Presentation on theme: "Gravity Force Resisting Systems"— Presentation transcript:
1 Gravity Force Resisting Systems CE Design of Multi-Story StructuresT. B. QuimbyUAA School of EngineeringGravity Force Resisting Systems
2 Basic Elements • Horizontal Systems (Floors & Roofs) – Joists, purlins, girders– One-way slabs– Two-way slabs– Waffle Slabs– Flat plates– Space Trusses• Vertical Components– Columns– Load Bearing Walls• Horizontal systems are generally unaffected by lateral loads• Vertical components often are affected by both gravity and lateral loads.
3 Joists, Girders, Purlins The system consists of:a horizontal slab or sheathed surface.a system of beams (i.e. joists, purlins, girders) supporting the bearing surface.columns or walls that support the beam system.
6 Steel Deck Use manufacturers load tables. Used without concrete for roof decksUsed with concrete for floor decks.Lots of different profiles and gage thicknesses.Design connection to supports for diaphragm shears
7 Steel Joists Use Manufacturer's Span Tables Industry standards have been produced by the Steel Joist Institute.Most manufacturers build their joist to SJI specifications
8 One-Way Slabs Slab spans between supports on two opposite sides Generally true for slabs with an aspect ratio of 3:1 or more.Analyzed and Designed as a beam without shear reinforcement.
9 One-Way Slab and Beam Behavior Reference #1, pg. 164
10 Two-Way Slabs Support on all edges. May be “fixed” or “free” at supports.Moments and shears are somewhat less than seen in one-way slabs of comparable span.Precise analysis is somewhat complex.
16 Flat Plates Slabs supported by columns only. Slab is divided into strips.Each strip is designed as a beam to carry a portion of the load.Punching shear at columns is often a critical problem.The problem becomes very complex if the columns are not laid out on a rectangular grid.
19 Space Trusses Generally steel, sometimes wood or concrete. Used mostly for exposed for roof structures.Can be used to achieve many different shapes.Often used for long span roof structures.
20 Roof for a High School Gym Reference #2, pg. 54
21 Alternative Truss Layouts Reference #1, pg. 198
22 ReferencesLin, T.Y., and Stotesbury, S.D., Structural Concepts and Systems for Architects and Engineers, 2nd edition, Van Nostrand Reinhold, 1988.Ambrose, J., Building Structures, Wiley Interscience, 1988.Council on Tall Buildings & Urban Habitat, Advances in Tall Buildings, Van Nostrand Reinhold, 1986.