Compressive Peak Strain Research Articles

In vivo evaluation of ankle kinematics and tibiotalar joint contact strains using digital volume correlation and 3 T clinical MRI

BackgroundIn vivo evaluation of ankle joint biomechanics is key to investigating the effect of injuries on the mechanics of the joint and evaluating the effectiveness of treatments. The objectives of this study were to 1) investigate the kinematics and contact strains of the ankle joint and 2) to investigate the correlation between the tibiotalar joint contact strains and the prevalence of osteochondral lesions of the talus distribution. MethodsEight healthy human ankle joints were subjected to compressive load and 3 T MRIs were obtained before and after applying load. The MR images in combination with digital volume correlation enabled non-invasive measurement of ankle joint kinematics and tibiotalar joint contact strains in three dimensions. FindingsThe total translation of the calcaneus was smaller (0.48 ± 0.15 mm, p < 0.05) than the distal tibia (0.93 ± 0.16 mm) and the talus (1.03 ± 0.26 mm). These movements can produce compressive and shear joint contact strains (approaching 9%), which can cause development of lesions on joints. 87.5% of peak tensile, compressive, and shear strains in the tibiotalar joint took place in the medial and lateral zones. InterpretationThe findings suggested that ankle bones translate independently from each other, and in some cases in opposite directions. These findings help explain the distribution of osteochondral lesions of the talus which have previously been observed to be in medial and lateral regions of the talar dome in 90% of cases. They also provide a reason for the central region of talar dome being less susceptible to developing osteochondral lesions.

The influence of running shoe with different carbon-fiber plate designs on internal foot mechanics: A pilot computational analysis

A carbon-fiber plate (CFP) embedded into running shoes is a commonly applied method to improve running economy, but little is known in regard the effects of CFP design features on internal foot mechanics. This study aimed to explore how systematic changes in CFP geometrical variations (i.e., thickness and location) can alter plantar pressure and strain under the forefoot as well as metatarsal stress state through computational simulations. A foot-shoe finite element (FE) model was built and different CFP features including three thicknesses (1 mm, 2 mm, and 3 mm) and three placements (high-loaded (just below the insole), mid-loaded (in between the midsole), and low-loaded (just above the outsole)) were further modulated within the shoe sole. Simulations were conducted at the impact peak instant during forefoot strike running. Compared with the no-CFP shoe, peak plantar pressure and compressive strain under the forefoot consistently decreased when the CFP thickness increased, and the low-loaded conditions were found more effective (peak pressure decreased up to 31.91% and compressive strain decreased up to 18.61%). In terms of metatarsal stress, CFP designs resulted in varied effects and were dependent on their locations. Specifically, high-loaded CFP led to relatively higher peak metatarsal stress without the reduction trend as thickness increased (peak stress increased up to 12.91%), while low-loaded conditions showed a gradual reduction in peak stress, decreasing by 0.74%. Therefore, a low-loaded thicker CFP should be considered to achieve the pressure-relief effects of running shoes without the expense of increased metatarsal stress.

Study on axial compressive stress-strain relationship of alkali-activated slag lightweight aggregate concrete

Alkali slag lightweight aggregate concrete (AAS-LWAC) is a new type of green concrete prepared by alkali excited slag as cementing material and lightweight aggregate as coarse aggregate. It can effectively reduce the amount of Polandite cement and reduce carbon dioxide emission. However, there are no relevant studies on its axial compression constitutive properties. The effects of the type of lightweight aggregate, fiber type, and fiber content on the elastic modulus Ec, peak compressive strain εc, and axial compressive strength fcc of AAS-LWAC were studied in this paper. A suitable AAS-LWAC axial compression constitutive model is proposed. Scanning Electron Microscope (SEM) and Computed Tomography (CT) experiments were carried out to reveal the influence mechanism of the microstructure on the axial compressive properties of AAS-LWAC. The results show that AAS-LWAC with pulverized coal ash ceramsite as coarse aggregate has the highest axial compressive strength and peak compressive strain, and AAS-LWAC with shale ceramsite as coarse aggregate has the highest elastic modulus. Steel fiber can significantly enhance the axial compressive strength and peak compressive strain of AAS-LWAC, and the improvement effect is the best when the volume content of steel fiber is 0.6%. Three kinds of fibers can increase the elastic modulus of AAS-LWAC, and the effect of steel fiber is the most obvious.

