Static Overloading Research Articles

Centrifugal model test of deep covered karst collapse induced by static overloading of dense building groups

Centrifugal model test of deep covered karst collapse induced by static overloading of dense building groups

TRPV4 differentially controls inflammatory cytokine networks during static and dynamic compression of the intervertebral disc.

The ion channel transient receptor potential vanilloid 4 (TRPV4) critically transduces mechanical forces in the IVD, and its inhibition can prevent IVD degeneration due to static overloading. However, it remains unknown whether different modes of loading signals through TRPV4 to regulate the expression of inflammatory cytokines. We hypothesized that TRPV4 signaling is essential duringstatic and dynamic loading to mediate homeostasis and mechanotransduction. Mouse functional spine units were isolated and either cyclically compressed for 5 days (1 Hz, 1 h, 10% strain) or statically compressed (24 h, 0.2 MPa). Conditioned media were monitored at 6 h, 24 h, 2 days, and 5 days, with and without TRPV4 inhibition. Effects of TRPV4 activation was also evaluated without loading. The media was analyzed for a panel of 44 cytokines using a microbead array and then a correlative network was constructed to explore the regulatory relationships during loading and TRPV4 inhibition. After the loading regimen, the IVDs were evaluated histologically for degeneration. Activation of TRPV4 led to an increase interleukin-6 (IL-6) family of cytokines (IL-6, IL-11, IL-16, and leukemia inhibitory factor [LIF]) and decreased the T-cell (CCL3, CCL4, CCL17, CCL20, CCL22, and CXCL10) and monocyte (CCL2 and CCL12) recruiting chemokines by the IVD. Dynamic and static loading each provoked unique chemokine correlation networks. The inhibition of TRPV4 during dynamic loading dysregulated the relationship between LIF and other cytokines, while the inhibition of TRPV4 during static loading disrupted the connectivity of IL-16 and VEGFA. We demonstrated that TRPV4 critically mediates the cytokine production following dynamic and static loading. The activation of TRPV4 upregulated a diverse set of cytokines that may suppress the chemotaxis of T-cells and monocytes, implicating the role of TRPV4 in maintaining the immune privilege of healthy IVD.

Self-reporting damage and enhancing interfacial properties of carbon fiber composites via self-assembly host-guest mechanochromic fluorescent probe

Structural health monitoring (SHM) of carbon fiber reinforced polymer (CFRP) composites under dynamic or static overloading was essential to assure safety and service life. Herein, perylenediimides-γCyclodextrins (PDI-γCD) inclusion complex was first designed by self-assembly host-guest method and used as mechanochromic fluorescent probe to construct a novel carbon fiber (CF@PDI-γCD) interphase, and the interfacial self-reporting damage as well as interface property and reinforcing mechanism of CFRP composites were investigated. PDI-γCD was tailored by N⋯O–H hydrogen bonding between PDI and the cavity of γCD, and the fluorescence switching-on of PDI-γCD was observed under mechanical force. The chemical activity and roughness of CF@PDI-γCD surface were increased. The CF@PDI-γCD surface exhibited slight fluorescence instead of non-fluorescence on CF-pristine and CF-commercial surface, and the green fluorescent change in the interfacial regions was monitored due to the mechanochromic switching-on of PDI-γCD, indicating the micron-scale damage of CF@PDI-γCD composites. The interfacial shear strength (IFSS) of CF@PDI-γCD composites was much higher than that of CF-pristine and CF-commercial composites, which was attributed to synchronous enhancement of mechanical interlocking and chemical bonding between PDI-γCD and epoxy matrix. Consequently, this work presented a potential application in synergistically monitoring damage and enhancing interfacial properties of CFRP composites.

Flexural behaviour of strengthened damaged steel beams using carbon fibre-reinforced polymer sheets

