26 TRNews, November–December 1985

RESEARCH PAYS OFF

NCHRP Study—Methodsfor In-Place Repair ofDamaged PrestressedConcrete Bridges

When bridges are damaged by over-height vehicles, highway agencies mustquickly repair the damage and the pub-lic usually pays for the repairs. A re-search study recently completed byNCHRP has provided engineers re-sponsible for repairing damagedbridges with some practical guidance.

Problem

Each year, more than 150 prestressedconcrete girders nationwide are dam-aged by overheight vehicles. Concreteis crushed and reinforcement is some-times severed. The damage may behighly visible, the bridge could be un-safe, and the need to repair is usuallyurgent. In the past 25 years, thousandsof bridges have been built withprestressed superstructures. Becausemost of these structures are in goodcondition and are performing well,

many bridge engineers have little expe-rience in repairing prestressed concrete.As a result, damaged girders that could,in many instances, be repaired in placehave been removed and replaced withnew members at considerable cost.

SolutionIn a study recently completed under theAASHTO-sponsored National Coop-erative Highway Research Program(NCHRP), consulting engineers GeorgeShanafelt and Willis Horn of Olympia,Washington, evaluated several repair-in-place methods that have been usedby individual highway agencies withvarying degrees of success. They de-veloped modifications of these proce-dures, and recommended several meth-ods appropriate for immediate use,which were published in NCHRP Re-port 226: Damage Evaluation and Re-pair Methods for Prestressed ConcreteBridge Members. In this report, guid-ance is given on the use of varioustechniques such as splicing severedcables, internal prestressing, steel-sleeve splicing, patching under preload,and external post-tensioning. In a re-cently completed second phase of re-search, the efficacy of the recom-mended techniques was demonstratedin full-scale laboratory tests. A manualof recommended practice will be pub-lished at the end of 1985 as NCHRPReport 280: Guidelines for Evaluationand Repair of Damaged PrestressedConcrete Bridge Members. This reportwill include guidelines for (a) inspec-tion of damage, (b) assessment of dam-age, (c) selection of repair method, and(d) application of techniques for in-place repair.

TRNews, November–December 1985 27

Application and BenefitRepair methods recommended by theresearchers have been used by theWashington, Iowa, and North Carolinadepartments of transportation, as wellas by several other highway agencies,with satisfactory results and substantialcost savings. Moreover, since the pub-lication of NCHRP Report 226, interestin repair-in-place has spread to otherstates. The cost of complete replace-ment of a damaged girder averagesabout $50,000, and the cost of repair-in-place is estimated to be about$15,000; thus, the savings realized byapplying the results of this research toonly 20 percent of the approximately150 girders damaged each year willamount to more than $1 million.

This NCHRP research study pro-vides an excellent example of the bene-fits that can be derived by poolingfunds for research. Although the prob-lem of accidentally damagedprestressed concrete bridge membersmost likely is not sufficiently urgentfor any one highway agency to justify aseparate study, the NCHRP study andits results demonstrate what can beaccomplished when 52 highway agen-cies join in a cooperative research ef-fort. In this case, a relatively small in-vestment was transformed into nation-wide annual savings of millions ofdollars.

For further information, contact CrawfordF. Jencks, Projects Engineer, NCHRP,Transportation Research Board, 2101 Con-stitution Avenue, N.W., Washington, D.C.20418 (telephone 202-334-3224).