Load Height Research Articles

Out-of-plane advanced analysis of steel structures

Attempts to extend practical advanced analyses of the in-plane behaviour of 2-D steel frames under in-plane loading to out-of-plane behaviour have been largely unsuccessful because of difficulties in modeling the effects of yielded zones, load heights, interactions between twist and axial force and moments, and end warping restraints. Advanced analyses need to be able to account for the influences of moment and axial force distributions, load heights, and end restraints on elastic and inelastic lateral buckling, and to be consistent with the code formulations of beam and column out-of-plane strengths. This paper reviews extensions of methods of advanced analysis beyond those for the in-plane behaviour of 2-D frames for which local buckling is prevented towards the behaviour of 3-D frames under general loading. An early step towards this goal is the development of an advanced analysis for the out-of-plane behaviour of 2-D frames under in-plane loading. It has been proposed that this should be simplified by first carrying out an in-plane analysis using one of the presently available plastic hinge methods, and then by using a practical advanced analysis of the out-of-plane behaviour which is based on an inelastic lateral buckling analysis which includes allowances for residual stresses and initial crookednesses and twists. This paper discusses some of the difficulties to be overcome in the development of such a method, so that future attempts to develop advanced analyses for the lateral buckling of 2-D frames for which local buckling is prevented can systematically assess these difficulties and develop methods of overcoming them. Suggestions are also made for testing and benchmarking these analyses.

Lift-to-weight ratio dependence of lift and stability in an active-Maglev system

In an active-Maglev system composed of YBCO bulk and electromagnets, lift-to-weight ratio dependence of lift and stability was investigated experimentally and theoretically. A bulk was levitated by an electromagnet after a field-cooling process for magnetization. It has been shown that lift and stability of the bulk are closely related to both the magnitude of trapped magnetic field and the magnetic field distribution generated by the electromagnet. Minimum field-cooling current for stable levitation, the operating current of electromagnet at initial levitation, and maximum stable-levitation height were measured as a function of the load on the top surface of the bulk. It was observed that the minimum trapped field for stable levitation increased with the load. Maximum permissible displacement in the radial direction was also investigated experimentally as a function of the load and levitation height. The maximum permissible displacement decreases with levitation height and stable-levitation range decreases with weight of load. Numerical analysis based on the three-dimensional finite element method was performed to investigate electromagnetic behaviors within bulk, especially stability at initial levitation. The stability depends on the ratio of operating current at initial levitation to field-cooling current.

Emissions and efficiency of a domestic gas stove burning natural gases with various compositions

The heating value of a fuel, which depends on its composition, strongly affects burner performance. Using the same gas stove to burn natural gas with various heating values is inappropriate and hazardous due to the possible occurrence of incomplete combustion (i.e. a great increase of CO emissions and/or soot formation), liftoff, flashback and inadequate heat input. In this study, we aim to assess the effects of changes in gas composition on burner performance and propose suitable design or operational factors of domestic gas stoves burning natural gas with various heating values. A single gas burner, originally designed for burning natural gas with low heating value, is adopted to investigate the effects of variations in gas composition on the burner performance. The influence of five significant parameters, including gas composition, primary aeration, gas flow rate (heat input), gas supply pressure, and loading height, on the thermal efficiency and CO emissions were reported and discussed. Using natural gas with high heating value instead of natural gas with low heating value results in a decrease in thermal efficiency (due to higher thermal input) and an increase in CO emission (caused by incomplete combustion). These problems can be significantly improved by decreasing the gas pressure to a suitable value, by enlarging the primary aeration to a favorable level, by selecting a proper thermal input, or by adjusting the optimized heating height.

An investigation of stability limits while holding a load

The objective of this study was to investigate the effects of load height and foot placement on the functional base of support (FBOS) limits and the postures that participants used when they reached their FBOS limits. Twelve young male participants were tested while holding a 12-kg load at reach (above their heads), at shoulder and knuckle height, and unladen under both wide and narrow foot placements. The FBOS limits and the centre of pressure (COP) excursion length were calculated based on data from a force platform. Postural angles when participants reached their FBOS limits were calculated from records of a 2-D motion analysis system. The results showed that the load height had greater effect on the posterior FBOS limit. As the load height decreased, the COP excursion length decreased. Participants were prone to using a hip strategy to maintain postural balance when reaching their FBOS limits. Quantitative data of FBOS limits and postural control while participants hold a load at various heights when reaching their FBOS limits is of value for designing a safe materials handling workplace.

