Effect of spacing between the CGRIDS

The effect of the spacing between vertical line of CGRID is examined in the following section. Predicted behaviors for the panels with several CGRID spacings containing EPS and XPS-SB foams are compared along with corresponding measured results in Figure 6-40 through Figure 6-42 and Figure 6-44 through Figure 6-46, respectively. Panel with 2 inch foam thickness is chosen to compare the results. Comparison of analytical results for various grid spacing with EPS and XPS-SB are shown in Figure 6-43 and Figure 6-47 respectively.

Figure 6-41: Panel with 24” grid spacing and 2” EPS (48”x72”)

Figure 6-45: Panel with 24” grid spacing and 2” XPS-SB (48”x72”)

The analysis showed reasonable agreement with the measured values for initial phase of load-deflection curves. However, the accuracy of the ultimate strength prediction for the finite element model shows considerable amount of variation. This difference is attributable to the uncertainties involved in construction process of these wall panels. For panels with EPS foam, the accuracy in predicting ultimate shear flow strength values using finite element model ranged from 2% to 8%. While the accuracy of predicting ultimate shear flow strength values for XPS-SB foam ranged from 2% to 39%. The large variation of accuracy in predicting shear flow strengths for XPS-SB foam is due to variable nature of the bond properties of foam-concrete interfaces. The bond strength is a function of type of surface that is prepared through sand blasting process. There are no specific criteria to control amount and nature of sand blasting. Analytical results for all the panels with EPS and XPS-SB foam are summarized in Figure 6-48 and Figure 6-49, respectively.

Comparisons of the predicted strength to the measured values indicate capability of finite element program in predicting the strength assuming the perfect bond of the foam to the concrete surface. Throughout this research program, it was observed that there are higher chances of formation of air pockets in panels built with XPS-SB foam as compared to panels with EPS foams. Hence, FE results for panels with different CGRID spacings and thicknesses with EPS foam showed higher accuracy in predicting shear flow strength values as compared to panels with XPS-SB foam due large variation in presence of air pockets resulting variable bond strength of foam-concrete interfaces.

Figure 6-48: Summary of Analytical results for panels with EPS foam Foam Thickness (inch) 2 4 6 2 4 6 2 4 6 Grid Spacing (inch) 12 24 48

FE prediction

Measured Strengths

Figure 6-49: Summary of Analytical results for panels with XPS-SB foam Foam Thickness (inch) 2 4 2 4 2 4 Grid Spacing (inch) 12 24 48

Measured Strengths

FE prediction

7 SUMMARY AND CONCLUSIONS

The research reported in this thesis summarizes test results and analysis of a comprehensive research program undertaken to study a proposed CGRID/foam system as shear transfer mechanism used in precast concrete sandwich wall panels. All the wall panels were built with three concrete wythes connected with four 6 feet long vertical strips of CGRID along with two layers of rigid foams. Various parameters believed to affect the shear flow strength for this CGRID/foam system were examined by testing one hundred panels. The parameters included: the type of rigid foam, the thickness of rigid foam, and the spacing between the individual vertical lines of CGRID. Test results were used to develop design equations to estimate the shear flow strength and shear modulus for CGRID/rigid foam system as affected by these parameters. A non-linear 3-D finite element analysis was performed using a commercial software utilizing non-linear geometry and non-linear material properties. Research findings based on the test results and analysis can be summarized as follows.

1. Panels produced with EPS and XPS-SB rigid foam developed higher shear strengths in

comparison to panels insulated with XPS-R and POLY-ISO foam when compared with the same quantity of CGRID spacing.

2. For panels with EPS and XPS-SB foam, increasing the spacing between vertical lines of

3. Test results for the panels with XPS-R and POLY-ISO foam indicated that spacing between CGRID seems to have minimal effect on shear flow strength. This phenomenon was not similar to panels with EPS and XPS-SB due to low bond strength development between foam and concrete interface.

4. Test results also indicated that increasing the thicknesses of the EPS as well as XPS-SB insulations showed decrease in the shear flow strength of the panel.

5. Shear cracking, shear sliding and mix mode (cracking + sliding) were three different

modes of failure observed throughout testing.

6. A spreadsheet program used to establish the factors for design equations exhibited

reasonable prediction of the shear flow strengths and shear moduli for given CGRID/foam systems.

7. The large variation of accuracy in predicting shear flow strengths for XPS-SB foam is

due to variable nature of the bond strengths of foam-concrete interfaces as there are no specific quality control criteria for sand blasting.

8. FE results for panels with different CGRID spacings and thicknesses with EPS foam

showed higher accuracy in predicting shear flow strength values as compared to panels with XPS-SB foam due large variation in presence of air pockets resulting from variable bond conditions at foam-concrete interfaces.

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