ESTUDIO TÉCNICO
3.2.4.4 MANUAL OPERATIVO POR ÁREA DE TRABAJO
3.2.5. MARCO LEGAL
3.2.5.2. Requisitos de funcionamiento y formalización para restaurantes
Frame members of civil and building structures are typically represented by element centerlines. Whereas, physical joint sizes (panel zones) actually do exist at the intersections of the element centerlines. Ignoring such panel zones in an analysis will result in larger displacements and moments. In order to account for element end eccentricities and panel zone effects at beam-column connections, MIDAS/Civil provides the following two methods: Note that the terms, beams and girders are interchangeably used in this section. (See Figures 1.63 & 1.64)
1. MIDAS/Civil automatically calculates rigid end offset distances for all panel zones where column and beam members intersect.
2. The user directly defines the rigid end offset distances at beam-ends.
Rigid end offset distances are applicable only to beam elements, including tapered beam elements, in MIDAS/Civil.
JAutomatic consideration of panel zone stiffness
If the bending and shear deformations in the panel zones are ignored, the effective length for member stiffness can be written as:
1 i j
L = L - (R +R )
where, L is the length between the end nodes, and Ri and Rj are the rigid end offset distances at both ends. If the element length is simply taken as L1, the result will contain some errors by ignoring the actual rigid end deformations. MIDAS/Civil, therefore, allows the user to alleviate such errors by introducing a compensating factor for panel zones (Offset Factor).
1 F i j
L = L - Z (R +R )
where, ZF is an offset factor for panel zones.
The value of the offset factor for panel zones varies from 0 to 1.0. The user’s discretion is required for determining the factor as it depends on the shapes of connections and the use of reinforcement.
The panel zone factor (interchangeably used with rigid end offset factor) does not affect the calculation of axial and torsional deformations. The entire element length (L) is used for such purposes.
Refer to “Model> Boundaries> Panel Zone Effects” of On-line Manual.
Refer to “Model> Boundaries> Beam End Offsets” of On-line Manual.
Figure 1.63 Formation of Rigid panel zone at beam-column connection (a) Column connection with eccentricity (b) Beam-column connection with eccentricity
Figure 1.64 Examples of end offsets due to discordant neutral axes between beam elements
centerline of a beam coincides with a story level
Panel Zone
rigid end offset distance of a beam member rigid e nd offse t dista n ce of a co lu mn me mb er eccentricity eccentricity in the Y-direction eccent ri city in the Z -direction eccentricity in the X-direction
Using Model>Boundaries>Panel Zone Effects in MIDAS/Civil, the GCS Z-
axis is automatically established opposite to the gravity direction, and the rigid end offset distances of the panel zones are automatically considered. Note that the rigid end offset distances are applicable only to the beam–column connections. The columns represent the elements parallel to the GCS Z-axis, and the beams represent the elements parallel to the GCS X-Y plane.
When the Panel Zone Effects function is used to calculate the rigid end offset
distances automatically, the user may select the “Offset Position” for the “Output Position”. In that case, the element stiffness, applications of self-weight and distributed loads, and the output locations of member forces vary with the offset locations adjusted by the offset factor. If “Panel Zone” is selected, the offset factor is reflected in the element lengths for the element stiffness only. The locations for applying self-weight and distributed loads and the output locations of member forces are determined on the basis of the boundaries of the panel zones, i.e., column faces for beams and beam faces for columns.
Selecting “Offset Position” with an offset factor, 1.0 for “Output Position” in
Panel Zone Effects is tantamount to selecting “Panel Zone” with an offset factor
of 1.0. Conversely, selecting “Offset Position” with an offset factor of 0.0 for “Output Position” becomes equivalent to a case where no rigid end offset distances are considered.
When rigid end offset distances are to be automatically calculated by using
Panel Zone Effects, “Output Position” determines the way in which self-weight
and distributed loads are applied and the output locations of member forces. Element stiffness calculation
In calculating the axial and torsional stiffnesses of an element, the distance between the end nodes is used. Whereas, an adjusted length, L1=L-
ZF(Ri+Rj), which reflects the offset factor, is used for the calculation of the shear and bending stiffnesses, regardless of the selection of the location for member force output (See Figure 1.65).
Calculation of distributed loads
If “Panel Zone” is selected for “Output Position”, any distributed load within a rigid end offset distance is transferred to the corresponding node. The remaining distributed loads are converted to shear forces and moments as shown in Figure 1.66. If “Offset Position” is selected for “Output Position”, the above forces are calculated relative to the rigid end offset locations that reflect the offset factor.
