Editor’s Note

The February 2006 issue of the Practice Periodical includes the Structural Design Forum, which in this issue deals with the “Update on Current Changes and Future Directions for Structural Masonry Design” and was prepared by Nestor R. Iwankiw, the Editor of the Structural Design Forum. Cliff Schexnayder, the Editor of the Construction Forum, prepared an interesting and well-illustrated article on “Early American Railroad Construction.” The main section of the periodical includes seven papers, six of which are classified as being in the structures category and one in the materials category. All of these papers are summarized below.

The first paper in this issue is entitled “Blast and Construction Vibration Monitoring and Control: Thirty-Five Year Perspective.” It was prepared by Professor Charles H. Dowding of Northwestern University, Evanston, Ill. As the title suggests, this paper covers a significant portion of the author’s career and traces important aspects of blast and construction vibration monitoring in which the author was involved in his academic work and consulting practice. This is an important paper and is highly recommended by this editor who has known this distinguished engineer, educator, and author for many years and, at least on one occasion, has worked with him on a project.

The second paper is entitled “Design of Circular Base Plates” and was authored by Dr. Dajin Liu, a Senior Structural Engineer from the Chicago, Illinois Parsons’ office. This is the second time that this writer has contributed a paper on this subject to the Practice Periodical and we appreciate his work in developing design aids for the practicing engineering profession. Although explicit solutions for rectangular base plates can be found in many textbooks and in AISC publications, a complete design procedure for circular base plates under different loading conditions has not been documented except for large eccentric loads. In this paper, the author has developed a complete Allowable Stress Design (ASD) procedure for design/analysis of circular base plates with axial loads, small eccentric loads, and moderate eccentric loads. The procedure is illustrated by several examples involving different loading conditions.

The third paper in this issue is entitled “Performance of Structures before and during Failure” and was prepared by Dave K. Adams of Lane Engineers, Inc., Tulare, Calif. This paper provides guidelines for investigating structural failures. We all know that investigation of structural failures is very different from the task of designing new or upgrading existing structures. It is important to know what data to look for and record; what samples to take, store, and evaluate; and what records to obtain and examine. A rational data gathering procedure is needed so that all important information is obtained in a timely manner and none is lost. This author does an excellent job of providing guidance that can be used for structuring an effective structural failure investigation. This is a timely paper in the light of the many natural disasters that have occurred in this country in the recent past and whose damage is being investigated by numerous engineers.

The fourth paper is entitled “Simplified Structural Analysis of Retaining Walls on Stepped Footings” and was prepared by Professor Sami W. Tabsh of the School of Engineering, American University of Sharjah, Sharjah, UAE (United Arab Emirates) and Omar Geblawi of Houston Community College–Southwest, Stafford, Tex. This paper provides practical information on the design of stepped footings supporting retaining walls. The behavior of walls supported on a stepped footing is a complex design problem due to the presence of reentrant corners and double curvature. The authors used the finite-element method to analyze a large number of retaining walls with different geometries. The results of their analysis showed that both positive and negative bending moments can exist in retaining walls supported on stepped footings, thus, both faces of the wall need to be reinforced for flexure. It is also stated that very high stresses due to shear and bending occur at the reentrant corner of the stepped footing. Such forces, however, cannot realistically exist in thin reinforced concrete structures due to postcracking deformations. Therefore, structural design at such locations should be based on values of shear force and bending moment just off the reentrant corner, provided that proper detailing with diagonal steel reinforcement is utilized at the tip of the step.

The fifth paper in this issue is entitled “Validation of Shoring Made of HDPE Pipe or CGS Pipe Normally Used for Culverts and Sewers.” It was prepared by Andre Lan of the Institut Robert Sauve en sante et en securite du travail (IRSST), Montreal; Professor Denis LeBoeuf of Laval University, Quebec; Professor Omar Chaallal of Ecole de Technologie Superieure (ETS), Montreal; and Renaud Daigle of Institut Robert Sauve en sante et en securite du travail (IRSST), Montreal. All excavations require some form of shoring and since there are numerous different excavations, there is a need for different types and methods of shoring. For water supply and sewer networks involving small-dimension excavations of short duration, proven shoring and shielding systems cannot be effectively used. An attempt was made to use HDPE and CGS pipes for this purpose. Although such pipes are designed in accordance with water and sewer pipe requirements, their behavior when used for shoring has never been subject to quantification tests. The study described in this paper dealt with the analysis and testing of HDPE and CGS pipes as shoring for small-dimension excavations of short duration on the water supply and sewer networks.

The sixth structurally oriented paper in this issue is entitled “Effects of Soil-Structure Interaction on the Analysis of Cylindrical Tanks” and was prepared by Professor Nasreddin el Mezaini of the Islamic University of Gaza. This paper deals with cylindrical tanks commonly used in water and sewage treatment plants. Such tanks are generally built of cast-place-concrete with flat or conical bases. Design codes specify high standards of serviceability and rigid requirements for water tightness and crack control to prevent leakage and corrosion of reinforcing steel. In determining liquid or earth pressure forces acting on the tank wall, the designer can utilize the design coefficients determined by the Portland Cement Association (PCA). The PCA tables consider different conditions for the wall-base joints but do not consider the effects of varying sub-base soil conditions or geometry of the base slab. The objective of the study reported in this paper was to investigate how different soil conditions and base geometries affect the forces acting on the tanks. A finite-element analysis model of the tanks, using shell elements, was employed using the SAP2000 finite-element analysis program. Results indicated significant discrepancies in the design forces when compared with those obtained from the PCA tables.

The final paper in this issue is entitled “High-Volume Fly Ash Concrete: Analysis and Application.” It was prepared by Mark Reiner, PhD candidate, and Professor Kevin Rens, both of the University of Colorado at Denver. As the title indicates, this paper deals with the use of “large” quantities of fly ash in the making of concrete. We all know that fly ash has been used as a partial replacement for cement for many years. However, its use has been mostly limited to low volume percentages such as 10 to 20% replacement. This paper looks at high volume percentage replacements from 40 to 70%. A minimix study revealed that 50 to 60% cement replacement percentages were the best candidates for full-scale testing. According to the authors, the environmental and economic benefits were significant when compared to the same element constructed with 100% Portland cement mix. The products built included an alley panel and curb and gutter sections in the city and county of Denver, a precast manhole and lid, and a twin tee prestressed girder.

The Discussion and Closures section of the Periodical includes a discussion of an earlier (May 2004) article prepared for the Structural Design Forum by Howard J. Hill and entitled “Rational and Irrational Design Loads for ‘Temporary’ Structures.” The discussion was prepared by Professor J. Mohammadi. The discussion also includes a preface prepared by Nestor R. Iwankiw, the Structural Design Forum Editor. The discussion is then followed by a closure which was prepared by Howard J. Hill.

The editorial board asks its readers to submit discussions and comment on the subject matter and quality of papers included in this issue. Letters to the editor should be directed to Nestor R. Iwankiw if the issue deals with structures and to Cliff Schexnayder if the issue deals with construction and materials.