Mark Anstrom Structural option MAE/BAE

1. Mark AnstromStructural option MAE/BAE AE Senior Thesis presentation Strathmore Park at Grosvenor Metro North Bethesda, MD

2. Strathmore Park at Grosvenor Metro

3. Project Overview • Located in North Bethesda, MD. A Washington, D.C. suburb. • 3 identical buildings – same design structurally • 4 identical floors of luxury condominiums over a 1 story parking garage • 2 hydraulic elevators • 2 stair towers • Individual HVAC units per Condo • High end finishes, fixtures and appliances • Very spacious 2-3 bedroom units • Building has sprinkler system

4. Strathmore Park at Grosvenor Metro 3 2 1 4 5

5. Current Construction • Completed December, 2002 • 10” CIP concrete flat slab f’c = 4 ksi • Punching shear reinforcement provided by steel studrails • Lateral forces resisted by centrally located shearwalls

6. Thesis Proposal • Redesign Strathmore Park using: • Wood construction • Steel construction • Why? – Many reasons, these were the most viable systems for the layout • Compare and contrast the three systems • What are the advantages and disadvantages?

7. Considerations • Maintain same architectural appearance as original design (such as ceiling height) • Layout and design members for optimal performance • Preserve acoustical quality • Check trusses for vibration • Ensure proper fire ratings • Check ponding on flat roof

8. Presentation preview • Wood design summary • Steel design summary • Breadth - fire protection and acoustics • Comparison – wood, steel, and concrete • Conclusion

9. Wood Design 16” Wood trusses with dimension lumber bearing walls

10. The design

11. The design

12. The designfloor system • 16” deep single 2x4 top and bottom chord plate-connected floor trusses • Based on deflection, moment of inertia and span • Simple span condition throughout building • Topped with 23/32” T&G structural panels and ¾” cementitious topping (UL # L521) • 12” transfer slab at first floor (From ADOSS)

13. The designroof system • 32” deep 2x6 single top and bottom chord metal plate-connected floor trusses • Based on deflection, moment of inertia, and span • Simple span condition throughout building • Rigid insulation on roof sloped to drain to avoid ponding • Bottom chord bearing

14. The designbearing wall system • 2x4 SPF #2 dimensional lumber • Designed for combined axial and wind load • Double top plate per code • Spacing ranges from (1) stud @ 24” o.c to studs at 12” o.c. doubled under trusses.

15. The designbeams, headers, and columns • Built-up SPF #2 dimensional lumber members. (2)2x6 to (2)2x12 • Structural composite lumber members used where required. 1.9E microllam (2)1 ¾” x 9 ½” LVL to (2)1 ¾ x 14” LVL • Columns are built-up 2x4s, worst case (6) studs

16. The designLateral system • Bearing walls sheathed in Structural Panels or Gyp Board for lateral resistance • Wind loads distributed to walls by tributary area • Unit separation walls and corridor walls act as shear walls • Overturning not an issue

17. Architectural modifications • Columns can be eliminated • Floor depth increases to ~18”, but… • Dropped ceilings for MEP can be eliminated • Wall thickness changes (unnoticeable)

18. Advantages • Wood is less expensive • ~$109/sf vs. ~$165/sf total costs • Wood construction is faster • The design doesn’t require a great deal of skilled labor • No intrusive concrete or steel columns • No ceiling drops – plenum • No formwork – No stripping • Shorter lead time for trusses than steel

19. Disadvantages • Because these are high end condos, the owner chose concrete over this option because of the durability of concrete over wood • Direct relationship between architectural form and structural form • Transfer slab required at garage level

20. Composite steel Design Steel trusses with w-shape steel girders and columns

21. The design

22. The design

23. The design

24. The designFloor system • Topping slab – 5” thick 4000 psi concrete slab on 1 ½” B-lok composite metal deck • ¾”x 4 ½” shear studs • 50 ksi W-Shape beams, girders and columns • Beam and girder Sizes range from W8 to W16 • Column sizes W8 or W10 in some cases

