End Moments Research Articles

Comparative Study Among Direct Design Method, Equivalent Frame Method and Finite Element Method for Analysis of Slabs

Beam-column frame system and flat plate slab system are analysed by semi-empirical, Direct Design method (DDM) and approximate elastic method, Equivalent Frame method (FEM) and the results of both methods are compared with computer software based on Finite Element method (FEM), taking into account the effect of changing the beam and column stiffness and the panel length ratio, for 3, 4, and 5 equal span frames and three non-equal spans. The moment coefficients with respect to the maximum clear span moment are determined by the three methods for negative end moments at the face of support and mid span positive moment. These coefficients are constant in DDM, while in EFM are changed with changing the column and beam sizes. The results of EFM is more accurate than DDM, on the bases of results of EFM, new moment coefficients are suggested to use instead of DDM moment coefficients. In case of EFM calculation aren’t satisfactory for hand calculations the FEM is used by applying available computer software.

Effect of lung protective ventilation on coronary heart disease patients undergoing lung cancer resection

Mechanical ventilation, especially large tidal volume (Vt) one-lung ventilation (OLV), can cause ventilator-induced lung injury (VILI) that can stimulate cytokines. Meanwhile, cytokines are considered very important factor influencing coronary heart disease (CHD) patient prognosis. So minimization of pulmonary inflammatory responses by reduction of cytokine levels for CHD undergoing lung resection during OLV should be a priority. Because previous studies have demonstrated that lung-protective ventilation (LPV) reduced lung inflammation, this ventilation approach was studied for CHD patients undergoing lung resection here to evaluate the effects of LPV on pulmonary inflammatory responses. This is a single center, randomized controlled trial. Primary endpoint of the study are plasma concentrations of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-10 and C-reactive protein (CRP). Secondary endpoints include respiratory variables and hemodynamic variables. 60 CHD patients undergoing video-assisted thoracoscopic lung resection were randomly divided into conventional ventilation group [10 mL/kg Vt and 0 cmH2O positive end-expiratory pressure (PEEP), C group] and protective ventilation group (6 mL/kg Vt and 6 cmH2O PEEP, P group; 30 patients/group). Hemodynamic variables, peak inspiratory pressure (Ppeak), dynamic compliance (Cdyn), arterial oxygen tension (PaO2) and arterial carbon dioxide tension (PaCO2) were recorded as test data at three time points: T1-endotracheal intubation for two-lung ventilation (TLV) when breathing and hemodynamics were stable; T2-after TLV was substituted with OLV when breathing and hemodynamics were stable; T3-OLV was substituted with TLV at the end of surgery when breathing and hemodynamics were stable. The concentrations of TNF-α, IL-6, IL-10 and CRP in patients' blood in both groups at the very beginning of OLV (beginning of OLV) and the end moment of the surgery (end of surgery) were measured. The P group exhibited greater PaO2, higher Cdyn and lower Ppeak than the C group at T2, T3 (P<0.05). At the end moment of the surgery, although the P group tended to exhibit higher TNF-α and IL-10 values than the C group, the differences did not reach statistical significance(P=0.0817, P=0.0635). Compared with C group at the end moment of the surgery, IL-6 and CRP were lower in P group, the differences were statistically significant (P=0.0093, P=0.0005). There were no significant differences in hemodynamic variables between the two groups (P>0.05). LPV can effectively reduce the airway pressure, improve Cdyn and PaO2, reduce concentrations of IL-6 and CRP during lung resection of CHD patients.Trial registration: The trial was registered in the Chinese Clinical Trial Registry.

The numerical study on specialized treatment strategies of enhanced external counterpulsation for cardiovascular and cerebrovascular disease

Traditional clinical mode of enhanced external counterpulsation is not targeted for different diseases. Specialized strategies in the treatment of enhanced external counterpulsation for coronary heart disease and cerebral ischemic stroke are supposed to be distinguished. The goal of treatment for coronary heart disease is diastolic blood pressure/systolic blood pressure = Q ≥ 1.2 after counterpulsation, while the goal of treatment for cerebral ischemic stroke is the improvement of mean arterial pressure. A computational lumped parameter model was established for the simulation of hemodynamic effect of enhanced external counterpulsation on two diseases. Vessel collapse was considered during the simulation of counterpulsation. Based on different pressurized and decompressed rate, pressurized moment, pressure duration, and pressure amplitude, different counterpulsation modes were applied to the model and the immediate hemodynamic effects were compared. Results showed that the pressure duration and pressure amplitude had most influence on two diseases. For cerebral ischemic stroke, the longer pressure duration and the higher pressure amplitude of thighs, the higher mean arterial pressure; while for coronary heart disease, the value of Q was highest when the pressure end moment was 0.6s during a 0.88-s cardiac cycle, and Q had a linear increase in the pressure amplitude of buttocks, but little change with the increase of calves and thighs pressure amplitude. For patients with coronary heart disease, the pressure duration was not supposed to be too long to avoid the increase of systolic blood pressure, and the improvement of pressure amplitude of buttocks could promise a positive treatment effect for coronary heart disease. While for patients with cerebral ischemic stroke, both the long pressure duration of each part and the high pressure amplitude of thighs could result in the systolic blood pressure and diastolic blood pressure have a certain increase, thus promoting the maximum mean arterial pressure and a best treatment. Graphical abstract The specialized treatment strategies of EECP for cardiovascular and cerebrovascular disease.

