• Gusset Plate Rating Procedure Page 1


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    • Abstract: Gusset Plate Rating Procedure Page 1GUSSET PLATE RATING PROCEDUREGPR. 1. All available information shall be obtained in order to perform gusset plate ratings.This information shall include the original bridge plans, any subsequent repair plans, the shop

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Gusset Plate Rating Procedure Page 1
GUSSET PLATE RATING PROCEDURE
GPR. 1. All available information shall be obtained in order to perform gusset plate ratings.
This information shall include the original bridge plans, any subsequent repair plans, the shop
drawings, and the most current inspection report. Contact MassHighway to determine shop drawing
availability. Confirm that gusset plates shown in the plans match those shown in the shop drawings
in thickness and material. The most current inspection report shall be reviewed and gusset plates with
appreciable section loss shall be identified. If appreciable loss is reported, discuss this matter with the
MassHighway Bridge Inspection Engineer to determine the percentage of section loss to apply in the
ratings.
GPR. 2. Gusset plates will be rated for HS20 loading using the Load Factor Method. When
Lane Loading controls for a given member, note that the HS20 lane load concentrated load for
moment (18 kips) is to be used for determination of top and bottom chord loads and the HS20 lane
load concentrated load for shear (26 kips) is to be used for determination of diagonal and vertical
loads.
GPR. 3. The latest version of AASHTOWare™ Virtis shall be used to obtain member forces.
Coincident member live load forces shall be used.
GPR. 4. Stresses caused by the dead load moment of the member, as well as stresses due to
the eccentricity of joints or working lines shall be considered where applicable. Secondary stresses
due to truss distortion or floorbeam deflection need not be considered in any member whose width
measured parallel to the plane of distortion is less than one-tenth of its length (AASHTO Standard
Specifications for Highway Bridges Article 10.16.3 and AASHTO LRFD Article 6.14.2.3).
GPR. 5. Determine the bearing and shear capacity of the riveted connection as follows:
A. Consider all truss joints. Use engineering judgment to eliminate checking of similar
member connections.
B. Determine number of rivets in single shear and in double shear based on the number and
size of plates in the joint.
C. Determine load per rivet due to maximum tension and compression loads for DL and LL.
D. Determine the thickness of plates in bearing for the rivets in single shear and double
shear.
E. Determine factored bearing and shear capacity using the AASHTO Standard
Specifications for Highway Bridges Article 10.56.1.3 and the following:
φR =φFmAr
where:
φF = shear strength of one rivet. In cases where the shear strength is unknown, the values in
the following table may be used for φF based on the year of construction:
Gusset Plate Rating Procedure Page 2
Year of Construction φF
(ksi)
Constructed prior to 1936 or of unknown origin 18
Constructed after 1936 but of unknown origin 21
m = the number of shear planes
Ar = cross-sectional area of the rivet before driving.
The shear resistance of a rivet in connections greater than 50 inches in length shall be
taken as 0.80 times φF.
F. Determine rating factors and ratings in tons for HS20 loading:
RFINV = (0.9* × φR − 1.3PDL ) ÷ 2.17PHS 20
RFOPR = (0.9* × φR − 1.3PDL ) ÷1.3PHS 20
* Since the failure of gusset plates in non-redundant structures may result in collapse of the
bridge, the computed capacity is reduced 10% to increase the margin of safety.
GPR. 6. Determine the capacity of the gusset plates subject to axial tension by investigating
the yield capacity of the effective section and potential block shear rupture as follows:
A. Consider all truss joints with tension members. Use engineering judgment to eliminate
checking of similar member connections.
B. Determine factored resistance, Rr, as the least of the values given by either yielding on the
effective area or the block shear rupture resistance.
For Effective Gross Section Yielding:
Rr =AeFy
where:
Ae = effective gross cross-sectional area taking into account the possibility of net section
fracture.
Ae = An +βAg ≤ Ag
An = net cross-sectional area of the plates as specified in AASHTO Article 10.16.14.
β = 0.0 for M 270 Grade 100/100W steels, or when holes exceed 1¼ inch in diameter. =
0.15 for all other steels and when holes are less than or equal to 1¼ inch in diameter.
Ag = gross cross-sectional area of the plates.
Fy = minimum yield strength of the plates.
Gusset Plate Rating Procedure Page 3
Determine “Whitmore Effective Width” for each member. This is done by finding the first
set of rivets in the member to gusset plate connection and drawing lines that start at the outside rivets
radiating at 30 degrees outward from the direction of the member. The “Whitmore effective width” is
equal to the distance between the 30 degree lines where they intersect a line through the last set of
rivets. See Figure 1 as follows:
For Block Shear Rupture Resistance:
Figure 1: Examples of Whitmore Effective Width Geometry
Gusset Plate Rating Procedure Page 4
The resistance to block shear rupture is that resulting from the combined resistance of parallel
and perpendicular planes; one in axial tension and the others in shear. The resistance of the plate for
block shear rupture shall be taken as:
If Atn ≥ 0.58Avn, then Rr = 0.85(0.58Fy Avg + Fu Atn )
If Atn < 0.58Avn, then Rr = 0.85(0.58Fu Avn + Fy Atg )
where:
0.85 = resistance factor for block shear. This value is calculated as the LRFD resistance factor for net
section tension fracture (0.8) divided by the resistance factor for gross section tension yielding
(0.95).
Avg = gross area along the plane resisting shear stress.
Atg = gross area along the plane resisting tension stress.
Avn = net area along the plane resisting shear stress.
Atn = net area along the plane resisting tension stress.
Fy = minimum yield strength of the plate.
Fu = minimum tensile strength of the plate.
The analysis of block shear rupture involves the evaluation of several patterns of planes to
