Structures Design Guidelines | Jan 2009
5 - Superstructure - Steel |

## 5.11 Connections and Splices [6.13]

A. Specify and detail bolted (not welded) field connections. Field welding is allowed only by prior written approval by the SDO or the appropriate DSDO and then, only when bolting is impractical or impossible.

B. Where cantilever brackets are connected to exterior girders and tie plates are used to connect the top flange of the bracket to the top flange of the floor beam, do not show the tie plates connected to the girder top flange. To account for alignment tolerances, detail short, slotted holes in the top flange of the cantilever brackets (perpendicular to the bracket web). Reduce the allowable bolt stress accordingly.

### 5.11.1 Slip Resistance [6.13.2.8] (01/09) 2009 Jan: Expanded A. to "faying" and weathering steel. 2005 Jan: Revised bolted connections for Class A surface condition per TDB C04-5.

A. Design bolted connections for Class A faying surface condition except as noted below. For weathering steel bridges that are not to be painted, design bolted connections for Class B faying surface condition.

B. When the thickness of the plate adjacent to the nut is greater than or equal to ¾ inch, base the strength of the connection on the bolt shear strength with threads excluded from the shear plane.

Commentary: This surface condition agrees with Florida fabrication practice.

### 5.11.2 Welded Connections [6.13.3]

A. Do not show a specific, pre-qualified, complete-joint penetration weld designation on the plans unless a certain type of weld; i.e., “V,” ”J,” ”U,” etc., is required. See SDM 14 Structural Steel

Commentary: The fabricator should be allowed to select the type of complete-joint penetration weld to use, and should show all welds on the shop drawings.

B. On the plans, identify areas that are subject to tension and areas subject to stress reversal.

Commentary: This information will enable inspection personnel to identify the type and extent of testing required. Also, the shop drawings will further identify these areas.

C. When welding is required during rehabilitation or widening of an existing structure, show on the plans, the type of existing base metal. Advise the District Structures Design Office if the base metal type cannot be determined, or if the type is not an approved base metal included in the ANSI/AASHTO/AWS Bridge Welding Code. The State Materials Office and the Department’s independent inspection agency will then determine the welding procedures and welding inspection requirements for the project.

### 5.11.3 Welded Splices [6.13.6.2] (01/08) 2008 Jan: Added paragraphs D thru G.

A. At flange transitions, do not reduce the cross-sectional area by more than one-half the area of the larger flange plate.

Commentary: These proportions will allow a smooth flow of stress through the splice.

B. Maintain constant flange widths within each field-bolted section.

Commentary: By having constant width flange plates in a field section, the fabricator may order plates in multiples of the flange width, butt weld the plates full width, and then strip-out the flanges. Thus, the fabricator is required to make a minimum number of butt welds, handle a minimum number of pieces, and, thereby, minimize his fabrication costs.

C. The following criteria may be used to make a determination of the number of pounds, ∆w, of material that must be saved to justify the cost of introducing a flange transition:

1.) For 36 ksi material: ∆w = 300 + (25.0) x (area of the smaller flange plate, in2),

2.) For 50 ksi material : ∆w = 250 + (21.3) x (area of the smaller flange plate, in2),

3.) For 70 ksi material : ∆w = 220 + (18.8) x (area of the smaller flange plate, in2).

D. In general, the number of flange splices within a field section should never be greater than two. It is more economical to extend a thicker plate in many instances because of the labor cost involved in making a splice.

E. Keep the flange plates of adjacent girders the same thickness where possible.

F. Size plates based on the rolled sizes available from the mills.

G. Keep the number of different plate thicknesses reasonable for the size of the project. Avoid sizing flange thicknesses in 1/8" increments.