Study on the stress–strain full curve of recycled coarse aggregate concrete under uniaxial compression

The study of stress–strain full curves of recycled coarse aggregate concrete (RCAC) with different substitution rates at C25 and C35 strength grades is lacking, which is the basic theory for design and simulation. Therefore, this ignored problem was studied through experiment, theoretical analysis and simulation. Firstly, the load-deformation full curve, failure process and failure mode of 48 RCAC prismatic specimens were studied by uniaxial compression test. Secondly, the peak compressive stress, elastic modulus, peak compressive strain, and ultimate compressive strain of RCAC with different substitution rates under different strengths were analyzed, and the formula was proposed. Then, it was found that the slope of the descending section of the stress–strain curve fluctuated after the addition of recycled coarse aggregate, which is different from the monotonic increase rule found by other scholars. The constitutive equation of natural concrete was used for RCAC, and the parameters of the descending section for different substitution rates at C25 and C35 grades were obtained and verified. Subsequently, Software for Calculating RCAC Stress-Strain Curve was developed for the convenient application of the proposed constitutive equation. Finally, the tests were simulated by the concrete damage plastic (CDP) model, and the parametric study found that the expansion angle and mesh size had little effect on the results, but had a significant impact on the computational cost. The smaller the viscosity coefficient, the more accurate the calculation result and the longer the time-consuming. The conclusions are meaningful for the design and fine analysis of RCAC structure.

Creep and post-creep mechanical properties of reinforced concrete columns

In this study, 32 groups of reinforced concrete axial compression columns were examined using creep tests and axial compression failure tests after creep. The reinforced concrete columns were of strength grade C30–C60, load level 0.09–0.38, and total reinforcement ratio 0.79–2.01%. This study investigated the effects of the axial compressive strength of concrete under loading, the load level, and the total reinforcement ratio of longitudinal compression steel bars on the creep and post-creep mechanical properties of reinforced concrete short columns under axial compression. A formula for calculating the creep of reinforced concrete short columns under axial compression is proposed. A formula for calculating the peak compressive strain of reinforced concrete short columns under axial compression considering the effect of creep is established.

Experimental and numerical research of ultrahigh performance concrete layered shell element based on a two-dimensional fixed crack model

Ultrahigh performance concrete (UHPC) is a cement-based material with superior characteristics including tension strain-hardening and multi-cracking, which is attractive for application in the field of assembled structures. However, a reliable method for simulating the mechanical behaviour of UHPC structures is lacking. Thus, this study proposes a two-dimensional fixed crack constitutive model for UHPC using the MSC.MARC software based on the experimental results, which is expected to offer high reliability. The stirrup restraint effect, tensile strength hardening, stiffness degradation, and the tension–compression softening of UHPC were considered in the constitutive model. To calibrate the relevant parameters of the constitutive model, UHPC prism and dog-bone specimens with different steel fibre contents were fabricated. Through uniaxial compressive and tensile tests with different loading regimes, the effects of steel fibre content, maintenance mode, and the loading regime on the uniaxial mechanical properties of UHPC were analysed. The test results showed that the peak compressive strain of the specimen with 2% steel fibre content was significantly higher than those of the specimens with 1% and 3% steel fibre content. Furthermore, UHPC exhibits strain hardening and ductility in the tensile experiments. The steel fibre content and steam curing significantly improved the tensile strength of the UHPC specimens. Based on the test data, the skeleton curves and hysteresis criteria of UHPC under compression and tension were proposed, and the formulae describing the process of unloading and reloading, which can be used for the basic constitutive model of UHPC, were fitted. Finally, five UHPC shear wall specimens were designed and simulated through the proposed model. The numerical results obtained using the proposed constitutive model and modelling methodology, including the skeleton curves, failure modes, ductility, and the deformation capacity of the UHPC shear walls, agreed significantly with the experimental results, confirming the reliability and high accuracy of the proposed UHPC constitutive model, thereby increasing the applicability of UHPC.

