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Accommodating building deflection

The flexible pipe coupling remains a self-restrained joint, and the pressure-responsive gasket design provides positive sealing even during piping system movement.There are three standard methods for employing grooved mechanical couplings to accommodate piping thermal movement (expansion and contraction) in a building riser: Method 1: Use the angular-deflection capability of flexible pipe couplings to accommodate the movement at the top of the riser.

Differential column shortening should be estimated by considering the effects of actual concrete mix, environment, construction sequence, etc.For interior partitions, allowance is needed for differential deflection between two adjacent floors after the installation of interior partitions.There have been numerous examples where these joints have not been appropriately installed, particularly on tall slender buildings, which results in “creaking” complained by tenants because of rubbing joints as the buildings move under wind loading.It is also a general practice to use Finite-Element Analysis software to check floor deflections (especially for two-way flat slabs) based on actual reinforcing layout and reasonably assumed material parameters.When one checks floor system deflections, it is necessary to estimate floor slab edge deflections for cladding system installation, especially for large prefabricated concrete/stone panel facade system.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.

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.

The long-term deflections of girders, which pick up floors above, are particularly important and the deflection acceptance criteria should be more stringent than code-allowed values.

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.

Although the deformations and movements are not life threatening, inappropriate design of buildings and associated nonstructural components could induce expensive economic consequences in the long-run and, in order to ensure proper building behavior of the superstructures and the attached nonstructural elements, should not be ignored.

In this article the possible deformations and movements of reinforced concrete high-rise buildings and the accommodation of the affected components are discussed.

The grooved pipe couplings joining the riser piping sections are rigid, while those at the top on the first horizontal pipe are flexible, as shown in Figure 2.