estimate the reinforcement in shallow foundation

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Reinforcing Steel in Shallow Foundations

Technical Paper

ESTIMATE THE COST OF

submitted by Jonathan A. Rogers, CPE

What successful Cost Estimators know. . . . and you should, too.

AN ESTIMATOR’S GUIDE TO POLICIES, PROCEDURES, AND STRATEGIES

>>>>>>>>>>>>>>>>>>

After graduating from Georgia Tech’s school of Architecture in 1993, Jonathan A. (Andy) Rogers started his career in single family home construction and remodeling. In 1996 his career path led him to preconstruction, where he worked as a consultant to single and multi-family developers providing design, cost estimating, and purchasing systems set-up and management services. In 1999, a geographic move prompted a career change into strictly commercial construction. Since that time, Andy has developed and utilized his experience predominantly in commercial multi-family and institutional projects.Andy Rogers, CPE works as a Preconstruction Services Manager for Hardin Construction Company, LLC in Atlanta, Georgia.

1) Introduction

2) Types and Methods of Measurements

3) Overview of Labor, Material, Accessory, & Other Costs

4) Ratio & Analysis

5) Specific Factors Affecting Take-off and Pricing

6) Specific Risk Considerations

7) Sample Drawings and Details

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14 Est imating TodayNovember 2010

ESTIMATE THE COST OF: Reinforcing Steel in Shallow Foundations

InTRODuCTIOnThe intent of this technical paper is

to explain the systematic approach to estimating the cost of reinforcing steel in shallow foundations. The desire is to define basic terminology, explain com-mon details, and demonstrate a simpli-fied approach to the take-off of the most common components encountered in shallow foundation design. The reader should therefore be able to apply these principles to more complex systems and adapt them as needed to specific project details, design standards, and environ-mental conditions.

The basis for this paper is the Construction Speci-fication Institute Master Format (2004 Edition).

Division: 03 00 00 ConcreteSubdivision(s): 03 21 00 Reinforcing Steel

For the purpose of limiting the breadth of this article, this paper does not delve into concepts associated with reinforcing in deep foundations, slabs-on-grade, or vertical concrete struc-tures. Rather, it focuses on subgrade foundation components only. Many of the same concepts covered in this paper, however, may be employed in developing quantitative analysis of mild reinforcing in other concrete structures. Additionally, this article assumes that the estimator has access to 90-95% complete construction documents with necessary details, schedules, and specifi-cations included. This paper, therefore, focuses on final or contract estimating.

TYPES AnD METHODS OF MEASuREMEnT

Terminology

Footing and foundation schedules and details utilize a common set of abbrevia-tions and terms. Familiarity with these is vital to understanding the placement, quantity, and length of various members in the reinforcing design. Some of the most common abbreviations used are listed below.

Common terms used in referring to shallow foundation reinforcing are:

Coverage: the distance between the outer-most piece of reinforcing steel and the outside face of concrete which protects resteel from coming in contact with the elements. For this article, 3” minimum coverage has been used throughout.

Dowel: short length of reinforcing steel left extended from the face of a concrete pour in order to tie additional reinforcing and second-ary pours together.

Lap length: the minimum distance two rein-forcing bars must overlap to create a lap splice

Longitudinal bar: reinforcing bar which runs the length of a footing or wall

Mat: a single layer of reinforcing steel com-bining longitudinal and transverse bars

Net length: the length of a reinforcing bar determined by deducting minimum coverage(s) from a footing, pier, or wall dimension

Rebar, Resteel: terms used interchangeably for reinforcing steel

Splice: any of three meth-ods (lap splice, mechanical splice, or welded splice) used to join two pieces of reinforcing steel to create a single line of reinforcing

Tie: method of joining two pieces of rein-forcing steel using plastic ties, steel wire, smaller reinforcing bars or other means to create and secure lap splices, cages, and dowels prior to placing concrete.

Transverse Bar: reinforcing bar which runs the width of a footing or wall, generally perpendicular to the longitudinal bars.

Straight length: the total length of a fabri-cated (bent) piece or reinforcing steel.

