Docstoc

View Slide Show - PowerPoint Presentation

Document Sample
View Slide Show - PowerPoint Presentation Powered By Docstoc
					         ONE LIBERTY CENTER




MICHAEL ROMESBURG
STRUCTURAL OPTION
APRIL 15, 2003 SENIOR THESIS
THE PENNSYLVANIA STATE UNIVERSITY
DEPARTMENT OF ARCHITECTURAL ENGINEERING
        Presentation Outline
•   DESIGN TEAM
•   PROJECT OVERVIEW
•   EXISTING CONDITIONS
•   PROBLEM STATEMENT
•   PROPOSED SOLUTION
•   FIRE PROTECTION BREADTH
•   CONSTRUCTION BREADTH
•   RECCOMENDATIONS
            DESIGN TEAM:

ARCHITECT                  CIVIL ENGINEER

              GENERAL
              CONTRACTOR



                     MECHANICAL
     STRUCTURAL      ELECTRICAL AND
     ENGINEER        PLUMBING
         Background Information
• Office building; 13
  typical floors, 5 floors
  of sub-grade parking
• 300,000 sq. ft. of
  rentable office space
• Fully developed
  urban site
• Precast and glass
  facade
       Background Information
•   Estimated total cost of $42.5 million
•   Design documents completed August 2003
•   Project bid was 9-16-02
•   Site clearing and demolition started in October
•   Proposed finish is December 2004
      Original Structural Design
•   Floor system: Two-way flat slab with drops
•   Lateral system: Concrete frames
•   Foundation: Spread footings
•   Floor to floor height: 11’-6”
•   Total plenum depth: 36” leaving 8’-6” floor to
    ceiling heights
          Possible Problems
• Columns in office space
• Long schedule for concrete due to:
  forming,
  reinforcing,
  pouring,
  stripping,
  shoring, and
  reshoring
                     Solutions
• Use Fy = 50 ksi steel above grade in office spaces:
   – May speed up the schedule
   – Can get rid of columns in the office space while
     keeping the building the same size


• Different systems tried:
   – Steel beams and girders with composite deck
   – Steel joists and girders with composite deck
   – Composite beams and girders with composite deck
                Design Criteria
• Basis:
   – International Building Code (IBC 2000)
   – American Society of Civil Engineers (ASCE 7-98)
   – Load and Resistance Factor Design
        (LRFD Second Edition)


• Building Criteria:
   –   Floor to floor height remains 11’-6”
   –   Minimal impact on architecture and interiors
   –   Cost
   –   Schedule
      Selection of New System
• Non-composite steel members deflect too much
  over the new 50’ span; resulting in very deep
  members and enlarge plenum
• Joists are very difficult to fireproof; resulting in
  added labor costs
• Composite steel system preliminary sizes allow
  the plenum to remain the same size


Try a new floor design using composite steel.
       Composite Steel Design
• Slab (Information from United Steel Deck
  Manual):
  –   Light weight concrete
  –   5” total thickness
  –   16 gauge, 24” wide, 1.5” Lok-Floor
  –   Reasons selected:
       • Used on 2 or 3 spans no shoring is required under 10’
       • Meets fire rating requirements of 2 hours without added fire
         protection
       Composite Steel Design
• Typical beam:
  –   Spaced at 10’ on center
  –   Spans 30’
  –   LL = 100 psf (including partition loads)
  –   DL = 50 psf
  –   Resulting beam:
       •   W16x26 (16) camber = 1.0”
       •   Deflection due to wet concrete = 1.0”
       •   L/360 limit is 1.0”
       •   Live load deflection after composite action is less than 0.9”
       •   No Shoring Required
        Composite Steel Design
• Typical girder:
   –   Spaced at 30’ on center
   –   Spans 50’
   –   LL = 100 psf (including partition loads)
   –   DL = 50 psf
   –   Resulting beam:
        •   W30x116 (104) camber = 1.25”
        •   Deflection due to wet concrete = 1.48”
        •   L/360 limit is 1.67”
        •   Live load deflection after composite action is less than 1.60”
        •   No Shoring Required
     Composite Steel Design
• Typical column:

