Federal Highways Administration- Geophysical Imaging Resource Site

Bridge System - Superstructure...

IIn a bridge system, bridge superstructure is defined as all structure above bridge bearing elevation and bridge substructure is defined as everything below the superstructure. In this section, geophysical and nondestructive testing and evaluations (NDT&E) methods used mainly for evaluating bridge decks are discussed. This includes discussion of methods used for deck stability analysis in Deck Stability Analysis, followed by discussion of condition evaluation of new and existing decks in QA/QC of New Decks through Condition Evaluation of Existing Deck.

Background

Most of the transportation infrastructure in the United States has aged to the point where serious repairs and rehabilitation, replacement, or upgrade of pavement and bridge deck systems have become necessary.

Upgrades are necessary primarily because increases in demand for access to transportation structures require that they handle more volume or increased loads. Design deficiencies and updated construction codes mandate upgrades or require retrofits to ensure public safety. However, diagnosis, repair, rehabilitation, and replacement decisions are generally not entered into because a structure has become functionally obsolete or unsafe because of its design. These decisions are based on the condition of a structure as it ages, through many years of exposure to loading, environment, and even other maintenance activities intended to increase public safety, such as de-icing activities on bridge decks and pavements.

Proper Role of Geophysics in Condition Assessment of New and Existing Structures

Bridge deck monitoring is an essential component of early stage deterioration detection, whether the deterioration manifests itself through material degradation or defect generation. One of the most common problems in concrete bridge decks is corrosion-induced deck delamination, where expansive corrosion products at the reinforcement level create internal stresses that result in cracking and detachment of the concrete from the reinforcement it is intended to protect.

Routine employment of geophysical surveys can yield good results when assessing deck conditions if the proper method(s) are selected. The more successful and/or promising methods are discussed in this web manual, in order of their current overall value toward solving a variety of bridge deck-related problems or acterizing the presence, pattern, and density of reinforcement. Not every geophysical or NDT method is mentioned, or given detailed discussion within the following text. Only those considered successful, promising, or widespread (even if widespread, but not highly recommended) are given due treatment so that recommended practices for nondestructive evaluations of deck structures and critical information (positive or negative) about commonly used methods can be better understood.

In this website, bridge deck evaluations are categorized as initial (QA verification) and baseline condition, as well as condition assessment of older, existing structures, with discussion emphasizing proactive, regularly scheduled diagnostic evaluation throughout the life of a deck. The major topics identified for discussions are decks stability analysis, deck condition evaluation, rebar condition-corrosion, presence, pattern, density of rebar (PPD), and incipient spalling

DECK STABILITY ANALYSIS

QA/QC OF NEW DECKS

BASELINE CONDITION ASSESSMENT

CONDITION EVALUATION OF EXISTING DECK