![]() 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 connected to the other side of the gusset plate through bolts or rivets 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 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 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 joints' 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 steel reinforcement, 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 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. Steel frame has displaced its predecessor, the iron frame, in the early 20th century.
Formwork is molds into which concrete or similar materials are either precast or cast-in-place. In the context of concrete construction, the falsework supports the shuttering molds. In specialty applications formwork may be permanently incorporated into the final structure, adding insulation or helping reinforce the finished structure.
A tied-arch bridge is an arch bridge in which the outward-directed horizontal forces of the arch(es) are borne as tension by a chord tying the arch ends rather than by the ground or the bridge foundations. This strengthened chord may be the deck structure itself or consist of separate, independent tie-rods.
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.
The I-35W Mississippi River bridge was an eight-lane, steel truss arch bridge that carried Interstate 35W across the Mississippi River one-half mile downstream from the Saint Anthony Falls in Minneapolis, Minnesota, United States. The bridge opened in 1967, and was Minnesota's third busiest, carrying 140,000 vehicles daily. After only 39 years in service, it experienced a catastrophic failure during the evening rush hour on August 1, 2007, killing 13 people and injuring 145. The National Transportation Safety Board (NTSB) cited a design flaw as the likely cause of the collapse, noting that an excessively thin gusset plate ripped along a line of rivets. Additional weight on the bridge at the time of failure was also cited by the NTSB as a contributing factor.
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.
Section Beams are made of steel and they have a specific lengths and shapes like I-beam, L, C-channel and I flanged beam. These types of section are usually used in steel structures and it is common to connect them with plates of steel.
The Callender-Hamilton bridge is a modular portable pre-fabricated truss bridge. It is primarily designed for use as permanent civil bridging as well as for emergency bridge replacement and for construction by military engineering units. Assembling a Callender-Hamilton bridge takes much longer than the more familiar Bailey bridge as it is made up of individual lengths of galvanised steel bolted together with galvanised high-strength steel bolts, all of which require torque settings. It is stronger and simpler in design concept than the Bailey bridge.
The Clinton Falls Bridge, also known as the Old Mill Bridge and formally as Bridge L-5573, is a historic steel Pratt through truss bridge that spans the Straight River in Clinton Falls Township, Minnesota. It was listed on the National Register of Historic Places in 1997 as Bridge No. L-5573 for having local significance in the theme of engineering. It was nominated for being an example of early steel truss bridge design in Minnesota.
A bolt is an externally helical threaded fastener that fastens objects with unthreaded holes together. This is done by applying a twisting force (torque) to a matching nut. The bolt has an external male thread requiring a matching nut with a pre-formed female thread. Unlike a screw, which holds objects together by the restricting motion parallel to the axis of the screw via the normal and frictional forces between the screw's external threads and the internal threads in the objects to be fastened, a bolt prevents that linear motion via the frictional and normal forces between the bolt's external threads and the internal threads of the matching nut, which can be tightened by applying a torque which moves the nut linearly along the axis of the bolt and compresses the objects to be fastened.
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.
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.