Introduction to Structural Engineering Tony Freidman

Background Graduate of University of Missouri – Rolla B.S. in Civil Engineering B.S. in Architectural Engineering Research in Architectural specialties Research on V-T-M diagram development for reinforced concrete column design Currently enrolled as a Ph.D. student at Washington University – St. Louis Research on MR Damper performance Research on Structural Health Monitoring

http://www.youtube.com/watch?v=uKeENdyIluI&feature=related http://www.youtube.com/watch?v=AsCBK-fRNRk&feature=related http://www.youtube.com/watch?v=YCfgfccpHpc&feature=related http://em-ntserver.unl.edu/Mechanics-Pages/Group1/sld001.htm

Structural Engineering is used so that the events in the preceding videos never take place. “Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties. “ - 1st Fundamental Engineering Canon

Structural Engineering Overview What is a Structural Engineer? What do they do? What do they design?

Structural Engineering Overview What is a Structural Engineer? What do they do? What do they design?

What is a Structural Engineer? Mathematics of design Architect/Artist Vision Aesthetics of design Mediator Liason between parties on a project Salesman Must sell your idea, yourself

Structural Engineering Overview What is a Structural Engineer? What do Structural Engineers do? What do they design?

What do SE’s do? Designer Consultant Inspector Demolitions Take a design, and fit a structural system to that Expert witnesses in lawsuits Inspector Fieldwork, Job site inspections Oversee the materials (concrete, steel, etc.) Inspect the building – pre- and post-construction Demolitions Building deconstruction Structural Retro-fits

Structural Engineering Overview What is a Structural Engineer? What do Structural Engineers do? What do they design?

SE’s design/analyze Structures What is a structure? A system designed to resist or support loading and dissipate energy Building Structures Houses Skyscrapers Anything designed for continuous human occupation Non-building Structures Bridges Tunnels Dams

Forces Influence on an object that causes a change in a physical quantity Considered “vectors” – magnitude and direction Static Force Unchanging with time Walls Floors Dynamic Force Changing with time People Furniture

Forces Axial Forces Momential (Bending) Force Acting along one axis, directly on a point or surface Momential (Bending) Force Acting along an axis, at a certain distance from a point, causes a folding motion M = F*d F

Forces Tensile Force Compressive Force Pulling on an object – stretching it Steel shows “necking” when too much tensile force is applied Compressive Force Pushing on an object – collapsing it Concrete crushes when too much compressive force is applied

Forces Strain Stress Compare using stress-strain graph Tensile-related property Deformation / Length Stress Compression-related property Force / Area Compare using stress-strain graph

What constitutes loading? Loading is a force being enacted on the structure Many sources of load Gravity/Weight Wind Snow Earthquake Man-made Two Types of Structural Loading Dead Loads – static, ever-present (i.e. Walls, Floors, etc) Live Loads – dynamic, changing (i.e. People, Desk, etc)

What should we build our structures out of?? Common Structural Materials Timber Masonry Concrete Steel Composites

How do we judge the materials? Common Material Properties Strength – Tensile/Compressive Density Hardness Ductility / Brittleness Elasticity Toughness

Strength Ability of a material to withstand loading Tensile strength – ability of a material to withstand a pulling force Steel is good at this, but concrete performs very poorly. http://www.youtube.com/watch?v=YdqvGGFIbfc Compressive strength – ability of a material to withstand a pushing force Wood, concrete, steel, and masonry perform well http://www.youtube.com/watch?v=WC6AgX2N1Go&feature=related http://www.youtube.com/watch?v=i5qwvtEqC5o&feature=related

Density Mass per unit volume of a material Units – mass/vol - kg/m3 or lb-m/ft3 Typically, materials with a high density are very strong and offer great protection. However, a high density means that they are heavy and difficult to work with $$$$$

Hardness Ability of a material to resist permanent deformation under a sharp load Relates to the elasticity of a material Diamond is a very hard substance. If we built a wall out of diamond, we could be sure that very few things would scratch it. However, Diamond is incredibly expensive and not as tough as other engineering metals. It wouldn’t stand up as well in impact loading versus other materials.

