Prediction Of Stiffness Research Articles

Flexural Stiffness of Rectangular Hollow Section (RHS) Trusses

The deflection of the rectangular hollow section (RHS) truss in elastic stage can be divided into two parts: the deformation of the members and the joints. The effect of joint deformation on the overall deflection of the truss remains unclear. A new approach for the prediction of flexural stiffness of RHS truss was developed based on pin-jointed analysis. The chords and the braces of the truss were connected by the springs. The flexural stiffness of the RHS truss can be calculated after the stiffness of the springs was obtained. The approach took the axial stiffness of the truss joints as equal to the stiffness of the springs. Then the calculation of axial stiffness of the RHS K joint was proposed to employ the component method. Finally, the proposed approach was verified by the truss test and finite element (FE) results. The approach was also compared to other two existing approaches. The results showed that the proposed approach had the best accuracy in the prediction of the flexural stiffness of the RHS trusses. The maximum relative error of flexural stiffness against the FE results were always within the range of ±25%. The approach reasonably takes the joint deformation into account. The approach also has the potential to achieve high accuracy with different truss types and loading modes.

PREDICTION OF SYMPTOMS PROGRESSION FOR THE PATIENTS WITH KNEE OSTEOARTHRITIS BASED ON THE QUANTITATIVE STRUCTURAL FEATURES: DATA FROM THE FNIH OA BIOMARKERS CONSORTIUM

Cartilage repair can greatly alleviate the symptoms of the patients with knee osteoarthritis (KOA). However, some imaging results suggest that the patients with obvious cartilage repair may receive insignificant or even no improvement in their symptoms. This study aims to explore the possible reasons based on the structural feature of the knee joint and construct the models used to predict the progression of knee joint symptoms. 551 subjects from Osteoarthritis Biomarkers Consortium FNIH Project in the Osteoarthritis Initiative (OAI) were included and divided into training and test sets. A total of 153 structural features from five quantitative structural feature sets were included to access the structural characteristics of the knee joints. The Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index was used to evaluate the symptoms of the knee joints. A three-step feature selection method were used to screen the structural features. Finally, Naive Bayes (NB), logistic regression (LR), [Formula: see text]-nearest neighbor (KNN), support vector machine (SVM) and random forest (RF) models were constructed based on the selected features, and then compared using the receiver operating characteristic (ROC) curve. The distribution in the demographics and WOMAC symptoms scores of the participants was consistent in the training and test sets. Two demographic features and several structural features were selected using the three-step feature selection method. Among the constructed models, the models used for the progression prediction of pain, stiffness and total scores were better than that of physical function. The performance of RF model was the best while SVM model was the second best, and the performance of the remaining three models in predicting the progression of knee symptoms is indistinguishable. Structural feature-based models for the prediction of knee joint symptoms’ progression were constructed and compared. The constructed model showed good feasibility and accuracy, and may assist clinicians to predict the occurrence or progression of the knee joints symptoms in the evaluation and prognosis of cartilage repair.

Advancement in prediction of shear strength and stiffness of cross laminated timber beams

Cross laminated timber (CLT) beams are mainly used within wall panels, but also standalone in design situations where cross layers have a reinforcing effect concerning stress perpendicular to the beam axis. The stress state in CLT beam members is complex and shear failure is mainly governed by stresses and strains acting in the crossing areas between orthogonally bonded laminations, known as shear failure mode III. The current model suggested for the next version of Eurocode 5 regarding shear strength prediction has certain limitations. Based on model improvement, design proposals regarding shear failure mode III for CLT beams composed of 3 and 5 layers are expanded for CLT with 7 layers. Based on test results of small shear specimens, both design proposals successfully predict shear strength experimentally obtained on beam specimens. Evaluated full-field deformations by a digital image correlation (DIC) system and the improved model and design proposal coincide in regards to the critical crossing area position. The influence of reduced lamination widths on beam shear strength and shear strength ratio on the position of critical crossing areas are further analysed indicating a fairly minor contribution. The improved analytical model and design proposals were further modified to calculate the effective shear modulus of CLT beams. A good agreement between the analytical and test results is obtained for the slip modulus of the crossing areas proposed in the literature. However, a higher slip modulus seems appropriate for both design proposals in the design situation to avoid too conservative effective shear modulus and corresponding shear stiffness.

