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Q&A for MERLIN-DASH
MERLIN-DASH's Main Web Page
| Q: Do I need to input a decimal point all the time?
A: The current version should insert the decimal point wherever
needed.
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Q: How is the point of contraflexure determined and what is it used for?
A: DASH uses DL+SDL to determine the contraflexural points and the
dividing line between using composite and non-composite sections for the
stiffness analysis as well as the section property calculation.
Q: Would the locations of composite and non-composite vary depending on
the placement of live loads? Therefore, I could place a live load so that it
causes positive bending in a region, but based on the set locations from the
girder DL, it would use the steel girder only for section properties instead of
the composite one.
A: You may get different answers from different code writers. My
explanation, as well as some of my colleagues, is this:
- It is conservative to use non-composite section properties in the negative
moment region. From the stiffness analysis point of view, the negative moment
is less than assuming full composite in the negative moment region. (This
option can be controlled by the program input, % of composite in the negative
moment region). From the stress calculation point of view, depending on the
shear studs in the negative moment region, the stress can be calculated by
using steel section only or steel + rebar section.
- It is true that the moving live load will cause negative bending in the
negative moment region so as to cause moving of the contraflexural points. If
you want to put that scenario into consideration, you then have millions of
possibilities. So, in consensus, the contraflexural points are usually fixed
for the stiffness analysis. But for the stress calculation, there are two
schools of thought:
- Still use fixed contraflexural points; beyond those, use non-composite
section properties;
- Use the summation of moment to determine use of non-composite section
properties or not; if the sum is negative, use non-composite section
properties. Otherwise, use composite section properties. Compared to the
first option, this one is more conservative.
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Q: Stated in the User's Manual, "two utility programs are available to
alter the contents of Steel Section Table (FILEW.BIN). Please contact your user
support." I would like to update the Steel Section Table. Do you know where I
can obtain these utility programs?
Q: Further, I updated the SECTION.DAT file, but I am not sure how to
create a new FILEW.BIN file. The readme file states "when the SECTION.DAT file
editing has been completed, a new FILEW.BIN will be created by typing WRITEF."
Could you please provide more information about this step? Where do you type
WRITEF?
A: It is an execution file. You can either go to the DOS environment
and type "WRITEF" or use Windows Explorer to show all the files and click on "WRITEF.EXE."
Check the date of the FILEW.BIN created in the same folder, it should be today.
The new FILEW.BIN should reside in the same folder where the application files
located.
Note: Please override the section data file in the last few nominal
depth sections because every section is mapped to one corresponding cost data
for the design. If you override one of the sections, the corresponding cost data
will not map to the right section. Please keep the original FILEW.BIN file and
re-name it to the FILEW.BAK. After finishing your job, you can delete the new
bin file and re-name the backup bin file back to the original file name so that
every section has one correct corresponding cost data. If you forgot, the new
bin file will stay there. The program will still work fine because you change
only the last few nominal depth sections and nobody will use those sections. |
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Q: When using LRFD analysis, TABLE 0.0.6.1 AASHTO LIVE LOADING - LOAD TYPE
(A) shows... HL-93 VEHICLE X FACTOR OF 0.00 . What is this X factor? I don't
remember seeing this before.
A: It's a special request from one of the States which wants to
manipulate HL-93 by a certain factor, say 1.1, which is not recommended by
AASHTO. We also did not publicize it, but you noticed it.
Q: (LFD) I input HS loading and special vehicle at the same time for a LFD
code check and the results look weird.
A: The program ignores the HS loading when you input the special
vehicle (Load Type "C") in LFD.
Q: How does the program analyze a pedestrian bridge? For a two-span
pedestrian bridge, does loading (such as live load) at one span (one side of
bridge) determine the maximum positive moment?
A: Input "HS-1" to turn off the vehicular loading and then input or
let the program default to the sidewalk loading. See the description for
sidewalk loading. Sidewalk loading is a live load applied to get the maximum
effect like any vehicular loading.
Q: Same question about the sidewalk loading, isn't it true that sidewall
LL moments should result from the sidewalk LL input in XX k/ft. for both runs
HS-1 and H-1?
A: For HS-1, the result is from HS-1 + sidewalk because HS loading can
be factored, such as HS-25. For H-1, the result is from H-20 + sidewalk because
H cannot be factored so there is no control of H-XX where XX is not 10, 15 or
20.
Q: When you have sidewalk loading, the program applies it directly to the
beam that you are analyzing, regardless of whether it is an interior or exterior
beam. The User's Manual states that the program will apply the sidewalk loading
directly to the exterior beam. Should the program leave off the sidewalk loading
when the user specifies the beam as an interior beam, or should the user
manually remove the sidewalk loading when analyzing an interior beam?
