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Construction engineering

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This chapter covers the following topics:

Project administration: contract documents, procurement, bonds, and project delivery
Construction operations: safety, equipment productivity, and erosion control
Project controls: scheduling, PERT, earned value, and resources
Construction estimating
Interpreting engineering drawings

Project administration

Project administration covers the documents that define the work, how the owner buys it, the guarantees behind it, and who answers to whom.

Contract documents

The contract documents together define the work and the obligations of each party:

Agreement: the signed contract, naming the parties, the price, and the contract time.
General conditions: the standard terms for roles, payment, changes, claims, insurance, and termination.
Supplementary conditions: project-specific changes to the general conditions.
Drawings: the graphic description of the work - what goes where, and how big it is.
Specifications: the written description of the quality of materials and workmanship.
Addenda: changes to the bidding documents issued before bids are opened.

The Engineers Joint Contract Documents Committee (EJCDC), a joint venture of the National Society of Professional Engineers (NSPE), the American Society of Civil Engineers (ASCE), and the American Council of Engineering Companies (ACEC), publishes standard documents written for engineer-designed projects such as infrastructure. The American Institute of Architects (AIA) is not an EJCDC sponsor. It publishes its own separate family, used mainly for architect-led building projects.

Procurement

On public work the owner typically selects a contractor by competitive sealed bidding. Bids are opened publicly, and the contract goes to the lowest responsive, responsible bidder:

A responsive bid conforms to the requirements of the bidding documents.
A responsible bidder can actually perform - it has the experience, capacity, and financial standing to do the work, including the ability to obtain the required bonds.

Design services are procured differently. Under the Brooks Act, federal agencies choose architect-engineer firms on the basis of demonstrated competence and qualifications, not price. The agency selects the most highly qualified firms in order of preference and negotiates a fair and reasonable fee with the top firm. Only if that negotiation fails, and is formally ended, does it move to the next firm. This is called qualifications-based selection.

Bonds

A surety bond is a three-party guarantee: the surety guarantees to the owner (the obligee) that the contractor (the principal) will meet an obligation.

Bid bond: guarantees the bidder will sign the contract at its bid price and furnish the required bonds.
Performance bond: guarantees the contractor will complete the work according to the contract. If the contractor defaults, the surety completes the work or pays to have it completed.
Payment bond: guarantees the contractor will pay its subcontractors, laborers, and suppliers.

Project delivery methods

The delivery method sets who contracts with whom, and when design and construction happen.

Design-bid-build (DBB): the owner contracts separately with a designer and then, once design is complete, with a contractor chosen by bid. Roles are clear, but the schedule is longest, and the owner stands between designer and contractor when the documents contain errors.
Design-build (DB): one entity holds a single contract for both design and construction. The owner gets a single point of responsibility, and construction can start before design is finished (fast-tracking).
Construction manager at risk (CMAR): the owner hires a construction manager during design for preconstruction services such as estimating and constructability review. The CM then builds the project as the general contractor, usually under a guaranteed maximum price.

Payment terms - lump sum, unit price, cost-plus, or guaranteed maximum price - and the risk each shifts are covered in the ethics and professional practice chapter.

Construction operations and methods

Operations questions test three things: working safely, estimating what equipment produces, and keeping soil on the site.

Safety

Construction safety on the FE centers on the OSHA construction standards (29 CFR Part 1926).

The hierarchy of controls ranks protective measures from most to least effective: elimination, substitution, engineering controls, administrative controls, and personal protective equipment (PPE). PPE is the last line of defense, not the first.

Excavations and trenches

A protective system (sloping, benching, shoring, or a shield) is required in an excavation 5 ft deep or more. Below 5 ft, one may be omitted only if a competent person examines the ground and finds no indication of a potential cave-in. Excavations entirely in stable rock are exempt.
Soil type sets the maximum allowable slope. For cohesive soil, OSHA uses unconfined compressive strength: Type A needs 1.5 tons per square foot (tsf) or more, Type B is more than 0.5 but less than 1.5 tsf, and Type C is 0.5 tsf or less. Strength is not the only test: fissured, vibrated, or previously disturbed soil can never be Type A, and granular soils fall in Type B or C.
For excavations less than 20 ft deep, the maximum slopes (horizontal:vertical) are: stable rock vertical, Type A 3/4:1, Type B 1:1, and Type C 1½:1. Without classifying the soil, slope no steeper than 1½:1.
Sloping or benching for an excavation deeper than 20 ft must be designed by a registered professional engineer.
A trench 4 ft or more deep needs a ladder, stairway, or ramp within 25 ft of lateral travel for every worker.
Spoil piles and equipment must stay at least 2 ft back from the edge, unless retaining devices keep them from falling in.

