Type III Grouted Ductile Reinforcing Bar Connections for Precast Concrete Structures

This dissertation presents experimental and analytical investigations of a high-performance (Type III) grouted connection for ductile energy-dissipating (ED) deformed steel reinforcing bars across gap-opening joints in seismic precast concrete structures. The goal is to develop a simple, non-proprietary, low-cost connection that allows Grade 60 ED bars to reach close to their full ultimate tension strength and strain capacity over a short grouted bond length inside a steel sleeve (with or without a taper), thus reducing required field-grouting lengths.

Twenty large-scale quasi-static cyclic axial load tests of isolated ED bar-to-foundation connections were conducted to failure under a rigorous strain history, varying the following parameters: (1) ED bar diameter (No. 7, 9 and 11 bars); (2) ED bar bond length; (3) ED bar manufacturer/heat; (4) connection sleeve taper angle, (5) corrugated versus uncorrugated sleeves; (6) grout product and strength; (7) adverse construction conditions from excess water in grout and off-center placement of the ED bar inside the sleeve; and (8) a threaded bar splicer in combination with a grouted connector. The measured behaviors of the specimens were compared against simulations from nonlinear finite element models, and were used to establish effective connection configurations and material requirements.

The test specimens under the adverse construction conditions considered were able to achieve ductile failure through low-cycle fatigue fracture or bond slip. A greater bond length of 15 times the bar diameter was necessary for No. 11 ED bars as compared with a length of 12 times the bar diameter for No. 7 bars. The connector grout, the ED bar bond length, and the low-cycle fatigue capacity of the ED bar can limit the deformation capacity of the connection. Although tapered sleeves produced desirable results, straight sleeves with adequate corrugations also allowed large cyclic ED bar stresses and strains to be reached. Ultimately, the use of straight sleeves is recommended because of minimized connector spacings and cost-effective availability of corrugated steel pipe from multiple manufacturers. The test results were also used to validate a strut-and-tie method for the design of reinforcement to transfer the ED bar forces from the grouted connection to the foundation concrete.