Q. What is Shock transmission unit in bridges?

Shock transmission unit is fundamentally a device connecting separate structural units. It's characterized by its ability to transmit short-term impact forces between connecting structures while permitting long-term movements between structures.  

If two separate structures are linked together to resist dynamic loads, it's very difficult to connect them structurally with due allowance for long-term movements because of temperature variation and shrinkage effect. Instead, large forces will be produced between the structures. Though with the use of shock transmission unit it can cater for short-term transient loads whereas allowing long-term movements with negligible resistance. It benefits bridge structures by acting as a temporary link between structures to share and transfer transient loads.

Fig. Shock transmission unit.