AISC Design Guides A Resource for Practicing Engineers 10th International Symposium on Steel Structures Queretaro, Mexico March 4 – 7, 2009
Louis F. Geschwindner, Ph.D., P.E. Vice President American Institute of Steel Construction
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Design Guide 3: Design for Serviceability • • • • • •
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Camber Tolerances Drift Cladding / Skylights Equipment Vibration Flat and Level Floors • Summary Charts 5 and Guidelines
Deflection Criteria
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Deflection Criteria
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The Problem, To Camber or Not to Camber‌
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To Camber or Not to Camber… Select a W18 Floor Beam Span = 30 ft Supporting a Suspended Ceiling Grid End Plate Connections
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To Camber or Not to Camber… “To control excessive accumulation of concrete in the deflected bay… the total accumulated deflection in a bay due to dead load (should be) limited to L/360, not to exceed 1 in.” Δ = (30 ft × 12 in./ft)/360 = 1 in.
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To Camber or Not to Camber…
L = 30 ft.
W18×35 (Ix = 510 in.4)
Δx = 2.36 in.
W18×46 (Ix = 712 in.4)
Δx = 1.69 in.
W18×71 (Ix = 1170 in.4)
Δx = 1.03 in.
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To Camber or Not to Camber… W18×35, Δx = 2.36 in.
camber = 1-1/2 in.
W18×46, Δx = 1.69 in.
camber = 3/4 in.
W18×71, Δx = 1.03 in.
does not require cambering
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To Camber or Not to Camber… “It is common practice not to camber beams when the indicated camber is w in. or less” “…beams received by the Fabricator with 75 percent of the specified camber require no further cambering.”
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To Camber or Not to Camber… Cost to camber ≈ $30 - $75 Cost of steel ≈ $0.40 per pound Steel Savings = (71-35)(30)(0.40) = $432 > $75
Camber is an appropriate choice in this case For non-composite design, this will not as often be the case.
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To Camber or Not to Camber… • • • • •
Filler Beams Girder Beams Composite floor beams Members with uniform cross section Trusses
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To Camber or Not to Camber… • • • • • • • • • •
Spandrel beams (those supporting facia) Beams with cantilevers Beams with knee braces Members of non-uniform cross section. Beams with significant non-symmetrical loading. Beams subject to torsional loads. Beams less than 25' in length. Beams less than 14" in depth. Beams that require less than 1" of camber. Beams in braced frames. There's always a solution in steel
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Camber Cautions •Don’t over-camber beams that receive shear studs for composite action. •Cambering of members with web thicknesses ¼ in. or less may result in web buckling. •Beams that require square and parallel ends, such as for end plate or welded moment connections, must be cut after cambering. There's always a solution in steel
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Camber Tolerances From the AISC Code of Standard Practice Section 6.4: •For members less than 50-ft. long, the camber tolerance is minus zero/plus ½-in. •an additional 1/8-in. per each additional 10 ft of length (or fraction thereof) is allowed for lengths in excess of 50 ft. •These tolerances are serviceability guidelines and should not be considered absolute. There's always a solution in steel
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Camber Tolerances From the AISC Code of Standard Practice Section 6.4:
Remember that the AISC Code of Standard Practice indicates that camber is measured in the un-stressed position in the shop.
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Design Guide 7: Industrial Buildings • Roof Systems • Roof Trusses • Crane Loads and Runway Design • Fatigue • Column Anchorage
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The Problem: Crane Runway Girder Design
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Crane Runway Girder Design 1. Compute the required moments of inertia (Ix and Iy) to satisfy deflection control criteria. L/600 to L/1000 for Vertical Deflection. L/400 for Lateral Deflection.
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Crane Runway Girder Design 2. Position the crane to produce worst loading conditions‌
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Crane Runway Girder Design
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Crane Runway Girder Design
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Crane Runway Girder Design 3. Calculate Mx and My including effects of impact. Impact Factor Accounts for Dynamic Loads and location of force application, as well as impact itself
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Crane Runway Girder Design 4.For sections without channel caps, select a trial section ignoring lateral load (My) effects from: M Sx =
x
Fbx
• For sections with channel caps, Appendix A Tables 1 and 2 are of assistance.
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Crane Runway Girder Design
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Crane Runway Girder Design If A36 channel caps are used on A992 steel beams then lateral torsional buckling requirements must be based on the A36 material. Also the weak axis strength must be based on the channel cap material.
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Crane Runway Girder Design 5. Check this section by using:
M x S x M y St + ≤ 1.0 Fbx Fby St = Section modulus of top half of section about y-axis. • For rolled beams without channel caps, St should be taken as 1/2 of the total Sy of the shape, since the design assumption is that only the top flange resists the lateral crane loads. • For sections with channel caps, St is the section modulus of the channel and top flange area.
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Crane Runway Girder Design 6. Check the section with respect to sidesway web buckling as described the AISC Specification.
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AISC Design Guide 15: Retrofit and Rehabilitation of Existing Structures • Section Properties of Historic Shapes (1873 – 2000) • Historic Review of AISC Specifications • Evaluation of Existing Structures • Enhancement of Existing Structural Systems There's always a solution in steel
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Replaced “Iron and Steel Beams…”
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The Problem: Evaluation of an Existing Structure
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Existing Steel Structures
Determine the load that this girder can carry based on the original specification
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Evaluation of an Existing Structure
Project Completed 1931 (Drawing is for field performance observations)
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Evaluation of an Existing Structure
Ma = FaS = 18 ksi × 145.2 in.3 = 2613 in.-kips = 218 ft-kips There's always a solution in steel
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Evaluation of an Existing Structure P
P
a = 6.33 ft P = M/a = 218 ft-kips/6.33 ft = 34.4 kips There's always a solution in steel
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AISC Design Guide 11: Floor Vibrations • General Vibration Principles • Design for Walking Excitation • Design for Rhythmic Excitation • Design for Sensitive Equipment • Remedial Measures for Vibration Problems There's always a solution in steel
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The Problem: Evaluation of Vibration Characteristics
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Determine if the floor system below satisfies criteria for walking vibration.
