Design
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Rigid Structural Design

An introduction to concepts and empirical equations used in the structural design of rigid pavements.

Rigid Pavement Response Calculations

The following examples illustrate how rigid pavement responses to different stresses are calculated. Load Stress Example Calculations Example 1 Calculate the three critical stresses for 9 inch thick slabs. Use a 9,000 lb. FWD loading (a = 5.9 inches). Use k = 200 pci for calculation of the radius of relative stiffness (l).   1. … Read more »

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Rigid Pavement ESAL Equation

At first glance, this equation looks quite complex – it is.   Where: W = axle applications inverse of equivalency factors (where W18 = number of 18,000 lb (80 kN) single axle loads) Lx = axle load being evaluated (kips) L18 = 18 (standard axle load in kips) L2 = code for axle configuration 1 … Read more »

Figure 1. Slab curling.

Rigid Pavement Response

Rigid pavements respond to loading in a variety of ways that affect performance (both initial and long-term).  The three principal responses are: Curling stress.  Differences in temperature between the top and bottom surfaces of a PCC slab will cause the slab to curl.  Since slab weight and contact with the base restrict its movement, stresses … Read more »

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Rigid Pavement Empirical Design Example

Design a new rigid pavement for a major interstate highway using the following conditions (four lanes each direction):   Pavement location: Urban Pavement functional classification: Interstate Number of lanes: 3 lanes in each direction Traffic distribution: Assume 80% of the loading occurs in the design lane Annual growth rate: Assume 2% Design period: Investigate 20, … Read more »

Figure 1. Skewed joint showing a corner break.

Joint Design

Joints, which are integral to JPCP and JRCP, and also necessary in CRCP, must be designed to minimize slab cracking, joint deflection, joint stresses and roughness as well as accommodate the intended joint sealant.  Four key design components are manipulated to meet these goals: Joint spacing Joint orientation Joint size Load transfer design Joint Spacing … Read more »

Figure 5: Deflection view.

Rigid Mechanistic Models

Mechanistic models are used to mathematically model pavement physics.  There are different types of models available today (e.g., dynamic, viscoelastic models) but this section will present two, the layered elastic model and the finite elements model (FEM), as examples of the types of models typically used.  Both of these models can easily be run on … Read more »

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1993 AASHTO Rigid Pavement Structural Design

Empirical equations are used to relate observed or measurable phenomena with outcomes.  There are many different types of empirical equations available today but this section will present the 1993 AASHTO Guide basic design equation for rigid pavements as an example.  This equation is widely used and has the following form (see Figure 6.5 for the … Read more »

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Rigid M-E Failure Criteria

The main empirical portions of the mechanistic-empirical design process are the equations used to compute the number of loading cycles to failure.  These equations are derived by (1) determining the various stresses present in a rigid pavement section or slab, (2) observing the performance of pavements, and (3) relating the type and extent of observed … Read more »

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Rigid Pavement Truck Types

There are two basic truck types used for mix transport: Truck mixer.  Truck mixers, use a truck-mounted rotating drum that is capable of mixing (if necessary) and agitating the ready mixed PCC. Non-agitating truck.  Non-agitating trucks are not able to mix or agitate their payload and usually consist of end dump, bottom dump or side-dump … Read more »

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Reinforcing Steel Design

In CRCP and JRCP, reinforcing steel is used to hold tightly together any cracks that may form. Cracks formation depends upon temperature, moisture and base material friction. As the slab cools and loses moisture, it will contract. This contraction is resisted by friction with the base material. If this frictional force becomes greater than the … Read more »

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