NOMOGRAPHS FOR THE DESIGN OF STEEL REINFORCEMENT IN CONTINUOUSLY REINFORCED CONCRETE PAVEMENT

This study sought to develop graphic procedures (nomographs) for the design of continuously reinforced concrete pavement (CRCP) by the Texas State Department of Highways and Public Transportation for a range of specified local conditions. This set of nomographs, when used as a supplementary design tool with the CRCP-2 computer program model, will facilitate CRCP design. This will substantially reduce both the time and the cost involved in the design process, while at the same time taking into account the effect of regional and local environments. First, regression equations were developed for the prediction of three design parameters (crack spacing, crack width,and steel stress), and then principles of nomography were applied to these mathematical relations to prepare three corresponding nomographs. The choice of equations was made following multiple linear and nonlinear least-squares fits to a fractional factorial of simulated observations that were output from the CRCP-2 computer program. Theoretical models, developed at the Center for Highway Research in Austin, Texas, and variations of the three design parameters with each of the relevant input variables over the range of the simulated data were considered in deciding on the form of the regression equations. Standard-error-of-residuals and R squared (proportion of variance explained by the regression equation) statistics were considered in the final choice of coefficients for the regression equations. Confidence prediction limits were determined by using multiple linear- regression techniques for application to nomograph predictions. A recommended procedure for the use of the nomographs with appropriate limiting criteria is out-lined and an example given.