Over-height vehicle impacts can fracture prestressing strands, damage concrete, and disrupt bridge service. Following a strike, transportation agencies must determine whether a bridge can remain open, requires restrictions or temporary support, or needs repair or replacement. These decisions require reliable estimates of remaining structural capacity and an understanding of the effectiveness and limitations of available repairs.

Phase I of Transportation Pooled Fund study TPF-5(462), led by the Missouri Department of Transportation (MoDOT), investigated impact damage, residual capacity, and repair of individual prestressed concrete girders through full-scale tests on fourteen MoDOT Type II girders and calibrated numerical models. Phase II will extend this work to composite bridge assemblies, accounting for load transfer through the deck, intermediate diaphragms, and adjacent girders. It will also investigate repaired girders subjected to a subsequent impact, the fatigue performance of strand-splice repairs, and field methods for estimating the tension remaining in damaged strands.

The study will provide participating agencies with assessment procedures, repair-selection tools, tested repair details, and draft guidance for consideration by the AASHTO Committee on Bridges and Structures.

The overarching goal is to improve the assessment and repair of prestressed concrete girder bridges following over-height vehicle impacts. Specific objectives are to:

- Quantify how the composite deck and intermediate diaphragms influence impact damage, load redistribution, serviceability, and remaining system capacity.

- Evaluate strand-splice and carbon fiber-reinforced polymer (CFRP) repairs under subsequent impacts, and assess strand-splice performance under repeated loading.

- Extend and validate the Phase I load–deflection method for estimating residual tension in exposed prestressing strands, and evaluate a complementary natural-frequency method for exposed and damaged strands.

- Develop numerical models to investigate representative bridge configurations and impact conditions, with explicit limits on their applicability.

- Produce practical assessment procedures, repair-selection guidance, calculation tools, and draft specification language to support agency implementation.

The 36-month study will comprise eight coordinated tasks:

1. Agency needs and experimental planning. Collect participating-state impact cases, assessment practices, repair experience, and available cost and closure information. Finalize specimen details, damage targets, instrumentation, and testing protocols with the technical advisory committee.

2. Impact-system improvements. Upgrade and commission the existing impact facility to establish the operating conditions required for the system tests.

3. Bridge-system testing and residual-strand assessment. Test four composite assemblies, each comprising two full-size MoDOT Type II girders with a 46-ft span and an 8-in. concrete deck. Assemblies will include no intermediate diaphragm, a concrete diaphragm, or a steel diaphragm. Measure impact response, damage, load redistribution, and service behavior. Load two unrepaired assemblies to collapse and retain two for repair and subsequent-impact testing. Calibrate and evaluate the load–deflection (lateral-stiffness) and natural-frequency methods for estimating residual strand tension.

4. Repair and subsequent-impact testing. Repair one assembly using mechanical strand splices and concrete restoration, and another using externally bonded CFRP and concrete restoration. Evaluate service-response recovery, apply a second impact, and determine the remaining resistance through collapse testing. Document repair installation requirements and applicability limits.

5. Strand-splice fatigue and confinement testing. Test eight short-beam specimens representing 17% and 33% strand loss, with unconfined and confined splice details. Four specimens will undergo monotonic loading; four will undergo up to two million fatigue cycles or earlier failure, followed by retained-strength testing of surviving specimens. Results will establish performance for the tested details and stress ranges.

6. Numerical modeling and bounded extension. Calibrate models against experimental results and investigate the effects of bridge geometry, girder number, deck stiffness, diaphragm configuration, and impact conditions. Clearly distinguish experimentally supported conclusions from model-based extensions.

7. Practitioner guidance. Develop an inspection checklist, residual-strand-tension field procedure, calculation workbook, repair-selection matrix, assessment flowcharts, and worked examples. Address durability and field constructability using experimental observations, published research, and agency experience.

8. Coordination and implementation. Conduct regular technical advisory committee reviews, engage the AASHTO technical committees responsible for concrete design and bridge preservation, and deliver draft provisions, webinars, a final workshop, and documented research datasets.

MoDOT will serve as the lead agency. The preferred program targets thirteen participating states, including Missouri, contributing $65,000 annually for three years, or $195,000 per state, for a total of $2.535 million.