The effects of casting position and bar shape on the lap length of plain bars in concrete

Eighteen splice specimens were tested under four-point loading as part of a larger experimental investigation to study the behaviour of lap spliced plain steel bars in reinforced concrete specimens. Three of the specimens were instrumented with strain gauges adhered to the reinforcement and the concrete side face. Three lap splice lengths, two bar sizes for square bars, and one bar size for round bars were investigated. The principal reinforcement was either cast in the bottom or top position. The results of maximum loads, crack patterns, load versus deflection behaviour, and deflected profiles are presented for all specimens. The analysis of specimens with strain gauge instrumentation is also presented, and includes results of strain compatibility, bond stress distribution, and flexural section analysis. All specimens failed by bond, caused by a sudden pullout of the reinforcement within the splice region. An equivalent round diameter based upon the cross-section area of the square bars allowed for a single predictive equation between the maximum normalized load as a function of splice length, casting position and bar size. A top cast factor of 0.4 and 0.6 captures the reduction in the maximum normalized load for specimens cast with round and square bars, respectively, in the top position. The CEB-FIP Model Code (1993) predictive equations are reasonably conservative in capturing the behaviour of specimens reinforced with round bars cast in the bottom position, and square bars with side dimension of 25 mm cast in the bottom position. However, the CEB-FIP Model Code (1993) predictive equation is unconservative when predicting the behaviour of specimens reinforced with either square or round bars cast in the top position. On the other hand, the draft CEB-FIP Model Code (2010) provisions showed an overly conservative prediction for all specimens reinforced with either round or square bars cast in the top or bottom position. Instrumented specimens showed that strain compatibility between the longitudinal reinforcement and the surrounding concrete did not exist for much of the loading range due to bond loss. The evaluation of the neutral axis location within the shear span showed that shear is first transferred by beam action, followed by arch action. The use of three strain gauges adhered to the concrete side face provided flexural moments similar to that predicted theoretically