Refer to “Model> Structure Type” of On-line Manual.
Length considered for the self-weight
The self-weight of a column member is calculated for the full element length without the effect of rigid end offset distances. For the self-weight of a beam, the full nodal distance less the rigid end offset distances, L1= L-
(Ri+Rj), is used when “Panel Zone” is selected for “Output Position”. If “Offset Position” is selected for “Output Position”, the full nodal distance is reduced by the adjusted rigid end offset distances, L1 = L-ZF (Ri + Rj). The self-weight calculated in this manner is converted into shear forces and moments using the load calculation method described above.
Output position of member forces
If “Panel Zone” is selected for “Output Position”, the member forces for columns and beams are produced at the ends of the panel zones and the quarter points of the net lengths between the panel zones. If “Offset Position” is selected for “Output Position” in the case of beams, the results are produced at the similar positions relative to the adjusted rigid end offset distances. Note that the output positions for the “Panel Zone” are identical to the case where “Offset Position” is selected for “Output Position” with an offset factor of 1.0.
Rigid end offset distance when the beam end release is considered If one or both ends of a column or a beam are released to form pinned connections, the rigid end offset distances for the corresponding nodes will not be considered.
Method of considering column panel zones
The Panel zones of a column are calculated at the top and botoom of the column (See Figure 1.65).
At the connection point of a column member and beam (girder) members, the panel zones of the column is calculated on the basis of the depths and directions of the connected beams. In the case of a beam-column connection as shown in Figure 1.67, the panel zones of the column are calculated separately for the ECS y and z-axis.
When multi-directional beam members are connected to a column, the panel zone in each direction is calculated as follows: (See Figure 1.68)
RCy = BD × cos2 θ RCz = BD × sin2 θ
RCy : Rigid end offset distance about the ECS y-axis of the column top
RCz : Rigid end offset distance about the ECS z-axis of the column top
BD : Depth of a beam (girder) connected to the column
θ : Angle of a beam (girder) orientation to the ECS z-axis of the column The largest value of the panel zones calculated for the beam members is selected for the panel zone of the column in each direction.
(a) Panel zones of a column column centerline axis
(parallel with the z-axis) Panel Zone
Panel Zone
when the centerline of beam section coincides with the story level
rigid end offset distance (A)
co lu mn leng th (L )
(b) Panel zones of a beam
Offset Factor effective length for stiffness caculation
1.00 L−1.00 (× A B+ )
0.75 L−0.75 (× A B+ )
0.50 L−0.50 (× A B+ )
0.25 L−0.25 (× A B+ )
0.00 L−0.00 (× A B+ )
Offset Fctor: rigid end offset factor entered in “Panel Zone Effects” (c) Effective lengths for stiffness calculation (B=0 for columns)
Figure 1.65 Effective lengths used to calculate bending/shear stiffness when “Panel Zone Effects” is used
column centerline axis column member
Panel Zone
beam member
clear length of beam length between nodes (L)
Story (Floor) level
Panel Zone
column member column centerline axis
Li = 1.0 × Ri “Panel Zone” is selected for the locations of member force output.
Li=ZF × Ri “Offset Position” is selected for the locations of member force output.
Lj = 1.0 × Rj “Panel Zone” is selected for the locations of member force output.
Lj=ZF × Rj “Offset Position” is selected for the locations of member force output.
