Type Of Applied Load Research Articles

Flexural behavior of two-layer reinforced concrete slab with hollow cores

Flexural behavior of a concrete slab system with an optimal weight-to-strength ratio comprising layered and hollow-core slab structures was investigated using two-layered slabs with hollow cores (LS/HCS). Six slabs with dimensions of 180, 450, and 1600 mm were tested experimentally and numerically using ANSYS software. Each layered slab comprises a 90-mm-thick lightweight concrete bottom layer and a 90-mm-thick high-strength concrete top layer. Three parameters were studied: core diameter (58, 86, and 110 mm), reinforcement ratio (0.37%, 0.53%, 0.95%), and treatment type (bonding agent, nails). Treatment types were analyzed via push-out testing; both nails and agents connected the slabs with sufficient bond strength. A control slab with 86-mm core diameter, shear-span-to-effective-depth ratio of 4, reinforcement ratio of 0.53%, and agent material was used. Concrete, steel bars, and loading support plates were modeled using SOLID65, LINK180, and SOLID185 elements, respectively. Analytical results were validated experimentally. A parametric study analyzed other parameters affecting LS/HCS behavior, including compressive strength, opening numbers, core shape, applied loading type, added top steel reinforcement, slab type, and slab height. Core diameter reduction, increased reinforcement ratios, and using nails enhanced the failure load. The LS/HCS gives an optimum weight-to-strength ratio with a 33.672% reduction compared with solid slabs.

SIMULATION OF JOINT STRENGTH OF SINGLE LAP JOINT OF COMPOSITE PLATES BASED ON VARIATIONS OF PLATE THICKNESS AND OVERLAP LENGTH

In this study, finite element simulation of joint strength of single lap joint of composite plates based on variations of joint thickness and overlap length is presented by using ANSYS software. In the simulation, plate thickness and overlap length of the joint structure are varied. Based on the variations of plate thickness and overlap length, it is found that the largest joint strength is obtained at the values of plate thickness and overlap length of 2 mm and 55 mm, respectively. Also, it appears that the applied loading type will affect to the simulation results.

Rehabilitation of severely-destructed endodontically treated premolar teeth with novel endocrown system: Biomechanical behavior assessment through 3D finite element and in vitro analyses

ObjectiveRehabilitation of endodontically treated premolars with extensive coronal destruction through endocrown approach remains a controversial topic in reconstructive dentistry. There is no clear consensus in the literature which endocrown design with which material is the most effective restoration option for severely-destructed endodontically treated premolars. The aim of this study was to assess the biomechanical behavior of endodontically treated maxillary first premolars restored with a novel endocrown system compared to the conventional one varying the applied load type through finite element and in vitro analyses. Materials and methodsFor finite element analysis, two models representing two endocrown systems used for restoration of severely-destructed endodontically treated maxillary first premolar tooth were generated: Model C for the conventional monolithic IPS e.max CAD endocrown and Model P for the novel bi-layered endocrown (PEKKTON ivory coping veneered with cemented IPS e.max CAD). Modified von Mises stress values on the remaining tooth structure, cement lines and restorative materials were evaluated separately under axial and oblique loading of 450 N. For in vitro analysis, forty sound human bifurcated maxillary first premolars were collected, endodontically-treated, and divided into 2 main groups (n = 20) according to the system used for endocrown fabrication; Group C: the conventional monolithic endocrowns and Group P: the novel bi-layered endocrowns. All specimens were subjected to an artificial thermomechanical aging protocol. Each main group was subdivided into two subgroups (n = 10) according to the loading type (axial and oblique) applied during the fracture resistance test. Qualitative analysis using Stereomicroscopy and Scanning Electron Microscopy was performed. Data were statistically analyzed at p-value ≤ 0.05. ResultsRegarding stress distribution pattern of remaining tooth structure (enamel and dentin), both endocrown systems and cement lines under both axial and oblique load application, Model P resulted in lower stresses than Model C. The oblique stress values of all analyzed structures were higher than corresponding values resulted axially. Considering failure load, a significantly higher load was recorded for Group P when axial or oblique loading was applied (p = 0.00). A significantly higher failure load was recorded with axial loading for both main groups. With regard to failure mode, a statistically significant difference was observed between main groups (p = 0.033), with more favorable failures detected for Group P axially. ConclusionsCompared to the conventional endocrown system, the studied novel system improved the biomechanical behavior within tooth/restoration complex of the restored severely-destructed endodontically treated maxillary first premolar teeth, whatever the applied load type. Clinical significanceThe novel endocrown system using a PEKK coping veneered with cemented IPS e.max CAD can be considered a favorable promising option for restoration of severely-destructed endodontically treated premolar teeth, with more protection for residual tooth structure. It can be considered as a conservative alternative option to the conventional treatment modalities not only for normal clinical conditions, but also for parafunctional cases.

