Steel Structure Basic Conceptes Statics • •
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Applied Forces – All external forces that act on a structure or member Center of Gravity – A point of balance where the tendency of forces to rotate one side of an object are countered by equal and opposite forces located on the other side of the object Center of Mass – In an object or system of objects in motion, the center of mass is one point that moves in the same path that a particle would if subjected to the same net force Centroid – The center of gravity for a two-dimensional shape Collinear Forces – Forces that act along the same line of action Component of a Force - Two or more forces that compose a single force Composite Shapes – Refers to a combination of 2 or more built up shapes Concurrent Forces - Forces that pass through the same point or intersect at a common point Coplanar Forces - Forces that act along lines that lie in the same plane Couple – The effect produced from two forces that have the same magnitude, parallel line of action and opposite sense Elastic Deformation - Temporary deformation of a material where the material subjected to a load or force returns to its original dimensions once the load or force is removed External Force - The applied forces that cause an object to translate, rotate or stay at rest Elastic Range – Range on the stress/strain curve in which a material will return to its original state once the stress is removed Fixed Support - A fixed support resists translation and rotation of a member at the connection point The reactions of a fixed support compose three unknown forces, including both a vertical and a horizontal component and a resisting moment. Force - The action of one object exerted on another Free Body Diagram - A simplified and conceptual diagram that isolates a structural member under investigation from the rest of the structure Internal Force – Forces that are developed within an object in response to the external loads Modulus of Elasticity - The ratio of the stress inflicted on an element to the strain that is produced Moment - The tendency to make an object or a point rotate Moment Arm - The perpendicular distance between the line of the action of the force and the point Moment of Inertia – A mathematical concept that incorporates the effect of cross sectional shape and orientation to study the strength of a structural member Non-Collinear Forces – Two or more forces that act along different lines of action Non-Concurrent Forces - Forces that do not pass the same point or do not intersect. Parallel forces are an example of non-concurrent forces.
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Non-Coplanar Forces - Forces that do not lie in the same plane and have a have a three dimensional arrangement Parallel Axis Theorem – A mathematical method by which the moment of inertia of a shape with respect to its centroidal axis can be transferred to a prescribed parallel axis that is normally the centroidal axis of the composite shape Pinned/Hinged Support – A pin or a hinge support resists translation of a member in both horizontal and vertical directions. The reactions of a pin support represent two unknown force components Plastic Deformation - Deformation that remains permanent in a material subjected to load or force and remains in place even after the load or force is removed Plastic Range – Range on the stress/strain curve where a material permanently deforms once stress is removed Radius of Gyration – Defined as the square root of the moment of inertia divided by the cross sectional area of the shape; a shape factor that measures the resistance to bending about a defined axis Reaction Forces - Equal and opposing forces that resist applies forces Resultant of a Force – A single force that replaces a system of concurrent forces Roller Support – A roller support resists translation of a member in the perpendicular direction to the contact surface. This reaction of a roller connection represents one unknown force component. Static Equilibrium – The state when the net effect of all the forces acting on an object equal zero Statics – One of three branches of mechanics that deals with the study of forces that are in a state of balance Stiffness – Measure of a material’s rigidity; a material’s ability to withstand deformations under stress; slope of the st ress/strain curve Strain – Deformation of the physical dimensions of an object subjected to a stress Stress – Describes the intensity of a force and is expressed by the amount of force acting per unit of area Transmissibility of Forces – Law that states that the point of application of an external force acting on a body can be moved anywhere along the line of action of the force without creating a change in the overall external forces applied on the body Ultimate Strength – The maximum force that can be applied to a material without breaking the material Yield Stress – The point at which stress causes a material to permanently deform Customize | Site Map ©2002-2004, All Rights Reserve
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Area Load – A uniform load that acts across the entire area or surface of a structural member Center of Mass – A point on an oject or system of objects in motion that moves in the same path that a particle would if subjected to the same net force Concentrated Load – Loading that is applied on a particular portion of a structural member Dead Load – Loads that consist of the weight of permanent and fixed components of a structure Deflection - The deviation of a structural member from its original position due to applied loading Gravity Load – Loading that is the result of the earth’s gravitational pull Lateral Load – Loading that occurs in the horizontal direction with respect to the ground Live Load – non-permanent and movable loads on a structure Occupancy Load – Live, gravity loads that consist of the weight of people, furniture, equipment, and stored materials. Overturning – A structural failure that is normally associated with tall and slender buildings with relatively small foundations Seismic Load – Earthquake forces that result from the slippage of rock plates along the fault line Sliding – Structural failure caused from the effect of lateral forces on inadequately designed foundation systems Snow Load – A gravity live load caused from the accumulation of snow on a horizontal surface Torsion – A twisting effect induced by the action of lateral forces Uniformly Distributed Load – Loading that occurs along a portion or the length of a structural member Uniformly Increasing Load – A load that is increased at a constant rate Wind Load – A lateral load caused from wind force
Mechanics of Materials •
