HOW TO
ESTIMATE the COST O F
S T R U C T U R A L
S T E E L
ROBERT R. BONENFANT, JR. - JULY 2008
CONTENTS 1.
INTRODUCTION Main CSI Division Specifc Sub-Division/Specifcation Section Brief Description of Structural Steel
2.
TYPES AND METHODS OF MEASUREMENT Steel Beam Sections and Dimensions
3.
7. 8. 9. 10.
RATIOS AND ANALYSIS MISCELLANEOUS MISCELLANEO US AND PERTINENT INFORMATION GLOSSARY REFERENCES
FACTORS THAT MAY AFFECT TAKE-OFF, PRICING, ETC . Large Quantities Versus Small – Economies of Scale Union Labor Versus Non-Union Labor Geographical Location Supply and Demand of Steel Height of Building Site Conditions Experience of Erection Crew Renovation Project Versus New Construction Connection Details Moment Connections Beam Penetrations
4. 5. 6.
OVERVIEW OF LABOR, EQUIPMENT, INDIRECT COSTS AND MARK-UPS SAMPLE TAKE-OFF AND PRICING SHEETS SPECIAL RISK CONSIDERATION CONSIDERATIONS S Material Pricing Escalation Surcharges Fuel Costs Value of the Dollar Lead Times
Estimating Today • January 09 15
1. INTRODUCTION
2. TYPES AND METHODS OF MEASUREMENT
The purpose of this technical paper is to provide a basic understanding of how to prepare an estimate for structural steel beams and columns. This paper will focus on how to do
In the construction of structural steel building some basic design criteria needs to be developed. One is the column spacing and an-
a quantity survey of steel members, bent plate (po ur stops), shear studs, connections, steel oor and roof decking, and
and beams to carry the building loads. A 30’ by 30’ column bay is
price accordingly. The paper will not address AESS, diagonally braced frames, open web steel joists, trusses, steel tube, steel stairs, grating and other miscellaneous components that may be part of a building system. In addition,
ancillary trades such as cementitious spray-reproong and intumescent reproong will not be considered in this technical paper. The intent of the paper is to isolate on a few key aspects of a structural steel framed building and
not all possible components. Please note that CSI’s 2004 MasterFormat edition has been used.
other is the oor-to-oor height. This leads to the sizing of columns typical and a 12’ deck height is typical in an ofce building. A 14’ deck height is normal in a laboratory building due to signicant HVAC requirements that need to be placed in the plenum space above ceilings. Structural steel beams and columns are designed on the basis of their yield stress. The most common design stress is 36 KSI and referenced by ASTM designation A36. Structural steel
is fabricated in many sections such as wide ange (W), American standard beam (S), miscellaneous beams (M), American standard channel (C), miscellaneous channel (MC), angle (L), and structural tees (T). A beam and column is designated in the following way; W18x35. The W references the section shape; 18 references the nominal height of the beam/column ange in inches; and 35 ref erences the weight of the beam in pounds per linear foot of beam
Main CSI Divisions Division 05 Metals Subdivisions - 050000 Metals 050100 Maintenance of Metals 050500 Common Work Results of Metals 050600 Schedules for Metals 050800 Commissioning of Metals 051000 Structural Metal Framing 051200 Structural Steel Framing 053000 Metal Decking 053100 Steel Decking
BRIEF DESCRIPTION A steel framed building is an alternative to a concrete framed building. The steel framed building is equally a good choice as a concrete framed building. They each have distinct
building materials, practices and benets that have to be carefully weighed, as timing and situation will dictate the best choice. However, steel is a material that has the highest strength-to-weight ratio and is very ductile. Steel is also shop fabricated and therefore has a higher quality control as it’s produced in a controlled environment. Steel beams and steel columns are used to structurally frame a building so that it supports the exterior façade, roof, interior construction, mechanical and electrical systems of the building and of course the personnel, furnishings and equipment that will occupy the building. The structural steel framed build-
ing also includes components such as steel oor decking, steel roof decking, steel joists, bolted connections, welded connections, base plates, slab pour stops, braced framing, moment connections, and other miscellaneous cold-formed metals to complete the steel framing system. Again, for the purposes of this paper I will only focus on a few of these components.
