Riverview Heights Darren K. Howard Structural Option Architectural Engineering Spring Thesis 2005 Advisor: Dr. Ali Memari
Riverview Heights Darren K. Howard Structural Option Table of Contents: 1.0 Project Background 2.0 Problem Statement 3.0 Solution Overview 4.0 Structural Redesign 5.0 Mechanical Issues 6.0 Acoustical Issues 7.0 Cost Estimates 8.0 Conclusions and Recommendations Acknowledgements Questions
Riverview Heights Darren K. Howard Structural Option 1.0 PROJECT BACKGROUND
Riverview Heights Darren K. Howard Structural Option 1.0 Project Background: • Conshohocken, Pennsylvania • 4 apartment levels • 2 levels of partially underground parking
Riverview Heights Darren K. Howard Structural Option 1.1 Apartment Structural Systems: • Bearing Walls: Wood stud walls • Floor: 20” deep, floor trusses • Lateral System: Wood Panel Shear Walls
Riverview Heights Darren K. Howard Structural Option 1.1 Parking Structural Systems: • Elevated Two-Way concrete slab with drop panels • Top slab is a 11” thick “transfer slab” • “Transfer slab” picks up random bearing wall loads • Concrete columns send loads to spread footings
Riverview Heights Darren K. Howard Structural Option 2.0 PROBLEM STATEMENT
Riverview Heights Darren K. Howard Structural Option 2.0 Problem Statement • Lumber is a renewable, but not unlimited resource • New building materials will eventually become necessary • Alternative materials and methods must be found
Riverview Heights Darren K. Howard Structural Option 3.0 SOLUTION OVERVIEW
Riverview Heights Darren K. Howard Structural Option 3.0 Solution Overview • Cold-formed steel buildings are growing in popularity • Recyclable material • Not susceptible to termite damage • Will not burn or harbor mold • Will not rot, shrink, warp or split • Prices for cold-formed steel have been more stable than lumber • Construction methods are very similar to wood framing
Riverview Heights Darren K. Howard Structural Option 4.0 STRUCTURAL REDESIGN
Riverview Heights Darren K. Howard Structural Option 4.0 Structural Redesign • Replace existing bearing walls with cold-formed studs • Replace wood floor trusses with cold-formed joists • Investigate the use of possible lateral systems: � Wood panel shear walls over cold-formed studs � Lateral strap bracing
Riverview Heights Darren K. Howard Structural Option 4.1 BEARING WALLS
Riverview Heights Darren K. Howard Structural Option 4.1 Bearing Wall Redesign • Existing bearing walls and unit separation walls:
Riverview Heights Darren K. Howard Structural Option 4.1 Bearing Wall Redesign • Design Considerations: � Replace existing unit separation walls with a single cold-formed stud wall � Set studs at a spacing of 24” o.c. rather than 16” o.c.
Riverview Heights Darren K. Howard Structural Option 4.1 Bearing Wall Redesign • Redesigned Walls: � Unit separation walls: 6” wide studs @ 24” o.c. � Interior bearing walls: 3-5/8” studs @ 24” o.c. � Gauge of stud varies from floor to floor
Riverview Heights Darren K. Howard Structural Option 4.1 Bearing Wall Redesign Unit Separation Walls Floor Stud Load (kips) Allowable (kips) 4 6SW-16 @24” 3.2-4.4 5.73 3 6SW-14@24” 5.3-6.6 7.56 2 6SW-12@24” 6-8 11.51 1 6SW-12@24” 8-11 11.51
Riverview Heights Darren K. Howard Structural Option 4.1 Bearing Wall Redesign Interior Unit Bearing Walls Floor Stud Load (kips) Allowable (kips) 4 358SW-18 @24” 2-2.4 2.75 3 358SW-16@24” 3-3.6 4.05 2 358SW-14@24” 4-4.48 5.12 1 358SW-12@24” 5-6 7.32
Riverview Heights Darren K. Howard Structural Option 4.2 FLOOR SYSTEM
Riverview Heights Darren K. Howard Structural Option 4.2 Floor System Redesign • Existing Floor: 16’ to 25’ interior spans
Riverview Heights Darren K. Howard Structural Option 4.2 Floor System Redesign • Design considerations: � Cold-formed steel joists should require less depth � This will add additional floor-to-floor height in units
Riverview Heights Darren K. Howard Structural Option 4.2 Floor System Redesign • Redesigned Joists: 14j10 Marino/Ware Joists � 14” deep, 10 gauge joists @ 24” o.c. � Allowable p.l.f. = 130 p.l.f. ( δ < L/360) � An additional 6” of floor-to-floor height is achieved
Riverview Heights Darren K. Howard Structural Option 4.3 LATERAL RESISTANCE