Heights

Under the general construction rule, fall protection is required on a surface with an unprotected side or edge 6 ft or more above a lower level. Scaffolds and steel erection have their own rules.
The side rails of a portable ladder must extend at least 3 ft above the landing it reaches, or the ladder must be secured at the top with a grab rail provided.

Example: Trench width at the surface

A trench 7 ft deep will be cut in Type B soil with a 4-ft bottom width, sloped on both sides. What is the minimum width at the ground surface?

Type B allows a maximum slope of 1H:1V, so each side sets back $7 \times 1 = 7$ ft.

$Top width = 4 + 2 (7) = 18 ft$

Answer: 18 ft. The spoil must then sit at least 2 ft beyond that edge.

Equipment productivity

Earthmoving equipment works in repeating cycles: load, haul, dump, and return. Cycle time is the sum of fixed time (loading, dumping, maneuvering) and variable time (hauling and returning, which depend on distance and speed).

$Production = Payload per cycle \times \frac{Cycles}{hour} \times Efficiency$

Efficiency covers lost time and is often stated as working minutes per hour, such as a 50-minute hour ( $50/60 = 0.83$ ). Bucket capacity is multiplied by a fill factor, since a bucket rarely loads exactly full, and production stays in loose volume until converted to bank volume (see swell and shrinkage).

To price the work, add the hourly ownership cost (depreciation, interest, insurance, taxes, storage), the hourly operating cost (fuel, lubricants, tires, repairs), and the operator’s wage, then divide by hourly production.

Example: Loader production and unit cost

A loader with a 4.0-LCY bucket and a 0.90 fill factor has a 0.6-minute cycle and works a 50-minute hour. The soil swells 25%. Its ownership cost is $48/hr, its operating cost $37/hr, and the operator earns $42/hr. Find the production in bank cubic yards per hour and the unit cost.

Cycles per hour: $50/0.6 = 83.3$

Loose production: $4.0 \times 0.90 \times 83.3 = 300$ LCY/hr

Bank production: $300/1.25 = 240$ BCY/hr

Unit cost: $($48 + $37 + $42) /240 = $127/240 = $0.53$ per BCY

Answer: 240 BCY/hr at $0.53 per BCY

Temporary erosion and sediment control

Under the Clean Water Act, a construction project needs a stormwater permit if it disturbs 1 acre or more of land, or less than 1 acre when it is part of a common plan of development or sale that will ultimately disturb 1 acre or more. Permit coverage requires a stormwater pollution prevention plan (SWPPP) describing the controls the site will use.

Erosion controls keep soil in place: limiting disturbed area and time, mulch, temporary seeding, and erosion control blankets.
Sediment controls capture soil already moving: silt fence, fiber rolls, check dams, inlet protection, sediment traps and basins, and a stabilized crushed-stone construction entrance.

Preventing erosion beats trapping sediment, so a good plan leans on erosion controls and keeps sediment controls as the backstop.

Project controls

Project controls track whether the work is on schedule and on budget. The CPM precedence relationships and the earned-value formulas below are under the Construction heading of the FE Reference Handbook’s Civil Engineering chapter.

Activity relationships and the critical path method

In an activity-on-node (AON) network, each activity is a node and arrows show dependencies:

Finish-to-start (FS): B can’t start until A finishes. This is the default relationship.
Start-to-start (SS): B can’t start until A starts.
Finish-to-finish (FF): B can’t finish until A finishes.
Start-to-finish (SF): B can’t finish until A starts. It is rarely used.

A lag adds a required wait to any relationship, such as FS with a 3-day lag for concrete to cure. Some exam questions use activity-on-arrow (AOA) networks instead, where activities are arrows between event nodes and zero-duration dummy activities carry dependencies. The passes and float work the same way.

The critical path method (CPM) finds the project duration with a forward pass (early dates) and a backward pass (late dates):

$ES$ = latest $EF$ among predecessors, and $EF = ES + D$
$L F$ = earliest $L S$ among successors, and $L S = L F - D$
Total float $= L S - ES = L F - EF$ : how long an activity can slip without delaying the project
Free float $= E S_{earliest successor} - EF$ : how long it can slip without delaying any successor

The critical path is the longest path through the network. Its activities have the least total float - zero when the required finish equals the calculated finish - and delaying any of them delays the project.

Example: Forward pass, backward pass, and float

Activities A (5 days) and B (3 days) both start the project. Activity C (2 days) can’t start until both finish.

