Design Memorandum



TO:                  All Design Section Staff

FROM:            Bijan Khaleghi
DATE:             August 26, 2006
SUBJECT:       Restriction on CIP Reinforced Concrete Box Girder Superstructures


This design memorandum is to restrict the use of cast-in-place (CIP) reinforced concrete (RC) box girders for WSDOT bridge superstructures. Listed below are guidelines to follow when considering CIP box girders for bridge superstructure.

    1.     Post tensioning shall be considered for all new CIP reinforced concrete single-span or multi-span box girder bridges.
            Partial Prestressing shall not be considered for design of RC box girders.

    2.     Cast-in-place reinforced concrete box girders could still be used for widening of existing RC box girder bridges.

    3.     Cast-in-place reinforced concrete box girders may be used for bridges with tight curvatures or irregular geometry

            upon Bridge Engineer’s approval.

    4.     Epoxy coated reinforcement shall only be used for top layer slab reinforcement per Design Memorandum issued

            on February 27, 2006.

The above requirements apply equally to CIP reinforced concrete T-beam and slab bridges. These types of superstructures, however, are not encouraged for bridge superstructures.


Background

The performance and longevity of cast-in-place concrete box girder bridges have recently been a major concern for bridge structures. Cracking in CIP reinforced box girders are flexural in nature and inherent part of reinforced concrete design. RC box girders are designed for ultimate strength and checked for distribution of reinforcement for service conditions and control of cracking. This means that concrete cracks under applied loads but cracks are under control. Open cracks in box girders result in rebar corrosion and concrete deterioration, affecting the longevity of bridge superstructures. Requiring post-tensioning for CIP box girders eliminates both cracks and corrosion, and improves structural performance. CIP reinforced concrete T-beam and slab superstructure are generally not encouraged for bridge superstructures.


If you have any questions regarding these issues, please contact Bijan Khaleghi at 705-7181.


cc:   Mohammad Sheikhizadeh, Bridge Construction - 47354

       F. Posner, Bridge and Structures – 47340