EGNEGN--5439 The Design of Tall Buildings5439 The Design of Tall BuildingsLecture 01Lecture 01

Why Tall Buildings?Why Tall Buildings?

L. A. Prieto-Portar 2008

Humans have always admired tall structures since ancient times because of their social status: they are visible to all. Their builders

were held in the highest respect of their societies, and their structures are the subjects of legends:

The early tall buildings:

The Seven Wonders of the Ancient World

The Temple of Artemis at Ephesus

The Lighthouse of Alexandria

The Mausoleum at Halycarnasus

The Hanging Gardens of Babylon

The Colossus of Rhodes

The Statue of Zeus at Olympia

The Great Pyramids of Egypt

So, in todays world, what is a Tall Building?

Tallness is a relative term.

However, for us structural engineers, a tall building is one that is primarily affected by lateral forces from wind and earthquakes.

Modern tall buildings were born in 1885 with the first all metal structure of the Home Insurance Building in Chicago.

The demand for tall buildings has almost exclusively been for commercial and residential use. Tall commercial buildings have served as prestige symbols for corporations (the Woolworth and Chrysler buildings, Trump Towers, etc.).

In Hong Kong and Rio de Janeiro housing is usually 40-story towers spaced only a few meters of each other.

The increasing growth of the tourist industry demands taller hotels in city centers where land is scarce and expensive.

The famous architect Louis Sullivan coined the phrase that in buildings, form follows function.

Perhaps a better phrase that applies to skyscrapers came from Case Gilbert in 1900 (he was the designer of the Woolworth Tower in 1913, the Worlds first skyscraper). Gilbert said: A skyscraper is a machine that makes the land pay.

Gilberts assertion is evident in the figure on the left, taken from a real estate publication of 1903. It shows the prices of land values in Lower Manhattan that same year. Practically every firm in New York wanted to be located within a few hundred feet within the tight canyons of Broadway and Wall Street.

Notice the contrast of the prices within a few hundred feet (from $400/sf to only $10/sf).

The Timeline of Structural Growth Ancient Rome

Seven-storey wooden tenement buildings of timber and masonry construction. After the great fire of Nero, new brick and concrete materials were used in the form of

arch and barrel vault structures. Masonry and timber the two leading materials for the next eighteen centuries.

Chicago 1891 16-story Monadnock Building reaches the limits of masonry with 2 m thick walls. 1885 11-story Home Insurance Building, the first high-rise totally supported by a metal

frame (wrought iron). 1889 9-story Rand-McNally Building, first all steel frame high-rise. 1891 20-story Masonic Temple, diagonal bracings introduced in the faade frames to form

vertical trusses.

New York 1913 60-story Woolworth Building (considered the worlds first skyscraper). 1931 102-story Empire State Building (1,250 ft tall).

The golden age of American skyscraper construction ended with the depression of the 1930s. It was not until several years after WW II that skyscraper construction recommenced. Instead of increases in height, modern developments brought new structural systems,

improved material qualities, and better design and construction techniques. It was not until 1970 that the Empire State Building was eclipsed by the 110-story WTC

North Tower (1,353 ft), and then in 1974 by the Sears Tower (1,450 ft).

The Timeline for the Growth of Tall BuildingsGrowth in height between 1850 and 2005

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1850 1870 1890 1910 1930 1950 1970 1990 2010Ye ar

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Harper & Brothers (5)

Home Insurance Building (10)

Masonic Temple (21)

Woolworth Building(60)

Empire State Building (102)

World Trade Center North (110)

Sears Tower (110)

JP Morgan Chase Tower (75)

US Bank Tower (73)

Petronas Tower (88)

Jin Mao Tower (88)

Two Finance Towers (88)Otis elevator

First wrought iron rolled sections

Cast iron era New York

First steel rolled section

Chicago School

New York era

Electric elevator

Growth in height between 1850 and 2005

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1850 1870 1890 1910 1930 1950 1970 1990 2010Years

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Harper & BrothersHome Insurance Building (138)

Masonic Temple (302)

Woolworth Building (761)

Empire State Building (1252)World Trade Center North (1353)

Sears Tower (1450)

JP Morgan Chase Tower (1002)

US Bank Tower (1018)

Petronas Tower (1483)

Jin Mao Tower (1380)

Two Finance Towers (1362)

Taipei Tower (1667)

Otis elevator

First wrought iron rolled sections

Cast iron era New York

First steel rolled section

Chicago School

New York era

Electric elevator

Growth in height of tall buildings (from 1885 to present).

A projection of all the building planned and under design versus existing tallest.

