Repairing and Upgrading of a Heavy-Duty R/C Slab

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Title: Repairing and Upgrading of a Heavy-Duty R/C Slab

Author(s): Pietro G. Gambarova, Francesco Lo Monte, Seyed M.S. Mousavi, Pietro L. Torregiani, and Mattia Zecchillo

Publication: Special Publication

Volume: 326

Issue:

Appears on pages(s): 104.1-104.10

Keywords: finite-element analysis (of slabs); mixed restraints (in slabs); reinforced-concrete slabs; stiffening beams (in slabs); structural fire design (of R/C slabs); yield-lines method

Date: 8/10/2018

Abstract:

A heavy-duty almost square R/C slab is studied in this paper based on two tests performed under the service loads, after adding a stiffening R/C beam along the only free edge. The very linear behavior exhibited during the tests was the starting point: (a) to perform a FE analysis to investigate the role of the mixed restraints; (b) to identify the most probable failure mechanisms – under distributed and concentrated loading - within the kinematic theorem of Limit Analysis (Yield-Line Method); (c) to quantify the extra strength provided by the stiffening beam; and (d) to study the bearing capacity in fire.

Slab sides are close to 8 m [27 ft] and the thickness is 35 cm [13.8 in.]. Two adjoining sides rest on walls, while the third side is partially supported and the fourth side - initially free – has been stiffened by casting an R/C beam along the extrados.

The mixed restraints show that (a) not always the yield lines and the failure mechanisms dictated by intuition are the most probable; (b) stiffening a free edge may not be required at the serviceability or ultimate limit states, but by the checks in fire; and (c) stiffening a free edge tends to shift the failure mechanism towards slab-localized mechanisms, because of the greater heat sensitivity of thin slabs compared with solid beams.