Short Corbel Design (TS 500 Clause 8.4)
Short corbels that project from the column face and carry a beam or a crane girder (av ≤ d) are designed in StatiCAD according to TS 500 Clause 8.4 with the shear friction and tension tie method. The corbels are defined in the Corbel tab of the column properties window; after the analysis, the demand is taken automatically from the beams seated on the corbel and from the predefined node at the corbel elevation (including the overhead travelling crane loads); the results go into the Precast Connection Design page of the report as KONSOL rows. See Precast Connection Design for the connection calculations, Overhead Crane Loads, Additional Seismic Masses and Different R–D for the overhead travelling crane loads, and the article Precast Structures Verification Studies for the comparison of the calculation with the handbook example and with hand calculations.
Which editions? The Corbel tab and the short corbel design are available in the StatiCAD Ultimate edition. The corbel definitions are stored in the project file (Section 8).
1. The corbel is part of the column
- The corbel is a sub-object of the column: at most four corbels can be defined on each reinforced concrete column with a rectangular section.
- When the column is copied, when its storey is copied, or when it is rotated about the Z axis or mirrored, its corbels are carried along with their directions transformed; a column that is cut and pasted does not carry its corbels.
- The corbel does not enter the finite element model as an element: defining, changing or designing a corbel does not change the analysis results. The corbel does not enter the drawings or the quantity takeoff either.
2. Corbel tab
In the Corbel tab of the column properties window, which is opened by right-clicking the column and choosing Change Properties, corbel 1–4 is selected with the selector at the top; a corbel is added to an empty slot with Add, and an occupied slot is removed with Delete. When 0 is entered in a box, the default value is used; the default is given in the tooltip of each box (Section 3). The decimal separator can be a comma or a point.
The boxes are arranged in four groups:
- Geometry (TS 500 8.4): Face (+X, −X, +Y, −Y or an Angle in degrees), Level reference (Down from column top / Up from column bottom) and Level (cm), h (required), bw, hf, lc, av and d (mm). The face is an absolute direction with respect to the model axes; on the plan screen +Y points downward. In a rotated column, the direction snaps to the nearest face normal and the captured face is shown below the box.
- Bearing pad (av derivation): Pad b, Pad l, Joint gap and Erection tol. (mm); when av = 0, av = joint gap + pad length/2 + erection tolerance is used.
- Material and design: fck, fyk, fywk, γmc, cc (concrete cover), Dmax (maximum aggregate size), Stirrup legs (number of horizontal stirrup legs), Bond position (anchorage position), μ (Table 8.1), Casting (precast / cast in place), Section limit 8.1.7 and Horizontal demand.
- Demand: Demand source (Automatic: beam + joint/crane + manual; Manual only; Beam + manual; Joint/crane + manual), Vd add. (vertical force addition), Vd,shear add. (shear addition with D), Hk (characteristic horizontal force) and HdEk (horizontal design force addition). The Crane column (Automatic / Interior column / End column) and Crane girder G options are active only when the demand includes a crane.
OK checks the inputs: h is required; d < h and hf ≤ h must hold, γmc must be 0 or ≥ 1.4 and the number of legs must be 0–8; the corbel must fit within the column height, and in a rotated column the direction must not be equally close to two faces. If there is an error, a message is given, the window does not close and the faulty corbel is shown; an invalid number is shown in red. With a single selection, only the changed or added corbels are checked. If the tab is opened and OK is pressed without any change, the corbels remain as they are; Cancel changes nothing; a change can be reverted with Undo.
Calculate (unsaved) designs the selected corbel with the unsaved values and with the stored geometry and material of the column; the status, demand and calculation lines appear in the window. The stored data and the report rows do not change; the report rows are refreshed when the report is generated.
