Structures Design Guidelines | July 2007
7 - Widening and Rehabilitation |

# 7 - Widening and Rehabilitation

## 7.1 General

### 7.1.1 Load Rating (07/07) July 2007 - Revised per TBD C07-01. Clarifies requirements for performing load ratings and Design Variations. July 2006 - Revised entire section per TDB C06-01. Jan 2005 - Revised entire section per TDB C05-01. Revised strength or service limit to less than 1.0 for the FL120 Permit Vehicle.

A. Before preparing widening or rehabilitation plans, review the inspection report and the existing load rating. If the existing load rating is inaccurate or was performed using an older method (e.g. Allowable Stress or Load Factor), perform a new load rating of the existing bridge in accordance with SDG 1.7
. Design all bridge widening or rehabilitation projects in accordance with SDG 7.3
. If the bridge to be widened/rehabilitated does not have a design load rating (and a permit load rating with LRFR) at inventory level greater than or equal to 1.0, regardless of the specification used, replacement or strengthening is required unless a Design Variation is approved.

B. If the widening or rehabilitation of a bridge does not produce a LRFR design inventory rating factor and a FL 120 permit rating factor greater than or equal to 1.0, calculate and report the appropriate rating factor using LRFR Appendix D.6 and send a copy of the Load Rating Summary and the Load Rating Details shown in Volume 8, Section G.6 to the State Structures Design Office. Calculate ratings for concrete box girders (segmental) using LRFR Appendix E.6.

C. If the load rating at inventory level using LRFR Appendix D.6 yields an inventory rating factor of less than 1.0, or less than 1.25 for cast-in-place and precast flat slab bridges, a revised load rating using one of the additional methods of analysis in C.1., C.2., C.3., or C.4.may be performed to obtain a satisfactory inventory rating. Submit a Design Variation for use of the additional methods of analysis or for an inventory load rating factor of less than 1.00 (or 1.25 for cast-in-place and precast flat slab bridges) to the State Structures Design Engineer. To support the Design Variation, submit two load rating summaries 1.) using standard analysis methods and 2.) using standard methods of analysis and only one of the following (combined methods not allowed):

1.) Approximate Method of Analysis: When using an approximate method of structural analysis defined in the specifications along with the specification defined live load distribution factors, a rating factor of 0.95 may be rounded up to 1.0.

2.) Refined Method of Analysis: Refined methods of structural analyses (e.g. using finite elements) may be performed in order to establish an enhanced live load distribution and improved load rating. For continuous post-tensioned concrete bridges, a more sophisticated, time-dependent construction analysis is required to determine overall longitudinal effects from permanent loads (e.g. BD 2 analysis).

3.) Shear Capacity - Segmental Concrete Box Girder - Crack Angle LRFD (LRFD 5.8.6): To calculate a crack angle more accurately than the assumed 45 degree angle used in the specifications, use the procedure found in Appendix B of "Volume 10 Load Rating Post-Tensioned Concrete Segmental Bridges" (dated Oct. 8, 2004) found on the Structures Design Office website.

4.) Service Limit State: If the load carrying capacity as determined by Service Limit State yields a rating factor less than 1.0 and the current bridge inspection is showing no signs of either shear or flexural cracking, the capacity may be established using Strength Limit State.

D. See Figure 7-5 for a flow chart of the widening/rehabilitation decision making process.

E. The final load rating for a bridge widening must use a consistent load rating method for both the existing and widened portions of the bridge.

Commentary: Bridge widening and rehabilitation projects require major capital expenditures therefore it is appropriate to update existing bridges within the project to the current design specification. When LRFR Appendix D.6 is utilized, a rating factor of 1.25 may be required for short span bridges (excluding culverts) as noted in 7.1.1 Load Rating. The legal limit in Florida for a single unit truck (SU4) is heavier than the notional HS-20 load; therefore, FDOT designs for the effect of this heavier loading by requiring an increase in the notional load to HS-25 (1.25 rating factor). For these short span bridges a rating factor of less than 1.25 may be considered, however, a variation is required. Because of heavy traffic and high volumes of overweight permit vehicles, variances should be considered only for bridges off the National Highway System.

### 7.1.2 Bridge Deck - See Chapter 4.

### 7.1.3 Expansion Joints - See Chapter 6
.

### 7.1.4 Traffic Railing - See Chapter 6
.