Closure to “Effect of Prestressing Level on the Time-Dependent Behavior of GFRP Prestressed Concrete Beams” by Mohamed Zawam, Khaled Soudki, and Jeffery S. West

The writers are pleased that their paper was read in depth and that it prompted other researchers to discuss its results.

Regarding the discussion about the effect of prestressing on the beam stiffness, there is no contradiction between what was stated in the paper and the discussion. Stiffness is a cross-sectional property and it is not affected by prestressing, and stating this fact was necessary to explain why beams with different prestressing levels had the same slope on the load–deflection curves. In addition, it was stated in the conclusions that beams with higher prestressing levels experienced less deflections.

The point mentioned in the discussion regarding the material properties of the bars is very important. The data for the production lot used in this study are not available because they were not provided by the manufacturer. The guaranteed values were used in the paper for the prestressing level to strength ratio because these prestressing ratios were compared to the CAN/CSA S6-14 (CSA 2014) code limit ratio (25% of the bar ultimate strength), which uses the guaranteed strength. Thus, it was important to be able to draw the conclusion mentioned in the paper regarding the CAN/CSA S6-14 limits. This conclusion was aimed at drawing attention to the fact that with the new advancements in the material properties of the glass fiber–reinforced polymer (GFRP) bars, the CAN/CSA S6-14 limitations became very conservative (since the flexural capacity did not seem to be affected by the sustained loading). The paper did not propose a value for a new limit because this requires a different set of tests that was not carried out in this research.

Creep and relaxation are complex and interconnected phenomena. While creep is the time-dependent deformation under sustained load, relaxation is the reduction in stress under constant strain. For the beams subjected to sustained loading in this research, the load applied on the beams was monitored using load cells and kept constant throughout the period of testing to justify modeling the creep of the GFRP bars and the concrete, rather than the relaxation in the analytical model presented in the paper.

In conclusion, the research described in the paper is part of a larger study to investigate the time-dependent behavior of concrete beams prestressed with GFRP bars. This research mainly aimed at adding to the current work on the structural behavior of GFRP prestressed concrete beams. The discussion it initiated is valuable and appreciated by the writers.