5.0 FIELD SPLICE DESIGN – GENERAL CONSIDERATIONS
5.1 Previous Bolted Field Splice Design Provisions
The bolted field splice provisions prior to the 8th edition of the AASHTO LRFD Bridge Design
Specifications were to be designed at the strength limit state for not less than the larger of:
• The average of the flexural moment-induced stress, shear, or axial force due to the
factored loadings at the point of the splice or connection and the factored flexural, shear,
or axial resistance of the member or element at the same point, or
• 75 percent of the factored flexural, shear, or axial resistance of the member or element.
Where the girder section changes at a splice, which is frequently the case, the “smaller” section
was to be used for determining the above requirements.
The above requirements were relatively straightforward when applied to a splice or connection
for a truss member subject only to axial tension or compression since the stress is equal in the
various components of the member. Application of this rule to the design of a bolted splice for a
composite steel flexural member becomes more complex however since the stresses in the
flanges are typically not equal, and the distribution of the stress in the web is a function of the
loads applied to the composite and non-composite sections. In most designs, the factored
resistance of the member controls the design of the bolted splice since the Engineer typically
places the splice in a low-moment region near the point of dead-load contraflexure.
These requirements were initially replaced in the 8
th
edition of the AASHTO LRFD Bridge
Design Specifications.
5.2 Current Bolted Field Splice Design Provisions
Beginning with the 8
th
edition AASHTO LRFD BDS, the bolted field splice provisions for
flexural members were significantly revised to simplify the design process. Experimental
research at the University of Texas showed that a simpler method of design, on which the design
procedure provided in the 8
th
Edition AASHTO LRFD BDS is based in principle, produced a
connection with adequate design resistance (7, 8). The results showed that the web did not carry
significant moment until the flange connection slipped. After the flange connection slipped, the
web connection slipped and the force in the web did not increase until the flange bolts went into
bearing and the flange yielded.
The design procedure for the design of bolted splices for flexural members introduced in the 8
th
edition AASHTO LRFD BDS, and subsequently provided in the 9
th
Edition LRFD Bridge
Design Specifications (1), is based upon designing the bolted flange and web splice connections
for 100 percent of the individual design resistances of the flange and web; that is, the individual
flange splices are designed for the smaller design yield resistance of the corresponding flanges
on either side of the splice, and the web splice is designed for the smaller factored shear
resistance of the web on either side of the splice. Therefore, the method satisfies the AASHTO