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Bearing Stress – Stress produced by the pressure or intensity of a force at the contact point of two bodies or structural members Breaking Point – The maximum point in which a material can elongate; the point at which a material fails or breaks when subjected to a stress Compression Force – A force caused from the compacting or pushing in of structural fibers Creep – Deformation of a structure over an extended time Elastic Deformation – Temporary deformation of a material where the material subjected to a load or force returns to its original dimensions once the load or force is removed Flexure – The bending of a material under load application Hook’s Law – Law discovered by Robert Hook in 1678 that describes the linear and proportional relationship of stress and strain in elastic materials subjected to moderate loading. Modulus of Elasticity (Young’s Modulus) – A measure of stiffness of a material that is measured by the slope of the elastic portion of the stress-strain curve Normal (Axial) Stress – Stress produced by a tension or compression force acting perpendicular to the surface area under stress Plastic Deformation – Deformation that remains permanent in a material subjected to load or force and remains in place even after the load or force is removed Shear Force – An effect that produces shifting of horizontal or vertical parallel plains of a material Shear Stress – Stress that is produced by a force applied parallel to the stressed area. Shear stress is calculated by dividing the shear force by the parallel area resisting the force. Stiffness – The ability of a material to withstand deformation under stress Strain – The deformation of the physical dimension of a body under stress Strain Hardening – A stage beyond yield stress where steel goes through structural changes that result in increased strength and resistance to further deformation Stress – Describes the intensity of a force and is expressed by the amount of force acting per unit of area Stress Concentration – The accumulation of stress on a small section or area of an object Tension Force – A force that pulls or stretches the fibers of a material away from each other Thermal Strain – The change in material dimensions as a result of temperature changes Thermal Stress – The expansion and contraction of a material due to thermal change Torsion – The twisting and distortion of a material’s fibers in response to an applied load Ultimate Stress – The maximum stress level of a material at which it breaks or ruptures Yield Stress – The point at which stress causes a material to permanently deform Customize | Site Map ©2002-2004, All Rights Reserved
Structural Materials •
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Angles – steel members used fro truss members and connection elements; designated by the letter ‘L’ Built-Up Section – steel section formed by welding or bolting various rolled shapes Cast Iron – a hard, brittle and nonmalleable alloy composed of iron, 2-4.5% carbon, and 1-4% silicon; strong in compression, weak in tension Cementiferous Spray – a concrete-vermiculite like substance that is sprayed on steel members for fireproofing Channels – C-shaped steel members mostly used for purlins and structural fascias; designated by the letter ‘C’ Concrete – a mixture of sand, cement, aggregate and water used in construction Corten (Weathering) Steel – a type of steel that contains high levels of copper and phosphorous that form a thin protective layer of brown rust on the surface that stops further corrosion when exposed to w eather Glu-Laminated Lumber – wood that is composed of an assembly of wood laminations I-Beams – steel member that has a lower depth to width ratio than wide flanges; designated by the letter ‘S’ Intumescent Coatings – thin film coatings that are sprayed or brushed on metal surfaces to provide fire protection Posttensioned Concrete – prestressed concrete in which steel tendons are tensioned after the concrete has cured Prestressed Concrete – concrete in which forces are applied prior to loading that counteract the effect of subsequent loads Pretensioned Concrete – prestessed concrete in which steel tendons are stretched and tensioned prior to the casting c asting of the concrete Reinforced Concrete – concrete that is supplemented with steel bars that make it more efficient in resisting tensile forces as well as compressive forces Reinforcing Steel – steel that is used to add strength to concrete Sawn Lumber – wood that is cut directly from a log Stainless Steel – steel that contains 10-30% chromium that provides resistance to rust Steel – an iron alloy with low carbon that is strong in both compression and tension Tee Sections – T shaped steel members used for truss chords and structural lintels Thermal Sprayed Metal Coatings – aluminum or zinc alloys that are melted and sprayed onto a metal surface to prevent corrosion Wide Flange – steel member that has a high depth to width ratio; designated by the letter ‘W’ Wrought Iron – an alloy of iron that contains carbon and silicon that was used throughout the 19th century in bridge and building construction Customize | Site Map ©2002-200
Connections •
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Arc Welding – a process of welding that passes an electric current through a metal electrode that produces intense heat that melts and fuses the electrode rod as well as a small portion of the connecting elements Beam Hangar – a steel connection that is used to anchor a flush/face beam connection Bolt – a type of fastener that can resist withdrawal and lateral loads significantly more than nails and screws Common Bolts (Unfinished Bolts, ASTM A307) – structural steel bolts composed of low carbon steel that have a smaller load capacity than high strength bolts Direct Tension Indicator Bolts – a type of high strength steel bolt that releases silicone that is embedded in the depressions of the washer when the desired amount of torque is applied Filet Weld – a type of weld that is used to join overlapping elements Framing Anchors – Groove Weld – a type of weld that is used between adjacent members High Strength Bolts (A325, A490) – structural bolts composed of high strength steel that are tightened with an impact wrench to produce friction type connections Impact/Torque Wrench – a wrench that can be calibrated to apply a specific amount on torque Joist Hangar – a steel connection that is used to anchor a flush/face joist connection Nail – a type of simple wood fastener used in small-scale construction that resists shear but does not resist tension forces Post Base/Cap – a steel fastener used to anchor a post or column into the foundation and/or ceiling Rebar Jacket Rigid Connection – a type of structural joinery that resists both shear forces and bending moments Rivet – a smooth, screw like fastener that is pushed through adjacent members and pneumatically hammered and heated to produce an anchoring head on the opposite side of the rivet head Screw - a type of simple wood fastener that is somewhat more efficient than nails used in small-scale construction that resists shear but does not resist tension forces Semi-Rigid Connection – a type of structural joinery that restrains translation and permits partial rotation of the connecting members Simple Connection – a type of structural joinery that resists shear forces but does not resist bending moments Twist Off/Tension Controlled Bolts – a type of high strength bolt that releases the splined extension of the bolt when the optimum amount of torque is applied Welding – a method of joining steel elements by heat Withdrawal Load Customize | Site Map