A: Based on users' requests, the program has been modified to such a
case:
- For interior beam, several users stated that when the sidewalk loading is
applied to the exterior beam, the interior might be under uplifting force. So,
the program now allows positive (downward) and negative (upward) loading input
for the interior beam based on engineering judgment.
- For exterior beam, you may input 100. to indicate 100 percent of the
AASHTO sidewalk loading where it varies by span length, or input loading (if
<10) directly to override AASHTO sidewalk loading (but with constant magnitude
regardless of the span length.) All should be positive to indicate downward
loading.
So, to answer your question, yes, the sidewalk loading could be removed for
interior beam if there is no effect based on engineering judgment. The effect
of the sidewalk to the interior beam is based on location of the sidewalk.
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Q: How to input the data for a rolled beam design?
A: In Data Type 12042, you need to select either 1 (compact wide
flange) or 2 (braced non-compact wide flange) in Section ID. Then, input a fixed
nominal depth in Data Type 12052 under Const. Web Depth for a specific nominal
depth you are interested in or input nominal depth range in Data Type 12062 in
the fields of Maximum Web Depth and Minimum Web Depth if the rolled sections can
be in same range.
Q: I am doing a design for WVDOH. They are requesting the use of Grade 70
steel in the negative moment region and Grade 50 steel in the positive moment
region. Can Merlin Dash design a steel girder in this fashion or do I have to do
a design in all Grade 70 and then in all Grade 50 and then combine the results?
I would like to keep a constant web depth but the flanges can vary.
A: DASH can do the mixed design (different grades of steel in
different regions)
but can't do hybrid design (different grades of steel within one section, flange
and web). Code check and rating are allowed for both (mixed and/or hybrid
sections). However, I recommend you use the design section to go back and code
check again.
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| 6. Distribution Factor/Impact Factor Input/Output |
Q: (LFD) Does the MERLIN-DASH program assume S/5.5 as per AASHTO 3.23.1.2?
Does it assume a distribution of S/5.5 for the wheel at the support or does it
assume the deck acts as a continuous beam for the end wheel? If it does, what is
the logic used in the program?
A: S/5.5 is used for all moment and shear distribution factors, except
for end shear. For end shear and reaction, the wheel on the top of the support
is using simple beam action distribution but the rest is still S/5.5. Reactions
have been verified and proved to be correct by us and many of our users. If you
use the assumption stated above, you should get the same answer.
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Q: A simple analysis using AISC Continuous Beam tables for a 3-span bridge
and redistributing 10% of the negative moment to the positive moment sections
gives me approximately 625, 470, and 690 kip ft respectively for three points,
the 4/10 point on span 1, over the pier (0/10) on span 2, and the 5/10 point on
span 2. MERLIN DASH yielded approximately 640, 390, and 750 for the same points.
The total moment agrees, but MERLIN DASH has redistributed the moment somewhat
differently.
A: Due to different practices by different states, we gave an option
for the structure analysis of a continuous beam in MERLIN-DASH. You may select
"% of composite in the negative moment region" on screen marked "Structural
Details". If you give 100%, the program will use 100% of the composite section
properties in the negative moment region when the stiffness is formed. In this
case, more moment will be attracted to the negative moment region. I guarantee
that you will get closer results. If left blank, as in your case here,
non-composite section properties are used in the negative moment region and
lower moments in this region are obtained, as you observed.
Q: Further, I entered 0% since the bridge is not composite in the negative
moment areas. I expected this to lower the moment in the negative steel area,
although I was somewhat surprised at the amount it was lowered. Was the moment
also redistributed by the 10% rule? Also, I was surprised that most of the
moment which ended up in the center span is somewhat counterintuitive. Any
thoughts on this?
A: There generally are three rules for the negative moment region:
- "Moment distribution based on stiffness" rule: As I stated before, you
want to use composite or non-composite section properties in the negative
moment region while calculating the moment. Your SDL and LL moment envelopes
will be "readjusted" between the two assumptions, as you observed.
- "Calculation of stress" rule: The moment calculation is based on Rule #1.
Rule #2 will use whatever you got from Rule #1 and divide the moments by
whatever section properties you specified by Rule #2. If you specify shear
studs and rebars in this region, the stress calculation will use "steel +
rebar" section properties. This will affect your stress calculation in this
region.
