 Gusset plate used on the I-35W Mississippi River bridge, which collapsed in 2007 | |
| Material | steel, copper, or aluminum |
|---|---|
| Uses | Bridges, buildings, and other structures |
| Connection methods | Welding, bolts, or rivets |
Gusset plate is a plate for connecting beams and girders to columns. A gusset plate can be fastened to a permanent member either by bolts, rivets or welding or a combination of the three. [1] They are used in bridges and buildings, as well as other structures. [1]
Gusset plates are usually either made from cold-rolled or galvanized steel, based upon their use. Galvanized steel offers more protection from rust, so this is usually used when the gusset plate is exposed to the elements. The gusset plate is usually painted to match nearby steel and fixtures and to give it an extra layer of protection. [2]
Occasionally gusset plates are made from copper or aluminum, but only with small structures that do not require much support. The copper and aluminum gusset plates also provide a more attractive finish for exposed structures. [2]
Gusset plates are used for various structures. Gusset plates are used to connect beams and columns together or to connect truss members. They can be either the only way of connecting the beam and columns or they can be used with bolts and welds.
Gusset plates are therefore used in most metal weight-bearing structures, but the material and size of the gusset plate varies based on the structure. Bridges usually require thick sheets of steel for their gusset plates, but trusses sometimes only require small sheets of aluminium for their gusset plate.
The size and strength of the gusset plate depends on size and the function of the structure. The larger the force on the connecting members, the larger the size of the gusset plate. Gusset plates provide an easy way to retrofit structures that can no longer safely support the applied loads.
Gusset plates can be made into a variety of shapes and sizes and from a range of materials.
Gusset plates are usually square or rectangular, but can be triangular or made into a customized shape to fit the joint. The shape of each plate is designed so that welding or bolts can be applied to different edges of the plate. [2]
A gusset plate can form the entire connection or it can be used in conjunction with bolts or welds. [2]
There are several prominent connection types that include gusset plates, which include KT gusset plates, uniform force bracing connections, and bolt groups.
A KT gusset plate connects several members together through one gusset plate. The gusset plate is welded to a beam, and then two or three columns, beams, or truss chord are connect to the other side of the gusset plate through bolts or welds. [3]
A uniform force bracing connection connects a beam, column, and one other member. The gusset plate is bolted to the column and welded to the beam. The connection of the last remaining member can be through either bolts or welds. [3]
The most notable bridge failure due to gusset plates is the collapse of I-35W Mississippi River bridge in Minneapolis, Minnesota on August 1, 2007. Investigators found that the bridge had 16 under-designed gusset plates that all fractured and ripped, and that the remaining gusset plates were properly designed and remained intact.
The 16 under-designed plates that failed were found to be only a 1/2 inch thick when they should have been thicker to be in accordance with the American Association of State Highway and Transportation Officials (AASHTO) “Standard Specifications for Highway Bridges”, 1961. [4] The National Transportation Safety Board attributed most of the cause of the failure of the bridge to this flaw. [5]
In addition to the gusset plates being under-designed for their original loading, there were other factors that led to the demise:
The current Green Bank Telescope at Green Bank, West Virginia, completed in 2000, was built following the collapse of the previous Green Bank telescope, a 90.44 m paraboloid erected in 1962. The previous telescope collapsed on 15 November 1988 due to the sudden loss of a gusset plate in the box girder assembly, which was a key component for the structural integrity of the telescope. [7] Most radio and telecommunications dishes have gusset plates somewhere in their design, some designs more than others. As a general maintenance practice, these plates should be checked every two or three years, depending on the size of the dish.
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of human-made structures. Structural engineers also must understand and calculate the stability, strength, rigidity and earthquake-susceptibility of built structures for buildings and nonbuilding structures. The structural designs are integrated with those of other designers such as architects and building services engineer and often supervise the construction of projects by contractors on site. They can also be involved in the design of machinery, medical equipment, and vehicles where structural integrity affects functioning and safety. See glossary of structural engineering.
Rebar, known when massed as reinforcing steel or reinforcement steel, is a steel bar used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. Concrete is strong under compression, but has low tensile strength. Rebar significantly increases the tensile strength of the structure. Rebar's surface features a continuous series of ribs, lugs or indentations to promote a better bond with the concrete and reduce the risk of slippage.
A truss is an assembly of members such as beams, connected by nodes, that creates a rigid structure.
Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged. Prior to the introduction of modern seismic codes in the late 1960s for developed countries and late 1970s for many other parts of the world, many structures were designed without adequate detailing and reinforcement for seismic protection. In view of the imminent problem, various research work has been carried out. State-of-the-art technical guidelines for seismic assessment, retrofit and rehabilitation have been published around the world – such as the ASCE-SEI 41 and the New Zealand Society for Earthquake Engineering (NZSEE)'s guidelines. These codes must be regularly updated; the 1994 Northridge earthquake brought to light the brittleness of welded steel frames, for example.
A plate girder bridge is a bridge supported by two or more plate girders.
Steel frame is a building technique with a "skeleton frame" of vertical steel columns and horizontal I-beams, constructed in a rectangular grid to support the floors, roof and walls of a building which are all attached to the frame. The development of this technique made the construction of the skyscraper possible.
A girder is a beam used in construction. It is the main horizontal support of a structure which supports smaller beams. Girders often have an I-beam cross section composed of two load-bearing flanges separated by a stabilizing web, but may also have a box shape, Z shape, or other forms. Girders are commonly used to build bridges.
A tied-arch bridge is an arch bridge in which the outward horizontal forces of the arch(es) caused by tension at the arch ends to a foundation are countered by equal tension of its own gravity plus any element of the total deck structure such great arch(es) support. The arch(es) have strengthened chord(s) that run to a strong part of the deck structure or to independent tie-rods below the arch ends.
A girder bridge is a bridge that uses girders as the means of supporting its deck. The two most common types of modern steel girder bridges are plate and box.
A box girder or tubular girder is a girder that forms an enclosed tube with multiple walls, as opposed to an I- or H-beam. Originally constructed of wrought iron joined by riveting, they are now made of rolled or welded steel, aluminium extrusions or prestressed concrete.
A lattice girder is a truss girder where the load is carried by a web of latticed metal.
Steel Design, or more specifically, Structural Steel Design, is an area of structural engineering used to design steel structures. These structures include schools, houses, bridges, commercial centers, tall buildings, warehouses, aircraft, ships and stadiums. The design and use of steel frames are commonly employed in the design of steel structures. More advanced structures include steel plates and shells.
A Howe truss is a truss bridge consisting of chords, verticals, and diagonals whose vertical members are in tension and whose diagonal members are in compression. The Howe truss was invented by William Howe in 1840, and was widely used as a bridge in the mid to late 1800s.
The Mabey Logistic Support Bridge is a portable pre-fabricated truss bridge, designed for use by military engineering units to upgrade routes for heavier traffic, replace civilian bridges damaged by enemy action or floods etc., replace assault and general support bridges and to provide a long span floating bridge capability. The bridge is a variant of the Mabey Compact 200 bridge, with alterations made to suit the military user as well as a ramp system to provide ground clearance to civilian and military vehicles.
A steel plate shear wall (SPSW) consists of steel infill plates bounded by boundary elements.
Progressive collapse is the process where a primary structural element fails, resulting in the failure of adjoining structural elements, which in turn causes further structural failure.
A buckling-restrained brace (BRB) is a structural brace in a building, designed to allow the building to withstand cyclical lateral loadings, typically earthquake-induced loading. It consists of a slender steel core, a concrete casing designed to continuously support the core and prevent buckling under axial compression, and an interface region that prevents undesired interactions between the two. Braced frames that use BRBs – known as buckling-restrained braced frames, or BRBFs – have significant advantages over typical braced frames.
Hybrid masonry is a new type of building system that uses engineered, reinforced masonry to brace frame structures. Typically, hybrid masonry is implemented with concrete masonry panels used to brace steel frame structures. The basic concept is to attach a reinforced concrete masonry panel to a structural steel frame such that some combination of gravity forces, story shears and overturning moments can be transferred to the masonry. The structural engineer can choose from three different types of hybrid masonry and two different reinforcement anchorage types. In conventional steel frame building systems, the vertical force resisting steel frame system is supported in the lateral direction by steel bracing or an equivalent system. When the architectural plans call for concrete masonry walls to be placed within the frame, extra labor is required to ensure the masonry fits around the steel frame. Usually, this placement does not take advantage of the structural properties of the masonry panels. In hybrid masonry, the masonry panels take the place of conventional steel bracing, utilizing the structural properties of reinforced concrete masonry walls.
Structural integrity and failure is an aspect of engineering that deals with the ability of a structure to support a designed structural load without breaking and includes the study of past structural failures in order to prevent failures in future designs.
On May 23, 2013, at approximately 7:00 pm PDT, a span of the bridge carrying Interstate 5 over the Skagit River in the U.S. state of Washington collapsed. Three people in two different vehicles fell into the river below and were rescued by boat, escaping serious injury. The cause of the catastrophic failure was determined to be an oversize load striking several of the bridge's overhead support beams, leading to an immediate collapse of the northernmost span.