Ductility / Brittleness Ability of a material to deform without fracture We want materials with high ductility, because they will indicate structural failure without a sudden collapse. http://www.youtube.com/watch?v=BXpqW9B0eT4&feature=related – “Brittle failure”

Elasticity Ability of a material to deform and return to it’s original shape. Important quantity Young’s Modulus Ratio of stress to strain Stress = Force / Area (lbs./in2 or N/m2) Strain = Deformation / Length (unitless) Generates a stress-strain graph Related to the ductility of a material

Toughness Ability of a material to resist fracture when stressed (amount of energy absorbed per unit volume) Units – J/m3 or Lb-f/ft3 Area under the stress-strain curve, evaluated from 0 to the desired strain.

So, we know what properties are important in structural materials So, we know what properties are important in structural materials. How do the common materials stack up against each other?

Timber Advantages Disadvantages Cheap, renewable resource Good in Tension – ~40 MPa Disadvantages Susceptible to fire, nature Not very hard Not very strong Limits on shape, size

Masonry Concrete blocks, clay bricks Advantages Disadvantages Large compressive strength Cheap Good thermal properties – holds heat well Disadvantages Not a cohesive material. The strength could depend on the mortar, other factors Poor tensile strength, unless reinforced Heavy material, requires skilled laborers to use $$$$$ Height restriction Susceptible to the weather

Concrete Combination of water, cement, small aggregate, and large aggregate. Advantages Very versatile – can be modified with admixtures for different effects High compressive strength (4~7 ksi) Fire resistant Many diverse sizes and shapes - formwork

Concrete Disadvantages Long curing time Low tension strength (~0.4 ksi) Fails in shear, unless reinforced Fairly heavy material to work with

Steel Advantages High tensile and compressive strength (A36 Steel ~ 60 ksi) Many varieties, depending on your need Carbon steel Stainless steel Galvanized steel Elastic material Ductile material Many shapes, sizes

Steel Disadvantages Expensive – limited quantities / competition Susceptible to fire, rust, impurities

Put them together and… Reinforced Concrete Concrete with steel reinforcement Concrete handles compression Steel takes the tension Can handle nearly 4 times the loading that concrete alone can handle More expensive material http://www.youtube.com/watch?v=dGbrp7Mfp2w

Composites Engineered compounds that have different physical or chemical properties FRP – Fiber reinforced polymers CFRP – Carbon-fiber reinforced polymers Plastics Categories of Glass Categories of Wood

So, now we know what material will best suit our needs So, now we know what material will best suit our needs.. What should we build with it?

Structural Shapes Rectangle / Square Triangle Truss Geodesic Dome Interested in stability Truss Geodesic Dome

Shape Stability Exercise Split into teams of 5 Build a triangle and square See which shape is the most stable Can the unstable shapes be made stable? How?

Rectangle Advantages Disadvantages Proficient in resisting vertical load. Disadvantages No lateral support

Triangle Advantages Disadvantage Able to withstand lateral & vertical loading Many triangular shapes available Disadvantage Wide base = $$$$

Rectangle Advantages Disadvantages Proficient in resisting vertical load. Disadvantages No lateral (horizontal) load support Need another bar for lateral support! --BRACING--

Truss Combination of square and triangle

Truss Combination of square and triangle Squares

Truss Combination of square and triangle Triangles

Truss Combination of square and triangle Both vertical and lateral support

Geodesic Dome

Domes

Domes Advantages Very strong shape, gets strong as the dome size increases Perfect load distribution No need for structural supports Great aerodynamic performance

Structural Components Beams Girders Columns Floors Foundations Column Girder Beam