Forward pass: $E F_{A} = 5$ , $E F_{B} = 3$ , $E S_{C} = max (5, 3) = 5$ , $E F_{C} = 7$

Backward pass: $L F_{C} = 7$ , $L S_{C} = 5$ , $L F_{A} = L F_{B} = 5$ , $L S_{A} = 0$ , $L S_{B} = 2$

Float: A and C have 0; B has a total float of $2 - 0 = 2$ days and a free float of $5 - 3 = 2$ days

Answer: The critical path is A-C (7 days), and B has 2 days of float.

PERT

The program evaluation and review technique (PERT) schedules a network whose activity durations are uncertain. It suits any one-time project made of distinct activities - a construction project, a software development effort, or preparing a bid - and uses three estimates per activity: optimistic $a$ , most likely $m$ , and pessimistic $b$ .

$t_{e} = \frac{a + 4 m + b}{6} σ = \frac{b - a}{6}$

The expected project duration is the sum of $t_{e}$ along the critical path, and its variance is the sum of the activity variances $σ^{2}$ along that path. A standard normal $z$ then gives the probability of finishing by a target date.

Example: Probability of meeting a deadline

A critical path has three activities with $(a, m, b)$ estimates of $(4, 6, 14)$ , $(3, 5, 7)$ , and $(5, 8, 17)$ days. What is the probability of finishing within 24 days?

Expected times: $7 + 5 + 9 = 21$ days

Variances: $(10/6)^{2} + (4/6)^{2} + (12/6)^{2} = 2.78 + 0.44 + 4.00 = 7.22$ , so $σ = 2.69$ days

$z = (24 - 21) /2.69 = 1.12$

Answer: About 87%

Earned value analysis

Earned value compares the work planned, the work actually done, and what it cost, all in dollars.

Definitions

Budgeted cost of work scheduled (BCWS): The budgeted value of the work planned to date, also called planned value.
Budgeted cost of work performed (BCWP): The budgeted value of the work actually completed to date, also called earned value.
Actual cost of work performed (ACWP): What the completed work actually cost, also called actual cost.

$C V = BC W P - A C W P S V = BC W P - BC W S$

$CP I = \frac{BC W P}{A C W P} SP I = \frac{BC W P}{BC W S}$

$ETC = \frac{B A C - BC W P}{CP I} E A C = A C W P + ETC$

$B A C$ is the budget at completion. A negative variance, or an index below 1, is unfavorable: $CP I < 1$ means over budget and $SP I < 1$ means behind schedule.

Example: Earned value status and forecast

A $2,000,000 project has BCWS = $500,000, BCWP = $450,000, and ACWP = $480,000.

$C V = 450, 000 - 480, 000 = - $30, 000$ and $S V = 450, 000 - 500, 000 = - $50, 000$

$CP I = 450, 000/480, 000 = 0.94$ and $SP I = 450, 000/500, 000 = 0.90$

$ETC = (2, 000, 000 - 450, 000) /0.9375 = $1, 653, 000$

$E A C = 480, 000 + 1, 653, 000 = $2, 133, 000$

Answer: The project is over budget and behind schedule, and at its current cost efficiency it will finish at about $2.13 million.

Allocating resources

Resource leveling shifts noncritical activities within their float to smooth crew and equipment demand without extending the project.
Resource-constrained scheduling accepts a longer project when a limited resource can’t cover every activity at once.
Crashing adds resources to critical activities, cheapest per day saved first. Only critical activities shorten the project, and once another path becomes as long as the critical one, both must be shortened together.

Construction estimating

Estimates grow more accurate as design advances:

Conceptual (order-of-magnitude): from cost per square foot or per unit of capacity, before design.
Preliminary (budget): from major systems and assemblies, during design.
Detailed (definitive): from a full quantity takeoff priced at unit costs, once the documents are complete. This is the bid estimate.

A detailed estimate adds up direct costs (labor, materials, equipment, and subcontracts), then indirect costs or overhead (field and home-office costs), a contingency for identified risk, and profit. In a contractor’s organization the estimating department obtains the bid documents, performs the takeoff, solicits subcontractor and supplier quotations, and prepares and submits the bid. Tracking actual costs against the budget after award is project cost accounting, a separate function.

A takeoff converts dimensions to ordering units and adds waste: a footing 40 ft long, 3 ft wide, and 1.5 ft deep holds $180 ft^{3} = 6.67$ yd³, so with 5% waste you order 7.0 yd³.

Example: Building up a bid

A job’s direct cost is $820,000. Overhead is 10% of direct cost, and profit is 8% of direct cost plus overhead.

Overhead: $0.10 \times 820, 000 = $82, 000$

Profit: $0.08 \times (820, 000 + 82, 000) = $72, 160$

Bid: $820, 000 + 82, 000 + 72, 160 = $974, 160$

Answer: $974,160. Read carefully whether a percentage applies to direct cost alone or to a running subtotal; the two give different bids.