Other terminology and abbreviations may be encountered specific to the geographic region or the project and/or the design firm responsible for the contract documents.

units of Measure

Reinforcing steel is most typically estimated by weight and imperially in pounds which are commonly con-verted to tons. For contractors who self-perform fabrication of reinforcing steel, these weights may be further converted to pieces for the purposes of quantifying and ordering straight reinforcing bars. Reinforcing steel in shallow foundations is most com-monly specified as Grade 40 (metric Grade 280), Grade 60 (metric Grade 420), or Grade 75 (metric Grade 520), deformed bars and available in 20-foot and 60-foot lengths with weights per linear foot as listed in Table 2.1.

Additionally, because the weight of reinforcing steel is related directly to the number of fabricated parts, calcu-lations which result in fractional parts (i.e. decimal places) are commonly rounded either up or down to the whole piece to provide more accurate resulting total weight. For the pur-

BTTM: Bottom

CONT: Continuous

EA: Each

EE: Each end

EF: Each face

ES: Each side

EW: Each way

FOC: Face of Concrete

F.F.E.: Finished Floor Elevation

FS: Footing step

HORIZ: Horizontal

LLH: Long leg horizontal

LLV: Long leg vertical

LW: Long way

OC: On Center

SW: Short way

T&B: Top and bottom

TF / T.O.F.: Top of Footing

TP / T.O.P.: Top of Pier

VERT: Vertical

Table 2.1

Common Reinforcing Bar Sizes

Bar

Designation

Nominal

Diameter (inches)

Weight

(lbs/lnft)

#3 0.375 0.376

#4 0.500 0.668

#5 0.625 1.043

#6 0.750 1.502

#7 0.875 2.044

#8 1.000 2.670

#9 1.128 3.400

#10 1.270 4.303

#11 1.410 5.313

#14 1.693 7.650

#18 2.257 13.600



pose of this paper, where values have been rounded, the symbols “=↑” shall represent “equals value rounded-up” and “=↓” shall represent “equals value rounded-down”.

Quantity Survey

Upon receipt of construction docu-ments, the estimator’s first responsibil-ity is to survey the documents, become familiar with the project details, and develop an outline of the primary components of the shallow foundation design. The most common of those components are:

1) spread footings2) strip footings3) piers4) foundation walls

Once a basic outline of the compo-nents is generated, take-off for each component can be done utilizing the formulas demonstrated in the ex-amples below. These formulas may be completed manually, calculated using common spreadsheet software, or programmed into more complex estimating software where assemblies may be used to quantify reinforcing steel as part of a complete foundation concrete package.

Prior to discussing the take-off for each foundation component, it is im-portant to address waste. If reinforcing steel members are fabricated off-site, some allowance may be given to order-ing extra pieces and/or straight bars to allow for culling of materials and for errors in installation which would

otherwise delay the installation. Ad-ditionally, waste may be considered for reinforcing bar supports, bends, hooks, splices, overlaps and other such bar specific details as might be required for the proper fabrication and installation of the reinforcing steel. For contrac-tors who self-fabricate reinforcing steel, waste factors will vary greatly depending on the specific design, ordered material lengths, and resulting off-cuts. Ad-ditionally culled waste may be used by the self-fabricator to offset some waste. For the purposes of this paper, we will assume all reinforcing bars are shipped, pre-fabricated, allowing for a 5% waste/cull factor which includes the aforemen-tioned bar specific details.

1) SPREAD FOOTINGS

Spread footings, also called column and/or pier footings, should be counted by type. Information regarding reinforcing members for each footing type is shown in a footing schedule (see Table 2.2).

For purposes of demonstration, we will utilize this sample footing schedule and the partial foundation plan shown in the appendix, Figure 1.

