本帖最后由 三T上人 于 2016-7-22 15:15 编辑 <br /><br />
Susan Dowty, S.E.
The applications of Sections 12.3.3.4 and 12.10.2.1 have caused some confusion, and we hope that this Code Simple will clear things up. Section 12.3.3.4 states that for seismic design category (SDC) D-F buildings having listed irregularities, the design forces determined from the equivalent lateral force procedure of Section 12.8.1 must be increased 25 percent for connections of diaphragms to vertical elements and to collectors, and for connections of collectors to the vertical elements of the seismic force-resisting system. The listed irregularities are: torsional irregularity, extreme torsional irregularity, re-entrant corners, diaphragm discontinuity, out-of-plane offsets of the vertical lateral force-resisting elements (Horizontal Structural Irregularity Type 1a, 1b, 2, 3, or 4 of ASCE 7-05 Table 12.3-1) and in-plane discontinuity in vertical lateral force-resisting elements (Vertical Structural Irregularity Type 4, ASCE 7-05 Table 12.3-2). with overstrength apply, no further increase is warranted." The primary source of confusion has been the last sentence of Section 12.3.3.4, which states that collectors and their connections should also be designed for the increased forces, unless they are designed for the seismic load combinations with overstrength factor in accordance with Section 12.10.2.1. Section 12.10.2.1 requires collector elements and their connections to be designed to resist load combinations with overstrength factor in structures assigned to SDC C-F. The question that is asked by engineers is: For the design of collectors and their connections, doesn't Section 12.10.2.1 always govern and therefore Section 12.3.3.4 won't apply? In order to answer this question, it is helpful to summarize Sections 12.3.3.4 and 12.10.2.1 as follows: [table=98%,transparent]
[tr][td]ASCE 7-05 Section 12.3.3.4
(25 percent increase in design force)[/td][td]ASCE 7-05 Section 12.10.2.1
(design using load combinations with overstrength factor)[/td][/tr]
[tr][td]Triggers:[/td][td]Trigger:[/td][/tr]
[tr][td][/td][td][/td][/tr]
[tr][td]Applicable to:[/td][td]Applicable to:[/td][/tr]
[tr][td]- Design of collectors
- Connections of collectors elements to vertical elements
- Connections of diaphragms to vertical elements
[/td][td]- Design of collectors and splices
- Connections of collectors to resisting
[/td][/tr]
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