RESEARCH & DEVELOPMENT
INVESTIGATING TALL BUILDINGS
The increased development of high-rise buildings where a developer achieves a greater yield on the area of developed land is a growing and accelerating trend across the globe.
This is a market that will continue on this path as more of the populous look to live in urbanised areas.
In designing these buildings, developers have decisions to make based on the fact that their buildings will be affected by variable meteorological conditions and primarily, due to the nature of their tall design, exposure and wind.
The effects of airflow on a building is highly variable and can be considered as either a direct force, or, as the result of differentials in air pressure on opposing sides of the construction.
These air pressure variations are formed from air currents that are being induced by the building’s profile and its co-located structures. This air flow phenomena is known as Vortex Shedding and the resultant air currents have the effect of pulling buildings towards the lower air pressure value; the higher the differential in air pressure, the greater the pull and its associated movement.
Developers have principally two choices, they can make their structure super stiff through bracing oversized columns and beams together ensuring that the building remains almost entirely fixed in position, or they can allow, and therefore engineer, a level of movement. In most cases the options to make the structure stiff is too costly in both materials and labour, with construction times significantly extended. The commercially viable option is to enable and control building movement
Design options that enable Engineers to control the amount of movement include building tapering, periodic offset, softening of edges and damper systems.
In all cases, these design details reduce the effect of building movement and add a level of calculated control.
Tall buildings move by design, and from extensive scientific studies it is understood that this movement is not uniform.
Within high rise buildings the effects become apparent from between a quarter and a third of the building’s height to its topmost floor. A significant biproduct and adverse effect of engineered building movement within the structure is noise. During periods of induced oscillation, building residents are reporting audible creaking emanating from their apartment walls and in extreme cases, noise levels are reported to be as high as 70dB - equivalent to the sound volume generated by a vacuum cleaner.
Understandably, this has become a significant issue for all associated parties and is having a damaging effect in every construction market across the globe, from high rise residential and hotels through to commercial and public sector. Rent withholding is now becoming more widespread as tenants experience exacerbated levels of discomfort from their living and working environments as they look to their Landlords for answers.
Construction never stops and a resolution to the issue at hand remains outstanding, leaving an ongoing and extending trail of legacy issues in its wake which will affect the sector for years to come.
RESEARCH & DEVELOPMENT
TALL BUILDINGS - OUR FINDINGS
MotionFrame has undertaken studies into the effects of total building movement to understand its impact on a floor by floor basis and the dynamics induced on traditionally constructed internal walling and other internal fitout features and services.
Small displacements occur at each floor level, however the ceiling slab movement on any given floor is greater than that of the associated floor slab and this has the effect of taking a perpendicular, rectangular floor cross section and deforming it into a trapezoidal section
Our desktop modelling has confirmed to us that traditional construction methodologies for internal structures has not advanced at the pace of superstructure innovation and its associated engineered building movement – there is now a significant shortfall in the design of internal systems that needs to be retrospectively corrected whilst ‘fit for purpose’ solutions need to be developed for future projects that negate their effects for all involved.
Traditional methods of walling system construction make provision for movement in one axis only. This design consideration accommodates loads imposed on the floor above and therefore the ceiling of the floor on which the elevation is erected. The resultant vertical downward force is engineered into the design detail through the provision of a Deflection Head, which is common in all internal walling designs.
This design was developed many years ago and whilst it remains functional, it has become limited in its effectiveness and has not developed in line with advancements in building design, materials or practices. Fundamentally, the standard deflection head is now limiting and restricting the internal walling systems performance in relation to the broader deflection requirement of modern construction.
RESEARCH & DEVELOPMENT
TALL BUILDINGS - OUR CONCLUSION
We are now in the midst of an industry wide challenge with currently no firm resolutions to the problem at hand; and therefore, no view as to how to approach the past, present or future.
Traditional thinking and practices have been superseded by the extended boundaries of superstructure design and are no longer delivering the performance required. The MotionFrame ethos is to challenge convention in the sector with new thought processes and methods that evolve into innovation in design.
Bi-directional forces have become more evident and accentuated through the development of tall building design.
We have a solution.