A Project Management Approach: Design Challenges?(Part 1)
“Design is not just what it looks like and feels like. Design is how it works.” - Steve Jobs?
Design challenges with going super tall are numerous, and the tendency for developers to have such lofty motivations is a relatively recent phenomenon. Since the completion of the Petronas Towers in Kuala Lumpur in 1996, super tall building construction has dramatically increased in both pace and frequency. Whereas previous construction methods constrained buildings to specific structural and construct-ability limitations, innovations in concrete mix design and pumping methods have opened the door for taller and more ambitious buildings.1
Above : Number of 200-meter-plus buildings completed in each year from 1980 to 2020, with a 2021 projection.?
Source: CTBUH Year in Review : Tall Trends of 2020?
However, there are still a great many design challenges to consider, a selection of which has been summarized in this section. While not an exhaustive list by any means, this section will cover considerations related to (1) dividing the work between design architect / engineer and the architect / engineer of record, local building codes, and (2) fire and life safety. The next article will be covering the followings; (3) structure, (4) building movement, (5) vertical transportation, and (5) stack effect.?
(1) Design Adoption & Transfer??
The first design issue relates to the conventional approach to designing super tall, which is to commission a design architect and engineer(s) to design the building through either schematic design or design development and to then hand over the balance to a different (often local) architect and engineer(s) of record. In some cases, this is based on local laws requiring knowledge transfer between international consultants and local consultants. In other cases, this decision is taken to reduce design fees.?
Benefit to Super Tall Projects. While this approach is practical for the majority of buildings, one has to question the benefit this brings to super tall buildings, particularly in developing countries. Super tall buildings are complex and only a select few architects and engineers have the qualifications and requisite experience to design them. Spending hundreds of millions of dollars developing a super tall building while leaving any phase of design in the hands of a firm whose credentials could be challenged or experience lacking is questionable. Buying additional scope from expert consultants and having them involved throughout the entire design process, whether through reviews of completed design or design of specialty elements, is a sound investment which often pays dividends related to efficiency, construction cost, coordination, and quality.?
(2) Fire & Life Safety??
Fire and Life Safety becomes increasingly difficult as building height increases. Super tall buildings extend well above the height where modern fire-fighting equipment can reach and where occupants can reasonably be expected to walk down.?
Project Specific Planning. Therefore, project-specific codes have to be agreed during the design phase, as existing local codes may not properly address the issues presented by a super tall building. Even though additional codes can be applied, local authorities still have ultimate governance and firefighting control. Accordingly, a hybrid of local, international, and performance-based studies must be conducted and agreed with the authorities having jurisdiction. Some general characteristics of super tall buildings that impact fire and life safety include:?
These characteristics demand implementation of a “defend-in-place” strategy where evacuation during a fire is limited to moving occupants away from the fire and into safe refuge areas. Full and complete building evacuation is considered a last resort for practical reasons and because modern building fire suppression systems available today can typically contain a fire to a single floor.?
Active & Passing Suppression Systems. Occupants of the building are protected from the effects of a fire primarily by controlling fire growth and limiting fire and smoke spread to a single floor or fire-prevention zone. This is accomplished through design of both active systems (fire detection, suppression, and ventilation containment) and passive systems (specifying fire-resistance materials and building fire resistant structural features into the design). It can be said that a majority of firefighting takes place before any event occurs through good design and building management.?
Fire Fighting & Evacuation. In the event of a fire, the “fire floor” is placed under negative pressure via the smoke exhaust system. As shown in Figure 9 on the right, one or two floors above and below the fire floor are then put under positive pressure to prevent fire or smoke from escaping the fire floor and to provide a barrier between the fire floor and the non-fire floors, which allows the automated sprinkler system time to do its work. This containment and suppression of the fire allows the other building occupants to remain in their unaffected floors, from where they will evacuate only if their zone becomes endangered. Occupants on affected floors take the building’s fire stairs to designated areas of refuge within the building, where they safely await further instruction from building management or the relevant authorities.
Communication. For buildings utilizing partial evacuation, communication becomes even more critical since instructions need to be conveyed regarding what floors should be evacuated, where to evacuate to, and what other building occupants need to know. The building must not only accommodate communication of emergency instructions to building occupants but also communications between fire service personnel as well.??
Elevator “Life Boat” Evacuation. If necessary, super tall occupants can be evacuated from areas of refuge using elevators under fire department control with a “lifeboat evacuation” mode that shuttles occupants from areas of refuge to the ground floor. These firefighting elevators are specifically fortified for use during a fire, including shaft cameras to verify the elevator can clearly pass through at the fire floors, as well as other enhancements. The areas of refuge are generally located at least at every 20 floors (or as prescribed by the prevailing code). The use of high-speed elevators for passenger evacuation has become more accepted of late for super tall buildings, and the systems for elevator evacuation are continuing to evolve beyond manually-controlled elevators toward automated systems.??
Even though the above evacuation strategies are proven solutions, there still may be challenges convincing the relevant authorities, especially in jurisdictions where international codes have not been fully adopted or where elevator evacuation is not yet recognized. For example, in some jurisdictions, full building evacuation must be possible in under two hours. If the jurisdiction does not recognize elevator-assisted evacuation, buildings over 500 meters tall (100+ stories) will struggle to achieve this criteria. It is therefore critical to identify the requirements of your particular jurisdiction as early as possible in order to develop an evacuation plan that is not only practical but also locally recognized as a reliable method.??
Emergency Utilities. The best machine-assisted evacuation plans are still dependent on power, and fire suppression requires water that cannot be pumped up from street level during a fire. Emergency power is always critical during fire evacuation but becomes even more so when the building’s evacuation system depends on functioning elevators, alarm systems, stair pressurization, and smoke exhaust for up to 2 hours or more. Due to the comparative inadequacy of firefighting equipment to the height of a super tall tower, firefighting operations must be conducted primarily from inside the building, often times in locations that are remote from fire service apparatus and ground support. Emergency power requirements must then be adjusted for these considerations, including redundancy scenarios and adequate fuel supply.?
?The next article will be covering the followings; (3) structure, (4) building movement, (5) vertical transportation, and (5) stack effect.?
1 CTBUH.org. 2015: A Tall Building Review?