16 January 09 • Estimating Today
or column length. This description is interpreted as a wide ange beam with a nominal depth of 18 inches and a weight of 35 pounds per linear foot.
The standard unit of measurement for steel beams and columns is tons. The formula for calculating tons of steel will be: Wt. (Tons) = (L x Wt.) / 2,000 L = Length of Beam of Column Wt. = Unit Weight of Beam or Column in Pounds 2,000 = Conversion Factor from Pounds to Tons The unit measurement for oor and roof deck is square feet (SF). Area (SF) = (L x W) x 1.15 L = Length of Building in Feet W = Width of Building in Feet 1.10 = Excess Factor for Seams (10%) The unit measurement for pour stop is Tons. Wt. (tons) = (P x Wt.) / 2,000 P = (L + W) x 2 if rectangular or square building and measured perimeter (P) if irregular shaped L = Length of Building in Feet W = Width of Building in Feet Wt. = Unit Weight of Beam or Column in Pounds 2,000 = Conversion Factor from Pounds to Tons The unit measure of shear studs is Each. Shear Studs (Each) = Quantity Count from Structural Steel Drawings x 1.05 1.05 = Excess Factor for Defective or Broken Studs (5%)
Structural steel drawings will be provided that shows plan views, column schedules, and connection details. The plan drawings will show beam lengths and sizes with shear stud counts and cambering and the column schedules will show column heights and sizes. Detail drawings will also show items such as beam penetrations, moment connections, base plates, deck opening framing, HVAC support framing, and other special framing conditions. The following charts will show some typical steel sections, specifcations, dimensions and welding symbols.
(Diagrams Cont. page 18)
Estimating Today • January 09 17
18 January 09 • Estimating Today
SUPPLY AND DEMAND OF STEEL Currently the strong global demand of steel; particularly in China, India and Russia is driving up the cost of steel. Even though steel mills have become more efcient and there are additional mills coming online demand is outstripping supply leading to higher prices. Foreign mills are also not exporting to the U.S. as they once did.
HEIGHT OF BUILDING The height of the building will dictate the type of crane to be used on the project. Smaller projects may be able to use a mobile wheel-mounted or track-crawler crane. Tall buildings will need a tower crane that will require concrete pad foundations and electrical power requirements.
SITE CONDITIONS The site conditions and constraints will also dictate the type crane that will be utilized. Tight sites in city areas will need tower cranes versus the ability to use mobile cranes in open sites assuming heights aren’t an issue.
EXPERIENCE OF ERECTION CREW The experience of the erection crew can affect the number of picks they make in day. The less experienced the crew the longer the erection duration will be resulting in higher erection costs.
3. FACTORS THAT MAY EFFECT TAKE-OFF AND PRICING
EFFECT OF SMALL QUANTITIES VERSUS LARGE QUANTITIES; ECONOMIES OF SCALE If the project is small and there’s a minimal amount of tonnage the unit cost will be higher than a project with a signicant amount of tonnage. The mobilization and crane costs that need to get absorbed into the small project with less efciency in production will make for a higher unit cost than on a large project.
UNION VERSUS NON-UNION If the project is based on union labor the project will have a higher cost than non-union labor. Unions negotiate higher wage rate and benet packages than would be provided by open-shop contractors.
RENOVATION PROJECT VERSUS NEW CONSTRUCTION Sometimes an existing building has to be structurally reinforced. The unit cost of structural steel will be higher on a renovation project than on a new building. On a renovation project the steel has to be fabricated in smaller sections to access the existing building and scissor lifts and other small hydraulic lift equipment has to be utilized in order to position the steel in place. The production rate is much slower working in an existing building, as you will be utilizing lighter equipment and probably using some handwork.
