Economical Guidelines for Design
of Structural Steel
By Gary Glenn 07/30/13
1
Structural Steel Costs
(Where is the Money?)
2
Breakdown of Structural Steel Costs (by %)
Other, 4.8%
Tax, 3.5%
Detailing, 3.9%
Freight, 4.4%
Material, 33.6%
BRB, 7.7%
Fabrication, 19.5%
Erection, 22.7%
3
Breakdown of Structural Steel Costs (in Dollars)
Other, $254,526
Tax, $184,008
Detailing, $205,599
Freight, $235,420
Material, $1,781,490
BRB, $406,899
Fabrication, $1,037,316
Above is based on 1,773 ton avg project,
$5,309,823 avg price,
$3,117/ton avg.
Erection, $1,204,564
4
Conclusions from Steel Costs
1.
Fabrication and Erection costs are same magnitude as
Material.
In addition to Material costs, Fabrication and Erection
costs should be a consideration in design.
2.
Detailing costs are significantly lower than the cost of
Fabrication and Erection (by a factor of 10).
Efforts to minimize Detailing costs at the expense of
Fabrication and Erection costs should be avoided.
5
Material Availability Factors
1. Domestic vs Offshore (or Single Source) Material
2. A36 (Flatbar) vs A572 Gr 50 (Sheet)
3. A529 Gr 50/55 (Flatbar) vs A572 Gr 50 (Sheet)
4. Anchor Bolt Grades
5. A325 vs A490 Bolts and Diameters
6. Sole Source Product
6
WF Availability
7
Domestic WF Mills
1. Nucor Yamato – WF mill located in Arkansas.
–
–
–
W6 to W44s. W14s up to W14x730 (A992) (50 yield).
W14x550s and larger may be rolled based on tonnage accumulation.
Check w/ Fabricator for availability.
2. Steel Dynamics Inc. (SDI) `– WF mills located in Indiana.
–
Lighter WF sections from W6 to W36.
3. Chapparel – WF mill located in Texas.
–
Smaller, lighter WF sections.
4. Warehouses (PDM, Gerdue Ameristeel, R&S, etc) –
–
–
–
Lighter WF sections.
Premium in cost to purchase through warehouses.
Some fabricators do you have credit with mills, thus purchase thru warehouse.
5. Mill material is normally shipped via rail to fabricator yard. Warehouse is
normally shipped via truck.
8
Offshore WF Mills
1.
Arcelor / Mittal – Mills located in Luxemburg.
–
W14x550 thru 730s, in A992 (50 ksi yield) that may not be domestically produced.
–
Also, various WF sections in A913 Gr 65.
2.
Nippon - Mills located in Japan.
–
WF sections including W14x550 thru 730s in A992 (50 ksi yield) that may not be
domestically produced.
–
Currently developing equivalent to A913 Gr 65, but not yet approved by ASTM.
3.
Pros of Offshore Material
–
Availability of larger sections not domestically produced in lieu of builtup WF or box
columns.
–
Availability of A913 Gr 65 that is not domestically produced.
4.
Cons of Offshore Material
–
Prone to schedule problems (no commitment is literally written into their Purchase
Agreements; Fabricators have little influence over offshore mills).
(Rolls are based on tonnage accumulation; mills are shutdown for maintenance; vessels
depart once a month; vessels can offload at wrong port; delays in customs/offloading,
etc).
–
Cost premium. For example, W14x730 A913 Gr 65 at $.75/#. W14 A992 domestic sizes
might be around $.39/#.
–
Sole source material.
–
Welding of A913 Gr 65 requires E80 electrodes or qualification of welding procuedures to
achieve high yield at welds. Only applies when welding Gr 65 to Gr 65 material (splicing).
9
Specifying WF
1. Desirable to specify domestic (not offshore),
unless domestic size will not work.
2. In general, you can check Nucor Yamato
website for produced sections. For heavier
sections, suggest checking w/ fabricator to
confirm.