Multiple selection: With Change Properties on selected columns, three options are offered: Do not change (default; the corbels are kept), Remove corbels and Apply these corbels. When a box is changed, “Apply these corbels” becomes selected. If the corbels of the selected columns differ, those of the right-clicked column are shown and a confirmation is requested at OK. Applying writes only to reinforced concrete rectangular columns; at OK, the elevation and direction are checked for every selected column, and if even one of them fails, none of them is changed.
The tab is disabled for a column that is not a reinforced concrete rectangular column (corbels remaining on such a column can be removed with Delete). The new column drawing window has no Corbel tab; a newly drawn column starts without corbels.
3. Inputs and default values
| Input | Meaning (unit) | If 0 is entered or the box is left empty |
|---|---|---|
| Face or Angle | Face from which the corbel projects: +X, −X, +Y, −Y or the plan angle of the outward face normal (degrees; +X = 0, +Y = 90). The angle snaps to the nearest column face; in a rotated column, an angle equally close to two faces is rejected | +X |
| Level reference, Level | Distance of the corbel top face down from the top end of the column or up from its bottom end (cm) | Top end of the column |
| h | Total depth of the corbel at the column face (mm) | Required |
| bw | Corbel width (mm) | Width of the column face carrying the corbel |
| d | Effective depth (mm) | h − concrete cover − Ømaks/2 (Ømaks: the largest of the candidate main reinforcement diameters) |
| av | Distance of the vertical load from the column face (mm) | For a crane corbel, from the crane eccentricity; otherwise, if the pad length > 0, joint gap + pad length/2 + erection tolerance; if neither applies, no calculation is made (ERROR: av could not be derived) |
| Pad b, Pad l, Joint gap, Erection tol. | Width and length of the bearing pad, joint gap between the column face and the beam end, erection tolerance (mm) | — |
| hf | Outer (free) end depth (mm); hf ≥ d/2 is checked | Not checked (noted in the report) |
| lc | Projection of the corbel from the face (mm); widens the zone in which the end of a seated beam is searched for, does not enter the reinforcement calculation | Column section only |
| fck, fyk, fywk | Characteristic strengths of the concrete and the reinforcement, yield strength of the horizontal stirrup steel (MPa) | Material of the column (library material, otherwise the project material); fywk = fyk |
| Casting, γmc | Production method of the corbel and material factor of the concrete | Precast; γmc 1.4 for precast, the project value for cast-in-place |
| μ | Friction coefficient (TS 500 Table 8.1: 1.4 / 1.0 / 0.6 / 0.7) | 1.4 (monolithic) |
| cc, Dmax, Stirrup legs, Bond position | Clear concrete cover (mm), maximum aggregate size (mm), number of horizontal stirrup legs, anchorage position (TS 500 9.1.2.1) | 25 mm; the 4/3·Dmaks condition is not checked; 2 legs; Position I |
| Section limit 8.1.7 | Section area in the TS 500 8.1.7 upper limit: bw·d, bw·h, or no limit applied | bw·d |
| Horizontal demand | How the additional horizontal force is included in Hd: added, or compared with the lower bound value (Section 5) | Added |
| Demand source | Automatic (seated beam + corbel node or crane + manual), beam + manual, joint/crane + manual, or manual only | Automatic |
| Vd add. | Manually added vertical design force (kN; factored, without D; added to the automatic demand) | 0 |
| Vd,shear add. | Vertical force with the D factor for the shear checks (kN; TBDY 8.3.1.8) | Same as the Vd addition |
| Hk | Characteristic horizontal force (kN; the program multiplies it by 1.6) | 0 |
| HdEk | Additional horizontal design force (kN; e.g. the crane horizontal force, factored) | 0 |
| Crane column, Crane girder G | Position of the column for the self-weight of the crane girder and rail (interior: q·L, end: q·L/2) and whether the self-weight is added | From the rail list (a column at either end of the rail is an end column); added |
4. Taking the demand from the analysis
The demand source is automatic by default: after a valid analysis, the end shears of the beams seated on the corbel and the loads of the predefined node at the corbel elevation (including the overhead travelling crane loads) are summed in each load combination, and their envelope is taken; the manually entered values are added to this. If the analysis has not been run or the model has changed after the analysis, the result is NOT CHECKED (analysis required); repeat the analysis. To give the demand manually only, select Manual only as the Demand source.