CONNECTION DETAILS A project that utilizes welded connections takes longer to erect than with bolted connections. In addition, the eldtesting of welded connections will also add time to the schedule. Curtainwall support connections will add to the cost as well as precast panel connections. Therefore, it’s important to know what the façade of the building will be so connection detail costs can be accounted for.
MOMENT CONNECTIONS GEOGRAPHICAL LOCATION The location of the project may have an inuence on cost due to regional material, labor, and equipment costs based on availability of resources and manpower. R.S. Means uses a coefcient factor to adjust for regional differences.
Moment connections carry a premium cost to be installed, as they’re a special condition connection to make a rigid or semi-rigid connection between a column and a beam. They’re more labor intensive to install so the result is slower production leading to increased erection costs.
Estimating Today • January 09 19
BEAM PENETRATIONS
EQUIPMENT
Beam penetrations are cutouts made in the steel beams so that mechanical piping and ductwork can pass through. There will be unreinforced and reinforced beam penetrations depending on the size of the opening. Sometimes the architectural, structural, and mechanical drawings are coordinated enough to allow the Engineer to show on the plans where a portion of these beam penetrations may occur. The beam penetrations shown on the plans that can be fabricated in the shop will have a much lower cost than the beam
The equipment utilized will be mobile cranes or tower cranes. Tower cranes will be predominantly utilized on high buildings in tight city quarters.
penetrations that will have to be provided for in the eld. There will inevitably be beam penetrations that will need
to be cutout and reinforced in the eld at a higher unit cost.
4. OVERVIEW OF LABOR, MATERIAL, EQUIPMENT AND INDIRECT COSTS
The following example is intended to demonstrate a simple take-off and pricing method for a structural steel frame system including beams, columns, decking, shear studs, bent
plate (pour stop), and connections. With today’s technology many companies perform takeoff using OST and digitizers. OST allows you to take-off quantities on your computer screen while color coding the
element you’re taking off and recording up to three (3) units of measure for that element at the same time. However, for the purposes of this paper I will complete the take-off and pricing sheets on Excel to demonstrate the method being used.
MATERIAL Take-off the lengths of each different size beam and column. Next I’ll multiply the length of each beam and column by its respective weight. From the sum of all these beams and columns I’ll then calculate the total tonnage. The shear studs will be counted for each beam and a total tallied. The perimeter of the oor plates will be calcu -
lated in order to gure the length of pour stop. The area of the oors will be calculated to determine the deck ing quantity. And lastly, the connections will be gured by calculating percentages of the total steel tonnage.
LABOR Since the steel is fabricated in the shop the labor portion refers to the erection crew. Generally, it’s assumed
that for erection a crane can pick between 35 and 60 pieces a day. Assuming the average is 45 picks per day, and using common sizes of beams and columns that would probably equate to around 30 tons erected per day.
20 January 09 • Estimating Today
INDIRECT COSTS Tower cranes also require concrete pad foundations to be set on and also require electrical power service. Safety costs for perimeter cabling needs to be considered along with other temporary construction costs to provide a secure and safe working environment. Other indirect costs to consider are sales tax, payment and performance bonds and liability insurance.
Bent Plate Take-Off
Office Building Parameters
Assume 6"x6" x7/16" bent plate at 18 pounds per linear foot (plf). Structure
Floor
SOG SOMD SOMD SOMD
1st Floor 2nd Floor 3rd Floor 4th Floor
L Length (lf)
W Width (lf)
90 90 90 90
P A Perimeter (lf) Area (sf)
90 90 90 90
360 360 360 360
Total Interior Building SF: SOMD
Floor
90
90
360
360 360 360 360
Uni t W t.
LF LF LF LF
Un
18.00 18.00 18.00 18.00
Tota l W t.
PLF PLF PLF PLF
6,480 6,480 6,480 6,480
Total Weight:
32,400
Roof
Perim ete r Un
2nd Floor SOMD 3rd Floor SOMD 4th Floor SOMD Roof SOMD
8,100 8,100 8,100 8,100
Un
Tota l W t.