Riverview Heights Darren K. Howard Structural Option 4.3 Lateral System Redesign • Existing Lateral System: Wood Shear Panel Walls
Riverview Heights Darren K. Howard Structural Option 4.3 Lateral System Redesign • Design Considerations:
Riverview Heights Darren K. Howard Structural Option 4.3.1 Lateral System Redesign • Alternative #1: Wood shear panels over cold-formed studs � Greater strength = fewer shear walls required # of Shear Walls Required Floor Wood CF Steel 4 36 22 3 36 25 2 36 33 1 36 36
Riverview Heights Darren K. Howard Structural Option 4.3.2 Lateral System Redesign • Alternative #2: Lateral Strap Bracing
Riverview Heights Darren K. Howard Structural Option 4.3.2 Lateral System Redesign • Alternative #2: Lateral Strap Bracing • STAAD frame model of tension braces
Riverview Heights Darren K. Howard Structural Option 4.3.2 Lateral System Redesign Floor Allowable Load (kips) Lateral Strap Sizes 4 2” x 18ga (both sides) 3.56 3 2” x 18ga (both sides) 3.56 2 4” x 18ga (both sides) 7.14 1 4” x 18ga (both sides) 7.14
Riverview Heights Darren K. Howard Structural Option 5.0 MECHANICAL
Riverview Heights Darren K. Howard Structural Option 5.0 Mechanical Issue • Major disadvantage of cold-formed steel � Thermal conductivity HOT COLD
Riverview Heights Darren K. Howard Structural Option 5.0 Mechanical Issue • Add a thermal break between the exterior and interior space • An additional layer of 1” rigid insulation must be installed
Riverview Heights Darren K. Howard Structural Option 5.0 Mechanical Issue Wall Assembly Clear-Wall R-Value Whole-Wall R-Value Existing Wall: 10.6 9.6 2x4 Studs, 16” o.c., R-11 batts, ½” ext. plywood, ½” int. gypsum CF Wall (no thermal break) 9.4 7.1 3 ½” steel studs, 24” o.c., R-11 batts, ½” ext. plywood, ½” int. gypsum CF Wall (thermal break) 3 ½” steel studs, 24” o.c., R-11 batts, 13.3 10.2 ½” ext. plywood, ½” int. gypsum, 1” rigid insulation over ext. plywood
Riverview Heights Darren K. Howard Structural Option 6.0 ACOUSTICS
Riverview Heights Darren K. Howard Structural Option 6.0 Acoustics • Cold-formed studs have lower acoustical properties • Riverview Heights was designed as an “average” site • Unit separation walls and floors need to meet an STC rating of 52
Riverview Heights Darren K. Howard Structural Option 6.0 Acoustics • An additional 5/8” of gypsum is required on both sides of walls to meet acoustical requirements • Existing wood floor trusses and the redesigned joists required resilient channels on the ceiling side
Riverview Heights Darren K. Howard Structural Option 6.0 Acoustics System STC rating CF Unit Separation Walls 57 and Corridor Walls Existing Walls 53 CF Floor Assembly 56 Existing Floor 57
Riverview Heights Darren K. Howard Structural Option 7.0 COST ESTIMATES
Riverview Heights Darren K. Howard Structural Option 7.0 Cost Estimates Estimate of Wood Framing System Cost Wood Panel Shear Walls $70,502.40 2x4 Stud Walls $553, 316.40 Floor Trusses $241, 647.00 Total Cost $780,340.20
Riverview Heights Darren K. Howard Structural Option 7.0 Cost Estimates Estimate of Cold-Formed Framing System Cost Wood Panel Shear Walls $52,387.20 Lateral Strap Bracing $51,984.00 Cold-formed Joists $710,955 Cold-formed Stud Walls $383,875.92 Total with Either Lateral System $1,146,830.20
Riverview Heights Darren K. Howard Structural Option 7.0 Cost Estimates Cold-Formed Framing Additional Costs System Cost 1” rigid insulation $27,000 Additional layer of 5/8” $53.707.68 drywall on walls Total $80,707.68 Total Cold-Formed Cost $1,227,538.60
Riverview Heights Darren K. Howard Structural Option 7.0 Cost Estimates Total Costs System Cost Wood Framing $780,340.20 Cold-Formed Framing $1,227,538.60 Difference in cost - $447,198.40 CF joists are more than twice the cost of wood floor trusses!!
Riverview Heights Darren K. Howard Structural Option 7.0 Cost Estimates Total Costs without Floor Systems System Cost Wood Framing minus $538,693.20 Floor System Cold-Formed Framing $516,583.60 minus Floor System Difference in Cost + $22,109.60
Riverview Heights Darren K. Howard Structural Option CONCLUSIONS AND RECOMMENDATIONS
Recommend
More recommend