Interpreting engineering drawings

Civil drawings show the work as a plan (looking down from above), a profile (elevation plotted against station along a centerline, often paired with the plan on one sheet), a section (a cut through the work, such as a typical roadway cross-section), and details (enlarged views of small parts).

Stationing measures distance along a centerline in 100-ft stations from station 0+00: 12+50.00 is 1,250.00 ft along the line, so the distance between two stations is their difference. SI drawings use 1-km stations, so 1+250.000 is 1,250 m.

Scale. Civil drawings use an engineer’s scale (such as 1 in = 40 ft), so a line measuring 3.25 in on that sheet is $3.25 \times 40 = 130$ ft long. Building drawings use an architect’s scale (such as 1/4 in = 1 ft). A graphic (bar) scale stays correct when a sheet is reduced or enlarged; a stated ratio does not.

Contours are lines of equal elevation. Closely spaced contours mean steep ground, and where contours cross a stream they bend into a V that points upstream. Cut is needed where existing ground is above the proposed grade, and fill where it is below.

Profiles also carry pipe inverts, and a pipe’s slope is its drop over its run: an invert of 104.20 ft at station 3+00 and 102.60 ft at station 7+00 gives $S = 1.60/400 = 0.40%$ .

Next | Wrapping up

Construction engineering

This chapter covers the following topics:

Project administration: contract documents, procurement, bonds, and project delivery
Construction operations: safety, equipment productivity, and erosion control
Project controls: scheduling, PERT, earned value, and resources
Construction estimating
Interpreting engineering drawings

Project administration

Project administration covers the documents that define the work, how the owner buys it, the guarantees behind it, and who answers to whom.

Contract documents

The contract documents together define the work and the obligations of each party:

Agreement: the signed contract, naming the parties, the price, and the contract time.
General conditions: the standard terms for roles, payment, changes, claims, insurance, and termination.
Supplementary conditions: project-specific changes to the general conditions.
Drawings: the graphic description of the work - what goes where, and how big it is.
Specifications: the written description of the quality of materials and workmanship.
Addenda: changes to the bidding documents issued before bids are opened.

Procurement

On public work the owner typically selects a contractor by competitive sealed bidding. Bids are opened publicly, and the contract goes to the lowest responsive, responsible bidder:

A responsive bid conforms to the requirements of the bidding documents.
A responsible bidder can actually perform - it has the experience, capacity, and financial standing to do the work, including the ability to obtain the required bonds.

Bonds

A surety bond is a three-party guarantee: the surety guarantees to the owner (the obligee) that the contractor (the principal) will meet an obligation.

Bid bond: guarantees the bidder will sign the contract at its bid price and furnish the required bonds.
Performance bond: guarantees the contractor will complete the work according to the contract. If the contractor defaults, the surety completes the work or pays to have it completed.
Payment bond: guarantees the contractor will pay its subcontractors, laborers, and suppliers.

Project delivery methods

The delivery method sets who contracts with whom, and when design and construction happen.

Design-bid-build (DBB): the owner contracts separately with a designer and then, once design is complete, with a contractor chosen by bid. Roles are clear, but the schedule is longest, and the owner stands between designer and contractor when the documents contain errors.
Design-build (DB): one entity holds a single contract for both design and construction. The owner gets a single point of responsibility, and construction can start before design is finished (fast-tracking).
Construction manager at risk (CMAR): the owner hires a construction manager during design for preconstruction services such as estimating and constructability review. The CM then builds the project as the general contractor, usually under a guaranteed maximum price.

Payment terms - lump sum, unit price, cost-plus, or guaranteed maximum price - and the risk each shifts are covered in the ethics and professional practice chapter.

Construction operations and methods

Operations questions test three things: working safely, estimating what equipment produces, and keeping soil on the site.

Safety

Construction safety on the FE centers on the OSHA construction standards (29 CFR Part 1926).

Excavations and trenches

A protective system (sloping, benching, shoring, or a shield) is required in an excavation 5 ft deep or more. Below 5 ft, one may be omitted only if a competent person examines the ground and finds no indication of a potential cave-in. Excavations entirely in stable rock are exempt.
Soil type sets the maximum allowable slope. For cohesive soil, OSHA uses unconfined compressive strength: Type A needs 1.5 tons per square foot (tsf) or more, Type B is more than 0.5 but less than 1.5 tsf, and Type C is 0.5 tsf or less. Strength is not the only test: fissured, vibrated, or previously disturbed soil can never be Type A, and granular soils fall in Type B or C.
For excavations less than 20 ft deep, the maximum slopes (horizontal:vertical) are: stable rock vertical, Type A 3/4:1, Type B 1:1, and Type C 1½:1. Without classifying the soil, slope no steeper than 1½:1.
Sloping or benching for an excavation deeper than 20 ft must be designed by a registered professional engineer.
A trench 4 ft or more deep needs a ladder, stairway, or ramp within 25 ft of lateral travel for every worker.
Spoil piles and equipment must stay at least 2 ft back from the edge, unless retaining devices keep them from falling in.

