James D. Baker                                                                                                                      

Structural Discipline                                                                                                  

ALCOA Corporate Center                                                                                         

Pittsburgh Pa.

Building Statistics                            

 

 

 

Introduction of the overall structural system is described as the following:

 

The main aspects of the ALCOA Corporate Centers structural system comes in several parts, the first of which is the southern facing portion of the building.  The southern portion of this office building is comprised of a 90 foot office area which was designed with and open aired pretense to allow easy contact and communication between staff and supervisory positions.  This is done structurally by removing all interior columns in the main office area and placing large spanning girders in their place.  The office section of the building is housed structurally by some eleven north-south running gridlines of long span girders (60-ft.) which have 15 foot cantilevered ends that carry full moment connections on the span side as well as the cantilevered ends.  Each of these columns is offset in a sine wave fashion that defines the structures main shape.  Grid lines BB, BC, CC & DD follow this curving pattern (refer to the typical floor plan on the next page).  This allows a 60 foot open space within the office section of the building between the columns that extend upwards through the structure.  The size of the member required to hold this capacity is a uniform ASTM A572 grade 50 size W36x245 wide flange girders.  These main girders in the office section of the building are supporting a system of W18x35 grade 36 beams that are spaced at 8ft.-6in. on center with pin type shear connections.  On the perimeter of this system of W36x245 girders and W18x35 beams are a line of W24x45 grade 36 beams which circumnavigate the buildings southern curving façade, as well as the buildings western and eastern edges.  This construction is replicated from the first floor through the sixth.

The north side of the building consists of a supporting / facility area for the occupants of ALCOA Headquarters.  This area is connected to the southern side of the building through an open atrium via a set of people bridges and escalator tracts. Supporting these bridges and the point loads of the escalators are common W24x55 with 1-in. thick web stiffeners at 1-ft. on center across the span of the escalators supporting frame.  These W24x55’s connect to directly to the structural frame of the escalator across this span.  Opposing the escalator and bridge system is the remainder of the north side of the building.  This portion of the building contains the lateral wind resisting systems and houses an assortment of different sized beams and connection types due to the local loads.  The range of beams in this section of the building is from W8x10 to W40x397.  Reasoning for such a huge variation in size is due to the small span length covered by some of the beams, and others which carry column loads from above.  In the northwest corner which is a gathering are in the building, the most common size is the W16x50.  The mechanical room on the north side of the building is comprised of mainly W18x40’s.  The northeastern quadrant of the building is mainly comprised of W21x44, and W16x31 sizes with several very large beams to support column loads that coming down from upper floors in the building.  The column lines in the northern half of the building become linear and more regularly spaced, although they are in no real geometric grid.

 

 

 

 

 

James D. Baker                                                                                                                      

Structural Discipline                                                                                                  

ALCOA Corporate Center                                                                                         

Pittsburgh Pa.

Building Statistics                                        

 

 

 

 

 

ALCOA CORPORATE CENTER  --TYPICAL FLOOR LAYOUT

           

Structural steel columns in the ALCOA Corporate Center come in a wide variety as well.  All of the columns in the building are of strength A 572 Grade 50.  Starting with the office area, the column sizes along grid lines BB & CC are a W14x311 from the bottom of the first floor to the bottom of the fourth floor with a transition to W14x283, pin connected. These extend to the low roof where they connect to 8-in. diameter pipe columns.  These bottom columns are the biggest in the building.  They support the 60-ft. span girders that traverse the main open office area, and are connected in full moment connections at each level with these massive supporting systems.  These W14x311 columns rest on 32”x 32” concrete piers that transfer load onto 4 ½ ft. thick, 12 foot square pile cap bases that continue on into 18 friction piles each traveling 39 feet into the soil.  The most common other size of column in the building is W12x79 splicing into W12x53’s.  The wind force resisting systems column lines are marked with W12x79 splicing into W12x72’s that are moment connected at floors 4 and 6.  The columns in the mechanical room extend from the second floor to the fourth, and the load is transferred into the largest set of beams on the second floor.  As noted previously, the beams vary from W8x10 to W40x397, as the larger ones are those that are supporting the column loads that come from above.