Accurate log‐normal approximation to the signal‐to‐interference ratio in massive multiple‐input multiple‐output systems

In this paper, a very tight approximation is derived for the signal‐to‐interference ratio of a multicell massive multiple‐input multiple‐output system with a finite number of base station (BS) antennas. The approximation is derived considering that each term in the SIR is log‐normal distributed. To this end, the first and second moments of the logarithm of each variable are used. In addition, an exact expression is derived for the cumulative distribution function for the net capacity. In order to corroborate our derivations, simulations using the Monte Carlo method were carried out, and it was observed that the proposed analytical results tightly match the numerical simulations. The asymptotic result is also obtained for the case in which the number of BS antennas tends to infinity (M → ∞), considering both uniform and nonuniform spatial user distributions.

Applicability of North American standards for lateral torsional buckling of welded I-beams

Design specifications in North America, unlike their European counterpart, use same equations for design of rolled and welded shape beams for lateral torsional buckling (LTB). A recent study by MacPhedran and Grondin (2011) has shown that the current Canadian design equations might overestimate the capacity of welded wide flange (WWF) beams, which are welded I-shapes, requiring further investigation. This paper evaluates the performance of the current design equations for LTB capacities of welded I-shape beams. Nonlinear Finite Element (FE) analysis is performed for simply supported WWF beams subjected to constant moment, linear and nonlinear moment gradient. Three types of linear moment gradients are investigated: end moment ratios of 0.5, 0.0, and − 1.0. Also, two types of transverse loadings are considered: a concentrated load at mid-span and uniformly distributed load along the length, and applied at the top flange, shear center, and at the bottom flange. In total, 416 FE models are analyzed and it is observed that for constant moment loading both CSA and AISC overestimate the LTB capacity of welded I-shape beams by as much as 37%. FE analysis also shows that current CSA strength curve overestimates significantly the strength of WWF beams by as much as 40% for end moment ratio of 0.5. For transverse loading, current CSA strength curve overestimates the capacity significantly for top flange loading and underestimates for bottom flange loading. Also, Eurocode is found to be conservative for all cases and the proposed equation by MacPhedran and Grondin (2011) provides better predictions of LTB strengths of WWF shapes than the current CSA approach.

Analysis of influencing factors on transient temperature field of wet clutch friction plate used in marine gearbox

PurposeThis paper aims to introduce the moment of inertia of the driving and driven end of the clutch into the analysis of the transient temperature field of a friction plate and studied the influencing factors on that, especially to a marine gearbox.Design/methodology/approachA three-dimensional transient heat transfer analysis model of a wet clutch friction plate used in a marine gearbox is developed, and the transient characteristics of the temperature field during engagement are analyzed with taking account of the influence factors such as the sliding friction coefficient, engaging revolving speed, moment of inertia and applied engagement pressure.FindingsThe paper found out that the hot spot appears on the surface of the friction plate, taking account of the effect of radial slots and spiral groove. To avoid damage to the friction plate as a result of overheating, the appropriate sliding friction coefficient, lower engaging revolving speed and reasonable selection of applied engagement pressure curve can ensure a favorable heating situation of the friction plate. The reasonable structural design for the clutch with a bigger moment of inertia of driving end and smaller moment of inertia of driven end can reduce the engaging time effectively and decrease the peak temperature of the friction plate.Originality/valueThis paper fulfils a method to study the transient temperature field of a wet clutch friction plate, especially used in a marine gearbox.

