## ASD – Allowable Stress Design

LFD – Load Factor Design

LRFD – Load and Resistance Factor Design

### ASD: Allowable Stress Design

ASD does not recognize different variabilities of different load types.

### LFD: Load Factor Design

In LFD, load and resistance are not considered simultaneously.

### LRFD: Load & Resistance Factor Design

The LRFD philosophy provides a more uniform, systematic, and rational approach to the selection of load factors and resistance factors than LFD.

### Variability of Loads and Resistances:

Suppose that we measure the weight of 100 students

Now suppose that we measure the strength of 100 ropes

Reliability Index:

AISC:

Resistance Factor:

AISC Steel Construction Manual, 13th Edition

- Dimensions and Properties
- 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 Flexible Moment Connections
- Design of Fully Restrained Moment Connections
- Design of Bracing Connections and Truss Connections
- Design of Bearing Plates, Base Plates, and Column Splices
- Design of Hanger Connections, Brackets Plates, etc.
- Specifications and Codes
- Miscellaneous Data and Mathematical Information Index

## Load Combinations:

### LRFD

- 1.4D
- 1.2D + 1.6L + 0.5(Lr or S or R)
- 1.2D + 1.6(Lr or S or R) + (0.5L or 0.8W)
- 1.2D + 1.6W + 0.5L + 0.5(Lr or S or R)
- 1.2D ± 1.0E + 0.5L + 0.2S
- 0.9D ± (1.6W or 1.0E)

### ASD (Consistent with ASCE 7)

- D
- D + L
- D + (Lr or S or R)
- D + 0.75L + 0.75(Lr or S or R)
- D ± (W or E)
- D ± 0.75(W or E) + 0.75L + 0.75(Lr or S or R)
- 0.6D ± (W or 0.7E)