Strength load factors

A conservative assumption is that O can be set equal to zero. When the stress O equals the characteristic strength O the faUure probabUity is 63.2%. Under conditions other than tensUe loading, the stress distribution in a body is inhomogeneous. To account for this, a loading factor k is used to calculate the effective volume under stress and kVreplaces V. 

Example 2.21 A rod of plastic is subjected to a steady axial pull of 50 N and superimposed on this is an alternating axial load of 100 N. If the fatigue limit for the material is 13 MN/m and the creep rupture strength at the equivalent time is 40 MN/m, estimate a suitable diameter for the rod. Thermal effects may be ignored and a fatigue strength reduction factor of 1.5 with a safety factor of 2.5 should be used. 

The allowable stress for occasional loads of short duration, such as surge, extreme wind, or earthquake, may be taken as the strength reduction factor times 90% of the yield strength at temperature times Mj for materials with ductile behavior. This yield strength shall be as listed in ASME BPV Code Section II, Part D, Table Y-l (ensure materials are suitable for hydrogen service see API 941), or determined in accordance with para. 

Longitudinal stresses Sl- The sum of longitudinal stresses Sl in any component in a piping system, due to sustained loads such as pressure and weight, shall not exceed the product S W, where is the basic allowable stress at maximum metal temperature expected during the displacement cycle under analysis, and W is the weld joint strength reduction factor. 

The differences among the breaking strengths of the several adhesives may be attributed, in part, to the variation in amount of adhesive present in the sample. The loading factors, the mass of dried adhesive per unit area of paper support, however, reveal no such correlation. For example,... 

Everflex A and Airflex 400 have virtually identical loading factors yet the breaking strength of Everflex A is 25% greater than that of Airflex 400 (3). The differences in breaking strength appear to derive from differences in the mechanical properties of the base copolymers. 

First, for a certain strength reduction factor co the entire loading process will be applied to. The conventional elastoplastic numeric calculation will be carried out in accordance with the strength indexes after reduction. In elastoplastic numerical calculations we use incremental iterative nonlinear itera-... 

Table 3.8-1 shows the load combinations specified in ACI 349 as modified by Regulatory Guide 1.142, Revision 1, Regulatory Position 6 (see Section 3.8.1). These load combinations are based on the strength design philosophy. As stated in Section 3.6, some of these load factors and load combinations are believed to be too conservative (load combinations 7 and 8,... 

In terms of fire resistance considerations, as E-glass fibers and a polyester resin were used, a filled, low viscosity, and self-extinguishing polyester resin was adopted that further showed low flammabihty and medium smoke formation. As fire is an accidental action, the partial load factors could be reduced to 1.0 in the structural design according to the Swiss code. A consideration in the stmctural design of fire situation was that a surface of 2.0 m x 2.0 m of the lower face sheets could fail without collapse of the roof stmcture. This further took into account the reduction of 50% in material strength and stiffness for a 1.0 m wide strip around this surface [19]. 

The situation may be somewhat complicated when one surface is lubricated and the other is not. In that case, one often finds that with each pass of the unlubricated surface, some amount of lubricant film is transferred to the bare surface, leaving bare spots on the lubricated surface. With excessive transfer, the effectiveness of the lubrication will clearly decline. The rate of such transfer will depend on several factors, the most important of which are the applied load and the strength of adsorption of the lubricating film. The load factor is, of course, an operating parameter that lies outside the realm of surface chemistry it is the adsorption process that is of most direct significance for our present purposes. 

The limit states design standards usually include a standard (or set of standards) specifying the design loads and load factors to be used and often also the analysis techniques to be used a standard (or set of standards) specifying the component strengths and resistance factors to be used and standards recommending appropriate serviceability levels. 

Many current design manuals for transportation projects use the load and resistant factor design (LRFD) method (AASHTO 1998 and 2012). This procedure is based on the latest multiple ultimate states theory combining with statistic data treatment results as much as possible. This method uses different load factors for the different limit states and strength reduction factors. All stability checks and section strength checks are based on the same procedure, but there are different load and resistant factors for each specific case. 

With the exception of the load factors given in Table 6.1, this structure shall be designed in accordance with the ultimate strength design provision of ACI 318-71. 

Anchors should be designed for the factored load combinations in accordance with the selected code as discussed above. Care should be taken to ensure that the proper strength reduction factor, (p, is used. There are two distinct sets of strength reduction factors one set applies to using the load combinations from ACI 318 Section 9.2 and a second set for use when load combinations from ACI 318 Appendix C are used. 

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