Journal of Performance of Constructed Facilities

Inspection and rating of public infrastructure has become a focus of many recent studies because of well-documented deterioration and failure case studies. A new indirect inspection technique using ultrasonic spread-spectrum methods can significantly improve distress identification and monitoring of deteriorating infrastructure. This paper presents the general concept and application of using a continuous spread-spectrum signal to test structural objects. First of all, the basic theory for this technique will be outlined. Secondly, the basic hardware setup will be described. And finally, the results of two laboratory experiments will be presented. The laboratory results indicate that this new method may be feasible for monitoring and evaluating existing large or complicated structural members. The method does, however, have its limitations, as the signal is very sensitive to transducer orientations, couplant, and ambient conditions as is the case in all contact transducer-based nondestructive evaluation techniques.

A soil nailing technique was used to stabilize a 9-m-deep permanent cut in residual soil for an expressway project in Singapore. This paper describes the construction details, instrumentation, and performance of the nailed soil wall and the results of a field pullout test on a grouted nail. Results of numerical analysis are compared with the measured performance of the wall. The nailed soil wall performed well. Postconstruction performance of the wall showed moderate increase in wall displacements and nail forces due to loss of soil suction resulting from seepage of rainwater into the soil.

This paper presents a case study of repair and strengthening work carried out on a defective reinforced concrete pier. The pier manifested severe cracking and spalling at the joint between its walls and platform. The distress was due to twisting of the platform as a result of torsional stress, which had also caused diagonal shear cracks to appear on the walls. A comprehensive investigation was carried out in order to determine the causes and extent of the problem and to define the remedial measures needed to rectify the problem and prevent future deterioration. The investigation included three phases: field investigation, which included soil borings, platform temperature measurement, and measurement of twist and tilt of the platform; laboratory investigation, which included soil testing and concrete core testing; and analysis of the structure. The repair work consisted mainly of providing a silica-fume-blended cement shotcrete jacketing system around the structure. The repair work was successful, economical, technically feasible, and not very labor-intensive.

In 1829 Stephen Harriman Long built a wood truss with details well suited to the mechanical behavior of wood. The truss was statically indeterminate, prestressed by wedges and required no tensile connections for the diagonals. In 1840 William Howe and Amasa Stone improved Long's design by using threaded vertical iron rods for prestressing. In 1839 Long patented a truss with diagonals that were pretensioned by using wedges on the vertical members. Long's method of prestressing the diagonals in tension was improved by Thomas and Caleb Pratt, who prestressed by tightening threaded iron diagonals. However, their design was not immediately successful for bridges with wood chords because prestressing often caused local crushing of the wood. Therefore, the dominant American truss at mid-century was the Howe truss, wonderfully adapted to the properties of wood, statically indeterminate, prestressed, easily adjusted and maintained, and with precompressed diagonals bearing on joint castings without positive connections to the chords and verticals. All these features were destined to be abandoned by American engineers over the next 20 years.

Following the introduction of iron in the 1840s, bridge companies came to dominate bridge procurement. Their designs featured proprietary compressive elements and joint details. As analysis of statically determinate trusses evolved into an ordinary skill, statically indeterminate forms and prestressing fell into disuse. The statically determinate “American pinned truss” with built-up compressive elements and eyebars became the mainstream design. American fabricators produced ductile eyebars with extraordinary dimensional accuracy. However, all-riveted lattice trusses, principally designed by New York Central Railroad engineers, provided competition. In general, such designs performed satisfactorily and helped to calibrate approximate design procedures for riveted joints. The development of shop and field riveting equipment finally made riveted, gusset-plate connections practical by the turn of the century.

The stability of a lift slab structure is vulnerable during some construction stages, even though the structure becomes perfectly safe when completed. Some stages of the construction can lead to instability, because of the way the lifted slabs are parked before they reach their final destination, where they are integrated with the columns. A formula is derived that can be applied to any construction stage and any configuration of parked slabs. The formula finds the critical load of a typical slab that might cause the structure to collapse during the construction of any specific stage. An example of one such collapse during a construction stage was the case of L'Ambiance Plaza in Bridgeport, Conn. The formula is easy to apply numerically and good enough to indicate whether a specific stage of construction is stable or not. Although the formula does not take into consideration the P-δ effect, it is conservative enough to offset its small influence.

The creation of standing waves in systems vulnerable to harmonics is of interest in both mechanical and electrical contexts. There are cases of harmonics in electrical oscillating systems as well as mechanical ones. Common characteristics of these “wave” phenomena are transport energy, reflection, and resonance, to list a few. Failures of systems that transport this wave energy, either in the form of sound (longitudinal) waves or electromagnetic (transverse) waves have significant similarities. This paper examines the failure of an energy transport system for electromagnetic waves, a television transmission system, and interprets the investigation of the failure in terms common to both mechanical and electrical systems. Investigating failures that sometimes have an obscure cause-effect relationship, especially if they are rare occurrences, often leads to enhanced design parameters that will prevent future occurrences. The paper concludes that if the cause of the failure cannot be significantly reduced, it can be minimized by closer attention to methods that diminish the effects.