360R-06 Design of Slabs-on-Ground
—Industrial slabs with post-tensioned
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| 9.6—Industrial slabs with post-tensioned
reinforcement for structural support 9.6.1 Design methods—The thickness design methods listed in Section 9.4.1 can be used. These industrial floor design methods allow for an accurate analysis of the effects from the common load cases for warehouse slabs. Conven- tional structural concrete design methods should be used when the assumption of an uncracked section is not valid. Also, the provisions of Section 9.5 apply accordingly to control cracking and to help determine the placement and tendon layouts. 9.6.2 Safety factors—The use of multiple safety factors should be avoided. The post-tensioning reinforcement provides reserve capacities, and in no case should safety factors greater than those for nonprestressed slabs be used. Cracking under the concentrated load can be permissible for prestressed slabs, and it can be taken into account by using structural design requirements of ACI 318. 9.6.3 Subgrade friction reduction—Refer to Section 9.5.2 for the recommended range of friction coefficients. To fully use the advantages of post-tensioning slabs, the strip lengths or placement sizes should be as large as practical. For this reason, subgrade friction reduction is desirable. For slabs, one or two layers of polyethylene sheeting directly beneath the slab are typically used. Curling can be reduced by perfo- rated sheeting. A thin layer of sand choker under the slab can also reduce the subgrade friction. It is difficult to place concrete directly on the thin layer of sand. This should be considered for thicker slabs only and with special care during concrete placement. 9.6.4 Joint requirements—There are no joints in post- tensioned slabs besides the construction joints surrounding the section being placed. There is no need for sawcut contraction joints. As the lengths between the joints are long and the shortening of the slabs should not be restricted, a few considerations should be noted. tải về 2.35 Mb. Chia sẻ với bạn bè của bạn:
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