This paper presents the test and finite element analysis results of a study on the flexural behaviour of damaged steel beams strengthened with carbon fibre-reinforced polymer (CFRP) sheets. The test results showed that the yield load, ultimate load and elastic stiffness of the steel beams with 100% loss of tension flange were 68.3%, 73.8% and 13.5% greater than the yield load, ultimate load and elastic stiffness of the steel beam with 28% loss of the web after static loading. The yield load and elastic stiffness of the steel beam after overloading were 8.7% and 24.5% greater than the yield load and elastic stiffness of the steel beam without overloading. The damage level had a significant effect on the yield load, ultimate bearing capacity and elastic stiffness of the steel beams regardless of whether the steel beams were under static loading or overloading. The damaged steel beam could be repaired by CFRP sheets, the increased layers of CFRP sheets could improve the yield load, ultimate bearing capacity and elastic stiffness of the steel beams, and the strains of CFRP sheets would decrease because of overloading. The numerical analysis results showed that compared with the steel beam without overloading, the deflection and strains of the steel beam after overloading were much smaller. The yield load and the elastic stiffness increased with the increment of the overloading amplitude, and the increment of overloading number could reduce the yield load and elastic stiffness. All the yield loads of the steel beams after overloading were greater than the yield loads of the steel beams without overloading, but the ultimate bearing capacities were smaller.

Pre-damage effect on the residual behavior of externally post-tensioned fatigued steel-concrete composite beams

Steel-concrete composite beams in highway bridges are susceptible to various types of damage during their service life. These damages can greatly affect the structural performance and shorten the fatigue life of bridges. The efficacy of adding external post-tensioning, as a strengthening technique, to steel–concrete composite beams that are subjected to fatigue loading is not well investigated. Therefore, this study includes fatigue testing of post-tensioned steel–concrete composite beams with various types of pre-damage. Three of the tested samples were subjected to outdoor environmental changes, cyclic preloading, and static overloading as pre-damages before applying the external post-tensioning. The strengthened samples were exposed to fatigue tests to a million cycles under four-point bending. Samples without pre-damage were tested as references to those with pre-damages. The crack patterns in the concrete decks were evaluated during these tests. Static tests to failure were performed to explore the residual capacities, deformations, and strains of all fatigued samples. The crack patterns in concrete decks were significantly affected by the type of pre-damage that was applied before the post-tensioning. The static overloading pre-damage reduced the number of cracks and their rate of propagation while the exposure to outdoor environment pre-damage induced more cracks, which negatively affected the crack patterns during fatigue loading. Subjecting the sample to plastic deformation pre-damage slightly improved its performance in terms of residual stiffness and ultimate load. The residual ultimate load was increased by 7% relative to the fatigued sample without pre-damage. However, the ductility was reduced by 40% due to the initial plastic deformation. This reduction in ductility was combined with a decrease in the interface slippage between the concrete deck and steel flange.

Modelling delaminations using adaptive cohesive segments with rotations in dynamic explicit analysis

Multiple delamination planes can form when a composite structure is subjected to out-of-plane stresses during static over-loading or impact loading. Numerical modelling of such events is often prohibitively expensive because large numbers of cracks can co-exist and interact, and fracture models usually affect the time step size in explicit solutions. Here a new method called Adaptive Mesh Segmentation is proposed, which introduces segmentation ‘on-the-fly’ in meshes of quadratic finite elements with six degrees of freedom per node, without any intervention from the user and without any reductions in time step size for solution stability. A novel cohesive formulation with rotational degrees of freedom is introduced which increases the resolution of the numerical cohesive zone and allows the use of relatively coarse meshes. Once a critical stress criterion is met, new degrees of freedom are added at element boundaries to model strong discontinuities. A new moment–damage relationship is proposed to link the discontinuity in rotational degrees of freedom with the cohesive zone law which is translational by definition. A method for initiating cohesive tractions and moments with minimal disturbances to the surrounding stress field is also presented. Finally, the model is applied in the analysis of composite delamination benchmarks using relatively coarse meshes and modest model sizes. Considerable improvements in accuracy are observed when compared to conventional methods.

Numerical Study on Failure of Thin Composite Conoidal Shell Roofs Considering Geometric Nonlinearity

Thin laminated composite conoidal shell roofs are popular among civil engineers due to its stiff, singly ruled and aesthetically appealing geometry. Such surfaces may undergo large displacements under transverse static overloading. Since no researchers reported failure of laminated conoids using nonlinear strains the authors aim to fill the void in the literature. A finite element code is proposed considering von-Karman nonlinearity. The study of linear and nonlinear failure loads clearly indicates that the linear formulation wrongly overestimates the failure loads and hence, not acceptable from practical engineering standpoint. Moreover, displacements at failure, the coordinate locations from where the failure initiates and the lamina stress initiating failure in the shell are also studied.

Static axial overloading primes lumbar caprine intervertebral discs for posterior herniation.

