Theory of Structures - Core Concepts and Terminology

Vocabulary practice flashcards covering structural engineering fundamentals, load classifications, structural determinacy/stability, plane and space trusses, arches, cables, virtual work, and beam deflection methods from the Theory of Structures lecture notes.

Structure

A system of connected parts used to support a load.

Structural Engineering

The science and art of planning, designing, and constructing safe and economical structures that will serve their intended purposes.

Structural Analysis

The prediction of a structure's behavior when subjected to specified arbitrary external loads.

Structural Design

A process that follows a series of successive approximations in which every cycle requires a structural analysis.

Planning Phase

The initial phase of a structural engineering project during which the functional requirements of the proposed structure are established.

Preliminary Structural Design

The phase in which the sizes of the various members of the structural system selected during planning are estimated.

Estimation of Loads

The phase dedicated to determining all expected loads that will act on the structure during its planned lifespan.

Prestressed Concrete Girder

A simply supported beam type frequently used for highway bridges.

Spliced Plate Joints

Joint connections used to join the steel girders of a highway bridge.

Steel Reinforcement Cage

A structure placed inside concrete formwork to resist tensile forces that develop within concrete beams.

Dead Loads

The self-weight of the structural system itself and any other materials permanently attached to it.

Live Loads

Moveable or moving loads resulting from the use or occupancy of the structure, exhibiting varying magnitudes and positions.

Impact Loads

Dynamic effects produced when moving vehicles bounce or sidesway across a bridge deck, causing increased stress in the structure.

Wind Loads

Loadings generated when a structure obstructs wind flow, converting kinetic wind energy into potential energy of pressure.

Earthquake Loads

Loadings resulting from ground motion interactions and structural distortions influenced by ground acceleration and lateral resistance.

Load Resistance Factor Design (LRFD)

A strength design method that separates material uncertainty from load uncertainty by applying specific load factors to applied loads.

Allowable Strength Design (ASD)

A design method combining both material and load uncertainties into a single factor of safety.

Equilibrium of Structures

The state where a structure initially at rest remains at rest under applied forces and couples, with all individual members and parts also remaining in equilibrium.

Concurrent Force System

A force system where lines of action of all forces intersect at a single point, automatically satisfying moment equilibrium equations.

External Forces

Forces and reactions applied to the boundary of a structure by external agents, including gravity, wind, live loads, and support reactions.

Internal Forces

Resultant axial normal forces, shear forces, and bending moments developed inside a structural member's material to resist external loads.

Supports

Connections attaching a structure to the ground or other bodies that restrict movement by exerting static reaction forces.

Determinacy

The relationship between the number of unknown force components ($r$) and the number of available static equilibrium equations ($3n$ for coplanar systems).

Statically Indeterminate Structure

A structure where unknown forces exceed available equilibrium equations ($r > 3n$), requiring additional compatibility equations to solve.

Stability

The property ensuring a structure's equilibrium through adequate constraints and support arrangements, preventing rigid-body motion or collapse.

Partial Constraints

A condition where a structure has fewer support reactions than equilibrium equations ($r < 3n$), causing static instability.

Improper Constraints

A condition causing structural instability despite having sufficient reaction count ($r \ge 3n$), occurring when reactions are concurrent, parallel, or form a mechanism.

Gusset Plate

A metal or wooden plate used at truss joints to connect intersecting slender structural members.

Plane Trusses

Trusses whose structural members and external applied loads all lie within a single two-dimensional plane.

Method of Joints

A truss analysis technique that isolates individual joints to solve for axial forces using coplanar concurrent equilibrium equations ($\sum F_x = 0$ and $\sum F_y = 0$).

Method of Sections

A truss analysis technique that passes an imaginary cut through specific members to form a rigid body, utilizing all three coplanar equilibrium equations ($\sum F_x = 0$, $\sum F_y = 0$, $\sum M = 0$).

Funicular Arch

An arch shaped such that under specific loading conditions (such as a parabolic arch under uniform horizontal load), internal forces are purely compressive without bending or shear.

Virtual Work Method for Trusses

A principle used to determine truss deflections using $\Delta = \sum \frac{S u L}{A E}$, where $S$ is real member force and $u$ is member force under a virtual unit load.

Double Integration Method (DIM)

A method for determining beam slope ($y'$) and deflection ($y$) by integrating the bending equation $E I y'' = M(x)$ twice.

Fixed End Method (FEM)

A method used to analyze single-span fixed structural members by finding reaction moments ($FEM_{AB}$ and $FEM_{BA}$) at clamped boundaries.

Three-Moment Equation (3ME)

An analysis method for continuous multi-span beams that expresses equilibrium relations among bending moments at three consecutive supports.