42 ■ Transportation Research Record 1809 Paper No. 02-2426 With the further adoption of mechanistic-empirical design methods in the pavement industry, the calculation of critical responses and cumulative damage for a variety of parameters will be imperative. Traditionally, the critical tensile stress developed by loads at the midslab edge has been used as a mechanistic parameter to determine the required thickness in jointed concrete pavements. However, the inclusion of both temperature and shrinkage gradients in concrete pavement analysis can drastically alter the critical stress location and subsequent distress type that predicts pavement performance. Longitudinal and corner cracking have been found in California to be distresses as significant as transverse cracking. Most of the longitudinal and corner cracking can be explained by exces- sive differential drying shrinkage. Using finite-element analysis, this study compared the critical tensile stress near the transverse joint with the critical tensile stress at the midslab edge (relative reference stress) for California-type jointed plain concrete pavements. The analysis of the data showed that transverse joint loads were more significant in critical stress calculations for a considerable number of input parameters. These loads at the transverse joint can manifest themselves as top-down or bottom-up longitudinal, transverse, or corner fatigue cracks unlike the bottom-up transverse cracks traditionally predicted by midslab edge loads. The likelihood of critical slab stresses near the transverse joint was considerably increased with the use of negative temperature gradients and extended lane widths. With the development and refinement of finite– element analysis (FEA), the pavement engineering industry is moving toward the use of mechanistic–empirical (M-E) design methods in an attempt to bet- ter understand cracking distress mechanisms and to provide more reli- able design methodologies. The majority of M-E design has focused on transverse fatigue cracking criteria initiated by loads placed at the midslab edge, since this design would accommodate the major dis- tress seen on many rigid pavement sections. However, condition sur- veys of pavements in California have shown that longitudinal and corner cracking occur as frequently as does transverse cracking (1–3). Studies (4–7 ) have shown that many factors can cause an up- ward curling of the slab, which suggests that transverse joint load- ing deserves greater consideration in concrete pavement design than it has previously been given. If large positive temperature gradi- ents (temperature of slab is hotter on the top than on the bottom) exist as the concrete hardens shortly after construction, the slab will curl upward as the pavement cools and reaches a zero-gradient condition. This occurrence is common during the hot summer con- struction season. This built-in curling can reach magnitudes of 0.055°C/mm or more (8 ). Preliminary analysis has shown that paving under typical nighttime conditions can have an opposite effect on this built-in curling (9 ). Differential drying shrinkage of the concrete has been shown to occur to depths of 50 mm (10, pp. 185–197) and may extend to the mid-depth of the slab (11). Because of the ability of the top of the slab to lose moisture, the rest of the slab tends to remain at a higher level of saturation. This effect can be more pronounced in drier, less humid climates such as those found in the southwestern United States. The drying shrinkage through a slab can be influenced by the concrete mix design and materials, supporting layers, construction practices, climatic conditions, slab thickness, and restraint against movement. These shrinkage distributions have been found in a California study to be high enough that slabs crack under environmental influences before any traffic loading is even applied (12). These curling and warping effects can be modeled as equivalent temperature gradients by relating their strain measurements to the thermal properties of the concrete and adding these equivalent gra- dients to actual temperature gradients. Upward curling due to the residual equivalent negative temperature gradients can shift the temperature frequency distribution significantly. Studies have shown that this shift can be on the order of 5°C to 11°C (4, 5 ) toward a nega- tive temperature differential. This shift can ultimately lead to increased importance of axle loads at the transverse joints. PROBLEM STATEMENT To better characterize the mechanisms resulting in longitudinal and corner cracking, a parametric study was conducted in which loaded axles were modeled at the transverse joint and the resulting stresses were referenced to the maximum stress caused by placing the same load at the midslab edge location: where RRS = relative reference stress, σ trans i = tensile stress at location i caused by load at transverse joint, and σ ref max = maximum tensile stress caused by load at midslab edge. Using Equation 1, an RRS greater than 1.0 would suggest that the stress caused by a load along the transverse joint is greater than the stress caused by the same load placed at the midslab edge location RRS i = σ σ trans ref max () 1 Transverse Joint Analysis for Mechanistic–Empirical Design of Rigid Pavements Jacob E. Hiller and Jeffery R. Roesler J. E. Hiller, B134, and J. R. Roesler, 1211, Newmark Civil Engineering Labora- tory, MC-250, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, IL 61801.