Reviewing the standards , issues & requirements for

Tall buildings

Sanjay R SrivastavaArchitect Urban Planner

• Tuesday Oct 16th 1956……. Frank Lloyd Wright unveiled a plan for a mile high building.

• His dream was restricted by the strength of materials.

• The "eighth wonder of the world" was to be erected of steel and glass, with floors extending outward from a central core like branches from a tree trunk.

• Wright’s design drew both jeers and cheers.

but Wright insisted the structure was "practical and expedient.”

62 yrs down the line we are yet to complete this journey

Dreams

• However, Wright also acknowledged that construction materials available at the time were inadequate for his vision.

• “But it’s certainly possible now,” says Joseph Colaco, president of CBM Engineers in Houston and present here in person amongst us.

• So what do Dr Colaco & his contemporaries like Dr Andy Davids have that FLW didn’t?

• Well, to begin with, much better materials. The strongest concrete available in the 1950’s could withstand compression on the order of 21 megapascals, placing the ceiling on all-concrete construction at roughly 20 stories.

• Better Seismic information, design methods substantiated by research & learning's from practice and computing powers.

Since 1950’s Design methods for tall buildings have been developed to cope with earthquakes in places such as California and ……

Earth Quake & Wind Tall buildings

…..along with the force of typhoons in cities such as Huston / Hong Kong.

Effects of lateral loading due to wind on the building frame are dramatically magnified for towers over about 60 storey, as their slenderness increases.

For very tall buildings like the FLW’s mile high tower…. the main issue for stability, is technology that can resist wind by frames designed for loads & earthquakes.

Wind & Tall buildings

Let’s quickly try to touch base with these issues in the Indian context

Indian codes divide the sub

continent into 4 seismic zones.

Numbered 2,3,4,5

The darkest color shows the place

of maximum probability &

highest intensity and is zone 5.It is based on

extrapolation of past events

EQ Zoning

4.8

4.0

3.2

2.4

1.6

0.8

0.4

0.2

0.0

Peak Ground acceleration

in m/sec 2

This map shows the peak ground acceleration that can be expected basis past history of Earth Quake events and other extrapolative tools

SHAKE MAP FOR INDIA

• The Indian codes relevant to these concern areas of design are:

• Concrete: IS 456-2000 reaffirmed 2005 Plain and Reinforced Concrete –The method used in this code is ”Limit state of Design”.

• Steel IS: 800:2006 for normal and high strength steels,

• Light Gauge steel : IS :801 cold formed light gauge steel

• Steel Tubes : IS 806 for steel tubes .

Codes for earthquake and wind issues in Tall Buildings

Types of cement

• Types of cement included in the revised IS : 456-2000 & available in the market are as follows:

•Ordinary Portland Cement 33, 43, 53 grade (OPC), 53-S(Sleeper Cement)

•Portland Pozzolana Cement (PPC), both Fly Ash & Calcined Clay based

• Rapid Hardening Portland Cement• Portland Slag Cement (PSC) • Low Heat Portland Cement • Sulphate Resisting Portland Cement (SRC) • Hydrophobic Cement

• Grades of concrete: included in the code from M10 to M80 are readily available with reputed manufacturers

But what is really worth mentioning here is :Ultra-High Performance Concrete or UHPC:

Cement & Concrete

• The ductile behavior of this material is a first for concrete, with the capacity to deform and support flexural and tensile loads, even after initial cracking. The use of this material for construction is simplified by the elimination of reinforcing steel and the ability of the material to be virtually self placing or dry cast.

• Ultra-High Performance Concrete (UHPC), also known as reactive powder concrete (RPC), is a high-strength, ductile material formulated by combining portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers. The material provides compressive strengths up to 200 MPa (29000 psi) and flexural strengths up to 50 MPa (7000 psi).

• The materials are usually supplied in a three-component premix: powders (Portland cement, silica fume, quartz flour, and fine silica sand) pre-blended in bulk-bags; super plasticizers; and organic fibers.

• Superior durability characteristics are due to a combination of fine powders selected for their grain size (maximum 600 micrometer) and chemical reactivity. The net effect is a maximum compactness and a small, disconnected pore structure.

• It is yet to find a mention in IS : 456. Its manufacturing , mixing handling is yet to be standardized. In short industry has moved ahead and is pulling away.

• Some of today’s tall concrete structures, such as the 88-story (420-meter) Jin Mao Tower by Skidmore Owings & Merrill in Shanghai, have been built (1999) with this type of concrete that has a compression strength greater than 130 MPa.

Fazlur R Khan’s systematic approach to structural frame efficiency is still relevant to towers of Mumbai scale, where the buildings are predominantly upto 60 floors and even now striving to touch the 100 mark The efficiency of the building frame has the greatest

influence on the embodied energy of a tall building.He and his colleagues created a continuum of 4 typologies

depending on heights and structural systems for most efficient use of materials

In the US, early development of steel led to its use as the favored material for high-rise structures. In broad terms, buildings could be divided into categories based on type of structural system selected for the most efficient use of material.