Long-term prediction method for the green water load and volume for an assessment of the load line

To develop a practical prediction method for the green water load and volume on the bow deck in irregular waves, model tests were conducted using a tanker and a cargo ship on a domestic Japanese voyage. The relation between green water load and relative water height at the stem was considered. Based on the finding that the maximum value of the green water load is proportional to the square of the maximum value of the water elevation over the bow top, the probability density functions of the green water load and volume in short-term predictions were proposed. It was verified that the proposed functions show good agreement with the measured distributions, especially in the tails, and were better than conventional functions. Using these functions, long-term predictions of the green water load were carried out. It was confirmed that the present method is more rational than the conventional one for estimating the long-term probability of the green water load. An assessment of the bow height of a domestic Japanese ship from the viewpoint of deck wetness was carried out using these prediction methods. This research was used as the technical background for the revision of domestic rules on load lines, which was enforced in October 2001.

Theoretical and numerical stability analyses of unrestrained, mono-symmetric thin-walled beams

In this paper, a contribution to the overall stability of unrestrained thin-walled elements with open sections is investigated. A model is developed for beam lateral buckling stability analysis. According to the European steel code, Eurocode 3, an analytical solution is used for checking the stability of laterally unrestrained beams. It depends on bending distribution, on load height effect and on degree of the monosymmetry of the section called Wagner’s parameter. Coefficients C1, C2 and C3 are respectively affected to these parameters and are given for some selected load cases. Based on the present model, these coefficients are recomputed for simply supported beams. Ritz and Galerkin’s methods are applied. Following Galerkin’s method, the coefficients C1 and C2 are the same as those adopted in Eurocode 3, but some of Wagner’s proposed C3 coefficients are very different from those usually used. The different solutions are first discussed and then compared to finite element results. ABAQUS software is used in numerical simulations where three-dimensional beams with warping and shell elements are chosen in modelling lateral buckling phenomena. The presented results are close to shell element results but the regular solutions overestimate the lateral buckling resistance of mono-symmetric I beams.  2002 Elsevier Science Ltd. All rights reserved.

Brewery wastewater treatment in a fluidised bed bioreactor

A hydrodynamic characteristic performance of a three phase fluidised bed bioreactor has been studied with brewery wastewater. The influence of operating parameters, such as phase hold up, phase mixing, aspect ratio and superficial gas velocity, on an aerobic biodegradation in a bioreactor of 0.16 m i.d. and 2.7 m in height, was analysed. A low-density (960 kg/m 3) support particle with an internal interstice was employed. The particle and liquid loading were varied in order to determine the effect of phase hold up on bed homogeneity. The ranges in which particle loading and bed height affect fluidisation, and consequently chemical oxygen demand (COD) reduction, were determined. The distributor used in this work was designed such that fluid flow pattern similar to that of a draft tube was induced in the reactor. The low-density particles enabled cost effective operation at a relatively low gas superficial velocity (2.5 cm/s). Aspect ratio significantly influenced the overall bed homogeneity, and the optimum aspect ratio was 10, with volume of the support particles being 21% of the reactor volume.

Response of trunk muscle coactivation to changes in spinal stability

The goal of this effort was to assess the neuromuscular response to changes in spinal stability. Biomechanical models suggest that antagonistic co-contraction may be related to stability constraints during lifting exertions. A two-dimensional biomechanical model of spinal equilibrium and stability was developed to predict trunk muscle co-contraction as a function of lifting height and external load. The model predicted antagonistic co-contraction must increase with potential energy of the system even when the external moment was maintained at a constant value. Predicted trends were compared with measured electromyographic (EMG) data recorded during static trunk extension exertions wherein subjects held weighted barbells at specific horizontal and vertical locations relative to the lumbo-sacral spine junction. The task was designed to assure the applied moment was identical during each height condition, thereby changing potential energy without influencing moment. Measured EMG activity in the trunk flexors increased with height of the external load as predicted by the model. Gender difference in spinal stability were also noted. Results empirically demonstrate that the neuromuscular system responds to changes in spinal stability and provide insight into the recruitment of trunk muscle activity.

