EDITOR’S NOTE

The May 2005 issue of the Practice Periodical on Structural Design and Construction contains eight interesting articles∕papers prepared by authors from different parts of the world, such as the United States, Sri Lanka, Finland, People's Republic of China, United Arab Emirates, Canada, Hong Kong, and Greece. These are briefly summarized here.

The first paper deals with wood shear walls and is entitled “Effect of Hold-Down Misplacement on the Strength and Stiffness of Wood Shear Walls.” It was prepared by D. J. Lebeda of Kiewit Pacific Co., Vancouver, WA, R. Gupta and D. V. Rosowsky of Oregon State University, and J. D. Dolan of Washington State University. The objective of the study on which this paper is based was to determine the effect of misplaced hold-downs on the behavior of wood shear walls when subjected to monotonic and cyclic loading. Three shear wall configurations were considered, i.e., a wall with hold-downs at the ends, walls with one misplaced hold-down to the first interior stud, and walls with misplaced hold-down plus additional nailing applied to the stud attached to misplaced hold-downs. Results showed that misplaced hold-downs caused reduction in strength and absorbed energy as expected. The magnitude of this reduction depended on whether the loading was monotonic or cyclic. Specimens with misplaced hold-downs achieved strength values 42% lower under monotonic loading, and 35% lower under cyclic loading when compared with hold-downs at the ends. Specimens with misplaced hold-down plus additional nailing reached an average strength that was 21% lower under monotonic loading and 19% lower under cyclic loading when compared to specimens with hold-downs at the ends.

The second paper in this issue deals with the “Effect of Relative Humidity on Absolute and Differential Shortening of Columns and Walls on Multistory Reinforced Concrete Buildings.” It was prepared by M. T. R. Jayasinghe and W. M. V. P. K. Jayasena, both of the University of Moratuwa, Sri Lanka. The authors state that in tall multistory reinforced concrete buildings, absolute and differential shortening between adjacent vertical members became a significant problem due to cladding failures in the recent past. Factors that cause these problems have been identified as time dependent creep and shrinkage coupled with elastic shortening, both of which depend on the relative humidity of the surrounding environment. This paper discusses the effect of relative humidity on absolute and differential shortening of vertical elements in reinforced concrete buildings and suggests solutions.

“Typical Moisture Failures of Slab-on-Ground Structures in Finland” is a paper prepared by V. Leivo and J. Rantala of Tempere University of Technology, Finland. This paper includes a summary and a discussion of case studies on moisture damaged slab-on-ground structures. The common causes for moisture damage are classified into four categories: design issues, construction issues, repair issues, and maintenance issues. The most common cause is faulty design. The most common design faults are lack of a capillary breaking drainage layer under the slab, lack of thermal insulation, and incorrect placement of the vapor barrier.

“Techniques and Performance of Post-Prestressed Tunnel Liner” was prepared by Jingfu Kang and Yuming Hu of Tianjin University, People's Republic of China. This paper describes what the authors claim to be a new type of concrete tunnel liner post-tensioned with double looped unbonded tendons. The performance of the liner was investigated by full-scale model tests with instrumentation in the field. This liner is purported to have advantages over similar posttensioned concrete liners. These advantages include a more uniform stress distribution due to reduction of friction losses, deletion of corrugated metal ducts, reduction of the number of anchor heads, shortened construction time, reduction in cost, and improved structural integrity.

Another interesting and potentially useful paper dealing with concrete is entitled “Effect of Spread Footing Flexibility on Structural Response” by S. W. Tabsh of the American University of Sharaj and A. R. Al-Shawa of ABB Transmission and Distribution, Abu Dhabi, both of the United Arab Emirates. The authors state that design codes and specifications allow a linear soil pressure distribution to be assumed for the design of spread footings. This approach is valid for infinitely rigid footings. Although past experience has shown that this approach is satisfactory for most footings, there are cases where a shallow foundation needs to be analyzed as a flexible structure, particularly in those cases where a footing is long∕wide and thin. In this study, a stiffness factor is developed that can determine whether a footing can be considered rigid. This factor is a modified version of an expression first proposed by Meyerhof in 1953, but takes into account the size of the column supported by the footing. The study is based on modeling spread footings subjected to concentric and eccentric loading by the use of finite elements. The footings are modeled using thick rectangular plate elements, and the soil is modeled using elastic springs.