Two types of spread footings are examined, starting with spread footing type F4. Reinforcing bars are noted as 9-#5 E.W. (9 each, #5 bars, each way). Referring to Figure 2, the typical spread footing detail, the net length of the lon-gitudinal reinforcing bars in footing F4 is calculated:

(footing length) – (minimum coverage(s)) =net length of longitudinal bars

7.0’ - (3” + 3”) = 6.5’

The weight of longi-tudinal bars in footing F4 is then calculated:

(net length) x (number of bars) x (weight per linear

foot)

6.5’ x 9 bars x 1.043 lbs/lnft =↓ 61 lbs

The weight of trans-verse bars is calculated in the same manor. For this example, the length and weight of

longitudinal bars and transverse bars is the same.

(net length) x (number of bars) x (weight per linear foot)

(7.0’ – (3” + 3”)) x 9 bars x 1.043 lbs/lnft =↓ 61 lbs

The sample foundation plan indicates there are 3-each, F4 footings. The result-ing total weight of reinforcing steel for footings type F4 is calculated:

((weight of longitudinal bars) + (weight of trans-verse bars)) x (number of footings)

(61 lbs + 61 lbs) x 3 each = 366 lbs

For the second example, consider footing type F8. The same principles are used in calculating the weight of reinforcing steel for this footing. Foot-ing type F8, however, has no indicated length on the footing schedule. Instead the estimator must reference the foun-dation plan to determine the length of footing(s) F8. In this case the length for the one footing type F8 is 57’-0”. Longi-tudinal reinforcing is noted as “LW: 7-#6 T&B” (long way, 7 each, #6 bars, top and bottom) and calculated:

(net length) x (number of bars @ top + number of bars @ bottom) x (weight per linear foot)

(57.0’ – (3” + 3”)) x (7 bars + 7bars) x 1.502 lbs/lnft =↓ 1,188 lbs

An additional step is required to calculate the weight of transverse bars in footing F8. Transverse bars are indicated as “SW: #6@10” OC T&B” (short way, #6 bars at 10” on center, top and bottom) for the length of the footing. Therefore, the quantity of transverse bars is calculated:

((footing length – (minimum coverages)) / bar spacing) x (number of mats) = quantity of trans-

verse bars

((57.0’ – (3” + 3”)) / 10”) x 2 mats =↑ 136 bars

The resulting bar quantity should be rounded up for both top and bottom mats, thus allowing that the maximum bar spacing be no more than 10” as in-dicated. The weight, then of transverse bars is calculated:


(7.0’ – (3” + 3”)) x 136 bars x 1.502 lbs/lnft =↑ 1,328 lbs

Table 2.2

Sample Footing Schedule

Footing

Mark

Size

Reinforcing

F1 4’-0” x 4’-0” x 12” 5-#5 E.W.

F2 5’-0” x 5’-0” x 12” 6-#5 E.W.

F3 6’-0” x 6’-0” x 18” 8-#5 E.W.

F4 7’-0” x 7’-0” x 18” 9-#5 E.W.

F5 8’-0” x 8’-0” x 18” 8-#6 E.W.

F7 9’-0” x 9’-0” x 24” 10-#6 E.W. T&B

F8 7’-0” x SEE PLAN x 24” LW: 7-#6 T&B

SW: #6@10” O.C. T&B

F9 8’-0”xSEE PLAN x 24” LW: 8-#6 T&B

SW: #6@10” O.C. T&B




The resulting total weight of reinforc-ing steel for the footings type F8, having length 57’0”, is calculated:

((weight of longitudinal bars) + (weight of trans-verse bars)) x (number of footings)

(1,188 lbs + 1,328 lbs) x 1 each = 2,516 lbs

Note that were there more than one footing type F8, then reinforcing steel for each footing length would be calculated separately as the net length of longitu-dinal bars and the quantity of transverse bars would vary.

Finally, refer again to Figure 2. The “L” shaped reinforcing bars, or dowels, in the footing are not taken off as part of the footing reinforcing. Instead, because the bar size and quantity is integrated with the pier design, they are taken-off with the concrete piers (see subsection #3 below).

2) STRIP FOOTINGS

The process for estimating reinforcing steel in strip footings, also known as con-tinuous footings, is very much the same as for spread footings. The primary difference in the take-off of strip foot-ings is in the location of the reinforcing steel design information. Unlike spread footings, strip footings are not generally scheduled. Instead they are referenced by detail.

