Prediction of splitting tensile strength from the compressive strength of concrete using GEP

Splitting tensile strength is one of the important mechanical properties of concrete that is used in structural design. In this paper, it is aimed to propose formulation for predicting cylinder splitting tensile strength of concrete by using gene expression programming (GEP). The database used for training, testing, and validation sets of the GEP models is obtained from the literature. The GEP formulations are developed for prediction of splitting tensile strength of concrete as a function of water-binder ratio, age of specimen, and 100-mm cube compressive strength. The training and testing sets of the GEP models are randomly selected from the complete experimental data. The GEP formulations are also validated with additional experimental data except from the data used in training and testing sets of the GEP models. GEP formulations’ results are compared with experimental results. Results of this study revealed that GEP formulations exhibited better performance to predict the splitting tensile strength of concrete.     

The effects of strength testing schedules on muscle strength recovery following static work

In order to measure the recovery of muscle strength after static contractions, strength tests must be performed at various times recovery. This is shown to be an invasive procedure, particularly at typically-recommended schedules of one measurement every 30 s or every 60 s, as the measurement interferes with the recovery process. A predictive equation is given to correct recovery data for this invasiveness.     

A relation between dynamic strength and manual materials-handling strategy affected by knowledge of strength

OBJECTIVE: We studied the relation between dynamic (isokinetic) strength and the batch-assorting strategy to initiate a manual materials-handling task and the effect of knowledge of strength on that relation. BACKGROUND: The debated, complex relationship between muscular strength and the risk of injury can be better understood from a behavioral perspective by examining performance strategies in physical acts such as lifting. METHODS: Thirty-two participants (16 men and 16 women) were first tested for their isokinetic strengths of trunk extension, knee extension, shoulder extension, and shoulder abduction. The participants were then divided into two groups, one provided with knowledge feedback of their strength testing results and the other not provided with such feedback. Participants subsequently performed the same load-handling task in which they carried batches of various weight plates while allowed to assort batches of more than one plate into any combination. RESULTS: Dynamic strength, as represented by a total isokinetic strength score, and knowledge feedback both had significant effects on measures quantifying the batch-assorting strategy. CONCLUSION: Individuals with greater strength tended to adopt a strategy corresponding to a heavier load per carry and fewer carries per batch. Receiving knowledge feedback evoked a tendency toward handling a heavier load, and this tendency was more salient in the weaker individuals. APPLICATION: Potential applications include the use of strength testing in worker selection and training as well as in job design to promote better strategies of balancing productivity and injury prevention.     

Post-buckling strength of thin-walled members

The finite element displacement method considering both geometrical nonlinearity and material non-linearity has been used to investigate the post-buckling behaviour and the ultimate strength of thin-walled nonplanar (three-dimensional) structural members. The two types of nonlinearities are based on Lagrangian coordinates and the flow theory of plasticity, and the formulations are developed using the variational principle and the incremental variational principle. The tangent stiffness matrix which is derived explicitly up to a point prior to volume integration, has been found to be quite efficient. The cases of a hat-section beam under a concentrated load for a web crippling study and a channel section subjected to combined bending and torsion are used to show the capabilities of the computer program. Results indicate that the conventional linear, elastic analysis over-estimates the strength of thin-walled members and may not even be a useful approximation and that the structure may be excessively deformed when approaching the ultimate load. The study also demonstrates the merit of using the finite element method for detailed investigations of particular problems.     

Yield strength of thin-film parylene-C

For the first time, the yield strength of thin-film parylene-C is measured from membrane load-deflection experiments and surface profile analysis. To do so, the onset pressure which causes plastic deformation of the membrane is first experimentally measured. Then a new 2-step displacement model, together with the energy minimization technique [1], is developed to convert the onset pressure to the yield strength on the pre-stressed parylene membrane under a uniform pressure loading. The results depict a Yield Strength of 59 MPa (or 0.012 of strain) for thin-film parylene-C in comparison to 55 MPa reported by parylene vendor (measured from large samples) [2]. To double check with the result, the balloon model [3] is further used to compare with the stress value from our model at the center of parylene membranes and good agreements are obtained. This work is supported by the NSF Center for Neuromorphic Systems Engineering (CNSE) at Caltech.     