VEGFA from osteoblasts is not required for lamellar bone formation following tibial loading.

The relationship between osteogenesis and angiogenesis is complex. Normal bone development requires angiogenesis, mediated by vascular endothelial growth factor A (VEGFA). Studies have demonstrated through systemic inhibition or genetic modification that VEGFA is indispensable for several types of bone repair, presumably via its role in supporting angiogenesis. But a direct role for VEGFA within osteoblasts, in the absence of angiogenesis, has also been suggested. To address the question of whether VEGFA from osteoblasts supports bone formation directly, we applied anabolic loading to induce lamellar bone formation in mice, a process shown to be independent of angiogenesis. We hypothesized that VEGFA from osteoblasts is required for lamellar bone formation. To test this hypothesis, we applied axial tibial compression to inducible Cre/LoxP mice from three lines. Vegfafl/fl mice were crossed with Ubiquitin C (UBC), Osterix (Osx) and Dentin-Matrix Protein 1 (DMP1) Cre-ERT2 mice to target all cells, (pre)osteoblast-lineage cells, and mature osteoblasts and osteocytes, respectively. Genotype effects were determined by comparing control (Vegfafl/fl) and Cre+ (VegfaΔ) mice for each line. At 5months of age tamoxifen was injected for 5days followed by a 3-week clearance prior to loading. Female and male mice (N=100) were loaded for 5days to peak forces to engender -3100με peak compressive strain and processed for dynamic histomorphometry (day 12). Percent MS/BS increased 20-70% as a result of loading, with no effect of genotype in Osx or Dmp1 lines. In contrast, the UBC groups had a significant decrease in relative periosteal BFR/BS in VegfaΔ vs. Vegfafl/fl mice. The UBC line did not have any cortical bone phenotype in non-loaded femurs. In summary, dynamic histomorphometry data confirmed that tibial loading induces lamellar bone formation. Contrary to our hypothesis, there was no decrease in loading-induced bone formation in the Osx or Dmp1 lines in the absence of VEGFA. There was a decrease in bone formation in the UBC line where all cells were targeted. This result indicates that VEGFA from a non-osteoblast cell source supports loading-induced lamellar bone formation, although osteoblast/osteocyte VEGFA is dispensable. These findings support a paracrine model whereby non-osteoblast VEGFA supports lamellar bone formation, independent of angiogenesis.

A flexural ductility model for UHPC beams reinforced with FRP bars

Ultra-high performance concrete (UHPC) beams reinforced with fiber-reinforced polymer (FRP) bars (FRP-UHPC beams) exhibit high flexural stiffness and small crack width at the serviceability limit state. However, a proper model considering FRP-UHPC beams’ mechanical characteristics is lacking to evaluate their flexural ductility. In this paper, based on a rigorous nonlinear cross-section analysis and the conjugate beam method, the applicability of existing ductility models of FRP bar-reinforced normal concrete beams (FRP-NC beams) to FRP-UHPC beams was discussed, and these ductility models were modified after investigating the FRP-UHPC beams’ strain limits in serviceability limit state. A new model by setting the FRP’s allowable strain in Newhook model as 3000με was finally adopted after considering that FRP-UHPC beams have smaller crack width. Calculation results by the modified Newhook model suggested that high reinforcement ratio in FRP-UHPC beams has unfavorable effect on the flexural ductility. Moreover, the influence of key material parameters, including the compressive strength of UHPC, peak compressive strain of UHPC, first cracking strength of UHPC and the type of FRP bars, on the flexural ductility was analyzed. Finally, a theoretical model for predicting overall factor-reinforcement ratio curve calculated by the modified Newhook model was proposed.

Mechanical Properties and Uniaxial Failure Behavior of Concrete with Different Solid Waste Coarse Aggregates.