(Invited) Automotive Proton Exchange Membrane Fuel Cells Subzero Performance

Subzero automotive cold-starts are a challenge for proton exchange membrane fuel cell (PEMFC) stacks, in that both the thermal and mass fluxes from the cathode oxygen reduction reaction must be balanced. The heat generated, from both the exothermic reaction and resistive heating, enables rapid thermal responses of the interior cells of a stack (>300-cells) under high applied loads (galvanostatic loads above 300 mA cm-2 or potentiostatic loads below 0.5 V). Stacks of greater than 20-cells are required for -30°C cold-starts to overcome the thermal losses to the endplates [1]. The Faradic water production rate trends with the magnitude of the applied load, requiring the internal temperature of the stack to rapidly be elevated above 0°C. This circumvents oxidant starvation due to ice accumulation and failed cold-start. The U.S. Department of Energy’s subzero cold-start targets for PEMFC stacks include starts from -30°C, limited parasitic shut-down/start-up energy of 5 MJ, and time of 20 sec to reach 50% rated power [2].Presently, the majority of the published subzero cold-start PEMFC studies are performed on single cells and are dominated by isothermal water fill tests (WFT), due to the cost of stack testing [3]. As opposed to subzero stack cold-starts used under high applied loads to evacuate product water, isothermal WFT are performed under low galvanostatic loads (£ 150 mA cm-2) to quantify the water storage capacity of the cathode. To bridge the gap between subzero isothermal WFT and cold-starts, quasi-adiabatic PEMFC single-cell fixtures have been designed to insulate the cell from the endplates and emulate adjacent cell heating that occurs in a stack [4, 5].In Figure 1, three -20°C cold-starts are compared in terms of initial water content (l) and applied load type (600 mA cm-2 and 0.1 V). The higher water content results in an initially enhanced (A) power density output and (B) thermal response. The potentiostatic hold increases the initial usable power. The isothermal WFT under an applied load of only 10 mA cm-2 was able to store 1.8 mg cm-2 of water before freezeout after 32 min on load (complete data not shown), while the cold-start for the same of 3.2 produced the same amount of water within 48 sec and had warmed up to above 0°C. Khandelwal, M., S. Lee, and M.M. Mench. J. Power Sources, 2007. 172(2): p. 816-830. www.energy.gov/eere/fuelcells/doe-technical-targets-fuel-cell-systems-and-stacks-transportation-applications.Rice, C. J. Electrochem. Soc., 2021. (Accepted).Pistono, A.O. and C.A. Rice. Molecules, 2020. 25(6): p. 1410.Balliet, R.J. and J. Newman. J. Electrochem. Soc., 2011. 158(8): p. B939-B947. Figure 1

Comparative mechanical performances of cement-treated sand reinforced with fiber for road and pavement applications

Cement-treated sand reinforced with fiber (CTSF) has been extensively utilized as the base and subbase layers in road and pavement applications to enhance the mechanical properties of cement-treated sand (CTS). This paper aims to study the influence of seven distinct types of synthetic fibers on the mechanical performances of CTSF specimens. The 5% cement and 2% fiber were mixed with sand and water to create the CTSF specimens. The different seven fiber types used included (i) 12-mm-long polypropylene, (ii) 19-mm-long polypropylene, (iii) 33-mm-long steel, (iv) 40-mm-long polypropylene, (v) 50-mm-long steel, (vi) 55-mm-long polypropylene, and (vii) 58-mm-long polyolefin fibers. Three mechanical tests were performed on the CTSF specimens: unconfined compressive, splitting tensile, and flexural strength tests. The overall performance of the CTSF for each test was determined by six subperformance parameters: (1) improvement peak strength ratio; (2) brittleness index; (3) improvement deformation ratio; (4) improvement toughness ratio; (5) toughness index; and (6) strength index. The debonded interface between the surface of each fiber and the cemented sand matrix was observed using scanning electron microscopy. Finally, the comparative overall mechanical performance was analyzed based on the subperformance indicators to determine the most suitable fiber type corresponding to each applied loading type. The results illustrated that the most suitable fiber types for CTSF subjected to unconfined compressive, splitting tensile, and flexural stresses were 58-mm-long polyolefin fiber, 50-mm-long steel fiber, and 55-mm-long polypropylene fiber. The current study proved that synthetic fiber types significantly affect the mechanical performance of CTSF used for road and pavement applications. Thus, the overall performance concept presented in the current study is useful for selecting the most suitable fiber type corresponding to different failure mechanisms, which is of practical significance in pavement performance and design.