- Seated beam: The end of a beam on the same storey as the corbel must be inside the column section (and the lc projection), the beam must run outward from the corbel face, and its bottom face at that end must differ from the top face of the corbel by at most 5 cm. The shear force of the beam at this end enters the vertical demand; its axial force is not added to the horizontal demand (its tension with D is written for information). Nonprismatic beams and beams inclined by more than 5° are not matched; if they appear to be seated on the corbel, the demand is counted as incomplete. A warning is given at a beam end that is not pinned.
- Corbel node: The loads (Predefined joint properties → Forces) of the predefined node on the column axis at an elevation that differs from the top face of the corbel by at most 5 cm are assigned to the corbel: the vertical component enters the vertical demand, and the horizontal component perpendicular to the corbel face enters the horizontal demand. If there is more than one corbel at that elevation (except for the crane node), the node load cannot be assigned and the demand is counted as incomplete.
- Overhead travelling crane: The crane node is assigned to the corbel facing the opposite rail. If av is not entered, it is derived from the crane eccentricity (av = e − distance from the column centre to the corbel face). If there is no G load at the node, the self-weight of the crane girder and rail is added to the G load case as q·L/2 at an end column and q·L at an interior column; adding the self-weight is turned off with the Crane girder G option, and the position of the column is set with the Crane column option. The seismic force of the bridge mass does not enter the horizontal demand of the corbel automatically; if needed, enter it in the HdEk box. If the crane node does not match the corbel elevation or the crane combinations have not been generated (risky building combinations), the demand is counted as incomplete.
- Combinations: The coefficients are those of the load combinations used in the design; the TBDY 8.3.1.8 D factor (the value used in the column design) is applied only in the shear checks, to the seismic load cases.
Effect on the column design: The reaction of the beam seated on the corbel is transferred to the column at the beam end in the model; the position of the load on the corbel is not represented in the model. Therefore the eccentricity moment of the reaction about the column axis, approximately V·(c/2 + av) (c/2: distance from the column centre to the corbel face), does not enter the column design or enters it only partly. On a crane corbel, the V·e moment of the crane load cases enters the design because it is written to the crane node. If this moment of the seated beam is significant, apply it as a moment load for each load case (Predefined joint properties → Forces) to a predefined node on the column axis at the corbel elevation (Macros → Add predefined node...). If there is more than one corbel at the same elevation, the node load cannot be assigned to the corbel and the corbel becomes NOT CHECKED; in that case, place the node at an elevation more than 5 cm away from the top face of the corbel.
5. Calculation basis (TS 500 Clause 8.4)
Column corbels with av ≤ d are designed according to TS 500:2000 Clause 8.4 with shear friction (Clause 8.1.7) and a tension tie. TBDY 2018 has no calculation clause specific to corbels; the minimum concrete class for precast members is C30 (TBDY 8.2.3.2). If av > d, Clause 8.4 does not apply; the corbel must be designed as a beam (NOT APPLICABLE). Material: fcd = fck/γmc (1.4 for precast, ≥ 1.5 for cast-in-place; TS 500 6.2.5), fyd = fyk/1.15.