- "10% redistribution" rule: This one says that if a compact section is used
in the negative moment region, especially at the pier location, AASHTO allows
you to "redistribute" 10% of the negative moment to the positive moment
region. In other words, you may allow 10% over the capacity at the pier if the
redistribution shows that your positive moment region capacities are enough
after redistribution. For "redistribution," please see MERLIN-DASH output
Table 1.2.22.14. If non-compact at the pier, you may see no change between
"before" and "after" moment envelopes.
These 3 rules are independent and shouldn't be treated as the same.
Q: Questions concerning the LRFD reactions on Table 1.2.7.1 - Live load
Reactions. How to separate truck and lane?
A: There is a hidden message here, the impact factor. You know the
impact for truck is 1.33 and the impact for lane is none. The program gives you
an "equivalent" impact factor, as well as LL and LL+I. Following is an example
on how to separate truck and lane reactions.
- From Table 1.2.7.1, LL=368.51, (Equivalent) IF=1.237, LL+I=455.88
- Assuming truck reaction is X, we now have the equation: 1.33X + (368.51-X)
= 455.88 (=368.51 x 1.237)
- X is solves as 264.77. So, LL for truck is 264.77 and LL for lane is
103.74.
- To back check LL+I for truck is 264.77 x 1.33 = 352.14 and LL+I for lane
is still 103.74. So, the total LL+I is 455.88, matched with the table readout.
Q: MERLIN-DASH seems to have a new table now (Table 1.2.8.1C Camber
Information at 30th Point) that it didn't include before. The columns for Steel
and Other Non-composite Dead Loads (slab + any other non-composite dead loads)
and Composite Dead Loads seem to contain the correct values. But, I think the
values for the Total Dead Load are incorrect. This column seems to be the sum of
the Other Non-composite Dead Loads plus Composite Dead Loads, but does not
include the beam Dead Load. Compare this table with 1.2.8.1A (Camber
Information). Also, why is the program using 30th points?
A: From time to time we accommodate various States' requests to
implement certain features. The table is a request from NCDOT for any span
length over 200'. In the future, if you have any request, you may send me a note
and we may consider it in the future version. |
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Q: When I check the moment capacity in Table 1.2.22.14 it showed OK but the
stress in Table 1.2.9.5 is over the yield stress. What is wrong with the
program?
A: You may have a compact section with moment capacity Mp. In this
case, the stress in Table 1.2.9.5 using linear relationship is invalid.
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Q: Table 1.2.22.8 under "strength category for lateral bracing," #2 says
"Braced non-compact section (so far), need to further check AASHTO LRFD compact
requirement." Is this a bad thing?
A: It is a misunderstanding. "So far" means that the first check for lateral
bracing uses the "braced non-compact" criteria, which does not involve moments
at bracing. The next 4 Tables 1.2.22.8A-D involve finding the moments at bracing
and satisfying the compactness requirement. Please see the last two columns for
lateral bracing compactness requirement. Then, all are summarized on Table
1.2.22.9. The program has done all the checking for you. So, you are supposed to
know the status by reading Table 1.2.22.9.
Q: Table 1.2.22.24a under Status says it needs to be checked. What does this
mean? And why does it also say "NG" under Table 1.2.30.1 - Code check?
A: When Table 1.2.22.24 was calculated and established, the process was to be
stopped and engineer's judgment made. However, when there is no interruption,
Table 1.2.22.24a has to be made with internal judgment. Our judgment is to find
the minimum spacing between (1) abutment and max positive moment, (2) max
positive moment and point of contraflexure, and (3) the negative range. Based on
the minimum spacing calculated from Table 1.2.22.24, we may get the total
numbers within these three regions. It happened here that based on the fatigue
criteria, the total number so shear connectors within region 1 is ok, region 2
is not and region 3 has no connector. So, you may do your own calculation on the
side, based on your own spacing, to check the established N1 (or N2) based on
ultimate strength criteria.
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Q: (LFD) MERLIN-DASH table 1.2.22.24 list Vr=119.8Kips and Q/I=0.01876 and
Sr=1.5. Sr=Vr*Q/I = 119.8x.01876=2.25 Kips and the pitch = 3x6.01/2.25=8.01 In.
instead of 12.05". Can you explain to me if there is a mistake in the program in
computing Sr and the spacing of the connectors? Keep in mind that shear range
listed in Table 1.2.22.24 matches the shear range from Table 1.2.6.3A.
A: Shear connector design by fatigue criteria follows:
- For road type =2 or 3 only one case each has to be checked;
- For road type =1, according to AASHTO Table 10.3.2A, there are two cases
to be checked for truck loading: 2 million cycles and over 2 million cycles.
