expansion joints

huangyhg

expansion joints
an expansion joint is introduced when the internal forces of a building due to expansion become too great.  forces perpendicular to the joint are no longer possible while vertical forces and forces parallel to the joint are still possible.  it is also possible to divide the two parts totally, not allowing any forces between the two parts. essentaill you have to buildings next to each other.  i was just wondering if there are any preferences?  if so, in which conditions and what are the advantages and disadvantages of the two possibilities?   
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because concrete shrinks it is seldom necesary to provide a joint for expansion alone. more often you will provide a shrinkage control joint and then the gap that opens due to shrinkage will provide relief for later expansion.
i would normally dowel floor joints to ensure the two sides stay in alignment and prevent a step developing.
i would probably dowel most joints by default to allow shear transfer and structural continuity; eg locate the joint at a point of contraflexure.
kindly make sure to allow a slip joint developing in the dowels
in a steel building structure, the most common expansion joint i know of is to do exactly as you say -- create two rows of columns side by side, thus creating two separate buildings.
daveatkins