Stiffness-proportional method

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... 

In terms of overall distribution, the uniform and stififiiess-proportional schemes are the most effective at reducing accelerations at floors 5-10. For example, under the MCE at the roof, the uniform scheme achieves a 10% reduction and the stiffness proportional approach a 14% reduction from the nearest of the advanced methods, SSSA. This may be attributed to the standard methods apportioning large damping at the base and roof of the building. 

While all methods investigated were effective, the three optimal placement techniques studied, the SSSA, Takewaki and Lavan methods, all offered greater reductions in interstory drifts than the uniform and stiffness-proportional schemes. It is therefore evident that there is benefit to be gained from the additional effort of implementing an iterative scheme, in terms of further response reductions for a given outlay. It is notable that this benefit of the advanced schemes is not so evident when considering peak absolute floor accelerations, which do not reveal large differences between any of the added damper schemes, apart from consistently smaller acceleration distributions in the upper floors for the standard placement methods. 

More experimental work has been done with DDT than with all the other five chlorinated hydrocarbons combined, probably because DDT was the first of the group found to have insecticidal value. Carter (10) has summarized the several colorimetric methods for DDT. The one proposed by Stiff and Castillo (51), as modified by Claborn (14), and the one by Schechter and Haller (47) have probably been most widely used. In the Stiff and Castillo method, when the DDT is heated in pyridine solution containing xanthydrol and potassium hydroxide, a red color develops which is proportional to the quantity of DDT present. The reaction is sensitive to 10 micrograms. As TDE does not give a color with this reagent, Claborn (14) has proposed the reaction for the determination of DDT in the presence of TDE. He has also shown that for the development of the color the amount of water in the pyridine is critical. 

The second successful dense smokeless powder was the ballistite which was invented by Alfred Nobel.6 This was a stiff gelatinous mixture of nitroglycerin and soluble nitrocellulose in proportions varying between 1 to 2 and 2 to 1, prepared with the use of a solvent which was later removed and recovered. Nobel appears to have been led to the invention by thinking about celluloid, for the patent specification states that the substitution of almost all the camphor in celluloid by nitroglycerin yields a material which is suitable for use as a propellant. In the method of manufacture first proposed, camphor was dissolved in nitroglycerin, benzene was added, and then dry, pulped, soluble nitrocellulose the mixture was kneaded, the benzene was allowed to evaporate, and the material was rolled between warm rollers... 

These are physical blends of NR and polypropylene, mixed in different proportions to give mbbers with different stiffness properties. The method of dynamic vulcanization is possible in TPNR [15]. They are suitable for injection molding into products for automotive applications such as flexible sight shields and bumper components. Grafting is another method used for the modification of NR. The properties of PMMA-g-NR, PS-gg-NR, and PAN-g-NR have been analyzed by Thomas and co-workers [16, 17]. 

Since, ligand accessibility and template definition are maximal in stiff polymers, whilst good kinetics and rapid equilibration are favoured in flexible polymers, the choice of cross-linker must inevitably be a compromise [47], It should be pointed out that, in addition to the type and proportion of cross-linker involved, the porogenic solvent and method of polymerisation both also affect the macro structure of the polymer in terms of porosity and internal surface area. 

Soil has highly non-linear stress-strain behavior and consequently soil stiffness is dependent on its stress state, as shown in Fig. 23.1. It can be seen that at low stress in a small scale model, a soil is significantly softer than would be the case for the same soil at higher stress in the prototype. It is therefore important when modelling soil to replicate the stress level of the prototype in the model. Without doing so, the soil stiffness would not be correct and hence test results would have no quantifiable relation to the prototype scenario. There are two possible methods available to ensure the stress state in the soil model is correct. The first method is to carry out tests at nearly full prototype scale proportions, hence accurately replicating the stress state in the soil. However this method is both time consuming and expensive. 

A wave of ultrasound will reflect from a lubricant film between two bearing components. The response of the film to a sound wave depends on the acoustic and geometrical properties of the oil layer. For thin lubricant films the layer behaves as a spring and the proportion of the wave reflected (or the reflection coefficient ) is related to the stiffness of the oil layer. This provides a method for determining the film thickness. 

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