Referring to the sample foundation plan, a section cut through the foun-dation between columns A1 and A2 references Figure 4. Longitudinal bars are indicated as 6-#5 T & 3-#5 B (6 each, #5 bars at top and 3 each, #5 bars at bot-tom). The estimator must either scale from the foundation plan or add labeled dimensions to determine the footing length (in this case, 47’-0” long between columns A1 and A2 only). The weight of longitudinal reinforcing steel for the strip footing is calculated:

(net length) x ((number of bars @ top) x (weight per linear foot)) + ((number of bars @ bottom) x

(weight per linear foot))

(47.0’ – (0” + 0”)) x ((6 bars x 1.043 lbs/lnft) + (3 bars x 1.043 lbs/lnft)) =↓441 lbs

*note that there are no reductions in the footing length for minimum coverages since this footing is bounded on each end by spread footings, thus

eliminating any exposure of these bars to the elements.

Next we calculated transverse bars which are noted as #6@12” (#6 bars at 12” on center). The quantity of trans-verse bars is calculated:

(net length) / 12” = quantity of transverse bars

47.0’ / 12” = 47 bars

The weight of transverse bars is calculated:


(3.0’ – (3” + 3”)) x 47 bars x 1.502 lbs/lnft =↑ 176 lbs

Finally, we must calculate the foot-ing dowels. Unlike the spread footing dowels which are often estimated as part of the pier reinforcing, strip footing dowels are both a function of the strip footing length (which determines dowel quantity) as well as the foundation wall design (which determines bar size). In some cases, however, the footing dowel may be tied to reinforcing in a CMU wall instead of a concrete wall. For that rea-son, the estimator might be less apt to miss this reinforcing if it is taken off with the strip footing.

To calculate the dimensions of the footing dowels, the estimator must understand lap splices in reinforcing steel. Lap splices are the most common method for attaching two pieces of rein-forcing steel to form a continuous line of rebar. The length of laps varies depend-

ing on concrete strength, rebar size, and spacing. The use of dowels and lap splices minimizes the length of exposed rebar which reduces the risk of damage to the reinforcing steel. Lap splice calcu-lations are based on ACI 318-02. Table 2.3 shows lap splice lengths for common shallow foundation design.

Notes:

1. Values are based on Grade 60 reinforcing bars and normal-weight concrete.

2. Compression development lengths and lap splice lengths are based on ACI 318-02, Sections 12.3 and 12.16.

3. Lengths are in inches.

4. ACI 318-02 does not allow lap splices of #14 [#43] and #18 [#57] bars.

Utilizing the lap splice lengths for #6 reinforcing bars as scheduled above, the vertical dimension of the footing dowel shown in Figure 3 is calculated:

(footing thickness – (minimum coverage(s)at foot-ing) + (minimum coverage(s) at wall) + (lap splice

length)

(18” – 3” + 3”) + 23” = 41” =↑ 3.42’

The horizontal dimension is calculated:

(footing offset + wall thickness) - (minimum coverage(s)at footing) - (minimum coverage(s) at

wall)

(6” + 18”) – 3” – 3” = 18” = 1.5’

Table 2.3

Grade 60 Rebar, ACI Compression Development and Lap Splice Lengths

Compression Development Lengths per f’c

Bar

Designation f’c=3,000psi f’c=4,000psi f’c=5,000psi

Lap Splice Length

#3 9 8 8 12

#4 11 10 9 15

#5 14 12 12 19

#6 17 15 14 23

#7 19 17 16 27

#8 22 19 18 30

#9 25 22 21 34

#10 28 24 23 38

#11 31 27 26 43

#14 37 32 31 n/a

#18 50 43 41 n/a



The weight of each footing dowel is calculated:

((vertical Leg) + (horizontal Leg)) x (weight per linear foot)

(3.42’ + 1.50’) x 1.502 lbs/lnft =↓ 7 lbs

The total weight for footing dowels, is calculated by finding the number of dow-els multiplied by the weight per dowel.

