Editor’s Note

This issue of the Practice Periodical includes four papers and two case studies originating from Sudan, the United States, Australia/Singapore, China, and Spain. Topics include the design of box culverts, curved girder deformation prediction, optimal design of molded polyethylene water tanks, design and construction of a roller-compacted gravity dam in a seismic region, construction of a utility tunnel, and a system for construction of a railway underpass without disrupting rail traffic. The following narrative provides a brief summary.

The first paper, entitled “Development Formulation for Structural Design of Concrete Box Culverts,” discusses the development of a structural design procedure. Requirements given in the Design Manual for Roads and Bridges (DMRB, BD31/01) were used in the formulation of the structural design with reference to the AASHTO standard specifications for highway bridges. The writers list and discuss in some detail all relevant loading conditions and design limit states, most of which are referenced from the United Kingdom and Canada; a few are from the United States. The writers indicate the method has been applied to many practical problems and results compare favorably with those obtained from commercially available software. The procedure is said to be applicable to single-cell, twin-cell, and multiple-cell culverts.

In addition to presenting the design procedure, the writers include a very concise discussion of culverts in general, including rigid and flexible culverts, their uses, materials, construction methods, and design and serviceability problems. This paper was prepared by Sudanese engineers and principally for the Sudan climate and soil conditions. Engineers dealing with design, analysis, and construction of culverts in the United States may find this formulation instructive as a basis for comparison with their own procedures.

The study described in “Curved Girder Deformation Prediction Effectiveness Using First-Order, Linear Geometric Finite-Element Models” examines whether a first-order, linear geometric finite-element static model analysis is capable of accurately predicting the deflection and rotation response of a curved steel I-girder bridge and curved steel I-girders. Girder deflections obtained during the erection of a horizontally curved steel I-girder bridge, and deflection and rotation data from curved-beam laboratory tests were used to determine whether a linear geometric finite element analysis could accurately predict their static behavior.

Results indicate that this analytic approach accurately predicts the deflection behavior of horizontally curved I-girders under point loads. The results also indicate this method’s ability to predict the general rotation trends of the experimental beam accurately; however, the analysis model overpredicted peak flange tip displacements, when compared with experimental results.

Circular, rotationally molded polyethylene water tanks have been designed and built since the 1950s, when the technology for this manufacturing process became available. For circular tanks manufactured using this process, the traditional design method has been on the basis of on-hand calculations, considering hydrostatic pressure from the stored liquid as the primary applied load. In “Optimal Structural Design of Circular Rotationally Molded Above-Ground Polyethylene Water Storage Tanks,” the writers present the result of a study of the optimal structural design of 16 circular polyethylene water tanks of various sizes. On the basis of the results obtained, optimal design recommendations for such tank structures are provided, considering both hydrostatic pressure and wind loads.

Gravity dams in seismic regions present a unique challenge. In “Innovative Design and Construction of a High RCC Gravity Dam in High Seismic Intensity Region,” the writers introduce several innovative design and construction measures to build a roller-compacted concrete (RRC) gravity dam with a height of 160 m (524.96 ft), in which the design peak ground acceleration of the dam site is 0.3995 g. The grouting of construction joints between the plant and dam parts is used to enhance the earthquake-resistance ability of the dam. To enhance the lateral stability of the dam, the depth of the construction joint is only $2/3$ of the dam thickness in each roller-compacted layer, and the joints are filled with nonwoven fabrics. This treatment causes the construction joints to be weakly connected, which is not only good for temperature stress release, but also enhances the integrity of the dam. Steel bars are embedded in high tensile stress zones to ensure dam safety. Other aspects, such as layout of the stilling basin, spillway chute design, high-pressure consolidation grouting of the dam foundation, and the reinforcement of slumping mass, are also described.

Underground utility tunnels present unique constructional and operational considerations that require specific approaches to achieve optimal performance and maintenance. From a construction point of view, the main issue may be the accumulation of water surrounding the structure. The design and construction of an adequate drainage system is thus important in avoiding added pressure on gable walls and subslab pressure on the bottom plate. It is also important in avoiding contact between water and the structure, which could lead to water infiltrations resulting in additional construction costs. There is the added problem of assuring the safety and integrity of the facility. In the case study titled “The Lezkairu Utilities Tunnel,” the writers relate such considerations to a specific case of underground utility tunnel or gallery, of approximately 7,885 m, recently built for a new urban expansion area in the city of Pamplona, Spain.

The case study entitled “System for Construction of a Railway Underpass” describes in some detail the building of an underpass below railway tracks by using jacks and pushing a prefabricated reinforced concrete box structure. The system implemented proved particularly delicate, given the constraint of maintaining normal rail traffic throughout the construction of the underpass.

The primary responsibility was to design and effectively carry out a process to adequately guarantee the stability and maintenance of the track bed while the prefabricated underpass box was pushed underneath, at what was undeniably shallow depth—approximately 1 m.

The system developed, although laborious, proved to be highly efficient, because at no time during the course of the work did there arise any circumstances to jeopardize either the safety of the rail track or the physical integrity of the workers on the site.

The editors invite the readers to send in their comments on these papers and case studies.