Gusset plate
Encyclopedia
Gusset plates are thick sheets of steel that are used to connect beams
and girder
s to columns or to connect truss
members . A gusset plate can be fastened to a permanent member either by bolts, rivet
s or welding
or a combination of the three . Gusset plates not only serve as a method of joining steel members together but they also strengthen the joint . They can be used in bridge
s and building
s along with other structures
.
On August 1, 2007, the I-35W Mississippi River Bridge failed due to the improper designing of the gusset plates. The gusset plates that failed were found to be only a 1/2 inch thick rather than a larger size appropriate to the application; with an increase in loading due to construction projects
over the years, the gusset plates became even more inadequate . The National Transportation Safety Board
attributed most of the cause of the failure of the bridge to the inadequacy of the gusset plates .
Materials=
Gusset plates are usually either made from cold rolled or galvanized steel based upon its use. Galvanized steel offers more protection from rust
, so when the gusset plate is outside galvanized steel is usually used. The gusset plate is usually painted to match nearby steel and fixtures to give it an added layer of protection.
Occasionally gusset plates will be made from copper or aluminum, but only with small structures that don't require much support. The copper and aluminum gusset plates also provide a more attractive finish for exposed structures.
Uses=
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 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 aluminum 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.
Design Considerations=
Gusset plates can be made into a variety of shape
s and sizes from a range of material
s. These calculations are made based upon the forces and loads applied to the gusset plate through the nearby steel components. A gusset plate can be either the only connection method or it can be used in with bolts or welds .
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 applied to different edges
of the plate.
There are several different prominent connection types that include gusset plates which include KT gusset plate, uniform force bracing connection, and bolt group.
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 .
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 .
Notable Bridge Failures=
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 that the remaining gusset plates were properly designed and remained intact. The 16 under-designed plates were all about a half inch thick when they should have been larger sizes to be in accordance with the American Association of State Highway Officials (AASHO) “Standard Specifications for Highway Bridges,” 1961 .
In addition to the gusset plates being under-designed for their original loading, there were other factors that led to the demise of the gusset plates.
Beam (structure)
A beam is a horizontal structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span and external reactions to these loads is called a bending moment.- Overview...
and girder
Girder
A girder is a support beam used in construction. Girders often have an I-beam cross section for strength, but may also have a box shape, Z shape or other forms. Girder is the term used to denote the main horizontal support of a structure which supports smaller beams...
s to columns or to connect truss
Truss
In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...
members . A gusset plate can be fastened to a permanent member either by bolts, rivet
Rivet
A rivet is a permanent mechanical fastener. Before being installed a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail. On installation the rivet is placed in a punched or pre-drilled hole, and the tail is upset, or bucked A rivet...
s or welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
or a combination of the three . Gusset plates not only serve as a method of joining steel members together but they also strengthen the joint . They can be used in bridge
Bridge
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...
s and building
Building
In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...
s along with other structures
Nonbuilding structure
Nonbuilding structures, also referred to simply as structures, are those not designed for continuous human occupancy. The term is used by architects and structural engineers to distinctly identify structures that are not buildings....
.
On August 1, 2007, the I-35W Mississippi River Bridge failed due to the improper designing of the gusset plates. The gusset plates that failed were found to be only a 1/2 inch thick rather than a larger size appropriate to the application; with an increase in loading due to construction projects
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...
over the years, the gusset plates became even more inadequate . The National Transportation Safety Board
National Transportation Safety Board
The National Transportation Safety Board is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and incidents, certain types of highway crashes, ship and marine...
attributed most of the cause of the failure of the bridge to the inadequacy of the gusset plates .
Materials=
Gusset plates are usually either made from cold rolled or galvanized steel based upon its use. Galvanized steel offers more protection from rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...
, so when the gusset plate is outside galvanized steel is usually used. The gusset plate is usually painted to match nearby steel and fixtures to give it an added layer of protection.
Occasionally gusset plates will be made from copper or aluminum, but only with small structures that don't require much support. The copper and aluminum gusset plates also provide a more attractive finish for exposed structures.
Uses=
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 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 aluminum 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.
Design Considerations=
Gusset plates can be made into a variety of shape
Shape
The shape of an object located in some space is a geometrical description of the part of that space occupied by the object, as determined by its external boundary – abstracting from location and orientation in space, size, and other properties such as colour, content, and material...
s and sizes from a range of material
Material
Material is anything made of matter, constituted of one or more substances. Wood, cement, hydrogen, air and water are all examples of materials. Sometimes the term "material" is used more narrowly to refer to substances or components with certain physical properties that are used as inputs to...
s. These calculations are made based upon the forces and loads applied to the gusset plate through the nearby steel components. A gusset plate can be either the only connection method or it can be used in with bolts or welds .
Gusset plates are usually square
Square (geometry)
In geometry, a square is a regular quadrilateral. This means that it has four equal sides and four equal angles...
or rectangular
Rectangle
In Euclidean plane geometry, a rectangle is any quadrilateral with four right angles. The term "oblong" is occasionally used to refer to a non-square rectangle...
, but can be triangular
Triangle
A triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments. A triangle with vertices A, B, and C is denoted ....
or made into a customized shape to fit the joint. The shape of each plate is designed so that welding or bolts can applied to different edges
Edge (geometry)
In geometry, an edge is a one-dimensional line segment joining two adjacent zero-dimensional vertices in a polygon. Thus applied, an edge is a connector for a one-dimensional line segment and two zero-dimensional objects....
of the plate.
There are several different prominent connection types that include gusset plates which include KT gusset plate, uniform force bracing connection, and bolt group.
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 .
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 .
Notable Bridge Failures=
In addition to the gusset plates being under-designed for their original loading, there were other factors that led to the demise of the gusset plates.
- At the time of the collapse of the bridge, approximately 300 tons of construction equipment was located near several of the under-designed gusset plates.
- The bridge was completed in 1967, but in 1977 and 1998, a median barrier, larger outside walls, and a thicker concrete deck were added to the bridge, causing additional loading on the already under-designed gusset plates.
- The temperature on the day of the collapse also could have introduced additional stresses on the gusset plates since the bearingsBearing (mechanical)A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...
on the bridge were partially frozen limiting their effectiveness