Primus V. Mtenga

Effect of Construction Induced Vibrations on Green Concrete in Drilled Shafts

This study was concerned with vibrations induced during drilled shaft construction on green concrete in adjacent drilled shafts. To characterize the types of vibrations, a full-scale field test was conducted using a 0.9-m (3-ft)-diameter steel casing vibrated at a peak particle velocity (ppv) of 250 mm/s (10 in./s) to various depths in a sandy soil layer. In addition to the steel casing, the peak particle velocities were recorded at different distances and depths from the vibration source. Empirical relationships from measurements were developed to predict the velocity values on the surface and in the ground along the penetration depth of the steel casing. Laboratory tests were conducted on two groups of green concrete samples to determine the effect of ppv and curing time on concrete properties. These tests showed a 10% reduction in the 28-day compressive strength for samples subjected to continuous vibration at ppv of 50 mm/s (2 in./s) for a duration ranging from the initial to the final setting time. O...

The effect of materials and surface preparation on joining methods: A review

Materials have been the primary element of the structural community from the existence of ceramics to the more durable and efficient polymers. The uniqueness of these materials stems from a necessity of a particular era. Because of the uniqueness of each material, the study of damage is of key interest in materials research. In conjunction with the essential materials, proper joining techniques are also fundamental in infrastructure; however, joints represent one of the greatest challenges in the design of structures. Current forms of joining include mechanical and adhesive, where adhesive bonding is preferred. However, no joint can be properly designed without adequate surface preparation. Proper methods for surface preparation and joining techniques will be reviewed for composite materials. This review will highlight some of the common approaches used to enhance the strength of the joint and, therefore, the structure itself.

Performance of Screen Enclosures under Repeated Loading Cycles

AbstractAluminum screen enclosures suffer from significant damage in hurricanes. In an attempt to identify ways to minimize the damage to screen enclosures, experimental investigations were conducted to study how screen enclosures perform when they are subjected to repeated loading cycles. The loading cycles mimic gradually increasing hurricane winds, while considering the fluctuating nature of the wind. Three types of specimens were constructed and tested. Their overall geometry was the same but their bracing strategies were different. Three damage indices were used to analyze the data. Qualitative assessment and comparison of damage was also conducted. Overall, K-type bracing was most effective followed by cable bracing. Lack of bracing resulted in sudden failure. Beam-to-host connections were very critical in preventing catastrophic failure. Suggestions on how to improve beam-to-host connections are provided along with other measures to mitigate the damage on screen enclosures. Where feasible, the most...

Performance of Metal-Plated Wood Joints Exposed to Periods of Soaking Moisture

AbstractMetal-plated wood truss systems may be rained upon during the construction phase, resulting in the soaking of the connections. In this paper, the results of an investigation of the behavior of metal-plated wood joints subjected to periods of soaking are presented. The wetting regimes included (1) 4-h shower, (2) alternating cycles of a period of shower wetting followed by a period of no shower, and (3) 24-h soaking in a water tank. Results of tests conducted after wetting and after wet-dry cycles were compared with results of dry control tests. The results show the wet joints lost over 40% of their load-carrying capacity in all three wetting regimes. Upon drying, the strength loss was about 10%. Likewise, the stiffness of the joints deteriorated, with stiffness loss ranging from 12 to 37%. In contrast to the load-carrying capacities, there were insignificant recoveries in joint stiffness upon the drying of the specimen, with additional loss of stiffness during the drying process in one of the grou...

Integration of a Database and a Decision Support Tool for Crash Cushion Selection

The efficiency and effectiveness of designers can be improved tremendously by the availability of tools to assist in the integration of information pertinent to the design parameters. Developments in computing power have allowed fast handling of large databases. This has enabled designers and facility owners to start considering life-cycle engineering design approach. This approach takes into consideration the actual capital cost, operating costs and level of service or performance together with associated opportunity cost throughout the life of a structure. This approach leads to a more balanced view of investment based on construction, operation, renewal, replacement and decommission considerations. Consideration of all phases of the life-cycle supports intelligent and informed decision-making. In this paper the development of a Decision Support Tool (DST) for the design of attenuators is presented. DST includes the modeling of critical parameters such as the site characteristics, attenuator specifications scored against historical performance data from a similar or closely related site, and operating conditions. The tool can be used to rank expected performance of existing attenuator system or the design of a new system.