Dean Deschenes

Experimental Investigation of Prestress Losses in Full-Scale Bridge Girders

An experimental study was conducted in which 30 full-scale, precast, pretensioned bridge girders were constructed and instrumented with the intention of investigating prestress loss. Several different precast beam fabrication plants were used to investigate the influence of different concrete materials and construction techniques. The constructed girders were conditioned in several different climates for up to 3 years. During this period, prestress loss was measured by using vibrating wire gauges (VWG) embedded in test specimens. Following the conditioning period, the girders were flexural service load-tested to quantify the prestress loss at the time of testing and in turn verify the losses measured using VWGs. Prestress losses were found to be heavily influenced by concrete stiffness, which was dependent on coarse aggregate type and quantity. The measured short- And long-term prestress losses were compared to those determined using several different estimation procedures, suggested by ACI Committee 423.

Prestress loss database for pretensioned concrete members

A comprehensive experimental database containing 237 specimens from 27 different research studies was assembled during a larger research effort undertaken at the University of Texas at Austin to investigate three different short-term loss and four different longterm loss estimation procedures. The assembled database was filtered to eliminate specimens with incomplete information or those not adequately representing those found in the field (as a result of either being too small or overstressed at release). The specimens contained within this filtered database offered a diversity of characteristics well representative of beams found in bridges. This database was used to evaluate several different short-and longterm loss estimation procedures. The results of these evaluations can help to aid the designer in selection of an appropriate procedure for estimating prestress loss.

Shear capacity of large-scale bridge bent specimens subject to alkali-silica reaction and delayed ettringite formation

The rapid pace of infrastructure growth in the State of Texas is responsible for the recent increase in the number of concrete structures prematurely damaged by alkali-silica reaction (ASR) and/or delayed ettringite formation (DEF). Common use of „high-sack‟ early strength concrete accelerated construction schedules, but also resulted in elevated alkali loadings, high curing temperatures, and substantially increased chances for ASR and DEF deterioration. The consequences of accelerated construction practices are apparent in the Houston District of the Texas Department of Transportation (TxDOT). A number of reinforced concrete bent caps, constructed within the last ten to fifteen years, have developed map cracking and spalls characteristic of ASR and DEF (Figure 1). Outdated material specifications were only recently updated to address the deficiencies and more cases are likely to be discovered in the future. Concerned that future damage may result in a loss of strength and require substantial resources for remediation, the Houston District commissioned the University of Texas at Austin to investigate the structural safety of bridge bents subjected to ASR and DEF.