Practice Periodical on Structural Design and Construction

This paper describes developments of integrated tools for predicting, monitoring, and controlling ground movements associated with excavations in urban areas. The paper describes developments in the following areas: (1) laser scanning and webcams for developing an accurate record of construction activities; (2) automated and remote instrumentations to measure movements; (3) intelligent, self-updating numerical models to compute anticipated ground movements, and to learn from field observations; and (4) integration of heterogeneous data using a geographic-information-system. These new technologies and improvements are illustrated using excavations in the Chicago area.

The objective of this study is to measure the effectiveness of three commonly used changeable message sign (CMS) messages in reducing vehicular speeds and variances in highway work zones. This paper presents the results of a field study conducted on Interstate-90 in western New York State to evaluate the use of three different types of messages displayed on a CMS, as a speed control measure. The study included speed measurements of nearly 180,000 vehicles. The three types of CMS messages tested were: (1) $\mathit{\text{RIGHT}}\mid \mathit{\text{LANE}}\mid \mathit{\text{CLOSED}}\sim \mathit{\text{KEEP}}\mid \mathit{\text{LEFT}}$ ; (2) $\mathit{\text{WORK}}\mathit{\text{ZONE}}\mid \mathit{\text{MAX}}\mathit{\text{SPEED}}\mid \mathit{45}\mathit{MPH}\sim \mathit{\text{BE}}\mid \mathit{\text{PREPARED}}\mid \mathit{\text{TO}}\mathit{\text{STOP}}$ ; and (3) $\mathit{\text{LEFT}}\mid \mathit{\text{LANE}}\mid \mathit{\text{CLOSED}}\sim \mathit{\text{KEEP}}\mid \mathit{\text{RIGHT}}$ . Of the three CMS messages tested, the CMS message stating “ $\mathit{\text{WORK}}\mathit{\text{ZONE}}\mid \mathit{\text{MAX}}\mathit{\text{SPEED}}\mid \mathit{45}\mathit{MPH}\sim \mathit{\text{BE}}\mid \mathit{\text{PREPARED}}\mid \mathit{\text{TO}}\mathit{\text{STOP}}$ ” proved the most effective, significantly reducing vehicle speeds by $3.3–6.7\mathrm{mi}∕\mathrm{h}$ $(5.3–10.8\mathrm{km}∕\mathrm{h})$ . The other two CMS messages were not as effective. The standard deviation of speed for the CMS message: $\mathit{\text{WORK}}\mathit{\text{ZONE}}\mid \mathit{\text{MAX}}\mathit{\text{SPEED}}\mid \mathit{45}\mathit{MPH}\sim \mathit{\text{BE}}\mid \mathit{\text{PREPARED}}\mid \mathit{\text{TO}}\mathit{\text{STOP}}$ increased by $1.1–1.7\mathrm{mi}∕\mathrm{h}$ $(1.8–2.7\mathrm{km}∕\mathrm{h})$ in the driving lane and $0.2–2.0\mathrm{mi}∕\mathrm{h}$ $(0.3–3.2\mathrm{km}∕\mathrm{h})$ in the passing lane. The speed variances for the other two CMS messages ranged from $-2.00\text{to}1.13\mathrm{mi}∕\mathrm{h}$ (from $-3.23\mathrm{km}∕\mathrm{h}\text{to}1.83\mathrm{km}∕\mathrm{h}$ ).

Images of structural collapse crowd our globalized television screens; from wars, terrorist bombs, and earthquakes. The outcomes often look quite similar, but what are the engineering differences? Look first for differences relating to collapse mechanisms: (1) earthquake engineering focuses on sway collapse mechanisms in which the building as a whole moves sideways and may collapse under its own weight; and (2) explosions may remove one or several load-bearing columns, walls or transfer structures leading to vertical collapse and the “double-span mechanisms” of GSA (2003). Records of earthquake damage show that earthquakes can also remove supports, often corner columns causing two-way cantilever mechanisms. Earthquake engineering does need to include recognition of “lost column” events and to incorporate design against progressive collapse. Common to earthquakes and to explosions is the need for ductile detailing and ductile detailing for lost column events is similar to that for earthquakes if not always for the same reasons. Ductility does need to relate to specific collapse mechanisms and so, although earthquake engineering is an excellent starting point for design against progressive collapse, it does need to adapt so as to include the “double span” mechanisms at lost supports.

Structural engineering design is replete with uncertainties, some of which are obvious and some of which many engineers may never have considered. This paper is an examination of the uncertainties facing structural engineers and the ways that engineers have developed to handle those uncertainties. Uncertainty can be separated into two categories: Aleatory, related to luck or chance, and epistemic, related to knowledge. This breakdown has an impact on how we handle the various types of uncertainty. Uncertainty has a range of sources; we consider five broad sources: time, statistical limits, model limits, randomness, and human error. These five sources will be examined using examples from structural engineering, particularly with respect to the allowable stress design and LRFD code formats. Some uncertainties are explicitly dealt with in design codes, some are dealt with through quality control measures, and some are dealt with in implicit ways that we often do not think much about, e.g., heuristics. Design codes can deal with uncertainties caused by randomness, statistical limits, some aspects of time, and modeling. Other uncertainties such as human error must be dealt with using quality control methods, such as peer reviews and construction inspection.

This paper is an overview of the characterization, analyses, design, and retrofit construction for the seismic upgrade and retrofit of a historic (circa 1860) unreinforced masonry church tower. The methodology utilized for this project was developed by the late Dr. Fernando Lizzi and is known in the United States as the internal reinforcement method, with micropiles for the additional foundation elements. The strengthening objectives were to correct the environmental mode of material degradation, upgrade the average compressive strength of the masonry tower piers and limit further axial deformation, and provide necessary internal reinforcement and foundation retrofit to resist probable seismic attack.