IS BP LOAD ON AMBULATORY MONITORING A PREDICTOR OF TARGET ORGAN DAMAGE IN YOUTH? THE SHIP AHOY STUDY

Objective: Ambulatory BP monitoring (ABPM) is increasingly utilized for the diagnosis of hypertension (HTN). Pediatric guidelines consider BP load (% of reading above the ‘normal’ threshold) in risk-stratification of the ABPM phenotype. We sought to determine if load was an independent predictor of target organ damage (TOD) in youth. Design and method: Casual BP, ABPM, anthropometrics, echo for LV mass index (LVMI), systolic strain, diastolic function (E’/e’ ratio) and pulse wave velocity (PWV) for arterial stiffness (PWV) were measured in 367 adolescents (mean 15.6 + 1.7 years, 63% white, 58% male). ABPM was performed with Ontrak device (Spacelabs Inc., Snoqualmie, WA). Subjects were stratified by load (low <25% = 215, mid 25-<50% = 62, high >=50% =47) according to sex- and height-specific pediatric cut points. ANOVA was used to evaluate differences in CV risk factors and TOD across load groups. General linear models were used to evaluate load as an independent predictor of TOD after adjusting age, demographics, body mass index (BMI), and mean daytime SBP on ABPM. Results: There was a graded increase in most clinic and ambulatory BP means and loads across load groups (all p < 0.05). There was only a trend for higher LVMI (p = 0.06) and reduced strain (p = 0.05) in low vs high load groups. Diastolic function (E/e’) was lower in high vs low and mid groups and there was a graded increase in arterial stiffness (PWV) across load groups. Daytime SBP load was an independent determinant of all forms of TOD after adjusting for age and sex but lost significance for LVMI after adjusting for BMI%. Load remained a significant determinant of PWV & E/e’ after adjusting for BMI% and mean daytime ambulatory SBP. Load group was also a significant determinant of PWV and E/e’ even after adjustment for age, sex, BMI% and daytime ambulatory SBP (all p < 0.0001). Conclusions: Daytime SBP load adds to prediction of diastolic dysfunction and arterial stiffness but not LVMI or systolic function. Increased load on ABPM may indicate need for advanced imaging to detect early TOD in youth with HTN.

A new method of stiffness prediction for periodic beam-like structures

This paper presents a new method for stiffness prediction of periodic beam-like structures based on the self-equilibrium equation of the unit cell. In this method, actual displacements of a composite beam are separated into homogenized displacements and warping displacements. The effective stiffness matrix of a periodic heterogeneous beam is explicitly formulated based on the energy equivalence or the internal force equivalence of the unit cell at both macroscopic and microscopic levels, and it follows that these two approaches are equivalent in essence. In addition, six normalization constraints to determine the unique solution of the self-equilibrium equation of the unit cell are introduced and well elaborated from physical interpretations. Furthermore, a standard finite element formulation for calculating the warping displacements is derived by using the principle of the minimum potential energy. This method can be easily implemented in commercial software Comsol. Finally, numerical comparisons with the results in literature validate the effectiveness and accuracy of the proposed method.

