Eccentric Cyclic Loading Research Articles

Application of the Cyclic Strain Accumulation Method on Shallow Foundations under Eccentric Cyclic Loading in Sand

Application of the Cyclic Strain Accumulation Method on Shallow Foundations under Eccentric Cyclic Loading in Sand

Behavior of RC columns and those strengthened with FRP composite under an innovative reversing cyclic eccentric axial loading

The fundamental role of columns in structural stability calls for an in-depth understanding of their behavior under different loadings. In this study, an innovative test was designed and the required apparatus was manufactured to apply axial eccentric cyclic loading in two opposite directions as an effort to create more realistic conditions for eccentric axial loading of columns in the structures under cyclic loads. For this purpose, six reinforced concrete (RC) columns were tested. The columns included non-strengthened specimens, those strengthened with longitudinal FRP strips installed using the externally bonded reinforcement on groove (EBROG) technique, and those strengthened with full FRP wraps. All the specimens subjected to axial loading with an eccentricity of 90 mm in both monotonic and reversing cyclic method (the innovative method developed herein) to compare the effects of both cyclic and monotonic loadings. The specimens exhibited reduced bearing capacity and ductility under cyclic loading when compared with those subjected to monotonic. Moreover, the trend of the load-deformation relationship of RC columns and those strengthened with FRP wraps were almost the same under monotonic and cyclic loads, while strengthened specimens with longitudinal FRP exhibited different load-deformation trends. Comparison of the specimens strengthened via the two methods used in this study revealed that using longitudinal FRP sheets via the EBROG technique caused a significant (about 60%) increase in bearing capacity under high eccentric loads through a reduction in ductility. Application of FRP wraps, however, exhibited almost no effect on bearing capacity under the same loads but led to the columns’ enhanced ductility.

Experimental and numerical analyses on aluminium alloy H-section members under eccentric cyclic loading

This paper considered the combination of cyclic load and eccentric load to study the hysteretic performance of H-section 6061-T6 aluminium alloy members For this reason, this study designs and conducts the eccentric cyclic loading test of three H-section 6061-T6 aluminium alloy members with different slenderness ratios based on a reliable test system. The failure form, failure process, and bearing capacity of each member are analysed. The results show that for eccentrically loaded members, no overall buckling is observed during loading. Moreover, the members along the longitudinal direction do not fully develop plasticity, whereby such plasticity in the full sections is avoided. Plastic local buckling controls the failure mechanism of all specimens, leading to degradation in the stiffness of the specimens and generation of subsequent cracks at the local buckling sites of the webs, which in turn leads to fracture failure. Simultaneously, on the basis of the Chaboche hybrid strengthening model, the member model was established using the ABAQUS finite element (FE) software. Furthermore, the material parameters were calibrated using material test data and fitted the cyclic constitutive relationship of aluminium alloy. The effectiveness of the FE simulation method and the rationality of the constitutive model was accurately verified by experimental results. Additionally, the parameter analysis of eighteen members with different cross-sections, slenderness ratios, and eccentricities was carried out. It is shown that the increase of slenderness ratio and eccentricity result in weakening of the energy consumption capacity and bearing capacity obviously, which thereby provides a reference for the seismic design of aluminium alloy structures.

Influence of eccentric cyclic loading on implant components: Comparison between titanium and zirconia abutments

The objective of this study was to investigate the effects of eccentric cyclic loading on implant components using the internal joint system with titanium and zirconia abutments. Abutments were made of either pure titanium (Ti group) or zirconia (TZP group). Cyclic loading test was conducted according to the specifications of ISO 14801. Loading condition was at 2 points assuming axial load and eccentric load. The reverse torque value reduced after the eccentric load and reduced more in the TZP group than the Ti group. Marginal gap changed after eccentric loading, and was greater in the TZP group. In the TZP group, changes in configuration were observed in the implant body, and Ti was detected on the abutment surface. From the above, the eccentric load may have worse effects than axial loads. It was suggested that the TZP group was clinically disadvantageous compared to the Ti group.

Experimental study on cracked steel plates with different damage levels strengthened by CFRP laminates

Strengthening steel structures using CFRP Laminates has recently attracted increasing attention. Several studies focused on the efficiency of this strengthening technique. However, little is known regarding efficiency when applied to steel plates with different levels of damage considering various strengthening schemes for loading conditions other than pure tension. In this research, fatigue behavior of cracked steel plates strengthened with CFRP laminates is experimentally investigated considering several parameters including strengthening scheme and level of damage. Samples are tested under eccentric cyclic loading and efficiency of repair is concluded. Then, a study is followed to examine reliability of available analytical models.

