Council on Tall Buildings and Urban Habitat
 

The Brisbane 2016 Summer Seminar:
Design of Tall Buildings
November 24, 2016
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See Speaker 1 Video: Dr. Craig Gibbons
See Speaker 2 Video: Mr. Richard Cass
See Speaker 3 Video: Mr. Andrew Genter
See Speaker 4 Video: Dr. Leighton Cochran
See Speaker 5 Video: Prof. Jose L Torero
See Speaker 6 Video: Prof. Harry Poulos
BRISBANE – The CTBUH Australia Chapter’s Brisbane Committee held their Brisbane Summer Seminar on Thursday November 24 in conjunction with the American Society of Civil Engineers (ASCE). The topic of discussion was “Design of Tall Buildings,” with expert presentations on tall building trends, structures, sustainability, wind, façades, and foundations.
Stuart Rothwell, Vice President of ASCE’s Australian Section, opened the event and welcomed the first of six presenters, CTBUH Brisbane Representative Craig Gibbons, Arup Fellow. Gibbons introduced the event with an overview of some tall building trends. He first observed that buildings are increasingly more slender to maximize use of smaller Central Business District (CBD) sites. Secondly, he noted the rise in activity in “New Timber” and remarked on how innovative manufacturing techniques have opened up new possibilities for timber in tall buildings.
Craig Gibbons, Arup Fellow, discussed tall building trends.
Cross laminated timber is dimensionally stable and can be prefabricated using computer numerical control (CNC) machining. A key benefit is the quick construction time for timber buildings. Gibbons also discussed “happy hybrid” structures featuring a combination of timber and conventional construction

In conclusion, Gibbons noted the importance of green buildings and the ability of the industry to improve the aesthetics of cities through features such as green walls. By 2050, it is predicted that the human population will reach nine billion with 75 percent living in cities. Gibbons argued that this pressure of urbanization must inform our thinking in the design of tall buildings.

Next, Richard Cass, Technical Director, Bonacci Group Pty Ltd, continued the discussion on trends in tall buildings by addressing their increasing complexity and the impact on structural design, analysis, modeling, and real world verification. Cass presented an interesting overview of recent tall building projects in Brisbane including Soleil, Infinity Tower, Sky Tower, 300 George Street, and 111 Mary Street. The design of tall buildings is dictated by how the building moves; key design concerns are sway accelerations and differential shortening.

Cass noted that the sway accelerations are a service limit that drives the form of the structure more than the ultimate limit state because they must be within the new ISO building acceleration standards. The sway accelerations of a tall building can be managed through the use of shape, steps, variation to plan, vertical tapers, and notched corners. These measures can reduce the wind force on a tall building by up to 10–25 percent by disrupting the pattern of the wind vortices. Wind forces can also be managed through structural elements such as outriggers, mega-columns, and belt trusses. Taiwan’s Taipei 101 features a 720-ton steel pendulum that serves as a tuned mass damper.

Richard Cass, Technical Director, Bonacci Group Pty Ltd presents on the complexity of skyscraper design.

In tall buildings, the shortening of columns and the core is significant. Differential axial shortening can be managed using stress matching. Cass described the process of sequential construction, which utilizes the floor pre-set and a sequential construction correction to counteract creep and shrinkage to produce level construction on completion. Access to modal and creep shortening measurements has enabled refinement of analysis modelling to more accurately reflect the real world situation. Cass identified the importance of appropriate modelling and analysis for tall buildings with complex geometry features. The first key point was that Australian design codes are not design manuals; that is, a solution may comply with the codes but be invalid. The second key point was to use computer modelling as a tool that requires verification with alternative analyses and on-site measurements.

Rothwell next introduced the third speaker, Andrew Gentner, Director, Norman Disney & Young.

Gentner presented an overview of sustainability and the changes in the industry in the context of tall buildings. The building industry produces 40 percent of the world’s emissions. Gentner explained the current regulations and introduced the “Low Carbon, High Performance” ASBEC report that focusses on how buildings can make a major contribution to Australia’s emissions and productivity goals. He further discussed the multiple rating tools available to promote sustainability. The key considerations specific to tall buildings include lifecycle impacts of materials, energy related to façade performance, and emissions (i.e., storm water management).

Andrew Gentner, Director, Norman Disney & Young
discussed sustainability in tall buildings.

Gentner explained the important legislation, including the Commercial Building Disclosure Act 2010 (BEEC), requiring commercial spaces of over 2000 square meters to obtain the National Australian Built Environment Rating System (NABERS) Energy Star rating and Tenancy Lighting Assessment (TLA). The number of green buildings continues to double every three years, and new standards are being developed including the WELL Building Standard.

After a short afternoon tea break, Rothwell introduced Leighton Cochran, Director (Northern Australia and Asia), MEL Consultants. Cochran provided insight into the origin and meteorology of windstorms and the role of wind engineering. Wind-tunnel testing is useful for “unusual” structures where shielding or channeling exists, for terrain effects, for more accurate results, and to optimize design and save money. Firstly, Cochran described the considerations for cladding pressures: with the shift in tall building uses from primarily business to residential, operable windows must be considered in design and can result in unusual pressure points.
Secondly, Cochran considered the dynamic response of tall buildings and illustrated the resonant wind loads generated by the building’s shape and location, mitigating the sway accelerations caused by the cross-wind response. Cochran detailed the common building damping systems but highlighted that through effective design, the use of dampers can be minimized. For example, the sway accelerations for 432 Park Avenue in New York City were reduced from 65 to 33 milli-g through aerodynamics. Cochran further considered the impact of wind on pedestrians, which can be tested in a wind-tunnel.
Leighton Cochran, Director (Northern Australia and Asia), MEL Consultants, presents on wind engineering.
Dangerous winds can be concentrated at the pedestrian level of buildings that are significantly taller than their surroundings. Cochran warned of the dangers of insufficient design for wind loads on features in public areas such as sunshades.