IntroductionLumbar hernias occur mostly in the posterolateral region of IVDs and mechanical loading is an important risk factor. Studies show that dynamic and static overloading affect the nucleus and annulus of the IVD differently. We hypothesize there is also variance in the effect of overloading on the IVD’s anterior, lateral and posterior annulus, which could explain the predilection of herniations in the posterolateral region. We assessed the regional mechanical and cellular responses of lumbar caprine discs to dynamic and static overloading.Material and methodsIVDs (n = 125) were cultured in a bioreactor and subjected to simulated-physiological loading (SPL), high dynamic (HD), or high static (HS) overloading. The effect of loading was determined in five disc regions: nucleus, inner-annulus and anterior, lateral and posterior outer-annulus. IVD height loss and external pressure transfer during loading were measured, cell viability was mapped and quantified, and matrix integrity was assessed.ResultsDuring culture, overloaded IVDs lost a significant amount of height, yet the distribution of axial pressure remained unchanged. HD loading caused cell death and disruption of matrix in all IVD regions, whereas HS loading particularly affected cell viability and matrix integrity in the posterior region of the outer annulus.ConclusionAxial overloading is detrimental to the lumbar IVD. Static overloading affects the posterior annulus more strongly, while the nucleus is relatively spared. Hence, static overloading predisposes the disc for posterior herniation. These findings could have implications for working conditions, in particular of sedentary occupations, and the design of interventions aimed at prevention and treatment of early intervertebral disc degeneration.

Influence of the connection design and titanium grades of the implant complex on resistance under static loading

PURPOSEThe purpose of this study was to evaluate the resistance to deformation under static overloading by measuring yield and fracture strength, and to analyze the failure characteristics of implant assemblies made of different titanium grades and connections.MATERIALS AND METHODSSix groups of implant assemblies were fabricated according to ISO 14801 (n=10). These consisted of the combinations of 3 platform connections (external, internal, and morse tapered) and 2 materials (titanium grade 2 and titanium grade 4). Yield strength and fracture strength were evaluated with a computer-controlled Universal Testing Machine, and failed implant assemblies were classified and analyzed by optical microscopy. The data were analyzed using the One-way analysis of variance (ANOVA) and Student's t-test with the level of significance at P=.05.RESULTSThe group IT4S had the significantly highest values and group IT2 the lowest, for both yield strength and fracture strength. Groups IT4N and ET4 had similar yield and fracture strengths despite having different connection designs. Group MT2 and group IT2 had significant differences in yield and fracture strength although they were made by the same material as titanium grade 2. The implant system of the similar fixture-abutment interfaces and the same materials showed the similar characteristics of deformation.CONCLUSIONA longer internal connection and titanium grade 4 of the implant system is advantageous for static overloading condition. However, it is not only the connection design that affects the stability. The strength of the titanium grade as material is also important since it affects the implant stability. When using the implant system made of titanium grade 2, a larger diameter fixture should be selected in order to provide enough strength to withstand overloading.

Dynamic and static overloading induce early degenerative processes in caprine lumbar intervertebral discs.

Mechanical overloading of the spine is associated with low back pain and intervertebral disc (IVD) degeneration. How excessive loading elicits degenerative changes in the IVD is poorly understood. Comprehensive knowledge of the interaction between mechanical loading, cell responses and changes in the extracellular matrix of the disc is needed in order to successfully intervene in this process. The purpose of the current study was to investigate whether dynamic and static overloading affect caprine lumbar discs differently and what mechanisms lead to mechanically induced IVD degeneration. Lumbar caprine IVDs (n = 175) were cultured 7, 14 and 21 days under simulated-physiological loading (control), high dynamic or high static loading. Axial deformation and stiffness were continuously measured. Cell viability, cell density, and gene expression were assessed in the nucleus, inner- and outer annulus. The extracellular matrix (ECM) was analyzed for water, glycosaminoglycan and collagen content. IVD height loss and changes in axial deformation were gradual with dynamic and acute with static overloading. Dynamic overloading caused cell death in all IVD regions, whereas static overloading mostly affected the outer annulus. IVDs expression of catabolic and inflammation-related genes was up-regulated directly, whereas loss of water and glycosaminoglycan were significant only after 21 days. Static and dynamic overloading both induced pathological changes to caprine lumbar IVDs within 21 days. The mechanism by which they inflict biomechanical, cellular, and extracellular changes to the nucleus and annulus differed. The described cascades provide leads for the development of new pharmacological and rehabilitative therapies to halt the progression of DDD.