- 2 million cycle case is for multi-lane loading case and over 2 million
cycle case is for single-lane loading case. Their corresponding distribution
factors are different (WSD/LFD: S/5.5 vs S/7) and their corresponding shear
ranges are reduced shown in Sr, but not in Vr shown in Tables 1.2.6.3A and
1.2.22.24.
- Alpha values are also different for 2 million cycles (7,850) and over 2
million cycles (5,500). So, I recommend you to input diameter size only, not
Zr, unless you want to overwrite the internal set values (7,850 and 5,500).
- If you plug both numbers in, you will find for fatigue criteria check of
road type 1, the over 2 million cycle case always governs because
Pitch = Zr/Sr
Case 1: Pitch = (Vr * Q/I) (7.85 * d^2) = 7.85 (Vr * Q/I) (d^2)
Case 2: Pitch = (Vr * [(S/5.5)/(S/7)] (5.5 * d^2) = 7 (Vr * Q/I) (d^2)
So, you may see Case 2 (over 2 million cycles) gives smaller pitch (7 vs 7.85)
and governs. Probably not too many people caught the small footnote shown on
Table 10.3.2A (as well as the Alpha for over 2 million cycles shown in Art.
10.38.5.1.1). But this is the governing case. If you input connector diameter,
instead of Zr, the program will calculate everything correctly.
Q: (LFD) Is the maximum allowable shear connector pitch (fatigue criteria)
in Table 1.2.22.24 based on an HS25 truck if this is the design vehicle? Or does
it revert to HS20 as indicated in Tables 1.2.22.22 and 1.2.22.23?
A: For shear connector fatigue design, we are conservatively using no
reduction from HS25 and single lane loaded (over 2 million cycles) for road type
1 to get the pitch distance. HS20, instead of HS25, used in Tables 1.2.22.22 and
1.2.22.23 was discussed in AASHTO Specs.
Q: I am using MERLIN-DASH for Windows to design a 42" plate girder for a
simple span composite structure. I chose program flow 6 (Design + Recycle + Code
check) for the design. I'm specifying 50ksi steel, but when I check the output,
several tables are using 36ksi as the yield stress.
A: On the input screen group there are two places for the yield
strength input (actually there are three for the new version). For the
homogeneous/mixed steel code check and rating, use "Yield stress and lateral
bracing data" screen in the "Detail" input screen group. For design, use
"Material and fabrication cost" screen in the "Design" input screen group. (The
third one is for the hybrid steel code check and rating. It should use
"Definition of members" in the "Beam definition" input screen group to replace
the 1st one.) All defaults are 36ksi steel.
So, I'm guessing that when you use the design option you didn't specify the
"design material" on the "Material and fabrication cost" screen. Please specify. |
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Q: (LFD) Does Merlin Dash calculate the HS 20 lane load when it is entered
on the AASHTO live load input screen or just the truck load? If it only
calculates the truck load, how is the lane load entered? I have an inconsistency
between BRASS and Merlin Dash. They both agree nearly exactly for the truck
load, but BRASS has lower numbers and they are attributed to the lane load. The
summary for the Merlin Dash output says "Rating information for AASHTO Truck".
Where do I look for the lane load ratings?
A: Merlin-DASH uses both truck and lane loading in the evaluation. The
title should be "Rating information for AASHTO Loading" instead. I checked your
output and found that lane loading governs at the interior support for Rating
based on Maximum Design Load (Table 1.2.32.1), but Rating based on
Serviceability Strength (Table 1.2.32.1) at the same location governs. You may
use the detailed output level to give you more information for comparison.
Q: Which table shows the constructibility and serviceability for live
load?
A: For constructability: Tables 1.2.22.10 shows the capacity to the
section under construction and Table 1.2.22.10A shows the web buckling and
compression flange buckling checks while under construction.
For live load deflection rating: Table 1.2.32.3A shows two lines of output;
the 1st is for "possible" 2-lane loading and the 2nd is for "possible" 3-lane
loading. You may pick the one fit the actual case.
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Q: I tried to use the staging features but it doesn't work.
A: In Data type 01032, you need to select either 7 (DL STAGE ANALYSIS)
or 8 (DL STAGE + LL ANALYSIS). If you input other options, the slab load is per
span.
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Q: (WSD) It appears as though the required number of bolts in the top and
bottom flanges, as well as the web are inspected for slip-critical criteria
only. That is, the allowable load on the bolt was inspected by AASHTO
10.32.3.2.1. Why are the bolts not inspected for the criteria under AASHTO
T10.32.3B? Is it due to the fact that the A325 bolts are generally being used
with a Class A contact surface, thus resulting in the slip resistance per bolt
of 15 ksi which is less than the shear per bolt of 19 ksi outlined in AASHTO
T10.32.3B?