Estimation of lateral stiffness for gypsum-filled cold-formed steel shear walls

This paper reports an experimental and theoretical investigation of gypsum-filled cold-formed steel (CFS) shear walls, for the purpose of addressing the estimation of lateral stiffness. A series of gypsum-filled CFS shear walls were tested under reversed cyclic loading. The infill walls declare the limit states in the failure of screw connections as well as the compressive failure of gypsum fillings. Besides, the shear performance of screw connections between CFS profiles and sheathings were also investigated by the local tests. The contributions of lateral stiffness under shear force mainly include the sheathings as stressed skins and the infill gypsum as bracing bars. A theoretical prediction of lateral stiffness for CFS infill walls was proposed based on superposition methods, which has a good agreement with the wall tests. Moreover, the shear stiffness of screw connections is required to determine the contribution of sheathings to lateral stiffness. Considering the extrusion deformation of sheathings along with the bending deformation of CFS profiles caused by the tilt of screws, a theoretical method was recommended to estimate the shear stiffness of screw connections.

Experimental and analytical study of the shear strength and stiffness of studs embedded in high strength concrete

Push-out test was carried out to investigate the influence of the ratio of the stud height to the concrete slab thickness and the reinforcement layout on the shear performance of the headed stud embedded in high strength concrete (HSC). Test results indicated that the influence of the ratio of stud height to concrete slab thickness on the shear stiffness should be taken into consideration. A shear stiffness prediction formula, which has clear physical meaning and simple expression, was proposed and validated. The predicted shear stiffness by the proposed equation is in good agreement with experimentally determined value. According to this formula, the shear stiffness of studs is affected by the stud diameter, compressive strength and elastic modulus of HSC. In addition, a formula to predict the shear strength of a stud embedded in HSC considering both the interaction between stud and concrete and the enhancement effect of the welded collar was also proposed and evaluated. The mean ratio of predicted results obtained from the proposed formula to experimental results is 0.98.

Evaluating vertical conditions of bridge substructures of heavy-haul railway lines based on dynamic stiffness and pier vibration response

When it is necessary to increase the freight volume, the related increase in the train axle loads can potentially affect the bearing capacity of bridge substructures. Therefore, the structural integrity of bridge substructures should be evaluated, and their capacities need to be estimated. Existing studies have only investigated the lateral health condition of piers and foundations of bridges. To evaluate the vertical condition of bridge substructures, in this study, a dynamic transient response method (TRM) was developed using newly designed equipment. The vertical dynamic stiffness of a bridge foundation was employed as the main evaluation index. Subsequently, in situ experiments were performed on 62 bridge foundations of a heavy-haul railway line, including three types of foundations. Train-induced vertical and lateral vibration responses on the pier tops were also measured. The relationship between the vertical dynamic stiffness of the foundations and the train-induced vibration amplitudes on the pier tops was analysed. Subsequently, the support vector machine (SVM) method was employed to predict the dynamic stiffness of the bridge foundations when the TRM test could not be performed and the train-induced vertical vibration response on pier tops could be tested. Finally, a three-step evaluation strategy was proposed to comprehensively assess the vertical conditions of bridge substructures using the above methods. The study indicates the following: (1) The redundancy of the vertical bearing capacity is completely different from that of the horizontal vibration amplitude. There may be a certain error in the evaluation of a pier foundation when only the horizontal vibration amplitude is used to analyse its health condition. (2) The dynamic stiffness obtained by the TRM can effectively reflect the vertical condition of a bridge substructure and can be employed as an index in the detailed evaluation stage. (3) Using SVM, the dynamic stiffness of a foundation can be predicted with the measured amplitudes of the train-induced vertical vibration on the pier tops. The amplitudes of train-induced vibration and SVM-based prediction of dynamic stiffness can be used as early warning indicators in the scoping evaluation stage.

Bayesian Network Prediction of Stiffness and Shear Strength of Sand

AbstractThis paper proposes a Bayesian network approach to predict the shear modulus and maximum friction angle of sand. The nonlinear correlations between sand parameters can be incorporated in th...

