Development of moment-rotation model equations for flush end-plate connections

This paper presents the development of Ramberg-Osgood and Three-Parameter Power model prediction equations for the moment-rotation (M-θ) behavior of flush end-plate connections with one row of bolts below tension and compression flanges. A finite element model (FEM) of the connection region along with the connected beam and column is developed for load deformation analyses, which included material, geometric, and contact nonlinearities. The FEM model was verified with test results conducted and reported for flush end-plate connections in the literature during the 1980s. A matrix of test cases was obtained by varying the geometric variables of flush end-plate connections within their practical ranges. The connection M-θ data for these test cases were obtained by FEM analyses, which were then curve fitted to Ramberg-Osgood and Three-Parameter Power model equations to obtain parameters defining these equations. Finally, prediction equations were developed for parameters of the model equations as functions of geometric variables of the flush end-plate connections.     

Effect of backwashing on perchlorate removal in fixed bed biofilm reactors

The influence of backwashing on biological perchlorate reduction was evaluated in two laboratory scale fixed bed biofilm reactors using 1- or 3-mm glass beads as support media. Influent perchlorate concentrations were 50 microg/L and acetate was added as the electron donor at a concentration of 2 mg C/L. Perchlorate removal was evaluated at various influent dissolved oxygen (DO) concentrations. Complete perchlorate removal was achieved with an influent DO concentration of 1mg/L resulting in bulk phase DO concentrations below the detection limit of 0.01 mg/L. The influence of increasing influent DO concentrations for 12 h periods was evaluated before and after individual backwash events. Partial perchlorate removal was achieved with an influent DO concentration of 3.5 mg/L before a strong backwash (bulk phase DO concentrations of approximately 0.2mg/L), while no perchlorate removal was observed after the strong backwash at the same influent DO level (bulk phase DO concentrations of approximately 0.8 mg/L). The immediate effect of backwashing depended on influent DO concentrations. With influent DO concentrations of 1 mg/L, strong backwashing resulted in a brief (<12 h) increase of effluent perchlorate concentrations up to 20 microg/L; more pronounced effects were observed with influent DO concentrations of 3mg/L. Daily weak backwashing had a small and, over time, decreasing negative influence on perchlorate reduction, while daily strong backwashing ultimately resulted in the breakdown of perchlorate removal with influent DO concentrations of 3 mg/L.     

Fire stops for plastic pipe

Undue fire hazards may arise when plastic pipe penetrates fire-rated walls or floors. Fire stops for protecting these penetration openings are available commercially. This paper discusses the physical characteristics and operating modes of these devices. A selected number of fire stops were tested in accordance with CAN 4-S115-M85 in either horizontal (wall) or vertical (floor) configurations, using two small-scale furnaces. Reference: K. K. Choi, Fire Stops for Plastic Pipe,Fire Technology, Vol. 23, No. 4, November 1987, pp. 267–279.     

Free vibration analysis of horizontally curved steel I-girder bridges

Presented herein is a finite element formulation for free vibration analysis of horizontally curved steel I-girder bridges. Stiffness as well as mass matrices of the curved and the straight beam elements is formulated. Each node of both of them possesses seven degrees of freedom including the warping degree of freedom. The curved beam element is derived based on the Kang and Yoo's thin-walled curved beam theory in 1994. A computer program is developed to carry out free vibration analyses of the various bridges. Comparing with the frequencies using the general purpose program ABAQUS, the validity of the presented numerical formulation is shown. The numerical formulation is extensively applied to investigate free vibration characteristics of the bridges considering effects of the initial curvature, boundary condition, modeling method, and degrees of freedom of cross frame. Invaluable information which help practicing engineers better understand the vibration characteristics is provided.     

Characterization of ozone decomposition in a soil slurry: kinetics and mechanism.

