Flexural requirements (beams seismic: ACI 318)
Minimum number of bars
The minimum allowed number of bars continuous along the beam span is required to be checked in the layers closest to the top and bottom faces of any beam in the SFRS.
The number of bars should be ≥ 2.
Maximum allowed bar size
This applies to end regions of beams where the beam reinforcement extends into the column core. The required development length of reinforcement bars extending into the column core restricts the minimum size of the column and vice-versa.
If SFRS Type = Special Moment Frame
“Anchorage requirements at the joint of special moment frames limit the maximum bar size at each end of the beam”
Minimum flexural strength
The minimum area of top and bottom steel required at any section of a beam part of a Moment Resisting Frame needs to comply with flexural strength requirements when considering earthquake effects.
Note that no seismic design requirements apply to beams that are part of Ordinary Moment Frames. All other Moment Resisting Frame types have minimum longitudinal moment requirements.
Minimum allowed area of reinforcement
The minimum allowed area of steel throughout the bottom and top faces of a beam part of a Special Moment Frame is limited as per ACI 318-11 equation (10-3).
Maximum allowed area of reinforcement
For the purpose of increasing the ductility response of beams in Special Moment Frames the area of reinforcement both at the top and bottom faces is limited.
If SFRS Type = Special Moment Frame
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(As- and As+) | ≤ | As,max = 0.025 * bw * d |
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where |
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As | = | Area of non-prestressed longitudinal tension reinforcement |
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bw | = | Beam web width |
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d | = | Distance from extreme compression fiber to centroid of longitudinal tension reinforcement |
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No other Moment Resisting Frame type has a maximum area of steel requirement.
Maximum allowed center spacing of longitudinal bars
Limitations on the longitudinal bar spacing apply to beams part of Special Moment Frames.
If SFRS Type = Special Moment Frame, then the maximum allowed center spacing is checked for confinement regions as follows:
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scr,max | = | 350 mm | Metric-units |
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As | = | 14 in. | US-units |
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where |
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scr,max | = | maximum allowed center spacing | |
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Non-reversing plastic hinges
Non-reversing plastic hinges are regions along the span of the beam where flexural yielding is likely to occur.
Note: Non-reversing plastic hinges are beyond scope in the current release of Tekla Structural Designer.
Splices
Restrictions apply to the locations of reinforcement lap splices along the span of a beam part of Special Moment Frames.
Strength design of mechanical splices and restrictions to the use of welded splices as required by ACI318-11 apply to Special Moment Frames.
Note: These restrictions are not implemented in the current release of Tekla Structural Designer.