Featherweight Java with dynamic and static overloading

We propose FMJ (Featherweight Multi Java), an extension of Featherweight Java with encapsulated multi-methods thus providing dynamic overloading. Multi-methods (collections of overloaded methods associated to the same message, whose selection takes place dynamically instead of statically as in standard overloading) are a useful and flexible mechanism which enhances re-usability and separation of responsibilities. However, many mainstream languages, such as, e.g., Java, do not provide it, resorting to only static overloading. The proposed extension is conservative and type safe: both “message-not-understood” and “message-ambiguous” are statically ruled out. Possible ambiguities are checked during type checking only on method invocation expressions, without requiring to inspect all the classes of a program. A static annotation with type information guarantees that in a well-typed program no ambiguity can arise at run-time. This annotation mechanism also permits modeling static overloading in a smooth way. Our core language can be used as the formal basis for an actual implementation of dynamic (and static) overloading in Java-like languages.

Translating Double Dispatch into Single Dispatch

Goals of flexibility and re-usability in typed object-oriented languages suggest the requirement of double dispatch, i.e., the mechanism of dynamically selecting a method not only according to the run-time type of the receiver (single dispatch), but also to the run-time type of the argument. However, many mainstream languages, such as, e.g., C++ and Java, do not provide it, resorting to only single dispatch. In this paper we present a general technique for adding double dispatch as a type-safe language feature, so yielding dynamic overloading and covariant specialization of methods, without extending basic semantics. To this aim we introduce a toy core language, extended to a full form of (non encapsulated) multi methods. Then we define a translation algorithm from multi methods to the core language, that implements double dispatch by using only standard mechanisms of static overloading and single dispatch. As a main feature, our translation preserves type safety, it uses neither RTTI nor type downcasts and does not introduce crucial overhead during method selection.

Microassay for the assessment of low levels of hydroxyproline.

Microassay for the assessment of low levels of hydroxyproline.

Structurally integrated fiber optic damage assessment system for composite materials

Progress toward the development of a fiber optic damage assessment system for composite materials is reported. This system, based on the fracture of embedded optical fibers, has been characterized with respect to the orientation and location of the optical fibers in the composite. Together with a special treatment, these parameters have been tailored to yield a system capable of detecting the threshold of damage for various impacted Kevlar/epoxy panels. The technique has been extended to measure the growth of a damage region which could arise from either impact, manufacturing flaws, or static overloading. The mechanism of optical fiber fracture has also been investigated. In addition, the influence of embedded optical fibers on the tensile and compressive strength of the composite material has been studied. Image enhanced backlighting has been shown to be a powerful and convenient method of assessing internal damage to translucent composite materials.

衝撃過大荷重による疲労き裂進展の遅延現象について

As one of the on-going studies to investigate the fatigue crack growth characteristics in impact fatigue, the fatigue crack growth behavior resulting from the single application of impact over-load was investigated by using Dual-Phase steel with ultimate tensile strength of about 800MPa as an experimental material. Discussions were made on the retardation of crack growth rate, crack opening behavior after over-loading and fractographical aspect in comparison with the results obtained through the application of single static over-load with peak stress hold time of 3min.The major conclusions obtained are summarized as follows:(1) Retardation of crack growth rate after impact over-loading was not so distinct when compared with the case after static over-loading.(2) The values of crack opening ratio after impact over-loading were higher than after static over-loading.(3) Fractographical observations showed that abrasions were caused on the fractured surfaces after impact over-loading, but not so after static over-loading. The following speculation on the crack tip plastic deformed zone was needed to explain the peculiar crack growth behavior after im- pact over-loading as mentioned above. In comparison with the condition of the plastic zone constructed by static over-load, the size of the zone constructed by impact over-load is smaller, but the strength of this small plastic zone is higher, in other words, the higher density of slip bands is attained under impact over-load.

Behavior of Shear Keys and Ordinary Concrete Surface Under Fatigue and Static Overloading

A STANDARD, FULL-SIZED I-SHAPED BRIDGE GIRDER, WITH CAST- IN-PLACE COMPOSITE DECK, WAS BUILT WITH HALF OF THE GIRDER TOP SURFACE CONTAINING STIRRUPS AND SHEAR KEYS AND THE OTHER HALF CONTAINING ONLY SHEAR STIRRUPS. STATIC TESTS, DYNAMIC TESTS, AND A FINAL TEST TO FAILURE REVEALED SIGNIFICANT DATA ON THE RELATIVE PERFORMANCE OF THE TWO TYPES OF SHEAR CONNECTION.