Static loading design

Reinforced concrete is the most commonly used construction material for structures designed to resist explosive blast loads. It is used extensively in blast hardened structures because of its strength, ductility (when properly designed), mass, penetration resistance, relative economy, and universal availability. Its strength, mass, and ductility provide high resistance to the extreme blast pressure (psi) and impulse (psi-ms) loads. It is important to remember that (unlike in static load design) in the... 

API Standard 4A (superseded by Standard 4F) provides rating of derrick capacities in terms of maximum safe load. This is simply the load capacity of a single leg multiplied by four. It does not account for pipe setback, wind loads, the number of lines between the crown block and the traveling block, the location of the dead line, or vibratory and impact loads. Thus, it is recommended that the maximum safe static load of derricks designed under Standard 4A exceed the derrick load as follows ... 

The behavior of materials (plastics, steels, etc.) under dynamic loads is important in certain mechanical analyses of design problems. Unfortunately, sometimes the engineering design is based on the static loading properties of the material rather than dynamic properties. Quite often this means over-design at best and incorrect design resulting... 

The next step in the design procedure is to select the materials. The considerations are the physical properties, tensile and compressive strength, impact properties, temperature resistance, differential expansion environmental resistance, stiffness, and the dynamic properties. In this example, the only factor of major concern is the long-term stiffness since this is a statically loaded product with minimum heat and environmental exposure. While some degree of impact strength is desirable to take occasional abuse, it is not really subjected to any significant impacts. 

The following example provides information on designing of plastic structural products to take static loads. It is a structural problem common to a number of different structures to show how the different structural requirements will affect the choice architectural designers has to make. The design problem will be a roof section which may be used for anything from a work shed,... 

The example of the roof structure represents the simplest type of problem in static loading in that the loads are clearly long term and well defined. Creep effects can be easily predicted and the structure can be designed with a sufficiently large safety factor to avoid the probability of failure. 

A seating application is a more complicated static load problem than the building example just reviewed because of the loading situation. The self load on a chair seat is a small fraction of the normal load and can be neglected in the design. The loads are applied for relatively short periods of time of the order of 1 to 5 hours, and the economics of the application requires that the product be carefully designed with a small safety factor. 

The process of design for static loads involves a great deal more than the mechanical operation of the stress-strain data to determine the performance of a section. The results obtained from the stress analysis are used to determine the functionality of the product and then, combined with the other factors involved to decide on a suitable design. 

Figures 2 through 9 are design charts for ultraviolet stabilized polycarbonate under blast load. Charts are provided for pane thicknesses of 1/4, 3/8, 1/2, and 1 inch for pane areas up to 25 ft at pane aspect ratios (pane length to width ratios) of 1.00, 1.50, 2.00 and 4.00. The charts relate the peak experienced blast overpressure capacity, B, for convenient pane dimensions across the spectrum of encountered blast durations. Depending on the orientation of the window to the charge, the blast overpressure may either be incident or reflected. The pane dimensions (measured across the span from the gasket centerline) peak blast capacity at 1000 msec, B, static frame design pressure, r, and the required bite are printed to the right...

The braced frame must develop the ultimate capacity of the members which it supports, namely the girts and end wall columns. The force applied to the top of the column is equal to the tributary area times the resistance as a static load. Each braced frame will be designed to resist the entire load even though there will be a frame at each end of the building. This will provide redundancy and will eliminate large axial forces in the top perimeter beams at the interior frames. 

In the Equivalent Static Design Method, foundations are typically designed for the peak reactions obtained from the superstructure dynamic analysis. These reactions are treated as static loads, disregarding any time phase relationship. The basis for equivalent static design is discussed in 7M 5-856. 

Since a conservative approach is used, it is quite common practice to design the foundation using static loads. Typically, this involves applying the resistance of the roof and walls as uniform static loads and computing reactions. Support reactions from frame analyses arc also checked to ensure that local foundation failures don t occur. Dynamic analysts of foundations can be accomplished if appropriate soil properties are provided. 

Since the duration of one batch cycle is about 1 day -which calculates to 7,000 cycles for 20 years- the design was governed basically by the static load. 

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