3. Avoid offshore material, except when domestic
sizes will not work. Suggest reviewing w/
fabricator when considering offshore steel.
10
Flatbar (FB)
11
Plate (PL) or Sheet
12
FB Availability
1.
Available in std widths of ½” or 1” increments, and thickness
increments of 1/8”
2.
A36 FB readily available from warehouse. (A36 also available in
plate (sheet)).
3.
A529 Gr 50/55
–
–
–
4.
FB available from mills and usually must be ordered in bundle qnty or
min tonnage.
Available widths and thickness is more limited than what is available
for A36.
A529 Gr 50/55 is a material now specified in AISC Steel Construction
Manual (13th Ed Black).
A572 Gr 50 is not generally produced in FB. Instead, it is
available in Plate or Sheet (5’ x 12’, 10’ x 12’, 10’ x 20’, etc).
13
Example of Widths/Thickness Used for Detailing
FB Parts
1/2
1
1 1/2
2
2 1/2
3
3 1/2
4
4 1/2
5
6
7
8
9
10
12
5/8
3/4
7/8
1
Detailed Width
Chart 2 - Use this for Gr 50 material.
Thickness 3/16*
1/4
5/16
3/8
4
4 1/2
5
5
5
6
6
6
7
7
7
8
8
8
9
10
10
12
1/2
4
4 1/2
5
6
7
8
9
10
12
5/8
3/4
7/8*
1
> 1 **
6
6
6
8
8
8
10
12
10
12
10
12
> 1**
See Chart 1
3/8
Detailed Width
Chart 1 - Use this for A36 material.
Thickness
1/8
3/16
1/4
5/16
** For material that is > 1", material is available in 1 1/8", 1 1/4", and 1/4" increments above 1 1/4".
14
FB vs Plate
15
Advantages of FB over PL (Sheet)
1.
By multing shear PLs, Stiffeners, etc. into lengths of
FB, only one edge of part must be cut.
2.
FB is easier to handle than PL (sheet), and takes up
less floor space.
3.
There is less drop in producing parts from FB over PL
(mult end to end out of FB where as parts nested in
PL)
4.
There is slight premium in Gr 50 PL over A36.
Probably $.01/# premium.
16
Multing vs Nesting
S h e a r P L , 4 ½ ” lo n g , 5 /8 " th ic k
4 ½ x 5 /8 x 2 0 ' - 0 F la t B a r
M ill R o lle d E d g e s
S h e a r P L s “M u lte d ” in F la t B a r
O n ly E n d s a re C u t
E n d s a n d S id e s a re C u t
S h e a r P L s “N e s te d ” in P L
17
Specifying PL and FB Material
1.
Spec A36 where possible. Allows fabricator to produce parts out
of A36 FB widths.
2.
Spec that A529 Gr 50/55 or A572 Gr 50 may be utilized in lieu of
A36 as fabricator option. Allows fabricator max flexibility to utilize
materials on hand and to minimize drop.
3.
Where 50 ksi Fy is necessary, spec A529 Gr 50/55 and A572 Gr
50. Allows fabricator flexibility to use FB as an option in lieu of
having to cut from PL where possible.
4.
Make it very clear where 50 ksi Fy is required so fabricator need
not have to clarify extent in RFI (specify it right at details??).
18
Anchor Bolt (AB) Availability
1. A36 Rod or F1554 A36 (all thread) –
–
–
Most readily available and cost effective.
Specify either, giving fabricator flexibility.
2. High Strength ABs –
–
–
–
Heat treated, increasing cost and leadtime.
F1554 Gr 55 or 105 or A354 BD are common and available.
A307, A325, A490 are generally bolt (fastener) specifications and
should not be used at anchor bolts (due to lack of availability).
A449 and A572 are less commonly available and should be avoided.
3. Double Nut End is desirable over a Headed or J End –
–
–
Head or J end must be fabricated by supplier and has leadtime.
Double Nut End allows straight bolts to be used with all thread or
threaded shaft, which is more economical.