            The F’c required at 28 days is as follows:  Foundations – 3000 psi, 

Interior / Exterior Slabs – 4000 psi,       Concrete Piers / Walls – 5000 psi

 

 

 

 

 

 

 

James D. Baker                                                                                                                      

Structural Discipline                                                                                                  

ALCOA Corporate Center                                                                                         

Pittsburgh Pa.

Building Statistics                                        

 

 

 

 

 

List of Codes and code requirements:

 

  • BOCA  National Building Code – 1989

Building Officials & Code Administrators, Inc.

  • AISC 1989, Specifications for Structural Steel Buildings
  • Minimum Design Loads for Buildings & Other Structures ASCE 7-95

American Society of Civil Engineers

 

List of the Codes that I will be using during the Research and inquiry of Analysis:

 

·        IBC 2000

·        International Code Council

Ø      Section 1606 Dead Loads

Ø      Section 1607 Live Loads

Ø      Section 1608 Snow Loads

Ø      Section 1609 Wind Loads

·        PCI Design Handbook of the Precast Concrete Institute, latest editon

·        ASCE 7-98 Minimum Design Loads for Buildings and Other Structures

Ø      Section 2.0 Combination of Loads

Ø      Section 3.0 Dead Loads

Ø      Section 4.0 Live Loads

Ø      Section 4.7 Impact Loads

Ø      Section 5.0 Soil and Hydrostatic Pressure and Flood Loads

Ø      Section 5.2 Uplift on Floors and Foundations

Ø      Section 6.0 Wind Loads

Ø      Section 7.0 Snow Loads

Ø      Section 9.0 Earthquake Loads

·        AISC 1989, Specifications for Structural Steel Buildings

·        ACI 318 Building Code Requirements for Concrete Structures

           American Concrete Institute

·        ASD, 9th Edition, 1989 Manual of Steel Construction, vol. I & II

·        LRFD, 2nd Edition, 1998 Manual of Steel Construction, vol. I & II

·        Design Manual – Floor Decks and Roof Decks, Steel Deck Institute

 

 

 

 

 

 

 

 

James D. Baker                                                                                                                      

Structural Discipline                                                                                                  

ALCOA Corporate Center                                                                                         

Pittsburgh Pa.

Building Statistics                                        

 

 

 

 

Identification of Loads:

·        Self Weight:

Structural Steel – 12.0 psf

Concrete (regular wt.) – 43.75 psf

·        Dead Loads:

Raised Floor - 10 psf

Mechanical – 5 psf

Electrical – 5 psf

Finishes – 10 psf

Telecommunications – 2.5 psf

·        Live Loads :

Lobbies & 1st Floor Corridor – 100psf

Corridors Above 1st Floor + Partition Walls – 80+20 = 100psf

·        Roof Loads:

4 ½” Concrete Composite Slab – 34 psf

Miscellaneous – 15 psf  (Mechanical & Window Washing)

Ø      Ground Snow Loads:

Pf = 0.7(Ce)(Ct)(I)(Pg)

Pf = 0.7(1.0)(1.1)(0.8)(25 psf)

Pf = 15.4 psf.   -therefore a  snow load of 30 psf. was taken.

Ø      Weight of Roof:  Total = 49 psf

Composite Metal Deck = 34 psf

Miscellaneous = 15psf

Ø      Weight of Floors: Total = 188.25 psf

Self = 55.75 psf

Dead = 32.5 psf

Live = 100 psf

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

James D. Baker                                                                                                                      

Structural Discipline                                                                                                  

ALCOA Corporate Center                                                                                         

Pittsburgh Pa.

