Gusset plates are thick sheets of steel that are used to connect beams and
girders to columns or to connect truss members. A gusset plate can be fastened
to a permanent member either by bolts, rivets 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 are used in bridges and
buildings as well as other structures. Materials
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. 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
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. Design reconsideration
Gusset plates can be made into a variety of shapes and sizes from a range of
materials. 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 conjunction 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 be
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 failures
= Steel Bridges = 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 like paper, 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 larger sizes to be in accordance with the American
Association of State Highway and Transportation Officials “Standard
Specifications for Highway Bridges,” 1961. The National Transportation Safety
Board attributed most of the cause of the failure of the bridge to this flaw.
In addition to the gusset plates being under-designed for their original
loading, there were other factors that led to the demise
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 bearings on the bridge were partially frozen limiting their
effectiveness = Radio telescopes =
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. Most radio and telecommuncations 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.
References