The afternoon’s fifth speaker, Jose Torero, Professor and Head of Civil Engineering, The University of Queensland, provided a history of fire design for tall buildings, identifying the key trends since the 1960s. The aim of fire design for tall buildings is to contain the conflagration on one floor to avoid vertical spread through the external cladding.
However, with the rise in complex façades, the ability to contain fires has been reduced.
This is the result of a number of key changes to the building envelope including new construction methodologies and flammable insulation materials.

Torero explained that problems are caused by changing and subsequently testing single components rather than the complex building system as a whole. He proposed a solution that requires “bespoke” testing for each particular system and expressed the importance of a shift in design from one test for all materials to a bespoke test protocol for each system. Overall, Torero maintained that fire design is not a material problem but a system problem.
Jose Torero, Professor, The University of Queensland, provided a history of fire design for tall buildings.
Professor Harry Poulos, Senior Consultant, Coffey Services Australia was the day’s final speaker. Poulos identified some of the key challenges for the design of foundations of tall buildings including high vertical loads, low-rise podium areas, high lateral forces and moments from wind, the cyclical nature of loading, seismic forces on foundations, and dynamic response issues. The most common foundation option is piled rafts. Rafts are often required for building basements and, unavoidably, piles are necessary in many cases. The use of both rafts and piles for building foundations leads to an economically efficient system.
Poulos described the design process and argued that the design tools should be consistent with the stage of design. He identified the key parameters to assess in design through completed tall buildings such as Dubai’s Burj Khalifa and the Incheon 151 Tower in South Korea.

Poulos highlighted three sets of analyses: overall stability analysis, serviceability analysis, and analysis for structural design. Cooperation between geotechnical and structural designers is essential for a successful outcome.
Poulos further emphasized an important theme of the day: that advanced numerical models also require simpler methods for checking.
Harry Poulos, Senior Consultant, Coffey Services Australia, spoke about tall building foundations.
Rothwell concluded the event and delivered a vote of thanks to the presenters. The seminar was followed by networking and refreshments.
Registrants
John Cillekens ADG
Andy Bergh ADG
Derek Forbes Aecom
Gerrit Lebbink Arup
Benjamin Griffin Arup
Richard Vincent Arup
Jing Zhang Arup
Scott Rathie Arup
Andrea Lawnton Arup
Mahijs Van Heumen Arup
Glen Farinazzo BG Group
Anthony Carey BG Group
Harry Bohler Bohler Facades
Jana Thangarajarah Bonacci
Brett Taylor Bornhorst and Ward
Paul Kelly Bornhorst and Ward
Richard Cheng Bornhorst and Ward
Joshua Chua Bornhorst and Ward
Alastair Flynn BVN
Lucas Leo BVN
Terry Braddock BVN
Ricky Worn Calibre Consulting
Ramil Alzate Calibre Consulting
Catherine Morris Calibre Consulting
Hannah Herbst Calibre Consulting
Denis Vedelago Cardno
Darryl Feodoroff Cardno
Dave Hargreaves Cardno
Brett Wellauer Cozens Regan
Adam Gibbons Cozens Regan
Rod Prove Cozens Regan
Steve Thams Cozens Regan
Ben Redding Cozens Regan
Josh Searl Cozens Regan
Dorival Pedroso CPMECH
Denis J Brown Design Solutions (Qld)
Jeremy Skues Destination Brisbane
Ross McDonald Destination Brisbane
Daniel Davey Destination Brisbane
Jarrod Novosel Excio
William Sinclair Excio
Didier Lassus Excio
John Gaskin Gaskin Construction Services
Jamie Nichols Gaskin Construction Services
John Taylor Gaskin Construction Services
Hugo Salmon Gaskin Construction Services
Mohammad Shahin Gold Coast City
Sebastian Torralba Jacobs
Jeffrey Roulston Lemcke
Peter Czyszek Lemcke
Yves Du Bois MBMpl
David Sheikh Meinhardt Australia
Paul Doody Meinhardt Australia
Frank Letchford Mindustrial Design
Matt Irwin Multiplex
Brian O'Donovan Multiplex
Michael Makeham Multiplex
Joe O'Brien Northrop
Luke Worthington Northrop
Jeremy Sue Northrop
Neil Petherbridge Northrop
Mark Sturgess Northrop
Ali Habibi Northrop
Lachlan Sykes Northrop
Nick Idziak Northrop
Brian Wooldridge Opus
Michael Moran Philip Chun
Cath Patterson Philip Chun
Nino Muffatti Robert Bird
Mark Avery Robert Bird Group
Willy Huang Robert Bird Group
James Killen Robert Bird Group
Dhammikla Mahaarachchi Robert Bird Group
Russell Brothers self
Siva Sritharan SMEC
Saeed Mahini University of New England
Martin O'Connor Wood & Grieve
Justin Turner Wood & Grieve