Background
There is limited knowledge regarding the strength of zirconia abutments with internal and external implant abutment connections and zirconia abutments supported by a titanium resin base ...(Variobase, Straumann) for narrow diameter implants.
Objectives
To compare the fracture strength of narrow diameter abutments with different types of implant abutment connections after chewing simulation.
Material and methods
Hundred and twenty identical customized abutments with different materials and implant abutment connections were fabricated for five groups: 1‐piece zirconia abutment with internal connection (T1, Cares‐abutment‐Straumann BL‐NC implant, Straumann Switzerland), 1‐piece zirconia abutment with external hex connection (T2, Procera abutment‐Branemark NP implant, Nobel Biocare, Sweden), 2‐piece zirconia abutments with metallic insert for internal connection (T3, Procera abutment‐Replace NP implant, Nobel Biocare), 2‐piece zirconia abutment on titanium resin base (T4, LavaPlus abutment‐VarioBase‐Straumann BL‐NC implant, 3M ESPE, Germany) and 1‐piece titanium abutment with internal connection (C, Cares‐abutment‐Straumann BL‐NC implant, Straumann, Switzerland). All implants had a narrow diameter ranging from 3.3 to 3.5 mm. Sixty un‐restored abutments and 60 abutments restored with glass‐ceramic crowns were tested. Mean bending moments were compared using ANOVA with p‐values adjusted for multiple comparisons using Tukey's procedure.
Results
The mean bending moments were 521 ± 33 Ncm (T4), 404 ± 36 Ncm (C), 311 ± 106 Ncm (T1) 265 ± 22 Ncm (T3) and 225 ± 29 (T2) for un‐restored abutments and 278 ± 84 Ncm (T4), 302 ± 170 Ncm (C), 190 ± 55 Ncm (T1) 80 ± 102 Ncm (T3) and 125 ± 57 (T2) for restored abutments. For un‐restored abutments, C and T4 had similar mean bending moments, significantly higher than those of the three other groups (p < .05). Titanium abutments (C) had significantly higher bending moments than identical zirconia abutments (T1) (p < .05). Zirconia abutments (T1) with internal connection had higher bending moments than zirconia abutments with external connection (T2) (p < .05). For all test groups, the bending moments were significantly reduced when restored with all‐ceramic crowns.
Conclusions
For narrow diameter abutments, the fracture strength of 2‐piece internal connected zirconia abutments fixed on titanium resin bases was similar to those obtained for 1‐piece titanium abutments. Narrow diameter zirconia abutments with internal connection exhibited higher fracture strength than zirconia abutments with an external connection. Titanium abutments with an internal connection were significantly stronger than identical zirconia abutments.
The Jacket of an offshore structure is made up of tubular members. These tubular members are made up of steel and designed to resist yield and buckling loads. The tubular sections form various types ...of joints like K joint, KT joint, Y joint, etc. These joints are subjected to various types of cyclic loading conditions, due to which fatigue failure starts and increases as the time passes. As a result, the most critical section of the jacket fails first epically joint. The excessive strains due to axial forces, in-plane, and out plane bending moment accelerate the failure mechanism. In this paper, the comparative study is made between K joint and KT joint for the same loading conditions is made by selecting a finite method approach. By referring to API RP 2A and DNV RP C203. The observations are made on the behavior of joints for the same loading conditions, to the made conclusion of this project. Keywords: K Joint, KT joint, Axial force, in plane bending moment, out plane Bending moment, API RP 2A, DNV RP C203
Wave-induced vertical bending moment (VBM) and horizontal bending moment (HBM) on a large-scale segmented model with a box-type backbone beam in short-crested irregular seas are systematically ...analyzed using sea trial measurement data. New insights into the relationship between nonlinear VBM and HBM of the ship sailing in short-crested sea waves are explored and presented. The results indicate that the HBM significantly contributes to the total sectional loads when the ship is sailing in a seaway and the HBM has a strong correlation with VBM in both magnitude and tendency. Therefore, design loads of HBM and the corresponding lateral structural strength issues should also be concerned in addition to VBM at the ship design phase.
•A large-scale segmented model is systematically tested in sea trials in short-crested irregular seas and moments are measured.•Vertical (VBM) and horizontal (HBM) bending moments on a large-scale segmented model in short-crested seas are analyzed.•The results indicate that the HBM significantly contributes to the total sectional loads when the ship is sailing in a seaway.
Offshore wind turbines (OWTs) can be equipped with two types of monitoring systems: (1) a Supervisory Control and Data Acquisition (SCADA) system that monitors operational data such as wind speed and ...power generation, and (2) vibration sensors like accelerometers and strain gauges to track structural dynamics. While strain gauges enable fatigue damage calculations, not all OWTs in a wind farm have these sensors installed. This paper proposes a Gaussian process regression (GPR) strategy to predict the bending moment time-histories of an OWT. The model takes into account various SCADA data such as wind speed, power, and nacelle acceleration as input and learns to predict the high and low-frequency dynamic response of the system. The strategy is implemented and tested to predict the bending moment response of a 6 MW offshore wind turbine in the fore-aft and side-side directions of the turbine. The accuracy and reliability of the proposed strategy are evaluated and demonstrated considering different operational conditions and multiple hotspot locations along the height of the turbine. The proposed strategy proves to be an efficient virtual sensing strategy and can be easily transferred to other turbines in the same wind farm without the need for widespread installation of strain gauges.