Fatal injuries caused by logs rolling off trucks: Kentucky 1994-1998

Logging is one of the most hazardous occupations and fatality rates are consistently among the highest of all industries. A review of fatalities caused by logs rolling off trucks is presented. The Kentucky Fatality Assessment and Control Evaluation Project is a statewide surveillance system for occupational fatalities. Investigations are conducted on selected injuries with an emphasis on prevention strategy development. Logging was an area of high priority for case investigation. During 1994-1998, we identified seven incidents in which a worker was killed by a log rolling off a truck at a sawmill, accounting for 15% of the 45 deaths related to logging activities. These cases were reviewed to identify similar characteristics and risk factors. Investigations led to recommendations for behavioral, administrative, and engineering controls. Potential interventions include limiting load height on trucks, installing unloading cages at sawmills and prohibiting overloaded trucks on public roadways.

Lateral buckling strengths of cold-formed Z-section beams

This paper is concerned with the inelastic lateral buckling strengths of cold-formed Z-section (CFZ) beams. The point symmetry of the cross-section of a CFZ beam introduces characteristics that are not encountered in a doubly symmetric I-beam. Firstly, the effective section rotates after yielding, so that a CFZ beam under in-plane bending about the geometrical major principal axis is subjected to bending moments about the effective minor axis and bimoments. Secondly, the minor axis bending and warping strain distributions and therefore the lateral inelastic buckling behaviour and strengths of CFZ beams are related to the twist rotation and minor axis displacement directions. The stress–strain curves, residual stresses, initial imperfections, and lipped flanges of CFZ beams are all different to those of hot-rolled I-beams. This paper develops a realistic finite element model for the analysis of CFZ beams and uses it to investigate the elastic lateral-distortional buckling, inelastic behaviour, and strengths of CFZ beams with residual stresses and initial imperfections. The results of the study are used to develop improved design rules which are suitable for CFZ beams. The effects of moment distribution and load height on the lateral buckling strengths are also studied.

Removal Efficiency of the Combined Desulfurization/Denitration Process Using Powder-Particle Fluidized Bed.

A combined desulfurization/denitration (DeSOx/DeNOx) process has recently been proposed by using the powder-particle fluidized bed (PPFB). In the process, SOx is removed by a fine DeSOx sorbent continuously supplied and NOx is reduced to N2 by ammonia under the catalysis of a coarse DeNOx catalyst, the fluidization medium particles. By using the simplest model gas, SO2-NO-Air, in a laboratory scale reactor, SO2 and NO removals in the process are evaluated in this paper by testing the possible side reactions related to SO2 and NO. Then, investigations are extended to the removal efficiency for the simulated flue gas SO2-NO-N2-H2O-Air and to the effects of operating conditions, both gas velocity and the static height of catalyst bed, upon the SO2 and NO abatements. The DeSOx sorbents used were CuO·V2O5·K2SO4/Al2O3 and NaHCO3, and the DeNOx catalysts were V2O5·WO3/TiO2 and WO3/TiO2. It was found that this process suffers little from SO3 exhaust at the reactor exit. SO2 may be chemically adsorbed onto DeNOx catalyst, but it can be suppressed by using a highly efficient sorbent such as CuO·V2O5·K2SO4/Al2O3. Under NH3/NO = 1, both NO and NO2 can be similarly reduced into N2 and the possible side reactions between sorbent and NOx can also be completely abated by the NOx reduction. SO2 and NO removals in the process are more or less affected by water vapor and oxygen fractions, but the removals greater than 90% for SO2 and no less than 80% for NO can still be maintained for actual flue gas, even in a shallow bed with a static catalyst load height of 0.1 m.

