Improving the Performance of Reinforced Concrete Beam-Column Joints Designed for Seismic Resistance

Abstract

The testing of thirteen large scale beam-column joints forms the framework for the content of this thesis. The thirteen tests were divided into three series, each of which investigated an aspect of earthquake resistant design of moment resisting frames. The results obtained from testing the first series of four beam-column joints contradicted the conclusion of earlier research that design criterion specifying the ratio of column depth to bar diameter required to anchor beam longitudinal reinforcement at interior beam-column joints was non-conservative when applied to Grade 500E reinforcement. As a result, a database of approximately 100 beam-column joints was assembled and used to parametrically develop an improved design criterion that was shown to satisfactorily predict experimental performance based on the anchorage length provided. It was also shown in the first part of the thesis that the flexural overstrength factor should be the same irrespective of whether Grade 300E or Grade 500E longitudinal reinforcement is used in a beam. This finding contradicts current New Zealand practice, which specifies a higher flexural overstrength factor for Grade 500E reinforcement. The second set of four tests assessed the performance of beam-column joints constructed using inorganic polymer concrete. The properties of inorganic polymer concrete are similar to those of concrete produced using Portland cement, but the production of inorganic polymer concrete releases 80% less "greenhouse gases" into the atmosphere than the production of Portland cement concrete. The results of these tests showed that satisfactory performance can be expected from beam-column joints designed using existing New Zealand standards but constructed using inorganic polymer concrete. The final series of five tests were conducted to assess the performance of beam-column joints when the joint core was constructed using high performance fibre reinforced cementitious composites (HPFRCC) and contained no conventional transverse reinforcement. The results of this testing showed that satisfactory performance could be achieved when the magnitude of the joint core shear stress was commensurate with the strength of the HPFRCC used. It was also evident that HPFRCC is significantly superior to plain concrete with regards to the anchorage of reinforcement within the joint core. A number of comments were made regarding the practicalities of using HPFRCC joint cores in real structures, from which it was concluded that for most structures HPFRCC joint cores are unlikely to be a practical alternative to conventionally reinforced joint cores.