Overhead Crane Loads, Additional Seismic Masses and Different R–D
This article covers three topics specific to precast industrial buildings: additional masses that participate in the structural system only as seismic mass, overhead travelling crane loads, and different R and D coefficients for the upper and lower parts in buildings with a mezzanine floor. For the modeling steps, see the article Modeling Precast Structures.
1. Façade panel and crane masses (additional seismic mass)
For masses that must participate in the structural system only as seismic mass and not as weight, such as façade panels hung on columns or the crane bridge:
- Select the columns on which the mass will act in the plan and open the Macros → Add predefined node... window. With the On the axis of the selected posts/columns option, the node is placed at the top end of the column (gutter beam elevation) or at the given absolute Z elevation (e.g. the crane corbel); enter the mass in tonnes (= kN·s²/m) in the Additional seismic mass box. For a point other than a column, use the By coordinates (X, Y, Z) option. The nodes appear in the plan with an empty square symbol.
- To change the value later, right-click the node symbol and open the Predefined Joint Properties window; enter the mass in tonnes in the Additional Seismic Mass box on the General tab. In the same window, the node loads (kN, kN·m; global axes, Z up) are entered on the Forces tab and the support conditions on the General tab.
In the analysis, the node is connected to the finite element node with the matching coordinates. If the node lies within the storey height of a column and inside its section, the column is divided at that elevation. The mass of a point that cannot be connected to any node enters only the storey total and is reported in the analysis warning list.
The additional mass is included in the seismic mass of the floor where the joint is located, in the modal analysis mass matrix, in the equivalent seismic load, in the second-order indicator and in the upper/lower part ratios. Since it is not weight, it is not added to the vertical loads or the foundation loads. The floor assignment is made according to the joint’s elevation.
When several joints are selected, if the box is left empty the existing values are kept. Typical use: half of the panel weight (the share carried by the upper connection) at the tops of the columns at the gutter beam elevation. Do not enter the crane bridge mass separately here: the Write bridge mass option in the crane window writes the total bridge mass (bridge weight / g) by dividing it equally among the corbel nodes of the mass columns (Section 2); if the two ways are used together, the mass is counted twice.
2. Overhead travelling crane loads
The Macros → Overhead travelling crane loads... window calculates the crane girder design forces and the vertical and horizontal forces transferred to the columns from the wheel reactions, and writes the crane loads to the model as separate predefined load cases. The program solves these load cases separately in the analysis and builds the crane combinations itself. The window is non-modal: you can select columns in the plan while it is open.
Which edition, which load scheme? The crane load cases work in the StatiCAD Ultimate edition and with the predefined load cases and combinations (TBDY combinations): Use Reinforced Concrete–Masonry Load Combinations must be selected under Project General Settings → Load Combinations. The crane load cases cannot be applied while Use Timber Structure Load Combinations (the user-defined load case scheme) is selected.
| Input | Description | Default (book) |
|---|---|---|
| Lifting capacity (kN) | Crane capacity | 200 |
| R1max, R1min, R2max, R2min (kN) | Wheel reactions from the manufacturer’s table: loaded side (R1) and opposite side (R2); maximum and minimum for the two trolley positions | 153 / 49 / 134 / 30 |
| Wheel spacing a (m) | Distance between the two wheels on one crane girder | 3.84 |
| Dynamic factor ψ | Magnifies the vertical and horizontal crane forces | 1.40 |
| Crane girder span L (m) | Axis spacing | 7.5 |
| Girder + rail q (kN/m) | Self-weight of the crane girder and rail | 5.1 |
| Corbel top elevation Z (cm, absolute) | Elevation of the crane corbel; the loads are written at this elevation to the node on the column axis (the column is divided at that elevation). Z must be between the bottom and top elevations of the rail columns | 800 |
| Corbel eccentricity e (cm) | Distance of the rail axis from the column axis. The corbel is assumed to extend toward the opposite rail; the sign is automatic (MX = −V·ey if the rails run in the X direction, MY = +V·ex if they run in the Y direction) | 0 |
| Rail direction | Direction of the rails in plan (X or Y). The horizontal force in the bridge direction (Rkol/10) is taken perpendicular to the rail, the braking force (Rkol/7) in the rail direction | X |
| Horizontal force at the opposite rail with the min wheel load (book) | If checked, the horizontal force is taken from Rkol,max at the loaded rail and from Rkol,min at the opposite rail, in the same direction; if unchecked, the max value is used at both rails (safe side) | checked |
| KG: bridge self-weight in earthquake combinations | The bridge self-weight (ΣR − capacity) enters only the earthquake combinations, as a separate load case | checked |
| γK (crane combination factor) | Factor of KV and KH in the crane combinations (TS 500, crane live load) | 1.6 |
| Write bridge mass | The bridge mass (bridge weight / g) is divided equally among the mass columns and written as additional seismic mass (Section 1) | checked |
- Calculate: The bridge self-weight and mass, the corbel self-weight point loads, the crane girder moments and shears (Md, Vd, horizontal Md), the column reactions (loaded rail / opposite rail) and the horizontal forces per column are listed. The crane girder is designed separately with these values. With the book inputs: ΣR = 366 kN, bridge weight 166 kN (16.92 t), column reaction 305.7 kN at the loaded rail and 89.1 kN at the opposite rail; horizontal force per column (loaded / opposite rail) 30.6 / 8.9 kN in the bridge direction and 43.7 / 12.7 kN in the rail direction.
