Practice Periodical on Structural Design and Construction

The objective of this study was to determine the effect of misplaced hold-downs on the monotonic and cyclic behavior of wood shear walls. Three shear wall configurations were considered: (1) walls with hold-downs at the ends; (2) walls with one misplaced hold-down to the first interior stud; and (3) walls with misplaced hold-downs plus additional nailing applied to the stud attached to misplaced hold-downs. Results showed that misplaced hold-downs cause reductions in strength and absorbed energy. Specimens with misplaced hold-downs achieved strength values 42% lower under monotonic loading and 35% lower under cyclic loading when compared to the specimens with hold-downs at the ends. Specimens with misplaced hold-downs plus additional nailing reached an average strength that was 21% lower under monotonic loading and 19% lower under cyclic loading when compared to the specimens with hold-downs at the ends. Denser nail spacing applied to the stud with misplaced hold-downs significantly increased the amount of energy absorbed by the shear walls. The monotonic and cyclic test results showed that misplaced hold-downs have detrimental effects on the structural performance of wood shear walls. Application of denser nail spacing can help such walls regain strength.

 In tall, multistory reinforced concrete buildings, absolute and differential shortening between adjacent vertical members has become a significant problem during the recent past due to the use of high performance concrete and more advanced design techniques that resulted in smaller member sizes. The failure of nonstructural elements such as claddings has been observed in several structures constructed in the past few decades. The factors that cause these problems could be identified as time-dependent creep and shrinkage coupled with elastic shortening. Both creep and shrinkage 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.

This paper includes a summary of several case studies on moisture-damaged slab-on-ground structures. The object of the paper is to suggest a classification of the causes for moisture damage and introduce the typical moisture failure of slab-on-ground structures in Finland. The common causes for moisture damage in the slab-on-ground structure can be classified into four categories: design, construction, repair, and maintenance. According to the studied moisture-damage cases, the most common cause is design fault. Usually the slab-on-ground structure is unfit in the light of present knowledge. 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.

This research examined a new type of tunnel liner–concrete liner postprestressed with double-looped unbonded tendons. The performance of the liner was investigated by full-scale model tests and field instrumentations conducted for the Xiao Langdi sediment tunnel, which is the first water convey tunnel constructed using this method in the world. There are many remarkable advantages of this new type of tunnel liner over liner postprestressed with uncoated tendons, including its more uniform stress distribution due to the significant reduction of friction losses; its lower construction cost through deletion of corrugated metal ducts, reducing 50% of the total number of anchor heads and 30% of the strands required; its shortened construction cycle due to the simplicity of tensioning and boxout backfilling; and its improved structural integrity from reduction of about 50% of boxouts. The subject tunnels have been in use for more than three years to date and indicated that a postprestressed tunel liner is a desirable solution for water conveyance tunnels with a high antiseepage requirement but poor geological conditions. The technique can also be used in other structures, such as cylindrical concrete tanks and hydroelectrical power tunnels.

Spread footings are normally used under individual columns of buildings and bridge piers. They are economical to use and are applicable for any soil conditions where the bearing capacity for the applied loads is adequate. Structural 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. Past experience has shown that the assumption of a linear pressure distribution is satisfactory for most footings; however, there are some cases in which a shallow foundation must be analyzed as a flexible structure, particularly if the footing is excessively long/wide and thin. In this study, a relative stiffness factor, $K_r^{\prime }$ , is developed that can determine whether a footing can be considered rigid for the purposes of structural analysis and design. 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 on the footing. The study is based on modeling square and rectangular spread footings subjected to concentric and eccentric loadings by finite elements. The footings are modeled using thick rectangular plate elements and the soil with elastic springs. The results of the study showed that a footing with $K_r^{\prime }$ factor greater than 1.0 indicates that it can be analyzed as a rigid footing with reasonable accuracy. This includes determination of soil pressures, vertical footing displacements, shear forces, and bending moments. The study also showed that maximum shear forces within a spread footing are less sensitive to changes in the stiffness of a footing than bending moments.

Recently, questions have arisen concerning the compactive nature of drilling fluids within the annular space during horizontal directional drilling (HDD) operations. 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 $61\mathrm{m}$ $\left(200\mathrm{ft}\right)$ bore lengths of $100\mathrm{mm}$ $\left(4\mathrm{in.}\right)$ , $200\mathrm{mm}$ $\left(8\mathrm{in.}\right)$ , and $300\mathrm{mm}$ $\left(12\mathrm{in.}\right)$ SDR 17 high density polyethylene 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 $1\text{day}$ , $1\text{week}$ , $2\text{weeks}$ , $4\text{weeks}$ , and $1\text{year}$ after installation to assess the annular space region over time. Additionally, samples of the drilling fluid were evaluated both in the field and at a laboratory. This paper presents the results of this research initiative and provides qualitative and quantitative information on borehole annular space integrity during HDD installations. The study revealed that: (1) the integrity of the annular space was maintained, as little evidence of voids was present; and (2) the strength properties increased over time through apparent consolidation, or equalization, with the native soil.

The design and analysis of transfer beams that support in-plane loaded shear walls have been receiving added emphasis of late due to their importance in connection with the design of tall buildings. The current practice in designing the transfer beam–shear wall systems does not generally consider the significant interaction of the transfer beam and the upper shear walls, thus leading to an unreasonable design for the internal forces of structural members and the corresponding steel reinforcement detailing. This paper presents interaction-based design formulas, which are derived by use of a box foundation analogy, for determining the bending moment and axial force of the transfer beams that support the in-plane loaded shear walls. The design formulas have been shown to provide practicing engineers a very simple and efficient, yet accurate, means of calculation of the bending moment and axial force in the transfer beams.

In this paper, the strength of masonry walls subjected to concentrated vertical loads is investigated. An orthotropic finite-element model is used to simulate the wall behavior. Nonlinear deformation characteristics of masonry material as well as its anisotropic (orthotropic) behavior 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 the wall geometry. Based on the results of the parametric investigation, a new design rule that takes into account the aforementioned parameters is proposed.