LB LB LB LB
Un
3.24 3.24 3.24 3.24
25,920 LB
TN TN TN TN
12.96 TN
8,100 Structural Steel Connections Take-Off
S ub to ta l o f S te e l T on na ge Steel Tonnage
Steel Columns Take-Off
# of Col. Size
2nd Floor 3rd Floor 4th Floor Roof
16 16 16 16
Max. %
2.00% 4.00% 4. 00%
Min. W t.
3.00% 5.00% 5. 00%
Un Max. Wt. Un
3.20 TN 6.40 TN 6. 40 TN
Total Weight:
Floor-to-Floor Height is 12'0"
Floor
Min. %
Base Plates Column Splices Mi sc ellaneous Det ail s
1 60. 07 T N
Unit Wt. (plf) Height (vf) Len (lf)
W14x82 W14x61 W14x61 W14x53
82 61 61 53
12 12 12 12
192 192 192 192
Total Weight:
Total Wt. 15,744 11,712 11,712 10,176
Un
Total Wt. Un
LB LB LB LB
7.87 5.86 5.86 5.09
49,344 LB
20.81 TN
41,618 LB
L Length (lf)
Floor 2nd Floor 3rd Floor 4th Floor
W Width (lf)
90.00 90.00 90.00
A Area (sf)
90.00 90.00 90.00
Waste (10%)
8,100 8,100 8,100
Total SF
810 810 810
8,910 8,910 8,910
Total Steel Floor Deck:
26,730 SF
Roof
90.00
90.00
8,100
810
8,910
Total Steel Roof Deck:
8,910 SF
Total Steel Decking:
Steel Beam s Take-Off
Un
9,604 LB 16,007 LB 16, 007 LB
Steel Deck
TN TN TN TN
24.67 TN
Total Wt.
4.80 TN 8.00 TN 8. 00 TN
35,640 SF
Typical for 2nd floor t hrough the r oof (4 levels) 4- StoryO ffice Building Estimate (32,400GSF)
2nd floor Qty
Size
Le ngth
Unit Wt.
GSF
Tota l Wt. (lbs.) Tota l Wt. (tns.)
8
W24x55
30
55
13,200
6.60
Item
4 8
W36x135 W21x44
30 30
135 44
16,200 10,560
8.10 5.28
8 22
W8x10 W16x31
10 30
10 31
800 20,460
0.40 10.23
1. 2. 3. 4. 5. 6.
61,220
30.61
Description St ruc tur al S teel B eam s & Colum ns Bent Plate at Pour Stops Connection Steel Shear Studs - 3/4"x5" Steel Floor Deck - 3"x18 Gauge Steel Roof Deck - 3"x20 Gauge
Qty 147. 11 12.96 20.81 5,124 26,730 8,910
Un
Mat Un Pr
Mat Total
Lab Un Pr
Lab Tot
Equip Un Pr Equip Total Total Cost
t ons t ons tons each sf sf
$ $ $ $ $ $
$ $ $ $ $ $
323,642 28,512 69,714 13,732 58,271 17,909
$ 900.00 $ 1,100.00 $ 1,650.00 $ 1.32 $ 1.07 $ 0.99
$ $ $ $ $ $
132,399 14,256 34,337 6,764 28,601 8,821
$ $ $ $ $ $
$
511,780
$
225,177
Direct ConstructionCost
Subtota l We ight:
Overhead & Profit
32,400
20.00%
Total Construction Cost
2, 200. 00 2,200.00 3,350.00 2.68 2.18 2.01
200.00 -
$/SF
$ 29,422.00 $ $ $ $ $ -
$ $ $ $ $ $
485,463 42,768 104,050 20,496 86,873 26,730
$ $ $ $ $ $
14.98 1.32 3.21 0.63 2.68 0.83
$
$
766,380
$
23.65
$
153,276
$
4.73
$
919,655 $
28.38
29,422
3rd flo or Qty
Size
Le ngth
Unit Wt.