- In the plan, select the columns seated on one rail and press Rail A ← selected columns, then select the columns of the opposite rail and press Rail B ← selected columns. The columns over which the bridge self-weight (KG) and mass will be distributed are assigned with Mass ← selected columns; if there is no assignment, KG and the mass are divided equally among all the rail columns. The buttons take the columns that are selected on all storeys: no column on another storey should remain selected.
- Apply crane load cases: A predefined node is created (or the existing node is used) on the axis of each rail and mass column at the corbel elevation, and the loads are written. When applied again, the previous crane loads and masses are cleared first (no double summation). Then run the analysis again.
- Remove crane: The crane load cases and the nodes created by the crane application (those with no other data) are deleted; the mass of the nodes to which the bridge mass was written returns to its value before the crane. The window inputs and the column assignments are preserved.
The inputs and options in the window are taken into the project only when Apply crane load cases is pressed: after changing an input, apply the crane again; if you only press Calculate and close the window, the change is not stored. The Rail A, Rail B and Mass assignments, on the other hand, are stored the moment the button is pressed. The crane definition and the crane load cases are saved with the project. Apply crane load cases and Remove crane can each be undone with a single Undo step.
2.1 Crane load cases
When the crane is applied, the number of load cases in the project rises from 13 to 20; the crane load cases are added with the numbers 13–19 and are seen in the Predefined Joint Properties → Forces table of the node. In projects without a crane definition, the number of load cases, the combinations and the results do not change.
| Load case | Content |
|---|---|
| KV1 / KV2 | Vertical column reactions and corbel moment: in KV1, Rkol,max on the rail A columns and Rkol,min on the rail B columns; the opposite in KV2. Rkol,max = ψ·(R1max + R2max·(L − a)/L), Rkol,min = ψ·(R1min + R2min·(L − a)/L) (crane girder simply supported, using the influence line) |
| KHX1 / KHX2 | Horizontal forces in the global X direction; KHX1 is paired with the KV1 position (rail A loaded), KHX2 with the KV2 position |
| KHY1 / KHY2 | Horizontal forces in the global Y direction, same pairing |
| KG | Bridge self-weight W = ΣR − capacity (static, without ψ; only for the earthquake combinations); divided equally among the mass columns |
In one load case, all the columns of each rail are loaded at the same time (single crane position). The crane load cases are solved with the same stiffness and the same diaphragm rule as G and Q.
2.2 Crane combinations
While crane load cases exist, the program adds at most ten crane combinations to the end of the combination list: 1.4G + 1.6Q + γK·KVi, 1.4G + 1.6Q + γK·KVi ± γK·KHXi and 1.4G + 1.6Q + γK·KVi ± γK·KHYi (i = 1, 2). The crane combination carries the coefficients of the 1.4G + 1.6Q combination unchanged; KHX and KHY do not enter the same combination; snow (S) is not included.
- The crane combinations are not counted as earthquake combinations: they do not enter the seismic axial force in columns and shear walls (the 0.40·fck·Ac limit in columns); they enter the TS 500 design forces and the shear envelope.
- The crane loads do not enter the earthquake combinations (TBDY Eq. 4.11 and 4.12); only KG is added, with the G coefficient of that combination (1.0 / 0.9).
- The crane combinations are also used in the design of columns, beams, shear walls, foundations and raft foundations, in the soil stress check and in the combination envelope of the precast connection demands.
- Only the bridge self-weight participates in the seismic mass, not the lifted load (TBDY 4.5.9.2).
