Mark Anstrom Structural option MAE/BAE AE Senior Thesis presentation Strathmore Park at Grosvenor Metro North Bethesda, MD

Mark AnstromStructural option MAE/BAE

AE Senior Thesis presentationStrathmore Park at Grosvenor Metro North

Bethesda, MD

Strathmore Park at Grosvenor Metro

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

Strathmore Park at Grosvenor Metro

1 2 3

4 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

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?

Considerations Maintain same architectural appearance as

original design (such as ceiling height) Preserve acoustical quality Check trusses for vibration Ensure proper fire ratings Check ponding on flat roof

Presentation preview Wood design summary

Steel design summary

Breadth – fire, acoustics, vibration, cost

Comparison – wood, steel, and concrete

Conclusion

Wood Design

16” Wood trusses with dimension lumber bearing walls

The design

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)

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.

TYP. EXTERIOR WALLTRUSSES PERPENDICULAR

2x4 BLOCKING MIDWAY BETWEEN TRUSSES

23/32" PLYWOOD FLOOR SHEATHING

2x4 CONTINUOUS RIBBON

WOOD STUDS SEE SCHEDULE

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

FLUSH BEAM SEE PLAN FOR SIZE

BOTTOM CHORD BEARING W/ HANGERS

TYPICAL FLUSH BEAM

16" DEEP PREFABRICATED PLATE CONNECTED FLOOR TRUSSES

SIMPSON TRUSS HANGER

3/4" GYPCRETE TOPPING


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

15.2 PSF

14.3 PSF

13.2 PSF

11.9 PSF

11.2 PSF

10.4 PSF

9.5 PSF

13.6 PSF UPLIFT

5.0 PSF LEEWARD

WINDWARD

Architectural modifications

Columns can be eliminated

Floor depth increases to ~18”, but…

Dropped ceilings for MEP can be eliminated

Wall thickness changes (unnoticeable)

ORIGINAL CONCRETE DESIGN WOOD DESIGN - COLUMNS ELIMINATED

ORIGINAL CONCRETE DESIGN WOOD DESIGN - COLUMNS ELIMINATED

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

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

Composite steel Design

w-shape Steel beams, girders and columns

The design

The design

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

WIDE FLANGE BEAM TOP FLANGE COPEDSEE PLAN FOR SIZE

5" NORMAL WEIGHT CONCRETE TOPPING (f'c=4000)

3/4" x 4" SHEAR STUDS SEE PLAN FOR NUMBERINVERTED USD B-LOK DECK 18 GAGE - RIBS PERP. TO BEAM

WIDE FLANGE GIRDERSEE PLAN FOR SIZE

1/4" E70XX

BEAM - GIRDER CONNECTION

L4x3x3/8 SINGLE ANGLE SHEAR CONNECTION

3/4" A325-N BOLTS

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

The designConnections

Single angle welded-bolted or bolted-bolted connection

A36 steel L4x4x3/8 with (2) A325N bolts





1/4" E70XX



3/4" A325-N BOLTS

WIDE FLANGE GIRDER

PLAN

WIDE FLANGE BEAM

SINGLE ANGLE SHEAR CONNECTION

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.

BEAM - CONCRETE WALL CONNECTION


12"x12"x1/2" PLATE W/ (4) 1/2"x6" ANCHOR BOLTS


INVERTED USD B-LOK DECK 18 GAGE - RIBS PERP. TO BEAM

3/4" x 4" SHEAR STUDS SEE PLAN FOR NUMBER


#4 DOWELS AT 12" O.C.15" EMBED. LENGTH

Architectural modifications

16 columns eliminated

Floor depth Increases to ~22”, but…

Most dropped ceilings for MEP eliminated

Smaller columns

Advantages Less columns = less steel

Drops are not always needed for MEP

No formwork – no stripping

Lighter – less base shear

Disadvantages

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

Breadth study

fire protection, acoustics, vibration, estimating

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

Breadthacoustics

FHA: STC > 50, IIC > 52Wood 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

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

Cost estimateConcrete

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)

0

20

40

60

80

100

120

140

160

180

$ / SF

WoodSteelConcrete

A Comparison

Concrete, wood, and steel

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

Wood Advantages & disadvantages

Pros Least Expensive of the three No columns necessary Less lead time than steel Plenum – No dropsCons Transfer Slab necessary Lacks permanence of

Concrete, Steel Close Architectural and

Structural relationshipORIGINAL CONCRETE DESIGN WOOD DESIGN - COLUMNS

ELIMINATEDORIGINAL CONCRETE DESIGN WOOD DESIGN - COLUMNS

ELIMINATED

Steel Advantages & disadvantages

Pros Durability and strength Fewer columns than concrete Plenum space Lighter – less base shear

not critical hereCons No money saved Long lead time for steel shapes shear studs Welding steel Must fireproofed

Conclusion

Lessons learned

Is there a best option?

After weighing all of the designs…

Concrete

is the best optionWhy? 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

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

Wrap up

Acknowledgements

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

Thank you

Mike Stansbury, P.E.Dr. BoothbyDr. Hanagan

Dr. Ling

Any Questions?

The design

TYP. EXTERIOR WALLTRUSSES PERPENDICULAR

1/2" OSB WALL SHEATHING CONTINUOUS ACROSS TRUSSES

2x4 CONTINUOUS BAND

BRICK VENEER ATTACHED TO WALL STUDS WITH BRICK TIES AT 24" O.C. HORIZONTALLY AND VERTICALLY




BUILT-UP HEADER. SEE PLANS FOR SIZE AND LOCATION

DOUBLE TOP PLATE

16" DEEP PREFABRICATED PLATE CONNECTED FLOOR TRUSSES

TYP. INTERIOR BEARING WALLPIGGY BACK TRUSS CONDITION

1/2" MAX CLR.

TOP CHORD BEARING TRUSS

16" DEEP PREFABRICATED PLATE CONNECTED FLOOR TRUSSES (LONGER SPAN)

DOUBLE TOP PLATE




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

BUILT-UP HEADER. SEE PLANS FOR SIZE AND LOCATION

TRUSSES PERPENDICULAR

TYP. EXTERIOR WALL

BRICK VENEER ATTACHED TO WALL STUDS WITH BRICK TIES AT 24" O.C. HORIZONTALLY AND VERTICALLY

1/2" OSB WALL SHEATHING CONTINUOUS ACROSS TRUSSES

DOUBLE TOP PLATE

32" DEEP PREFABRICATED PLATE CONNECTED ROOF TRUSSES W/ 2x6 TOP AND BOTTOM CHORDS

SLOPE INSULATION 1/4" PER FOOT MIN.

The design





1/4" E70XX



3/4" A325-N BOLTS


INVERTED USD B-LOK DECK 18 GAGE - RIBS PARALLEL TO GIRDER

3/4" x 4" SHEAR STUDS SEE PLAN FOR NUMBER


1/4" E70XX

3/4" A325-N BOLTS


GIRDER - COLUMN WEB CONNECTION

Documents

Mark Anstrom Structural option MAE/BAE AE Senior Thesis presentation Strathmore Park at Grosvenor Metro North Bethesda, MD