Browsing by Author "Lucko, Gunnar"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Means and Methods Analysis of a Cast-In-Place Balanced Cantilever Segmental Bridge: The Wilson Creek Bridge Case Study
    Lucko, Gunnar (Virginia Tech, 1999-11-30)
    Different means and methods exist in the construction industry to erect bridge superstructures. In planning and execution of the complex construction operations the effects of the chosen erection method need to be considered to achieve a safe and economical process. Failures of bridges under construction have underlined the importance of this issue. Hence, constructability issues need to be considered from the very beginning of projects. Structural analysis mathematically models geometry, boundary conditions, and other structural details, material properties, and so-called actions and incorporates factors of safety. Aforementioned actions, i.e. loads or restraints of deformations may act only temporarily during construction, depending on the method and sequence of erection. However, these construction loads can create considerable stresses in the unfinished structure prior to completion when it still lacks additional redundancy against failure. Furthermore, time-dependent material properties such as creep, shrinkage, and relaxation play a major role, especially in segmental construction. A case study is provided as an example of how constructability issues are dealt with in engineering practice. The Wilson Creek Bridge is a five-span cast-in-place concrete segmental bridge that was erected with Balanced Cantilever Construction. The bridge superstructure incorporated a camber to account for time-dependent deflections in final alignment. Form travelers were used in an alternating manner about the bridge piers to construct cantilever arms that were finally connected at midspan. These travelers remained in place until the box girder segments had reached sufficient strength to be post-tensioned to their predecessors. Casting cycle duration on this project was one week.
  • Thumbnail Image
    A Statistical Analysis and Model of the Residual Value of Different Types of Heavy Construction Equipment
    Lucko, Gunnar (Virginia Tech, 2003-12-03)
    Residual value is defined as the price for which a used piece of equipment can be sold in the market at a particular time. It is an important element of the owning costs of equipment and needs to be estimated by equipment managers for making investment decisions. The purpose of this study is to gain insights into the residual value of selected groups of heavy construction equipment and to develop a mathematical model for its prediction. Auction sales data were collected from two online databases. Manufacturer publications and an online source provided size parameters and manufacturers suggested retail prices matching the auction records. Macroeconomic indicator values were collected from a variety of sources, including government agencies. The data were brought into the same electronic format and were matched by model name and calendar date, respectively. Data from auctions in the U.S. and in Canada were considered for this study. Equipment from four principal manufacturers of up to 15 years of age at the time of sale was included. A total of 35,542 entries were grouped into 11 different equipment types and 28 categories by size as measured by horse power, standard operating weight, or bucket volume. Equipment types considered were track and wheel excavators, wheel and track loaders, backhoe loaders, integrated toolcarriers, rigid frame and articulated trucks, track dozers, motor graders, and wheel tractor scrapers. Multiple linear regression analyses of the 28 datasets were carried out after outliers had been deleted. Explanatory variables for the regression model were age in years, the indicator variables manufacturer, condition rating, and geographic region, and selected macroeconomic indicators. The response variable was residual value percent, defined as auction price divided by manufacturers suggested retail price. Different first, second, and third-order polynomial models and exponential and logarithmic models of age were examined. A second-order polynomial was selected from these functional forms based on the adjusted coefficient of determination. Coefficients for the 28 models and related statistics were tabulated. A spreadsheet tool incorporating the final regression model and its coefficients was developed. It allows performing the residual value prediction in an interactive and intuitive manner.