Lateral Systems •
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Braced Frames – truss structures that provide diagonal paths for moving the lateral loads through the structure in vertical planes Building Configuration – the form, geometry, scale, arrangement of the building mass and structure Cross Bracing – bracing used in frames that resist lateral forces in two or more directions Diaphragms – structural elements that resist and collect lateral forces in the horizontal planes of a structure and transfer them to the vertical bearing elements Drift – deflection of a building under lateral loads Earthquake (Seismic) Forces – lateral forces caused by the shifting of plates below the earth’s surface that act mostly m ostly at the base of a structure Knee (K) Bracing – short diagonal bracing linking horizontal and vertical members that effectively makes a rigid connection where two members are pinned Moment Resistant Frames – structural systems that are constructed with rigidly connected joints Re-Entrant Corners – differential stiffness in a structure caused by irregular geometries Shear Walls – structural elements made of rigid materials that resist lateral loads in the vertical plane Soft Story – the result of insufficient strength and stiffness of a specific floor structure that is inconsistent with the rest of the building floors Torsion – a twisting effect that results when applied loads located at the center of mass of a structure do not coincide with the center of stiffness Wind Forces – lateral forces caused by wind that affect the exposed surface area of a structure
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Battered Pile – a type of pile that is used when lateral forces exceed the loading capacity of vertical piles Bearing Pile – a type of pile that is used to resist lateral loads and uplift forces Cantilever Wall – a type of foundation wall that consists of a stem and a base slab that is held in equilibrium by self-weight, horizontal soil pressure, and the reaction of the base structure acting upward Combined Footing Crib Wall – a type of foundation wall Deep Foundation – a type of foundation that is used when the soil near the ground surface is weak Foundation – the interface of a building structure with the ground Foundation Wall – a structural element that is constructed below grade to support the earth and resist water pressure Friction Pile – a type of pile that resists gravity loads by friction and transfers loads to the surrounding soil using the adhesive resistance between the pile surface and its surrounding soil Gravity Wall – a type of foundation wall Mat/Raft Foundation – a type of shallow footing that is equal to the area of the building footprint Pile – a long and slender prefabricated type of deep foundation that are driven into the ground Shallow Foundation – a type of foundation that is used when the earth directly beneath a structure has sufficient bearing capacity to sustai n the loads from the structure Sheet Pile - a type of foundation wall Spread Footing – the most widely used type of shallow foundation that are designed to receive the concentrated gravity loads directly on their centroid to prevent unequal pressure distribution and overturning of the footing Table Wall Footing – a type of shallow foundation
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Baltimore Truss - A trapezoidal, flat truss Bowstring Truss - A truss with an arched upper chord and a central triangual configuration converging on the upper chord Cambered Fink Truss - A triangular truss characterized by parallel diagonal compression members that are perpendicular to the top chord and a cambered lower chord Fan Truss - A simple or multi-paneled triangular truss where all of the diagonal members radiate from one point on the lower chord Fink Truss - A triangular truss characterized by parallel diagonal compression members that are perpendicular to the top chord Gusset Plate – A common plate that is used to connect truss members at their ends Howe Truss – Truss in which the top chords and diagonal members are in compression, and all vertical members and bottom chord members are in tension Ideal Truss – A truss that assumes that all members are connected with pinned joints, that members will remain straight after loading, and that all loading is concentrated only at panel points K-Truss - A truss in which the vertical and diagonal members are arranged in the shape of a "k" King Post - A truss that is composed of a simple triangle with a central post Method of Joints – Method of analyzing trusses that uses the equilibrium of each truss joint to determine the forces in the members Method of Sections – Method of analyzing trusses that conceptually cuts the truss into sections and thus allowing the analysis of each section by using the equations of static equilibrium Open Web Joists – a steel truss that is used and spaced like a joist to support floor or roof decking Panel Points – Joints located along the top member of a truss that are directly connected to the structure. The uniform load of the structure is concentrated at the panel points and thus allows the truss to behave like a simply supported beam. Parker Truss - A truss with an arched upper chord and a central triangular arrangement converging on the bottom chord Pins/Bolts – Connection type used to join truss members Pratt Truss – A truss in which the top chords and vertical members are in compression, and diagonals and bottom chord in tension Scissors Truss – A truss in which the bottom chord is raised to increase the clear height near the mid span; top chords are in compression and vertical members in the center of the truss are in tension Static Equilibrium - The state when the net effect of all the forces acting on an object equal zero Statically Determinate Truss (Simple Truss) – A truss in which the static equations of equilibrium can be used to determine the force in each member Statically Indeterminate Truss – A truss that contains a series of redundant members that cannot be resolved with the equations of static equilibrium Tension Member - Structural member subjected to tension forces Truss – A structural system composed of short and straight structural members that are arranged in a pattern of triangles Two-Force Member – A structural member that is hinged or pinned at each end and does not carry any loads between the ends Warren Truss – A flat truss with parallel and equal length top and bottom chord members
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Zero Force Member – Members in a truss that do not carry loads that are used to provide stability and insure triangulation
