|Tritanium is a substance durable
enough that UFP hand weapons on their highest settings cannot melt it,
producing at best cosmetic damage; it is the primary component of
starship hulls in the 24th (and probably the late 23rd) centuries.
UFP hand weapons can dump out gigajoules of energy on their highest settings. If one gigajoule of energy can vaporize a cubic centimeter of tritanium - i.e., cause cosmetic damage on par with the melt damage seen in "Arsenal of Freedom" - then blasting clear through hulls and corridors requires a petajoule per cubic meter. If the hull of a Constitution class vessel is roughly a meter thick, blasting away 1% of the exterior hull would require ~1.4 gigatons of yield. To cause significant structural damage to a starship whose structure and outer hull are made of tritanium requires exajoule range yields. A meter of hull is sufficient to protect from a gigaton blast twenty meters away.
With shields having a potential capacity of up to hundreds of times the energy of a photon torpedo, the upper limit for shield energy capacity falls at 100 gigatons for a Constitution class; by extension, a GCS should have an 0.5-3 teraton shield capacity. We may note that there are a number of ways of bringing down or destroying shields.