Structural beams are used in bridges, buildings, and homes. Cantilevers are horizontal pieces supported at one end or both ends and unsupported in between. Cantilever deflection is the vertical movement when loads are added. Cantilevers are used in bridges for design or terrain restrictions, and in buildings for open floor plans. Cantilever deflection depends on material, length, and load location. Designers use data tables and factor in safety allowances for maximum expected loads.
Structural beams are used in the construction of bridges, commercial buildings and homes. A cantilever is typically a horizontal piece supported at one end only, or supported at both ends and unsupported in between. Cantilever deflection is the amount of vertical movement that occurs when additional loads are applied to the beam.
Bridges use structural beams to support vehicle and pedestrian loads. Design or terrain restrictions may require beam supports to be placed at one end of the beam or in bridges only at the ends to allow for an open area under the bridge. These cantilevers may be supported on one end for aesthetic or artistic design reasons, or because the ground may not be suitable for the bridge supports at the other end. Drawbridges, which can open and close to allow vessels to pass, often rely on cantilever beam systems to allow them to tilt or open.
Buildings use beams to support floors and transfer loads to vertical supports called columns. Cantilevered beams in buildings create open floor plans with minimal support columns. Single supported cantilever beams are often used for balconies, walkways or extended roof lines.
When a beam is placed in a structure, loads pass horizontally at both ends when supported at the ends, but the beam sags to its center under load. A cantilever supported at one end will bend at the free end as loads are added and by the load of the structure itself. This is the cantilever deflection and it is important to determine the effect of loads prior to construction. Adding structural support from cables or other beams can help reduce deflection and allow for higher acceptable load limits.
The amount of cantilever deflection depends on several factors. Wood, steel, or plastic all have different deflection values under load. The length of the beam will create different static loads, or loads due to weight, and dynamic loads, which are loads caused by the movement of people or vehicles. The location of the load is very important in understanding cantilever deflection, because a load at one point will create different deflection characteristics than a load distributed over the length of the beam.
Designers typically design beams for maximum expected loads and a factor of safety. A bridge will carry different loads depending on traffic and pedestrian factors, such as the time of day. Studies are normally performed for a proposed bridge design to determine the maximum traffic density.
Building design loads are affected by décor, occupancy, and wind conditions. Structural engineers have data tables available for different building floor designs, beam lengths, and materials. Wind data can be determined from historical weather conditions for the area. As the building is subjected to different people or wind loads, the amount of cantilever deflection changes regularly. The design data will include these changes and additional safety allowances.
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