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Beam Deflection – The deviation of a beam from its original position due to applied loading Bearing Stresses – Forces that exist when forces are transferred from one member to another Bending – Deformation of a horizontal structural member that is a result of the application of external loads Bending Stresses – Stresses that are produced in a structural member’s cross section when subjected to bending. Compressive stresses are generated at concave fibers and tensile stresses are generated at convex fibers. Cantilever Beams – Beams that are fixed or anchored at one end and free at the other end Center of Gravity – A point of balance where the tendency of forces to rotate one side of an object are countered by equal and opposite forces located at the other side of the object; the resultant force of the earth’s gravitational forces acting on individual particles composing an object Centroid – The center of gravity for the area of a two dimensional shape Centroidal Axis – Also called the neutral axis; a line that passes through the centroid of a beam’s cross- section where beam fibers are neither shortened under compression or elongated under tension Compression Forces – Forces that tend to crush or buckle an element; forces act inwardly on an object Concentrated Loads – Loads that act on a single or concentrated point of a structural member Continuous Beams – Beams that span over more than two supports Equations of Static Equilibrium – Equations used to determine unknown reactions that assume all forces and moments in all directions sum to zero External Forces – Forces applied to a structure Fixed End Beams – A beam that is restrained from any movement or rotation at both of its two end supports Fixed Support – A support condition that does not permit translation or rotation and thus develops three unknown reactions, including a vertical and horizontal component and a resisting moment Fixed-Pinned Beams – A beam that is fixed at one end and pinned at the other end Free Body Diagram - A simplified and conceptual diagram that isolates a structural member under investigation from the rest of the structure Horizontal Shear Force – Equal and opposite forces that are generated in adjacent horizontal fibers of a structural member in response to applied loads Horizontal Shear Stress – Stresses produced by the movement of the adjacent fibers of a member in the horizontal direction due to opposing and equal forces Internal Forces – Forces that occur within a structural member Internal Resisting Moment – Moment generated from tension and compression forces in a beam cross section that counterbalance the external moment produced by the applied loads Lateral Buckling – Buckling in the horizontal direction Neutral Axis (see centroidal axis)
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Open Web Joist - A steel truss that is used and spaced like a joist to support floor or roof decking Overhanging Beams – A simply supported beam that has one or both of its ends extending beyond the supports Pin/Hinge Support – A support condition that that can resist a single force in any direction on the plane containing and thus develops two unknown force components Principle of Superposition – Method that consists of finding the effect of several loading conditions acting on a beam simultaneously by determining the effect of each individual load on the beam separately Resisting Moment – A moment generated by tension and compression forces in the cross section of a structural member me mber that counterbalances the external moment produced by the applied loads Roller Support – A support condition that develops a reaction force perpendicular to the point of contact, thus restricting movement in that direction Shear – A force that is the result of opposing forces that cause the sliding of one portion of a structural member along an adjacent portion Shear and Moment Diagram – Graphical diagrams that determine the intensity of shear force and bending moment at any point along a structural member Simply Supported Beams – A beam in which one end is connected by a hinge and the other end is connected by a roller Statically Determinate Beams – Beams that allow the application of the basic equations of static equilibrium to determine up to three unknown reactions Statically Indeterminate Beams – A beam that contains more than three unknown reactions and thus does not permit the use of the static equations of equilibrium Tension Forces – Forces that tend to pull an element apart Torsion – A twisting effect on an object Tributary Area – The portion of an area load that is carried by each beam in a frame Uniformly Distributed Loads – An evenly distributed load that is applied over an area Uniformly Increasing Loads – Loads that are applied over a given area that gradually increase over or at certain c ertain portions of the structure Vertical Shear Force – Equal and opposite forces that are generated in adjacent vertical fibers of a structural member in response to applied loads Vertical Shear Stress – Stress produced by the movement of the adjacent fibers of a member in the vertical direction due to opposing and equal forces resulted from the external loading Wide Flange – A rolled steel section in the shape of an I Customize | Site Map
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Allowable Stress – Maximum amount of stress a column can take before it fails Beam Columns – Columns that are subjected to moment and axial forces Buckling – The bowing or bending of a column when subjected to loading Buckling Direction – The direction that a column will tend to bend when subjected to loading Column Effective Length – Column length subjected to buckling Column End Condition – The type of connection between the column and the adjacent structural elements Column Moment Diagrams – Diagram that graphically depicts the moments of a column under loading Compression Elements – Structural elements that collect loads from horizontal spanning members and transfer them to the foundation or other structural elements Concentric Loading (Axial Loading) – Loading that is directly applied at the centroid of the column cross section along its long axis Crushing – Common failure mode of short columns Critical Load –The maximum load at which a column buckles Eccentric Loading – Loading that is applied at a distance from the centroid of a column Effective Length (Critical Length) - The length of a column that is susceptible to buckling Euler Elastic Theory – Formula that predicts the value of critical load and critical stresses for long columns Fixed Columns - Columns that are fixed or restrained from movement at both ends Hinged Columns – A Column that is hinged at both of its ends Inflection Points (Contraflexure Points) – Location of curvature changes in the buckled column; the bending moment is zero at this point. Intermediate Column – A column that fails by a combination of crushing and buckling K Value – A modifier that takes into account the end condition of the column and thus effects the slenderness ratio; a larger k-value will increase the slenderness ratio Lateral Loads – Loads applied in the horizontal direction such as wind, earthquakes, and impacts Leonard Euler – A Swiss mathematician who recognized that a long column’s failure under axial loads is caused by buckling and not by strength failure. Load Capacity – The amount of load a structure or structural element can take before failing Long Column – A column that is defined as having a small cross sectional area in relation to its length Masts – A type of large column Modules of Elasticity –The ratio of the stress inflicted on an element to the strain that is produced; Moment of Inertia – A mathematical concept that is used to study the strength of a structural member by factoring the effect of cross sectional shape and orientation of the member with respect to loading Piers – A type of large column Pilasters – A type of large column Posts – A type of smaller column Pylons – A type of larger column
