Title: Bare Reinforced Concrete Roofs; The Puerto Rican Experience

Author(s): Ignacio Martin

Publication: Concrete International

Volume: 1

Issue: 1

Appears on pages(s): 59-63

Keywords: building codes; concrete construction; concrete slabs; cracking (fracturing); crack width and spacing; permeability; reinforced concrete; reinforcing steels; roofs; shrinkage; structural design; thermal stresses.

DOI:

Date: 1/1/1979

Abstract:
Concrete is used extensively in mass-produced residential construction in Puerto Rico. The typical roof slab is 4 in. (10 cm) thick and is usually left unprotected. In recent years, leaks in roofs are becoming more frequent and appear at an earlier age. In Puerto Rico, the contractor is liable for construction defects for 10 years; therefore, leaks are an item of cost in call-back repairs and litigation. The width of flexural cracks is a function of the reinforcing steel stress. The allowable steel stress for members with a light live load has been increased in the ACI Building code (ACI 318-77) in recent years. When the shrinkage and temperature stresses, which are normally neglected in design, are added to the dead load stresses, the steel stress reaches the level where the crack width may permit the penetration of water. It is recommended to design roof slabs for an allowable crack width taking into consideration the shrinkage and temperature stresses. [Author]