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ELASTIC NEUTRAL AXIS

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PLASTIC NEUTRAL AXIS The plastic section modulus depends on the location of the plastic neutral axis (PNA). The PNA is defined as the axis that splits the cross section such that the compression force from the area in compression equals the tension force from the area in tension.

ELASTIC SECTION MODULUS

For general design, the elastic section modulus is used, applying up to the yield point for most metals and other common materials. The elastic section modulus is defined as S = I / y, where I = is the second moment of area (or moment of inertia) y = is the distance from the neutral axis to any given fibre. https://en.wikipedia.org/wiki/Section_modulus (koya yung drawing nasa link)

Plastic section modulus The plastic section modulus is used for materials where elastic yielding is acceptable and plastic behavior is assumed to be an acceptable limit. Designs generally strive to ultimately remain below the plastic limit to avoid permanent deformations, often comparing the plastic capacity against amplified forces or stresses. The plastic section modulus depends on the location of the plastic neutral axis (PNA). The PNA is defined as the axis that splits the cross section such that the compression force from the area in compression equals the tension force from the area in tension. So, for sections with constant yielding stress, the area above and below the PNA will be equal, but for composite sections, this is not necessarily the case. The plastic section modulus is then the sum of the areas of the cross section on each side of the PNA (which may or may not be equal) multiplied by the distance from the local centroids of the two areas to the PNA: https://en.wikipedia.org/wiki/Section_modulus (koya yung drawing nasa link)

Shape factor Shape factors are dimensionless quantities used in image analysis and microscopy that numerically describe the shape of a particle, independent of its size. Shape factors are calculated from measured dimensions, such as diameter, chord lengths, area, perimeter, centroid, moments, etc. The dimensions of the particles are usually measured from two-dimensional crosssections or projections, as in a microscope field, but shape factors also apply to three-dimensional objects. The particles could be the grains in a metallurgicalor ceramic microstructure, or the microorganisms in a culture, for example. The dimensionless quantities often represent the degree of deviation from an ideal shape, such as acircle, sphere or equilateral polyhedron.[1] Shape factors are often normalized, that is, the value ranges from zero to one. A shape factor equal to one usually represents an ideal case or maximum symmetry, such as a circle, sphere, square or cube.

https://en.wikipedia.org/wiki/Shape_factor_(image_analysis_and_microscopy) (ung aspect ratio, circularity, elongation shape factor , compactness shape factor, waviness shape factor,)

Load Factors 􀁑 The

load factors are usually amplifying factors that are used in LRFD design equation to increase the loads. 􀁑 The purpose of increasing the loads is to account for the uncertainties involved in estimating the magnitudes of dead and/or live loads. 􀁑 Since

the dead loads can be estimated more accurately than live loads, the factor for live load is usually higher than that used for dead loads. Examples: – A load factor of 1.6 for live loads in LRFD steel manual as compared to 1.2 for dead loads. – A load factor of 1.7 for live loads in ACI Code as compared to 1.4 for dead loads.

Load Factors 􀁑 Loads

and Load Combinations

1.4 (D + F) (1) 1.2 (D + F + T) + 1.6 (L + H) + 0.5 (Lr or S or R) (2) 1.2 D + 1.6 (Lr or S or R) + (0.5 L or 0.8 W) (3) 1.2 D + 1.6 W + 0.5 L + 0.5 (Lr or S or R) (4) 1.2 D + 1.0 E + 0.5 L + 0.2 S (5) 0.9 D + 1.6 W + 1.6 H (6) 0.9 D + 1.0 E + 1.6 H (7) 􀁑 Notations

U = the design (ultimate) load

D = dead load F = fluid load T = self straining force L = live load Lr = roof live load H = lateral earth pressure load, ground water pressure. S = snow load R = rain load W = wind load E = earthquake load