(net length of footing) / (dowel spacing) x (weight per dowel)

(47.0’ / 12”) = 47 dowels x 7 lbs = 329 lbs

Finally, the total weight of reinforcing steel in footing type F8 is calculated:

(weight of longitudinal bars) + (weight of trans-verse bars) + (weight footing dowels bars)

(441 lbs) + (176 lbs) + (329 lbs) = 946 lbs

3) PIERS

Information regarding reinforcing in piers is scheduled in the same way as spread footings, although additional details are often referenced in the pier schedule (see Table 2.4). For each pier type, the top and bottom elevation should be charted individually in order to calculate the height of the pier and thereby the length and weight of the vertical bars and the number of hori-zontal ties (see Table 2.5). This informa-tion may be found on the foundation plan (noted as T.O.F. and T.O.P.) or by referencing section cuts and details (see Figure 4).

For example, refer to the table above and to the sample foundation plan, to follow the procedure for estimating rein-forcing steel for pier P1 at column C3.

Using the same technique as for strip footings, pier dowels must be calcu-lated. The size of the pier dowels in a function of both the pier height and the dimension of the footing below. In circumstances where the pier height is close to or less than the scheduled lap splice length, the vertical reinforcing bar and the dowel may be fabricated as a single piece. For the sake of explain-ing the take-off in more detail, consider the vertical bar and dowel separately in this example. Referring to Figure 5, and

using the information collected in Table 2.5, we calculate the vertical leg of the pier dowel:

(footing depth) - (minimum coverage) + (3”) + (lap splice length)

(18”) – (3”) + (3”) + (23”) = 41” =↑ 3.42’

The length of the horizontal leg of the pier dowel is calculated using a minimum dowel length which is usually specific in the structural notes. This di-mension will vary by design, but for shal-low foundations, a good rule of thumb is 30 times the bar diameter. In this case, for #6 bars, the horizontal dowel length is calculated:

30 x (bar diameter) = minimum dowel length = horizontal leg length

30 x .75” = 22.5” = 1.875’

The total straight bar length of the pier dowel and resulting weight of dowels is calculated:

((vertical leg length) + (horizontal leg length)) x (number of dowels) x (weight per linear foot)

(3.42’ + 1.875’) x (8 bars) x (1.502 lbs/lnft) =↑ 64 lbs

Vertical reinforcing bar length in-cluding the lap splice at pier dowels is calculated:

(pier height) - (minimum coverage(s)) = vertical bar length

(12.0’) – (3” + 3”) = 11.5’

Vertical reinforcing bar weight is calculated:

(vertical bar length) x (number of bars) x (weight per linear foot)

(11.5’) x (8 bars) x 1.502 lbs/lnft =↓138 lbs

Finally, reinforcing ties, or pier ties are calculated. Pier ties are rectangular or square bands of reinforcing steel with hooks or bends at each end to secure them to vertical bars. These hooks can be counted as part of the total length of the reinforcing tie, or may be assumed, as in this case, to be included as part of the established waste factor. The straight bar length for pier ties at pier P1 is a function of the pier perimeter less minimum coverages and is calculated:

(((pier dimension A) – (minimum coverages)) x 2) + (((pier dimension B) – (minimum coverages)) x 2)

(((2.0’) – (3” + 3”)) x 2) + (((2.0’) – (3” + 3”)) x 2) = 6.0’

Next the number of pier ties is calcu-lated. The height of the pier is divided by the tie spacing as noted in the pier schedule. In the case of P1 as shown in Figure 5, the top 9” of the pier is reserved for 3 bands at 3” on center. Therefore the number of standard pier ties is calculated using the equation below.

Table 2.4

Sample Pier Schedule

Reinforcing Footing

Mark

Size Vertical Ties

P1 24” x 24” 8-#6 #3 @ 12” O.C.

P2 24” x 36” 12-#6 #3 @ 12” O.C.

P3 24” x 40” 12-#6 #3 @ 12” O.C.

Table 2.5

Pier Type P1 – By Location

Pier

Type

Pier

Location

Pier

Dim.

A

Pier

Dim.