To reveal the differences between the mechanical properties of solid waste coarse aggregate concrete and natural coarse aggregate concrete (NCAC) under equal strength, the basic mechanical properties of coarse aggregate concrete with seven different solid wastes (i.e., self-combusted coal gangue, uncombusted coal gangue, marble sheet waste, granite sheet waste, iron waste rock, recycled concrete, and self-combusted coal gangue ceramicite) were tested, and the trends in failure morphology, elastic modulus, and the stress–strain full curves of the different solid waste coarse aggregate concretes were analyzed and compared with NCAC. Finally, the interfacial structure of the concrete was characterized by SEM. The results showed that C30 strength grade concrete was prepared with different solid waste coarse aggregates; however, the 28 d compressive strength, split tensile strength, axial compression strength, flexural strength, and elastic modulus of the concrete was 35.26–47.35, 2.13–3.35, 26.43–42.70, 2.83–3.94, and 17.3–31.2, respectively. The modulus of elasticity of the solid waste coarse aggregate concrete was smaller than the NCAC under equal strength, with a maximum difference of 45%. The peak compressive strain and ultimate compressive strain were larger than the NCAC, with a maximum difference of 43%. The crushing value of the solid waste coarse aggregate affected the splitting tensile strength, flexural strength, and modulus of elasticity of the concrete to a greater extent than the compressive strength. The transition zone at the concrete interface of the coarse aggregates with different solid wastes varied widely. The porous micro-pumping effect of the self-combusted gangue and self-combusted gangue vitrified reinforced the concrete interface transition zone, and the polished surface of sheet waste, uncombusted gangue, and recycled concrete aggregate surface adhesion weakened the interface transition zone; Finally, the uniaxial compressive stress–strain curve model for concrete with different solid waste coarse aggregates was established based on the Guo Zhenhai model.

Development of new layered compression casting approach for concrete

Compression casting is a highly effective approach for improving the performance of normal concrete significantly without any additional material/chemical and extra costs. The technology is suitable for manufacturing precast concrete members. However, compression casting of full-scale structural members like beams and columns is challenging due to the high compression pressure required and the limitations of the load-bearing capacity of mould and casting facilities. This study proposes a Layered Compression Casting (LCC) method to overcome the aforementioned problems. For this reason, the influence of casting parameters, including compression pressure P, height of casting layer H, compression duration T, cement content C, water to cement ratio W/C, and Recycled Aggregates (RA) dosage, on the compressive strength, peak strain, elastic modulus, and stress-strain behavior of LCC concrete is investigated. The results reveal that the compressive strength and modulus of elasticity of LCC concrete are significantly improved compared to traditional concrete (up to almost 100% and 50%, respectively). Based on the results obtained from this study and considering compression casting efficiency, the following optimum LCC parameters are recommended: H = 300 mm, P = 15 MPa, and T = 2 min. Furthermore, empirical models are developed/evaluated to predict the compressive strength, peak compressive strain, elastic modulus, and stress-strain relationship of the LCC concrete.

Prediction of Mechanical Behaviours of FRP-Confined Circular Concrete Columns Using Artificial Neural Network and Support Vector Regression: Modelling and Performance Evaluation.

The prediction and control of the mechanical behaviours of fibre-reinforced polymer (FRP)-confined circular concrete columns subjected to axial loading are directly related to the safety of the structures. One challenge in building a mechanical model is understanding the complex relationship between the main parameters affecting the phenomenon. Artificial intelligence (AI) algorithms can overcome this challenge. In this study, 298 test data points were considered for FRP-confined circular concrete columns. Six parameters, such as the diameter-to-fibre thickness ratio (D/t) and the tensile strength of the FRP (ffrp) were set as the input sets. The existing models were compared with the test data. In addition, artificial neural networks (ANNs) and support vector regression (SVR) were used to predict the mechanical behaviour of FRP-confined circular concrete columns. The study showed that the predictive accuracy of the compressive strength in the existing models was higher than the peak compressive strain for the high dispersion of material deformation. The predictive accuracy of the ANN and SVR was higher than that of the existing models. The ANN and SVR can predict the compressive strength and peak compressive strain of FRP-confined circular concrete columns and can be used to predict the mechanical behaviour of FRP-confined circular concrete columns.