양단 균일 모멘트를 받는 수평곡선 I형 강재 거더의 횡-비틀림 거동 및 강도 산정 방안

양단 균일 모멘트를 받는 수평곡선 I형 강재 거더의 횡-비틀림 거동 및 강도 산정 방안

Effect of inter layer idle time on thermal behavior for multi-layer single-pass thin-walled parts in GMAW-based additive manufacturing

Components fabricated in gas metal arc welding (GMAW)-based additive manufacturing undergo a special thermal process with many reheating cycles, resulting in the complicated thermal behavior. Many process variables can affect the thermal history in GMAW-based additive manufacturing, especially the interlayer idle time. In this paper, three-dimensional transient models were established to research the effect of interlayer idle time on thermal process in GMAW-based additive manufacturing. Meanwhile, a confirmatory test was conducted to verify the effectiveness of the model. The results indicate that the total maximum temperature gradients of the molten pool at the middle points in the models with the interlayer idle time of 2 min, 5 min, and cooling to room temperature are approximately consistent after the fourth layer, and those in the case with continuous deposition decrease gradually. As the deposition height increases, the maximum temperature gradient in molten pool along the deposition path keeps steady in the model with cooling to room temperature. At the deposition ending moment, with the increasing interlayer idle time, the total temperature gradients at the middle points of the layers decrease in the first eight layers and increase in the ninth and tenth layers, while the circumferential temperature gradients increase progressively.

Flexural Properties of Buckling-Restrained Brace Connections

Buckling-restrained braces (BRBs) achieve large peak and cumulative ductility capacities by restricting yielding to an encased core, while maintaining global stability. However, stability is often governed by the connections and is sensitive to the end fixity provided by the adjacent framing and gusset, and flexural continuity between the neck and restrainer. This paper presents simple analytical methods to determine the flexural properties of these key components. Full-depth gusset stiffeners are found to be highly effective in increasing the out-of-plane rotational stiffness (KRg), equivalent to doubling the thickness. An equivalent connection is proposed to account for the adjacent framing (KRf), but this may be neglected if KRf &gt; 10∙KRg. This is typically satisfied if a diaphragm slab and transverse beam are provided, but may exceed beam torsional bracing requirements. The restrainer end moment transfer capacity is extended to mortar-filled RHS restrainers, confirming that neck insert ratios of Lin/Bn &gt; 2.0 are required for full continuity.

A Finite Element Formulation for Bending‐Torsion Coupled Vibration Analysis of Delaminated Beams under Combined Axial Load and End Moment

Free vibration analysis of beams with single delamination undergoing bending‐torsion coupling is made, using traditional finite element technique. The Galerkin weighted residual method is applied to convert the coupled differential equations of motion into to a discrete problem, where, in addition to the conventional mass and stiffness matrices, a delamination stiffness matrix, representing the extra stiffening effects at the delamination tips, is introduced. The linear eigenvalue problem resulting from the discretization along the length of the beam is solved to determine the frequencies and modes of free vibration. Both “free mode” and “constrained mode” delamination models are considered in formulation, and it is shown that the continuity (both kinematic and force) conditions at the beam span‐wise locations corresponding to the extremities of the delaminated region, in particular, play a great role in “free mode” model formulation. Current trends in the literature are examined, and insight into different types of modeling techniques and constraint types are introduced. In addition, the data previously available in the literature and those obtained from a finite element‐based commercial software are utilized to validate the presented modeling scheme and to verify the correctness of natural frequencies of the systems analyzed here. The paper ends with general discussions and conclusions on the presented theories and modeling approaches.

Analysis and research on new mechanical characteristics of narrow base steel tube tower for transmission line

Compared with the common angle steel tower, the narrow base steel pipe tower has the advantages of simple structure, beautiful appearance, small floor area and better coordination with the urban environment. In the construction of urban high pressure transmission line, the narrow base tower has its own unique advantages and wide application prospects. It has the advantages of ordinary iron tower processing, transportation, assembly, cost saving, small occupancy of single column steel pipe rod, small line corridor and beautiful beauty. In the optimization design of the narrow tower, how to take the wind vibration coefficient of the tower, how to consider the bending moment of the rod end, the design of the narrow base tower and the structure optimization of the narrow tower tower are all the problems to be solved urgently. In this paper, the modal analysis of a single tower is carried out to determine its vibration mode, and then the wind vibration coefficient of a narrow tower is analyzed. Finally, the influence of x and y direction vibration on the frequency of the tower is obtained.

