INTRODUCTION TO STRUCTURAL ENGINEERING WHAT IS A STRUCTURAL ENGINEER? WHAT DO • Structural Engineering is a specialty within Civil Engineering. Structural Engineers create drawings and specifications, perform calculations, review the work of other engineers, write reports and evaluations, and observe construction sites. STRUCTURAL ENGINEERS DO? • Take a design, and fit a structural system to that • Expert witnesses in lawsuits • Inspector • Fieldwork, Job site inspections • Designer • Oversee the materials (concrete, steel, etc.) • • Consultant Inspect the building – pre- and post-construction • Demolitions • Structural Retro-fits Structural Engineering • Building deconstruction WHAT DO THEY DESIGN? Structural Engineer 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 AXIAL FORCE • Acting along one axis, directly on a point or surface Tensile 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 Momential (Bending) Force ► Acting along an axis, at a certain distance from a point, causes a folding motion ► M = F*d 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 properties • FRP – Fiber reinforced polymers • CFRP – Carbon-fiber reinforced polymers • Steel • Plastics • Composites • Categories of Glass • Engineered compounds that have different physical or chemical • Categories of Wood HOW DO WE JUDGE THE MATERIALS? • Common Material Properties • Strength • Hardness • Density • 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 • Compressive strength – ability of a material to withstand a pushing force • Wood, concrete, steel, and masonry perform well 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. 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 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. ELASTICITY ABILITY OF A MATERIAL TO DEFORM AND RETURN TO ITS ORIGINAL SHAPE 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. COMMON STRUCTURAL MATERIALS AND ITS ADVANTAGES & DISADVANTAGE TIMBER Advantages • Cheap, renewable resource • Good in Tension Disadvantages • Susceptible to fire, nature • Not very hard • Not very strong • Limits on shape, size MASONRY • Masonry consists of building structures from single units that are laid and bound together with mortar • Concrete blocks (40cm x 20 cm and for thickness 4” or 6”) • Advantages • 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, coarse aggregate, and fine aggregate. • Advantages • Very versatile – can be modified with admixtures for different effects • High compressive strength • Fire resistant • Many diverse sizes and shapes – formwork • Disadvantages • Long curing time • Low tension strength • Fails in shear, unless reinforced • Fairly heavy material to work with STEEL • Advantages • High tensile and compressive strength • Many varieties, depending on your need • Carbon steel • Stainless steel • Galvanized steel • Elastic material • Ductile material • Many shapes, sizes • Disadvantages • Expensive – limited quantities / competition • Susceptible to fire, rust, impurities REINFORCED CONCRETE • Concrete with steel reinforcement • Concrete handles compression • Steel takes the tension WHAT SHOULD WE BUILD WITH IT? STRUCTURAL SHAPES • Rectangle / Square • Triangle • Truss RECTANGLE/SQUARE • Advantages • Proficient in resisting vertical load. • Disadvantages 🠜No lateral support TRIANGLE • Advantages • Able to withstand lateral & vertical loading • Many triangular shapes available • Disadvantage • Wide base • Combination of square and triangle • Both vertical and lateral support STRUCTURAL COMPONENTS LOAD PATH FOUNDATIONS • Support the building • Typically attached to columns • Types • 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 SOURCE • Lecture1_Structures_WU_MASE101
