Can we place a Column over Beam mid-span?

Beams:

Top reinforcement in beam is lapped at mid span as the beam does not experience any negative moment at midspan and so lapping is great in that region. In case of bottom reinforcement it is lapped near the ends and again the same concept applies as there will be no positive moment at the ends of the beam.

But if we look at moment frame beams, these beams because of cyclic loading experience both negative and positive moments during earthquake as moment frame is the LFRS of the building resisting earthquakes. All the diaphragm load is dumped on these moment frames which carries the lateral shear.

So in case of moment frames both top and bottom bars are spliced at the center of the beam and sometimes at third the span of the beam so that reinforcement bond slip does not occur at the beam ends which acts as the plastic hinge zone to absorb and dissipate all the earthquake energy.

In case of lap zone in moment frame beams and columns, a higher confinement of stirrups or tie is required so that bar does not buckle and concrete also does not spall as the bond between steel and concrete is weak.

Columns:

Rebars in column should be lapped at around 5 feet from the story. The most important reason behind this is workability.

We know that during lateral forces and because of interstory drifts columns experience maximum moments at the top and bottom of the story. Now we cannot lap the bars into the joint as those are the locations of maximum stresses. So the best possible location is around 5 ft from story height. This way, when the floor below is constructed the workers can easily stand on the floor and work on the column without worrying about the formwork and heights. Thus the construction process is accelerated.

There is one more reason of providing closely spaced ties in the end zones of columns. It is because of these splices the strength of the section gets slightly reduced and the ductility is also reduced. So to increase ductility and column confinement we have to provide smaller spacing of ties.

In case of Moment frames reinforcement should be spliced at the middle height of the column as moment frame is LFRS system and it will experience very high moments. So the splicing is particularly shifted to middle height in moment frames. No matter how high is the story height it should be in the center of the column as it is a region of zero moment.