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Radius of Gyration – Defined as the square root of the moment of inertia divided by the cross sectional area of the shape; a shape factor that measures the resistance to bending about a defined axis Section Modulus – A measure of bending resistance Short Column – A column that has a relatively large cross sectional area when compared to its length; usually fails by crushing Slenderness Ratio – Defined as the column’s effective length divided by the radius of gyration; a dimensional property that identifies the critical length of the column Strong/ Major Axis – The axis of a column about which there exists greater resistance to buckling Struts – A type of smaller column Weak/Minor Axis – The axis of a column that will be initially subjected to buckling
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Cross Bracing – Structural members that are configured between columns and beams that stabilized a frame from lateral loads that are applied in both directions Deflection – The deformation or bowing of a structural member when subjected to a load Knee Bracing – A type of bracing used in frames that strengthens the joints and prevents them from lateral deformation Moment Resistant Joints – Rigid joints that resist horizontal and vertical forces and moments Post and Beam Frames – A frame in which the horizontal and vertical members of the frame are connected with simple joints Rigid Frames – A frame in which the horizontal and vertical members are connected with moment resistant joints that prevent independent action of the beam element from the columns Rigid Diaphragms (Panels) – Structural systems that act as thin horizontal beam elements spanning between vertical shear planes Shear Walls – Walls that are organized in the short dimension of a building that provide lateral stability Single Bay Frames – Frames that are one story in height and one single unit spanned along the ground plane Stacked Frames – A series of single bay frames repeated in the vertical and horizontal direction producing a multi-story frame Statically Determinate Frame – A frame that has only three reaction components Statically Indeterminate First Degree – A frame that has four unknown reaction components Statically Indeterminate Third Degree – A frame that has five or six unknown reaction components Three Hinged Frames – A frame with three hinged connections; develops higher moments and higher deflections than a two hinged frame Two Hinged Frames – A frame with two hinged connection
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Cables – Flexible structural elements often made of steel, polypropylene, nylon, or fiberglass that carry tensile loads Cable Net Systems – A category of cable systems that includes cable-stayed systems and double cable systems; refers to a system of cables designed to resist lateral loads Cable Stayed Systems – A structure in which a series of linear cables directly support rigid horizontal members and masts under all anticipated loading conditions Cold Stretching – a process that produces high strength steel Double Cable Systems – A cable system that contains a linear main cable carrying the gravity load that is stiffened by secondary cables Parabolic Cables – A cable that is subjected to a uniformly distributed load Single Bolt Clam – A connection used for joining cables in a net Strand – A composition of a number of wires that are helically formed around a central wire Two Force Member - A structural member that is hinged or pinned at each end and does not carry any loads between the ends U-Bolts – A connection used for joining cables in a net
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Arch – a structural element that carries loads by developing compressive forces Axial Thrust Counter-Front Walls Fixed Ended Arches – Arches that have fixed end connections Flying Buttress – an external bracing system that resists the effect of outw ard thrust Ideal Arch – An arch that carries loads by compression only and cannot resist any lateral forces Shear Force Statically Determinate Arches – Arches with three or less number of reactions Statically Indeterminate Arches – Arches with greater than three reactions, including both two-hinged and fixed arches Struts Three Hinged Arch – An arch with three hinge connections Tied Arch – An arch that resists outward thrust by tying the two supports below the floor level Two-Hinged Arch (Parabolic Arch) – An arch with two hinges at the supports that transfers the axial thrust and the shear force as horizontal and vertical forces to the foundation
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Surface Structures – non linear rigid or soft structural elements that are continuous in two axes Fabric Structure – a soft surface spanning structure that can only resist tensile forces Slab – a monolithic surface spanning structure usually made of concrete that carry loads by bending One-Way Slab – a reinforced concrete plate that is supported at two opposite edges and that carries loads by bending in one direction only Two-Way Slab – a reinforced concrete plate that is supported at four corners and that carries loads in two directions perpendicular to each other Flat Plates – a category of reinforced concrete two-way slabs that are reinforced in two directions and transfer loads directly to vertical supporting elements without using beams or girders Folded Plates – a type of two-way slab that is folded or corrugated thus providing stiffness and a high moment of inertia Shells – thin, lightweight, curved structures that resist axial and shear forces Cylindrical Shells – a shell structure that is extended in the longitudinal direction Shell Dome – an arch that is revolved about its vertical axis forming a hemispherical shell Hyper-bolic Paraboloids – a structure that is composed of a double contour curved plane that can carry surface tension, compression, and shear stress Tension Structures – structures that are composed of light weight materials such as cables and fabrics Cable Nets – a type of tension structure that is composed of cable segments that are connected to form a three dimensional framework Fabric Structure – a tensile structure where w here fabric is curved and stretched between supporting elements to provide a continuous surface for the flow of tension forces Air Supported Structures – a tensile structure that uses air pressure to support and stabilize fabric or other membranes
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Basic Concepts
The basic concepts section contains terms that are fundamental in understanding statics, strength of materials, and structural behavior. Many of the terms and definitions include images, animations, and tabulated information to communicate the concepts.