The crane is modeled with a single position; there is no crane position scan and no multiple cranes. The crane load cases do not enter the beam deflection check or the slab shell internal forces. The crane combinations are not generated in risky building (RBTE) combinations; with timber load combinations or in an edition other than Ultimate, the crane loads do not enter the analysis (both cases are reported in the analysis warning list; the bridge mass continues to participate in the seismic mass). The crane corbel is designed if it is defined as a short corbel in the Corbel tab of the column properties window: its demand is taken automatically from the crane node, while the seismic force of the bridge mass does not enter the horizontal demand (see Short Corbel Design). The crane calculation summary is not transferred to the report.
3. Different R and D for the upper and lower parts (TBDY 4.3.6)
For buildings in which the lower part (e.g. the mezzanine section) has a different structural system from the upper part, the Macros → Different R-D for upper/lower parts (TBDY 4.3.6)... window is used. The analysis is carried out for the whole building with the coefficients of the upper part (R, D in Project General Settings); the internal forces of the lower part members are corrected with the ν coefficient given in the code.
| Input | Description | Default |
|---|---|---|
| Apply different R and D coefficients for the upper/lower parts | Enables the option | off |
| Last floor of the lower part (floor no.) | This floor and the floors below it are considered the “lower part” | 1 |
| Lower part R (X), R (Y) | Response modification coefficient of the lower part structural system (TBDY Table 4.1) | 8 |
| Lower part D (X), D (Y) | Overstrength factor of the lower part (TBDY Table 4.1) | 3 |
| νupper (X), νupper (Y) | Ratio of the upper part base shear to the total base shear; if 0 is entered, it is calculated automatically from the floor weights and heights | 0 |
The Calculate / Show button displays the values νupper, νlower, ν, (R̄a)lower and D̄lower.
In the analysis: the ductile internal forces of the lower part members coming from the seismic load cases are magnified with ν, non-ductile behavior (shear force capacity calculations) is carried out with D̄lower, and the relative storey drift of the lower part is calculated with (R̄a)lower. The setting is saved with the project.
Example (book building): Upper part R = 3, D = 2; lower part R = 5, D = 2.5; last lower floor 1; νupper = 0.408 (X) / 0.406 (Y) → ν = 0.763 / 0.762, (R̄a)lower = 3.93, D̄lower = 1.81. If a one-to-one comparison is required, the νupper value can also be entered manually.
4. Frequently encountered situations
| Symptom | Solution |
|---|---|
| The “Apply crane load cases” button is disabled. | Use Timber Structure Load Combinations is selected under Project General Settings → Load Combinations. Select Use Reinforced Concrete–Masonry Load Combinations, then close the crane window and open it again (Section 2). |
| The message “Projede gezer vinç (kren) yüklemeleri tanımlı ancak analize katılmadı” (the overhead travelling crane load cases are defined in the project but did not take part in the analysis) in the analysis warnings. | Timber load combinations are selected, or the edition is not Ultimate. Select Use Reinforced Concrete–Masonry Load Combinations and repeat the analysis; if the crane is not needed, run Remove crane in the crane window. |
| The crane combinations are not in the list. | The crane has not been applied or has been removed; Apply crane load cases must be run before the analysis. The crane combinations are not built while risky building (RBTE) combinations are in use (in risky building assessment, or when “Apply the Earthquake Directions Separately Only in the X and Y Directions” is selected for the Seismic Effect Combination in Project General Settings). |
| The warning “Ray A ve ray B aynı hatta görünüyor” (rail A and rail B appear to be on the same line); the corbel moment was not written. | The rail direction does not match the direction of the rails in plan, or columns on the same line have been assigned to rail A and rail B. Correct the rail direction or the column assignments and apply the crane again. |
| The message “Köprü özağırlığı (ΣR − kapasite) sıfır: KG ve kütle yazılmadı.” (the bridge self-weight (ΣR − capacity) is zero: KG and mass were not written). | The lifting capacity must be less than the sum of the wheel reactions (ΣR); check that the R1/R2 values in the manufacturer’s table include the bridge weight. |
| The total seismic mass is more than expected. | The bridge mass has been written both by hand (Additional Seismic Mass) and with the crane window. Uncheck Write bridge mass and apply the crane again, or remove the mass that was entered by hand. |
| The additional mass does not appear in the foundation loads. | This is the expected behavior: the additional seismic mass is not weight and participates only in the seismic calculation. |