Sport Performance Structure in Female Pole Vault from the Point of View of Physical Activity Kinematic Parameters

This research is oriented at explanation of sport performance by angle, speed, time and space char-acteristics of centre of gravity, positions of body, extremities and pole during approach, take-off and jump realization in female pole vault. Kinematic parameters were gained by two-dimension analyser Consport Motion Analysis System (CMAS). There are involved 19 female pole vault jumpers with sport performance 408.1–490.5 cm (average result 431.2 cm). From the point of biomechanical movement activity analyse we consider as a more objective performance criterion (dependent variable) maximal centre of gravity height that were reached at valid attempts by female pole vault jumpers. By two-dimension (2-D) analyse of group of female pole vault jumpers there were revealed 76 independent variables that entered into process of multiple correlation and regression analysis. On 1st sport structure performance factor level we isolated two complex parameters absolute grip and standing over by which we can explain dependent variable maximal centre of gravity height on 100%. With stated proceeding we could separate seven factors on 2nd level. Three of the parameters horizontal speed of centre of gravity at moment of take-off end, centre of gravity height at moment of take-off end and operating angle during take-off are bound with explanation of absolute grip variable. Four others parameters vertical speed of centre of gravity at the end of pull with turn, centre of gravity height at moment of end of lifting, time duration of take-off and climb angle explain standing over. 14 more factors are found on 3rd sport structure performance level. Thus we succeeded in this process to reduce number of decisive variables with their mutual relationships and hierarchy. Transparent and simplified model of female pole vault sport performance structure enables to coaches and jumpers improve technical training.

Symmetric and antisymmetric lateral–torsional buckling of prestressed steel I-beams

Until now, there are no analytical solutions published of the lateral-torsional buckling (LTB) of the prestressed steel I-beams. In this paper, the symmetric and antisymmetric elastic LTB buckling performance of prestressed steel I-beams, with rectilinear tendons, under equal end moments has been examined. Firstly, a simplified mechanical model is put forward. Secondly, based upon the Euler-Beam model & the Kirchhoff-Plate model, the strain energy equation as well as the potential energy of the prestressed steel I-beam are derived in detail. Then the total potential equation and the differential equilibrium equations along with the boundary conditions are obtained. As a result, the analytical solutions of the symmetric and antisymmetric elastic LTB of prestressed I-beams are obtained, for the first time, and the correctness of the analytical solution of the critical moment of the symmetric buckling of the prestressed I-beam is verified by those simulated by using ANSYS. Finally, parameter analysis is carried out. It is found that: (1) the critical moment of the prestressed steel I-beam, with rectilinear tendons, under equal end moments can be determined by that of the symmetric buckling; (2) the critical prestressing force can be determined by that of the symmetric buckling or antisymmetric buckling depending on the relationship between the dimensionless eccentricity and its threshold value.

Ultimate strength of horizontally curved steel I-girders with equal end moments

Even under gravitational loading alone, horizontally curved girders experience not only bending moment but also torsional moment. The torsional moment acting on open sections simultaneously produces shear and normal stress due to pure and warping torsion respectively. Consequently, bending moment, pure torsion and warping torsion are coupled, which results in a very complicated stress state that makes it difficult to calculate the ultimate strength of horizontally curved members. This study revealed that the initial curvature can reduce the ultimate strength of horizontally curved members by up to 50%. Although current design specifications such as the AASHTO LRFD Bridge Design Specifications, suggest some alternatives, the exact behavior of a curved member cannot be considered well with those provisions. While it is true that the one-third rule is convenient to apply and gives good results, there is no strength equation for curved members. In order to derive an adequate strength equation for curved members, this research suggests a new concept of ultimate state. Finite element analysis using ABAQUS is used to consider the effects of sectional rigidities for bending, pure torsion and non-uniform torsion separately. Finally, an ultimate strength equation is suggested for simply supported curved girders that are subjected to equal end moments.

Elastic Lateral Torsional Buckling of Simply Supported Beams under Concentrated Load and Linear Moment Gradient

Lateral torsional buckling is a limit state for I-shaped steel beams that may often be a controlling issue in structural steel design. When these members are not appropriately braced so as to prevent lateral deformations and torsion, they are subjected to risk of failure by lateral torsional buckling before reaching their ultimate capacity. This paper investigates elastic lateral torsional buckling of simply supported I-shaped steel beams under concentrated load and linear moment gradient using design standards and codes, approaches from the literature and finite element analysis. Several unbraced member lengths and end moment values are taken into account to compare and evaluate these approaches in terms of elastic critical moment and end moment ratios. Analysis results show that lateral torsional buckling is a crucial stability problem for I-shaped steel members that are under flexure and it is reflected with adequate safety in the design codes and standards considering finite element analysis outcomes.

