Investigating the effect of different type of bearing pad on the behavior of reinforced concrete half-joint structure under repeated loads

Four samples of half joints were tested with four types of pads: elastomeric rubber, steel, polytetrafluoroethylene (PTFE), and steel roller. A device is prepared with a horizontally applied load to make these tests. The repeated load pattern is used to investigate the half joint because this type is an essential factor in affecting the behavior of such elements. The PCI code's equations (5.44) and (5.45) are used to estimate the ultimate load of half joint, which gives 313 kN and 181.4 kN for equations (5.44) and (5.45), respectively. The values obtained by using of equation (5.44) were 313 and showed a good agreement with experimental tests result for pad types under tests which were 303, 326, 328.3, and 306.9. While the equation (5.45) can be considered, underestimate. The results show that stress concentration under both steel plate pads and PTFE pads. Meanwhile, the other types (elastomeric rubber and steel roller pads) failed with lesser stress concentration. The first cracks for steel and PTFE pads are more than the elastomeric pads 40% and 140%, respectively, while the steel pad gives the first crack value the same as an elastomeric pad. The ultimate loads gained from using different types of pads show that the sample with PTFE gives the highest maximum load than the steel pads and the steel roller compared with elastomeric pads. Ultimate loads percentage differences of 7.59%, 8.35%, and 1.29% are obtained for Steel plate, PTFE, and Steel Roller, respectively comparing with elastomeric. The ultimate defection for both Elastomeric and Steel Roller pads is almost the same, in the other hand, the steel pad giving more deflection than elastomeric by about 49%, which is due to the local failure happen in this type of pad. The PTFE pad records a deflection about 20% more than elastomeric. The strain at the top and middle bars are investigated using linear variable differential transformers (LVDT). It is obviously can be shown that the strain at the bottom bar changed from compression to tension in a load value between 270-290 kN, which are approaches ultimate load. It may explain the failure of top reinforcement, giving a high value of strain. The bottom strain for the steel pad shows a maximum in comparison to the other pad types. Again this is due to the local failure. Elastomeric pads record the maximum top strain due to the horizontal forces resulting from shape arcing occur in the pad. The Steel roller pad shows a strange behavior curve for top stra