UHPC can help reduce Seismic Forces in multi-storied buildings!

Sir Isaac Newton might not have known about UHPC, but he sure plays on the mind of structural engineers designing buildings for earthquake resistance. The famous equation F = ma simply tells us that more the mass of the structure, more the seismic force experienced by the structure.

UHPC’s density is about the same as reinforced concrete but its superior mechanical properties like high compressive strength, ductile behavior, low creep, and high elastic modulus opens new possibilities in building design. All this should lead to a structure that could have a much lower self-weight as compared to a conventional concrete structure.

No…. I am not suggesting that the whole building should be made from UHPC…that would be outrageously cost-prohibitive but when specifically applied with concrete can be quite advantageous. Two things immediately come to mind:  

1. Hybrid UHPC-Concrete Floor System: Post-tensioned flat slabs are typically 15 percent or so lighter than RC flat slabs. UHPC’s extraordinarily high compressive strength allows more prestressing to be added to a UHPC member and make it sleek. A combination of precast prestressed UHPC members compositely connected to a RC topping slab results in floor systems that can be additionally lighter by 25 to 30 percent as compared to PT slabs not to mention the resulting expedited construction schedule.

2. UHPC Columns: Let us stretch the envelope a bit more. Predominantly gravity loaded columns in high-rise structures can easily use UHPC in the bottom stories to help reduce their size by over 50 percent. Alternatively, there is also the possibility of having hollow-core UHPC columns to further the weight reduction in the structure.

The possibilities are limitless - as far as our imagination can wander but keeping the economics and the structural behavior in mind, one can seriously consider a 30 percent reduction in the overall self-weight of the building structure using UHPC.  This directly results in a 30 percent reduced seismic base shear, which also means a possible reduction in elements of the lateral force resulting system.

Now that is one-way UHPC can mitigate seismic forces in a building structure!