| Quantity | Relation |
|---|---|
| Horizontal design force | Hd = max(1.6·Hk; 0.2·Vd) + Hd,ek (Hd is always taken as tension); if the second form is selected in Horizontal demand, Hd = max(1.6·Hk + Hd,ek; 0.2·Vd) |
| Section limits | Vd,kesme ≤ 0.22·fcd·bw·d (Eq. 8.26); Vd,kesme ≤ 0.2·min(fcd; 25 MPa)·Ac (Clause 8.1.7; default Ac = bw·d) |
| Shear friction reinforcement | Awf = Vd,kesme / (fyd·μ) (Eq. 8.8; Table 8.1: monolithic 1.4, roughened joint 1.0, smooth joint 0.6, steel–concrete 0.7) |
| Flexural and tension reinforcement | As = [Vd·av + Hd·(h − d)] / (0.8·fyd·d) (Eq. 8.28); An = Hd / fyd (Eq. 8.29) |
| Main reinforcement | Ast = max(As + An; (2/3)·Awf + An; 0.05·(fcd/fyd)·bw·d) (Eq. 8.27) |
| Horizontal stirrups | Asv ≥ 0.5·(Ast − An)·max(1; fyd/fywd) (Eq. 8.30; within a depth of 2d/3 from the top face) |
| Free end | hf ≥ d/2 (Figure 8.6) |
D factor only in the shear checks: According to TBDY 8.3.1.8, the shear demand of precast connections is magnified by the overstrength factor D of the seismic effect. The program applies this demand with D (Vd,kesme) only to the section limits (Eq. 8.26, Clause 8.1.7) and to the shear friction reinforcement (Awf); the flexural tension reinforcement As, the Hd ≥ 0.2·Vd lower bound and An are calculated with Vd without D. If Vd,kesme is not given, Vd is used; if a value smaller than Vd is given, Vd is used (D ≥ 1) and a warning is written. If the horizontal stirrup steel is weaker than the main reinforcement (fywk < fyk, e.g. S220), Asv is increased for an equal force; if it is stronger, the plain value of Eq. 8.30 is kept and not reduced.
Reinforcement selection (not specified by TS 500; the program’s rule): Main reinforcement in a single layer, at least two bars, Ø ≤ 40 mm, clear spacing in the same layer ≥ max(Ø; 4/3·Dmaks; 25 mm) (TS 500 9.5.2), dgerçek = h − concrete cover − Ø/2. Horizontal stirrups below the main reinforcement, within 2d/3 from the top face, at least two rows. The main reinforcement and the stirrups are selected together: a candidate that preserves the entered d and whose stirrups also fit comes first. Among the candidates, the smallest provided area is the basis; if there are candidates with up to 5% more than the smallest area and at least three bars, the one with the fewest bars among them is selected (with the Ø12–Ø20 list, 7Ø16 instead of 12Ø12 in the example corbel). If dgerçek > d, Ast, Asv and hf ≥ d/2 are repeated with the actual d; if dgerçek < d, the entered d is unconservative and a warning is written. The candidate diameters are taken from the checked diameters of the Reinforcement Selection window: the main and bottom reinforcement from the Column longitudinal list, the horizontal stirrups from the Column stirrup list (if the window has no valid diameter, the default list is used and a warning is written).
Turkish Precast Association handbook additions: The additions from pp. 96–99 of the handbook Prefabrike Betonarme Yapılar Tasarım, Üretim ve Montaj Esasları (Principles of Design, Production and Erection of Precast Reinforced Concrete Structures) do not change the TS 500 design or the result status; they are written for information: the recommendation for inclined face (bottom) reinforcement A's ≥ 0.002·bw·h; anchorage inside the column lb = max(Eq. 9.1; 1.7·lb0); Fs = Ast·fyd ≥ 0.5·Vd; comparison with the handbook’s (PCI-based) method: Vr = 0.20·min(fcd; 25)·b·d, μe = 6.9·λ²·b·h·μ/Vu ≤ Table 4.16 limit, As = max([Vd·av + Hd·(h − d)]/(fyd·d) + An; (2/3)·Vd,kesme/(fyd·μe) + An), Avh ≥ As/2·fyd/fywd (in the d/2 band below the main reinforcement). In the examples examined, the TS 500 tension reinforcement came out 33–38% more than with the handbook method.