B

Footing

Type Bottom of

Pier (TF)

Top of

Pier (TP)

Pier

Height

(feet)

P1 B1 2’0” 2’0” F5 82.00 95.50 13.50

P1 C1 2’0” 2’0” F5 82.00 95.50 13.50

P1 C3 2’0” 2’0” F4 84.00 96.00 12.00

P1 D1 2’0” 2’0” F5 82.00 95.50 13.50

P1 D4 2’0” 2’0” F4 86.00 96.00 12.00

P1 E1 2’0” 2’0” F5 82.00 95.50 13.50

P1 E3 2’0” 2’0” F4 86.00 96.00 12.00




((pier height) – (minimum coverage) – 9”) / (band spacing)

((12.0’) – (3”) – ( 9”)) / 12” = 11 bands

The weight of pier reinforcing ties is calculated:

((number of pier ties) + (number of ties in top 9” inches)) x (pier tie length) x (weight per linear feet)

((11 bands) + (3 bands)) x 6.0’ x .376 lbs/lnft =↑ 32 lbs

Finally, the total weight of reinforcing steel in pier P1 at column C3 is calculated:

(weight of pier dowels) + (weight of vertical bars) + (weight of horizontal pier ties)

(64 lbs) + (138 lbs) + (32 lbs) = 234 lbs

The procedure outlined above should be complete for each pier type (P1, P2, P3, etc.) and for each varying height. This can be time consuming, so the estima-tor is encouraged to group like piers with matching heights whenever possible.

4) FOUNDATION WALLS

Design data for foundation walls is most often found in foundation details. Sometimes, however, foundation walls may be schedules similarly to spread footings and piers. Referring to the sample foundation plan, we consider the take-off of foundation walls between col-umns lines A1 and A2, shown in section at Figure 4. Measuring the wall’s length from the foundation plan, we find it is 47’-0” long.

The quantity of horizontal reinforcing bars at each face of the foundation wall is calculated:

((top of wall elevation) - (top of footing elevation) – (minimum coverage(s))) / (bar spacing)

(95.50’ – 82.00’ – (3” + 3”)) / 12” = 13 bars

Horizontal reinforcing bars in long foundation components are subject to lap splices every 20 or 60 feet depending on the material length shipped. Since 20 foot bars are more commonly used and easier to handle, we assume splices at 20’0” on center.

(wall length) / 20’0” = (number of splices) x (lap splice length) = (total length of splices)

47.0’ / 20’0” =↓ 2 laps x 15” = 2.5’

Since the detail indicates horizontal

reinforcing in each face of the founda-tion wall, the weight of reinforcing can be calculated:

((number of bars) x (number of faces) x (wall length + length of splices) x (weight per linear foot)

(13 bars) x (2 faces) x (47.0’ + 2.5’) x .668 lbs/lnft =↑ 860 lbs

The presence of a brick ledge at the outside face of the sample wall requires that vertical reinforcing bars be estimat-ed separately for each face. The weight of vertical bars on the exterior face of the wall is calculated by first determining the number of vertical bars

(wall length) / (vertical bar spacing)

(47.0’) / 12” = 47 bars

Vertical bars weight is calculated:

(wall height) +(bar overlap at brick ledge) – (minimum coverages) x (number of bars) x (weight

per lineal foot)

((13.5’) + (3.0’) – (3” + 3”)) x (47 bars) x 1.502 lbs/lnft =↑ 1,130 lbs

The weight of vertical bars on the inte-rior face of the wall is calculated by first determining the number of vertical bars.

(wall length) / (vertical bar spacing)

(47.0’) / 12” = 47 bars

Vertical bar weight is calculated:

(wall height) – (minimum coverages) x (number of bars) x (weight per lineal foot)

((13.5’) – (3” + 3”)) x (47 bars) x 1.502 lbs/lnft =↑ 918 lbs

As noted in subsection 2 above, wall footing dowels are calculated as part of the strip footing take-off. Therefore, the total weight of reinforcing steel in the foundation wall is calculated:

(weight of horizontal reinforcing) + (weight of verti-cal reinforcing at exterior face) + (weight of vertical

reinforcing at interior face)

