The beams and columns of structure are characterized by lines in the computer model.
In the actual structure, a beam spans distance which in the clear span between the faces of columns. But in the computer model, the line for the beam spans among the centerlines of the column. The half depth portion of either column is significantly stiffer than the beam itself from the stand point of bending. To take benefit of this extra stiffness, we may affirm that the start and end faces of the beam are offset from the node by a distance identical to the half-column-depths.
Member offsets can be specified in other situations too. Examples are
When a bracing member does not meet the node which is defined in its incidence list.
A girder and top slab in the bridge where the centerline of the girder is several inches below the centerline of the slab.
This facility becomes very useful when the user wants to have the structural parameters of a member viz. shear force, bending moment by considering the clear distance of the member between the supports. This facility can accessed from the General |
Specification also. When you select the offset menu option in the command menu, the Member Specification dialog box appears as shown below.
Location:
Location defines the offset end of the member. Start is the starting point of the member and End is the Ending point of the member. Start and End depends on the Member Incidence of the member. Selecting one of these options defines the member offset to be at the start point or at the end point of the member.
Direction:
Choose the Local for assigning the offsets in the local axis system. Otherwise, choose the global axis system.
Offsets:
Type the offset distance from the joint in the three global directions. Click the Add button to add this specification to the structure or click Assign to assign the
specification to selected member as well as add this specification to the structure.
Chapter- 5:
In STAAD.Pro V8i, loads in a structure can be detailed as Dead load, Live load, Wind load, Snow load, Seismic load, temperature load and fixed-end member load.
STAAD.Pro V8i can also calculate the self-weight of the structure and make it as uniformly distributed loads (UDL) in analysis. Self-weight of the members can be applied in any desired direction.
Click Commands→ Loading→ Primary Loading.
Now the Create New Definitions / Load Cases / Load Items dialog box appears. Now you have to define the loads, then click Add button.
Dead Load or Self-weight:
Self-weight of all active members of the structure are calculated and applied as a uniformly distributed load. Please note that the property of the member must be defined before this command used.
Direction- Specify the direction in the self-weight load is to be applied by clicking on the X, Y or Z buttons.
Factor- Specify the factor with which the calculated self-weight are to be multiplied. A negative value indicates that the load is applies along the negative direction of the selected axis.
Nodal Load:
Nodal loads is the combination of forces and moments, it may be applied to any free node of a structure. These loads act in the global coordinate system of the structure.
Two options are available under Nodal Load: Node and Support Displacement. Positive value forces acts in the positive coordinate directions of the axis.
Member Load:
The Member Load tab allows the user to apply loads on the span of frame members.
Concentrated Load:
To specify a concentrated force or moment, click the Concentrated Force or Concentrated Moment tab. The data items are explained below.
Linear Varying Load:
The load is applied over the entire length of the member, varies with respect to the distance.
Loading – 2
Area Load: This allows the user to apply load over area, which will be distributed on surrounding beams based on the one way distribution. This load is a one-way
distributed pressure load on members that circumstances a panel. Enter the value of area load in current units. This load always acts along the positive local y direction on the two longest member on each panel.
Note: Area load should not specified on members declared as Member Cable, Member Truss or Member Tension.
Floor Load: User can apply the load over the panel, which will be distributed on surrounding beams based on a two-way distribution. This load is two-way distributed pressure load on members that circumscribe a panel. The data items are explained below:
Load – Floor load value in the current units. This load will act parallel to the global vertical axis.
Direction – The floor may be considered as acting perpendicular to plane of the panel on which it is defined. This is normal load static condition.
Range – Define X Range/ Y Range/ Z Range. Specify the location of the floor using the Define X Range option. The load will be calculated for all members lying between this range.
One Way Distribution – Check the box for one way distribution to get a one way type distribution of the pressure. In such cases, the program find out the shorter side of the panel. It then divides the load in between the long direction beams. No load is
generated by this option if the panel is square in shape.
