Steel design

Steel design, or more specifically, structural steel design, is an area of knowledge of structural engineering used to design steel structures. The structures can range from schools to homes to bridges.

In structural engineering, a structure is a body or combination of pieces of rigid bodies in space to form a fitness system for supporting loads. Structures such as buildings, bridges, aircraft and ships are all examples under steel structure. The effects of loads on structures are determined through structural analysis. Steel structure is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties.

There are currently two common methods of steel design: The first method is the Allowable Strength Design (ASD) method. The second is the Load and Resistance Factor Design (LRFD) method. Both use a strength, or ultimate level design approach. ^[1]

Load combination equations

Allowable Strength Design

For ASD, the required strength, R_a, is determined from the following load combinations (according to the AISC SCM, 13 ed.) and:^[2]

D + F
D + H + F + L + T
D + H + F + (L_r or S or R)
D + H + F + 0.75(L + T) + 0.75(L_r or S or R)
D + H + F ± (W or 0.7E)
D + H + F + (0.75W or 0.7E) + 0.75L + 0.75(L_r or S or R)
0.6D + W + H 0.6D ± (W or 0.7E)

where:

D = dead load,
D_i = weight of Ice,
E = earthquake load,
F = load due to fluids with well-defined pressures and maximum heights,
F_a = flood load,
H = load due to lateral earth pressure, ground water pressure, or pressure of bulk materials,
L = live load due to occupancy,
L_r = roof live load,
S = snow load,
R = nominal load due to initial rainwater or ice, exclusive of the ponding contribution,
T = self straining load,
W = wind load,
W_i = wind on ice..

Special Provisions exist for accounting flood loads and atmospheric loads i.e. D_i and W_i

Note that Allowable Strength Design is NOT equivalent to Allowable Stress Design, as governed by AISC 9th Edition. Allowable Strength Design still uses a strength, or ultimate level, design approach.

Load and Resistance Factor Design

For LRFD, the required strength, R_u, is determined from the following factored load combinations:

1.4(D + F)
1.2(D + F + T) + 1.6(L + H) + 0.5(L_r or S or R)
1.2D + 1.6(L_r or S or R) + (L or 0.8W)
1.2D + 1.0W + L + 0.5(L_r or S or R)
1.2D ± 1.0E + L + 0.2S + 0.9D + 1.6W + 1.6H
0.9D + 1.6 H ± (1.6W or 1.0E)

where the letters for the loads are the same as for ASD.

For the wind consideration, the ASCE allows a "position correction factor" which turns the coefficient of wind action to 1,36:

1,2D + 1,36W + .... the same above or 0,9D - 1,36W

AISC Steel Construction Manual

The American Institute of Steel Construction (AISC), Inc. publishes the Steel Construction Manual (Steel construction manual, or SCM), which is currently in its 14th edition. Structural engineers use this manual in analyzing, and designing various steel structures. Some of the chapters of the book are as follows.

Dimensions and properties of various types of steel sections available on the market (W, S, C, WT, HSS, etc.)
General Design Considerations
Design of Flexural Members
Design of Compression Members
Design of Tension members
Design of Members Subject to Combined Loading
Design Consideration for Bolts
Design Considerations for Welds
Design of Connecting Elements
Design of Simple Shear Connections
Design of Flexure Moment Connections
Design of Fully Restrained (FR) Moment Connections
Design of Bracing Connections and Truss Connections
Design of Beam Bearing Plates, Column Base Plates, Anchor Rods, and Column Splices
Design of Hanger Connections, Bracket Plates, and Crane-Rail Connections
General Nomenclature
Specification and Commentary for Structural Steel Buildings
RCSC Specification and Commentary for Structural Joints Using High-Strength Bolts
Code of Standard Practice and Commentary for Structural Steel Buildings and Bridges
Miscellaneous Data and Mathematical Information

CISC Handbook of Steel Construction

Canadian Institute of Steel Construction publishes the "CISC Handbook of steel Construction". CISC is a national industry organization representing the structural steel, open-web steel joist and steel plate fabrication industries in Canada. It serves the same purpose as the AISC manual, but conforms with Canadian standards.

References

↑ Steel Construction Manual (13th ed.). American Institute of Steel Construction. 2006. ISBN 1-56424-055-X.
↑ http://peer.berkeley.edu/~yang/courses/ce248/CE248_CN_Loading_and_Gravity_loads.pdf

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