Heights

Under the general construction rule, fall protection is required on a surface with an unprotected side or edge 6 ft or more above a lower level. Scaffolds and steel erection have their own rules.
The side rails of a portable ladder must extend at least 3 ft above the landing it reaches, or the ladder must be secured at the top with a grab rail provided.

Example: Trench width at the surface

A trench 7 ft deep will be cut in Type B soil with a 4-ft bottom width, sloped on both sides. What is the minimum width at the ground surface?

Type B allows a maximum slope of 1H:1V, so each side sets back $7 \times 1 = 7$ ft.

$Top width = 4 + 2 (7) = 18 ft$

Answer: 18 ft. The spoil must then sit at least 2 ft beyond that edge.

Equipment productivity

$Production = Payload per cycle \times \frac{Cycles}{hour} \times Efficiency$

Example: Loader production and unit cost

A loader with a 4.0-LCY bucket and a 0.90 fill factor has a 0.6-minute cycle and works a 50-minute hour. The soil swells 25%. Its ownership cost is $48/hr, its operating cost $37/hr, and the operator earns $42/hr. Find the production in bank cubic yards per hour and the unit cost.

Cycles per hour: $50/0.6 = 83.3$

Loose production: $4.0 \times 0.90 \times 83.3 = 300$ LCY/hr

Bank production: $300/1.25 = 240$ BCY/hr

Unit cost: $($48 + $37 + $42) /240 = $127/240 = $0.53$ per BCY

Answer: 240 BCY/hr at $0.53 per BCY

Temporary erosion and sediment control

Erosion controls keep soil in place: limiting disturbed area and time, mulch, temporary seeding, and erosion control blankets.
Sediment controls capture soil already moving: silt fence, fiber rolls, check dams, inlet protection, sediment traps and basins, and a stabilized crushed-stone construction entrance.

Preventing erosion beats trapping sediment, so a good plan leans on erosion controls and keeps sediment controls as the backstop.

Project controls

Activity relationships and the critical path method

In an activity-on-node (AON) network, each activity is a node and arrows show dependencies:

Finish-to-start (FS): B can’t start until A finishes. This is the default relationship.
Start-to-start (SS): B can’t start until A starts.
Finish-to-finish (FF): B can’t finish until A finishes.
Start-to-finish (SF): B can’t finish until A starts. It is rarely used.

The critical path method (CPM) finds the project duration with a forward pass (early dates) and a backward pass (late dates):

$ES$ = latest $EF$ among predecessors, and $EF = ES + D$
$L F$ = earliest $L S$ among successors, and $L S = L F - D$
Total float $= L S - ES = L F - EF$ : how long an activity can slip without delaying the project
Free float $= E S_{earliest successor} - EF$ : how long it can slip without delaying any successor

Example: Forward pass, backward pass, and float

Activities A (5 days) and B (3 days) both start the project. Activity C (2 days) can’t start until both finish.

Forward pass: $E F_{A} = 5$ , $E F_{B} = 3$ , $E S_{C} = max (5, 3) = 5$ , $E F_{C} = 7$

Backward pass: $L F_{C} = 7$ , $L S_{C} = 5$ , $L F_{A} = L F_{B} = 5$ , $L S_{A} = 0$ , $L S_{B} = 2$

Float: A and C have 0; B has a total float of $2 - 0 = 2$ days and a free float of $5 - 3 = 2$ days

Answer: The critical path is A-C (7 days), and B has 2 days of float.

PERT

$t_{e} = \frac{a + 4 m + b}{6} σ = \frac{b - a}{6}$

Example: Probability of meeting a deadline

A critical path has three activities with $(a, m, b)$ estimates of $(4, 6, 14)$ , $(3, 5, 7)$ , and $(5, 8, 17)$ days. What is the probability of finishing within 24 days?

Expected times: $7 + 5 + 9 = 21$ days

Variances: $(10/6)^{2} + (4/6)^{2} + (12/6)^{2} = 2.78 + 0.44 + 4.00 = 7.22$ , so $σ = 2.69$ days

$z = (24 - 21) /2.69 = 1.12$

Answer: About 87%

Earned value analysis

Earned value compares the work planned, the work actually done, and what it cost, all in dollars.

