Transcript Engineering Graphics - ITS: Publishing Academic Web Pages

Fundamentals of Structural
Engineering
End Reactions
Beams
A beam is a horizontal or inclined member that carries a load and is supported at
two or more points.
Reactions
Reactions are the forces acting at the supports of the beam. The reactions
resist the beam load and hold the beam in equilibrium.
Loads
The two most common types of loads considered in design are dead loads and
live loads.
Dead loads are loads that remain essentially constant after they are applied.
They include the weight of the beam, walls, partitions, floors, and other material
which make up the finished structure.
Live loads are loads that vary. Live loads include loads from occupants of the
building, elevators, machinery, traveling cranes, moving vehicles, and material or
equipment stored in the structure. Other types of loads considered in design are
wind loads, earthquake loads, and impact loads caused by machinery or
moving vehicles.
Uniform Loads
A uniform load is a load that is uniformly distributed over a length of beam.
Uniform loads are usually represented by closely spaced vertical lines as
shown.
Concentrated Loads
A concentrated load is a load assumed to act at one point. A single
vertical arrow indicates the location and direction of the load as shown.
Laws of Equilibrium
Reactions for different beam loads are calculated using the laws
of equilibrium. These laws are based on the observation that if a
beam does not move as loads are applied, all forces acting on the
beam are in equilibrium, that is, they are balanced.
The laws are expressed by the following formulas:
∑M = 0
∑F (v) = 0
∑F (h) = 0
Formula ∑M = 0 states that the algebraic sum (indicated by the
symbol ∑ ) of the moments of all the forces equals zero.
Formula ∑F (v) = 0 states that the algebraic sum (indicated by
the symbol ∑ ) of all vertical forces equals zero.
Laws of Equilibrium
For convenience, the vertical downward forces are considered negative
and the vertical upward forces are considered positive.
Moments
A moment is the product of a force expressed in units of weight (kips)
times a distance expressed in units of length (feet). The distance is the
shortest distance (measured along a line at right angles to the force to the
point about which the moment is taken (A). The numerical value of a
moment is expressed in units of force and distance such as kip-feet.
Moments
For convenience in computation, moments tending to produce rotation in a
clockwise direction are considered positive and those in a counterclockwise
direction are considered negative.
Loading Diagrams
Steel Design
There are currently two common methods of steel design:
The first (and older) method is the Allowable Strength Design
(ASD) method.
Service loads and load combinations with a factor of safety
applied to the resistance are used.
The second (newer) is the Load and Resistance Factor Design
(LRFD) method.
Factored loads and load combinations with separate factors for
each load and for the resistance are used.
Steel Design
Steel Design