  – Factored loads
     • Roof Load = 105psf
     • Reduced Live Load = 65psf except 85psf top floor
     • Total Load = 1310k at bottom floor


  – Typical sizes: W14x120 and W14x132
      Composite Steel Design
• Typical change in spread footing:

  – Flat slab concrete design:
     • 8’-0” square by 46” deep


  – Composite steel design:
     • 6’-6” square by 36” deep


  – Savings of 5 to 15 yards of concrete for every footing
      Composite Steel Design
Typical floor cross section:


                               Structural and
                               duct system fit
                               tightly into the 36”
                               plenum space with
                               an inch to spare
New Floor Plan
              Lateral System
• Without concrete frames a new problem
  arises:
  – What will the new lateral system be?

     • Shear walls: Height of the building creates
       moments that are difficult for the shear walls to
       resist

     • Braced frames: Limited number of locations, but
       can work with relatively large members
  Lateral System and Center of
            Rigidity




All frames are cross braced with 2L8x8x1-1/8 and
2L4x4x3/4 horizontally and vertically respectively
       Fire Protection Breadth
• Changing to steel requires new fire protection
  measures for the structure
   – Spray on fire proofing is quick and easy


• Basis:
   – Underwriters Laboratories Inc. (UL)
     Directory of Fire Resistance Vol. 1
     ANSI/UL 263
       Fire Protection Breadth
• Building Criteria:
   – 2 hr. rated floor construction (including beams)
   – 3 hr. rated column coverage

• Solution:
   – Slab: USD manual and Design # D916 in UL
      • 16 gauge, 24” wide, 1.5” Lok-Floor
      • 3.5” LW concrete above flutes, no additional fireproofing
   – Beams and Girders: Design # D916 in UL
      • 0.75” Spray-on fireproofing
      • 0.33” Fireproofing on lower flange edge to allow slightly
        more room in plenum
      Fire Protection Breadth
• Solution:
  – Columns: Design # Y724 in UL
     • 1.75” Spray-on fireproofing


• Acceptable products for both columns and
  beams by:
  – WR Grace & Co. – Conn.
  – Construction Products Div.
  – Grace Korea Inc.
        Construction Breadth
• Assumptions in estimating costs and
  scheduling
  – R.S. Means 2003
  – One crew designated by Means used for each item
    unless noted otherwise
  – All material, labor, and equipment costs are included
  – Broken into steel members, slab, deck, wire fabric,
    steel studs, and fire proofing
        Construction Breadth


• Cost analysis (structure above grade):
   – Initial concrete cost: $5,989,000
      • $18.34 / sq.ft.
   – Initial steel cost: $4,559,000
      • $13.96 / sq.ft.


   – Total Savings: $1,430,000
      • $4.38 / sq.ft.
     Construction Breadth
        New Schedule
• Steel members erected 37 pieces per day
  leaving a 20 day float
• Wire fabric is the critical item taking 96 days
         Construction Breadth
            New Schedule
• Shear studs are
  erected in two phases
  to stay ahead of
  concrete and behind
  steel erection
• Total duration is 106
  days and is 34 work
  days less than the
  original concrete
  schedule
                Conclusion
• Steel is erected faster (one months extra rent
  may be charged)
• Steel is cheaper by 24%
• Composite steel system eliminates columns in
  office spaces
• Redesign is succesful
          Recommendations
• Based on cost and scheduling choose
  composite steel and composite deck system in
  above grade office spaces

• Investigate use of similar system in below grade
  parking deck, savings may not be as great due
  to lower loads and less premium space
        Thank You

• SK&A
• AE Faculty and Staff
• AE Class of 2003
QUESTIONS ?

				
DOCUMENT INFO
Shared By:
Categories:
Stats:
views:5
posted:12/20/2010
language:English
pages:30