Inner strut morphology is the key parameter in producing highly porous and mechanically stable poly(ε-caprolactone) scaffolds via selective laser sintering

Selective laser sintering (SLS) is an established method to produce dimensionally accurate scaffolds for tissue engineering (TE) applications, especially in bone. In this context, the FDA-approved, biodegradable polymer poly(ε-caprolactone) (PCL) has been suggested as a suitable scaffold material. However, PCL scaffold mechanical stability – an attribute of particular importance in the field of bone TE – was not considered as a primary target for SLS process parameters optimization so far. Here, we investigated the influence of SLS process parameters on the sintered scaffolds with the aim of producing highly porous (>70% porosity) PCL scaffolds with sub-mm geometrical features for bone TE. Specifically, we studied the influence of laser power, beam compensation and laser beam diameter on the dimensional accuracy and mechanical stiffness of the produced PCL scaffolds. We found that the ratio between the diameter of the molten cross-section within scaffold struts and the outer strut diameter (including partially sintered particles) depended on the SLS process parameters. By maximizing this ratio, the mechanical stability could be optimized. The comparison with in silico predictions of scaffold mechanical stiffness revealed that the diameter of the molten cross-section within struts and not the strut diameter controlled the mechanical behaviour of the scaffold. These observations should be considered when evaluating the quality of the sintering process based on dimensional accuracy, especially for features <1 mm. Based on these findings, we suggested an approach to evaluate the sintering outcome and to define SLS process parameters that enable the production of highly porous scaffolds that are both dimensionally accurate and mechanically stable. Moreover, the cytocompatibility of PCL scaffolds was evaluated by elution tests with primary human mesenchymal stromal cells. No evidence of cytotoxicity was found in any of the investigated scaffolds, confirming the suitability of SLS as production technique of PCL scaffolds for bone TE over a wide range of SLS process parameters.

Flexural behavior of reinforced concrete T-section beams strengthened by NSM FRP bars

Strengthening of deficient reinforced concrete (RC) beams using near surface mounted (NSM) fiber-reinforced polymer (FRP) bars has in recent years been gaining greater interest and increased field applications. While considerable research has explored the behavior of NSM-FRP strengthened rectangular-section RC beams and the effects of influential parameters, there is dearth of similar studies on RC T-section beams. Moreover, analytical models for predicting the flexural strength of NSM strengthened RC beams are yet to be confirmed experimentally. Thus, the present study investigates the behavior of RC T-section beams strengthened with NSM FRP bars under monotonic flexural loading and compares the experimental results with predictions of a flexural model derived from first principles. Ten RC T-section beam specimens strengthened with NSM FRP bars and three standard specimens were considered. The failure mode, cracking resistance, yielding, ultimate capacity, flexural stiffness, and ductility of specimens were compared and analyzed. Based on the experimental results, a general increase in flexural stiffness of the strengthened specimens was observed, especially at the post yield stage of loading. Analytical flexural strength predictions were calculated and corroborated with the experimental results. An adjustment parameter to the flexural stiffness prediction model was proposed to account for reductions in the effective area of the FRP bars used in the sectional strength calculations.

Theoretical prediction of effective stiffness of nonwoven fibrous networks with straight and curved nanofibers

The nonwoven random fibrous network materials have been widely used in many fields due to their excellent physical and chemical properties. To understand the mechanical behavior of these nonwoven fibrous networks, a theoretical model is developed based on the network microstructure and microstructure evolution in the loading process. It is revealed that the effective stiffness of nonwoven fibrous networks is not only contributed by the fiber stretching and bending, but also depending on the rotation deformation of crosslinks between fibers. Since the nonwoven fibrous networks are constructed by straight or curved fibers, especially at nanoscale, the curvature effects on the effective stiffness are also studied systematically. Furthermore, finite element simulation is conducted to verify the theoretical predictions on the elastic properties of nonwoven fibrous networks consisting of straight and curved fibers, respectively. The theoretical model presented here is a general model, enabling to capture the elastic mechanical behavior of many complex nonwoven network systems from micro to nano length scales.