Statics
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Mechanics of Material
Connections
Structural Loads and Structural Behavior
Structural Materials
Lateral Systems Systems
Foundations
Statics Statics is one of three branches of mechanics that deals with the study of forces that are in a state of balance. Topics that are examined in statics include force characteristics, equilibrium, moments and reactions, and structural properties of areas. • • • • •
Forces Force Systems Support Conditions Cross-Sectional properties of areas Moment and Couples
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Forces
Type
Description
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Force
the action of one object exerted on another
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Applied Forces
all external forces that act on a structure or member
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Internal Forces
forces that are developed within an object in response to the external loads
External Forces
the applied forces that cause an object to translate rotate or stay at rest
Components of a Force
a single force can be replaced by two or more forces that produce the same effect. These forces are called components of the force.
Resultant of Forces
a single force that replaces a3 2.- system of concurrent forces is called a resultant force
law that states that the point of application of an external force acting Transmissibility Transmissibility of on a body can be moved anywhere along the line of action of the force Forces without creating a change in the overall external forces applied on the body
Reaction Forces
equal and opposing forces that resist applies forces
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Force Systems Type
Static Equilibrium
Description
the state when the net effect of all the forces acting on an object equal zero
Free Body
a simplified and conceptual diagram that isolates a structural member
Diagram
under investigation from the rest of the structure
Concurrent Forces
forces that pass through the same point or intersect at a common point
Non-Concurrent
forces that do not pass the same point or do not intersect. Parallel forces
Forces
are an example of non-concurrent forces
Collinear Forces
forces that act along the same line of action
Non-Collinear Forces
Coplanar Forces
two or more forces that act along different lines of action.
forces that act along the same plane
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Non-Coplanar
forces that do not lie in the same plane and have a have a three
Forces
dimensional arrangement
Support Conditions Type
Description
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Fixed Support
a fixed support resists translation and rotation of a member at the connection point. The reactions of a fixed support compose three unknown forces, including both a vertical and a horizontal component and a resisting moment.
Rocker Support
a rocker support resists translation of a structural member in the perpendicular direction to the contact surface. This reaction of a rocker connection represents one unknown force component.
Pin/Hinge Support
pinned/hinged support – A pin or a hinge support resists translation of a structural member in both horizontal and vertical directions. The reactions of a pin support represent two unknown force components
Roller Support
a roller support resists translation of a structural member in the perpendicular direction to the contact surface. This reaction of a roller connection represents one unknown force component.
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Free-Body Diagram
Cross-Sectional Properties of Areas Type Center Gravity
Description of a point of balance where the tendency of forces to rotate one side of an object are countered by equal and opposite forces located on the other side of the object
Centroid
the center of gravity for a two-dimensional two-dimensional shape
Composite Shapes
refers to a combination of 2 or more structural shapes that compose a structural member’s cross section
Moment Inertia
of a mathematical concept that incorporates the effect of cross sectional shape and orientation to study the strength of a structural member
a mathematical method by which the moment of inertia of a shape with respect to its Parallel Axis centroidal axis can be transferred to a prescribed parallel axis which is normally the Theorem centroidal axis of the composite shape
Radius Gyration
of defined as the square root of the moment of inertia divided by the cross sectional area of the shape; a shape factor that measures the resistance to bending about a defined axis
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Moment and Couples Type
Description
Moment
the tendency of a force to make an object or a point rotate
Moment Arm
the perpendicular distance between the line of the action of the force and the point about which the moment is produced.
