| Performance of reinforced concrete moment resisting frames during recent earthquakes has shown that these systems are efficient in providing seismic resistance if satisfactory performance of the beam-column joint region is provided. Research on beam-column joint behavior has been limited primarily to joints constructed using conventional strength steel reinforcement (Grade 40 or 60) and concrete with compressive strengths below 6,000 psi. Since, current design guidelines were based on tests conducted on specimens constructed using normal strength materials, their use in the design of high strength beam-column joints may be inappropriate. With the increasing usage of high strength materials in medium and high-rise construction, building code officials and structural engineers have expressed concern over the use of current design recommendations for joints constructed using high strength concrete (compressive strength above 12,000 psi), high strength steel reinforcement (Grade 75) and high strength (f{dollar}sb{lcub}rm y{rcub}{dollar} = 80 ksi) welded wire fabric.; An experimental research project was developed at the University of Texas at Austin to investigate the behavior of interior slab-beam-column joints constructed with high strength materials. Four full-scale specimens constructed using normal and high strength materials were tested under cyclic bidirectional loading. High strength concrete, high strength steel reinforcement and welded wire fabric reinforcing cages were used in three of the specimens. A fourth specimen was constructed using normal strength materials (f{dollar}spprimesb{lcub}rm c{rcub}{dollar} = 4,000 psi and Grade 60 bars). The specimens were designed according to current American Concrete Institute guidelines.; Test results indicate that the high strength beam-column joints performed quite satisfactorily. The performance of the normal and high strength steel reinforcement was comparable indicating that current recommendations can be extended to include the use of Grade 75 longitudinal reinforcement and welded wire fabric (f{dollar}sb{lcub}rm y{rcub}{dollar} up to 80 ksi) as joint transverse reinforcement. Effect of high strength concrete in behavior was notable, especially with respect to stiffness, cracking, and energy dissipation. Current design recommendations for joint shear strength can be used for a safe estimate of unidirectional joint shear strength of interior joints constructed with high strength materials. |
