Experimental Investigation of Concrete Beams with Novel Parallel-Lap Reinforcement Under Flexure

To address the technical challenges associated with complex connection configurations and excessively long lap zones in the industrialized and prefabricated construction of reinforcements, this study proposes a novel parallel-lap splice that incorporates a third overlapping reinforcement. This innovative design offers several advantages, including neat ends, ease of construction, and enhanced economic efficiency. An experimental investigation was conducted to evaluate the effects of this new splice on the flexural behavior of reinforced concrete (RC) beams, with lap length (ll) as the key variable (ll = 64d, 40d, and 25d). A total of nine simply supported RC beams (three groups of three specimens each), all incorporating parallel-lap splices, were tested under four-point bending. The key mechanical properties were analyzed, including the mechanical characteristics, failure modes, flexural capacity, bending stiffness, and maximum flexural crack width. The experimental and analytical results reveal that RC beams with the new parallel-lap splice exhibit a distinctive “one primary + two secondary” crack pattern, characterized by a dominant flexural crack at midspan and secondary cracks at the ends of the lap zone. At the ultimate limit state, specimens with ll = 64d experienced concrete crushing at the top surface of the midspan while those with ll = 40d and ll = 25d did not. Additionally, the ll = 64d and ll = 40d beams showed slight strength hardening, whereas the ll = 25d beams exhibited rapid strength degradation. In terms of load-bearing capacity, both the ll = 64d and ll = 40d beams met the requirements specified in current design codes, while the ll = 25d specimens showed a reduction in capacity exceeding 20%. Under serviceability limit states, midspan deflections and maximum crack widths for the ll = 64d, ll = 40d, and ll = 25d specimens were found to fully comply with, marginally satisfy, and fail to meet the requirements of the design code, respectively. Based on these findings, as well as regression analysis of the relationship between peak load and lap length, it is recommended that a reasonable lap length for the proposed parallel-lap splice be taken as 60d, with a lap length correction factor of 1.5.