Structural System Redesign • Existing Conditions • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Existing Conditions • Existing Conditions • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact Location: New York, NY Owner: NYC HHC • Conclusions Architect: RMJM Hillier Structural Engineer: Greenman-Pedersen Inc. Construction: September 2008 – Mid 2012 Cost: $160 million overall project cost Delivery: Design-Bid-Build with multiple prime contracts
Existing Conditions • Existing Conditions • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact •75,000 sq. ft. Addition to Existing Hospital • Conclusions •13 Stories •Steel Framed Addition •Concrete Existing Structure •11’ Floor-to-Floor
Existing Conditions • Existing Conditions • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions 3 rd Floor Framing Plan 8 th Floor Framing Plan •Cellular Beams for all Gravity Members •Moment Frames •Braced Frames
Design Choices Existing Conditions - Use of Steel Framing • Existing Conditions - Removal of Column Line - Use of Moment Frames • Proposal • Gravity Design Impact • Lateral Design - Need Cellular Beams • Cost Comparison - Heavy Lateral Members • Schedule Impact - Further Restrictions on MEP systems • Conclusions
Proposal - Redesign current, steel-framed addition • Existing Conditions as a concrete structure utilizing two-way • Proposal flat plate slab and shearwalls Proposal • Gravity Design • Lateral Design Design Goals • Cost Comparison - Maintain regularity in design Slab • Schedule Impact Column • Conclusions Shearwalls - Provide design freedom for other systems - Design a more cost effective structural system
Codes - ASCE7-05 • Existing Conditions - Wind Loads as per Chapter 6 • Proposal - Seismic Loads using Equivalent Later Force Proposal - ACI 318-08 • Gravity Design • Lateral Design • Cost Comparison Methodology • Schedule Impact - ETABS • Conclusions - RAM Concept - PCA Column - Microsoft Excel
Gravity System Structure Overview -12” slab • Existing Conditions - f c ’ = 6ksi • Proposal - 22’ x 24’ bay -16” columns • Gravity Design - 20” columns • Lateral Design Lateral System • Cost Comparison - 6 shearwalls • Schedule Impact -16” shearwalls • Conclusions - 20” shearwalls 3 rd Floor Plan
Design Loads • Existing Conditions - 26 psf Superimposed Dead Load Gravity Design - 80 psf Live Load • Proposal • Gravity Design Deflection Limits • Lateral Design - L/360 Immediate Live Load Defl. - L/480 Long-term Deflection • Cost Comparison - L/240 Long-term Deflection • Schedule Impact Creep Factor = 2 • Conclusions 20% of Live Load
• Existing Conditions • Proposal Slab Design • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions Bottom Reinforcing 3 rd Floor Reinforcing Plan
• Existing Conditions • Proposal Slab Design • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions Top Reinforcing 3 rd Floor Reinforcing Plan
• Existing Conditions • Proposal Slab Design • Gravity Design Initial. LL Deflection: • Lateral Design 0.0555 in • Cost Comparison Allowable: L/360 = 0.80 in • Schedule Impact Max. long-term Deflection: • Conclusions 0.4438 in Allowable: L/480 = 0.60 in 3 rd Floor Deflection Plan
• Existing Conditions Column Design • Proposal • Gravity Design • Lateral Design • Cost Comparison Columns supporting 6 stories: 16” x 16” f c ’= 6 ksi • Schedule Impact Columns supporting 13 stories: • Conclusions 20” x 20” f c ’= 6 ksi Typical Column Details
• Existing Conditions Column Design • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions Slender Column Design
• Existing Conditions Column Design • Proposal • Gravity Design • Lateral Design • Cost Comparison Column G/5.8 (6 stories): 16” x 16” f c ’= 6 ksi • Schedule Impact Column F/5.8 (13 stories): • Conclusions 22” x 22” f c ’= 6 ksi Slender Column Design
Transfer Beam Design Column Shift - Control Deflections • Existing Conditions - Match Floorplan • Proposal Layout • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions 9 th Floor Plan
