I requisiti delle aste sono trattati in un articolo separato, Kb | AISC 341-16 Verifica di aste del telaio a momento in RFEM 6 .
More in-depth details on the Seismic Configuration input are covered in article Kb | Verifica sismica AISC 341 in RFEM 6 .
Connection Requirements
The "Seismic Requirements" include the Required Flexural Strength and the Required Shear Strength of the beam-to-column connection. They are listed in the Moment Frame Connection by Member tab. The design check details are not available for the connection strength. However, the equations and standard references are listed. The symbols and definitions are summarized in the table below (Image 1).
AISC Seismic Design Manual – Example 4.3.7 SMF Bolted Flange Plate (BFP) Connection Design
For simplicity, the RFEM model consists only of a single frame instead of the entire building that is presented in the AISC example (Image 2). The gravity load on the beam = 1.15 kip/ft.
The numbering of the steps in this example follows the step-by-step design procedure outlined in AISC 358-16 Section 7.6 [3].
Step 1. Compute probable maximum moment at the plastic hinge location, Mpr
| yM5 | Coefficiente parziale di sicurezza |
| Mop, i, Rd | Valore di progetto della resistenza al momento del collegamento per la flessione fuori dal piano del sistema strutturale per il componente strutturale i |
| ν | Viscosità cinematica |
| d | Costante |
| ωd | frequenza angolare |
Steps 2 to 5 contain the bolt requirements and are outside the scope of the Steel Design add-on.
Step 6. Compute shear forces at the beam plastic hinge location, Vpr + Vg
| Vpr |
Taglio richiesto per produrre il momento probabile massimo sulla cerniera plastica Vpr = 2Mpr/Lh
|
| Vg |
Taglio da carichi gravitazionali nella posizione del vincolo plastico Vg = wu Lh/2
|
| Mpr | Momento massimo probabile nella posizione della cerniera plastica |
| P10 | Sovrapressione massima di picco di esplosione a distanza (Kinney & Graham) [kPa] |
| Z | Distanza ridotta[m/kg 1/3 ] per Z> 2,8 |
Step 7. Determine moment expected at the face of the column flange, Mf
| α | Coefficiente di forma |
| td | Durata dell'azione a pressione positiva |
| cr- | Sottopressione del coefficiente di riflessione |
| t~d | Durata virtuale dell'azione a pressione positiva |
| B | Area integrata |
The above equation neglects the gravity load on the small portion of the beam between the plastic hinge and the face of the column (1.15 kip/ft*1.875 ft = 2.16 kips*22.5 in = 48.6 k-in). This value is permitted to be included [3].
Step 14. Determine the required shear strength at the face of the column, Vu
The required shear strength at the face of the column is used to design the beam web-to-column (single-plate) shear connection.
| pr0(t) | Modello di carico per il diagramma pressione-tempo completamente riflesso |
| p4(t) | Funzione de carico esponenziale (approccio di Friedlander) |
| y | Senkrechter Abstand der z-Achse zum Element dA |
| Fy | tensione di snervamento |
| MC | Valore assoluto del momento nel punto dei tre quarti del segmento non controventato |
To be more precise, the calculation above shows Vg taken at the face of the column instead of at the centerline (as shown in the AISC example [2]). The small difference can be seen in the shear diagrams (Image 3).
The values obtained from the formulas above can be compared to the result produced by RFEM under the “Seismic Requirements” (Image 1). Small discrepancies are due to rounding. The result can also be included in the printout report (Image 4).
The detailed procedures to design bolts, flange plates, single-plate, continuity plates, and doubler plates are not part of the scope. Therefore, the steps for these checks were omitted in this article.
The moment and shear demand based on the worst-case scenario of the overstrength load combinations, ΩoM and ΩoV are also listed. For the design of ordinary moment frames (OMF), the potentially limiting aspects of the connection strength include the overstrength seismic load [AISC Seismic Design Manual Section 4.2(b)].