In-plane failure mechanisms and strength design of circular steel planar tubular Vierendeel truss arches

Vierendeel steel truss arches are often used in lighting zones of the spatial roof to obtain good permeability and lighting effects. They are different from conventional steel truss arches in terms of failure mechanism and strength design because they have only transverse tubes without diagonal tubes between chords. The chords of the Vierendeel truss arch undertake axial, bending and shear actions while the transverse tubes only resist the bending action. Hence, their structural design against strength is different from conventional steel truss arches. However, this aspect is not well analyzed in literature. This study analyzed the in-plane instability mechanism, failure mode and corresponding strength of the Vierendeel truss arch under a uniform radial load, a full-span uniform vertical load, a half-span uniform vertical load and their combinations. The global in-plane elastic buckling load of the arch under a uniform radial load is derived firstly and an interaction design formula for predicting the global in-plane strength of the arch under a uniform axial compression is proposed. It is found that the chords of the arch may fail in fully sectional plastic moment mode. Transverse tubes may fail because of the end moments. Slender enough arches may also undergo global failure. Strength design equations for local chord failure and for global failure of arches are developed. All of the equations proposed for predicting global in-plane elastic buckling, global in-plane ultimate strength and chord local strength of the arch agree quite well with the finite element results.

Heat propagation of circular thin-walled parts fabricated in additive manufacturing using gas metal arc welding

A finite element model is developed to calculate the heat propagation of a circular thin-walled component fabricated in gas metal arc welding based additive manufacturing. The heat evolution, thermal cycle feature, and temperature gradient in molten pool and deposited layers are revealed. The temperature simulations at some locations are in agreement with measured values from thermocouples. As the deposition process proceeds, the high-temperature regions of the substrate and molten pool increase. The temperature gradient in the molten pool decreases with the increasing deposition height. The heat dissipation condition in the molten pool of current layer tightly depends on the deposition direction of fore layer. At the deposition ending moment, the heat conduction in the axial direction is the predominant heat dissipation orientation, whereas the circumferential orientation becomes the main heat dissipation direction in the top layers.

Effect of moment gradient and load height with respect to centroid on the reliability of wide flange steel beams subject to elastic lateral torsional buckling

The reliability of doubly-symmetric wide flange steel beams designed to the AISC Specification for Structural Steel Buildings subjected to elastic lateral torsional buckling was evaluated when considering variation in moment gradient and load height. The analysis considers continuous loads on spans subjected to various end moments with supports that are torsionally fixed and laterally supported, without additional intermediate restraints. Dead load, occupancy live load, and beam resistance random variables were considered. Beam lateral torsional buckling resistance was evaluated from numerical solution of a fundamental differential equation that accounts for the effect of moment gradient and load height. In some cases, it was found that use of the AISC design procedure results in significant inaccuracies for estimation of elastic lateral torsional buckling resistance, where underestimations occur in regions of reverse curvature bending and when loads are placed below the beam shear center, while large overestimations can occur when loads are placed above the beam shear center. These discrepancies result in significant variation in beam reliability. However, the use of accurate equivalent uniform moment factors can restore uniformity in notional reliability level.

Finite element analysis and experimental validation of thermal behavior for thin-walled parts in GMAW-based additive manufacturing with various substrate preheating temperatures

Reducing thermal stress and preventing cracking of fabricated parts have been key issues in wire and arc additive manufacturing (WAAM). It is believed that complex thermal behavior in WAAM is a significant cause for thermal stress and cracking of components. Substrate preheating is an efficient approach to treat these issues. A 3D transient heat transfer model of a circular ten-layer single-pass part was built to investigate the thermal behavior in gas metal arc welding (GMAW) based additive manufacturing. Meanwhile, the validation experiment was carried out to check the effectiveness of the finite element model through thermal cycle tests. The simulated thermal cycle curves matched the experimental results well. The effect of substrate preheating on thermal behavior was studied by the verified model. The modeling results show that substrate preheating can make the thermal cycles much smoother and decrease the cooling rate of the molten pool. The maximum temperature gradient in the molten pool decreases with the increasing substrate preheating temperature. At the deposition ending moment, preheating can increase the temperatures of deposited layers, whereas it has little effect on the temperature gradient distribution of the layers.

MOMENT AMPLIFICATION FACTOR OF BEAM-COLUMNS WITH INITIAL DEFLECTION

In the design of slender steel beam-columns, the moment amplification factor is used to estimate the maximum bending moment. The formulas for evaluating the factor have been presented on the basis of the elastic or elastic-plastic analysis, however the initial deflection of beam-columns is not considered. This paper discusses the effect of initial deflection on the value of the moment amplification factor by performing the analytical work. The analytical model is a simply supported beam-column subjected to constant axial compressive force and end moments. First of all, the equilibrium differential equation which governs the problem is solved and the formula for calculating the bending moment is obtained. In the parametric study, magnitude of the initial deflection, the axial load ratio, the slenderness ratio and the end moment ratio are selected as the parameters. The effects of magnitude of the initial deflection and the end moment ratio on the moment amplification factor are discussed.