Concrete exhibits time-dependent behavior. Under sustained stress, “creep” causes ongoing strains. Even with no loads, concrete shrinkage strains occur. Prestressing steel exhibits a gradual loss of stress under constant strain known as “relaxation.” Under these combined effects, prestressed concrete members gradually deform with time. Several techniques are available to account for these effects. Both approximate and detailed methods are taught in this course. Elastic changes in steel stress due to application of external loads are considered and presented. Conditions are given when approximate estimates are applicable. Bridges with composite concrete decks introduce another level of complexity that is taught in the next course, T140.

After completing this course, the student will be able to:

• Identify the effects of time and construction on stresses, before decking or without decks
• Recall the conditions where the various methods for calculating time-dependent losses can be used
• Discriminate the meaning of the various time segments used in the refined estimate method
• Calculate losses due to concrete shrinkage using the refined estimate for a member without decking
• Calculate losses due to steel relaxation using the refined estimate for a member without decking
• Calculate losses due to creep using the refined estimate for a member without decking