World Population Growth

The Design Process

Commence with a Preliminary calculations to Propose preliminary x-sections Propose prelim. beams and slabsSTART functional design establish member sizes of all vertical m em bers based on M and V via the 2-cycle

(eg, column layout) (typically gravity only x 1.3) (columns and shear walls) moment distribution or using mid-and end-span values

Review and coordinate Prepare final constructionall documents with the documentation: Check the drift index = /H 0.0015Architect, and HVAC, - CAD drawing set

plumbing and electrical - Specificationsspecialty engineers - Engineer's cost estimate

yes

Finalize documents Check creep andfor permitting and shrinkage effects noclarify comments

Perform wind tunnel tests Check forces in major structuralTry to get paid and refine design members with rapid approximation

analysis

FINISH Perform a dynam ic analys isfor wind and seism ic loads

yes

Add 2nd-order gravity loads yeson lateral deflections (P-) no

noPrepare the final accurate Finalize the satisfactory

design with a refined model preliminary design

The (Iterative) Design Process

Is the driftindex

excessive?

Are Forcesexcessive?

Are there changes to the

plans by the Architect or the

Ow ner?

START Conceptual design and evaluation

(eg. Column layout)

Preliminary calculations to establish member sizes

(typically gravity only x 1.3)

Propose preliminary x-sections of all vertical members (columns

and shear wall)

Proposed preliminary beams and slabs based

on M and V via the 2-cycle moment distribution or

using mid and end-span values

Check the drift index = ?/H = 0.0015

Is the drift index

excessive

Check forces in major structural members with

rapid approximation analysis

yes

no

Are Forces excessive

yes

no

Finalize the satisfactory preliminary design

Are there changes to the

plans by the Architect or the

Owner?

yesno

Prepare the final accurate design with a

refined model

Add 2nd-order gravity loads on lateral deflections (P-?)

Perform a dynamic analysis for wind

seismic loads

Perform wind tunnel tests and refine design

Prepare final construction documentation: -CAD drawing set -Specifications -Engineers cost estimate

Review and coordinate all

documents with the Architect, HVAC,

plumbing and electrical specialty

engineers

Finalize documents for permitting and clarify

comments

Remind the Client to send the check for

payment

FINISH

Site visitGet

geotechnical report, Site survey and As-Builts

Alternate design flow chart.

How should we approach new structural methods?

The evolution of new structural systems

Structural systems for residential and office buildings have evolved to reflect their differing functional requirements.

Office Tall Buildings: The need to satisfy differing requirements of tenants leads to the provision of large

column-free open areas to allow flexibility in constantly changing office layouts.

Improved levels of services frequently necessitate an entire floor devoted to mechanical plant. However, this lost space can often be compensated by accommodating deep girders or trusses connecting the exterior and interior structural systems.

Earlier heavy internal partitions and masonry cladding, with their contributions to the reserve of stiffness and strength, have given way to light removable partitions and cubicles and glass curtain walls, forcing the basic structure alone to provide the required strength and stiffness against both vertical and lateral loads.

Large entrances and open lobby areas at ground level, multi-storey atriums, and high-level restaurants and viewing galleries may require more sophisticated elevator systems and multiple sky lobbies.

Office buildings need large open spaces for flexible rental arrangements.

Chevron or K-braces can used to stiffen the structure at mechanical levels.

The Espiritu Sanctus building at Brickell Avenue in downtown Miami.

Residential Tall Buildings:

The basic function is the provision of self-contained individual dwelling units, separated by substantial partitions that provide adequate fire and acoustical insulation.

Because the partitions are repeated from story to story, modern designs have utilised them in a structural capacity.

This has led to the shear wall, cross wall, and infilled-frame methods of construction.

Residential buildings are heavier and many partitions separating each apartment.

A 17-story condominium in Naples, Florida.

The principal load resisting elements.

The two primary types of vertical load resisting elements of tall buildings are columns and walls.

Walls may act either independently as shear walls, or in assemblies as shear wall cores, around stairwells and elevators.

Columns will be provided in otherwise unsupported regions to transmit gravity loads, and in some types of structures, lateral loads (wind and seismic).

Since the gravity loading on different floors tends to be similar, the weight of the floor system per unit floor area is constant, regardless of building height.

Since the load on a column is cumulative of the floors above it, the weight of column per unit area increases linearly with the building height.

The bending moments caused by lateral loads increase with at least the square of building height, becoming more important as building height increases.

Typical steel quantity requirements versus the buildings height

Height of Building

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Floor Framing Steel

Column Steel

Wind Steel

ReferencesMonograph on Planning and Design of Tall Buildings, Volumes CB, CL, PC, SB and SC,

ASCE, 1980.

1. www.greatbuildings.com

2. www.engr.psu.edu/ae/wtctragedy.html

3. www.kaleidagraph.com/teach.htm

Sweet Williams