A: Yes, this is the presumption when we programmed it.
Q: (WSD) In reviewing AASHTO Sections 10.18.1.3, 10.18.2.2 & 10.18.2.2.3,
it appears as though for each element (flange or web), there are two criteria to
inspect for: 1) for the inspection of the bolts for shear & the plates for
bearing and 2) for the inspection of the slip force.
- With this in mind and referring to AASHTO 10.18.1.3, it states that
"¡?For this case, the shear strength of the connections shall be checked for
the maximum calculated splice plate force acting on a single shear plane¡?" Why
a single shear plane? Isn't the flange splices and web splice a double shear
application requiring the inspection of both shear planes?
- With reference to AASHTO 10.18.2.2.3, last paragraph, it states "¡?As a
minimum, high-strength bolted connections shall also be proportioned to
prevent slip at a force¡?for the small section at the point of splice times the
smaller value of the gross flange area on either side of the splice¡?" Is it
AASHTO's intent not to employ the effective area, Ae, found in AASHTO
10.18.2.2.4 in the computations involving slip critical criteria? Are we only
to use the effective area, Ae, when inspecting for bolt shear and plate
bearing?
I am reading the AASHTO 17th Edition, 2002. My reference to the sections
may not be absolutely clear. Where I find the conflict between gross and net
area references is within the last paragraph of Section 10.18.2.2.3, page 274.
For the slip force criteria, AASHTO states "¡?As a minimum, high-strength bolted
connections shall also be proportioned to prevent slip at a force equal to the
maximum elastic flexural stress due to D + (L+I) at the mid-thickness of the
flange under consideration for the smaller section at the point of splice times
the smaller value of the gross flange area¡?" It seems as though AASHTO refers to
net section for checking the shear on the bolt, but gross section for the slip
resistance. Is this a misinterpretation, or is this AASHTO's intent?
This same concept is later repeated in AASHTO 10.18.2.3.9 where it states,
"¡?In addition, as a minimum, high-strength bolted connections for web splices
shall be proportioned as eccentrically loaded connections to prevent slip¡?the
horizontal force resultant shall be computed using the gross section of the
member¡?" This is different from the one mentioned before.
A:
- Since you already divided the flange design force to two parts. Each one
is considered single shear.
- I re-read the section and got the same conclusion as you got without
reading your comments first. This probably doesn't make too much sense with
WSD. But when designed by LFD or LRFD, slip critical design due to D+(L+I)
means using un-factored loading with gross section and shear/bearing design is
using factored loading with net section.
This sentence is just to give the guideline for the calculation of flexural
moment and horizontal force resultant of the web and should be treated
differently from previous article. AASHTO is indicating to use gross section
beam properties in determining the moment and service load stresses, fcf &
fncf, in the check of the slip resistance for the load combination of D+(L+I).
Q: (WSD) With respect to fillers, in AASHTO 10.18.1.2, first paragraph, it
states that filler plates over ?ù inch need not be extended, provided the
fasteners are reduced by a factor R. It later goes on in the last paragraph and
states that for slip-critical connections shall not be adjusted for the effect
of the fillers. Is it AASHTO's intention to treat fillers differently depending
on if you are inspecting shear in the bolt or plate bearing versus the
slip-resistance criteria?
A: Yes, R is only for shear and bearing and not for slip resistance. I
would have to concur at this point in the interpretation of AASHTO. Which means
for a Class A, slip critical connection with A325 bolts, a designer should not
reduce the slip resistance of the bolt from 15ksi. This means that the shear on
the bolt would have to be inspected to ensure that R*19ksi doesn't fall below
15ksi, or it will control over the slip critical criteria. |
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Q: Did you have different installation packages for different computer
operating systems?
A: For the single-user version, there are two installation versions,
one for NT/98 and one for the others. For the network user version, there are
one concurrent user and three concurrent users by using different HARDLOCK keys
Q: (Network Version) When I open the software, and it is finished loading,
I click on "Input" and I get the following error message:
Run-time error "372": Failed to load control "SSTab" from TABCTL32.OCX. Your
version of TABCTL32.OCX may be outdated. Make sure you are using the version of
the control that was provided with your application.
A: It is the OCX (path) registration problem for your PC. It can be
easily fixed by following the steps listed below:
- Connect to the File Server from end user's workstation. (If there is a
privilege problem, please log in as the System Administrator.)
- Go to the server folder where the MERLIN-DASH program was installed.
- Click on the "RegTab.exe" to install the TABCTL32.OCX. Message
"Registration of OCX attempted" will show up.
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