George Tsiatas

Durability Evaluation of Concrete Crack Repair Systems

Concrete cracking in highway bridges is a major problem because it not only accelerates the rate of deterioration, but it also can reduce the structural strength of the bridge. Crack repair systems have been developed to address this problem. For repairing structural cracks, six repair materials were evaluated for durability. The repair materials include one cementitious system, one modified cementitious system, two epoxy-based systems, and two high-molecular-weight methacrylate (HMWM) repair products. Each product was applied according to its manufacturer’s directions to repair beams with crack widths of 0.51 mm (0.02 in.), 6.35 mm (0.25 in.), and 12.70 mm (0.50 in.). The specimens are subjected to a standard freezing and thawing test followed by fatigue testing to failure. In general, epoxies and HMWMs performed the best. However, individual products varied significantly. Specimens repaired with the cementitious system were unable to resist any significant amount of fatigue-loading cycles.

Fatigue evaluation of highway bridges

The present work provides a comparison of current AASHTO bridge fatigue guidelines with fracture mechanics procedures. Specifically, the remaining fatigue life of several actual bridges with welded cover plate ends is estimated using the AASHTO specifications. The estimates are compared with predictions made using linear elastic fracture mechanics principles where the time required for an initial flaw to propagate to a critical depth is calculated. It is found that fatigue lives of actual steel highway bridges as determined using fracture mechanics far exceed the remaining safe fatigue life predictions made with current AASHTO guide specifications. For the case of redundant bridges, an adjustment factor is introduced which, at various probability levels, can produce closer estimates of bridge fatigue lives between the AASHTO specifications and fracture mechanics.

Use of Fatigue Fuses for Prediction of Fatigue Life of Steel Bridges

The fatigue fuse is a device for predicting the fatigue life of steel highway bridge members when the bridge is subject to variable loads. The fuse is calibrated so that the cracking of each of its four legs can be related to damage in the structure. In a preliminary laboratory study, fatigue fuses are attached to eight steel girders, selected to represent three types of structural details found in existing highway bridges. The fuses are cemented to the girders and the girders subjected to a constant-amplitude fatigue loading. Cracking of the fatigue fuses is monitored by checking electrical continuity across each fuse leg. Tests are continued until girder failure or until all fuse legs are broken and the mean fatigue life of the girder as predicted by AASHTO is reached. The breaking of the fuse legs is used to predict the fatigue life of each girder, which is then compared with the actual cycles to failure of the girder and the AASHTO mean life. The prediction gives satisfactory agreement with the AASHTO...

Ground Motion Model for Puget Sound Cohesionless Soil Sites

Surface response spectra for earthquake events must be based upon proper input seismic modelling. The surface response spectrum can be determined by convoluting a base response spectrum with a spectral amplification for the site. This required that an appropriate base spectrum of the earthquake motion and soil response model must have been used to develop the surface response spectra. Earthquakes in the Puget Sound basin are generally deep focus subduction zone events. These earthquakes are significantly different than the shallow focus strike slip events of California which are commonly used for this purpose. The spectral site amplification must be determined for the soils of the region. This paper considers the cohesionless soil sites only. The computer program SHAKE was used to evaluate the spectral amplification of different sites. Parameters for SHAKE were determined from Standard Penetration Test data. Parametric sensitivity studies were conducted for the spectral site amplification.