Exception is short anchor bolts at ledger angles. In this situation,
headed A307 bolts may be desirable.
19
Anchor Bolt Availability & Issues
1. Nut Types –
–
–
ASTM defines exactly which types of nuts are to be provided
for grade of anchor bolt, such that the shaft fails prior to the
nut. The supplier must follow ASTM.
So, it should not be necessary to specify the exact nut grade
and type (such as A563 Gr A for example), as this simply
creates confusion and additional cost to fabricator.
2. Welding at Anchor Bolts – Should be avoided. Cannot
occur at high strength bolts as it destroys the heat
treatment properties.
3. Spoiling Threads – Double Nuts jambed together is
preferable over spoiling threads.
20
Field Bolts
21
Field Bolts - A325 vs A490 Bolts
1. Bolt Cost (based on 2” long TC bolts)
–
–
–
–
–
–
7/8” A325
7/8” A490
1” A325
1” A490
1 1/8” A325
1 1/8” A490
$0.14
$0.16
$0.18
$0.22
$0.22
$0.28
2. Installation Cost of Bolts
–
–
–
7/8” and 1” cost about same to install.
1 1/8” costs about 15% more than 7/8” or 1” to install.
1 ¼” costs about 30% more than 7/8” or 1” to install.
3. 1 ½” A325 or A490 bolts should be avoided due to tightening issues (if fully torqued,
requires hydraulic gun vs TC gun or traditional impact wrench).
4. A325s tend to be more readily available than A490s. Minor risk in switching.
5. Conclusion – 1” dia. A325 may be most cost effective for typical connections.
6. Minimize Different Diameters/Grades used on Project (use all 1” bolts). This allows:
–
–
–
–
Erector to utilize one dia set of guns onsite.
Allows fabricator/erector to consolidate bolts together.
Simplifies detailing, fabrication, erection.
Reduces errors.
22
Field Bolts – Other Consideration
1. TC vs Std Hex Head
–
–
Spec both giving fabricator/erector flexibility to use either.
Considerations such as length, access, equipment, thru bolts at HSS dictate which will be
used.
2. Bearing Type Bolts
–
–
Generally, there is no cost difference in X over N in the bolt or installation.
So, suggest specifying X so as to take advantage of higher bearing capacity.
3. Slip Critical Type Bolts
–
–
There is a slight cost difference in specifying SC, primarily due to inspection.
Suggest only specifying SC at SLRS (collectors, frames, etc) locations.
4. LIWs (Load Indicator Washers)
–
–
–
Can cost as much as the bolt itself.
Also, costly to install.
TC, Calibrated Wrench, or Turn of the Nut methods for achieving SC are cost effective and
reliable methods, so LIWs should be avoided.
5. Lock Washers – Not applicable to high strength bolts and should be avoided.
23
Sole Source Products (Avoid)
24
Tolerance and Deflection Issues
1. Variation in WF – Depth and out of
squareness.
2. Anchor Bolt Tolerance & Oversize Holes –
3. Steel vs Finish System Tolerances –
4. Lack of Camber and Floor Deflection 25
Varying Depth of WF
C JP,
Typ
Typ
5 /1 6
4 -2 4
1 ", ty p .
COSTLY
PREFERED
26
Oversizing AB Holes
1. Anchor Bolt Tolerance
–
–
–
Patterns can be ¼” off from grid.
Patterns can be ¼” off relative to each other.
Bolts w/in pattern can be 1/8” off from each other.
2. Erection Tolerance – Column base can be ¼” off in location.
3. Oversized Holes in Base PLs (Necessary for 1 and 2 above)
–
–
–
Recommend oversized holes per AISC ASD 9th Ed (Green Manual pg 4-130).
Size is adequate for AB tolerances, yet not too large to where std washers
begin cupping.
Oversized holes per AISC 13th Ed (Black Manual pg 14-21) requires use of PL
washers in lieu of std washers, increasing costs.
4. DSA – We have seen DSA try to limit AB hole diameters to 3/16” oversized,
creating substantial issues.
