This paper presented the results of an experimental study of the behaviour of flexural beams strengthened with the glass fiber reinforced polymer (GFRP-S). This research was carried out to determine the effect of fatigue loads on the flexural capacity of reinforced concrete beams. The specimens were rectangular with a dimension of 150 mm in width, 200 mm in height, and 3300 mm in length. Four distinct conditions had been applied to this experiment. For the initial condition, two beams were tested under monotonic loads (maximum load control) as a control beam (BN). Sinusoidal fatigue loads were applied to four specimens from 4 kN to 24 kN (BF). Our comparative results of the experiment had presented that the normal beams (BN) failed after 800,000 loads cycle, while, the reinforced beams with GFRP (BF) failed after 1,231,860 loads cycle. Based on our results, it can be stated generally that fatigue life of the reinforcement beams (BF) could increase to more than 100% compared to that of the normal beams (BN). The failure of the beams is probably caused by fatigue of the reinforcement bar and debonding of the GFRP-S, both are secondary failure mechanism of reinforced concrete beams.

This study aims to analyse glass fibre reinforced polymer (GFRP) reinforcement on reinforced concrete beams under fatigue and monotonic loads influenced by sea water. The research was conducted in the laboratory on flexural concrete beams with the quality of f´c= 25 MPa. One normal concrete flexural beam (BN) with repetitive load was without seawater and no reinforcement. One flexural beam was without sea water immersion but with GFRP-reinforcement. Another flexural beam reinforced by GFRP sheets is immersed in a pond containing seawater with time variations up to 12 months. The test was performed with a fatigue load of 1.25 Hz frequency to failure. The results showed an increase in capacity due to 58.3% for GFRP-reinforcement. There is a decrease in the capacity of GFRP sheet influenced by seawater immersion. The same trend with the decrease in ductility occurred in the flexural beam to 14% due to seawater immersion. Maximum beam failure repetition occurred at 1,230,000 cycles on beam with reinforcement (BF). The failure occurring in the flexural beam was preceded by the failure of the attachment between the concrete and the GFRP sheet at the load centre (mid of span) slowly to the support until failure (debonding) initialized. The GFRP-S bonding capacity to the concrete skin has decreased in 12 months by 15%. Therefore, there is a significant effect of decreasing strength due to fatigue loads and seawater immersion.

Bridges or docks on coasts often fail due to fatigue loads. Sea waves striking bridge or the dock give a fatigue effect to the structure thus accelerating structural failure. This study aims to analyse glass fibre reinforced polymer (GFRP) reinforcement on reinforced concrete beams under fatigue and monotonic loads influenced by sea water. One normal concrete flexural beam (BN) with repetitive load was without seawater and no reinforcement. One flexural beam was without seawater immersion but with GFRP-reinforcement. Another flexural beam reinforced by GFRP sheets is immersed in a pond containing seawater with time variations up to twelve months. The results showed an increase in capacity due to GFRP-reinforcement. There is a decrease in the capacity of GFRP sheet influenced by seawater immersion. The same trend with the decrease in ductility occurred in the flexural beam to seawater immersion. The failure occurring in the flexural beam was preceded by the failure of the attachment between the concrete and the GFRP sheet at the load centre (mid of span) slowly to the support until failure (debonding) initialized. The GFRP-S bonding capacity to the concrete skin has decreased in twelve months. Therefore, there is a significant effect of decreasing strength due to seawater immersion.