Statics and Strength of Materials

Zero Force Member

: A member within a truss that does not carry any tension or compression force. These members are typically included to increase stability of the truss during construction and/or to provide support for changes in the loading scenario.

Line of Action

: Orientation of the path of a force

Live Loads

: Transient and moving loads that include occupancy loads, furnishings, and storage.

Static Equilibrium

A balanced state or condition, usually used to describe a situation in which opposed force effects neutralize each other to produce a net effect of zero (no motion occurring).

Tension Force:

A force that "pulls" along a member, attempting to elongate it. It is shown on a free body diagram as an arrow pulling away from the joint or cut.

Compression Force

A force that "pushes" along a member, attempting to shorten it. It is shown on a free body diagram as an arrow pushing toward the joint or cut.

Pinned Frame:

A frame composed of multiple members connected by pins. Forces can be applied anywhere along the member and the pins transfer the forces to adjacent members and eventually to the supports.

Multiforce Members

A member acted upon by three or more forces. These forces are generally not axial, thus the resultant member force direction is unknown.

Resultant

A single force that has the same effect as the various forces in the system acting simultaneously.

Three-Hinged Arch

A structural arch, with pinned supports and a pin somewhere along the arch. The benefit of the pin within the arch section is to reduce bending moments within the structure.

Planar trusses

A structure system comprised of linear members assembled in triangulated frameworks.

Statically Determinate Structure

A system of forces and reactions that can be solved using basic statics. The number of unknown reactions is equal to or less than the number of available equilibrium equations to solve the system.

Collinear Forces

All forces act in a single straight line

Coplanar Forces

All forces acting in a single plane.

Parallel Forces

All forces having the same direction

Concurrent Forces

All forces having their lines of action intersect at a common point.

Magnitude

Amount of a force

Statics

Branch of mechanics that deals with bodies held in a state of unchanging motion by the balanced nature of forces acting on them.

Resolution

Breaking down a single force into its components.

Earthquake Loads

Dynamic load that creates lateral forces as a function of the building's mass, configuration, building type, height, and geographic location. The force develops at the base of the building and is known as base shear.

Wind Loads

Dynamic load that is typically calculated as a static force condition, approximated as a mean pressure that acts on the windward side of the building.

Dynamic Loads

Forces caused by inertia or momentum of the structural mass

Braced Frame

Frame reinforced with "truss" type elements to transfer lateral loads through structure to foundation. Different types include diagonal, cross, eccentric, k, and knee bracing.

Moment Frame

Frame with rigid column/beam connections that transfers bending throughout the system under lateral loading conditions.

Static Loads

Gravity type forces

Dead Loads

Loads resulting from the self-weight of the building or structure and of any permanently attached components, such as partition walls, flooring, framing elements, and fixed equipment.

Load Periphery Method

Means of distributing dead and live loads to supporting members. Also referred to as the Tributary Area Method. The load carried by each member is determined by the layout and dimensions of the framing system.

Method of Sections:

Method of solving internal forces in the members of a planar truss by isolating any section of the truss and solving the unknown internal forces acting within the members acting along the "cut." Involves solving non-concurrent forces and therefore utilizes all three equations of equilibrium (horizontal forces, vertical forces, and moments). Each section must have independent equilibrium.

Method of Joints:

Method of solving internal forces in the members of a planar truss by isolating a joint and solving the unknown internal forces acting within the members acting at each joint. Involves solving concurrent forces and therefore utilizes only two equations of equilibrium (horizontal and vertical forces). Each joint must have independent equilibrium.

Moment Arm

Perpendicular distance to the line of action of a force.

Vector

Quantity that involves magnitude and direction.

Scalar

Quantity that involves only magnitude.

Strength of Materials

Study of the properties of material bodies that enable them to resist the actions of external forces, of the stresses within the bodies, and of the deformation of bodies that result from external forces

Equivalent Concentrated Load

The equivalent concentrated force acting at the appropriate location for a given distributed load. (Example: for a given uniformly distributed load of 10 lb/ft acting over a 5 ft length, the corresponding concentrated load is 10 lb/ft x 5 ft = 50 lbs acting at the center of the distributed load. Note: the equivalent concentrated force is determined only to help solve the system of forces. The actual load still acts in a distributed manner.)

LOAD TRACING STEPS

The primary steps in load tracing are: 1) Visualize the various elements of the structure and the relationship between each 2) Draw a free body diagram of each member 3) Beginning with the uppermost member, use the tributary area method to calculate the applied loads 4) Repeat the process for the next member down, by applying the appropriate loads from the first member and any additional externally applied loads 5) Continue the process all the way to the footings

Moment

The tendency of a force to cause rotation about a given point or axis. It is equal to a force multiplied by a distance

Equations of Equilibrium

There are three equations to consider for static equilibrium. The sum of all vertical forces equals zero. (Up forces are equal and opposite down forces) The sum of all horizontal forces equals zero. (Left forces are equal and opposite right forces) The sum of moments about any point equals zero. (Note: sum about ANY point)

Snow Loads

Treated as special type of live load because of variability in snow accumulation based on geographical jurisdiction.

Shear Wall

"Solid" wall designed to transfer lateral loads to through structure to foundation.

Sense

Which way the force is traveling along a line of action (i.e., up or down).