Study on Mechanical Mode of Frame Column Underpinning Joint

Abstract

An orthogonal experiment of sixteen frame column underpinning joints was introduced, experiment was designed by a normal table of “five-factor and four-level”, five factors referred to ratio of shear-span of moving beam, ratio of underpinning beam stirrup steel bar, underpinning beam longitudinal steel bar parameter, concrete strength, and planted reinforcement, in addition every factor had four experiment datum. Then, the underpinning joint stress mechanism and failure mode was determined, based on the experiment the conclusion was drawn that the ratio of shear-span of moving beam was the key factor to the joint failure mode; and the failure course was divided two stages which were before and after interface punching slip by theoretical analysis, for the phase before interface punching slip a space and plane “tension-bar-arch” mechanical model was presented for the underpinning joint, then mechanic analysis was put into the models, and two series theoretical calculation correlations for this underpinning joint were obtained, by comparison with the test result one model and one formula was choose, this theoretical results were agreement with experiments results.