User:Rwhites89/Gusset Plate Notes

Outline

Lead Section-What they are made of and when they are used

• Gusset plates have been used in riveted steel trusses of early bridge, buildings and industrial structures. Today, gusset plates are frequently used in steel braced frames to connect bracing members to columns and beams as shown in Figure 1.1. In addition, gusset plates are still used in steel trusses to connect truss members. Since 1960’s, bolts and welds have almost totally replaced rivets in these connections.-steel tips
• figures (page 7)-steel tips
• A gusset plate is a thick sheet of steel used for joining structural steel components. The gusset plate is installed at the intersection of two or more adjacent beams, chords, or columns. It may be fastened to each steel framing member using mechanical fasteners like bolts, or permanent bonds, such as welding. The gusset plates serves as both a method of joining the steel together and of adding strength and support to each joint.-wise geek

Materials used and why

• Gusset plates can be made from cold-rolled or galvanized steel, depending on the application. When the plates are used outdoors or around corrosive materials, they are often galvanized to prevent damage from rust. When these plates will be left exposed, they may be painted to match surrounding steel or other nearby fixtures. On some smaller exposed structures, gusset plates may be constructed from copper or aluminum to give a more attractive finish when minimal support is needed. -wise geek

Times used-bridges, buildings, connections

• Gusset plates can be found on many types of steel structures. A bridge gusset plate generally consists of a heavy-duty plate used at vehicle and pedestrian bridges. Different types of plates are also used to join steel while framing a building, or constructing a large piece of mechanical equipment. Smaller gusset plates can be found in truss construction. Depending on the size and function of the truss, the gusset plate may consist of a thin sheet of aluminum or a very heavy steel sheet.-wise geek

Design-considerations for design

• Structural engineers determine the required size and thickness of these plates, as well as the best fastening method. These calculations are made based on the force and loads applied to each plate, as well as the loads applied to nearby steel components. A gusset plate may be used as the sole fastening method between various beams and chords, or used in conjunction with bolts or welding. In some cases, the plate is added to the structure after completion to add strength or stiffness to joints. Gusset plates offer a fairly easy retrofit option for structures that cannot safely support the applied amount of force.-wise geek
• Different types of gusset plate design can be characterized by size, shape, and fastening requirements. These plates often feature square or rectangular designs, but some more specialized models may even feature a triangular or custom shape to fit around nearby steel. Each plate may be designed for welding along different edges, or for both welding and bolting. Plate manufacturers typically pre-drill bolt patterns for easier installation in the field, though some may be delivered blank for maximum flexibility.-wise geek
• KT Gusset Plate-A compound bracing connection with two or three members connected to a gusset plate, which is welded to a beam, column, or truss chord. Each branch connection may be any one of the available single brace connection types. (Available only with maintenance contract.)-steel connections
• Uniform Force Bracing Connection-A compound bracing connection with one or two bracing members, each of which is connected to a gusset plate welded to a beam and bolted to a column. Each bracing connection may be any one of the available single brace connection types. (Available only with maintenance contract.)-steel connections
• Bolt Group-Rectangular array of bolts in gusset of specified grade and thickness. May be analysed by either elastic or instantaneous center method.-steel connections

Notable Failures-Minnesota bridge

• investigators found that certain gusset plates that connect bridge structural members were under-designed according to American Association of State Highway Officials (AASHO) “Standard Specifications for Highway Bridges,” 1961. This resulted in several gusset plates installed with a ½ inch thickness instead of some larger thickness. -NTSB
• Figure 1 (bridge) - NTSB
• It was also mentioned that approximately 300 tons of construction equipment was located over gusset plates U10 and U11 in the southbound lanes (green area Figure 1). According to the NTSB, all 16 of the under-designed gusset plates were found to be fractured while the remaining were typically intact. The original design calculations made by the bridge designers (Sverdrup and Parcel) could not be found. Accordingly, the NTSB could not determine how the apparent calculation error occurred. No deficiencies were found in the steel or concrete that could have caused a failure. The I-35W bridge was designed before 1964 and was completed in 1967 with additional dead (weight) loads added over time (1977 and 1998), which included a median barrier, larger outside walls and increased thickness of the concrete deck. According to the NTSB, this added significantly to the weight of the structure. No bridge design analyses could be found regarding the acceptability of the additional dead loads. -NTSB
• Corrosion has been evident throughout the bridge structure. Figure 3 is a view of corrosive pitting found at the L11 gusset during an inspection in June, 2006. (Reference 3) Gusset L11 was one of the gussets that was apparently under-designed according to the NTSB. Widespread cracking in the structure was found, much of it due to metal fatigue. -NTSB
• Construction loads on the order of 300 tons dead load, plus vibratory loads, were applied in the southbound lanes, as shown in Figure 1 (green area) and were unsymmetrical in application (Reference 4). It should be noted that this loading was applied in the general area of gussets U10 and L11. -NTSB
• Temperature changes on the day of the collapse, coupled with partially frozen bridge bearings, may have also introduced additional stresses to the gusset plates.-SD
• financial restitution?
• figures (pg 42 pdf)-wsdot

History

• Gusset plates have been used in riveted steel trusses of early bridge, buildings and industrial structures. Today, gusset plates are frequently used in steel braced frames to connect bracing members to columns and beams as shown in Figure 1.1. In addition, gusset plates are still used in steel trusses to connect truss members. Since 1960’s, bolts and welds have almost totally replaced rivets in these connections.-steel tips

Lead Section

Change Photo

Gusset plate used on the I-35W Mississippi River bridge

joint

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 can be used in bridges and buildings 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 were found to be only .5 inches thick rather than a larger size and with the increase in loading due to construction projects over the years, the gusset plates became 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 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 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 .

Design-considerations for design

• Bolt Group-Rectangular array of bolts in gusset of specified grade and thickness. May be analysed by either elastic or instantaneous center method.-steel connections

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 lead 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, but the bearings on the bridge were partially frozen limiting their effectiveness

Notable Failures-Minnesota bridge

• Figure 1 (bridge) - NTSB
• financial restitution?
• figures (pg 42 pdf)-wsdot

Sources

References