Couples
the of action and opposite sense
Moment
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Moment Arm
Couples
Structural Loads and Structural Behavior Structural loads are defined as forces that tend to produce deformation in a structure. This section includes concepts dealing with the classification and analysis of loads and how structures withstand the effect of the applied loads with safety and adequacy. • • •
Load Types Load Distribution Categories Structural Behavior under Loads
Load Types Loads
Description
Table
Dead Loads
Loads that consist of the weight of permanent and fixed components of a structure
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Live Loads
non-permanent and movable loads on a structure
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Wind Load
A live load caused from wind force
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Gravity Load
Loads that are the result of the earth’s gravitational pull
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Snow Load
A gravity live load caused from the accumulation of snow on a horizontal surface
Occupancy Load
Gravity live loads that consist of the weight of people, furniture, equipment, and stored materials.
Seismic Load
Live load produced in Earthquakes that result from the slippage of rock plates along the fault line
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Lateral Load
Loading that occurs in the horizontal direction with respect to the ground
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Load Distribution Categories Description
Concentrated Load
Loading that is applied on a particular portion of a structural member
Uniformly Load
A load that is increased at a constant rate
Increasing
Uniformly Distributed Loading that occurs along a portion or the length of a structural Load member
Area Load
A uniform load that acts across the entire area or surface of a structural member
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Structural Behavior under Loads Description
Animations
Sliding
Structural failure caused from the effect of lateral forces on inadequately designed foundation systems
Torsion
A twisting effect induced by the action of lateral forces
Deflection
The deviation of a structural member from its original position due to applied loading
Overturning
A structural failure that is normally associated with tall and slender buildings with relatively small foundations
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Mechanics of Material Forces and Stress Stress/Strain
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Force and Stress Type
Animation/ Image
Description
Axial Stress
stress produced by a tension or compression force that acts perpendicular (or normal) to the surface area under stress. Normal stress is calculated -by dividing the tension or compression force by the cross-sectional area resisting the force.
Bearing Stress
stress produced by the pressure or intensity of a force at the contact point of two bodies or structural members
Compression Force
a force that pushes the fibers of a material closer to each other
Creep
deformation of a structure over an extended time
Flexure
the bending of a material under load application
Lateral Forces
forces applied in the horizontal direction
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Normal (axial) Stress
stress produced by a tension or compression force acting perpendicular to the surface area under stress
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Shear Force
an effect that produces shifting of horizontal or vertical parallel plains of a material
Shear stress
stress that is produced by a force applied parallel to the stressed area. Shear stress is calculated by dividing the shear force by the parallel area resisting the force.
Stress
describes the intensity of a force and is expressed by the amount of force acting per unit of area
Stress Concentration
the accumulation of stress on a small section or area of an object
Tension Force
a force that pulls or stretches the fibers of a material away from each other
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Thermal Strain the change in material dimensions as a result of temperature changes
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Thermal Stress the expansion and contraction of a material due to thermal change
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Torsion
the twisting and distortion of a material’s fibers in response to an applied load
Stress/Strain Type
Breaking Point
Description
The maximum point in which a material can elongate; the point at which a material fails or breaks when subjected to a stress
Elastic Deformation
Temporary deformation of a material where the material subjected to a load or force, returns to its original dimensions once the load or force is removed
Elastic Range
Range on the stress/strain curve in which a material will return to its original state once the stress is removed
Hook’s Law
Law named after Robert Hook in 1678 that describes the stressstrain relationship in elastic materials is linear and proportional under moderate loading.
Modulus of Elasticity The ratio of the stress inflicted on an element to the strain that is (Young’s Modulus) produced
Plastic Deformation
Permanent deformation in a material subjected to load that remains in place after the load is removed
Plastic Range
Range on the stress/strain curve where a material permanently deforms and remains deformed after the stress is removed
Stiffness
Measure of a material’s rigidity; a material’s ability to withstand deformations under stress; slope of the stress/strain curve
Diagrams
Strain
Deformation of the physical dimensions of an object subjected to a stress
Strain Hardening
A stage beyond yield stress where steel goes through structural changes that result in increased strength and resistance to further deformation
Stress
Describes the intensity of a force and is expressed by the amount of force acting per unit of area
Ultimate Strength
The maximum force that can be applied to a material without breaking the material
Yield Stress
The point at which stress causes a material to permanently deform
Connections Connections are key elements that bind one or more structural elements together. Connections can be used to allow or disallow certain types of motion and vary according to material and/or system. • • • •
Connection Types Connection Type Matrix Wood Connections Steel and Concrete Connections
Connection Types Type
Description
Simple (Shear) Connection
a type of structural joinery that resists shear forces but does not resist bending moments
Semi-Rigid Connection
a type of structural joinery that restrains translation and permits partial rotation of the connecting members
Rigid (Moment) Connection
a type of structural joinery that resists both shear forces and bending moments
Animations
Connection Types Type
Wood
Steel
Concrete
Simple
Semi-Rigid
Rigid
Not Available
Not Available
Steel and Concrete Connections Type
Description
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Arc Welding
a welding process to connect steel elements. An electric current passes through a metal electrode producing intense heat that melts and fuses the electrode rod as well as a small portion of the connecting elements
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Bolt
a type of fastener that can resist withdrawal and lateral loads significantly more than nails and screws
Common Bolts structural steel bolts composed of low carbon steel that have a (Unfinished Bolts, ASTM smaller load capacity than high strength bolts A307)
an extrusion or cleat on a concrete column in which beams rest on
Corbel
a type of high strength steel bolt that releases silicone that is Direct Tension Indicator embedded in the depressions of the washer when the desired Bolts amount of torque is applied
Fillet Weld
a type of weld that is used to join overlapping elements
Groove Weld
a type of weld that is used between adjacent members
High Strength (A325, A490)
Bolts
structural bolts composed of high strength steel that are tightened with an impact wrench to produce friction type connections
Haunch
a structural steel section cast in a column that provides an overhanging bracket for beam attachment
Impact/Torque Wrench
a wrench that can be calibrated to apply a specific amount on torque
Rivet
a smooth, screw like fastener that is pushed through adjacent members and pneumatically hammered and heated to produce an anchoring head on the opposite side of the rivet head
Rebar Jacket
a sleeve that is used to join reinforcement steel bars to provide a continuous connection between two structural elements
Twist Off/Tension a type of high strength bolt that releases the splined extension Controlled Bolts of the bolt when the optimum amount of torque is applied
Welding
a method of joining steel elements by heat
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Lateral Systems Lateral Systems are structural devices that supplement the primary components of a structure to provide additional stability against lateral forces •
Lateral Load Resisting Systems
Lateral Load Resisting Systems Type
Braced Frames
Description
Truss structures that provide diagonal paths for transferring lateral loads through a structure in vertical planes. Examples include cross bracing and knee bracing.
