citicorp center building structural analysis

7/23/2019 CitiCorp Center Building Structural Analysis

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Jonathan Hopkins & Shawn Johnson

IDEA 3: Structural Precedent Analysis

RWU SAAHP

Arch 435 Fall 2011

Prof. Mete Turan

TA Katie Kanakos

A Case Study of

CitiGroup Center

New York, New York

The Open Ground Plane

In An Urbanizing World


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CitiGroup Center

601 Lexington Ave, MidTown, New York City

Architect: Hugh Stubbins Jr.

Engineer: William J. Messurier

Design Feature: Steel Frame Skyscraper without

Columns at Corners

IDEA 3 Precedent Analysis

-Theoretical Framework-

-Precedent Information-

-Structural Analysis-

-Design Solution-

-Conclusions-


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Theoretical Framework

- The number of cities with population above one million has already risen from six to 19 in the

past 40 years, and will continue to rise1

- By 2030 [the number of people living in towns and cities] will swell to almost 5 billion2

___________________________________________________________________________________________________________1Yeang, Ken. The Tall Building Typology and Cities Reinventing the Skyscraper (Academy Press, 2002) pgs. 33-552UNFPA. Urbanization: A Majority in Cities Linking Population, Poverty and Development (UNDESA, 2005)

Urbanized Population (2006)


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Theoretical Framework

- The presence of trees and grass has also been associated with reduced crime rates, possibly

because residents of a well landscaped building spend more time outside, allowing them to get

to know one another and develop a sense of community.3

- Humans living in landscapes that lack trees or other natural features undergo patterns of

social, psychological and physical breakdown4

___________________________________________________________________________________________________________3Davis, Dave. Developing a Sense of Community Designs and Codes that Reduce Crime around Mulitfamily

Housing (Local Government Commission) p. 3

4Staff. Science Suggests Access To Nature Is Essential To Human Health Science Daily (February 17, 2009)


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CitiGroup Center, New York


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Precedent Information5

- CitiGroup Office Building Conceptualized in early 1970s

- The site, across from CitiGroup HeadQuarters at 54th Street and Lexington Avenue, was

occupied by St. Peters Church

- A deal was struck to build the office tower while retaining the churchs location

- This circumstance prevented conventional structuring of the office tower with corner columns

- Stubbins and LeMessurier Proposed a 59-story building supported by enormous chevrons, each

carrying and distributing the load of 6-8 stories to a central reinforced concrete column

- The building is lifted off the ground 9-story by centrally located columns

_______________________________________________________________________________________________________________________________________________________________________________________________________________________

5Morgenstern, Joe. The Fifty-Nine Story Crisis The New Yorker (May 29, 1995)


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Assemblies & Construction

- Designed with Welded Joints

- Structured for the 55-year Wind Storm

- Calculations done with Perpendicular Wind

Loads

- Construction began in 1974

- The building was constructed outward from

the core in 6-8 story sections

- The structure is a steel frame

- Floor Plates are structured with reinforced

concrete

- Corners cantilever 70 feet beyond columns

- Aluminum and glass exterior cladding

- 7th Tallest building in New York City at 915

feet with 59 floors


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Crisis of 1978

- Construction Completed in 1977

- Contractors switched out welded joints with

bolted joints

- The Building deals with 45 degree angle wind

loads

- The Hurricane of 78 was a 100-year wind

storm

- Recalculations of loads revealed severe

structural deficiencies

- 2-inch steel plates were welded to each joint

on the building to counteract the shearing

forces on the bolted connections

- There were serious uncertainties about the

structural integrity of the building during the

storm


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Structural AnalysisGravity Load Analysis

- 1000 Kip vertical loads acting downward

on each 6-8 story section

- In the frames the [gravity] load is

transferred from the minor columns to the

mast column by diagonals at eight-story

intervals6

- The chevrons concentrate the loads to the

center, thus freeing up the corners, which

cantilever beyond the central columns 72

feet

_________________________________________________6Smith, Bryan Stafford and Alex Coull. Use of

Large Scale Bracing Tall Building Structures:

Analysis and Design (John Wiley & Sons, Inc. 1991)

p. 127 Compression Tension Moment


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Structural AnalysisWind Load Analysis

- Wind Shear is collected by the core over

eight-story-height regions and transferred to

the braced outer frames at the base of each

tier

- At the base of the tower the entire shear is

transferred back to the core and hence to the

ground

- Wind moment is carried mainly by the mast

columns and legs in the faces normal to the

wind, and partly by the core7

__________________________________________________________________________________________________________

7Ibid.Deflection

dx = 6.591 in

20 kip Horizontal Load


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Structural AnalysisCombined Load Analysis

- Since the diagonals carry a significant part

of the gravity loading, the structure may be

classified as either a space truss or a braced

frame8

- CitiGroup Building is a relatively light-weight

frame that is effected by lateral wind loads,

which is compensated for with a mass damper

(the first skyscraper to use one)

- The Brace frame is obstructive to facade

elements like windows

____________________________________________________________________________________________________________

8Ibid. MultiFrame Model

Shear

Moment

Axial

Tuned Mass Damper


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Alternative proposalSuspended, Reinforced Core Structure

Characteristics:

- Large, Reinforced Central Core

- Horizontal Cantilevers at Roof Level

- Floor Slabs Suspended from Hangers

- Open Concourse Level

- The Hangers, because they are in tension

and consequently can be of high strength

steel, have a minimum sized section...9

Advantages:

- More Open Ground Plane

- Shorter Cantilever

- Freed Facade

- Reduced Deflection 5.635 vs 6.591

__________________________________________________________________________________________________________

9Smith, Bryan Stafford and Alex Coull. Structural

Form Tall Building Structures: Analysis and Design

(John Wiley & Sons, Inc. 1991) p. 5010 Ibid.11 Schodek, Daniel L. and Martin Bechthold. Structural

Systems: Design for Lateral Loadings Structures

(Pearson Education, Inc. 2008) p. 546Model Moment

Suspended Frame10

Suspended Frame11

Shear Diagram


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Conclusions

CitiGroup Building, New York

- Inventive Solution to Existing Condition on a

Site

- Innovative Implementation of New Technology

- Inadequate Lateral Load Calculations that did

not account for 45 degree angle winds

- Poor Construction Administration Oversight

- Poorly Secured Joints

- Braced Frame Restricts the Facade

Alternative Suspended Frame Solution

- Frees up the Facade

- Opens up the Ground Plane

- Reduced Deflection


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Works Cited

Davis, Dave. Designs and Codes that Reduce Crime around Mulitfamily Housing (Local Government Commission)

Morgenstern, Joe. The New Yorker (May 29, 1995)

Schodek, Daniel L. and Martin Bechthold. Structures (Pearson Education, Inc. 2008)

Science Daily (February 17, 2009)

Smith, Bryan Stafford and Alex Coull. Tall Building Structures: Analysis and Design (John Wiley & Sons, Inc.

1991)

UNFPA. Linking Population, Poverty and Development (UNDESA, 2005)

Yeang, Ken. Reinventing the Skyscraper (Academy Press, 2002)

citicorp center building structural analysis

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