Load Path Floor Beams Girders Columns Foundation Soil/Bedrock

Foundations Support the building Types Typically attached to columns Shallow Spread footing – concrete strip/pad below the frost line Slab-on-grade – concrete pad on the surface Deep Drilled Shafts Piles

Columns Carry the load from floors to the foundation Never want the columns to fail COLLAPSE Typically reinforced concrete or steel Many sizes and shapes

Girders Attached column-to-column Take the load from the beams Transfer it to the columns Generally shaped as an I-Beam

Beams Attached between the girders Take load from the flooring system Transfer it to the girders Generally solid squares, I-beams

Flooring Composed of a subfloor and floor covering Usually leave space for ductwork, wiring, etc. Floor covering ranges from application to application

Picture Credits Geodesic Dome Truss Truss 2 Truss 3 Stress-Strain http://www.ecophotoexplorers.com/images/antarctica/Dome.jpg Truss http://www.classictruss.com/art/wodd_truss_types_examples.gif Truss 2 http://www.wwta.ab.ca/images/pic%201.jpg Truss 3 http://www.garrettsbridges.com/images/pratt-truss-bridge.jpg Stress-Strain http://www.mittalsteel.com/NR/rdonlyres/8E6DAA96-67F0-4C32-8702-FB02211647D9/0/InlandAutoApps_MildCS_ssGraph.gif Crushing Concrete http://images.google.com/imgres?imgurl=http://cee.engr.ucdavis.edu/faculty/chai/Research/Planar%2520Wall%2520Stability/Wallcolumn5.jpg&imgrefurl=http://cee.engr.ucdavis.edu/faculty/chai/Research/Planar%2520Wall%2520Stability/struct-walls.htm&h=432&w=293&sz=38&hl=en&start=10&sig2=u3TW2TnwJ_IRSpfaQhJuUQ&tbnid=7g-JN0VhU59wxM:&tbnh=126&tbnw=85&ei=qUTYR56oL6jmigGFuaiFAg&prev=/images%3Fq%3Dconcrete%2Bcrushing%2Bcompression%26gbv%3D2%26hl%3Den

Pile Machine Pile Machine 2 Foundation Type Rebar Cage http://upload.wikimedia.org/wikipedia/commons/5/54/DFmachine.JPG Pile Machine 2 http://upload.wikimedia.org/wikipedia/commons/8/8b/PileDriving.jpg Foundation Type http://upload.wikimedia.org/wikipedia/en/6/66/Found-House-Apt.png Rebar Cage http://i.pbase.com/u29/camera0bug/upload/17213579.P5070031.JPGcopy Circular Columns http://web.mit.edu/istgroup/ist/images/research_images/microwave/figure1.gif

Timber Steel Concrete Masonry http://www.certified-teak.com/images/timber_india.jpg http://www.timberframeworks.com/images/File0001.jpg Steel http://www.lakewoodconferences.com/direct/dbimage/50261363/Stainless_Steel_Seamless_Tubes.jpg http://ocw.mit.edu/NR/rdonlyres/Global/6/695E8EC6-5161-4B05-B6F1-8BE09DC40F68/0/chp_steel_struct.jpg Concrete http://www.imagico.de/pov/pict/concrete.jpg Masonry http://www.gomedia.us/arsenal/images/texturepacks/masonry-prev1.jpg http://www.cca.org.nz/images/masonry.jpg

Structural Engineer Building Girder Beam Flooring http://vaengineer.com/images/mr__snell_0462.jpg Building http://www.brasfieldgorrie.com/_images/portfolio/84/2.jpg Girder http://www.popartuk.com/g/l/lgfp0432+men-on-a-girder-having-lunch-new-york-city-collection-poster.jpg http://oldcooperriverbridge.org/small/oct_31_1927_pearman_resting_girder.jpg Beam http://www.cedar-log-homes.com/log-homes-images2/beams-glulam-6.gif Flooring http://www.domoteck.org/domoteck_com_images/floor_cross_section.jpg