27
Steel vs Finish System Tolerance
1. Allowable Steel Tolerance Exceeds Finish
System Tolerances significantly.
2. Suggest designing 1” to 1 ½” gap between
studwall/window wall system and edge of steel
horizontally and vertically.
3. Applies to perimeter of building, canopies,
soffits, roof screens, etc.
28
Example of Accumulation of
Tolerances Affecting Elevations
B
+3/16"
A
0"
+3/8"
-¼”
FLR 0
-5/16"
-¾”
-¾”
-1"
-1/16"
+1/16"
-5/16"
+1 3/8"
-¼”
FLR 0
-7/16
-¼”
-¾”
-1"
-5/16"
-¾”
-1"
= +1/8"-5/16"-¼”
+1/8"
Elevation Along Grid A
AISC Tolerances:
1. Base may be +/-1/8".
2. Length may be +/- 1/16"
3. Connection may be +3/16", -5/16" from splice.
4. Outriggers can slope 1/500 = 1/8".
Defection from Concrete Loading:
5. Outrigger = -1/8"?
6. Center Span of beam = ¼”?
= -1/8"-5/16"-¼”-1/16"
-1/8"
In Summary:
1. Flr to Flr height @
steel along grid A could
be off up to 1 3/8" due to
accumulation of steel
tolerances + deflection
of steel under concrete
loading.
2. Top of steel could
vary from +3/8", -¾” @
grids, and up to -1" @
center of bays
29
Example of Deflection Issue
30
Example of Deflection Issue
31
Warpage and Distortion
Considerations
Some items contributing to warpage/distortion:
1.
Continuous Welding (vs Stitch Welding)
2.
Unsymmetrical Sections
3.
Relatively Thin Material
32
Problematic Section
F in is h
S y s te m
H S S 8 x 8 x 1 /4
10G A B ent PL
C 3 x 4 .1
33
Improved Section
Finish
System
(1/8)
1/8
2-24
HSS8x8x1/4
2-24
1/8
2-24
1/8
2-24
¼” Bent PL
HSS 3 x 2 x 0.180
34
Stitch Welding
35
Weld Types
1. Fillet Welds
2. PJP Welds
3. CJP Welds
36
Fillet Weld Guidelines
1. AWS D1.1 - Single pass fillet welds up to 3/8”
in flat / horizontal positions allowed.
2. In practicality, some 3/8” fillet welds cannot be
made in a single pass.
3. ½” fillet weld ≈ 3 passes.
4. 5/8” fillet weld ≈ 4 passes.
5. ¾” fillet weld ≈ 6 passes.
6. 1” fillet weld ≈ 10 passes.
In summary, 5/16” or smaller fillet welds desirable.
37
Minimum Fillet Weld Size
Per AWS D1.1 2008 Structural Welding Code:
Base Metal Thickness
T < ¼”
¼” < T < ½”
½” < T < ¾”
¾” < T
Min Fillet Weld Size
1/8”
3/16”
¼”
5/16”
38
PJP Weld vs Fillet Welds
1.
PJP (vs Fillet)
–
–
–
Requires prepping.
Fitup is more costly.
Meeting inspection more costly.
2.
5/16” fillet weld generally desirable over PJP welds.
3.
> 3/8” fillet welds require multipasses, so GMC starts
reviewing as to whether a PJP or CJP may be more
cost effective than the fillet weld.
4.
Suggest reviewing fillet welds > 3/8” w/ fabricator as to
cost effectiveness.
39
CJP vs PJP vs Fillet
1. CJP (vs PJP or Fillet)
–
–
–
–
Requires beveling.
Either requires backup bar & runnoff tabs, or back
gouging (fitup is costly).
UT inspection is costly.
Again, this requires additional labor and process
over fillet welding.
2. Again, GMC starts to consider PJP or CJP
welding when fillet welds are > 3/8”.
40
SLRS Members, DC Welds,
Charpy Electrode, and Preheat
1. SLRS Members
–
Clearly define which members are SLRS (show on plans,
frame elevations, and column schedule).
