Dynamic strength factors

Dynamic Strength. The dynamic design strengths for steel reinforcing and concrete are equal to their static design strengths times the appropriate Dynamic Increase Factor (DIF). 

It is possible to determine the actual strain rate of a material during calculation of dynamic response using an iterative procedure. A rate must be assumed and a DIF selected. The dynamic strength is determined by multiplying the static strength (increased by the strength increase factor) by the DIF. The time required to reach maximum response can be used to determine a revised strain rate and a revised DIF. This process is repealed until the computed strain rate matches the assumed value. There are uncertainties in many of the variables used to calculate this response and determination of strain rates with great accuracy is not warranted. 

Dynamic Increase Factor - The ratio of dynamic to static strength which is used to compute the effect of a rapidly applied load to the strength of a structural element. 

To incorporate the effect of material strength increase with strain rate, a dynamic increase factor (DIF) is applied to static strength values. DIFs are simply ratios of dynamic material strength to static strength and are a function of material type as well as strain rate as described above. DIFs are also dependent on the type of stress (i.e. flexural, direct shear) because peak values for these stresses occur at different times. Flexural stresses occur very quickly while peak shears may occur relatively late in time resulting in a lower strain rate for shear. 

The following sections review some methods to quantify performance and lifting capability of isolated trunk muscles during a multilink coordinated manual materials-handling task. Relevant factors that influence the static and dynamic strength and endurance measures of trunk muscles will be addressed, and the clinical applications of these assessment techniques will be illustrated. 

We shall henceforth refer to (58) and (59) as of generalizations of the London formula [55] and the Casimir-Polder formula [56], respectively. The latter, in fact, refer to Cg dispersion coefficients for atoms expressed in terms of static (London) or dynamic (Casimir-Polder) polarizabilities, whereas (58) and (59) describe, in a completely general way, non-expanded dispersion between atoms or molecules. (59) expresses the coupling of two electrostatic interactions (l/ri2 and l/r ) involving four space points in the two molecules, with a strength factor which depends on how readily density fluctuations propagate between r and on A, r 2 and F2 on B (Fig. 4). 

Vincent [133] has examined the statistical significance of a possible inverse correlation between impact strength and dynamic modulus and concluded that, at best, this correlation only accounts for about two-thirds of the variance in impact strength. Factors such as the influence of molecular mass, and details of molecular structure such as the presence of bulky side groups, are not accounted for. He also reported impact tests over a wide temperature range on some polymers, notably polytetrafluorethylene and polysulfone, where peaks in brittle impact strength were observed at temperatures close to dynamic loss peaks, suggesting that in some instances it may be necessary to consider the relevance of a more... 

The design ground motion is one of the primary factors used to determine the required seismic resistance (strength) of structures and supported nonstmctural components. In many seismic codes the design ground acceleration is used as a product of an acceleratirMi factor which depends on the seismic zone and a dynamic amplification factor which depends rm the soil class and the... 

Figure 4.11. Diagrammatic sketches of atomic lattice rearrangements as a result of dynamic compression, which give rise to (a) elastic shock, (b) deformational shock, and (c) shock-induced phase change. In the case of an elastic shock in an isotropic medium, the lateral stress is a factor v/(l — v) less than the stress in the shock propagation direction. Here v is Poisson s ratio. In cases (b) and (c) stresses are assumed equal in all directions if the shock stress amplitude is much greater than the material strength.

The next step in the design procedure is to select the materials. The considerations are the physical properties, tensile and compressive strength, impact properties, temperature resistance, differential expansion environmental resistance, stiffness, and the dynamic properties. In this example, the only factor of major concern is the long-term stiffness since this is a statically loaded product with minimum heat and environmental exposure. While some degree of impact strength is desirable to take occasional abuse, it is not really subjected to any significant impacts. 

Although energy conservation constraints dictate which VP channels are open, it is the nature of the intermolecular interactions, the density of states and the coupling strengths between the states that ultimately dictate the nature of the dynamics and the onset of IVR. These factors are dependent on the particular combinations of rare gas atom and dihalogen molecule species constituting the complex. For example, Cline et al. showed that, in contrast to He Bra, Av = 2 VP in the He Cla and Ne Cla complexes proceeds via a direct... 

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