design dynamic stabilization system, FlexPLUS, to restore the load transmission of degenerated intervertebral L4-L5 lumbar motion segment spine under compression. Detailed three-dimensional FE models of L4-L5 motion segment and the FlexPLUS were developed. Compressive loading up to 1000 N was applied to the intact L4-L5 model, the L4-L5 models with slight and moderate degenerated disc, and the implanted L4-L5 model. Further more, the load transmission characteristics of Dynesys and a rigid rod was also simulated for comparison. The resultant load–displacement curves and the load transferred through annulus under various conditions were compared. The predicted axial displacement of L4 top surface against applied compressive force of the intact L4-L5 model agreed well with experimental data. The predicted results showed that degenerated disc has significant effect on the lumbar segment load bearing capacity. Not only the stiffness of the segment was greatly increased, the uniform nature of the disc stress distribution was also altered. The FlexPLUS can effectively reduce the disc loading of degenerated model. Although the non-uniform load distribution pattern through annulus was not improved, the overall stress magnitude was greatly reduced to the level of intact model for grade II degeneration.