Editor’s Note

The August issue of the Practice Periodical includes five papers on several different topics:

The first paper is an evaluation of a silt fence tieback system at a highway construction site. The authors state that every year, construction activities in the United States expose millions of acres of soil to wind, rain, and snow. This increases the potential for erosion and thus the need for efficient erosion and sediment control practices. This paper presents the results of a study dealing with the performance of a silt fence system with tie-backs (j-hooks). The data presented provide a qualitative perspective showing sediment migration over time along with the occurrence of lack of failures among two silt fence systems tested. Field test results show that silt fence tieback systems are more effective in containing eroded sediment from construction than traditional linear silt fence systems, and also reduce the risk of silt fence system failures.

The ductile design of glued and laminated beams is the topic considered in the second paper of this issue. Ductility is a fundamental component in the design of structures. For timber structures, the unfavorable material characteristics pose a challenge to the designer. Two approaches for improving the behavior of glue and laminated timber beams were investigated by testing and numerical analysis. The first is based on forming mixed beams with suitably assembled lamellae of different strength class; in the second, steel reinforcement is used. Satisfactory results have been obtained through mixing laminations of different grades, whether from a single or different species, as long as the strengths of the lamellae are well differentiated. Steel-reinforced timber beams require taking special provisions to develop a ductile bending behavior, because material irregularities induce brittle failure of wood in tension before the steel bars yield. Positive results were obtained, specifically preventing local failure modes, by releasing tension stresses in wood, by inserting small diameter steel screws, or with a suitably balanced distribution of steel area. Steel reinforcement provided a simple and reliable solution.

The third paper deals with wood-framed shear walls. The study reported evaluates an innovative use of water- and seismic-damage-resistant, wood-concrete composite (WCC). The WCC design consists of a thin layer of engineered cementitious composite cast in a traditional wood frame. Structural performance and damage sustained during lateral loading and costs were evaluated and compared to traditional wood-framed construction. The authors suggest that this is a viable shear wall system but one that should be refined and tested further.

The fourth paper in this issue deals with an analysis of “floating rail system.” A fairly unique structural problem and solution is presented on the analysis and design of a continuous structural concrete slab track on grade. Rails embedded into the structural concrete with an elastomeric grout system act as part of the overall load resisting system. The classical theory of “beams on an elastic foundation” is used to predict the response of the floating rail system.

The fifth paper addresses wind tunnel studies of low-rise buildings. Measurement of wind force on 1:100 scaled models representing a typical two-story building with flat roof and with parapet was carried out. The model buildings were tested in isolation and when located in a rectangular array of $5\times 4$ building cluster under simulated terrain conditions. Three groups of building clusters with spacing of 60, 90, and $220\mathrm{mm}$ in the direction of wind were considered. The effect of wind angle on building clusters was studied between yaw angles of $-45°$ to $+45°$ at equal intervals of 15°. Mean and rms force coefficients for the panels were evaluated using quasi-static and pseudo-steady approximations. Factors of shielding and enhancement were computed. Test results were compared and validated with data obtained from available literature.