Deriving the inputs from the model: bw = width of the column face carrying the corbel; d = h − concrete cover − Ømaks/2; av = joint gap + pad length/2 + erection tolerance; fck and fyk from the column material (library material, otherwise the project material); γmc 1.4 for precast, the project value for cast-in-place. The absolute elevation of the corbel is determined from the column ends, and its face from the absolute direction in plan (transformed in rotation and mirroring).
Building the demand: For each load combination k, the end shears of the beams seated on the corbel and the loads of the predefined node assigned to the corbel are summed. The coefficients are those of the combinations used in the design; the damage, G^/Q^ and vertical earthquake load cases enter the combinations with the same rules as in the design.
- Rv,k = Σc Kk,c · (Σkiriş Vuç,c − Fz,c) and Hk = Σc Kk,c · (Fx,c·nx + Fy,c·ny); Kk,c: coefficient of load case c in combination k.
- Rv,kD: the same sum with the seismic load cases magnified by DX / DY (the D of the column design, including a rigid basement and a different D in the lower part).
- Vd = maxk Rv,k + Vd,elle; Vd,kesme = maxk max(Rv,k; Rv,kD) + Vd,kesme,elle; Hd,ek = maxk |Hk| + Hd,ek,elle.
Vuç: shear force at the end of the beam on the corbel (load downward on the corbel positive); F: node load (Z up); n: outward normal of the corbel. If mink Rv,k < 0, an uplift warning is written (the corbel does not resist uplift). For the overhead travelling crane, the crane load cases (KV vertical Rkol, KH horizontal Rkol/10 and Rkol/7, the V·e moment) are taken as written to the crane node; the face of the corbel is found from the sign of the moment (toward the opposite rail), and av = e − c/2 (c/2: distance from the column centre to the corbel face). If there is no G load at the node, the self-weight of the crane girder and rail is added to the G load case as q·L/2 at an end column and q·L at an interior column (with the G^ coefficient in the earthquake combinations); the end column is the first or last column along the rail. The seismic inertia force of the bridge mass does not enter the horizontal demand.
Checks that are not applied: The reduction of Awf by permanent compression in Clause 8.1.7 and the inclined shear friction reinforcement (Eq. 8.9); local bearing pressure under the plate and the elastomer (TBDY 8.3.1.5), dowel edge distance ≥ 6Ø (8.3.3.1) and confinement of the dowel zone (8.3.3.5), out-of-plane force (8.3.2.1), the prohibition of seating a column on a corbel (3.6.2.4(a)), welding of the anchor bar and extension of the anchor bar beyond the loaded area (there is no geometry input).
6. Result statuses
| Status (Result column of the report) | Meaning |
|---|---|
| OK (SAĞLANIYOR) | The section limits and all checks are satisfied; the selected reinforcement fits |
| INSUFFICIENT (YETERSİZ) | A section limit (Eq. 8.26 or Clause 8.1.7) or a check (outer end depth, at least C30 for precast) is not satisfied, or the reinforcement does not fit in a single layer / in the 2d/3 zone |
| NOT APPLICABLE (UYGULANAMAZ) | av > d: Clause 8.4 does not apply; the corbel must be designed as a beam |
| NOT CHECKED (DENETLENMEDİ) | Demand incomplete: there is no valid analysis, no demand source was found, or the matching is ambiguous (nonprismatic / inclined beam, a node that cannot be assigned, an unmatched crane node); the calculation is made with the part that was found |
| ERROR (HATA) | An input could not be derived or is invalid (e.g. av could not be derived, γmc < 1.5 for cast-in-place, Vd ≤ 0) |
7. Reporting
The corbels go into the Precast Connection Design (TBDY Chapter 8) page under the Foundation Calculations group in the Report Selection → Report tree as KONSOL rows after the connection rows; if the project has short corbels, the page comes checked by default. The page is printed when the Foundation Calculations group or only this page is checked.