Definitions

Budgeted cost of work scheduled (BCWS): The budgeted value of the work planned to date, also called planned value.
Budgeted cost of work performed (BCWP): The budgeted value of the work actually completed to date, also called earned value.
Actual cost of work performed (ACWP): What the completed work actually cost, also called actual cost.

$C V = BC W P - A C W P S V = BC W P - BC W S$

$CP I = \frac{BC W P}{A C W P} SP I = \frac{BC W P}{BC W S}$

$ETC = \frac{B A C - BC W P}{CP I} E A C = A C W P + ETC$

$B A C$ is the budget at completion. A negative variance, or an index below 1, is unfavorable: $CP I < 1$ means over budget and $SP I < 1$ means behind schedule.

Example: Earned value status and forecast

A $2,000,000 project has BCWS = $500,000, BCWP = $450,000, and ACWP = $480,000.

$C V = 450, 000 - 480, 000 = - $30, 000$ and $S V = 450, 000 - 500, 000 = - $50, 000$

$CP I = 450, 000/480, 000 = 0.94$ and $SP I = 450, 000/500, 000 = 0.90$

$ETC = (2, 000, 000 - 450, 000) /0.9375 = $1, 653, 000$

$E A C = 480, 000 + 1, 653, 000 = $2, 133, 000$

Answer: The project is over budget and behind schedule, and at its current cost efficiency it will finish at about $2.13 million.

Allocating resources

Resource leveling shifts noncritical activities within their float to smooth crew and equipment demand without extending the project.
Resource-constrained scheduling accepts a longer project when a limited resource can’t cover every activity at once.
Crashing adds resources to critical activities, cheapest per day saved first. Only critical activities shorten the project, and once another path becomes as long as the critical one, both must be shortened together.

Construction estimating

Estimates grow more accurate as design advances:

Conceptual (order-of-magnitude): from cost per square foot or per unit of capacity, before design.
Preliminary (budget): from major systems and assemblies, during design.
Detailed (definitive): from a full quantity takeoff priced at unit costs, once the documents are complete. This is the bid estimate.

A takeoff converts dimensions to ordering units and adds waste: a footing 40 ft long, 3 ft wide, and 1.5 ft deep holds $180 ft^{3} = 6.67$ yd³, so with 5% waste you order 7.0 yd³.

Example: Building up a bid

A job’s direct cost is $820,000. Overhead is 10% of direct cost, and profit is 8% of direct cost plus overhead.

Overhead: $0.10 \times 820, 000 = $82, 000$

Profit: $0.08 \times (820, 000 + 82, 000) = $72, 160$

Bid: $820, 000 + 82, 000 + 72, 160 = $974, 160$

Answer: $974,160. Read carefully whether a percentage applies to direct cost alone or to a running subtotal; the two give different bids.

Interpreting engineering drawings

Profiles also carry pipe inverts, and a pipe’s slope is its drop over its run: an invert of 104.20 ft at station 3+00 and 102.60 ft at station 7+00 gives $S = 1.60/400 = 0.40%$ .

This chapter covers the following topics:

Project administration: contract documents, procurement, bonds, and project delivery
Construction operations: safety, equipment productivity, and erosion control
Project controls: scheduling, PERT, earned value, and resources
Construction estimating
Interpreting engineering drawings

Project administration

Project administration covers the documents that define the work, how the owner buys it, the guarantees behind it, and who answers to whom.

Contract documents

The contract documents together define the work and the obligations of each party:

Agreement: the signed contract, naming the parties, the price, and the contract time.
General conditions: the standard terms for roles, payment, changes, claims, insurance, and termination.
Supplementary conditions: project-specific changes to the general conditions.
Drawings: the graphic description of the work - what goes where, and how big it is.
Specifications: the written description of the quality of materials and workmanship.
Addenda: changes to the bidding documents issued before bids are opened.

Procurement

On public work the owner typically selects a contractor by competitive sealed bidding. Bids are opened publicly, and the contract goes to the lowest responsive, responsible bidder:

A responsive bid conforms to the requirements of the bidding documents.
A responsible bidder can actually perform - it has the experience, capacity, and financial standing to do the work, including the ability to obtain the required bonds.

Bonds

A surety bond is a three-party guarantee: the surety guarantees to the owner (the obligee) that the contractor (the principal) will meet an obligation.

Bid bond: guarantees the bidder will sign the contract at its bid price and furnish the required bonds.
Performance bond: guarantees the contractor will complete the work according to the contract. If the contractor defaults, the surety completes the work or pays to have it completed.
Payment bond: guarantees the contractor will pay its subcontractors, laborers, and suppliers.

Project delivery methods

The delivery method sets who contracts with whom, and when design and construction happen.

