Thomas Sandford

Experimental characterization of FRP composite-wood pile structural response by bending tests

Abstract A special prefabricated fiber reinforced polymer (FRP) composite shield or jacket was developed to repair wood piles in the field. Two types of load-transfer mechanisms between the wood pile and the FRP composite shield were developed and tested: (1) cement-based structural grout; and (2) steel shear connectors with an expanding polyurethane chemical grout. The objective of this paper is to characterize the structural response of full-size pre-damaged wood piles repaired with the FRP composite shield system. A three-point bending test procedure was used to simulate the response of a pile subjected to lateral loads. The load-deformation response, deflected shape profile, relative longitudinal displacements (slip), strain distribution, ultimate bending moment capacity and mode of failure were evaluated. Wood piles were pre-damaged by reducing approximately 60% of the cross-section over a portion of the pile. It was found that a pre-damaged wood pile repaired using the FRP composite shield with cement-based grout exceeded the bending capacity of a reference wood pile. The repair system using the FRP composite shield with steel shear connectors and polyurethane grout did not fully restore the bending capacity of a reference wood pile; however it can be used for marine borer protection when wood damage is not critical.

FULL-SCALE FIELD TRIALS OF TIRE SHREDS AS LIGHTWEIGHT RETAINING WALL BACKFILL UNDER AT-REST CONDITIONS

A 4.88-m (16-ft), full-scale retaining wall test facility was constructed to investigate the use of tire shreds as backfill for conventional retaining walls. The facility can test backfill at at-rest and active conditions and is instrumental for measuring horizontal stress and interface shear. Tire shreds from three suppliers were tested. The results for at-rest conditions are presented. The average at-rest horizontal stress for tire shreds was about 45 percent less than expected for conventional granular backfill. Moreover, the at-rest horizontal stress was about the same for tire shreds from the three suppliers. Design parameters were developed by using two procedures. The first used the coefficient of lateral earth pressure and the other was based on equivalent fluid pressure. The horizontal and shear forces acting on the concrete face of the wall were used to determine the angle of wall friction, which ranged from 30° to 32° for tire shreds from the three suppliers.

Construction-induced stresses in H-piles supporting an integral abutment bridge

Although the advantages of integral abutment bridges are widely known, design practices and assumptions vary extensively, especially when bridges have skew. Some agencies explicitly calculate bending effects on piles, but many do not consider the dead load bending. Piles traditionally have been required to be deep enough in soil to achieve fixity. The monitoring of the performance of a skewed integral abutment bridge on shallow bedrock in Coplin Plantation, Maine, during construction is reported. The sequence and procedure of construction was analyzed to assess its effects on stresses in the pilings. Stresses from bending in the direction of the centerline were equal to or greater than stresses from axial loading of the piles. These stresses were related to rotation of the abutment caused by dead loads. Stresses from bending perpendicular to the roadway centerline were apparently related to the skew and were less than one-third of the bending parallel to the centerline. Axial loads and maximum stresses varied among piles, although skew effects and pile foundation fixity differences accounted for some, but not all, variability. Maximum stresses were less in the piles without fixity; this indicates that construction loadings support the feasibility of designing integral abutment piling without fixity.

Soil Nail Forces Caused by Frost

Soil nailing can be an effective solution for wall construction but is not common in colder climates because unknown frost forces may occur in frost-susceptible soils behind the wall. Currently, no design criteria exist for these walls in frost conditions, but development of design guidelines under frost conditions would promote the use of this technology in cold climates. Soil nail head force results are presented for 3 years of monitoring of a soil-nailed wall in Moscow, Maine, in a frost-susceptible environment. Also, proposed methods for estimating nail head tensions arising from freezing in frost–susceptible conditions are discussed. Instrumentation was installed to determine the effectiveness of the wall’s facial insulation and to determine the effects of frost on an uninsulated wall. One monitoring station was insulated and the other comparable station was not. Instrumentation, including thermocouples, thermistors, vibrating wire strain gauges, piezometers, and earth pressure cells, revealed wall performance. During three milder than normal winters, frost action in the uninsulated areas produced tensions that exceeded design tensions. A portion of the annually induced nail head tensions was permanent and cumulative. Facial insulation minimized frost loads on nail and wall components below the top nail row. For frost-susceptible conditions, the magnitude of frost-induced maximum additional nail-head tension was related to the seasonal freezing index. The ultimate permanent nail head tension caused by frost was estimated from measurement data to be 2.5 times the peak seasonal tension increase.