Thermal and mechanical analysis of the China–Russia Crude Oil Pipeline suffering settlement disaster in permafrost regions

In permafrost regions, the soil settlement disaster owing to permafrost degradation has become one of the important reasons for buried warm-oil pipelines failure. In this paper, the 3D sequential thermo-mechanical coupled model is carried out to investigate the interaction between buried warm-oil pipeline and surrounding permafrost. The effects of parameters, including thaw-settlement coefficient, length of transition zone, diameter-thickness ratio and internal pressure, on the pipeline mechanical behavior are numerically investigated. Among them, the thaw-settlement coefficient and length of transition zone present more significant effects on the peak strain of the pipeline. In addition, the effects of insulation layer and two-phase closed thermosyphon (TPCT) on pipeline–soil interaction are investigated in thermal and mechanical fields. With no protective measure, the permafrost layer under pipeline will completely degrade in about 20 years with 0.33m/a. The pipeline is considered to reach failure limitation even within 10 years. However, under the influence of combined measure, the permafrost degradation rate is only about 1/10 of that without protective measure. The peak compressive strain is significantly lower than the critical compressive strain, and the pipeline remains safe for 50 years. Therefore, the combined measure is an ideal method for ensuring pipeline safety in permafrost regions.

Multidirectional basketball activities load different regions of the tibia: A subject-specific muscle-driven finite element study.

The tibia is a common site for bone stress injuries, which are believed to develop from microdamage accumulation to repetitive sub-yield strains. There is a need to understand how the tibia is loaded in vivo to understand how bone stress injuries develop and design exercises to build a more robust bone. Here, we use subject-specific, muscle-driven, finite element simulations of 11 basketball players to calculate strain and strain rate distributions at the midshaft and distal tibia during six activities: walking, sprinting, lateral cut, jumping after landing, changing direction from forward-to-backward sprinting, and changing direction while side shuffling. Maximum compressive strains were at least double maximum tensile strains during the stance phase of all activities. Sprinting and lateral cut had the highest compressive (-2,862±662 με and -2,697±495 με, respectively) and tensile (973±208 με and 942±223 με, respectively) strains. These activities also had the highest strains rates (peak compressive strain rate=64,602±19,068 με/s and 37,961±14,210 με/s, respectively). Compressive strains principally occurred in the posterior tibia for all activities; however, tensile strain location varied. Activities involving a change in direction increased tensile loads in the anterior tibia. These observations may guide preventative and management strategies for tibial bone stress injuries. In terms of prevention, the strain distributions suggest individuals should perform activities involving changes in direction during growth to adapt different parts of the tibia and develop a more fatigue resistant bone. In terms of management, the greater strain and strain rates during sprinting than jumping suggests jumping activities may be commenced earlier than full pace running. The greater anterior tensile strains during changes in direction suggest introduction of these types of activities should be delayed during recovery from an anterior tibial bone stress injury, which have a high-risk of healing complications.

A subject-specific FEM to predict deep tissue mechanical stresses when supine: Development of efficient contact interfaces using Shared Topology

Prior studies have demonstrated Finite Element (FE) analysis is a useful tool when analysing the complex interplay of tissue and body loads which act through the human pelvis in a subject lying supine. The computational accuracy and efficiency of FE models that contain complex non-linear geometric interfaces between different anatomical and tissue regions can be compromised by superfluous node interactions and contact penetrations. This study proposes a method for the development of efficient contact definitions using shared topology. The Shared Topology Finite Element Model (FEM) resulted in a 37% reduction in solution time compared to an equivalent FEM defined with Bonded contact. At all tissue interfaces, contact penetration occurred in the Bonded FEM, with subsequent under-prediction of peak compressive strains and stresses by 1–7% compared to the Shared Topology FEM. Simulating supine lying of a 19-year-old male, the Shared Topology FEM predicted peak compressive stress in the muscle interfacing the sacrum of 29.4 kPa, and peak compressive strain of 50%. The proposed methodology can be applied for any medical imaging derived FEM where there are multiple congruent 3D geometries with negligible sliding across interfaces.

Interactive Effects of Five Dental Implant Design Parameters on the Peak Strains at the Interfacial Bone: A Finite Element Study.