Design Guide Ex. 4.4 There's always a solution in steel
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Assumptions Determine Occupancy Type and Actual Floor Loads Office Floors without full height partitions: Floor live load = 11 psf Mechanical equipment + ceiling = 4 psf Slab + deck = 42 psf There's always a solution in steel
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Joist/Beam Mode Fundamental Frequency Δj =
5w j L4j 384 Es I j
f j = 0.18 = 0.18 There's always a solution in steel
= 0.384 in.
g Δj 386 = 5.71 Hz 0.384 46
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Girder Mode Fundamental Frequency Δg =
5wg Lg 4 384 Es I g
f g = 0.18 = 0.18
= 0.415 in.
g Δg 386 = 5.49 Hz 0.415
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Combined Mode Properties Because girder span (30 ft) is less than the beam panel effective width (32.2 ft), the girder deflection is reduced
Δ'g =
Lg Bj
Δg =
30 × 0.415 = 0.387 in. 32.2
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Combined Mode Fundamental Frequence f n = 0.18
g ( Δ j + Δ'g )
= 0.18
386 = 4.03 Hz ( 0.384 + 0.837 )
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Performance Evaluation Constants from Table 4.1 Effective Damping
β = 0.03 Force Constant
Po = 65 lbs Calculated value βW = 0.03 × 111 kips = 3.33 kips There's always a solution in steel
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Performance Evaluation Acceleration
ap g
= =
Po exp ( − 0.35 f n ) βW 65 exp (−0.35( 4.03))
3,300 = 0.0048 (0.48 percent gravity) There's always a solution in steel
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Performance Evaluation
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Performance Evaluation ap g
= 0.48% g
acceleration limit = 0.5% g Therefore, the floor is marginally acceptable
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Performance Evaluation Effective Damping
Modern Steel Construction, April 2004
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Performance Evaluation Effective Damping
Modern Steel Construction, April 2004
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Performance Evaluation Effective Damping
Modern Steel Construction, April 2004
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Performance Evaluation Effective Damping
Modern Steel Construction, April 2004
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Other AISC Design Guides and Resources • Design of column bases (both flat and triangular stress block)
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Materials and repairs Small moment bases Large moment bases Design examples
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Other AISC Design Guides and Resources • Moment and shear design of beams with web openings • Reinforced and unreinforced openings • Deflection considerations There's always a solution in steel
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Other AISC Design Guides and Resources • Unstiffened extended end plate connections • Stiffend extended end plate connections • Yield line procedure • Preliminary selection tables There's always a solution in steel
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Other AISC Design Guides and Resources • Economical system design • Loading requirements • Composite floor systems • Open web joist layout and design • Bay sizing There's always a solution in steel
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Other AISC Design Guides and Resources • Composite frame construction • Practical use of composite columns • Advantages and Limitations • Suggested details • Beam-column examples and design tables There's always a solution in steel
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Other AISC Design Guides and Resources • Design of frames with partially restrained connections • Moment-rotation curves for composite connections • PR beam deflections • Connection detailing • Tables and design aids There's always a solution in steel
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Other AISC Design Guides and Resources • Fundamentals of torsion design • Derivation of torsional properties • Torsional properties tables for rolled shapes • Design examples and aids There's always a solution in steel
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Other AISC Design Guides and Resources • Temporary lateral support systems • Construction loads • Prescriptive erection bracing requirements • Systems for constructability There's always a solution in steel
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Other AISC Design Guides and Resources • Retrofit of Seismic Systems – RBS Connection – Welded Haunch – Bolted Bracket
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Other AISC Design Guides and Resources • Stiffener/continuity Plate design • Web doubler plate design • Panel zone strength • Column selection to avoid stiffeners and doublers There's always a solution in steel
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Other AISC Design Guides and Resources • • • •
Truss member design Diaphragm design Fire Protection Erection considerations • Seismic Considerations There's always a solution in steel
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Other AISC Design Guides and Resources • Flush end plate Connections • Extended end plates • Design Procedures • Gable frame panel zones • Design flow charts There's always a solution in steel
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Other AISC Design Guides and Resources • • • • •
Methods of installation Methods of Inspection Strength of bolts Design of connections Strength of Rivets in retrofit applications
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Other AISC Design Guides and Resources • Deck Systems for Parking Structures • Framing Systems • Fire Protection Requirements • Corrosion Protection There's always a solution in steel
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Other AISC Design Guides and Resources • Design of fire resistant steel framing • Building code requirements • Fire protection methods – Prescriptive Fire Protection – Engineered Fire Protection
• Standard tests • Material Properties • Tables of Shape Surface Areas There's always a solution in steel
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Other AISC Design Guides and Resources • History and design • High- and lowseismic applications • Design procedures • Design examples • Case studies
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Other AISC Design Guides and Resources • General Reference • Selection of weld types • Weld design • Metallurgy • Weld repair • Quality • Inspection There's always a solution in steel
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Other AISC Design Guides and Resources • Economical slab edge details • Performance characteristics • Assistance for architects • Focuses on strategies and their effect on design There's always a solution in steel
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Other AISC Design Guides and Resources • Future Design Guides DG 23. Constructability DG 24. HSS Connections DG 25. Web-tapered Member Design DG 26. Stability Design of Steel Buildings DG 27. Blast and Progressive Collapse DG 28. Bracing Connections DG 29. Castellated Beams There's always a solution in steel
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Gracias
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