2. DC Welds
–
Clearly show DC in weld tails in design details to signify DC
welds.
3. Charpy Electrode
–
–
Avoid specing Charpy rated electrodes at all welds.
Charpy rated electrodes should only be needed at SLRS
members and DC welds.
4. Preheat, Interpass Temperature, Postheat Treatment
–
–
Avoid calling out preheat or interpass temperature above and
beyond typical AWS. Very costly to preheat.
Postheat treatment is not practical.
41
Charpy vs Non-Charpy Electrode
42
Preheat
43
Preheat
44
Bolted vs Welded Connections
• Oftentimes, a field bolted connection is desirable
over a field welded connection.
– Expedites erection considerably.
– Reduces inspection.
– Less skill required to install bolts.
– Improves safety.
45
Expedited Erection!
46
Expedited Erection!
47
Expedited Erection!
48
Bolted vs Field Welded Connection
49
Dimensional Concerns (Location of
Framing)
1.
Lack of dimensional information on Structural Drawings is costly
to Fabricators.
2.
When GMC has to release partial packages into production due to
missing dimensions, efficiency dramatically drops.
-
3.
Dbl handling of material due to beam multed in on mill stick
Can’t stage, fit, weld out all beams on floor at one time (must stage
twice)
Lost efficiency in loss of numbers.
Increased time needed for fabrication, requiring lost efficiency in
expediting work.
Disruption to flow of production of multiple projects through plants.
For example, releasing a 1,700 ton project for fabrication w/ 25%
beams on hold may cost over $100 k in lost efficiency.
50
Staged Floor
51
Methods to Communicate
Dimensions
1. Ideally, present dimensions to CL of all beams.
2. Alternatively, utilize EOS Drawings. Then,
spec standard set back from EOS to centerline
of WF or HSS members, and face of C or L at
openings and perimeter steel.
3. Make clear orientation of C or L (toe in relative
to edge of slab opening).
52
Reinforcement of Sections vs
Heavier Sections
1. Elimination of Continuity PLs –
–
–
–
May not be feasible if testing of SLRS system was done with
continuity plates.
Eight 1 ½” continuity PLs might cost $3,588.
Increasing W14x211 to W14x257 (45ft) might cost around $1,604.
Elimination of Doubler PLs –
2.
–
–
Two 7/8” x 24” long doubler PLs might cost around $974.
Increase W14x211 to W24x257 (45ft) might cost around $1,604.
3. Offshore A913 Gr 65 Steel vs Plated Columns or Cruciform
Columns –
–
–
A913 is around $.75/# and poses risk. (Domestic A992 is around
$.62/#).
However, it is likely more cost effective than plating columns or
constructing cruciform columns.
53
Considerations for Standard
Design Details
1. Show min/max dimensions (instead of fixed dimensions) at beam connection
details.
–
Allows fabricator to detail in FB widths.
–
Allows fabricator to standardize parts.
2. Edge Distance –
–
Avoid showing, unless edge distance > AISC min is req’d (fabricator must
use AISC edge distance regardless).
–
Allows fabricator maximum flexibility to utilize FB and standardize parts.
3. Beam End Clearance –
–
Design at least ¾” clearance from end of beam to face of connecting
surface.
–
Anything smaller requires control of weld size and cutting mill cut ends.
–
Avoid showing.
4. Shop vs Field Weld Symbols –
–
Avoid showing field vs shop symbol at welds on design.
–
Gives fabricator/erector maximum flexibility to do what is most
economical and safe.
54
Example of Ideal Detail
3" m ax
3 ",
ty p
A IS C m in .
55
Paint and Galvanizing
Considerations
Prime painting a beam w/ std primer, SP-2 preparation may increase cost of that member
by 10% (example: $179 out of $1,992 for W24x55 x 25’ long girder).
Galvanizing or Blast & Painting a member may increase cost of that member by 30%
(example: $567 out of $2,380 for W24x55 x 25’ long girder).
