– How come the base of tall buildings don’t pulverize under the weight of the building?

Question

Take for example the Taipei 101 Tower:

– 508.2 meters high
– Weighs 700,000 tons
– Ground floor is 57×63.5 meters, which is 3619.5 m²
– That means an area of 3619.5m² has to hold up 700.000 tons, which is ~193 tons per m² which is 193.000 kilograms per m²

I don’t know but 193.000 kilograms feels like an unbearable crushing all-pulverizing weight to me.

Obviously it works since the Taipei 101 tower and other huge buildings exist, but intuitively I don’t understand how the bases of large and tall buildings don’t instantly pulverize under the weight of everything above it.

In: 1790

Answer 1

The concrete has excellent load bearing capacity. They have used high performance concrete with 68 MPa strength in construction of load bearing parts of Taipei 101 tower.

68 MPa is significantly stronger than everyday concrete (which is usually in the 20-40 MPa range) but it is still quite achievable with standard cement types and carefully selected, but not exotic aggregates.

68 MPa is more than 7000 tons/m2 so in theory they could get away with using only 100 meter square of the 3620 meterquare ground floor for support. Obviously they are various other loads (most notably wind and earthquakes) and safety factors, so they should use a lot more than 100 m2.

Concrete is essentially aggregates glued with cement paste. Both aggregates and cement paste itself can achieve about 400 MPa strength separately. But concrete can only be as strong as its weakest link (aggregates, cement, or the interface between them) and the weakest link is the binding force between cement and aggregates. In practice 110-120 MPa is the limit.