Structures Design Guidelines | Jan 2009
7 - Widening and Rehabilitation |

## 7.4 Attachment to Existing Structure

### 7.4.1 Drilling

A. When drilling into heavily reinforced areas, specify exposure of the main reinforcing bars by chipping.

B. Specify that drilled holes have a minimum edge distance of three times the metal anchor diameter (3d) from free edges of concrete and 1-inch minimum clearance between the edges of the drilled holes and existing reinforcing bars.

C. Specify core drilling for holes with diameters larger than 1½-inches or when necessary to drill through reinforcing bars.

D. Adhesive Anchor Systems must be SDO approved and comply with the criteria and requirements of Chapter 1.

### 7.4.2 Dowel Embedments

Ensure that reinforcing bar dowel embedments meet minimum development length requirements whenever possible. If this is not possible (e.g., traffic railing dowels into the existing slab), the following options are available:

A. Reduce the allowable stresses in the reinforcing steel by the ratio of the actual embedment divided by the required embedment.

B. If embedded anchors used to develop the reinforcing steel, use Adhesive Anchor Systems
designed in accordance with Chapter 1.

### 7.4.3 Surface Preparation

Specify that surfaces be prepared for concreting in accordance with "Removal of Existing Structures" in Sections 110 and 400 of the FDOT’s Standard Specifications for Road and Bridge Construction.

### 7.4.4 Connection Details

A. Figures 7-1 through 7-4 are details that have been used successfully for bridge widenings for the following types of bridge superstructures.

B. Flat Slab Bridges (Figure 7-1): A portion of the existing slab should be removed in order to expose the existing transverse reinforcing for splicing. If the existing reinforcing steel cannot be exposed, the transverse slab reinforcing steel for the widening may be doweled directly into the existing bridge without meeting the normal splice requirement. When splicing to the existing steel is not practical, Adhesive Anchor Systems
, designed in accordance with Chapter 1, must be utilized for the slab connection details as shown in Figures 7-1 and 7-4.

C. T-Beam Bridges (Figure 7-2): The connection shown in Figure 7-2 for the slab connection is recommended. Limits of slab removal are at the discretion of the EOR but subject to the Department’s approval.

D. Steel and Concrete Girder Bridges (Figure 7-3): The detail shown in Figure 7-3 for the slab connection is recommended for either prestressed concrete or steel beam superstructures.

Commentary: These figures are for general information and are not intended to restrict the EOR in his judgment.

See Figure 7-1 Flat Slab Widening |
See Figure 7-2 Monolithic Beam and Slab Widening |
See Figure 7-3 AASHTO Beam Superstructure Widening |
See Figure 7-4 Dowel Installation |