arrive at the governing pattern. Figure 2 provides some examples of potential block shear rupture
planes for gusset plates in tension.
Figure 2: Potential Block Shear Rupture Planes
Gusset Plate Rating Procedure Page 5
C. Determine rating factors and ratings in tons for HS20 loading:
RFINV = (0.9* × Rr −1.3PDL ) ÷ 2.17PHS20
RFOPR = (0.9* × Rr −1.3PDL ) ÷1.3PHS20
* Since the failure of gusset plates in non-redundant structures may result in collapse of the
bridge, the computed capacity is reduced 10% to increase the margin of safety.
GPR. 7. Determine the capacity of the gusset plates subject to shear, which shall be taken as
the lesser of the shear yield and the shear fracture resistance as follows:
A. Consider all truss joints. Use engineering judgment to eliminate checking of similar
member connections.
B. Determine factored resistance, Rr, as the least of the values given by either shear yield and
shear rupture in the following equations, respectively:
R = 0.58FyAg × Ω
R = 0.85 × 0.58FuAn
where:
0.85 = resistance factor for shear fracture on the net section. This value is calculated as
the LRFD resistance factor for net section tension fracture (0.8) divided by the
resistance factor for gross section tension yielding (0.95)
Ag = gross area of the plates resisting shear
An = net area of the plates resisting shear
F = minimum yield strength of the plates
y
Fu = minimum tensile strength of the plates
Ω = reduction factor taken as:
• Ω = 1.00 for the case of uniform shear stress distribution where the gusset plates are of
ample stiffness to prevent buckling and develop the plastic shear force of the plates, or
• Ω = 0.74 for the case of flexural shear stress distribution. This value shall be used in
the absence of a more rigorous analysis or criterion to assure and quantify the stiffness
requirements to develop the plastic shear force of the plates.
The analysis of gusset plates for shear involves the evaluation of several shear sections
to arrive at the governing section. Figures 3 and 4 provide examples of shear sections to be
evaluated in gusset plates in gross section shear yielding and net section shear fracture.
Gusset Plate Rating Procedure Page 6
Figure 3: Example of Potential Shear Rupture Planes for Gross Section Yielding
Figure 4: Example of Potential Net Section Shear Fracture Planes
C. Determine rating factors and ratings in tons for HS20 loading:
RFINV = (0.9* × Rr − 1.3PDL ) ÷ 2.17PHS20
RFOPR = (0.9* × Rr − 1.3PDL ) ÷1.3PHS20
* Since the failure of gusset plates in non-redundant structures may result in collapse of the
Gusset Plate Rating Procedure Page 7
bridge, the computed capacity is reduced 10% to increase the margin of safety.
GPR. 8. Determine the capacity of the gusset plates subject to compression, which shall be
determined as that of idealized members in compression, in accordance with the following:
A. Consider all truss joints with compression members. Use engineering judgment to
eliminate checking of similar member connections.
B. Determine the effective width of the idealized compression member in accordance with
the Whitmore method. The unbraced length, Lc, shall be determined as the average of the
following three distances:
L2 = The distance from the last row of fasteners in the compression member under
consideration to the first row of fasteners in the closest adjacent member, measured along
the line of action of the compressive axial force.
L1, L3 = The distance from each of the ends of the Whitmore width to the first row of
fasteners in the closest adjacent member, measured parallel to the line of action of the
compressive axial force. When the Whitmore width enters into the adjacent member, the
associated distance at that end should be set to zero. Figure 5 provides an example showing
L1, L2, L3, and effective width for a gusset plate in compression.
Figure 5: Unbraced Length and Whitmore Width for Gusset Plates in Compression
Gusset Plate Rating Procedure Page 8
C. Determine buckling capacity for of the idealized compression member with unbraced
length as determined above using the AASHTO Standard Specifications for Highway
Bridges Article 10.54.1.1. Use the effective length factor, K = 1.00.
D. Determine rating factors and ratings in tons for HS20 loading:
RFINV = (0.9 × Pu −1.3PDL ) ÷ 2.17PHS 20
RFOPR = (0.9 × Pu −1.3PDL ) ÷1.3PHS20
* Since the failure of gusset plates in non-redundant structures may result in collapse of the
bridge, the computed capacity is reduced 10% to increase the margin of safety.
E. Repeat steps above, but use the effective length factor, K = 0.75. The range of results for
both values of K will be considered upon completion of the review. When lateral sway of
gusset plates is possible, the effective length factor, K, for gusset plates may be taken as a
value greater than 1.0, depending on the anticipated buckled shape.
GPR. 9. Gusset plates under combined flexural and axial loads need not be evaluated as
gusset plates behave as deep members. Therefore, the application of flexural theory to the analysis of
gusset plates is questionable and is not required at this time.
GPR. 10. The AASHTO Standard Specifications for Highway Bridges Article 10.16.11.3
contains a limit on the length of gusset plate unsupported edge of 11,000/√Fy times the gusset plate
thickness. Although an appropriate slenderness limit is advisable for the design of new gusset plates,
it is not required for load rating purposes.
GPR. 11. In addition to providing all standard Rating Report documentation, the following
additional documentation shall be provided within the body of the gusset plate load rating
calculations:
A. Copies of original plan sheets and shop drawings for the truss joints reviewed.
B. A copy of the truss member load table sheet from the original plan (if available).
C. Sketches of the truss joints analyzed showing the section cuts and dimensions used in the
analysis.
D. The calculations for the truss joints, including the date and name of the engineers who did
the calculations and the check.
References:
Ibrahim, Firas I., "FHWA Bridge Design Guidance No. 1, Load Rating Evaluation of
Gusset Plates in Truss Bridges, Part B, Gusset Plate Resistance in Accordance with the
Load Factor Rating Method (LFR)", August 28, 2008.


Use: 0.4666