The torsion load placed on it may cause failure, as the truss cannot deal with all of the additional forces. Axial load is one that passes through the centerline of the structural member; all portions of the structural member are equally stressed. An eccentric load is one that is concentrated to one side of the supporting wall or column. The load is straight but stresses only one side of the column. An example of an eccentric load would be the sidewall of a multistory balloon frame construction building.
The floor attachment is on a ribbon board that is attached to the side of the sidewall. This ribbon board may be mortised into the stud or just nailed to the stud.
The floor load will place the wall stud in compression on the load side and in tension on the opposite side. An exterior fire escape is another example of an imposed eccentric load. How the load is transmitted to the ground is of vital importance. While looking at this gravity resistance system, look at the components, and trace the load to the ground.
This will help you determine how structures are built. Understanding fire behavior and heat transfer will also assist in determining how the structure will react. Heat affects building components in various ways. Some components burn and add fuel to the fire; others absorb heat for a time and conduct the heat through the structural component to another location.
Understanding the compression, tension, and shear stresses the structural components have will assist you in determining the reactions that may occur when the structural components are exposed to the heat from a fire. The lower floors of the structure are constructed with steel and masonry materials; the upper stories are lightweight wood-frame construction.
As construction progresses, we will be able to determine if the steel columns and beams will be protected with a fireproofing material to give the steel a fire-resistance rating. Items under tension are resisting the forces trying to make them longer. Heat elongates metal objects; thus, the reaction to heating is manifested by exactly the same force the tensioned object is resisting.
This is thermal expansion; when heated, the atoms that make up the material increase movement. The strength is not in the material to push the wall out but with the elongation. Something has to give; thus, the deformity. For the most part, tensioned members are smaller than compressive members; thus, the mass is not present to absorb the heat transfer. The structural component will elongate or deform.
Simply playing a hose stream on the structural components and cooling them below the reaction temperature will return steel components to near their original strength. Keep in mind that the component will not return to its original shape. The structural steel may not now be shaped to support the structure, but it will be strong. Much has been written about the metal gusset plates or gang nails in wooden truss construction.
The gang-nail plate is also very thin, unable to absorb much heat. The nail plates on the bottom chord are in tension. When heated, they will deform and become unattached from the wood. This, again, is an example of a structural member under tension reacting to heat. Look at wooden trusses involved in fire. Most times, the gang-nail plates on the compression chords are intact and present, although deformed, while the gang-nail plates on the tensioned chords are missing. Members under tension may be the first to fail under fire conditions.
Construction members in shear stress may have various reactions to heat. In the case of the aforementioned concrete anchor, if the bolt is inserted into a lead anchor, heat will cause the lead to weaken and the anchor to pull out. Given a steel anchor in concrete, the steel may swell and become tighter as the concrete absorbs heat and transfers it to the metal anchor. Of course, once the steel reaches a certain threshold, it will itself become weaker. Nails, which resist pulling out because of shear, vary in shear strength.
A long and skinny nail, especially one that is cement coated, will conduct less heat to char wood than a common nail. Shear holds screws in place, offering greater holding power and less damage than nails to the core materials. Many variables exist when determining what will happen to building materials when they are exposed to fire.
We can talk in general terms of buildings, or we can speak in specifics of building or structural components. Much research has been posted on the Internet. When viewing material, look at when and how the experiment was conducted and determine if the results can be replicated. When reviewing material, look to see how the test was performed and to what standard. Very dry wood is not as strong as wood that contains moisture, such as when it is just out of the kiln.
Kiln-dried wood has a range of six to 15 percent, depending on the type of wood and the desired usage. The behavior of hybrid construction or construction that uses combinations of building materials concrete, steel, and wood is very difficult to predict in a fire situation. Many buildings are now built using mathematical formulas and lighter-weight materials.
Technology for energy conservation and for reducing costs using recycled materials and newly developed building materials will challenge the fire service in the future.
What we should be thinking about when walking in a building are the way the structural building components are loaded and how the stress will react under fire conditions. Try to make it a habit to be aware of what is around you, how structures are built, and how the load gets to the ground. Additionally, think in terms of how heat will affect the gravity-resistance system. Brannigan, Francis L..
Building Construction for the Fire Service, 3rd Edition , fifth printing. The National Fire Protection Association, Dunn, Vincent. Fire Engineering, Coleman, John. Tulsa, Okla: Fire Engineering, JAY D. His areas of expertise include incident management, building construction, and fire behavior.
Originally ran in Volume , Issue 6. More Fire Engineering Issue Articles. Fire Engineering Archives. Sign in. Forgot your password? Clarion Events Privacy Policy. Password recovery. Recover your password. Get help. Photos by Paul Dansbach. Latest Fire News and Features. The vertical loads consist of dead load, live load and impact load.
The horizontal loads comprises of wind load and earthquake load. The longitudinal loads i. Contents: Types of Loads on Structures and Buildings 1.
Dead Loads DL 2. Wind loads 4. Snow Loads SL 5. Earthquake Loads EL 6. Other Loads and Effects acting on Structures. No Material Weight 1 Brick Masonry As the name suggests the load acts on the structure due to an earthquake is known as Earthquake load.
Due to the ground movement acceleration, the building moves back and forth which causes the structure to fail. Earthquake loads are specific to the seismic region zone. The Bureau of Indian standards has published the seismic hazard maps for India. Every country has its own set seismic zone. Zone V is the most seismically active region, while zone II is the least. Structures in high seismic activity zones need to be carefully analyzed and designed to withstand the Earthquake loads.
Apart from the above 5 most common loads, there are some other special loads. Hope now you understand the basics of types of loads that are acting on a building or any structure. If it helps you give a heart to this post. We really appreciate it!
He is the author, editor of Civil Planets. Save my name, email, and website in this browser for the next time I comment. Home Earthquake Types of Loads. Table of Content hide. What are Structural Loads? Types of Loads 2. Dead Load.
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