(860 lbs) + (1,130 lbs) + (918 lbs) = 2,908 lbs

MATERIAl TAKEOFF SuMMARY

The examples above, though differ-ent in some ways, represent a common process for estimating the weight of

reinforcing steel. The basic steps are:

1. Locate pertinent details for each foundation component

2. Determine reinforcing bar types (verticals, horizontals, ties, dowels, etc.)

3. Calculate each bar type length

4. Multiply bar length by scheduled quantities and by weight per linear foot

5. Tally results and add waste factor(s) to determine total weight per foundation component

This process is the same for both simple and complex foundation systems. With practice, the estimator will develop a systematic approach to this take-off and be able to tackle more complex systems.

OvERvIEW OF lAbOR, MATERIAl, ACCESSORY, & OTHER COSTS

The total price for reinforcing steel is a combined total value of reinforcing steel labor, reinforcing steel material, and reinforcing steel accessories. Individual contractor equipment costs, mark-ups, and indirect costs will also play a factor.

labor Costs

Labor costs are primarily a function of production rates and should be calcu-lated and weighted to account for project size, repetitive details, and current market conditions. The best measure of labor costs is to acquire competitive bids.

Reinforcing steel labor is gener-ally quoted as a lump sum amount but should be analyzed at a yielded cost per ton. Some circumstances which may result in premium costs for labor are:

• Field vs. shop fabrication

• Project complexity

• Project size

• Mechanical or welded splices, rather than lap splices

Material Costs

Extreme market volatility in recent decades makes the cost of reinforcing steel material difficult to project. In the past 15 years, reinforcing steel has seen more than a 300% increase in material



cost. Due to the extreme consolidation of the steel industry, major steel produc-ers have not cut prices significantly in response to lower demand starting in 2009. Competition among smaller fab-rication shops and local distributors has helped overcome some of the material cost inflation.

Factors which affect material cost include:

• Overseas demand

• Mill production capacity

• Competition

• Recycled content

To mitigate risk, the experienced estima-tor should solicit current, market driven pricing for reinforcing steel materials.

Accessory Costs

In addition to reinforcing steel, mate-rial accessories must be considered as part of the overall project cost. Reinforc-ing steel accessories include:

Tie wire – used to connect lap splices and tie vertical & horizontal bars together.

Bar ties – precut wire drawn and annealed from high-quality rod. Used as a quick method of tying reinforcing steel.

Bar supports – used to elevate reinforcing bars above formed footing bottom. Supports can be in the form of plastic chairs, concrete bricks, or synthetic support blocks

Rebar caps – used to protect workmen from exposed rebar dowels protruding from con-crete foundations. Required by OSHA.

Material prices for reinforcing acces-sories will fluctuate as with other steel products. However, a good rule of thumb is that accessories for shallow foundation reinforcing steel should be between 1.5% and 2.5% of total material cost.

Other Costs

Tools and equipment are other costs that should be considered in the final pricing of the reinforcing steel. For con-tractors who purchase reinforcing steel pre-fabricated, these costs are minimal. The only equipment which might be used in the field for placing bars is hoist-ing equipment which is generally not a major factor when considering shallow foundations. For the most part, the

tools used in reinforcing steel place-ment should generally be considered expendable and may be assumed part of general conditions costs (clamps, wire cutters, pliers, etc.)

For the contractor who self performs resteel fabrication, the investment in rod benders, cutters, and sometimes mechanized fabrication systems can be significant. The cost of these items are beyond the scope of this article, but should be considered when developing a total material rate for fabricated bars.

RATIOS & AnAlYSISOnce completed, all take-off quantities

should be compiled in a recapitulation sheet (see table 4.1). Weights should be subtotaled by location (spread footings, strip footings, piers, walls, etc.). The experienced estimator should develop a series of checks using historically es-tablished “rules-of-thumb” to assess the total project quantities. Such measures can be developed as weight per cubic yard of concrete, weight per square foot of wall area, or percentage of total foun-dation volume.