Ri : rigid end offset distance at i-th node
Rj : rigid end offset distance at j-th node
ZF : rigid end Offset Factor
V1, V2 : shear forces due to distributed load between the offset ends
M1, M2 : moments due to distributed load between the offset ends
V3, V4 : shear forces due to distributed load between the offset ends
and the nodal points
(a) Beam member
V4 V2
V3 V1
M1 M2
˝
˝
˝
˝
rigid end offset location at i–th node rigid end offset location at j–th node distributed load on beam element
i-th node
zone in which load is converted into shear force only at i–th node
zone in which load is converted into both shear and moment
zone in which load is converted into shear force only at j–th node L1 (length for shear/bending
stiffness calculaton)
locations for member force output (6)
j–th node
Story Level
Li Lj
LR = 1.0 × R (“Panel Zone” is selected for the location of member force output)
LR = ZF× R (“Offset Position” is selected for the locations of member force output)
Where, R is the rigid end offset factor
V1, V2 : shear forces due to distributed load between the offset end and the bottom node)
M1, M2 : moments due to distributed load between the offset end and the bottom node
V3 : shear force due to distributed load between the offset end and the top node
(b) Column member
Figure 1.66 Load distribution and locations of member force output when “Panel Zone Effects” is used to consider rigid end offset distances
top node rigid end offset location distribut ed l oad on colum n e le m en t Li z o ne in w hich di st rib ut ed l oad i s co n ver ted i nt o bo th s h ear and mom ent zone in w hi ch load is c on ver ted i nt o shea r f o rce onl y at t he t op node Story Level Story Level bottom node Li LR L loca tions for memb er fo rc e ou tpu t ( )
(a) Plan
(b) Sectional Elevation
Figure 1.67 Rigid end offset distances of a column using “Panel Zone Effects”
ECS y-axis of column column member
ECS z–axis of column
column centerline axis
(parallel with the GCS Z–axis) beam member 1
beam member 2
Story (Floor) Level
column centerline axis
rigid end offset distance at the top of the column for bending about the ECS z-axis
rigid end offset distance at the top of the column for bending about the ECS y-axis
beam member 2
beam member 1
: 250 0 250 0 0.0 0 250.0 : 200 40 200 40 82.6 200 0 117.4 : 150 90 150 90 150 2 2 z y 2 2 z y 2 z y
beam member1 BD RC sin RC cos beam member2 BD RC sin RC cos beam member3 BD RC sin RC
= θ = = × = = = = θ = = × = = × = = θ = = × = 150 90 0.0 MAX(250.0,117.4,0.0) 250.0 MAX(0.0,82.6,150.0) 150.0 2 y z cos rigid end offset distance of the column
RC RC
= × =
= = = =
where, BD : beam depth
RCz : rigid end offset distance for bending about the minor axis
RCy : rigid end offset distance for bending about the major axis
Figure 1.68 Example for calculating rigid end offset distances of a column using “Panel Zone Effects”
θ
beam member 3
column centerline axis
beam member 1 beam member 2
ECS z–axis of the column
column member
Method of calculating rigid end offset distances of beam (girder) members
The rigid end offset distance of a beam (girder) member at a column is based on the depth and width of the column member at the beam-end and calculated as follows:
- Formula for calculating rigid end offset distance in each direction (See Figure 1.69) 2 2 cos sin 2 2 Depth Width RB= × θ + × θ
Depth: dimension of the column section in the ECS z-axis direction Width: dimension of the column section in the ECS y-axis direction θ: Angle of the beam (girder) orientation to the ECS z-axis of the column
Figure 1.69 Rigid end offset distances of beam (girder) members using “Panel Zone Effects”
θ beam member 3 beam member 1 beam member 2 ECS z–axis of the column column depth ECS y–axis of the column column width ECS x–axis of the column rigid end offset distance for beam member 2 rigid end offset distance for beam member 3
rigid end offset distance for beam member 1
150, 100 40 150 0 100 0 75.0 2 2 150 40 100 2 2 2 2 cos sin cos θ × + × = × + ×
depth of column section = width of column section= , for =
rigid end offset distance at i-th node =
rigid end offset distance at j-th node = 40 64.7 2
2
sin =
Figure 1.70 Example for calculating rigid end offset distances of a beam using “Panel Zone Effects”
J Method by which the user directly specifies the rigid end offset distances at both ends of beams using “Beam End Offsets”
“Beam End Offsets” allows the user to specify rigid end offset distances using
the following two methods.
1. Offset distances at both ends are specified in the X, Y and Z-axis direction components in the GCS
2. Offset distances at both ends are specified in the ECS x-direction The first method is generally used to specify eccentricities at connections. In this case, the length between the end offsets is used to calculate element stiffness, distributed load and self-weight. The locations for member force output and the end releases are also adjusted relative to the end offsets (See Figure 1.64 (b) & (c)).
The second method is used to specify eccentricities in the axial direction. It produces identical element stiffness, force output locations and end release conditions to the case where “Panel Zone” with an offset factor, 1.0 is selected in Panel Zone Effects. However, the full length between two nodes is used for
distributed loads, instead of the adjusted length. Refer to “Model>
Boundaries> Beam End Offsets” of On-line Manual.
beam member
column centerline at i– th node column centerline at j– th node
ECS x–axis of beam ECS z–axis