Design-bid-build (DBB): the owner contracts separately with a designer and then, once design is complete, with a contractor chosen by bid. Roles are clear, but the schedule is longest, and the owner stands between designer and contractor when the documents contain errors.
Design-build (DB): one entity holds a single contract for both design and construction. The owner gets a single point of responsibility, and construction can start before design is finished (fast-tracking).
Construction manager at risk (CMAR): the owner hires a construction manager during design for preconstruction services such as estimating and constructability review. The CM then builds the project as the general contractor, usually under a guaranteed maximum price.

Payment terms - lump sum, unit price, cost-plus, or guaranteed maximum price - and the risk each shifts are covered in the ethics and professional practice chapter.

Construction operations and methods

Operations questions test three things: working safely, estimating what equipment produces, and keeping soil on the site.

Safety

Construction safety on the FE centers on the OSHA construction standards (29 CFR Part 1926).

Excavations and trenches

A protective system (sloping, benching, shoring, or a shield) is required in an excavation 5 ft deep or more. Below 5 ft, one may be omitted only if a competent person examines the ground and finds no indication of a potential cave-in. Excavations entirely in stable rock are exempt.
Soil type sets the maximum allowable slope. For cohesive soil, OSHA uses unconfined compressive strength: Type A needs 1.5 tons per square foot (tsf) or more, Type B is more than 0.5 but less than 1.5 tsf, and Type C is 0.5 tsf or less. Strength is not the only test: fissured, vibrated, or previously disturbed soil can never be Type A, and granular soils fall in Type B or C.
For excavations less than 20 ft deep, the maximum slopes (horizontal:vertical) are: stable rock vertical, Type A 3/4:1, Type B 1:1, and Type C 1½:1. Without classifying the soil, slope no steeper than 1½:1.
Sloping or benching for an excavation deeper than 20 ft must be designed by a registered professional engineer.
A trench 4 ft or more deep needs a ladder, stairway, or ramp within 25 ft of lateral travel for every worker.
Spoil piles and equipment must stay at least 2 ft back from the edge, unless retaining devices keep them from falling in.

Heights

Under the general construction rule, fall protection is required on a surface with an unprotected side or edge 6 ft or more above a lower level. Scaffolds and steel erection have their own rules.
The side rails of a portable ladder must extend at least 3 ft above the landing it reaches, or the ladder must be secured at the top with a grab rail provided.

Example: Trench width at the surface

A trench 7 ft deep will be cut in Type B soil with a 4-ft bottom width, sloped on both sides. What is the minimum width at the ground surface?

Type B allows a maximum slope of 1H:1V, so each side sets back $7 \times 1 = 7$ ft.

$Top width = 4 + 2 (7) = 18 ft$

Answer: 18 ft. The spoil must then sit at least 2 ft beyond that edge.

Equipment productivity

$Production = Payload per cycle \times \frac{Cycles}{hour} \times Efficiency$

Example: Loader production and unit cost

A loader with a 4.0-LCY bucket and a 0.90 fill factor has a 0.6-minute cycle and works a 50-minute hour. The soil swells 25%. Its ownership cost is $48/hr, its operating cost $37/hr, and the operator earns $42/hr. Find the production in bank cubic yards per hour and the unit cost.

Cycles per hour: $50/0.6 = 83.3$

Loose production: $4.0 \times 0.90 \times 83.3 = 300$ LCY/hr

Bank production: $300/1.25 = 240$ BCY/hr

Unit cost: $($48 + $37 + $42) /240 = $127/240 = $0.53$ per BCY

Answer: 240 BCY/hr at $0.53 per BCY

Temporary erosion and sediment control

Erosion controls keep soil in place: limiting disturbed area and time, mulch, temporary seeding, and erosion control blankets.
Sediment controls capture soil already moving: silt fence, fiber rolls, check dams, inlet protection, sediment traps and basins, and a stabilized crushed-stone construction entrance.

Preventing erosion beats trapping sediment, so a good plan leans on erosion controls and keeps sediment controls as the backstop.

Project controls

Activity relationships and the critical path method

In an activity-on-node (AON) network, each activity is a node and arrows show dependencies:

Finish-to-start (FS): B can’t start until A finishes. This is the default relationship.
Start-to-start (SS): B can’t start until A starts.
Finish-to-finish (FF): B can’t finish until A finishes.
Start-to-finish (SF): B can’t finish until A starts. It is rarely used.

