360R-06 Design of Slabs-on-Ground
—Shear transfer at joints
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- 360R-32 ACI COMMITTEE REPORT 6.4—Maximum joint spacing
| 6.3—Shear transfer at joints
Recent analysis (Walker and Holland 1999) shows that edge curl is a principal concern governing the spacing of sawcut contraction joints in slabs-on-ground. Effective shear transfer at both construction and intermediate sawcut contraction joints is required to avoid a loaded free edge. Also, curl and shrinkage can reduce joint stability by disen- gaging aggregate interlock or keyed joints, allowing the free edges to deflect independently under wheeled traffic. Positive load-transfer devices, such as dowels, should be used for joints subjected to wheeled traffic where the joint is expected to open more than 0.035 in. (0.9 mm). Chapter 5 contains an expanded discussion of jointing of slabs-on-ground and protection of the joints. PCA (2001) provides extended consideration of the effectiveness of shear transfer at joints. 6.3.1 Steel dowels—Steel dowels are the most effective means to provide effective load transfer and to ensure adjacent curled joint edges deflect together. Refer to Chapter 5 for a discussion of different doweling approaches. When dowels are installed across a joint, the slab edges abutting the joint may still curl and deflect when loaded, but they do so in unison. When the wheel reaches the joint, no significant relative vertical displacement between the panels is encountered, and the impact loads imposed on the edges are greatly reduced. 360R-32 ACI COMMITTEE REPORT 6.4—Maximum joint spacing Assuming the subgrade is relatively free from abrupt changes in elevation, such as that caused by uncorrected wheel rutting, the tensile stresses created in the shrinking panel by subgrade frictional restraint are relatively minor in comparison to curling-induced stresses. These higher curling stresses are likely the principal cause of shrinkage cracking in most unreinforced concrete floor slabs (Walker and Holland 1999). In general, joint spacing should not exceed the spacing recommended in Fig. 5.6 and as discussed in Chapter 5 . Refer also to Chapter 13, Section 13.8 . tải về 2.35 Mb. Chia sẻ với bạn bè của bạn:
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