“Postconstruction Evaluation of HDD Installations” is a paper prepared by S. T. Ariaratnam of Arizona State University and I. J. Beljan of PCL Construction, Inc., Edmonton, Alberta, Canada. The authors state that questions concerning the compactive nature of drilling fluids within the annular space during horizontal directional drilling (HDD) operations have arisen in the recent past. To address these concerns, a field and laboratory study was conducted to provide both a qualitative and a quantitative assessment of the annular space. The study consisted of installing 61 m (200 ft) bore lengths of 100 mm (4 in.), 200 mm (8 in.), and 300 mm (12 in.) SDR 17 high density polyethylene (HDPE) pipe in two different soil mediums, clay and sand. Subsequently, the pipes were excavated with visual and strength measures of each of the installations taken at time periods of 1 day, 1 week, 2 weeks, 4 weeks, and 1 year after installation to assess the annular space region over time. Additionally, samples of the drilling fluid were evaluated both in the field and in the laboratory. This paper presents the results of this research initiative and provides qualitative and quantitative information on borehole annular space integrity during HDD installations. Results showed that the integrity of the annular space was maintained, and the strength properties increased over time through apparent consolidation or equalization with the native soil.

J. S. Kuang and S. Li, both of Hong Kong University, Kowloon, Hong Kong prepared an interesting and practical paper entitled “Interaction-Based Design Formulas for Transfer Beams: Box Foundation Analogy.” The authors state that the design and analysis of transfer beams that support in-plane loaded shear walls have received added emphasis in the design community owing to their importance in connection with the design of tall buildings. The current practice in designing transfer beam-shear wall systems does not generally consider the significant interaction of the transfer beam and the upper shear walls. This leads to an unreasonable design for the internal forces of structural members and the corresponding steel reinforcement detailing. This paper presents interaction-based design formulas for determining bending moments and axial forces of transfer beams that support in-plane loaded shear walls. These formulas were derived by the use of a box foundation analogy and have been shown to provide practicing engineers a very simple and efficient, yet accurate, means for calculating bending moments and axial forces in transfer beams.

“Strength of Unreinforced Masonry Walls Under Concentrated Compression Loads” is a paper prepared by P. G. Asteris of the Technological Educational Institute, Athens, Greece and C. A. Syrmakezis of the National Technical University of Athens, Greece. This paper investigates the strength of masonry walls subjected to concentrated vertical loads. An orthotropic finite-element model is used to simulate wall behavior. Nonlinear deformation characteristics and the anisotropic behavior of masonry material are taken into consideration. A new anisotropic yield∕failure surface of a masonry wall under biaxial stress in a cubic tensor polynomial form is proposed. A parametric study is carried out using several parameters such as the loaded area length to the total length ratio, the load position in relation to the end of the wall, and wall geometry. Based on the results of this parametric investigation, a new design rule is proposed.

This issue also includes articles in the Structural Design Forum and the Construction Forum portions of the Journal. The article for the Structural Forum entitled “Joint Details in Post and Beam Framing” was prepared by John Springfield, one of the two coeditors of the Structural Forum for this publication. The article for the Construction Forum entitled “Our History…Mega Projects West Coast… Conferences…” was prepared by Cliff Schexnayder, one of the two coeditors of the Construction Forum for this publication.

Included in this issue is a discussion of the paper entitled “Competitive Bid versus Negotiated Bid in Commercial Construction Industry—One Contractor’s Perspective” by Steve Zelasko and Cliff J. Schexnayder. The discussion was prepared by Robert F. Borg, Chairman, Kreisler Borg Florman General Construction Company, Scarsdale, N.Y. Also included is the closure to this paper∕discussion prepared by Cliff J. Schexnayder one of the two authors of the original paper.