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With the load factors fixed, the reliability ẞ can still be adjusted by varying the

states.

Chapter 4 and Appendices B

factor and the specification of nominal resistance for different materials and limit E on materials provide some indication as to where current specifications stand in terms of comparative reliabilities.

While these results

may be used as a guide, specification committees may very well feel that some relative adjustments are warranted within their provisions. Additional material data can be used

to refine and to increase the confidence in the resistance factors selected. The choice

of B to be used in selecting resistance criteria should consider, among other factors, the ductility associated with each mode of resistance, the effect of loading rate in enhancing the strength of certain materials, the relative frequency of occurrence of different design situations, and the consequence of failure.

Some simple aids have been prepared to assist material specification writing groups in making their selections. It has been assumed that the load combination of primary interest to standard committees is the D + L combination. This combination governs design

in many practical instances. Even when it does not, it is frequently used for preliminary sizing of members, which are then checked against lateral load effects. Accordingly, Figs. 5.10a through 5.10e present curves relating the reliability B, R/R, VR

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The curves are presented in terms of basic live load L (e.g., L because many designers find it more convenient to think in terms of L than L which may incorporate a reduction. The curves were computed for a basic influence area of A 1000 ft2 (93 m2) and therefore L

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= 0.724 L from Eq. 3.10. In all cases, however L/L 1.0. Thus, the corresponding values of L for any other influence area of interest can be calculated by multiplying the L in Figs. 5.10 by the factor

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Each of these figures describes the relation between B, R/R

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R/R

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values of which range from 0.6 0.9. For problems outside the range presented here, the computer analysis in Appendix F must be used; however, Figs. 5.10a through 5.10e cover most practical cases.

As an example of their use, suppose we are dealing with a material and limit state in which the capacity is described by R/R_ = 1.10 and V,

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