Empirical modeling of splitting tensile strength from cylinder compressive strength of concrete by genetic programming

Compressive strength and splitting tensile strength are both mechanical properties of concrete that are utilized in structural design. This study presents gene expression programming (GEP) as a new tool for the formulations of splitting tensile strength from compressive strength of concrete. For purpose of building the GEP-based formulations, 536 experimental data have been gathered from existing literature. The GEP-based formulations are developed for splitting tensile strength of concrete as a function of age of specimen and cylinder compressive strength. In experimental parts of this study, cylindrical specimens of 150 × 300 mm and 100 × 200 mm in dimensions are utilized. Training and testing sets of the GEP-based formulations are randomly separated from the complete experimental data. The GEP-based formulations are also validated with additional 173 data of experimental results other than the data used in training and testing sets of the GEP-based formulations. All of the results obtained from the GEP-based formulations are compared with the results obtained from experimental data, the developed regression-based formulation and formulas given by some national building codes. These comparisons showed that the GEP-based formulations appeared to well agree with the experimental data and found to be quite reliable.     

On the measurement of human strength

Generation of muscle strength is a complex procedure of myofilament activation, nervous feedforward and feedback control, and use of mechanical leverages within the human body. Since strength measurement directly at the muscle is (currently) not feasible, it is usually done at the outside of the body, at the interface with some kind of a dynamometer. This poses various challenges because of difficult mechanical and physiological modelling of the conditions, and because of difficulties in experimental control. To better understand and measure human motor performance, a model of muscle functions and control is discussed, and means for computer-aided position and motion observation are proposed. Experimental variables are classified, and a taxonomy for static (isometric) and several dynamic measurement techniques is described.     

Trunk strength during asymmetric trunk motion

It is important to understand how trunk strength varies as a function of workplace factors so that the work environment can be designed to minimize the risk of low back injury. In this study maximal trunk torque production around the lumbosacral junction was measured in 44 subjects as trunk concentric and eccentric isokinetic velocity and trunk asymmetric line of action were varied. Trunk torque decreased by approximately 8.5% of maximum for every 15 deg of asymmetric trunk angle. Increases in concentric velocity decreased trunk strength, whereas increases in eccentric trunk velocity increased strength. Significant interactions were also found, and it was determined that the common finding that eccentric strength exceeds concentric strength is true only for forward trunk angles at all asymmetric angles. These results should have significant implications for the design of manual materials handling tasks.     

Multi-material topology optimization with strength constraints

A heuristic approach to handle strength constraints based on material failure criteria in multi-material topology optimization is presented. This is particularly advantageous if different materials have different failure criteria. The change in the material failure function in an element due to a contemplated material change is estimated without the need for expensive matrix factorizations. This change is used along with the changes to the objective and deflection-based constraint functions, computed using pseudo-sensitivities, to determine a single aggregated ranking parameter for the element. Elements are ranked on the basis of their ranking parameters and this rank is used to modify the material ID-s of a few top-ranked elements during an optimization iteration. The working of the algorithm is demonstrated on a few example problems showing its effectiveness and utility in deriving optimal topologies with multiple materials in the presence of stress and strain-based failure criteria, in addition to the conventional stiffness-based constraints.     

大载荷下舵片的强度分析

为在设计过程中对导弹舵片进行强度校核,对存在截面尺寸变化的某导弹舵片进行线性静力分析和塑性分析;当舵片结构因大载荷而发生屈服时,线性静力分析可能会因为应力集中得到不正确的结果,而塑性分析的结果更合理,与试验结果更接近.     

Modelling wrist-twisting strength of the elderly

This paper presents a biomechanical model of wrist-twisting strength and uses it to explain maximum voluntary contractile (MVC) counter-clockwise torque and force generated by elderly subjects in attempting to unscrew rough and smooth circular screw-type container lids of diameters 31, 55, 74 and 113 mm. Forty-two subjects, aged 60-97 years, were tested. The results indicated-that for-commercially available lids, torque-diameter relationship was linear up to a certain lid size (diameter), and non-linear, with a decreasing trend, beyond that size. The non-linearity was different for lids with rough and smooth grip surface. An optimal diameter for smooth lids has been proposed. For both types of grip surfaces, force magnitudes were similar up to 74 mm. Beyond this diameter the effects of surface finish were manifested. This was explained by the relationship between hand size and type of grip used at the various diameters. Implications of these results for lid design are discussed. Regression models are also presented which portray good fit to the data.     