The paper presents a new way of solving the integrals that appear in the Mohr-Maxwell energy method for calculating the displacements or rotations of straight bars subjected to bending. The method ...proposed by the authors, studied and tested for many years in the Military Technical Academy in the Strength of Materials group led by Col. Prof. Vasile Palacianu, eliminates the need to build effort diagrams. To solve the integral on a certain domain, a formula is applied that takes into consideration only the value of the moments at the ends of the integration interval. The well-known restriction for Veresceaghin grapho-analytical integration is maintained: on the integration domain, the variation of the bending moment produced by the generalized load equal to unity must vary linearly. Therefore, the method proposed by the authors cannot be applied to curved bars. Our new method can be used for a beam and also for a beams system. After the presentation of the theoretical foundations of the method and the establishment of the calculation relationship in three variants: without the load distributed over the integration interval, with the load uniformly distributed and with the load distributed according to a linear law, some edifying examples are presented, which highlight the efficiency of the method and the modality for work.
Wind turbines experience countless shutdowns during their lifetimes. A shutdown is a transient process characterised by a pitch-to-feather manoeuvre of three blades. Such a pitch manoeuvre is often ...collective, open-loop, and can substantially slow the rotor speed within several seconds. However, undesirable structural responses may arise because of the imbalanced aerodynamic loads acting on the rotor. To address this issue, this paper proposes a method that actively adjusts the individual pitch rate of each blade during an emergency shutdown. This method is founded on a minimal intervention principle and uses the blade-root bending moment measurements as the only inputs. The control objective is to minimise the differences in the blade-root flapwise bending moment among the three blades during the shutdown. Using a high-fidelity aeroelastic model, we demonstrate the controller performance under representative steady wind conditions with vertical wind shear. Compared with the baseline shutdown strategy, the proposed method effectively reduces the maximum nontorque bending moment at the main shaft and the tower bottom bending moment; the reductions vary between 10% and 40% under the investigated conditions. The present work can be further extended to reduce structural fatigue damages or to handle complex loading scenarios of offshore wind turbines during shutdowns.
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•A method is proposed to reduce the structural loads during emergency shutdowns.•The blade-root flapwise bending moment is used as inputs to the pitch controller.•An emphasis is laid on large vertical wind shear conditions with rotor imbalance.•Aeroelastic simulations of a turbine with various shutdown methods are performed.•The method effectively reduces the extreme nontorque bending moments in the shaft.
Abstract
An engineering judgment is often used to determine the exponent of the verification formula for combined stresses applied to moment‐resisting joints using drift‐pins. In this study, the ...exponent was determined based on a mechanical model. (1) The exponent of the verification formula for moment‐resisting joints with drift‐pins subjected to combined stresses was theoretically derived considering the effect of the grain angle given by Hankinson's formula. (2) The combined stress verification formula was validated by numerical analyses, experiments, and past experimental studies. It was confirmed that the method of determining the exponent in this formula is reasonable.
In a space structure, each connection can be subjected to different ratios of axial force to bending moment. In this paper, a test procedure was presented that enables realistic testing of a steel ...space structure jointing system by applying different combinations of axial forces and bending moments to the connection. The main objective of the test programme was the experimental study of the effects of compressive axial force on the moment–rotation characteristic of a joint. A suitable test set-up was designed and constructed to achieve a reasonable simulation of real connection behaviour. From the experimental results, it has been found that the compressive axial force has three important effects on the moment–rotation characteristics. It increases the initial slope of the moment–rotation curve with the reduction in the stiffness occurring more slowly to begin with but increasing more rapidly afterwards. It decreases the ultimate moment capacity of the connection. It also gives rise to softening of the connection behaviour.
•We represented a test procedure that enables realistic testing of a space structure jointing system.•The main objective was the experimental study of the effects of compressive axial force on the moment-rotation behaviour.•Experimental results showe that the compressive axial force increases the initial slope of the moment-rotation curve.•Axial force gives rise to softening of the joint behaviour and it decreases the ultimate moment capacity of the joint.
•We calibrated a model and developed a systematic parametric analysis for oat lodging.•The drag area is the most influential parameter for both stem and root lodging.•Stem yield stress and root plate ...diameter play an important role in the stem and root lodging respectively.•Lodging can be prevented to a high extent by targeting plant resistance parameters, even in adverse weather conditions.
For the first time, this research enables a systematic parametric analysis of oat lodging to be undertaken. A generalised lodging model combining agronomy, biology and wind engineering has been used. Standard husbandry treatments have been deployed in order to ensure that the oat plants are grown in realistic conditions and to ensure that the results are widely applicable. It is shown that the drag area, which increases through the growing season as the oats become entangled, is the plant trait which influences both stem and root lodging the most. In addition (and consistent with other plants) stem yield stress and the number of stems per plant for stem lodging and the diameter of the root structure in the case of root lodging, are found to play an important role. It is also shown that there is a linear relationship between failure anchorage moment and the cube of the root diameter in oats. Moreover, monitoring the lodging in crops which were grown under different husbandry treatments revealed using a resistant variety coupled with low Nitrogen rates and low seed rates, whilst also applying a Plant Growth Regulator (PGR) can increase the resistance of oat against lodging.
This study aimed to design and evaluate the detachable corner joints used in wooden furniture frames, including a commonly used detachable joint (control) form using mortise and tenon with plug ...reinforcement and three novel proposed joints, i.e., novel joint I ~ III, which adopted in-line double-hole nuts, metal sheet connector, and embedded nuts and screws respectively, via numerical and experimental methods. The numerical analysis results indicated that the optimal proposed joint (novel joint І) had good mechanical performance when subjected to bending load with proper stress distributions and relatively low maximum stress compared with the other two proposed joints. The experimental results showed that the bending load resistance of the control and the optimal proposed joints were 1920 N (0.14) and 4390 N (0.05), respectively. The bending moment capacity and bending stiffness of the optimal joints were remarkably higher than the bending moment capacity and bending stiffness of the control joint. In addition, the combination of the numerical and experimental methods could effectively simplify the steps of furniture connection design and development and save costs in terms of time and materials.
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