SPECIFIC FACTORS AFFECTIng TAKE-OFF AnD PRICIng

Types and grades of Reinforcing Steel

While the focus of this article is the analysis of deformed carbon steel rein-forcing bars, other types of reinforcing materials are used. The same concepts are used to calculate the weight of these other bars, however, the weights per piece of these materials as well as at the resulting total tonnage and unit cost will vary. ASTM specifications for common types of reinforcing bars which might be encountered in shallow foun-dations include:

• ASTM A82: Plain Steel Wire for Concrete Reinforcement

• ASTM A184/A184M: Fabricated De-formed Steel Bar Mats for Reinforcement

• ASTM A185: Welded Plain Steel Wire Fabric for Concrete Reinforcement

• ASTM A496: Steel Wire for Concrete Reinforcement

• ASTM A497: Welded Deformed Steel Wire Fabric for Concrete Reinforcement

• ASTM A615/A615M: Deformed and plain carbon-steel bars for reinforcement

• ASTM A616/A616M: Rail-Steel De-formed and Plain Bars for Reinforcement

• ASTM A617/A617M: Axle-Steel De-formed and Plain Bars for Reinforcement

• ASTM A706/A706M: Low-alloy steel de-formed and plain bars for reinforcement

• ASTM A767/A767M: Zinc-Coated (Galva-nized) Steel Bars for Reinforcement

• ASTM A775/A775M: Epoxy-Coated Rein-forcing Steel Bars

• ASTM A934/A934M: Epoxy-Coated Pre-fabricated Steel Reinforcing Bars

• ASTM A955: Deformed and plain stainless-steel bars for concrete reinforcement

•ASTM A996: Rail-steel and axle-steel deformed bars for concrete reinforcement

Other Considerations

As with any estimate, special details can greatly influence project cost and


therefore break from the norm for costs and weight ratios. Due to the implied simplicity of shallow foundations, they are perhaps less likely to be subject to these abnormalities, but the estimator should always be aware that careful con-sideration of the project details should be paramount. Some common details which may significantly increase costs include:

Epoxy Dowels - Often used to tie existing foundations to new foundations

Welded connections – Though highly uncommon due to the reduced fatigue life of the bars, welding will influence la-bor rates significantly as well as material costs as very few grades of reinforcing steel are suitable for welding.

Mechanical splices – Where lap splices are not allowed, other methods of join-ing two pieces of reinforcing steel may be used. Mechanical splices which include threaded couplers, ribbed couplers, and bolted couplers. These methods of splic-ing can required preparation of bar ends and will greatly increase labor costs.

SPECIFIC RISK COnSIDERATIOnS

The experienced estimator will develop a methodology for calculating rebar quantities. Adhering to established conventions will help avoid errors and insure the validity of the take-off. Some common errors which should be avoided include:

Converting feet and inches – The variety of details and tables that must be used to develop a complete take-off will often combine measurements in feet (footing sizes) with measurements in inches (bar spacing). Being aware that accuracy depends heavily on converting values to a common convention will avoid errors in the estimate.

Converting pounds to tons – Similarly, combining multiple quantity surveys for each foundation component is necessary to establish an overall project weight for reinforcing steel. The estimator should be careful to combine quantities whose unit measure is the same (convert all or none of subtotaled values to tonnage).

Multipliers – As many of the foundation details require bar and piece counts, the estimator should not lose sight of com-ponent counts. A footing with 5 reinforc-ing bars should be taken-off as a weight per each footing and then multiplied by the footing count. This last step can be forgotten if the estimator gets too im-mersed in the details.

Drawing coordination – The estimator should be aware that not all information regarding reinforcing steel is found in the structural plans. Review of all contract documents is necessary for a complete and accurate estimate.

Estimators should take advantage of peer review whenever available. Fur-thermore, developing routine through practice will reduce possible errors in the quantity survey of shallow foundation reinforcing steel.

SAMPlE DRAWIngS AnD DETAIlS

Figures 1 – 5 Include:

1. Sample Foundation Plan

2. Typical Spread Footing Detail

3. Strip Footing Detail Enlargement

4. Foundation Wall Section

5. Foundation Pier Detail



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