So, minimize cost by:
•
Spec no primer at steel enclosed in finish.
•
Specify SP-2 or SP-3 (hand or hand tool cleaning) prep and primer for interior
exposed to view conditions.
•
Only specify SP-6 (sand blasting) zinc rich primers for steel exposed to weather.
•
Galvanizing is often desirable over SP-6 zinc rich primer.
•
Avoid priming over top of galvanized steel.
56
AISC Regarding Priming Steel
Enclosed in Finish
1. Steel Construction Manual, 13th Ed, pg 2-31
states:
–
“Corrosion Protection – In building structures,
corrosion protection is not required for steel that will
be enclosed by building finish… When enclosed,
the steel is trapped in a controlled environment and
the products required for corrosion are quickly
exhausted…”
2. Priming of member might increase it’s labor by
$90, or increasing labor for that member by 20
to 90%.
57
Galvanizing Considerations
1.
Fabricator will need to vent. Do not design venting, as
it will vary between fabricators and design details.
2.
Avoid thin wall materials (< ¼” in most conditions; a
larger wall may be desirable in some situations).
3.
Avoid unsymmetrical sections.
4.
End caps can be omitted at open ends of horizontals.
58
Vent Holes
59
Warpage from Galvanizing
60
AESS Considerations
Grinding of welds at AESS member may increase cost of
that member by 30 to 50%.
Removal of backup bars and filling of weld access holes
can further increase cost as well.
•
AESS does not require grinding of welds. We
generally make welds uniform and remove weld
spatter, but do not grind smooth.
•
Do not specify to grind welds.
•
Desirable to leave Backup bars and weld access holes
in place (not practical to fill WAHs)
61
BIM
62
BIM Considerations
1. There is likely not significant savings in providing model to fabricator:
–
–
–
Engineer rarely has work points set exactly, or members located in exact location.
Detailer must check model.
There are attributes and connections Detailer must incorporate into the fabrication model.
2. It is likely more cost effective for Detailer to create model from scratch due to above.
3.
If Engineer provides model, do not connect.
–
–
Fabricators have their own connection macros that are unique to their operations.
Fabricator will follow connection details shown on S-dwgs.
4.
Once model is handed off to Fabricator, Detailer cannot easily incorporate another
model at a later date. Wait till LRM to push Fabricator to model building.
5.
Utilization of Revit Model –
–
–
–
Revit model can be imported into Tekla so as to start a model.
Again, Detailer must check model, so there is not a significant advantage in doing this
(over simply creating model from scratch).
Also, there are attributes that Detailer will need to add to members that are unique to
fabricator. Such attributes must be added to imported members.
63
LEED
1.
Recycled content of
steel for project on
right is 30%.
2.
This is reflective of
projects in general.
3.
Avoid requiring an
exact recycled
content in project
specifications, as
fabricator has very
little control in the
recycled content in
steel (requiring a
specific range is
almost useless).
64
OSHPD and DSA Concerns
1. Develop relationship with OSHPD District
Engineer.
2. Fabricator will need OSHPD approved
(stamped) S-dwgs prior to fabricating.
3. Clear documents and specifications help
reduce confusion / issues arising from
OSHPD IOR.
65
Beam Camber
Cost to mechanically camber a beam may increase cost of that member by 3%
(example: $55 out of $1,868 for W24x55 x 25’ – 0).
Cost to flame camber a beam may increase cost of that member by 18%
(example: $328 versus $2,141 for W24x55x25’ – 0).
So:
•
Ability to mechanically camber is a function of camber, section, length.
•
Avoid excessive cambers.
For example, GMC can install up to ¾” camber in W24x55 up to 27’ – 6
length.
GMC can install up to 1 ½” camber in W24xt55 from 27’ – 6 to 37’ – 6
length.
GMC can install up to 2” camber in W24x55 from 37’ – 6 to 40’ – 6
length.
3.
Check with Fabricator when designing large cambers.
66