Comparisons involving the orientation of the plankswithin the diaphragm revealed that the most diaphragm actionwas obtained by placing the planks transverse to the appliedshear load. Higher strengths and stiffnesses were obtained in those systems which were oriented transverse to the loadingbeam. One possible theory associated with this phenomenon isthat the diaphragms with planks oriented parallel to theapplied shear load initially crack primarily in tension acrossthe seam joints. This event is most clearly demonstrated inTest #8. The FME and other seam cracks in this test weredocumented as being caused by a tensile splitting of the seambetween the two southernmost planks. Diaphragms #6 and #7also revealed a similar situation although not to the extentshown in Test #8. The boundary conditions of the two lattertests prohibited the dramatic tensile cracking which Test #8demonstrated. With the seams of the planks orientedtransverse to the applied shear load, the system cracked inshear-bond between the planks. Although tension was presentat these locations, it was not the controlling mode offailure. Calculations will be presented in Chapter 4 whichwill validate this theory.
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