Critical connection load evaluation of composite beams subjected to rapid corrosion and direct load

• Experimental study on corroded composite concrete beams under direct loading. • Rapid corrosion technique used to simulate severe deterioration. • GFRP bars applied using the NSM technique for beam strengthening. • Different reinforcement positions were tested for performance comparison. • Findings support effective rehabilitation of deteriorated composite beams. The present research focuses on the experimental assessment of the critical connection load capacity of corroded composite concrete-concrete beams. The experimental study included fifteen composite concrete beams. Each evaluated beam specimen consisted of two distinct components (separated by construction joints), bottom webs (with a cross-section of 250 × 150 mm), and top slabs (with a cross-section of 50 × 450 mm) to create the final composite T-shaped section. The examined beams had a total length of 1600 mm and a net clear length of 1500 mm between supports. The beam webs were constructed using self-compacting concrete (SCC), whilst the topping slabs (flanges) were fabricated using normal-strength concrete (NSC). The examined beam specimens were categorized into three groups based on the level of connection, with each group comprising five specimens. Four specimens underwent accelerated corrosion, with two having steel reinforcement solely in the upper section (deck slab) and two throughout the entire depth of the tested beam. Two degraded beam specimens of each group were reinforced utilizing NSM technology by (GFRP) bars following the end of the corrosion process. Subsequently, all the examined beam specimens endured the direct loading of two focused vertical monotonic loads up to failure. The test findings indicated that corrosion markedly diminishes the load-bearing capability and ductility of the examined composite beams. Partial corrosion (limited to the slab level) results in a decrease in ultimate load capacity of around 9–12 %, while full-depth corrosion leads to a drop of about 22–24 %. The ductility index of beam specimens subjected to corrosion at the deck slab level (50 mm depth) reduced by around 10.3–14.7 %, while the ductility index for specimens exposed to full-depth corrosion diminished by 28–38.4 %. The reinforcement of the compromised beam specimen in the tensile region of the beam web using the NSM approach with GFRP bars enhances the ultimate load-bearing capacity by about 22–30 % compared to the non-reinforced degraded beams. The reinforcement of the compromised beam specimen at the slab level alone using the NSM approach with GFRP bars results in a negligible effect, decreasing the ultimate load by around 1.6–7 %. The mid-span deflection was much greater in corroded beam specimens, especially those exhibiting full-depth corrosion, with an increase of up to 80 % compared to control beam specimens. The shear slip was mostly affected by the connection type and accelerated corrosion, whereas the NSM approach with GFRP bars had little effect on decreasing slip. The results elucidate the structural ramifications of corrosion in composite beams and highlight the specific advantages of GFRP-based NSM reinforcement, especially in the tensile region of corroded elements.