Tota l Wt. (lbs.) Tota l Wt. (tns.)
8 4
W24x55 W36x135
30 30
55 135
13,200 16,200
6.60 8.10
8 8
W21x44 W8x10
30 10
44 10
10,560 800
5.28 0.40
22
W16x31
30
31
20,460
10.23
61,220
30.61
Subtota l We ight:
5.
4th floor Qty
Size
Le ngth
Unit Wt.
Tota l Wt. (lbs.) Tota l Wt. (tns.)
8
W24x55
30
55
13,200
6.60
4 8
W36x135 W21x44
30 30
135 44
16,200 10,560
8.10 5.28
8 22
W8x10 W16x31
10 30
10 31
800 20,460
0.40 10.23
61,220
30.61
Subtota l We ight: Roof Qty
Size
Unit Wt.
Tota l Wt. (lbs.) Tota l Wt. (tns.)
8 4
W24x55 W36x135
30 30
55 135
13,200 16,200
6.60 8.10
8 8
W21x44 W8x10
30 10
44 10
10,560 800
5.28 0.40
22
W16x31
30
31
20,460
10.23
61,220
30.61
244,880
122.44
Subtota l We ight: Tota l We ight:
Le ngth
SPECIAL RISK CONSIDERATIONS
When estimating the cost of structural steel there is signi cant risk to mitigate. These risk items include the following:
MATERIAL COST The cost of structural steel is increasing, as there’s a huge global appetite for steel currently underway. Contributing to this escalation is also the fact that steelmakers are paying large premiums for raw materials from mining companies and passing this cost onto the consumer. Raw material costs have recently contributed to 50% of the steel cost where a short time ago they traditionally accounted for roughly 15% of the steel material cost. Steelmakers are now trying to acquire mines to provide raw materials for their own companies in order to be more self-sufcient.
Estimating Today • January 09 21
ESCALATION Escalation is a signicant cost factor when putting a steel bid together. Your project may not require the steel to be on-site for many months to a year, if not longer. Many steel contractors will not even try to guess what steel prices may be at that time because of price volatility. In order to level
the playing eld for the steel contractors during a bid you may have to forecast as best you can the projected future steel cost and carry an escalation allowance. This strategy should be discussed should be discussed with the Owner.
SURCHARGES Surcharges are added to the steel material costs because the material cost is volatile and it gives the steel supplier
more exibility to lower and raise his price. This practice eliminates the need to constantly adjust a xed price so that you can appear to remain competitive.
FUEL/ENERGY COSTS The cost of a barrel of oil is hovering around $140/barrel and the average cost of gasoline in the U.S. right now is
about $4.00/gallon. Fuel and energy costs are making steel more expensive to produce and ship steel.
VALUE OF THE DOLLAR The value of U.S. dollar has been declining steadily for several years now and is playing a large part in the high cost of exported steel to the U.S. Steel is exported at a higher cost to the U.S. because of the weak dollar. And many foreign companies buying U.S. steelmakers are exporting to their own country because of strong demand instead of selling to the U.S. Therefore, we’re left still paying higher prices because many U.S. steel companies are foreign owned.
LEAD TIME OF MATERIAL If the steel sections required for your project are not in stock then it becomes more critical to get your shop drawings approved in a timely manner to secure a place on the mill fabrication schedule. Depending on how many rolling jobs are ahead of you this lead-time will have to be taken into consideration relative to your construction schedule.
6.
