In reinforced concrete columns design, P-M interaction diagram is used as axial load control and column bending without taking into account the effect of lateral reinforcement bars. Design principles that ignore the effect of reinforcement bars will result in low value of actual axial capacity of column. This paper presents the effect of lateral reinforcement with a case study of square-sectional columns on high-strength concrete. The equation of unconfined concrete strength enhancement is based on Mander, Legeron, Imran, Antonius and Muguruma models. The reviewed parameters include compressive strength of concrete, reinforcement configuration, and spacings of confinement. The result of the analysis is a comparison of P-M diagram based on confinement models. It shows that confinement significantly influences axial capacity of column, yet it has a certain collapse point at point P = 0 in all models. This is caused by longitudinal reinforcement system. Configuration of reinforcement, spacing and confinement models greatly affects the collapse behavior of column, whether the collapse is classified as compressive collapse or tensile collapse based on the P-M diagram.

The splice length of the distribution depends on the concrete stress with reinforcement, generally the bond stress is tested by pull out testing where pull out testing can provide a good comparison between the efficiency of the attachment of various types of reinforcement surfaces. However, the bending behavior of the beam is very different from the pure tensile pull out test. This study presents the effects of variations of lap splice (30db, and 40db) in the area of beam pull. The first test object was a beam BN - 0 (non splice length) which was a normal beam. The second test object was a beam BN - 30db with the splices length(ld) of 480 mm and the third test object was a 40db beam with the splice length (ld) of 640 mm.  The test used a pure bending test method with loading of Two Point Loads on a simple support beam. The results gained from this study obtained flexural capacity in BN-0 (non lap splices) of 115.15 kN, flexural capacity of BN - 30db of 90.484 kN, and beam flexural capacity of BN-40db of 124.848 kN. The displacement ductility at BN-30db decreased 35% to BN-0 and displacement ductility at BN-40db increased 48% to BN-0, the bond strength attached to BN-40db increased 2.92% to BN-30db. The splice length (ld) 40db was able to develop the ability to achieve yield stress loads and the spread of crack concentration around the joints.