Lateral Buckling Strengths of Cold-Formed Channel Section Beams

This paper is concerned with the inelastic lateral buckling strengths of cold-formed channel section (CFC) beams. Code rules for designing steel beams against lateral buckling that are based on data for hot-rolled I-section beams may be unsuitable for CFC beams, because they have different stress-strain curves, residual stresses, and initial imperfections. Distortion may reduce the resistance of a CFC beam to lateral buckling. In addition, because of the monosymmetry of the cross section, the effective shear center moves toward the web and the effective section becomes asymmetrical after yielding, so that a CFC beam under major axis bending is subjected to minor axis bending and twisting. Also, the minor axis bending and warping strain distributions, and therefore the strengths of CFC beams, are related to the twist rotation and minor axis deflection directions. This paper deals with these problems by developing an advanced finite element model to investigate the elastic lateral-distortional buckling, inelastic behavior, and strengths of CFC beams with residual stresses and initial imperfections. The results are used to develop improved design rules for CFC beams. The effects of moment distribution and load height on the strengths are also studied.

Torsional Restraint against Elastic Lateral Buckling

It is well known that a central elastic torsional restraint restricts the lateral buckling shape of an elastic I-beam and increases its elastic flexural-torsional buckling resistance. However, available information on the effects of torsional restraints on elastic buckling are either incomplete, or in some cases inaccurate. This paper investigates the effects of moment distribution and load height on the elastic flexural-torsional buckling of beams with central torsional restraints. The effects of off-center and continuous restraints are also studied, and design approximations and procedures are developed.

Shell strength in the cockle Cerastoderma edule L. under simulated fishing impacts

Experiments were conducted on the cockle Cerastoderma edule L. to quantify effects of physical impacts on shell damage. The study was prompted by the need to address the information requirements to improve design of mechanical harvesting machines for reducing shell damage and mortality of undersized discards. The minimum free falling distance in air required to damage cockle shells is approximately 0.3–0.5 m. Compression tests at three shell striking points indicated a power curve relationship between shell failure load and shell height and a linear relationship with total animal weight. Large cockles (>25 mm shell height) have a weakened umbo compared with the domed high point, indicating a shell thickness differential at the umbo with increasing age and size. Minimising the free falling distance of cockles in rotary sorting equipment to <0.3 m through the design and installation of deflecting baffles in harvesting machinery may reduce shell breakage and mortality of undersized discards significantly.

K-factors for Unbraced Frames: Alignment Chart Accuracy for Practical Frame Variations

For design of steel columns in unbraced frames, the current AISC specification commentaries from both LRFD and ASD contain an alignment chart to determine the K factor for a particular column. The K factor is based on the effective length concept where K factors are used to equate the strength of a compression member of length L to an equivalent pinended member of length KL subjected to axial load only. The unbraced frame alignment chart is a graphical representation in nomograph form of a transcendental equation of a buckling solution of a subassemblage. This solution involves several assumptions not necessarily satisfied in a particular practical situation. The goals of this paper are to point out the practical limitations of the unbraced frame alignment chart effective length approach and to encourage the use of story-based effective length factors. This is done in the following manner. A parametric study shows the limits of accuracy and applicability of the unbraced frame alignment chart results from a linear buckling analysis. The benefits of the AISC Commentary equation C-C2-5 story-based effective length factor are shown through comparison to the alignment chart and linear buckling analysis results. The parametric study shows sufficient examples to encourage practitioners to use story-based techniques for stability assessment. The parametric study investigates variations in bay width, column moment of inertia, loading, and column height. All nomograph results reported include correction of girder factors to account for unequal girder end moments with noncenterspan inflection point. The alignment chart performance is relatively insensitive to bay width variation. Variations in column moment of inertia and column loading lead to large inaccuracies in the alignment chart K factor values but C-C2-5 better handles these cases. The alignment chart performance is most sensitive to column height variation. Configurations with large variation in column height require frame stability analysis to obtain accurate K factors.