Steel & Tall buildings

Type 1 : Semi Rigid & Rigid Frame: In broad terms, steel-framed buildings with a rigid frame can be economical for medium rise buildings up to 20 storey;

IBM Plaza Kansas

Type 2 : Frame with Shear Truss & Frame with shear band & out rigger truss :a vertical steel shear truss at the central core of the building can be economical for buildings up to 40 storey;

Frame with Shear

Truss

Frame with Shear band and out rigger

truss

Type 3 : End Channel framed tube with shear truss or framed truss:A combination of central vertical shear trusses with horizontal outrigger trusses is most suited for up to 60 storey

End Channel & middle framed

truss

End Channel framed tube with

interior shear trusses

Type 4 : Rigid framed tubes, Bundled tubes , Braced tubes:

For even taller buildings, it becomes essential to transfer all gravity loads to the exterior frame to avoid overturning effects. Rigid framed tubes, bundled tube & braced tube structures have been developed to reach up to & over 100 storey in buildings such as the Hancock and Sears towers in Chicago.

Sears tower in Chicago is an example of nine tubes framed to make a bundled tube with belt and outrigger trusses. The bundled tubes share common interior side frames

Hancock Tower is tapered tube truss system. It uses the principles of mega structures. The cellular structure has increased overall dimensions by using a hollow open center framed tube at the periphery. It is an example of transfer all gravity loads to the exterior frame to avoid overturning effects.

< ex. of Braced tubes & Rigid framed tubes

The relevant Indian Standards for Steel buildings and structural steel are:

IS: 800:2006 for normal and high strength steels,

IS :801 cold formed light gauge steel & IS 806 for steel tubes .

Site welding is not recommended and bolting is preferred.

Steel, steel fiber and composites are is in many ways improving the quality of concrete “Additives like whisker-thin steel fibers are enhancing concrete’s strength and rigidity,” says John Fernandez, a professor at MIT’s interdisciplinary building-technology program. “We’re also seeing research into smart fibers and carbon nano tubes that, when added to concrete, will increase compression strength beyond 200 MPa.” Fernandez’s work on smart fibers is also contributing to advances in so-called high-performance concrete, which is strong but optimized for other characteristics such as fire and blast resistance, vibration damping, and durability

In the previous slides we have seen measures for stability for structural loads & due to earth quake forces.Another force impacting Stability & Design is wind. Effects of lateral loading on the building frame are dramatically magnified for towers over about 60 storey, as their slenderness increases.

Wind & Tall buildings

WORLD MAP of Tropical Storms

The relevant IS codes for design of wind loads is IS: 875 part 3

The code provides with mathematical modeling methods starting by stating a) Basic winds speed for every town and a contour map plotting the entire

country into 6 wind speed zones these are 33, 39, 44, 47, 50, 55 m/sec.b) Then it classifies by building type and height ..For tall buildings the factor k1 of

1.08 will be applicable.c) And adjusts the model wind speed for Terrain quality ……. due to

inconsequential ht of building w.r.t to the tall structure the factor k2 will always turn out to be 1.4. IF k3 stays at 1.0 then

d) The peak design wind speeds at 500 m from ground surface in India will vary between 180 to 300 km per hour.

e) The code goes further to quantify through formulae wind load on Individual members, wall and inclined roofs etc.

f) It points out that rough sea storms normally dissipate inland within 60 km of shore line

g) Here is a compiled record of many storms for the sub continent.. Many storms are seen ripping right into the sub continent sometimes more than 200 km.

This map shows the tracks of all Tropical cyclones which formed in the Indian subcontinent from 1985 to 2005. The points show the locations of the storms at six-hourly intervals and use the color scheme from the Saffir-Simpson Hurricane Scale.

Saffir-Simpson Hurricane ScaleTD TS 1 2 3 4 5

TD = Tropical disturbance TS= Tropical Storm

1998

1996

1999

1997

The North Indian cyclone season has no official bounds, but cyclones tend to form between April and December, with peaks in May and November. This basin is divided into two different seas by India; the Arabian Sea to the west, abbreviated ARB , and the Bay of Bengal to the east, abbreviated BOB by the IMD. On an average, about 4 to 6 storms form in this basin every season.

CYCLONE SEASON SUMMARY

Year 2010 CYCLONE SEASON SUMMARY map for the North Indian Ocean

First date the North Indian Ocean storm formed

May 17, 2010

Last storm dissipated

December 8, 2010

Strongest storm Giri – 950 hPa (mbar), 195 km/h (120 mph) (3-minute sustained)

Depressions 8

Deep depressions 6

Cyclonic storms 5

Severe cyclonic storms

4

Very severe cyclonic storms

2

Super cyclonic storms

0

Total fatalities 402

Total damage At least $2.985 billion (2010 USD)

Year 2007 GONU CYCLONE

First date the North Indian Ocean storm formed

June 1, 2007

Last storm dissipated

June 7, 2007

Strongest storm Giri – 920 hPa (mbar), 270 km/h (165 mph) (1-minute sustained)

Depressions 8

Deep depressions 6

Cyclonic storms 5

Severe cyclonic storms

4

Very severe cyclonic storms

2

Super cyclonic storms

0

78 and 37 missing 402

Total damage At least $4.4billion (2007 USD)

GONU 270 km/h (165 mph))

• Tall buildings, today , are an inevitable building form. They are a part of the contemporary landscape. New design ideas are becoming common currency among progressive architects and developers.

