Q: We are trying to use SABRE to design a dodecagonal monotube, cantilever
traffic mast arm. Two arms are to be attached to the post, one above the other.
There doesn't seem to be a way in SABRE to design/analyze this type of
structure. Is this true, or can this configuration be modeled with this program?
A: You may first model it as a one arm cantilever structure, but with
the true post height. Once the model is set and mesh is done, all you have to do
is to add joints and members for the upper level arm. The new joints and members
can follow the current generated ones. You may also add concentrated load(s) to
the upper level arm. Once those modeled, don't press the "mesh" button again.
Otherwise, all the added information will be overridden.
The screens under the "Structural generation" are helping to easily generate the
sign structure modular model, but are not necessarily the only way. You may use
the screens for joints, members and optional joint loads to add or modify the
modulated model.
Q: Under ELEMENT DEFINITION, What exactly is a segment? Does it correspond
to the number of segments (panels) within the truss with the exception of the
connection length? What about number of segments for the posts? Does the output
give data at each segment?
A: For truss, segments are where truss nodes locate to create 3-D
truss panels. You should test one case and see how the program generates truss
span or post for you. For single post, segments are like output points. For
truss (double or four leg) post, it's the same as truss span.
Q: Concerning a VMS's sign offset, how does the program know how eccentric
the VMS is? Does it take the VAMS z-dimension as the offset dimension and then
add half the sign thickness in the z-direction? Or is the load applied to the
structure directly thru the VAM?
A: Yes, z-dimension is used as the eccentricity.
Q: Under the VAMS menu, the attached sign units and walkway units: If
there is no number here, does that mean that the sign is not attached to these
VAMS? Will the sign load be applied to the structure thru the VAM member?
A: Yes, the sign (and sign load implied) has to connect the sign
structure through VAMs. If not connected, when you click MESH button, warning
message will show.
Q: Can we control the Cd (drag coefficient)? If so, on which screen? Our
project criteria requires a Cd of 2.0 for the VMS, 1.16 for the static sign, and
1.10 for the tubular members.
A: Yes, you may, by an option screen (Data Type 6012).
Q: On the SIGNS menu, is the z-coordinate the CG of the thickness (i.e. if
the sign is 5-ft thick, would the z-dimension be ?ö the chord diameter + the VAM
thickness + 2.5-ft ?)
A: When the SABRE was developed, Variable sign is not as popular as
nowadays so z-coordinate is directly used for eccentricity. If variable sign
unit is used, you should enter the z-coordinate at the center of the load, i.e.
?ö the chord diameter + the VAM thickness + ?ö the sign.
Q: For the cantilever-with-plane-truss-chord example provided with the
program, the CROSS SECTION screen gives BLT, BRT and BLB. Why not BRB? Is it
defaulted? Or can't the bottom member be a variable section? Also in this
example, there is a Section 3 coded as 999 for a connection. I don't see where
the section 3 is used.
A: The way to generate the input data is quite flexible. BLB is really
the section number for the connection member and can be Section 3. I modify the
example to two different types: (1) a monotube type with variable sections for
both post and cantilever arm, and (2) single post/plane truss with variable
sections for both post and cantilever truss, for your reference.
Q: For the double-span example (dbl-span.dat), the CROSS SECTIONS screen
has Section 3 for the LBLB, LBRB, RBLB and RBRB. Section 3 is a 999
(connection). Why? I thought that LBLB, for example, is the "Left Beam Left
Bottom" meaning the section number of the bottom chord on the left? In general,
where would one use the 999 designation?
A: We should change the LBLB, LBRB, RBLB and RBRB to Connections. The
program assumes top and bottom chords use the same sections, unless you override
them on the "Definition of Member" screen.
Q: I still don't see what the 999 member does. Do we need one in every
run? Should BLB in the cantilever example be a 999 member? Or just the same as
BLT and BRT? [The TEST.dat you provided shows same section ID as top (BLT and
BRT). That being the case, I don't see why we would need 999. Would it make any
difference in the output if I used BLB = 999 versus BLB = 1 or 5?]. I see in the
Input Verification section of the output that the Section Type for connection
members is "mm". What does that mean? Where does the section properties (very
high) come from for a 999 member?
A: Section 999 is for a dummy rigid member. You may simulate it with
regular member with a relatively large section. The difference is not much. So,
you don't need for every run. Instead of BLB, it should be the connecting member
section. So, if there is a section 999, it should be input for BLB. "mm"
indicates a dummy section.
Q: For connection members (max length = 2.5-ft) would you recommend an
accurate portrayal of the model here? That is, is the connection member length
from the CL post to CL of the first vertical? Can we get the program to give us
forces/stresses at intermediate points along this member? (in order to check
fatigue stresses at stiffener terminus and splice plates which may be at
midpoint of the connection member length).
A: Yes, you may let the program to generate members and nodes. If
there is a need for additional intermediate node, just use the insert row
command on the screen of "Definition of Members" and divide the corresponding
member by inserting a node. This node number is the highest node + 1.
Q: If I can change the Cd factors in data screen 6012, what is the format?
Is there a way to change the Cd for the VMS sign versus the structural support
members? Our client requires a very high Cd for the VMS of 2.00 and a value of
1.10 for the tubular members.
A: (1) The default factors: For single vertical post case, K=2.0; For
double vertical post with truss members connected, K=1.2, Chords and truss
members, K=0.65 (2) To override factors, use Data Type 06011 as the leading line
and follow with 06012 with values. You may specify
- Member ID
- Wind data, Shield ID (Shield ID = 1 shielding on the -Z direction; = 2
shielding on the +Z direction; = 3 no shielding; = 4 Both shielding)
- Wind data, wind drag coefficient
- Wind data, Height coefficient
- Axial Allowable Fa
- Bending Allowable Fb
- Shear Allowable Fv
- Effective length K Factor
Q: Program assumes k = 0.65 which is for fixed end conditions. Is this the
k-value for both in-plane and out-of-plane buckling? Particularly for chord
member, can' t the chord buckle out-of-plane requiring a much larger L in
determining allowable compressive stress?
A: See above.