Lateral-Torsional Buckling of Singly Symmetric I-Beams

Finite-element buckling analyses of singly symmetric I-shaped girders subjected to transverse loading applied at different heights on the cross section were conducted. Single-curvature and reverse-curvature bending were considered. Moment gradient factors based on the finite-element results were calculated and compared with traditional values used to predict the buckling capacity of I-shaped doubly symmetric sections. The results from the computational study show that, for many cases, traditional moment gradient factors can be used for singly symmetric girders if effects of load height are measured relative to midheight of the cross section. Solutions for load-height effects are presented for singly symmetric I-sections.

Soil clogging in vertical flow reed beds – mechanisms, parameters, consequences and.......solutions?

The purification efficiency of vertical flow reed beds (VFB) is dependent on a very efficient soil aeration. In most systems this is achieved by intermittent pulse loading at the surface providing an oxygenation by mass flow and diffusion. These oxygen transportation mechanisms only function as long as the upper layers of the bed have a high drainage capacity. Purification efficiency drops significantly when constant ponding occurs. A review of the literature on clogging in sand filters is given. In our evaluations the following observations are made. Clogging occurs only in the upper 0-15 cm of the bed. Clogging is dependent on the height of organic mass loading. The content of volatile solids in the upper layers could not be proven as a significant parameter influencing clogging. The infiltration rate can be restored by giving the beds a recovery period of several weeks. The required length of rest is dependent on weather conditions, winter is the most critical time.

Elastic distortional buckling of continuous I-beams

The buckling of thin-walled I-beams is usually treated as being either local or lateral. However, these two buckling modes may interact with each other, and this phenomenon is referred to as ‘distortional buckling’. An elastic distortional buckling analysis of a two-span continuous I-beam with a concentrated load in each span is considered in the paper. The first part of the method performs a simple in-plane analysis of the beam in order to establish the stress resultants, which are then introduced into an out-of-plane distortional buckling analysis developed elsewhere. The effects of factors, such as the section geometry, beam slenderness, support restraint conditions, load height and location and span ratio on the elastic distortional buckling response, are then studied.

コーヌスクローネの維持力に関する研究 第２報 内冠直径と維持力との関係について

Recently conical telescopic denture has been used in many clinical treatments, but it has many problems with retentive force of conical double-crown that need to be solved. The purpose of this study was to elucidate the correlation between retentive force and various factors of conical telescopic double-crown. Various factors such as fabricating material, taper angle, height of cone and load were considered as problems in report 1. In this experiment, retentive force related to the diameter of the cone was examined.The results were as follows:1. Retentive force was greater as the diameter was decreased compared with retentive forces for two diameters of cone. This effect was greater as the height of the cone and load were increased and the taper angle was decreased.2. Retentive force decreased as the taper angle of any diameter of cone was increased and this effect was greater as the height of the cone and load were increased. Retentive force depends on the taper angle strongly in any diameter.3. Retentive force had a tendency to increase slightly as the height of the cone of any diameter of cone was increased and it was greater as the taper angle was decreased and the load was increased. But the increasing rate was less compared with any other factors.4. Retentive force increased in proportion to the load on any diameter of cone, and this effect was greater as the diameter and taper angle were decreased and the height of the cone was increased.

Soil clogging in vertical flow reed beds - mechanisms, parameters, consequences and.......solutions?

The purification efficiency of vertical flow reed beds (VFB) is dependent on a very efficient soil aeration. In most systems this is achieved by intermittent pulse loading at the surface providing an oxygenation by mass flow and diffusion. These oxygen transportation mechanisms only function as long as the upper layers of the bed have a high drainage capacity. Purification efficiency drops significantly when constant ponding occurs.A review of the literature on clogging in sand filters is given. In our evaluations the following observations are made. Clogging occurs only in the upper 0–15 cm of the bed. Clogging is dependent on the height of organic mass loading. The content of volatile solids in the upper layers could not be proven as a significant parameter influencing clogging. The infiltration rate can be restored by giving the beds a recovery period of several weeks. The required length of rest is dependent on weather conditions. winter is the most critical time.