- The Member column shows the column name, storey, column number, corbel number and face (e.g.
S12 k1 n4 K1+Y). - The Demand column contains Vd, the value with D for the shear checks if one is given (VdKesme; Vd,shear in the English report) and Hd; the Capacity column contains the section limit Vmax and the provided / required Ast; the Ratio column contains the largest of the utilization ratios of the section, the tension reinforcement and the horizontal stirrups.
- The Result column shows OK, INSUFFICIENT, NOT CHECKED (demand incomplete), NOT APPLICABLE (av > d) or ERROR (input could not be derived).
- The explanatory lines contain the inputs and their sources, the selected reinforcement (main reinforcement, horizontal stirrups, bottom reinforcement, anchorage length) and the messages; because of the file format, these lines contain no Turkish characters (e.g.
7fi16, ordurum DENETLENMEDIin a Turkish report).
Each time the report is generated, all corbels are redesigned and the rows are written in the report language; the printed page is always up to date. The detailed calculation trace is not printed in the report; the Calculate (unsaved) button in the Corbel tab shows the status, demand and calculation lines of the selected corbel.
8. Saving and file compatibility
The short corbel definitions are saved with the project file (.sy4 and .sbd); corbel changes can be reverted with Undo. The KONSOL report rows are stored together with the connection records. When a project is opened, the corbels of the previous project are cleared; the connection records and the corbels are also cleared when a new project is started. If a file with corbels is opened and saved again in a program version that predates the short corbel feature, the corbel definitions are lost.
9. Scope limits
- The automatic demand requires a valid analysis. Beams of adjacent storeys, nonprismatic beams and beams inclined by more than 5° are not matched; the seismic force of the crane bridge mass does not enter the horizontal demand.
- The corbel does not enter the drawings or the quantity takeoff and is not part of the finite element model; the eccentricity moment V·(c/2 + av) of the reaction of the beam seated on the corbel does not enter the column design (Section 4).
- Local bearing pressure under the plate and the elastomer, dowel edge distance and the prohibition of seating a column on a corbel (TBDY 8.3.1.5, 8.3.3.1, 3.6.2.4) are not checked.
- A corbel can be defined only on a reinforced concrete column with a rectangular section.
10. Frequently encountered situations
| Symptom | Solution |
|---|---|
| The result is NOT CHECKED. | The analysis has not been run, or the model has changed after the analysis (including switching the crane on or off): repeat the analysis. Or no beam seated on the corbel / loaded node was found, or the matching is ambiguous (elevation, direction, nonprismatic section, a node that cannot be assigned; Section 4). To give the demand manually only, select Manual only as the Demand source and enter Vd add., Hk and HdEk (for a shear demand with D, Vd,shear add.). |
| There is no demand on the crane corbel, or “av turetilemedi” (av could not be derived). | The crane node (the corbel top elevation in the crane window) must differ from the top face of the corbel by at most 5 cm, and the corbel must face the opposite rail (face). If the crane eccentricity e = 0, av cannot be derived; enter e and apply the crane again, or enter av directly. |
| The corbel is not accepted when OK is pressed. | A corbel is defined only on a reinforced concrete column with a rectangular section. The elevation is the distance of the corbel top face from the top end or the bottom end of the column (elevation reference); together with the corbel depth h, the corbel must fit within the column height. |
| The result is ERROR: “av turetilemedi” (av could not be derived). | av has not been entered and there is no bearing pad length. Give av directly, or give the pad length, joint gap and erection tolerance. |
| There are no KONSOL rows in the report. | No corbel is defined in the project, the connection page is not checked, or the edition is not Ultimate. The rows are regenerated when the report is generated; no separate action is needed. |
| The Corbel tab is missing or disabled. | The edition is not Ultimate, the column is not a reinforced concrete rectangular column, or the new column drawing window is open; the corbel is defined in the properties window of a column that has already been drawn. |