Updated: Jan 11, 2021
There are different kinds of lifts availbale these days. It varies from normal conventional lifts to vacuum lifts and hydraulic lifts used in duplexes.This blog is a result of a doubt posed by one of the students of our civil engineering software courses
We all know that lifts are needed in buildings for people to move vertically between floors. Also many times,when the number of floors are higher,people will find it difficult to move materials too and this requirement needs to be taken care by lifts.
There are different kinds of lifts.We will quickly discuss the main types though the main purpose of this blog is to discuss the structural requirement of conventional lfts. The conventional lift type is explained in the last section and a video is also provided.
A better understanding of available lift types will allow young civil and structural engineers to discuss the requirement with other stake holders like Architects and MEP consultants. This knowledge will help engineers to appreciate the supporting mechanism needed.
Hydraulic lifts uses a pump to push oil in to a cylinder which pushes a piston which inturn pushes the lift car up. To come down, a valve opens and oil is allowed to flow back in to a reservoir using the gravitational force of the lift car.
At floor levels, the lift pump is turneded off and the lift car sits on top of the piston, held in position by the oil which is trapped inside the cylinder.
There are mainly 2 types of hydraulic lifts viz. holed and hole less.This blog is not meant to discuss the difference but to focus on the structural requirements.The holed hydraulic lift is generally conventional and will need a lift pit.The unholed ones do not need a deep pit and is floor mounted. In both cases,the load is transfered at the bottom of the piston.There are models with and with out machine rooms. Generally used in very low rise buildings and individual duplex kind of homes.
It uses air to suck the lift car up.These lifts are powered by turbine motors positioned at the top.The motors sucks the air from the cylinder. To come down,the air pressure is adjusted electronically to restore the pressure gently and gradually so that the gravity decent is smooth and safe.
Vacuum lifts are very light and is floor mounted.The total weight would be around 500kg to 600kg which will not need a lot of special attention.
There is no need of lift pit or a machine room. Vacuum lifts are suitable for duplex homes.It can be easily installed with in a day at site.Very much suitable for even home renovation when an additional floor is added. Instead of creating larger openings for stairs, a vacuum lift can easily help achieve the requirement with minimal disturbance of space,time and inconvinience.
Conventional lifts are still needed when the number of floors are more.Most of the conventional lifts will need a lift pit at the bottom and a lift machine room at the top. We will discuss these points in detail.
Lift pit : The lift car moves in the lift shaft and tsome part of he mechanical systems of the lift is housed under the lift car. As you reach the lowest level, this needs a space and hence we have to provide a pit.This pit should be preferably in RCC and water proof.You need to provide special attention in its design and construction. A leaking pit can create a lot of issues to lifts electrical and mechanical systems.
Its generally a concrete box of 1500 to 1750 depth (based on the type and brand of the lift)
All a structural engineer need to do is to ensure it is designed for the lateral earth pressure as the box is under the ground.Also ensure proper detailing and construction with water proofing to ensure water tightness. Other than this, there is no much load on the lift pit base.
Please see the video which has more information regarding these points which will help you understand better if you are an entry level civil or structural engineer.
Lift Machine Room : A lift machine room houses most of the electrical and mechanical systems of the lift and also is the point where we access the lift for any maintenance.Some type of lifts (even conventional) will not need a machine room.However most of the ones used in midrise buildings and high risers will need a machine room. It is very important to co-ordinate this with architects and services engineers so that all the supporting and scheme requirement can be captured in the structural design. More details including the loading is explained in the video above.
Civil and structural engineers should have a basic idea of services requirements in a building structure so that they can take suitable action to ensure accurate considerations during design and construction. These practical project requirements are rarely covered in the normal university education or in any civil engineering classes online,unless it is structured to cover these gaps.