Confinement of deep beam nodal regions

The purpose of the testing program described in this paper was to evaluate the benefits of triaxial confinement that occurs when the loaded area of a strut-and-tie model (STM) is surrounded by concrete on all sides. To achieve this goal, five full-scale beams were fabricated and tested at the Ferguson Structural Engineering Laboratory in Austin, TX. Specimens were tested with a span-depth ratio (a/A) of 1.85. Two ends of each beam were tested, resulting in a total of 10 tests. Eight tests were conducted on beams with a 21 × 42 in. (530 × 1070 mm) cross section, and two tests were conducted on beams with a 36 × 48 in. (910 × 1220 mm) cross section. The primary experimental variables were the size of the load- and support-bearing plates and the amount of web reinforcement. Based on the results of the testing program, it is recommended that the permissible nodal stresses of an STM be increased for nodes triaxially confined by concrete.