Structures Design Guidelines | July 2007
4 - Superstructure - Concrete |

# 4 - Superstructure - Concrete

## 4.1 General (01/07) Jan 2007 - Moved modulus of elasticity requirement to SDG 1.4.1.

This Chapter contains information related to the design, reinforcing, detailing, and construction of concrete components. It also contains deviations from LRFD that are required in such areas as deck slab reinforcing and construction, pretensioned concrete components, and post-tensioning design and detailing.

### 4.1.1 Concrete Cover

See Table 1.2 Minimum Concrete Cover
in SDG 1.4 Concrete and Environment.

### 4.1.2 Reinforcing Steel [5.4.3]

A. Specify ASTM A615, Grade 60 reinforcing steel for concrete design.

B. Do not specify epoxy coated reinforcing steel for any FDOT project.

### 4.1.3 Girder Transportation

Coordinate the transportation of heavy and/or long girders with the Department’s Permit Office during the design phase of the project.

### 4.1.4 Shear Design [5.8.3] (01/07) Jan 2007 - added 4.1.4 for clarification of shear design requirements in LRFD.

When calculating the shear capacity, use the area of stirrup reinforcement intersected by the distance 0.5 dv cot q on each side of the design section, as shown in LRFD [Figure C5.8.3.2-3].

### 4.1.5 Minimum Reinforcement Requirements [5.7.3.3.2] (07/07) July 2007 - Added Section per TDB C07-3.

A. Apply the minimum reinforcement requirements of LRFD [5.7.3.3.2] to all sections being analyzed except at the ends of simply supported bridge girders.

B. The length of the girder from the simply supported end for which the minimum reinforcement will not be checked is defined below.

1. Do not check the minimum reinforcing for prestressed concrete girders for a distance equal to the bonded development length (e.g. for 270 ksi strand with f pe = 157 ksi, 1/2” dia, strand yields 11.0 feet and 0.6” dia. yields 13.2 feet) from the ends of the simply supported girder.

2. Do not check the minimum reinforcing for reinforced concrete girders for a distance equal to 2.5 times the superstructure depth from the centerline of bearing of the simply supported end.

C. For span lengths less than 27 feet for simple span bridges, check the minimum reinforcement at mid-span.

Commentary: The use of a minimum reinforcement check was developed to ensure a ductile failure mode for lightly reinforced deep beams. Bridge girders are slender and do not generally meet the definition of a deep beam. Deep beams are defined as members having a clear span less that 4 times the overall depth (as defined by ACI 318). The use of the minimum reinforcing check has evolved in the specifications from checking the critical section to checking every section. This evaluation at every section is justified in buildings where heavy concentrated loads may be present near supports. In bridges, this condition does not exist and the critical section for bending is not near the support for simply supported bridge beams. The ends of simply supported bridge girders are dominated by shear, not bending moment. At these locations it is unnecessary to check minimum reinforcing for bending in an area dominated by shear.