# Predicting Behavior of Grounded Dowel Connections Using Interfacial Cohesive Elements
## 2 Experimental Procedure and Results  
The test specimens used to derive the local bond stress vs. slip law are depicted in Figure 2. The specimens were carefully designed to mimic full-scale field conditions pertaining to precast concrete wall construction and to eliminate artificial compressive fields that could influence the bond. Test specimens comprised a reinforced concrete block that had dimensions of \(254\times 254\times 406.4\) mm (254 mm is a typical width in full-scale precast shear walls). A 76.2-mm corrugated duct was placed concentrically in the middle of the specimen. To assist in the application of the load, four high-strength 16-mm threaded rods [28] were used to reinforce the block longitudinally. Transverse reinforcement was in the form of 10-mm closed-branch stirrups spaced 203.4 mm apart. The dowel bar used in this study was No. 8, and the spacing of the ribs was 9.75 mm. The bars were de-bonded by wrapping them in 2-mm-thick polystyrene wrap. The bonded length was 4 and 6 \(d_{b}\). After concentric placement of the de-bonded bars inside the duct, non-shrink high-strength grout was mixed at low speed for 10 min and at high speeds for 5 min. Water (about 3.75 L) was added until a flowing consistency was achieved. Grouting was then done in the vertical position, as per full-scale field grouting applications. Subsequently, the specimens were cured for 28 days at a temperature of 22 \({}^{\circ}\)C and relative humidity of 60%. The strain in the bar was measured via a 50-mm extensometer as shown in Figure 2. Additionally, a 10-mm strain gauge was placed amid the bonded length to measure the strain. Finally, loading was applied in displacement control at a rate of 0.02-0.025 mm/s. For detailed information about these tests, the reader is referred to Reference [8].  
The test results and analytical bond-slip law presented by [PERSON] et al. [27] are portrayed in Figure 3. The local bond stresses were determined based on the classical equilibrium expression, as given in Equation (1).  
\[\tau=\frac{A}{\pi d_{b}}.\frac{d\sigma_{s}}{dx}, \tag{1}\]  
where \(\tau\) = bond stress, \(A\) = cross-sectional area of the bar, \(d_{b}\) = diameter of bar, and \(\sigma_{s}\) = stress in bar.  
The procedure for obtaining the bond stress was as follows: firstly, the strain distribution along the bonded length was determined knowing the strain value at the beginning (extensometer reading), amid the bonded length (strain gauge), and at the end (zero strain). Secondly, using information of the mechanical properties obtained from the coupons, the corresponding stress levels were determined. Thirdly, the stress values were linearly connected assuming a linear stress distribution, which is justified given the elasticity of the bar and shortness of the bonded length [27; 29]. By assuming a linear distribution of stress, the bond stresses were constant between two successive strain readings and could be directly calculated using the expression given in Equation (2).  
\[\tau=\frac{d_{b}}{2}.\frac{\sigma_{s}}{L_{d}}. \tag{2}\]  
Figure 2: (a) Experimental set-up; (b) failed bars by shearing of the grout keys at 6 \(d_{b}\) embedment.  
The experimental results were used to calibrate a local bond stress vs. slip envelope to be used in the model development. A discussion of the constitutive relationship used in the interface model is presented in the subsequent sections.