Plate Load: The Plate Load tab allows the user to apply elements loads. The Plate Load tab offers several sub-menu options as shown below.
Pressure On Full Plate:
Load – W1 is the variable using which the pressure value is defined, in pressure units.
Direction – The load may be applied along the local Z – axis, or along one of the global X, Y or Z – axis (GX, GY, GZ)
Concentrated Load:
Use this option to define a concentrated load that acts on specific point within the boundary of the element. If a load acts at a node point of an element, it is advisable to apply it using the Nodal Load option described in earlier pages.
Load – The magnitude of load is specified in the box alongside Force. X and Y define the location of the load, in terms of the distance from the origin of local X and Y axes of the element.
Direction – The load may be applied along the local Z-axis, or along one of the global X, Y or Z – axis (GX, GY, GZ).
Partial Plate Pressure:
To Specify a uniform pressure on the entire element or a non user specified portion of the element, use this facility. The data items are explained below:
Load – The element pressure (force per unit area) or Concentrated load (force unit).
For concentrated load the values of X2 and Y2 must be omitted, while X1 and Y1 must be specified.
X1, Y1, X2, Y2 – For element pressure (force per unit area), these values represent the coordinates of the rectangular bpundary on which the pressure is applied. If X1, Y1, X2 and Y2 are all zero; the pressure is applied over the entire element. If X1 and Y1 are specified but X2 and Y2 are omitted, then W1 is treated as concentrated load.
Direction – GX, GY, GZ represent the global X, Y and Z direction along which the pressure may be applied Local Z indicates that the pressure is applied normal to the element in the local Z direction.
Trapezoidal: To specify a trapezoidal varying pressure load on a plate, select the Trapezoidal tab. The load is applied over the entire element in the local Z direction, varying along the positive local X or Y direction. The data items are explained below.
Direction of Pressure – GX, GY and GZ represent the global X, Y and Z direction along which the pressure may be applied. Local Z indicates that the pressure is applied normal to the element in the local Z direction. Enter the pressure intensity F1 at the lowest local coordinate location (start) and the intensity F2 at the highest local
coordinate location (end), Start and End are defined basd on the positive direction of the local X-axis or local Y-axis.
Variation along element – Define the direction in which the pressure varies as either the local X ot Y direction or Choose the joint option, which is discussed next.
Joint – Check the joint option to apply different value of pressure at different nodes of the plate element. When checked, the dialog box will change as shown below. Apply different values of pressure in the edit boxes for the different nodes.
Hydrostatic: To model loads due to hydrostatic pressure on one or more adjacent elements, select the Hydrostatic tab. The hydorstatic load is converted to Trapezoidal
loads on the elements. The load is applied over the entire area of the element. The data items are explained below:
Force – Enter the value of the load at the minimum and maximum global axis in
current units. For example, to model a retaining wall with soil pressure, W1 is the force at the bottom of the wall and W2 is the force at the top of the wall.
Interpolate along Global Axis – Specify the global axis (X, Y or Z) along which the load vary from W1 to W2. For example, the load would vary along the Y – axis on a vertical retaining wall.
Select Plate(s) – Unlike the load definition options, we must select plate(s) for this option to became active. Click on this button to select plate(s). Click on the Select Plates button. A dialog box will appear. Select all the plates of a wall on which we wish to apply hydrostatic load. Click on Done. The hydrostatic dialog box will re-appear.
Direction of pressure – Specify the direction of design pressure as Local Z axis or global axes (GX, GY or GZ) and click on Add. This will assign a linearly varying hydrostatic load on all the selected elements.
Element Joint Load: To specify a varying pressure at each joint on a plate, select the Element Joint Load option. The data items are explained below.
Joint Load Data – Choose Three Noded Facet / Four Noded Facet depending on whether the plate element is 3 noded 4 noded.
Direction – The load may be applied along the local Z – axis or along one of the global X, Y or Z – axis (GX, GY, GZ)
Add – After defining a load, click the Add button to add this under current load case in the Loads dialog box.