A Master of Science thesis in Civil Engineering by Mohammad Mustafa Al Moukdad entitled, “Effect of Construction Void Defects on Flexural and Axial Load Capacity of Reinforced Concrete Members”, submitted in May 2018. Thesis advisor is Dr. Sami W. Tabsh. Soft and hard copy available.
A common construction defect in reinforced concrete is honeycombing, which consists of loosely connected coarse aggregates with little mortar in-between them over a small volume located within a structural member. Such a void defect has a detrimental effect on the structural behavior because it creates weak localized regions within the member. This study is concerned with the effect of such voids on the structural behavior and capacity of reinforced concrete members under the effect of flexure and axial compression. In order to know more about the causes, characteristics, and repair methods of void defects in concrete structures, practicing structural and construction engineers in the country were surveyed. Using the 54 received responses, a research plan was developed consisting of experimental and theoretical phases. The experimental part consisted of testing 20 intact and defective scaled beams under the effect of bending moment, and columns under the effect of pure axial compression. The flexural specimens were 2-m long with a 150 mm x 300 mm cross-section, whereas the axial compression specimens were 1-m height with a 200 mm square cross-section. The experimental program considered the size (5%-20% of the intact cross-section), shape (square and rectangular), and length (100-200 mm) of the void within the member. It addressed two different concrete compressive strengths (30 and 50 MPa) and two steel reinforcement ratios (1% and 2%). The experimental tests were complemented with theoretical analyses involving the software Response 2000 and SPColumn. The load-deflection relationships from the tests generally confirmed that the presence of a void decreases the stiffness of the member, ductility, and strength, and the decrease depends on the size of the defect. Voids that occupy 20% of the cross-sectional area of a beam can reduce its flexural capacity by 30-40%, depending on the concrete compressive strength, reinforcement ratio, and shape of the void. The corresponding decrease in the compressive capacity of a defective column is in the range of 19-22%. Theoretical predictions of the flexural capacity of beams and axial capacity of columns based on the ACI 318 code can be reasonable if the void is less than 5% of the intact section; however, this can lead to over-estimation of the actual capacity if the void is greater than 5%. Accounting for the eccentricity of the load from the plastic centroid of a voided column in the analysis can lead to conservative results.