A series of soil slurry experiments were performed in a carefully conceived reactor set-up to investigate the characteristics of the catalytic decomposition of ozone on a sand and iron surface. Real time on-line monitoring of ozone in the reaction module was possible using flow injection analysis coupled with a computer-controlled UV detector and data acquisition system. The effects of the soil media and size, ozone dosage, pH and p-CBA as a probe compound were examined at the given experimental conditions. Two apparent phases existed, and ozone instantaneously decomposed within one second in the first phase. These were defined as the instantaneous ozone demand (ID) phase, and the relatively slow decay stage. The interactions of ozone with the soil organic matter (SOM) and metal oxides were attributed mostly to the instantaneous decomposition of ozone. From the probe (p-CBA) experiments, 60-68% of total p-CBA removal occurred during the ID phase. The generation of hydroxyl radicals (OH.) was demonstrated and was closely related with metal oxides as well as SOM. Metal oxides in soil surface were considered to have relatively faster reaction rate with ozone and provide more favorable reactive sites to generate higher amount of OH. than SOM. Even at one-tenth concentration of the sands, a goethite-induced catalytic reaction outfitted the removal rate ofp-CBA among all the soils tested. More than 40% of total p-CBA removal occurred on the soil surface. It was inferred that the radical reaction with the probe compound seemed to take place not only on the soil surface but also in the solid-liquid interface. Ozone decomposition and the reaction between OH. and p-CBA appeared to be independent of any change in pH.     

Smart damper using sliding friction of aramid brake lining and self-centering of rubber springs

The purpose of this study is to develop a smart damper with flag-shaped behavior by using the sliding friction of aramid brake lining and the restoring capacity of pre-compressed rubber springs. For this purpose, the friction force of aramid brake lining pressed by bolts was used along with polyurethane rubbers, each with a length of 80 mm, a diameter of 95 mm, and a circular hole of 37 mm. In the experiments, loading frequency and torque force were considered. The loading frequency varied from 0.1 to 2.0 Hz, and frictional force was controlled by variable bolt torque force. The tests were conducted to demonstrate that the clamping force by the bolts could provide normal force to frictional material. The friction force by the aramid brake lining sliding was tested, followed by the pre-compressed rubber springs' behavior. Afterward, a damper combining the two components was tested to verify flag-shaped behavior by using a dynamic actuator, and the damping ratios were evaluated from the hysteretic curves. The behavior of the damper closely matched flag-shaped behavior, resulting in self-centering and energy dissipation capacity.     

Fragility Assessment Model of Building Structures Using Characteristics of Artificial Aftershock Motions

Any additional loads applied to a damaged structure can aggravate its instability and thus, the impact of successive earthquakes need to be considered. This study proposed a quantitative assessment model for the fragility of a damaged structure subjected to aftershock. Mean period and the strong motion duration were considered as characteristics of earthquake motions. Simulation models of two reinforced concrete structures and one steel structure were selected to examine the applicability of the model. Based on the suggested fragility and residual deformation coefficients, critical earthquake sequences for each structure were identified. The proposed model was efficient in selecting critical earthquake sequences by using the limited number of aftershocks, and these sequences are expected to be useful indicators in the establishment of a retrofit plan according to the predicted structural response and target performance levels.     

Moving average correction method for compensation of differential column shortenings in high‐rise buildings

The differential length changes of vertical members in a high‐rise building due to elastic, creep and shrinkage shortenings are of primary concern since the differential shortening of the vertical members causes unexpected damages on structural and nonstructural members. In contrast to researches on prediction methods for calculation of the amount of the shortenings, only few methods or algorithms of compensation of the differential column shortenings have been reported. In this paper, a practical compensation method using moving average correction is presented. The proposed method is applied to the compensation of the differential shortenings of the vertical members in a 70‐story high‐rise building. The performance of the moving average correction method is compared with the optimal compensation method based on simulated annealing algorithm. It is demonstrated that the magnitude of the differential shortening or the degree of the slab tilt due to the length changes in the vertical members can be controlled without using structural optimization techniques. Copyright © 2011 John Wiley & Sons, Ltd.     

Multifaceted public outreach and cost–benefit analysis for its effectiveness validation

A heavily trafficked 4.5km highway stretch on Interstate 15 east of Los Angeles was rebuilt using two extended closures, each spanning nine days with 24/7 operations. Before and during the closures, a multifaceted, extensive, dynamic public outreach programme was implemented to gain public support for the project and to minimize inconvenience to the public. That outreach programme is described, its overall effectiveness in terms of total net benefit and traffic inconvenience during lane closures is assessed, and changes in public perception of the accelerated construction strategy resulting from the outreach programme is examined. Pre‐ and post‐construction surveys performed using the project website mirrored the findings of the traffic measurement study, indicating that the outreach programme effectively reduced traffic demand. The results of two web‐based surveys with a combined total of approximately 400 respondents indicated a dramatic change in public perception of the accelerated construction strategy. The survey results showed that strong initial objection to the accelerated project eventually became supportive of future, accelerated projects. The cost–benefit analysis showed that the additional cost of the outreach programme was outweighed by the savings achieved from reduced road user delay costs.