A historical review of the traditional methods and the internal state variable theory for modeling composite materials

A review of the development and the usages of traditional non-internal state variable (ISV) models and ISV theory for modeling behaviors of composite materials are presented in this paper. The history of earliest composites models for predictions of material stiffness, failure, viscoelasticity and plasticity is discussed first. Then following the ISV theory, a fundamental thermodynamic framework that governs the dissipative effects caused by the inelastic phenomena is introduced. Applying the thermodynamic restrictions obtained from that framework, different researchers have employed the ISV theory to develop constitutive models for composites to capture their viscoelasticity, rate-independent plasticity, viscoplasticity, and continuum damage. ISVs introduced into those models for describing each inelastic behavior of composites as well as their evolution rules are also discussed. The knowledge obtained from this review in terms of the usages of the ISV theory for composite material modeling forms a theoretical background for the development of a general modeling framework to predict all inelastic phenomena of a wide variety of composite materials.

Short-Term Flexural Stiffness Prediction of CFRP Bars Reinforced Coral Concrete Beams.

FRP (Fiber Reinforced Polymer) Bar reinforced coral concrete beam is a new type of structural member that has been used more and more widely in marine engineering in recent years. In order to study and predict the flexural performance of CFRP reinforced coral concrete beams, the flexural rigidity, crack morphology and failure mode of concrete were studied in detail. The results show that under the condition of similar reinforcement ratio, the flexural rigidity of CFRP reinforced coral concrete beam is significantly lower than that of ordinary reinforced concrete beam. Increasing the cross-section reinforcement ratio within a certain range can increase the bending stiffness of the test beam or reduce the deflection, but the strength utilization rate of CFRP reinforcement is greatly reduced. The short-term bending stiffness of the CFRP reinforced coral concrete beam calculated by the existing standard formula is obviously higher. This paper proposes a modified formula for introducing the strain inhomogeneity coefficient () of CFRP bars and considers the relative slip between CFRP bars and coral concrete to predict the short-term flexural stiffness of coral concrete beams reinforced by CFRP bars. The formula was verified with the test results, and it was proved that the formula has a good consistency with the test results.

Stiffness Prediction and Analysis of Composite Leaf Springs

Composite leaf springs represent a key application of composite materials in the field of automotive lightweight materials. Stiffness, as a critical parameter of composite leaf springs, is closely related to the handling stability and ride comfort of automobiles. Therefore, this paper proposes an explicit theoretical model, which can consider the anisotropy of composite materials and detailed structure of the leaf spring, to predict the stiffness based on the law of energy conservation. The obtained results are verified against the results of the finite element method and bench test of basalt/epoxy samples. Moreover, the influence of the relevant design parameters on the stiffness is analyzed to provide guidance for the stiffness matching of composite leaf springs. The thickness of the composite leaf spring considerably influences its stiffness. As a key parameter representing the bearing capacity, the strength is closely related to the reliability of leaf springs. Based on the Tasi-Wu strength failure criterion, the influence of the relevant design parameters on the strength ratio of a composite leaf spring is analyzed under the constraint of stiffness. An increase in the width of the composite leaf spring enhances its bearing capacity when the stiffness is required to be within a certain range.

SIMPLE METHOD FOR DETERMINING BENDING STIFFNESS OF LARGE DIAMETER MULTI-LAYERED SPIRAL STRANDS

The response of a helical strand is difficult to model theoretically, as it involves lengthy mathematical formulations. It is highly desired by the practicing engineers to have a simple and reliable method for the prediction of bending stiffness of multi-layered strands. A method for the estimation of bending stiffness of large diameter multi-layered strands has been proposed in this paper. The development of this method was carried out using significantly large number of parametric studies on a variety of strand construction which were also validated using the experimental data. The proposed method is simple in nature for direct engineering applications which provides an effective tool for calculating effective bending stiffness of a strand subjected to any bending curvature.

