Tensile Strength Characteristics of GFRP Bars in Concrete Beams with Work Cracks under Sustained Loading and Severe Environments

To investigate the effect of different environmental conditions of GFRP bars in concrete beams with work cracks subjected to sustained loads, the beams were exposed in indoor, freeze/thaw cycles and immersed in alkaline solution at elevated temperature. The bars were carefully extracted from the beams and tested in order to evaluate residual tensile properties. The results show that the tensile strength decreased significantly in the highly aggressive conditions but not in the natural conditions. The effect of GFRP bars casting in concrete beams demonstrated approximately 2.5% decrease of tensile strength caused by pore water environment in concrete beams on basis of those of the original bars. The effect of sustained loading plus work cracks demonstrated about 10.5% tensile strength decrease on basis of those of the bars only casted in concrete beams. The effect of environments under sustained loading plus work cracks demonstrated about 17% tensile strength decrease caused by a saturated solution of Ca（OH）2 and 60-2 ℃ tap water （pH=12-13） and about 8% tensile strength decrease caused by freezing and thawing cycle （F/T）, both on basis of those of the bars of the indoor beams only under sustained loading plus work cracks. The results demonstrate the effects of the tensile strengths under different environmental conditions of GFRP bars in concrete beams with work cracks subjected to sustained loads.

SFRC Subjected to Domestic Sewage and Sustained Load

The article aimed to study the durability of steel fiber reinforced concrete under the coupled sewage-loading according to compressive strength,flexural strength,compressive strength corrosion coefficient,flexural strength corrosion coefficient,compressive strength balance coefficient,flexural strength balance coefficient.Through the homemade load frame applied to design specimens,the pre-loading level are equivalent the damage intensity of 0%,10%,30% and 50% four different ways.The experimental results show that the performance of concrete down gradually and sustaining load aggravated the degree of domestic sewage attacking concrete after six month;under different stress states,the more loading levels,the more serious domestic sewage attacked the steel fiber reinforced concrete.It is proved that the concrete damage can be inhibited by adding the steel fiber,when steel fiber volume fraction is 1.0%,the corrosion resistance of concrete is best.

Experimental Study of RC Beams Strengthened with CFRP Sheets Under Sustaining Loads

Seven reinforced concrete （ RC ） beams strengthened in flexure using carbon fiber reinforced polymer （CFRP） sheets subjected to different sustaining loads were tested. The effects of initial load and load history on the ultimate strength of strengthened RC beams were examined by externally bonded CFRP sheets. The main experimental parameters included different levels of sustaining load at the time of strengthening, and load history. Experimental results show that sustaining load levels at the time of strengthening have important influences on the ultimate strength of strengthened RC beams. If the initial load is the same, the ultimate strength of RC beams strengthened with CFRP sheets is almost the same regardless of load history at the time of strengthening.