Loads in High Rise Buildings
The design of buildings revolves around forces. Most common forces or loads applicable for high-rise buildings are categorized into two types.
- Gravity Loads
- lateral Loads
Gravity is for all loads that being applied in the direction of earth gravitational forces or simply vertically.
This includes dead load and live load, the majority of the gravity load is applied on the floor system, which transfers the load to columns and walls and eventually to the foundation system.
The magnitude of gravity loads has a direct effect on the floor system design which must have sufficient strength unlimited deflection and vibration at the same time.
There are many different types of floor systems used in high-rise buildings such as reinforced or post-tensioning concrete slabs or composite of steel and concrete deck.
The higher gravity load will produce more vertical displacement or deflection on the floor.
Deflection is mainly a serviceability condition and is limited to ensure comfortability for occupants.
There are two kinds of load
- Dead load
- Live load
The dead load itself has two components called self-weight and superimposed dead.
But why they call it dead well because it is going to remain constant during the structure lifetime and most probably not changed.
What is self-weight is simply the building frame material weight including beams floors columns walls or braces and is usually the largest component among other gravity loads.
Self-weight loads are calculated directly from the volume of materials proposed for the design.
Most common materials using high-rise towers are mainly concrete reinforcement and steel, while is steel has a higher density compared to concrete, it is a much stronger material and that makes sections made with the steel is smaller which results in a lighter building.
The biggest contributor to self-weight is usually the floor system which covers a large area of each s story and that is why a lighter floor system is preferable.
But there are more prone to vibration which is checked during the design process.
Self-weight loads can be calculated automatically by most design programs based on the member sizes that user has selected in the computer model.
Then we have superimposed them, which is to cover the floor finishes such as tiles office raised floors, partitions fall ceilings and mechanical pipes, or basically anything that is not a structural and will remain permanently.
It can also be the cladding load on the perimeter of the structure to represent the facade of the tower the value of the superimposed dead load is calculated based on the architectural details.
These loads are in the form of load value per square meter or square feet and will be written on the drawing so the owner of the building can access it in case of structural renovations or new requirements from tenants.
As it sounds live load doesn’t sound very depressing.
So unlike dead loads live loads are to account for things that can move temporarily.
This can be humans furniture storage cars or even snow, the amount of live load is usually taken from the standard or codes as engineers call it and are based on the intended usage.
For instance, the American code requires that private rooms in hotels or in multi-family houses to be designed for about forty pounds per square feet or 200 kilogram-force per square meters.
Like superimposed dead load live loads will be written on drawings called loading plans.
Something interesting to mention since it is unlikely to have a building with all floors and his face is filled with near the capacity live load at the same time, design codes allow engineers to reduce the live load by percentage when designing various elements such as columns or walls.
Now that the gravity loads are determined to engineer can focus on the lateral loads which we will cover in another post.