Precast Connection Design (TBDY Chapter 8)

In precast buildings, connections are designed in the Macros → Precast connection design (TBDY Chapter 8)... window. Each calculation creates a record that goes into the report. For the modeling steps, see the article Modeling Precast Structures. The design of column corbels according to TS 500 Clause 8.4 is described in the article Short Corbel Design; the corbel results also go into the same report page (Section 4).

1. Connection design window

The window has five tabs. The input boxes come filled with example values; enter the values of your own project or take them from the analysis (Section 2).

Tab	Main inputs	Checks
Pinned (MFB)	Connection mass, spectral acceleration, D, R/I; beam self-weight and loads carried on top (purlin, roofing, snow), centre of gravity and purlin bearing height; bearing vertical load; bearing width and dowel–edge distance; dowel bar yield strength; beam axial force; number and diameter of dowels, concrete strength; dowel centre–edge distance	Overturning (TBDY 8.3.2) → dowel bar; dowel shear (Eq. 8.2); dowel centre–edge/diameter ratio > 6
Wet on Top – Welded at Bottom (MAB3)	Height, cover, web width; negative and positive moment envelopes (without D) and envelopes with D for the weld; material strengths and coefficients; number/diameter of welded bars, plate thickness, weld thickness (0 = suggestion); provided top/bottom reinforcement; stirrups in the 2h region	Top continuity reinforcement, bottom reinforcement and bottom ≥ top/2 (7.4.2.3), weld area and length, horizontal shear dowels, MRd− ≥ Md− and MRd+ ≥ γR·Md+ (TBDY 8.4.4)
Purlin / Gutter Beam Connections	Connection axial force, D; dowel diameter, yield strength, friction coefficient (1.0 when grout-filled); number, thickness and length of weld seams; purlin modulus of elasticity, weak-axis moment of inertia, buckling length	Dowel shear–friction (TS 500 8.1.7), fillet weld, purlin buckling
Façade Panel (Chapter 6)	Panel mass, Be / Re (TBDY Table 6.1), building R/I, period, reduced displacement of the connection floor, building importance factor, SDS; hanging-type connection option	Equivalent seismic load (Eq. 6.1–6.2), lower limit (Eq. 6.5), vertical ±0.3·me·I·SDS·g, 1.4W for hanging type
Foundation Sliding (16.8.4)	Horizontal force, minimum vertical force (0.9G − E), friction coefficient (TBDY Table 16.3), coefficients, passive resistance (0 = neglected)	Vth ≤ Rth + 0.3·Rpt

2. Taking demands from the analysis

The MFB, MAB3 and Purlin/Gutter Beam tabs have a Take from selected beam (analysis result) button and a Left end / Right end selector. After the analysis, select a single beam in the model and press the button; the forces at the selected end of the beam are read load case by load case (G, Q, earthquake; and the crane load cases as well if a crane is defined) and fill the boxes:

• MFB: connection mass, total G load of the beam, bearing vertical load and the maximum axial force of the seismic load cases (reduced; D is applied in the window).
• MAB3: moment demands without D from the combination envelope and weld demands magnified by D for the seismic effect (with D̄lower in the lower part); height and width from the beam section.
• Purlin/Gutter Beam: the maximum axial force of the seismic load cases.

Each Calculate button writes the result into the text area at the bottom of the window and adds a row, with type and member name, to the connection record list; if it is recalculated with the same type and name, the record is updated. The records are stored with the project and feed the connection page in the report. The input values of the window are not saved; only the calculation records are stored.

note

Rigid diaphragm note: In a rigid roof diaphragm, the seismic axial force of a pinned roof beam comes out as zero (the inertia of the roof mass is carried by the diaphragm). A meaningful axial force for the dowel shear must be entered from the semi-rigid (Annex 8B braced) model or from a hand calculation.

info

MFB tension lever arm: The program takes the lever arm of the overturning tension force according to TBDY Figure 8.1; this approach is on the safe side.

3. Reinforcement design of polygonal and nonprismatic beams

The reinforcement of reinforced concrete beams with polygon, precast-template and nonprismatic sections is calculated automatically in the analysis:

• Flexure: Section analysis is carried out with the actual section geometry; for negative moment the section is flipped for the calculation. In a nonprismatic section, three design sections are used: left end, span and right end.
• Minimum reinforcement: 0.8·fctd/fyd·bw·d and the TBDY 7.4.3.1 / 7.4.2.3 ratios; bw is the narrowest web width over the section height (in I, U and box sections the web is found automatically).
• Reinforcement selection is the same as the program’s beam workflow (straight and bent-up bars, assembly bars, support additions, web reinforcement); the results go to the detailing drawing, the quantity takeoff and the report. In a prismatic polygon whose reinforcement layout is not defined, the layout is generated automatically.
• Stirrups: Confinement-zone and mid-zone spacings are calculated from the section.
• Drawing: In the beam cross-section drawings, the actual section outline, the cover contour and the reinforcement points are drawn instead of a rectangle.

4. Reporting

In the tree on the Report Selection → Report tab, under the Foundation Calculations group, there is the “Precast Connection Design (TBDY Chapter 8)” page; if the project has connection records or short corbels, it comes checked by default. The page is printed when the Foundation Calculations group or only this page is checked. For each record the page contains a Type / Member (end) / Demand / Capacity / Ratio / Result row and explanatory lines that summarize the inputs and intermediate results; at the end of the page the sources of demand and capacity are written as footnotes. The report is produced in Turkish or English according to the program language setting. The project must be saved before the report is generated. Short corbels appear on this page as KONSOL rows after the connection rows (see Short Corbel Design).

5. Scope limits

• The S, H and Hd load cases are not included in the envelope in connection demands; the crane combinations and the KG in the earthquake combinations are included in the envelope.
• For polygon and nonprismatic beams, the shear capacity (Vr ≥ Vd and capacity shear) and the moment capacities are not calculated in this edition; there are no station section drawings of the nonprismatic section and no detailing drawing with a sloped top edge.
• Socket foundation and erection-stage checks are out of scope. Short corbel design is described in a separate article (Short Corbel Design).

6. Frequently encountered situations

Symptom	Solution
“Take from selected beam” does not fill the boxes.	The analysis is not complete or a single beam is not selected in the model. Run the analysis and select only the relevant beam.
The dowel shear demand is zero in MFB.	In a rigid diaphragm, the seismic axial force of a pinned roof beam is zero. Enter the axial force from the semi-rigid model or from a hand calculation.
The connection page does not appear in the report.	There is no connection record or short corbel, the page is not checked in Report Selection, or the project is not saved. Make sure the report templates are up to date.