Building Statistics                                        

 

 

 

Wind Load Calculations:

 

            Wind loads were calculated using a spread sheet on Microsoft Excel.  Some considerations taken for these calculations are the shape of the building and the various changing angles in which the wind would strike the surfaces of the curving facade.  In the given architectural plans, a layout of the primary leeward and windward pressures were laid out in sections of the building.  These sections were divided up into small subdivisions and layers due to their height and closeness to the edges of the building as well as the angles of incidence of which it is facing the wind.  Due to this buildings shape and configuration, I took the building as being a rectangle shape, and will compare my results to those of the wind forces placed on the building in the given architectural plans.

In the buildings plans, it is noted that all of the connections in the lateral wind force resisting systems are designed as slip critical.

 

James D. Baker                                                                                                                      

Structural Discipline                                                                                                  

ALCOA Corporate Center                                                                                         

Pittsburgh Pa.

Building Statistics                                        

 

 

 

These wind loads come out to be quite off in comparison to the given architectural plans estimates.  Notable is the leeward pressures, as they were not given as being constants.  The following pressures and suctions were given in the plans:

Ø      Typical Wall Zone        +26 psf          -26 psf

Ø      Semi-corner                  +27 psf          -41 psf

Ø      Corner Area                  +31 psf          -63 psf

Note that if the Basic Wind Speed is given at 150 mph, such as along the coast lines, that the wind pressures calculate to being fairly close to the architectural plans’ estimates.  I have requested more information concerning this, and will report it to you when I have been notified of what considerations were taken into account for those estimates.  Given below is the spreadsheet information with a 150 mph basic wind speed.  It is noted that this building is in the Three Rivers valley along the Allegheny River, and there tends to be higher winds coming up the valley. Vertical Profile Sketch of Pressures:---North South Direction---

---East West Direction---

Seismic Load Calculations: 

            Seismic load calculations were done using a Microsoft Excel spreadsheet simply for comparison since the greater Pittsburgh area is not taken as seismic.

 

James D. Baker                                                                                                                      

Structural Discipline                                                                                                  

ALCOA Corporate Center                                                                                         

Pittsburgh Pa.

Building Statistics                                        

 

 

 

 

 

Summation of forces on the floors is yielded in this spreadsheet as well as the story shears accumulated down through the story heights.  In comparison to the wind forces that effect the building, the seismic forces are about 1/3rd that of the forces that the wind will place on the structure.  A calculation of loads is given above with the note that seismic forces are that of self loads and dead loads.  The overturning moments for the wind calculations in the E-W direction are 55,429 ft-kips, as the overturning moments for the seismic calculations in the E-W direction are 275 ft-kips.  The overturning moments for the wind calculations in the N-S direction are 117,400 ft-kips, as the overturning moments for the seismic calculations in the N-S direction are 412 ft-kips.  Base shear for wind calculations is 1754 & 826 (kips) for N/S & E/W respectively, as base shear for seismic calculations is 511 (kips) for both N/S & E/W directions.

 

Note on Seismic Calculations:

Since there is no seismic lateral force resisting system present in the building, the lateral force resisting system is designed to account for wind forces alone.  All bolted connections in the lateral force resisting system are to be designed as limited slip connections with slotted holes on the bolt connections.

 

Other Special Loadings as Appropriate at this Stage:

 

            Considerations will be taken when diagnosing the foundations system in detail for the uplift forces that may occur during flood conditions along side the Allegheny River.  The only information that I have for this topic currently is that some of the driven friction piles in the subsurface were designed to resist uplift conditions.  The foundation of the ALCOA Corporate Center sits on some 2400 driven concrete friction piles that extend approximately 40 feet into the soil, with a minimum depth of 20 feet into the medium dense course grained alluvium or to bedrock, whichever occurs first as given in the foundations general notes. The given capacity of the friction piles is rated as 50 tons each.(100kips).  Snow drift loads will be more deeply investigated in the Structural Report #2 as for the snow loads were taken as a flat roof in this portion of the analysis.

 

Description of Framing System:

 

Framing systems:

ü      Structural system

ü      Concrete parking levels

ü      Moment connections

ü      Splicing between columns

 

 

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This page was last updated on Thursday, August 22, 2002.

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