Drift limits

Gerhardt, P. D., Witt, J. M., Summary of Downwind Drift Limits, Comparison of Dust vs. Spray, Pesticide Residue Study, Univ. of Arizona, September 1963. 

The performance of all HPLC detectors can be characterised by certain parameters such as sensitivity, noise, drift, limit of detection, linear and dynamic range, and detection volume. Other factors are more specific to individual types of detectors, and are discussed in their respective sections. 

The indicated short-term error limits in Fig. 3.20 correspond to 3ot or 0.3%. It will be seen from study of the data that over almost any 30-min period, the data lie within the predicted short-term drift limits. Over a period of hours, however, an... 

Limited number of metals acceptable for application (expensive noble metals required) poor stability of ultrathin films at high temperatures drift limited number of analyte that can be tested... 

It is generally accepted that interstorey drift can be used to determine the expected damage. The relation between the drift limit ratios with the damage state, employed... 

The above expression is obtained by best fit of known Pi 0>0i) pairs. These pairs correspond to 2, 10 and 50 percent in 50 years earthquakes that have known probabilities of exceedance Pi. The corresponding maximum interstorey drift limit values 0i, for these three earthquakes, are obtained using the pushover analysis. According to Poisson s law the annual probability of exceedance of an earthquake with a probability of exceedance p int years is given by the formula ... 

Ghobarah, A. 2004. On drift limits associated with different damage levels. International Workshop on Performance-Based Seismic Design, 28 June - 1 July 2004. 

A fully-stressed design is achieved when all p. values tend to unity, i.e. the damping distribution is such that the drift limit is just achieved at each story. Ifthis optimum is not achieved in iteration (k), then the damping levels are adjusted in step (k+1) according to ... 

Finally, we offer some comments on the ease of implementation of the schemes, based on adherence to the damper placement methods procedures as outlined in literature. The uniform and stiffness proportional methods are the simplest to apply while still achieving the desired drift limit. Although requiring the use of only three time histories, the SSSA method is the most time consuming because it requires three time domain analyses at each of the twenty steps used in our analysis (i.e. a total of sixty linear time history... 

The effectiveness and usability of five damper placement methods has been evaluated by using them to achieve response reductions in ten-story, moment-resisting frames. It was shown that even the simplest methods can provide substantial improvements in building performance, as demonstrated by the median responses to a suite of 20 ground motions. In our example, all the schemes considered were able to meet the design drift limits, reduce floor accelerations and eliminate non-linearity at the DBE, resulting in zero residual drift. 

The crossover field for diffusion to drift limited recombination is given by n=x in d=l. Note that Vd = 2T)Wa is the drift velocity in this case. 

The crossover field to drift limited behaviour Increases with Increasing dimensionality of the system and becomes Independent of... 

Figure 6.9 Dependence of the mean FPT ti (xq) on initial particle position for two absorbing boundaries separated by distance L (a) diffusion-limited regime and (b) drift-limited regime.

The diffusion-limited result for the mean FPT (2Dti (xo)/T ) is plotted in Figure 6.9a as a function of Xo/L. The drift-limited result is given in Figure 6.9b as a plot of vT xa)/L versus Xo/L. In this limit, the time to reach the boundary downstream is simply the distance to be traveled divided by the velocity. Equation 6.120 gives the crossover behavior between the two limits provided in Figure 6.9. 

Therefore, in the drift-limited regime, where the effects of the diffusion, barrier, and convective flow may be ignored, the polymer flux is linearly proportional to the polymer concentration and the applied-voltage difference and is independent of the chain length. 

Drift-limited regime In this regime, the electrophoretic mobility of the polymer dominates over diffusion and barrier contributions. For large values of the applied voltage difference Vm, the steady-state flux is linear with the polymer concentration and Vm and is independent of the chain length... 

Damping system may be used in addition to the SFRS in order to meet interstorey drift limits and it may be located external or internal to the structure, while it shares or not the members of SFRS. In Fig. 4 is illustrated a SFRS consisting of one bay moment resisting frame (MRF) and a damping system composed of diagonal braces with installed FDs. The FD system is located independently to the MRF system. 

Frames are inherently flexible and the size of their members is often governed by the interstory drift limits under a moderate earthquake for which limitation of damage to stmctural and nonstmctural elements is sought. 

The dissipative devices should also comply with requirements for interstorey drift of buddings undergoing seismic action. The chosen value of maximum allowable drift, d = 0.003, for damage limitation is taken from OPCM (2005) which provides drift limits for damage limitation in wads of masonry buildings. This limit is also in fine with the expected drift stated in FEMA 356 (BSSC 2000) for unreinforced masonry buildings at the limit state of immediate occupancy. 

In the case of a frictional device, the drift limit is ensured by default because before activation of the friction mechanism, deformations are negligible and, beyond activation of sliding, the device displacement is limited by the assembly stops. The device can therefore perform for all limit states, as long as the coimections and stops in the assembly are designed to resist up to the state of near collapse. 

Regarding acceptance criteria for infills, codes (e.g., CEN 2004), in general, do not provide specific drift limits for infill elements, since it is not taken for granted the fact that infills are explicitly modeled. On the other hand, immediate occupancy and operational acceptance criteria are evaluated to implicitly account for damage to masoiuy infiUs. 

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