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| Structural Engineering involves the analysing of building structures, which is to determine loads applied to buildings. Once the loads are computed, they are analyzed using mathematical equations which have been developed over-time. These equations are based upon studies of the strength of materials and shapes. These building materials have different coefficients of expansion, modulus of elasticity and other charateristics which affect their ability to perform as designed. |
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Applied Structural Loads:
How to
Size Joists,
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Size Footings (Click to Enter)
Live Loads = People, Furniture, etc. Dead Loads = Building Structure and Components. Windloads = Loads produced by Hurricanes, Tornados or other High Winds. Rain Loads = Rain Water Stacking, Mainly due to Winds. Earthquake Loads = Seismic (earth moving) Snow Loads = Snow accumulation. |
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| Live Loads: |
Live Loads are all of the moveable loads placed upon the building or structure, such as, People, Furniture and any other non-permanent or non-fixed components. These loads are downward (gravity) loads. The Codes usually have a table of values and identify what are the Live Loads which are required to be considered when designing a building.
Examples of Minimum Design Live Loads Specified in the Southern Standard Building Code are: (These loads are in Table 1604.1 and are the Minimum Uniformly Distributed Love Loads in pounds per square feet (psf)). The Southern Standard Building Code is used in the South East region of the U.S. Apartments - Residential - Multifamily Houses: Private Apartments = 40 psf Public Rooms = 100 psf Corridors = 80 psf |
| Dead Loads: |
Dead Loads are all of the loads that make up the building or structure, such as, beams, columns, walls, trusses and any other permanent or fixed components. These loads are downward (gravity) loads. These Dead Loads are the actual weight of the building material or component. The Codes usually have a table of values and identify what are acceptable Dead Load values for building materials, if you do not know the building material weight.
Examples of Minimum acceptable building material Dead Load are shown in Appendix A of the Southern Standard Building Code: (These loads are shown in pounds per square feet (psf)). The Southern Standard Building Code is used in the South East region of the U.S. Ceilings: Acoustical Fiber Tile = 1 psf Plaster on Wood = 8 psf Mechanical Duct Allowance = 4 psf Other materials are shown and may be computed in weight per inch of thickness per square foot. |
| Windloads: |
Windloads are loads produced by wind pressures. These loads will be either added or subtracted from the total load analysis. Windloads (Tornado and Earthquake loads) need to be given extra consideration, since they are usually the most destructive of all of the loads applied to a building. They can occur when least expected.
The Building Codes have created contour maps of the United States which define zones of wind speeds ranging from a low of 70 mph to a high of 110 mph. This map with the wind speeds can be found in the Southern Standard Building Code, in Figure 1606 (note: Florida has 2 Building Codes, one which covers South Florida and the Southern Standard Building Code which covers the majority of the rest of the State of Florida). If you look at the map, you will see that the highest wind speeds are along the shore line of the south and east coast of the United States (this map applies to both Codes in Florida). Due to the complexity of windload design we will only be able to provide a detailed set of calculation per ASCE-7. (See Sample Wind Load Calculations) The Applied Wind Loads are either positive (pushing against the wall) or negative (pulling away from the wall). The change in pressure must be considered since the wind changes direction as it passes over a given location. Wind passing across a building is similar to that of an airplane wing. Wind passing over the top of the airplane wing causes uplift (pulling up on the wing), this is the negative pressure area and the opposite side would then be the positive pressure side. In building design the most common wind pressures studied are those caused by hurricanes and tornados. The Building Codes specify that windload analysis must be performed on all building structures. To perform windload analysis, the Building Codes allow various methods of determining the wind pressures. These wind pressures are converted to pounds per square feet (psf) for both, positive or negative loads. One of the methods of providing the windload calculations, is with the procedures established by the American Society of Civil Engineers (ASCE-7) . The ASCE-7 procedure is accepted by Building Departments. Usually Energy Calculations done for commercial buildings require that the calculations be signed and sealed by a Professional Engineer or Architect. For residences, Florida allows the use of prescriptive measures. This means that you may construct a residence using the components and fasteners which are specified in the State of Florida, Standard for Hurricane Resistant Residential Construction manual. These components and procedures for constructing a residence have been developed for a wide range of configeration. Using the manual and procedures omit the need of having an Engineer or Architect certify the design. However, if there are conditions that are out of the ordinary, it will still be necessary to obtain the services of an Engineer or Architect (this will usually be determined by the Building Department Official). The Standard for Hurricane Resistant Residential Construction manual can be obtained from the Department of Community Affairs in Tallahassee, Florida. It is imperative that you contact your local Building Department, if you plan to build a residence or addition. Remember, the Building Codes are designed to protect the Health, Safety and Welfare of the Public, this means you. "ALWAYS CHECK WITH YOUR LOCAL BUILDING DEPARTMENT BEFORE YOU GET PLANS DRAWN OR YOU START CONSTRUCTION ON ANY BUILDING". Once the windload calculation are done for a building, the engineer will use the information to design the walls, roof, beams and other building components, such as, the tie-downs, straps and other attachment components. Many building component manufacturers provide booklets that contain their attachment components. These components can be straps, clips, top and bottom post column connectors, etc. Listed in the booklet are the size and description of the connectors, number of nails needed, component identification number, the shear force capacity, the tension capacity and other pertinant information. |
| Rain Loads: |
Rain Loads are very important and are often ignored when designing buildings. Rain Loads are often the cause of roofs failing. It is important to consider Rain Loads, especially for Flat Roofs where water may possibly accumulate. This is particularly true when roofs have parapet walls, or where two buildings abutt and one is higher than another, and water cannot discharge rapidly. This water stacking should be of major concern to the designer, since water weighs more per volume than Snow. If you add the Wind Load to the Water Load, then this can become a serious problem. |
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Earthquake Loads:
(Seismic) |
Since our offices are located in Florida we have not addressed the Earthquake portion of the Codes. However, similar to the Wind Loads, there are contour maps in the Building Codes identifying the seismic regions and peak acceleration coefficients.
If you live in a Earthquake prone region, then contact you Building Department and find out what are their design requirements or refer to the Code. |
| Snow Loads: |
Since our offices are located in Florida we have not addressed the Snow Load portion of the Codes. (see Rain Loads above) If you live in a Snow Load prone region, then contact you Building Department and find out what are their design requirements or refer to the Code. |