Comparison of Testing Method Effects on Cracking Resistance of Asphalt Concrete Mixtures

As an inherent characteristic of materials, the fracture toughness is an important parameter to study the cracking behavior of asphalt concrete mixtures. Although material compositions and environmental conditions have a significant effect on the fracture toughness, for a certain material and testing environment, the test condition including the specimen configuration and loading type may also affect the obtained fracture toughness. In this paper, the effect of specimen configuration and applied loading type on the measured pure mode-I fracture toughness (KIc) is investigated. In order to achieve this purpose, using a typical asphalt mixture, four different test specimens including Semi-Circular Bend (SCB), Edge Notch Disc Bend (ENDB), Single Edge Notch Beam (SENB) and Edge Notch Diametral Compression (ENDC) disc are tested under pure mode I. The mentioned specimens have different shapes (i.e., full disc, semi-disc and rectangular beam) and are loaded either with symmetric three-point bending or diametral compressive force. The tests were performed at two low temperatures (−5 °C and −25 °C) and it was observed that the critical mode-I fracture toughness (KIc) was changed slightly (up to 10%) by changing the shape of the test specimen (i.e., disc and beam). This reveals that the fracture toughness is not significantly dependent on the shape of the test specimen. However, the type of applied loading has a significant influence on the determined mode I fracture toughness such that the fracture toughness determined by the disc shape specimen loaded by diametral compression (i.e., ENDC) is about 25% less than the KIc value with the same geometry but loaded with the three-point bending (i.e., ENDB) specimen. In addition, the fracture toughness values of all tested samples were increased linearly by decreasing the test temperature such that the fracture toughness ratio (KIc (@−25 °C)/KIc (@−5 °C)) was nearly constant for the ENDB, ENDC, SCB and SENB samples.

Abrasion Resistance of Thermally and Chemically Modified Timber

Wood modification is an appropriate way of improving the natural durability and dimensional stability of wood without the use of biocides. Different thermal and chemical wood modification processes are available for this purpose, very differently affecting the structural integrity of wood. In this study, thermally modified, melamine resin treated, acetylated, furfurylated, and mDMDHEU treated wood underwent abrasion tests according to two different methods representing different loads in practice. The Taber Abraser method caused crosswise cutting into the wood surface, while the Shaker method challenged mainly the specimen edges with dynamic loads. Abrasion resistance of wood was affected by all types of cell wall modification, but the effects were strongly dependent on the type of modification and the applied load type. For characterising the suitability of wooden materials with respect to wear resistance under outdoor conditions, it is recommended to apply a set of methods rather than a single test procedure to fully reflect the loads occurring in practice.

Nonlinear forced vibration of FG-GRC laminated plates resting on visco-Pasternak foundations

The nonlinear dynamic responses of laminated plates consisting of graphene reinforced composite (GRC) layers in thermal environments are studied in this paper. The effect of visco-elastic foundation is also considered in the analysis. All layers in an FG-GRC laminated plate are assumed to have the same thickness, whereas the graphene volume fractions for the layers are assumed to be linearly varying in a piece-wise pattern along the plate thickness direction. The material properties of GRC are estimated by a extended Halpin-Tsai model. To include the effect of small scale, the efficiency parameters for graphene are introduced in the model and determined from the results of molecular dynamics (MD) simulations. The plate is modeled based on the Reddy’s higher order shear deformation plate theory and the effects of the von Karman geometric nonlinearity and the initial loading are included in the derivation of the motion equations. Once the applied load is determined, the deflection as the function of time can be solved by the fourth-order Runge-Kutta numerical method. The impacts of functionally graded (FG) pattern, visco-elastic foundations, temperature change and applied load type on the dynamic behaviors of the FG-GRC plate are presented and discussed.

Effect of cyclic loading on composite behavior of insulated concrete sandwich wall panels with GFRP shear connectors

Abstract A full-scale experiment was conducted to investigate the composite behavior of insulated concrete sandwich wall panels (ICSWPs) under monotonic loads and wind-induced cyclic loads. The experimental program consists of two groups, according to the applied loading type and the type of insulation, with the same configurations of glass-fiber-reinforced polymer (GFRP) grids. The degree of composite action in terms of the initial stiffness and ultimate strength were compared at the global level, and the degree of composite action in terms of the shear flow were compared at the local level (in accordance with the variables). The test results showed that the adhesive bonds based on the insulation absorptiveness and the mechanical bonds based on the insulation surface roughness and groove treatment were effective for inducing the desired composite behavior of ICSWPs in both monotonic loading and cyclic loading tests. The cyclic test group showed a lower degree of composite action compared to the monotonic test group at a constant rate. This is the case because cumulative fatigue loading damaged the GFRP strands and debonded the interface between the concrete and insulation. These results indicated that the adhesive and mechanical bonds between the insulation and concrete wythes can be used to estimate the design strength of ICSWPs with GFRP shear grids. Additionally, the reduction factor for the design strength by the fatigue effect should be considered in estimation of design strength.

