360R-06 Design of Slabs-on-Ground
R-38 ACI COMMITTEE REPORT
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| 360R-38 ACI COMMITTEE REPORT
combination of both. The center lift moment is caused by the slab conforming to the doming configuration and is the strength required to resist this change in shape. The moment is usually expressed as a negative moment. Conversely, the edge lift condition is, in general, a seasonal or short-term condition that occurs when the soil beneath the perimeter becomes wetter than the soil beneath the interior of the slab, causing the edges to rise or heave. The edge lift moment is caused by the slab conforming to the dishing config- uration and is the strength required to resist this change in shape. This moment is usually expressed as a positive moment. relative stiffness length β—the distance from the edge of the slab at which the maximum moment occurs. The maximum moment does not occur at the point of actual soil-slab separation, but at some distance further inward the interior. The location of the maximum moment can be closely estimated by the Eq. (9-22) to calculate β, a length that depends on the relative stiffness of the soil and the stiffened slab. The moment increases rapidly from the edge of the slab until it reaches a maximum at approximately a distance of β. The magnitude of the moment then begins to reduce toward the midpoint of the slab. For slabs 48 ft (15 m) long or less, the amount of this reduction depends on the slab length. For slabs longer than 48 ft (15 m), the increased length results in no significant changes in moment. Further, the maximum shear forces develop at or near the perimeter of the slab, within one β-length from the edge of the slab. ribbed and stiffened slab—a slab of uniform thickness that has been stiffened against deflection by incorporating ribs or beams cast monolithically with the slab, such as a series of T-beams. The addition of the ribs greatly increases the moment of inertia of the concrete cross section, thereby increasing the ability of a section to resist deflection. tải về 2.35 Mb. Chia sẻ với bạn bè của bạn:
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