• “Bioclimatic skyscrapers” and well-designed tall buildings can be energy efficient and closely relate to their site.

• New buildings are increasingly user-friendly, offering a comfortable occupant-controlled environment all year. The creation of internal green “sky gardens” within buildings contributes to the natural environment.

ENERGY

In this context, Europe’s tallest building, the Commerzbank building in Frankfurt, stands out. To reduce energy consumption, all offices have natural ventilation and opening windows.It succeeds to an extent in creating a pleasant and energy efficient working environment.Generous sky gardens spiral up the tower, and act as a visual and social focus for clusters of offices.

A mile-high skyscraper should be more energy efficient than existing structures, which together already consume about one-third of the world’s generating capacity. ”With an integrated approach to the building envelope and the mechanical and electrical systems, we can significantly reduce energy consumption with little difference in construction costs,” says Spiro Pollalis, a professor at Harvard University’s Graduate School of Design. He envisions that photovoltaic panels along the length of the immense towers, along with strategically placed windmills and double-layer facades that act as giant heat sinks, will provide enough juice to power elevators and lights as well as heating, ventilation, and air conditioning systems.”The ultimate aim is creating buildings with zero net energy use,” says Mir M. Ali, a professor of architecture at the University of Illinois at Urbana-Champaign and member of the international Council on Tall Buildings and Urban Habitat. Several skyscrapers under construction, including the Pearl River Tower in Guangzhou, China, are employing new technologies to avoid using any energy from the grid.

“Structural engineering solutions must be integrated with the architectural and sustainable engineering designs so that they are inseparable,” said Bill Baker, SOM structural engineering partner. “It is the collaboration between our structural engineering, architecture and sustainable engineering practices that allow a building such as Pearl River Tower to become reality.”

Embodied EnergyBuildings not only use energy, it takes energy to make them. This is “embodied” energy, which is all the energy required to extract, manufacture and transport a building’s materials as well as that required to assemble and “finish” it. As buildings become increasingly energy-efficient, so the energy required to create them becomes proportionately more significant in relation to that required to run them. This is particularly true because some modern materials, such as aluminum, consume vast amounts of energy in their manufacture. The most common building material with least embodied energy is wood. Timber is regarded as the greenest building material. However, deforestation of the planet is also one of the gravest environmental issues and only wood used from sustainably-managed forests is truly green.

Brick is the material with the next lowest amount of embodied energy, followedby concrete, plastic, glass, steel and aluminum. A building with a high proportion of aluminum components can hardly be green when considered from the perspective of total lifecycle costing, no matter how energy-efficient it may be.

Taipei 101 Combination of previous systems are used to design new systems. Lateral resistance to drift and acceleration are overriding concerns. This makes damping an important issue.At acceleration beyond 25 milli-g human discomfort begins.Tuned mass damper help control sway

Strength and flexibility for TAIPEI 101 is achieved through the use of high-performance steel construction. Thirty-six columns support Taipei 101, including eight "mega-columns" packed with 10,000 psi (69 MPa) concrete. Every eight floors, outrigger trusses connect the columns in the building's core to those on the exterior.The foundation is reinforced by 380 piles driven 80 m (262 ft) into the ground, extending as far as 30 m (98 ft) into the bedrock. Each pile is 1.5 m (5 ft) in diameter and can bear a load of 1,000–1,320 ton .Facade system is therefore able to withstand up to 95mm of seismic lateral displacements without damage.

A 660 ton, 18 ft dia. steel pendulum that serves as a tuned mass damper, (US$4 million )

is suspended from the 92nd to the 87th floor, it sways to offset movements in the building caused by strong gusts. It can reduce up to 40% of the tower's movements . Two tuned mass dampers, each weighing 6 ton sit at the tip of the spire.

• Efficiencies in the design and construction of Tall buildings can make a significant difference both economically and environmentally.

• Engineers strive to find savings in materials through efficient design, making best use of concrete and steel in floors and structural frames. The environmental impact of their decisions is not always clearly understood.

• New methods and software packages are being developed to clarify the burdens on land, air and water resources.

• Integrated design and the use of structural materials for optimum performance in controlling the internal environment of buildings can provide added benefits at no extra cost.

• At the same time selection of façade materials, governed largely by architects, can greatly influence the thermal performance of buildings.

• As methodologies for the life cycle assessment of cladding materials develop, awareness is growing of their environmental impact among designers.

• The choice of materials for architectural finishes should now be made with improved understanding of their relative merits in sustainable terms.

SUMMING UP

Thank you for your patience

Acknowledgements: Dr Nitin Dindorkar Professor Maulana Azad National Institute of Technology Bhopal for his guidance and finding the time to adviseDr P Jayachandra : Tall buildings … Preliminary Design & OptimizationUSGS for its web based images and documents explaining conceptsWikipedia ,You Tube, Google Search for various photographs and web based information placed in the public domain made available through their servers All architects and developers whose projects have been referenced here as there were so discharged in the public domain for reference.