RATIOS AND ANALYSIS
will take the total steel tonnage and divide by the total
building square footage (assuming the ground is a slab-ongrade) and expect to get a unit weight of between 11 psf and 15 psf. If my tonnage is not in this range I will investigate further to determine why the structure is seemingly light or heavy. Having a structure with inadequate steel strength is one issue and having a structure with excessive weight may
be inefciency in beam usage leading to an unnecessarily higher cost. In regards to shear studs I would also divide the total building square footage by the total quantity of shear studs and expect this number to be in the range of 6-8 sf per stud
(or 0.13 – 0.17 studs per sf). If not, I’ll make adjustments to make sure that I carry enough shear studs in the estimate. The following logic chart below is a sample calculation used to check the validity of the estimate. I have shown how to complete a logic check on the structural steel beams, columns, bent plate, and connections to see if the unit weight of the structural steel system is in the projected range. I have also shown how to complete a logic check on the shear studs to make sure there are enough for the composite slabon-deck system. I have performed a quick check on the structural steel erection cost to see if it is in-line with my estimate. As you will the erection estimate at $161,821 is close to what I calculated in the estimate at $176,077. This again is a logic check to make sure that the numbers in the estimate are a reasonable cost for the scope of work.
Steel Logic Check
Weight Columns Beams Bent Plate Connections
49,344 244,880 25,920 41,619
Total Weight
361,763 LB
Building (SF)
32,400 SF
Unit Weight (PSF)
LB LB LB LB
11.2 PSF
Okay: The unit weight of steel for the structure falls in the range of 11-15 psf at 11.2 psf. Since this is an office building I would expect it to be closer to 11#. Shea r Stud Logic Check
There are a few ways to analyze whether your bid or esti-
mate is in the “ballpark” and reects whether or not you are providing a reasonable cost. One way is to look at historical data from similar projects and escalate those previous project costs to current day costs. Using past project costs can be a good benchmark to gauge your bid or estimate. Another way is to use conceptual design information that has been acquired through experience with putting together conceptual estimates and/or interaction with struc-
tural engineers. For the ofce building example used, I
22 January 09 • Estimating Today
Shear Studs Building (SF) Square Feet Per Stud
5,124 EA 32,400 SF 6.3 SF
Okay: The quantity of shear studs falls in t he range of one (1) stud per 6-8 sf of floor area. We're at one (1) stud per 6.3 sf of floor area for the structure.
GLOSSARY
Structural Steel Erection Cost
A36 – ASTM Steel Designation AESS – Architecturally Exposed Structural Steel Item
Qty
Steel Columns
Un 48 Each
OST – On-Screen Take-off SOG – Slab on grade
Steel Beams
200 Each
SOMD – Slab on metal deck
Total # of Beams & Columns
248 Each
BIM – Building Information Modeling Moment Connection – A rigid or semi-rigid column to
Total Weight of Beams & Columns Average Weight of Steel Member
147.11 Tons 0.59 Tons
If Pick 30 Tons Per Day Production =
51 Pieces
beam connection
Shear Stud – A metal stud welded to the top of a beam in a composite slab on deck
Intumescent – Referring to re retardant paint on Duration of Steel Erection Crew Unit Cost ($/Ton)
5 Days $
1,100.00
architecturally exposed steel Camber –
An arch fabricated in the beam so that
designed loads acting on the beam limit the deection of Crew Daily Cost (30 Tons Per Day)
$
33,000
Total Steel Erection Cost
$
161,821
Check Cost From Estimate
$
176,077
the beam. The intent is to have a level oor.
REFERENCES Means Estimating Handbook AISC Manual of Steel Construction
7. MISCELLANEOUS PERTINENT INFORMATION Recently, in order to evaluate the construction sequencing of erecting structural steel BIM modeling has been utilized. BIM stands for Building Information Modeling and is used to create a computer model of the building from the design drawings. This computer model is capable of detecting dimensional busts as well clashes with other building elements. It also has shown weaknesses in erection sequencing that can lead to a more efcient construction schedule. Another interesting development is the use of barcodes that are placed on the fabricated steel in the shop, scanned when shipped, scanned when delivered to the site, and scanned when erected in place. This real-time scanning process allows the BIM model to show the Construction Manager and Client when the steel has been fabricated, shipped, delivered to the site and erected. The computer model then displays that actual to-date work put in place showing a time sequence.
Estimating Today • January 09 23