Considering inhomogeneous material properties for stiffness and failure prediction of thin-walled additively manufactured parts

By overcoming manufacturing constraints imposed by traditional production technologies, additive manufacturing enables engineers to realize highly optimized lightweight components of unmatched geometrical complexity. However, the common dependency of the mechanical material properties on build orientation and wall thickness constitutes a challenge for valid structural analyses of thin-walled parts. Hence within this research, a previously proposed strategy to improve the structural simulations by mapping inhomogeneous material properties into finite shell element models is extended for failure prediction. Therefore, coupons in various build orientations and thicknesses were produced of short fiber-reinforced polyamid 12 via laser sintering and the mechanical properties evaluated by means of digital image correlation-assisted tensile testing. Consequently, the obtained data is utilized for modeling of the thickness dependent and anisotropic material behavior. The inhomogeneous material parameters are automatically mapped in the finite element models and ultimately, numeric simulations are validated by experimental testing of thin-walled parts. The comparisons of finite element analyses with mapped inhomogeneous and conventional constant properties disclosed considerably improved prediction of stiffness and failure. For the latter, however, substantial deviations between simulation and physical experiment remained, indicating that further research is necessary to effectively asses the load bearing capacity of thin-walled additively manufactured structures.

Prediction of Pipe Stiffness of Glass Fiber Reinforced Polymer Mortar Pipe Using Laminate Plate Theory

Prediction of Pipe Stiffness of Glass Fiber Reinforced Polymer Mortar Pipe Using Laminate Plate Theory

Experimental, regression learner, numerical, and artificial neural network analyses on a complex composite structure subjected to compression loading

This paper reports on an investigation into the relationship between stiffness and applied force of an advanced biological composite structure using four techniques: experimental observation; finite element analysis (FEA); regression learner analysis; and, artificial neural networks (ANNs). The entire hydrated third metacarpal bones (MC3) from 16 thoroughbred horses were loaded in compression in an MTS machine. The stiffness was then determined from the applied force, MC3 displacement, and load exposure time. A variety of mathematical functions were fitted to the sample data points using MATLAB to demonstrate force-dependent stiffness. Two functions were found that exhibited a strong correlation between force and stiffness (R 2 = 0.75). Additionally, a power function was found that demonstrated a stronger correlation between the stiffness and force (R 2 = 0.81) if the exposure time was also incorporated. FEA considered the calculated force-dependent stiffness when assigning material properties. FEA results were compared with experimental data (for verification and validation), and a good agreement was found for the displacement (RMSE = 0.032 mm) and strain (RMSE = 61.85 με). Machine learning regression models were also employed to predict the stiffness of this complex structure. Applied force, exposure time, MC3 geometry (length and area of cross sections), and age were defined as the independent variables. The regression learner offered excellent reliability (R 2 = 0.98) for the prediction of stiffness. Also, feedforward back-propagation artificial neural networks were employed to improve and generalize the stiffness prediction ability to a wider population. ANN regression analysis showed R = 0.992 for training, R = 0.99 for testing, and R = 0.991 for the all datasets. To confirm its accuracy, the ANN was used to predict stiffness of specific samples that were not used in its training. This offered excellent reliability in predicting real-world data that ANNs have not seen before (R = 0.976).

A Winkler model for suction caisson foundations in homogeneous and non-homogeneous linear elastic soil

Suction caisson foundations provide options for new foundation systems for offshore structures, particularly for wind turbine applications. During the foundation design process, it is necessary to make reliable predictions of the stiffness of the foundation, since this has an important influence on the dynamic performance of the overall support structure. The dynamic characteristics of the structure, in turn, influence its fatigue life. This paper describes a thermodynamically consistent Winkler model, called OxCaisson, that delivers computationally efficient estimates of foundation stiffness for caissons installed in homogeneous and non-homogeneous linear elastic soil, for general six degrees-of-freedom loading. OxCaisson is capable of delivering stiffness predictions that are comparable to those computed with three-dimensional finite-element analysis, but at a much lower computational cost. Therefore, the proposed model is suited to design applications where both speed and accuracy are essential, such as large-scale fatigue assessments of offshore wind farm structures. The paper demonstrates that the OxCaisson model can also be applied to short, rigid monopile foundations.