Building Configuration
the form, geometry, scale, arrangement of the building mass and structure
Cross Bracing
bracing used in frames that resist lateral forces in two or more directions
Diaphragms
structural elements that resist and collect lateral forces in the horizontal planes of a structure and transfer them to the vertical bearing elements
Drift
deflection of a building under lateral loads
Earthquake (Seismic) Forces
lateral forces caused by the shifting of plates below the earth’s surface that act mostly at the base of a structure
Knee (K) Bracing
short diagonal bracing linking horizontal and vertical members that effectively makes a rigid connection where two members are connected
Animation/ Image
Moment Resistant structural frames that are constructed with rigidly connected Frames joints
Re-Entrant Corners
differential stiffness in a structure caused by irregular geo metries
Shear Walls
structural walls made of rigid materials that resist lateral loads in the vertical plane
Soft Story
the result of insufficient strength and stiffness of a specific floor structure that is inconsistent with the rest of the building floors
Torsion
a twisting effect that results when applied loads located at the center of mass of a structure do not coincide with the center of stiffness
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Foundations Foundations consist of the array of structural elements that connect a structure to the ground. The design of foundations is affected by several factors, including the size and shape of the structure, and geological and geographical conditions of the site. • •
Shallow and Deep Foundations Retaining Walls
Shallow and Deep Foundations Foundation
the interface of a building structure with the ground
Shallow
a type of foundation that is used when the earth directly beneath a structure has sufficient
Foundation
bearing capacity to sustain the loads from the structure
Deep Foundation a type of foundation that is used when the soil near the g round surface is weak
Shallow Foundations Type
Cantilever Wall
Combined Footing
Mat/Raft Foundation
Description
a type of foundation wall that consists of a stem and a base slab that is held in equilibrium by self-weight, horizontal soil pressure, and the reaction of the base structure acting upward
a footing that is used under two or more vertical elements to prevent overturning from eccentric loading
a large slab foundation that is used instead of multiple spread footings
the most widely used type of shallow foundation that is designed to receive Spread Footing the concentrated loads directly on the centroid to prevent unequal pressure distribution and overturning of the footing
Strip Footing
Wall Footing
an extended footing used under foundation walls; strip footings are used in basements, crawlspaces, and for slabs-on grade.
elongated spread footings that transfer loads fro m load bearing walls. Wall footings are used in substructures such as slabs-on-grade, crawlspaces and basements.
Images
Deep Foundations Type
Battered
Description
Piles
an inclined pile that is used that can resist lateral forces as well as vertical forces
Bearing Piles
a type of pile that is used to resist lateral loads and uplift forces
Caissons
a type of deep foundation that is achieved by casting concrete into drilled holes
Friction Piles
a type of pile that resists loads by friction and transfers loads to the surrounding soil using the adhesive resistance between the pile surface and its surrounding soil
Pile
a long and slender deep foundation that is driven pushed into the ground
Images
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Retaining Walls Type
Description
Crib Wall
a retaining wall used for outdoor earthworks and landscaping
Images
Foundation Wall
a structural element that is constructed below grade to support the earth and resist water pressure
Gravity Wall
foundation wall that relies on its own weight to resist overturning forces from soil and water pressure
Key
extrusion on the base of a cantilevered retaining wall that prevents sliding
Sheeting
temporary walls that hold back the soil during excavation
Sheet Pile
type of sheeting that consists of vertical planks of wood, steel, or reinforced concrete that are driven into the earth
Slurry Wall
a type of sheeting that consists of trenching the ground, reinforcing the trench, and filling the trench with concrete.
Soldier Beams
a type of sheeting that uses vertical piles tied together by lagging
Stem
portion of foundation wall that extends or cantilevers into the soil
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