high school structural engineering powerpoint
Post on 10-Apr-2016
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Structural Engineering
Forces acting on a structure
DEAD
LIVE
SNO
W
WIND
EARTHQUAKE
How are these forces resisted?
Structural Element Properties
• Shape– W Shape vs Tube Shape– Section Modulus, S– Moment of Inertia, I– Length, L
• Material– Steel– Allowable Bending Stress, Fb (ksi)– Young’s Modulus (Stress/Strain ratio), E (ksi)
Section Modulus, S and Moment of Inertia, I
Structural Element Properties
• Shape– W Shape vs Tube Shape– Section Modulus, S– Moment of Inertia, I– Length, L
• Material– Steel– Allowable Bending Stress, Fb = 33.0 ksi– Young’s Modulus (Stress/Strain ratio), E = 29,000 ksi
Common Failure Modes?
• Strength (Snapping) • Deflection (Movement)
Maximum Deflection Allowed = L/360
Maximum deflection exceeded
Common Failure Modes?
• Strength (Snapping) • Deflection (Movement)• Shear• Torsion
Typical Beam, Plan View
1. Top Down Plan View
3. Tributary Width, Trib2. Beam Length, L
4. Linear Force, w w=PSF*Trib
Typical Beam, Isolated View
w, Linear Force
L, Beam Length
Design Equations
(Real) Design Equations• Strength:– Bending caused by Force, B = wL²/8– Bending Capacity of Beam, Bcap = SFb
• Deflection:– Maximum Deflection Allowed, Δmax = L/360– Actual Deflection caused by Force, Δ = 5wL⁴/384EI
• Solve for S and I and then choose Beam!
• NOTE: Be careful of units (ft vs. in and lbs vs k)
Design SummaryDESIGN GIVENS• Force, PSF = 55.00 psf• Length, L = 39.5 ft• Tributary Width, Trib= 6.0 ft• Allowable Bending Stress, Fb = 33.0 ksi• Young’s Modulus, E = 29,000 ksi
DESIGN EQUATIONS• w = PSF*Trib/1000• B = 12*wL²/8 • Bcap = SFb • Δmax = 12*L/360 • Δ = 1728*5wL⁴/384EI
DESIGN PROCEDURE• Solve for w• Solve for B• Equate B to Bcap and solve for S• Choose a beam based on strength• Solve for Δmax • Equate Δmax to Δ and solve for I• Choose a beam based on deflection• Select controlling beam shape
Selection Of Beam
• Sreq = 23.4 in³• Ireq = 480.0 in⁴
• W18x35• S = 57.6 in³ > 23.4 in³• I = 510 in⁴ > 480.0 in⁴• Note that W18x35 is the lightest shape that
meets these requirements therefore it is chosen because it costs the least.
Site Safety
What to look for?
Beams vs. GirdersWide Flange vs. Tubes
Steel Shear StudsAngles and other Miscellaneous Steel Shapes
Column Type and OrientationColumn Baseplates
X-BracesRebar Density
Concrete Slab Control JointsConcrete Foundations
Any Questions?
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