25. The designLateral system • 8” thick 4000 psi concrete shear walls reinforced with #4 bars @12” o.c. each face, each way • No drift problems (< H/400) • Accidental eccentricity of 5% x width Stairwell Stairwell elevator

26. The designConnections • Single angle welded-bolted or bolted-bolted connection • A36 steel L4x4x3/8 with (2) A325N bolts

27. The designConnections • Beam connected to concrete shearwalls using steel plate embed w/ anchor bolts • Uses same connection as beam – girder connection • Slab connected to shearwalls with #4 dowels @ 12” o.c.

28. Architectural modifications • 16 columns eliminated • Floor depth Increases to ~22”, but… • Most dropped ceilings for MEP eliminated • Smaller columns

29. Advantages • Less columns = less steel • Drops are not always needed for MEP • No formwork – no stripping • Lighter – less base shear

30. Disadvantages • No money saved • Long lead time for steel shapes • Welding shear studs • pre-composite deflection • Must fireproof steel • Vibration must be addressed

31. Breadth study acoustics, fire protection, vibration, estimating

32. Breadthacoustics FHA: STC > 50, IIC > 52 Wood Design • Unit separation wall – STC 56 • Floor assembly – STC 52, IIC 52 (72 at carpet) Steel Design • Unit Separation Wall – STC 56 • Floor Assembly – STC 50, IIC 53

33. Breadthfire ratings BOCA Type 5A construction: 1hr for floors, unit sep. walls 2 hr for exits, garage slab Wood Design • Unit separation wall – UL#U301 1 hr • Floor assembly – UL#L521 1 hr Steel Design • Unit separation wall – UL#U420 1 hr • Floor assembly – UL#D902 1 hr

34. Breadthvibration Wood Design • Floor Truss frequency >15 Hz optimal • Actual worst case Frequency 14Hz Steel Design • According to Design Guide 11: • floor acceleration < 0.5%xG • Actual floor acceleration = 0.288%xG

35. Cost estimate Concrete • Actual cost including Land, Development, and construction - $33.8M • =$165/sf Steel • Using R.S. Means sq. ft est. for construction and including land and development • =$170/sf Wood • Using estimate from owner and including land and development • =$109/sf (These are estimates)

36. A Comparison Concrete, wood, and steel

37. concrete Advantages & disadvantages Pros • Durability and Strength • Inherent Fire Protection, Vibration control, Sound Transmission control Cons • No Plenum for MEP • Cost > Wood • Columns are necessary

38. Wood Advantages & disadvantages Pros • Least Expensive of the three • No columns necessary • Less lead time than steel • Plenum – No drops Cons • Transfer Slab necessary • Lacks permanence of Concrete, Steel • Close Architectural and Structural relationship

39. Steel Advantages & disadvantages Pros • Durability and strength • Fewer columns than concrete • Plenum space • Lighter – less base shear • not critical here Cons • No money saved • Long lead time for steel shapes • shear studs Welding • steel Must fireproofed

40. Conclusion Lessons learned

41. Is there a best option? After weighing all of the designs… Concrete is the best option Why? • Its advantages outweigh its disadvantages • It is traditional for this type of project • It is common for the area • Cost is not much of an issue • Durability is a greater requirement

42. a larger view This study only applies to a single project, but it shows that: • There is a multitude of different criteria for different projects • There is a very close relationship between architectural development and structural scheme • The least expensive design is not always the best

43. Wrap up Acknowledgements

44. Design team • Owner – Eakin Youngentob Associates, Inc. • General Contractor – Clark Construction • Architect – Torti Gallas and Partners CHK, Inc. • Structural Engineer – Cates Engineering, Ltd. • MEP Engineer – Schwartz Engineering, Inc. • Civil Engineer – Loiderman Associates, Inc. • Landscape Architect – Parker Rodriguez

45. Mike Stansbury, P.E. Dr. Boothby Dr. Hanagan Dr. Ling Thank you Any Questions?