- 60” deep beam Transfer Beam Design Column Shift - 20” width - Control Deflections • Existing Conditions - Match Floorplan • Proposal Layout • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
- 60” deep beam Transfer Beam Design - 20” width • Existing Conditions • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Design Assumptions ETABS - Diaphragms modeled as Rigid and Semi-Rigid • Existing Conditions Lateral Design - Shearwalls modeled as Membranes • Proposal - 0.7 f 22 modifier for shearwalls • Gravity Design -0.35 I 3 modifier for coupling beam -Deflection: H/400 for wind • Lateral Design 0.015h x for seismic 3.00” overall floor deflection • Cost Comparison 3.50” overall deflection at roof • Schedule Impact • Conclusions 12.12.3 Building Separation. All portions of the structure shall be designed and constructed to act as an integral unit in resisting seismic forces unless separated structurally by a distance sufficient to avoid damaging contact under total deflection ( δ x ) as determined in Section 12.8.6
Seismic Forces Lateral Design - Seismic Equivalent Lateral Force Procedure - Seismic Design Category SDC = B • Existing Conditions - Importance Factor I = 1.15 • Proposal - Response Modification Coeff. R = 4 - Deflection Amplification Factor Cd = 4 • Gravity Design - Base Shear V = 303 k • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Seismic Deflection Lateral Design - Seismic ETABS Elastic Analysis - EX Overall Deflection = 1.6257” • Existing Conditions - EY Overall Deflection = 1.1233” • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Final Seismic Deflection Lateral Design - Seismic Accidental Torsion - Force applied at 5% eccentricity • Existing Conditions - Amplification of torsion: • Proposal A= (d max /(1.2*d avg )) 2 (Figure 12.8-1) • Gravity Design d max = 1.693” A x = 0.804 therefore A x = 1.00 d avg = 1.573” • Lateral Design Amplified Seismic Deflections - Amplification of Elastic Output • Cost Comparison δ x =C d δ xe /I *(T a /T) (eq 12.8-15) • Schedule Impact -Maximum Overall Floor Deflection • Conclusions 2.9393” (EXMZ) < 3.00” upper limit -Maximum Overall Roof Deflection 3.2132” (EXMZ) < 3.50” upper limit -Maximum Story Drift < 0.015 max allowable 0.0022 (EXMZ)
Wind Forces Lateral Design - Wind - Basic Wind Speed V = 100mph - Importance Factor I = 1.15 • Existing Conditions - Base Shear X-dir V = 382 k • Proposal - Base Shear Y-dir V = 314 k • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Controlling Case - Seismic Deflection governed design - Wind Combinations produced highest forces • Existing Conditions Lateral Design - Provide Minimum Reinforcing: • Proposal (2) #5 bars @ 12” O.C. Each Way • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Existing vs. Proposed - Compared elements of structure that change Cost Comparison - Assumed 3% O&P • Existing Conditions - Materials, Labor, and Equipment • Proposal - Moment Connections not considered • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Existing vs. Proposed - Existing Foundation $ 901,050 Cost Comparison - Proposed Foundation $ 1,281,495 • Existing Conditions - Percent Increase ~ 40% • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Existing vs. Proposed Cost Comparison • Existing Conditions • Proposal • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Existing vs. Proposed - Existing Structure $ 10,329,667 - Proposed Structure $ 9,760,392 Cost Comparison • Existing Conditions - Percent Saving ~ 5% • Proposal - Overall Project Cost $ 130,000,000 • Gravity Design • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
Existing vs. Proposed - Existing Structure sequenced in two portions - Existing Duration 6.5 Months Schedule Impact • Existing Conditions - Proposed Structure sequenced in three portions • Proposal ~ 3 weeks per floor • Gravity Design - Proposed Duration 12 Months • Lateral Design • Cost Comparison • Schedule Impact • Conclusions
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