Ductility dynamic loads

Quality of joist welds is also critical to achieving a ductile response. Welding is performed to Steel Joist Institute standards and the lack of specific criteria may prevent development of a predictable ultimate capacity. Special precautions must be taken to remedy this problem such as requiring manufacture in accordance with AWS criteria. Open web steel joists are intended for relatively low static loads and thus are suitable only for low dynamic loads as well. 

Figure 10.1 Time-temperature map. Shape of main boundaries for linear or network polymers. (I) Glassy brittle domain B, ductile-brittle transition. (II) Glassy ductile domain G, glass transition. (Ill) Rubbery domain. The location of the boundaries depends on the polymer structure but their shape is always the same. Typical limits for coordinates are 0-700 K for temperature and 10-3 s. (fast impact) to 1010 s e.g., 30 years static loading in civil engineering or building structures. Fpr dynamic loading, t would be the reciprocal of frequency. For monotone loading, it could be the reciprocal of strain rate s = dl/ Idt.

It can be said that the design of a product involves analytical, empirical, and/or experimental techniques to predict and thus control mechanical stresses. Strength is the ability of a material to bear both static (sustained) and dynamic (time-varying) loads without significant permanent deformation. Many non-ferrous materials suffer permanent deformation under sustained loads (creep). Ductile materials withstand dynamic loads better than brittle materials that may fracture under sudden load application. As reviewed, materials such as RPs can exhibit changes in material properties over a certain temperature range encountered by a product. 

When designing for jet forces, local yielding is permitted which will reduce the dynamic effects of the force on the structures. The dynamic load factor, K, shall be determined by using a ductility ratio (Tm/ ei) as described in Structural Dynamics by J. M. Biggs, 1961, pp. 69-81 and 222-223 or elsewhere. 

In Fig. II-5 the static pressure requiring the same load capacity as is required by a triangular shaped dynamic forcing function applied to a one-degree-of-freedom ductile system (dynamic load factor) is shown as a function of its ductility and duration divided by period of response. Parameters typically necessary to define the response of a particular structure include the duration of the load and the natural period of the structural response, as well as the damping and maximum level of ductility exhibited by the structure during the... 

As indicated in Fig. II-5, the effective blast loading on a structure, as represented by the dynamic load factor, is strongly dependent upon the ductility capacity p (mm) exhibited by the structure. This figure is applicable provided that the natural frequencies of the structure are far from the major frequency content of the load function and therefore no significant dynamic response is excited. A structure exhibiting a ductility level of approximately 5, for example, would typically require only of the order of 33% of the load capacity of a brittle structure with the same frequency characteristics in order to survive the same explosion. 

Anchor ductility is desirable for preventing brittle failure in the connection for two reasons 1) It provides greater margin against failure because it permits redistribution of load to adjacent anchors and 2) It reduces the maximum dynamic loads by energy absorption and reduction in stiffness. (Refer to ACI 349.) An anchor that is to be characterized as a ductile element should be shown by calculation to have adequate stretch length that is compatible with the ductility required. (See 3.11.5 for an example of how to do this.)... 

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