Presentation on theme: "Steel Design BCN 3431 Rinker School of Building Construction University of Florida."— Presentation transcript:
Steel Design BCN 3431 Rinker School of Building Construction University of Florida
BCN 3431- Steel Design2 Why Structural Design Courses? zAnyone managing the construction process needs a basic understanding of the engineers environment and the basic understanding of how a structure behaves. Constructors must be able to address a number of technical questions at the project site including structural issues that sometimes are not addressed by the design professionals. Since the safety of construction workers as well as the strength and stability of structures during the construction phase is of paramount importance, construction mangers need this knowledge.
BCN 3431- Steel Design3 Structural Design zDefinition: Determination of overall proportions and dimensions of the supporting framework and the selection of individual members. zResponsibility:The structural engineer, within the constraints imposed by the architect (number of stories, floor plan,..) is responsible for structural design.
BCN 3431- Steel Design4 Important Factors in Design zSafety (the structure doesnt fall down) zServiceability (how well the structure performs in term of appearance and deflection) zEconomy (an efficient use of materials and labor)
BCN 3431- Steel Design5 Alternatives zSeveral alternative designs should be prepared and their costs compared.
9 Types of Load zDead Loads (permanent; including self- weight, floor covering, suspended ceiling, partitions,..) zLive Loads (not permanent; the location is not fixed; including furniture, equipment, and occupants of buildings) zWind Load (exerts a pressure or suction on the exterior of a building)
BCN 3431- Steel Design10 Types of Load Continued zEarthquake Loads (the effects of ground motion are simulated by a system of horizontal forces) zSnow Load (varies with geographical location and drift) zOther Loads (hydrostatic pressure, soil pressure)
BCN 3431- Steel Design11 Types of Load Continued zIf the load is applied suddenly, the effects of IMPACT must be accounted for. zIf the load is applied and removed many times over the life of the structure, FATIGUE stress must be accounted for
BCN 3431- Steel Design12 Building Code zA legal document containing requirements related to such things as structural safety, fire safety, plumbing, and ventilation. zIt has the force of law and is administered by a city, a county, or other governmental agencies. zIt does not provide design procedures, but it specifies the design requirements.
BCN 3431- Steel Design13 National Model Codes zMost of the municipalities adopt a model code and modify it to suit their particular needs. zThe BOCA National Building Code zThe Uniform Building Code zThe Standard Building Code yThe ASCE7-95, Minimum Design Loads for Building and Other Structures, is another nationally accepted document.
BCN 3431- Steel Design14 Design Specifications zProvide guidance for the design of structural members and their connections. zThey have no legal standing on their own, but they can easily be adopted, by reference, as part of a building code. zAmerican Concrete Institute (ACI 318-99) Building Code Requirements for Structural Concrete zNational Design Specifications for Wood Construction by American Forest and Paper Association.
BCN 3431- Steel Design15 Specifications for the Design of Structural Steel Buildings zAmerican Institute of Steel Construction (AISC) Manual of Steel Construction
BCN 3431- Steel Design16 Structural Steel zSteel is an alloy of primarily iron, carbon (1 to 2%) and small amount of other components (manganese, nickel, …) zCarbon contributes to strength but reduces ductility.
BCN 3431- Steel Design17 Steel Properties zThe important characteristics of steel for design purposes are: yyield stress (F y ) yultimate stress (F u ) ymodulus of elasticity (E) ypercent elongation ( ) ycoefficient of thermal expansion ( )
BCN 3431- Steel Design24 ASD zA member is selected such that the max stress due to working loads does not exceed an allowable stress. zIt is also called elastic design or working stress design. yallowable stress=yield stress/factor of safety yactual stress allowable stress
BCN 3431- Steel Design25 LRFD zA member is selected such that its factored strength is more than the factored loads. y (loads x L factors) resistance x R factor zEach load effect (DL, LL,..)has a different load factor which its value depends on the combination of loads under consideration.
BCN 3431- Steel Design26 Load Factors zThe values are based on extensive statistical studies yDL only 1.4D yDL+LL+SL (LL domin.)1.2D+1.6L+0.5S yDL+LL+SL (SL domin.)1.2D+0.5L+1.6S yIn each combination, one of the effects is considered to be at its lifetime max value and the others at their arbitrary point in time values.
BCN 3431- Steel Design27 Resistance Factor zThe resistance factors range in value from 0.75 to 1.0 depending on the type of resistance (tension, bending, compression,..) zThese factors account for uncertainties in material properties, design theory, and fabrication and construction practices.
BCN 3431- Steel Design28 History zASD has been the primary method used for steel design since the first AISC specifications was issued in 1923. zIn 1986, AISC issued the first specification for LRFD. zThe trend today is toward LRFD method, but ASD is still in use.
BCN 3431- Steel Design29 Advantages of LRFD zIt provides a more uniform reliability in all structures subjected to many types of loading conditions. It does not treat DL and LL as equivalent, thereby leading to a more rational approach. zIt provides better economy as the DL make up a greater percentage on a given structure. yBecause DLs are less variable by nature than live loads, a lower load factor is used. yThis may lead to a reduction in member size and therefore better economy.
BCN 3431- Steel Design30 Degree of Precision zThe accuracy of engineering data is less than 0.2 percent (504 lbs not 504.3 lbs). zRepresent solutions numerically to an accuracy of three significant digits. yIf the number begins with 1, then use four significant digits. yExamples: 4.78, 728, 1.724, 0.1781, 32.1, 88300, 0.00968, 1056.