Effect of implant abutment connection designs, and implant diameters on screw loosening before and after cyclic loading: In-vitro study

AimsThe purpose of this in-vitro study was to evaluate the screw loosening of two different forms of implant abutment connection designs, and two implant diameters by measuring removal torque value (RTV) before and after cyclic loading. Materials and methodsTwenty implant fixtures were divided equally into 2 groups (N=10): group I fixture with conical hybrid connection (CH), and group II fixture with internal hex connection (IH). Each group was divided equally into two subgroups according to implant diameters: subgroup A (3.3mm), and subgroup B (4.2mm). Each fixture was vertically placed in the center of an acrylic resin block. The samples were fixed to the jig, and an implant abutment connected it with a 20 Ncm tightening torque. The samples were subjected to eccentric cyclic loading (at a distance of 5mm) away from center of abutment at 100,000 cycles. A digital torque gauge was used to evaluate screw loosening by measuring RTVs in (Ncm) before and after cyclic loading. The removal torque loss ratio before and after cyclic loading and the removal torque loss ratio between before and after cyclic loading were calculated and analyzed using the SPSS statistical analysis. ResultsFor GI the initial removal torque loss ratio measurement was (14.45±3.18) and decreased significantly after loading, it was (11.47±3.64). For GII the initial removal torque loss ratio measurement was (20.47±4.99) and increased significantly after loading, being (35.35±4.26). There is no significant effect upon screw loosening for two implant diameters. ConclusionWithin the limitations of this study, the results suggested that conical hybrid connections showed a better screw stability than an internal hex connection. Therefore, the use of conical implants can be promoted as they have better screw stability compared to other systems.

Effect of cyclic loading on marginal fit of implant–abutment interface for three different connections with telescopic attachment: in-vitro study

Objective The objective of this article was to evaluate the effect of dynamic cyclic loading on marginal fit at implant–abutment interface with three different implant connections using scanning electron microscope. Materials and methods Thirty implant fixtures were divided equally into three groups (N = 10): group I external hex fixture, group II internal hex fixture, group III conical hybrid fixture. Each fixture was vertically placed in the center of epoxy resin block using modified dental surveyor. Matched prefabricated titanium abutments were screwed to the implant and metal coping was adapted onto abutment. The samples were subjected to eccentric cyclic loading (at a distance 2–3 mm) away from center of abutment at three different intervals 10 000, 100 000, 500 000 cycles. Marginal fit was evaluated before and after each cycles by measuring microgap size in (μm) using scanning electron microscope with a magnification ×700. The values of microgap size in um before and after each cyclic loading were collected, tabulated and statistically analyzed using analysis of variance and Tukey's post-hoc test at 0.05 level of significance. Results After cyclic loading the microgap size was measured in all groups and high value was recorded to group I external hex connection 60.64 ± 4.3μm, while minimum value recorded to group III internal conical connections 0.94 ± 0.11 μm and internal hex connection in between 17.98 ± 2.07 μm. Two way analysis of variance showed significant effect upon marginal fit for both connection and cyclic loading. Conclusion The geometric factors of implant–abutment connection and dynamic cyclic loading have effect on marginal fit at implant–abutment interface. Internal conical connections showed a better marginal fit than internal and external hex connection so use of conical implants can be promoted as it has better sealing abilities compared to other systems.

Influence of eccentric cyclic loading on implant components: Comparison between external joint system and internal joint system.

The purpose of this in vitro study was to investigate the influence of eccentric loading on implant components by measuring screw loosening and observing these components under several load positions and magnitudes. The external and internal joint system implants with butt joint connection were subjected to cyclic loading tests according to the specifications of ISO 14801. Load position was set at 0, 4, or 8 mm, and load was set at 100 or 300 N. On the external joint system, the reverse torque values decreased with distal shift in the loading position and an increase in magnitude of load, and abrasion and deformation on the anti-rotation device were observed. On the internal joint system, no large decrease in reverse torque was observed even though increasing the load position and load, however, abrasion and deformation on the anti-rotation device as well as fracture at implant/abutment connection were observed.

