Author: C. Blackett-Ord (CARE + Blackett-Ord Conservation Limited)
4 January 2016
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C. Blackett-Ord (CARE + Blackett-Ord Conservation Limited)
The River Tyne has been a major discharge port for coal from the UK’s Northumberland and Durham coalfields for centuries. Staiths were constructed near the mouths of navigable rivers as a means of discharging coal from railway wagons into ships, and the Dunston Staiths were the largest timber structure in Europe at the end of the 19th century. Their repair history has been reasonably well documented and so they provide a good case study for timber deterioration, selection of repair species and strength analysis.
A tuned damping solution was developed to mitigate walking induced vibration of joist-framed floors in 25 rectangular, trapezoidal and irregular-shaped rooms in an educational facility. The make-up of the floors was concrete on metal deck, supported by open-web steel bar joists. The floors came in various sizes (800–1200sq.ft) and shapes, with the first resonant frequencies in the 6.5–7.5Hz range. Following the measurement of vibration and finite element analysis of the floors, 50 tuned mass dampers (TMDs) (two for each room) were designed, manufactured and installed to effectively address the vibration challenges of the first structural modes of the floors they were designed for. After installation of the TMDs, the effectiveness of the tuned damping solution was evaluated via further measurements. TMDs effectively dampened the first structural modes of the floors in various rooms and lowered their walking-induced vibration to acceptable levels.
This short article describes the rehabilitation of an office building in Baghdad damaged by a missile strike during the 2003 Iraq War. The author briefly sets out the damage to the building’s steel frame, explains how a structural model was created to enable the design of a supporting steel frame, and describes the installation of the temporary supporting frame and new steel columns using hydraulic jacks to raise the building’s upper stories.
Understanding the dynamic response of a structure or structural element can be a daunting task, particularly for practising engineers normally only concerned with the static design of structures. Many structural engineers will be familiar with the dynamic response of simple single-degree-of-freedom (SDOF) models. However, very few structures will correspond directly to such a form, which usually means computerised solutions are embarked upon, structures are radically altered, possibly needlessly, or problems passed to dynamics specialists. This paper simplifies the analysis to provide arithmetic solutions and a means of understanding the dynamic response of a structure. It also provides a means to verify computer modelling and estimate the characteristics (mass, stiffness and damping) of a TMD to address any residual problematic dynamic response. This enables the design provision for the additional weight attached to the structure and the required space, if a TMD is deemed to be necessary. A worked example of a simply supported welded steel box girder footbridge is presented.