The critical path method (CPM) finds the project duration with a forward pass (early dates) and a backward pass (late dates):

$ES$ = latest $EF$ among predecessors, and $EF = ES + D$
$L F$ = earliest $L S$ among successors, and $L S = L F - D$
Total float $= L S - ES = L F - EF$ : how long an activity can slip without delaying the project
Free float $= E S_{earliest successor} - EF$ : how long it can slip without delaying any successor

Example: Forward pass, backward pass, and float

Activities A (5 days) and B (3 days) both start the project. Activity C (2 days) can’t start until both finish.

Forward pass: $E F_{A} = 5$ , $E F_{B} = 3$ , $E S_{C} = max (5, 3) = 5$ , $E F_{C} = 7$

Backward pass: $L F_{C} = 7$ , $L S_{C} = 5$ , $L F_{A} = L F_{B} = 5$ , $L S_{A} = 0$ , $L S_{B} = 2$

Float: A and C have 0; B has a total float of $2 - 0 = 2$ days and a free float of $5 - 3 = 2$ days

Answer: The critical path is A-C (7 days), and B has 2 days of float.

PERT

$t_{e} = \frac{a + 4 m + b}{6} σ = \frac{b - a}{6}$

Example: Probability of meeting a deadline

A critical path has three activities with $(a, m, b)$ estimates of $(4, 6, 14)$ , $(3, 5, 7)$ , and $(5, 8, 17)$ days. What is the probability of finishing within 24 days?

Expected times: $7 + 5 + 9 = 21$ days

Variances: $(10/6)^{2} + (4/6)^{2} + (12/6)^{2} = 2.78 + 0.44 + 4.00 = 7.22$ , so $σ = 2.69$ days

$z = (24 - 21) /2.69 = 1.12$

Answer: About 87%

Earned value analysis

Earned value compares the work planned, the work actually done, and what it cost, all in dollars.

Definitions

Budgeted cost of work scheduled (BCWS): The budgeted value of the work planned to date, also called planned value.
Budgeted cost of work performed (BCWP): The budgeted value of the work actually completed to date, also called earned value.
Actual cost of work performed (ACWP): What the completed work actually cost, also called actual cost.

$C V = BC W P - A C W P S V = BC W P - BC W S$

$CP I = \frac{BC W P}{A C W P} SP I = \frac{BC W P}{BC W S}$

$ETC = \frac{B A C - BC W P}{CP I} E A C = A C W P + ETC$

$B A C$ is the budget at completion. A negative variance, or an index below 1, is unfavorable: $CP I < 1$ means over budget and $SP I < 1$ means behind schedule.

Example: Earned value status and forecast

A $2,000,000 project has BCWS = $500,000, BCWP = $450,000, and ACWP = $480,000.

$C V = 450, 000 - 480, 000 = - $30, 000$ and $S V = 450, 000 - 500, 000 = - $50, 000$

$CP I = 450, 000/480, 000 = 0.94$ and $SP I = 450, 000/500, 000 = 0.90$

$ETC = (2, 000, 000 - 450, 000) /0.9375 = $1, 653, 000$

$E A C = 480, 000 + 1, 653, 000 = $2, 133, 000$

Answer: The project is over budget and behind schedule, and at its current cost efficiency it will finish at about $2.13 million.

Allocating resources

Resource leveling shifts noncritical activities within their float to smooth crew and equipment demand without extending the project.
Resource-constrained scheduling accepts a longer project when a limited resource can’t cover every activity at once.
Crashing adds resources to critical activities, cheapest per day saved first. Only critical activities shorten the project, and once another path becomes as long as the critical one, both must be shortened together.

Construction estimating

Estimates grow more accurate as design advances:

Conceptual (order-of-magnitude): from cost per square foot or per unit of capacity, before design.
Preliminary (budget): from major systems and assemblies, during design.
Detailed (definitive): from a full quantity takeoff priced at unit costs, once the documents are complete. This is the bid estimate.

A takeoff converts dimensions to ordering units and adds waste: a footing 40 ft long, 3 ft wide, and 1.5 ft deep holds $180 ft^{3} = 6.67$ yd³, so with 5% waste you order 7.0 yd³.

Example: Building up a bid

A job’s direct cost is $820,000. Overhead is 10% of direct cost, and profit is 8% of direct cost plus overhead.

Overhead: $0.10 \times 820, 000 = $82, 000$

Profit: $0.08 \times (820, 000 + 82, 000) = $72, 160$

Bid: $820, 000 + 82, 000 + 72, 160 = $974, 160$

Answer: $974,160. Read carefully whether a percentage applies to direct cost alone or to a running subtotal; the two give different bids.

Interpreting engineering drawings

Profiles also carry pipe inverts, and a pipe’s slope is its drop over its run: an invert of 104.20 ft at station 3+00 and 102.60 ft at station 7+00 gives $S = 1.60/400 = 0.40%$ .