Short- and Long-Term Prestress Losses in Basalt FRP Prestressed Concrete Beams under Sustained Loading

Abstract

The favourable mechanical properties of basalt fibre-reinforced polymer (BFRP) bars, such as their excellent strength-to-weight ratio, resistance to corrosion, lower environmental impact and electromagnetic neutrality, make them attractive for internal reinforcement of concrete elements with specific service requirements. Prestressing has emerged as a possible method for limiting the deflections and cracking of BFRP reinforced flexural RC elements. However, long-term behaviour of such structural members has not yet been investigated extensively. Therefore, this paper aims to give information on long-term behaviour and prestress losses of pretensioned BFRP reinforced concrete beams based on the collected experimental data. The testing programme includes long-term analysis of six BFRP concrete beams pretensioned to different prestress levels; namely, 20%, 30% and 40% of the ultimate tensile capacity of the bars. The monitored testing stages included initial tensioning of the bars, casting and curing of concrete, transfer of prestressing force to the concrete, long-term unloaded phase after transfer, sustained loading application, long-term sustained loading phase, unloading and final destructive testing, conducted in a controlled indoor environment. During all phases of the testing strain levels in the BFRP bars and deflections were continuously monitored. The results of continuous strain monitoring show that the average loss of strain over the period of initial 90 days of Journal of Composites for Construction unloaded monitoring was 7% of the initial strain. During the following 6 months of monitoring under sustained loading recorded an additional 0.3% reduction on average. The loss was dependent on the initial strain.

Short-Term Efficiency of Using Sustainable BFRP Bars in Post-Tensioning Systems for One-Way RC Slab

“…The stress losses were 6.44% (experimental) after 68 hrs, and the slope of the analytical retain strain was decreased slightly at the interval of 68 hrs to 1000 hrs, which means the RC slab with a 30% external stress level continued to lose its capacity over time S-BF-10%-Int. 0 1.50 [2] 1.50 [2] 1.50 [2] 68 1.26 [3] 1.26 [3] 1.26 [3] 68 1.23 [4] 1.25 [4] 1.44 [1] 100 1.23 [4] 1.25 [4] 1.44 [1] 572 1.25 [3] 1.25 [3] 1.25 [3] 572 1.22 [4] 1.24 [4] 1.44 [1] 1000 1.21 [4] 1.23 [4] 1.44 [1] S-BF-50%-Int. 0 7.50 [2] 7.50 [2] 7.50 [2] 68 7.25 [3] 7.25 [3] 7.25 [3] 68 7.24 [4] 7.19 [4] 7.21 [1] 100 7.24 [4] 7.19 [4] 7.21 [1] 572 7.24 [3] 7.24 [3] 7.24 [3] 572 7.24 [4] 7.19 [4] 7.21 [1] 1000 7.23 [4] 7.18 [4] 7.21 [1] S-St-BF-10%-Ext.…”

“…0 1.50 [2] 1.50 [2] 1.50 [2] 68 1.26 [3] 1.26 [3] 1.26 [3] 68 1.23 [4] 1.25 [4] 1.44 [1] 100 1.23 [4] 1.25 [4] 1.44 [1] 572 1.25 [3] 1.25 [3] 1.25 [3] 572 1.22 [4] 1.24 [4] 1.44 [1] 1000 1.21 [4] 1.23 [4] 1.44 [1] S-BF-50%-Int. 0 7.50 [2] 7.50 [2] 7.50 [2] 68 7.25 [3] 7.25 [3] 7.25 [3] 68 7.24 [4] 7.19 [4] 7.21 [1] 100 7.24 [4] 7.19 [4] 7.21 [1] 572 7.24 [3] 7.24 [3] 7.24 [3] 572 7.24 [4] 7.19 [4] 7.21 [1] 1000 7.23 [4] 7.18 [4] 7.21 [1] S-St-BF-10%-Ext. 0 1.50 [2] 1.50 [2] 1.50 [2] 68 1.25 [3] 1.25 [3] 1.25 [3] 68 1.23 [4] 1.25…”

“…0 7.50 [2] 7.50 [2] 7.50 [2] 68 7.25 [3] 7.25 [3] 7.25 [3] 68 7.24 [4] 7.19 [4] 7.21 [1] 100 7.24 [4] 7.19 [4] 7.21 [1] 572 7.24 [3] 7.24 [3] 7.24 [3] 572 7.24 [4] 7.19 [4] 7.21 [1] 1000 7.23 [4] 7.18 [4] 7.21 [1] S-St-BF-10%-Ext. 0 1.50 [2] 1.50 [2] 1.50 [2] 68 1.25 [3] 1.25 [3] 1.25 [3] 68 1.23 [4] 1.25 [4] 1.44 [1] 100 1.23 [4] 1.25 [4] 1.44 [1] 572 1.24 [3] 1.24 [3] 1.24 [3] 572 1.22 [4] 1.24 [4] 1.44 [1] 1000 1.21 [4] 1.23 [4] 1.44 [1] S-St-BF-30%-Ext. 0 4.50 [2] 4.50 [2] 4.50 [2] 68 4.21 [3] 4.21 [3] 4.21 [3] 68 4.21 [4] 4.20…”

“…0 1.50 [2] 1.50 [2] 1.50 [2] 68 1.25 [3] 1.25 [3] 1.25 [3] 68 1.23 [4] 1.25 [4] 1.44 [1] 100 1.23 [4] 1.25 [4] 1.44 [1] 572 1.24 [3] 1.24 [3] 1.24 [3] 572 1.22 [4] 1.24 [4] 1.44 [1] 1000 1.21 [4] 1.23 [4] 1.44 [1] S-St-BF-30%-Ext. 0 4.50 [2] 4.50 [2] 4.50 [2] 68 4.21 [3] 4.21 [3] 4.21 [3] 68 4.21 [4] 4.20 [4] 4.33 [1] 100 4.21 [4] 4.20 [4] 4.33 [1] 572 4.20 [3] 4.20 [3] 4.20 [3] 572 4.19 [4] 4.18 [4] 4.33 [1] 1000 4.18 [4] 4.17 [4] 4.33 [1] analytically, see Fig. 21.…”

Long-Term Prestress Loss Calculation Considering the Interaction of Concrete Shrinkage, Concrete Creep, and Stress Relaxation

“…Prestress loss is the key factor affecting the cracking of prestressed concrete bridges under torsion; it can be divided into short-term prestress loss and long-term prestress loss. Short-term prestress loss mainly includes the prestress loss caused by the friction between the prestressed bar and the pipe wall, anchor deformation, retraction of the steel bar, etc., which is easy to measure and calculate because it is independent of time [ 1 , 2 , 3 , 4 ]. The long-term prestress loss caused by prestressed rib relaxation, concrete shrinkage, and concrete creep is time-sensitive and difficult to calculate [ 5 , 6 , 7 , 8 , 9 , 10 ].…”