Accommodating building deflection dating rotograph postcards
When subjected to gravity loads, vertical reinforced concrete structural members, such as columns and shear walls, experience short-term and long-term shortening that is zero at the base and accumulates to be the maximum at the roof level.
Magnitudes are dependent on concrete mix, gravity stress levels, construction sequences, loading histories, volume-to-surface ratios and ambient relative humidity, etc.
Absolute long-term deflection limit values for the girders are recommended to control associated deflection of floors above, instead of satisfying the code-allowable deflection-over-span ratio alone.
In many cases, cambers are specified in construction documents to ensure level slabs and minimum slab infill.
As a result, transient dynamic racking of the building is to be expected during the service life of buildings.
Allowances for building cladding systems and interior partitions should be provided to accommodate the transient story drift and dynamic racking motions under both wind loads and seismic loads.
Allowable seismic story drift criteria are given in ASCE 7 and vary with seismic risk category and the seismic force resisting structural system types (ASCE 7-2010).
In this article the possible deformations and movements of reinforced concrete high-rise buildings and the accommodation of the affected components are discussed.
Common, inevitable building movements and deformations include: differential column shortening, lateral story drift, building racking, slab and beam deflection, thermal deformation and building dynamic vibration, etc.