The aim of this study was to evaluate and compare the effect of changing five macrostructural design parameters of dental implants on the peak strains experienced by the interfacial bone. Five geometric variables, including three body-related (implant length, diameter, and taper) and two thread-related (thread depth and thread angle) parameters, were defined. The alveolar bone was modeled as a block with anisotropic and linearly elastic properties with 20-mm height and 12-mm buccolingual and mesiodistal dimensions. Oblique occlusal loads (100-N vertical and 20-N horizontal) were applied to the abutment surface. A total of 162 models with different designs were defined by implementation of a full-factorial design. The peak values of the compressive and tensile principal strains in the cortical and cancellous bones were calculated by finite element analysis (FEA). Implant diameter and length had maximum and minimum effects on the peak compressive and tensile strains at the cortical interface, respectively. Implant diameter and thread depth had maximum and minimum effects on the maximum compressive strain at the cancellous interface, while thread angle and length had maximum and minimum significant effects on the maximum tensile strain at the cancellous interface. The interaction of thread parameters and taper has the greatest effect on the peak compressive and tensile strains at the cancellous interface and also on the peak tensile strain at the cortical interface, while body-related parameters are more effective on the peak compressive strain at the cortical interface.

Multi-response optimization of hybrid fibre engineered cementitious composite using Grey-Taguchi method and utility concept

This paper presents an experimental investigation conducted to assess the suitability of Taguchi-Grey relational analysis (GRA) and Taguchi method with utility concept (UC) for mix design optimization of a hybrid fibre engineered cementitious composite (ECC). Slag, fly ash and dolomite are utilized as binder materials and the quantity of various constituents of ECC is optimized to achieve improved compressive and tensile performance. In addition, two weighting techniques based on equal weight and maximum deviation are employed in the analysis and their effects on improving the efficiency of the optimization approach is also assessed. The design of experiments is first carried out using a standard Taguchi orthogonal array consisting of five factors viz. total cement replacement level, dolomite to binder ratio, slag to fly ash ratio, fibre proportions, and water binder ratio, at four levels. Thereafter, GRA and UC are applied to evaluate the composite indices and compute the optimal proportions targeting five response parameters namely compressive strength, peak compressive strain, elastic modulus, tensile strength, and ultimate tensile strain. Results indicate that both GRA and UC can be effectively integrated with Taguchi method for obtaining an optimal mix design of the ECC. Moreover, the use of weighting technique based on the maximum deviation method is found to be more appropriate as it can distinguish between relative effectiveness of different response parameters. The best performing mix had total cement replacement of 60%, 15% dolomite content by binder, slag to FA ratio of 1:0.2, 2.25% total fibre content, water-binder ratio of 0.20 and exhibited desired compressive and tensile properties for structural applications.

Seismic design method and plastic hinge of square steel tube confined reinforced concrete (STRC) columns

Steel tube confined reinforced concrete columns have the advantages of high bearing capacity, good ductility and convenient construction, which meet the requirements of "building industrialization", so they are widely used in high-rise buildings. Based on the plastic-damage constitutive model of concrete and elastic-plastic mixed strengthen constitutive model of steel, finite element software ABAQUS was used to build an elaborate 3D finite element solid model and perform pseudo-static analysis of square steel tube confined RC(STRC) columns. The model considered the confinement effect of the steel tube exerting on the core concrete, as well as reasonable boundary conditions and loading modes. Good agreement was achieved between the finite element analysis results and the existing quasi static experimental results regarding to the failure modes, load-displacement hysteretic curves and load-displacement skeleton curves. Based on the validated model, 136 full scale model examples were established and extensive parametric analysis was conducted. The results show that the confinement of external steel tube can reduce the peak compressive strain and increase the peak compressive stress of concrete, thus delaying the failure of RC column and improving its bearing capacity and ductility effectively. Besides, the failure displacement angle and ultimate bearing capacity increase when the thickness of steel tube increases. Finally, the seismic design method including reasonable thickness and hoop index of the steel tube were proposed for 5 material strength matching and different axial compression ratios. A method to judge the plastic hinge based on concrete strain and steel tube strain was proposed, as well as a practical calculation formula of plastic hinge length. This study can provide basis and support for the seismic design of frame columns.

Intubation Biomechanics: Clinical Implications of Computational Modeling of Intervertebral Motion and Spinal Cord Strain during Tracheal Intubation in an Intact Cervical Spine.