Influence of lateral-oblique cyclic loading on abutment screw loosening of internal and external hexagon implants

To date, there is no evidence that internal anti-rotation configurations are better than external ones. The purpose of this study was to evaluate the effect of eccentric cyclic loading on abutment screw loosening in internal and external hexagon implants with either of these two screw materials, titanium (Ti) alloy versus gold alloy. The reverse torque value of the abutment screw was measured before (initial preload) and after loading (post-loading). The prepared assemblies were divided into four groups (A to D). Groups A and B used internal hex implants with gold alloy and Ti alloy abutment screws respectively. Groups C and D used external hex implants with gold alloy and Ti alloy abutment screws respectively. In all the groups, post-loading preload was significantly (p<0.05) higher than initial preload. Further, two-way ANOVA indicated that the implant-abutment connection did not have an effect, but the abutment screw material did. In particular, Ti abutment screws were less likely to come loose.

Isokinetic eccentric exercise can induce skeletal muscle injury within the physiologic excursion of muscle-tendon unit: a rabbit model.

Background and PurposeIntensive eccentric exercise can cause muscle damage. We simulated an animal model of isokinetic eccentric exercise by repetitively stretching stimulated triceps surae muscle-tendon units to determine if such exercise affects the mechanical properties of the unit within its physiologic excursion.MethodsBiomechanical parameters of the muscle-tendon unit were monitored during isokinetic eccentric loading in 12 rabbits. In each animal, one limb (control group) was stretched until failure. The other limb (study group) was first subjected to isokinetic and eccentric cyclic loading at the rate of 10.0 cm/min to 112% (group I) or 120% (group II) of its initial length for 1 hour and then stretched to failure. Load-deformation curves and biomechanical parameters were compared between the study and control groups.ResultsWhen the muscle-tendon unit received eccentric cyclic loading to 112%, changes in all biomechanical parameters – except for the slope of the load-deformation curve – were not significant. In contrast, most parameters, including the slope of the load-deformation curve, peak load, deformation at peak load, total energy absorption, and energy absorption before peak load, significantly decreased after isokinetic eccentric cyclic loading to 120%.ConclusionWe found a threshold for eccentrically induced injury of the rabbit triceps surae muscle at between 12% and 20% strain, which is within the physiologic excursion of the muscle-tendon units. Our study provided evidence that eccentric exercise may induce changes in the biomechanical properties of skeletal muscles, even within the physiologic range of the excursion of the muscle-tendon unit.

Biomechanical Evaluation of Vertebroplasty and Kyphoplasty With Polymethyl Methacrylate or Calcium Phosphate Cement Under Cyclic Loading

We developed a new method to simulating in vivo dynamic loading as closely as possible, which allows comparison of kyphoplasty and vertebroplasty, as well as augmentation materials. Special interest was given to calcium phosphate cement, which might fail due to its brittleness. Vertebroplasty and kyphoplasty are, with limitations, 2 promising alternative techniques to augment osteoporotic vertebrae with polymethyl methacrylate or calcium phosphate cements. However, little is known about the fatigue characteristics of the treated vertebrae under cyclic loading. Twenty-four intact, osteoporotic bi-segmental human specimens were divided into 4 groups: (1) vertebroplasty with polymethyl methacrylate, (2) kyphoplasty with polymethyl methacrylate, (3) kyphoplasty with calcium phosphate cement, and (4) untreated control group. After augmentation of the middle vertebrae, all specimens underwent 100,000 cycles of eccentric loading during which the specimen revolved around its longitudinal axis. Pre-loading and post-loading radiographs, and subsidence measurements at different sites of the vertebrae were taken. The overall height was additionally determined every 20,000 cycles in the material testing machine. Finally, the specimens were cryosectioned to examine the cements. Loss of height progressed with strong individual differences in all groups, with an increasing number of load cycles up to median values of 2.8 mm for both augmented groups and 4.2 mm for the nonaugmented group. At the center of the upper endplate, subsidence in kyphoplasty was greater than in vertebroplasty, with little differences with respect to the kind of cement. The cryosections did not show any signs of fatigue in the polymethyl methacrylate, but small cracks were in the calcium phosphate. Vertebroplasty and kyphoplasty seem to be equivalent methods in strengthening osteoporotic vertebrae. However, these results cannot be transferred to the treatment of fractures with these methods. A "physiologic" loading situation was achieved by complex motion, including all combinations of flexion/extension with lateral bending during eccentric cyclic loading.

The effect of eccentric loading on the fatigue performance of high-tensile bolts

The effect of eccentric cyclic loading on the fatigue life of bolts has been investigated. It was found that eccentric loading reduced the fatigue life of bolts by an amount proportional to the increase in the local stress amplitude produced by the eccentricity. The increase in local mean stress due to eccentricity was found not to affect the fatigue life, and eccentric loading was found not to affect significantly the shape of fatigue cracks.