Practice Periodical on Structural Design and Construction

The Construction Institute’s Committee on Social and Environmental Concerns in Construction has examined 24 items of social and environmental concerns in construction that will have to be considered by those who are going to be involved in the reconstruction of the World Trade Center. These topics include the economic aspects of the reconstruction, the planning and design, the environmental issues, the transportation challenges, the contractual problems, the memorial, and the security requirements. During the drafting of this report, the Committee received assistance and guidance from the engineering staff of the Port Authority of New York and New Jersey. Some Committee members visited the World Trade Center site at Ground Zero during the preparation of the report. Also consulted by the Committee were some well-known, highly qualified engineers on various aspects of the report. These contributions from nonmembers of the Committee made the report richer. It is the intent of this report to serve as a starting point for planning and redevelopment.

Silt and tidal land have very low bearing strength, and they are generally very thick. Hence, the time necessary for completion of settlement of a constructed building is very long. If it is not possible to adopt deep foundation methods such as pile driving, other methods, such as soil-substitution or heavily rammed gravel bedding on the foundation can be adopted to form a better surface soil to sustain the constructed building. According to the related principles and formulas of fluid mechanics, soil mechanics, and elasticity mechanics, the author’s have found the optimum thickness of rammed gravel bedding, with better economic and social benefits.

Tunneling in hard rock with tunnel boring machines is one of the most mechanized construction processes. Mechanization also applies to the installation of the temporary excavation support and the final lining. Computer-aided process systems have been developed, including: (1) sensor-supported gathering and computer-aided storage of all relevant tunnel operational and survey data; (2) computer-aided visualization and control of the most important boring machine systems; and (3) computer-aided, process-oriented control of all operational processes. Presented here are recent tunneling developments related to gripper and shielded boring machines. In the case of gripper boring machines, particular focus is directed to innovations such as the installation of ground stabilization directly behind the cutter head and adequate logistics to the excavation by engineered “back-up” systems. The back-up system requirements necessary to maintain the high performance of shielded boring machines are enumerated.

The Alabama Department of Transportation (ALDOT) currently maintains over three miles of interstate bridges near downtown Birmingham with significant levels of deck cracking and deterioration. The rehabilitation of these bridges is a matter of great concern to the ALDOT because of the enormous cost and potential for disruptions of traffic. The most viable rehabilitation options at this time appear to be (1) to rehabilitate the bridge decks via overlays; (2) to replace the decks; (3) to add additional longitudinal girders; or (4) to replace the bridge superstructures. The purpose of the research reported in this paper was to investigate and evaluate the option of adding additional longitudinal girders as a bridge deck/superstructure rehabilitation strategy on the existing bridge decks, support girders, bent caps, and foundation elements. Results of the analysis indicate that adding girders is a structurally viable strategy. Particular benefits include doubling the capacity of the deck membrane arching capacity, significant reductions in the superstructure deflections, and an increase in the remaining fatigue life of the existing bridge girders by approximately a factor of eight.

A companion paper reported on theoretical considerations associated with adding girder lines to rehabilitate highway bridge decks and superstructures. This article reports on practical, construction, and cost considerations associated with the addition of girder lines rehabilitation strategy. Results of the investigation indicate that adding longitudinal girders between the existing girders is a viable bridge superstructure rehabilitation strategy. The two primary merits of the strategy are (1) most of the work can be performed from the underside of the bridge, thus minimizing interference with traffic; and (2) the strategy strengthens and stiffens the deck/superstructure and, therefore, should significantly prolong the remaining service life of the existing girders and deck. The greatest drawback to the adding girder lines strategy is its high initial cost. Because of this high cost, the strategy is not recommended except in special cases.