In a closed claims study, most patients experiencing cervical spinal cord injury had stable cervical spines. This raises two questions. First, in the presence of an intact (stable) cervical spine, are there tracheal intubation conditions in which cervical intervertebral motions exceed physiologically normal maximum values? Second, with an intact spine, are there tracheal intubation conditions in which potentially injurious cervical cord strains can occur? This study utilized a computational model of the cervical spine and cord to predict intervertebral motions (rotation, translation) and cord strains (stretch, compression). Routine (Macintosh) intubation force conditions were defined by a specific application location (mid-C3 vertebral body), magnitude (48.8 N), and direction (70 degrees). A total of 48 intubation conditions were modeled: all combinations of 4 force locations (cephalad and caudad of routine), 4 magnitudes (50 to 200% of routine), and 3 directions (50, 70, and 90 degrees). Modeled maximum intervertebral motions were compared to motions reported in previous clinical studies of the range of voluntary cervical motion. Modeled peak cord strains were compared to potential strain injury thresholds. Modeled maximum intervertebral motions occurred with maximum force magnitude (97.6 N) and did not differ from physiologically normal maximum motion values. Peak tensile cord strains (stretch) did not exceed the potential injury threshold (0.14) in any of the 48 force conditions. Peak compressive strains exceeded the potential injury threshold (-0.20) in 3 of 48 conditions, all with maximum force magnitude applied in a nonroutine location. With an intact cervical spine, even with application of twice the routine value of force magnitude, intervertebral motions during intubation did not exceed physiologically normal maximum values. However, under nonroutine high-force conditions, compressive strains exceeded potentially injurious values. In patients whose cords have less than normal tolerance to acute strain, compressive strains occurring with routine intubation forces may reach potentially injurious values.

Self-sensing ultra-high performance concrete for in-situ monitoring

Owing to the excellent mechanical strength and durability, ultra-high performance concrete (UHPC) has been used for ultra-high, large-scale and military infrastructures. Endowing self-sensing properties to UHPC is conducive to realize in-situ monitoring and improve the safety of infrastructures. Therefore, the mechanical, electrical and self-sensing properties of UHPC with stainless steel fibers (SFs) and copper coated steel fibers (CCSFs) were studied in this paper. The results show that the addition of 1.2 vol% CCSFs can effectively improve the deformability of UHPC, as reflected by the improvement in peak compressive strain of 33.7%. UHPC with stainless SFs and CCSFs exhibits good synchronization and repeatability of self-sensing property under three different cyclic loading amplitudes within elastic regime. The highest strain sensitivity of UHPC with stainless SFs under 37.5 MPa of cyclic compressive loading is 26.6. Strain sensitivity of 28.2 is obtained for UHPC containing 1.2 vol% CCSFs under monotonic peak load, along with the monitoring compressive stress ranging from 0 to 125.7 MPa. The electrical resistivity of UHPC with stainless SFs and CCSFs can be used to in-situ monitor the stress, strain and damage development of structures.

Multi-fidelity approach for uncertainty quantification of buried pipeline response undergoing fault rupture displacements in sand

A new efficient approach for uncertainty quantification of pipeline structural response undergoing reverse-slip fault rupture displacements in sand is presented using multi-fidelity Gaussian processes. Uncertainty quantification problems generally take large numbers of scenarios to be analysed considering variations in the influencing parameters. Analysing large numbers of computationally expensive detailed geo-technical numerical models is practically not feasible. Hence, a multi-fidelity approach employing Gaussian process is proposed to tackle this problem which combines the accuracy of a relatively few number of detailed geo-technical numerical models and the efficiency of large numbers of simplified numerical models to track the uncertainty response. The detailed model utilizes a previously validated pipe-soil finite element (FE) model including a non-linear sand constitutive model implemented in finite element software ABAQUS. The simplified model utilizes beam element pipe and bi-linear soil springs. The multi-fidelity model is first trained using data from high-fidelity and low-fidelity model analyses, thereafter cross-validated and subsequently used to quantify uncertainty in the peak compressive strains generated and to identify the most sensitive input variables. Finally, fragility curves are derived for a site specific pipe-soil fault rupture problem.