Fracture strength of silicon carbide microspecimens

Polycrystalline silicon carbide tensile microspecimens 3.1 mm long were produced by deep reactive ion etching of wafers on the order of 150 /spl mu/m thick. The gage sections, which were nominally 200 /spl mu/m wide, were either straight, slightly curved, or contained double notches in order to vary the size of the highly stressed region. The fracture stresses of 190 specimens from three process runs were measured in a novel test setup. The average local fracture strengths for the last run were: straight 0.38/spl plusmn/0.13 GPa, curved 0.47/spl plusmn/0.15 GPa, notched 0.78/spl plusmn/0.28 GPa. The corresponding Weibull characteristic strengths were, 0.42 GPa, 0.53GPa, and 0.88 GPa with respective moduli 3.3, 3.4, and 3.1. These results show a clear increase in the strength of the material as the size of the highly stressed region decreases. Fractographic analyzes showed failures initiating from the bottoms of side grooves left by the etching process. The grains of the material were quite heterogeneous, varying from a few microns in size to columnar grains through the entire specimen thickness. The curved specimens were used as the base for predicting the probability of failure of the other two shapes. While the Weibull approach was quite accurate for the straight shape, it over-predicted the strengths of the notched specimens. Given the microstructure of the material relative to the size of the specimen, a continuum analysis is questionable.     

阳极键合强度及其评价方法

阳极键合作为一种在微机电系统(MEMS)中运用的关键技术,具有工艺简单、键合强度高、密封性好等优点。经过几十年的发展,该技术在键合机理和提高与评价键合强度等诸多方面都得到了很大的发展,并应用于越来越多的领域。对阳极键合技术的机理、键合基片材料的发展以及键合强度的评价方法等方面进行了综述和评价,并对阳极键合技术在MEMS中的发展趋势作出展望。     

Graphical displays of human strength data

To facilitate the effective use of strength data in a human-task simulation environment, we have developed graphical methods to display the multidimensional characteristics of strength data. We use human figures together with two and three dimensional graphical symbols, colours and animations to visualize the effects of different parameters on strength. These displays give a dynamic view of the effects of various parameters on strength, and illustrate safe and forbidden body postures (or regions) in terms of strength capabilities.     

Arm lift strength in work space

This study was conducted to determine arm strength values for isometric and isokinetic efforts around the human trunk. Thirty-eight normal young adults (20 male and 18 female) performed a total of 19 tasks. These consisted of one self-selected optimum posture with upright stance and elbows bent at 90 degrees , designated as standard posture for isometric test. In addition, isometric testing was done sagittally symmetrical 30 degrees and 60 degrees lateral planes at half-, three-quarters- and full-reach distances at knuckle height. The isokinetic tests were done between knuckle height and shoulder height in postures identical to isometric tests. The sequence of these tasks was randomised. The peak strength in standard posture was invariably lower than the peak strength at half-reach in isometric condition in all three planes for both sexes with the exception of one condition among females (60 degrees lateral plane, half-reach isometric). Peak and average arm lift strengths of males were significantly higher than those of females (p < 0.01) and ranged between 44% and 71%. For both sexes isometric strength was significantly higher than isokinetic strength (p < 0.01). The peak and average strengths in the sagittal plane were invariably higher than those of asymmetric postures, with one exception among females. With increasing reach distance the strength declined significantly for all conditions among both genders (p < 0.01). The ANOVA showed that the gender, mode of lifting, postural symmetry and reach of lifting, in addition to affecting the peak and average strength individually (p < 0.01), had significant 2-way and 3-way interactions (p < 0.01). All strength values were inter-correlated (p < 0.01). The regressions predicting peak and average strengths from anthropometric characteristics and sagittal plane strengths accounted for 63% to 89% of all variance and were highly significant (p < 0.01).