A nondestructive inspection procedure that uses the ultrasonic technique to determine the material properties of timber piles above and below water is described, and the equipment developed is presented. The technique is suitable primarily for piles such as those on the Denton Bridge (that collapsed in Maryland in 1976) and others that are immersed in fresh water for long periods of time and sustain damage to the wood microstructure, which can reduce pile capacity by actually changing material parameters, such as strength and density, without a loss of cross-sectional area. This type of destructive action cannot be detected by any existing inspection technique. Laboratory testing of a large number of new and old piles from four different bridges in the state of Maryland were used to establish relationships between the pulse velocity from the ultrasonic testing and the crushing strength of the timber piles. Variables that affect the relationships, such as type of wood, degree of decay, moisture content, and treatment of the wood, were also studied. The relationships developed were verified by determining the pulse velocity of in-place piling in a fifth bridge, then removing the piles, cutting them into sections, and axial load testing the sections to determine the strength of the piles. It has been concluded from the favorable comparison of the calculated and the experimentally determined strength that the technique and equipment developed could be confidently used in timber pile inspection. The quantitative determination of the remaining strength of timber piles in service will lead to appropriate judgments as to the ability of the piles to further support the loads imposed on them.

Federal and state legislation requires periodic inspection and evaluation of highway and railroad bridges and requires that they be rated as to their safe load-carrying capacity. It has been pointed out that 70 percent of the highway bridges in the United States were built before 1935 (1) and that almost 4 out every 10 are defective. Therefore, it is vital that these bridges be effectively inspected in order to predict their remaining life and verify their structural integrity. One aspect of the problem is the existence of a large number of timber piling structures that are old and rapidly deteriorating. Thus their periodic inspection is necessary to ensure the early detection of damage or deterioration and to prevent structural failure. Inspection is also essential for an economical decision with regard to bridge replacement or rehabilitation. Despite a recent underwater inspection of the piling, an unanticipated failure occurred to a timber-supported bridge at Denton, Maryland, in early 1976. The underwater inspection had indicated rea-