On the use of the Theory of Critical Distances to predict static failures in ductile metallic materials containing different geometrical features

This paper summarises an attempt to use the Theory of Critical Distances (TCD) to predict static failures in notched specimens made of a commercial cold-rolled low-carbon steel. Over the last 80 years, such a theory has been successfully employed to predict both static and fatigue failures in notched components, exploring its accuracy and its reliability in different ambits of the structural integrity field. In most of these previous applications, the stress fields in the relevant region close to the notch could be assumed to be linear-elastic without much loss of accuracy. The aim of the present paper is to investigate whether this linear-elastic TCD can also be successful in predicting static failures in notched components when the final breakage is preceded by large-scale plastic deformations. Notched specimens containing different geometrical features were tested under both tensile loading and three-point bending and failures were predicted by post-processing the results of linear-elastic Finite Element Analysis (FEA). The predictions thus obtained were found to be highly accurate, falling within an error interval of about 15%, independent of specimen thickness, notch geometry and applied load type. A similar degree of accuracy was obtained when elasto-plastic stress analysis was used. This result is very interesting, because it supports the idea that the linear-elastic TCD can successfully be used in situations of practical interest, reducing the time and costs of the design process.

A unifying approach to estimate the high‐cycle fatigue strength of notched components subjected to both uniaxial and multiaxial cyclic loadings

ABSTRACTThis paper proposes an engineering method suitable for predicting the fatigue limit of both plain and notched components subjected to uniaxial as well as to multiaxial fatigue loadings. Initially, some well‐known concepts formalized by considering the cracking behaviour of metallic material under uniaxial cyclic loads have been extended to multiaxial fatigue situations. This theoretical extension allowed us to form the hypothesis that fatigue limits can be estimated by considering the linear–elastic stress state calculated at the centre of the structural volume. This volume was assumed to be the zone where all the main physical processes take place in fatigue limit conditions. The size of the structural volume was demonstrated to be constant, that is, independent from the applied loading type, but different for different materials. Predictions have been made by Susmel and Lazzarin's multiaxial fatigue criterion, applied using the linear–elastic stress state determined at the centre of the structural volume. The accuracy of this method has been checked by using a number of data sets taken from the literature and generated by testing notch specimens both under uniaxial and multiaxial fatigue loadings. Our approach is demonstrated to be a powerful engineering tool for predicting the fatigue limit of notch components, independently of material, stress concentration feature and applied load type. In particular, it allowed us to perform predictions within an error interval of about ±25% in stress, even though some material mechanical properties were either estimated or taken from different sources.

A Study on Mechanical Behavior and Cracking Characteristics of Tunnel Lining by Model Experiment

ABSTRACTS The purpose of this paper is to evaluate the characteristics of possible cracks induced on tunnel lining according to the magnitude and shape of applied loads. For a study on mechanical behavior and cracking characteristics of tunnel lining, down scaled models were tested in consideration of applied loading type, side confinement, double lining, opening behind the concrete lining and so. Total twenty-four specimens including single and double lining models were prepared with concrete and mortar mixes. The mechanical behavior of tested models was discussed based on cracking load, failure load, critical section and finally load-deflection curve. A dimensionless support reaction formula was derived to generalize the relationship of applied loads and resultant deflections. Furthermore, we tried to modify the current designed flexural moment formula of the linings.

Time-dependent behavior of composite beams with flexible connectors

This paper deals with a numerical model for the time-dependent analysis of steel and concrete composite beams with partial shear connection. A linear partial interaction theory is adopted in formulation of slip behavior, and a linear load–slip relation is assumed for computational convenience. On the basis of governing equations representing the slip between steel beam and concrete slab, the numerical model is derived through the force equilibrium equations and strain compatibility conditions at each node, with an assumption of piecewise linear distribution of the bending moment. In advance, the migration of the stresses from the concrete slab to the steel beam and the increment of deflections, which occur gradually with time as a result of creep and shrinkage of the concrete part, are investigated by a numerical model proposed in this paper. The proposed model results in an effective use in simulating the slip and time-dependent behavior of multispan continuous composite beams regardless of applied loading type. Finally, the correlation studies between analytical and numerical results and several parameter studies are conducted with the objective to establish the validity of the proposed model.