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What Is a Dead Load?

Because hospital beds are designed to be moved instead of bolted down, they are not a part of a hospital's dead load.
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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 30 August 2014
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A dead load is the constant weight of a structure, including the structure itself, along with fixtures intended to be permanent. When structures are designed, the architect must make dead load calculations to ensure that the structure can support itself. In addition, the weight of variable live loads that change or move over the life of the structure must also be considered. Failure to account properly for the loads a structure will endure can result in collapses and other problems.

Calculating a dead load can be difficult because the final weight of a structure may not be known until it is completed. Architects and engineers use standardized information and estimates about known building materials to calculate as closely as possible. Design software often includes features that are designed to assist with estimating dead loads, allowing people to input known specifications and returning values. It is important to be aware that adjustments made to accommodate the dead load cause it to change. For example, if an engineer determines that a bridge needs bigger girders, this will add to the load.

The dead load does not change over the life of the structure. It neither increases nor decreases and does not shift or move over time. By contrast, live loads are flexible and they will change over time. They also impact structures in different ways, in addition to weighing down the structure, they also strain it as they move around. Cars moving across a bridge are an example of a live load.

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Anything that is permanently affixed to a structure is part of the dead load. In a structure like a hospital, for example, the dead load would include the building itself, along with medical imaging devices that are bolted down or otherwise fixed, fixed cabinetry, and similar objects. By contrast, the hospital beds, portable medical equipment, and other movable objects in the hospital would be part of the live load, as would personnel, patients, and visitors.

Structural design requires developing buildings that are strong and flexible enough to handle the combined dead and live loads. Buildings are usually required to exceed estimated capacities to reduce the risk of errors. Engineers must also consider sources of stress, like high wind and earthquakes that can also generate a load and lead to compromises to the structural integrity. In the case of older structures not designed with these issues in mind, retrofitting may be performed to address design shortcomings and make the structures safe for modern use.

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jonrss
Post 3

Here is a question for the engineers and architects out there. How do you calculate the load that the environment places on a structure and is this considered a dead load or a live load?

Here is what I mean. Say you have a bridge. It is going to get hit by a certain wind load though its entire life. In the event of a heavy storm this could be significant. If you have a tall building it will also get hit with wind and its rood will collects rain and snow. All of these factors place a strain on a structure that engineers must have to account for. How do they do this, how can you predict the wind? I'm really hoping someone can pick this question up because it really baffles me.

ZsaZsa56
Post 2

I have worked as an engineer for a number of years and I can tell you how valuable dead load calculators are.

This is still a relatively new technology. We didn't have anything like this until computers came along and even then the calculators didn't get really accurate and useful until about 10 years ago. They have taken a previously labor intensive and extremely tedious job and made them into pretty quick work. Just another example of how computers have revolutionized science in the last 30 years.

chivebasil
Post 1

This article reminds me of a story I heard about as a kid that has always stuck in my mind for some reason. In Kansas City where I grew up there is a huge mansion on top of a hill that was owned by a lumber magnate.

According to my dad, this rich man insisted on having a swimming pool built on the third floor of his house in a room made entirely of windows. His big dream was to be able to swim and look out and down on the city.

But apparently the architects and engineers made a miscalculation and when the pool was filled for the first time it broke away and crashed all the way through the center of the house. No one was hurt but obviously the house was trashed.

That story always makes me giggle just because its nice when you hear about a super rich person getting some retribution for all their silly decisions.

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