CONSTRUCTION PROJECT COST ESTIMATING.

Estimating the cost of a proposed construction project is a very complex process containing much variable factors.Proper study, training and experience are needed to become proficient in this area of engineering. There are several categories that can have significant impacts on project costs. The estimator should be aware of them and properly evaluate their effects.

Prior to finalizing the cost estimate. Here are some important points:

1) Similar Projects: The best references are similar projects. Refer to their final cost items and related expenses as a sound basis. Experience with similar projects is invaluable.

2) Material Costs: Obtain reliable costs for materials and supplies, plus shipping charges, prior to commencing tabulation.

3) Wage Rates: Determine if the project will mandate state or federal wage rates. Also, check if local wage rates are required. It is mandatory to factor this into the estimate.

4) Site Conditions: Project site conditions that can increase construction costs are: poor soil conditions, wetlands, contaminated materials, conflicting utilities (buried pipe, cables, overhead lines, etc.), environmentally sensitivity area, ground water, river or stream crossings, heavy traffic, buried storage tanks, archaeological sites, endangered species habitat and similar existing conditions.

5) Inflation Factor: The presence of inflation is always a factor that can be extremely variable. When utilizing previous, similar projects as a primary basis for estimating, consider the Construction Cost Index as published in the Engineering News Record. This nationwide tabulation of the construction industry has been continuously recorded for decades.

6) Bid Timing: The timing of the bid opening can have a significant impact on obtaining a low bid. Seasonal variations in construction activity and conflicts with other bid openings are critical factors.

7) Project Schedule: The construction schedule can certainly affect the cost. If the project requires too aggressive of a time frame, generally the price increases, especially if there is a significant liquidated damages condition for failure to complete within a specified deadline. Conversely, if the award notice is beyond a reasonable time and the notice to proceed is indefinite, the contractors fear inflation of material costs and may have other projects that have priority. Therefore, most bidders will inflate their bids to protect against these conditions. Any time beyond 60 days may result in higher bids.

8) Quality of Plans & Specifications: There is no substitute for well-prepared plans and specifications. It is extremely important that every detail and component of the design be properly executed and fully described. Any vague wording or poorly drawn plan not only causes confusion, but places doubt in the contractor’s mind which generally results in a higher bid.

9) Reputation of Engineer: If the project engineer or engineering firm has a good sound professional reputation with contractors, it is reflected in reasonably priced bids. If a contractor is comfortable working with a particular engineer, or engineering firm, the project runs smoother and therefore is more cost-effective.

10) Granting Agency: If a granting agency is involved in funding a portion of the project, contractors will take this into consideration when preparing their bids. Some granting agencies have considerable additional paperwork that is not normally required in a non-funded project. Sometimes this expected extra paperwork elevates the bid.

11) Regulatory Requirements: Sometimes there are conditions in regulatory agency approvals that will be costly to perform. Therefore, to be completely aboveboard with potential bidders, it is strongly recommended that copies of all regulatory approvals be contained in all bidding documents.

12) Insurance Requirements: General insurance requirements, such as performance bond, payment bond and contractors general liability are normal costs of doing business. However, there are special projects that require additional coverage. Railroad crossings are a prime example. Insurance premiums for these supplemental policies add to the project cost and must be considered up front.

13) Size of Project: The size and complexity of a project determines if local contractors have the capacity to execute the work. The larger and more intricate the proposed project is, the more it will potentially attract the attention of a broader number of prospective bidders. This is good for competition, but may increase mobilization costs.

14) Locale of Work Site: The locale of the proposed work can be a significant component in developing a realistic cost estimate. A rural setting usually has a limited labor force skilled in the construction trades. Therefore, the contractor must import tradesmen and generally pay per diem expenses; i.e., out-of-town lodging and related costs. Additionally, remote settings increase the charges for material shipment.

15) Value Engineering: Some agencies mandate that multi-million dollar projects perform a value engineering review, prior to finalizing the design or commencing the bidding process. Therefore, the estimator should be aware of this factor early in the process.

16) Contingency: The rule-of-thumb has historically added a 10% contingency on the construction total to cover those unforeseen costs that crop up as a project evolves. During times of high inflation or the limited amount of key construction materials and supplies, it is wise to increase the contingency to 15% or 20% for a more realistic estimate and provide a safety factor.

17) Supplemental Studies & Investigations: some project sites will require special studies and/or investigations. Costs for this special work should be included in the initial cost estimate to avoid future surprises.

18) Judgement: In the final analysis, the best component of a good cost estimate is the art of practicing sound technical judgement. This factor is acquired by experience and the mentoring of senior personnel.

CONCRETE FOUNDATION CONSTRUCTION GUIDE

Concrete Foundation Construction Work Procedure at Site

The purpose of this guide is to ensure that all the concrete foundation / plinth are constructed properly and according to standards and requirements.

Base Preparation

Before casting concrete the soil sub-grade shall be compacted and leveled, free from standing water and debris. If the sub-grade soil is of poor quality, it shall be excavated, and a layer of gravel 100mm thick shall be provided. The level tolerances for the prepared sub-grade shall not exceed +5mm, -15mm.

Formwork

1. All formwork materials shall be selected and installed to achieve the required concrete surface finishes.

2. All joints between formwork panels shall be adequately sealed, to prevent the leakage of grout during concrete casting and compaction.

3. All formwork shall be measured before concrete casting to confirm the locations, alignment and top of concrete levels.

4. Where the formwork extends above the top of concrete level, the top of concrete level shall be clearly marked on the formwork with nails and / or a chalk line.

5. All formwork shall be selected and arranged such that it has adequate strength, stiffness and stability to retain the weight of wet concrete during placement. The formwork shall be stiffened, as necessary, to ensure no significant deformation of the same during concrete casting.

Arrangement of Reinforcing bars

1. Arrangement of Reinforcing Bars – The minimum distance of individual bars shall be 150mm.

2. After installation of rebar, the following items shall be visually checked and confirmed:

(i) The minimum rebar size is 16mm.

(ii) The tolerance of the position of reinforcement bars shall not exceed ±6mm.

(iii) Cover and spacers for reinforcement. Note that spacers shall consist of either specifically designed plastic spacers, or concrete cubes with fixing wires. Should concrete cubes be utilized, they shall be made from the same grade of concrete (or higher) as the item to be cast.

(iv) Fixing of reinforcement shall be done using 16 SWG soft pliable annealed steel wires. The ends of the fixing wire shall be turned in from the face of the formwork, to avoid rust spots on the surface of the finished concrete.

Removal of formwork

The time for stripping of formwork is 12 hours. The formwork shall not be removed earlier than twelve(12) hours after completion of concrete finishing works.

Surface Defects Correction

After formwork has been removed, and curing completed, each concrete structure shall be visually inspected for surface defects. The points which shall be inspected shall be as follows:

(1) Levels of finished concrete.

(2) Alignment of Finished Concrete.

(3) Levels and Alignment of embedded items such as anchor bolts.

(4) Tolerances for levels and alignments

The finished surface of the concrete shall be checked for the following defects:

(1) Honeycombs.

(2) Spalling and dusting.

(3) Cracks.

(4) Depressions.

(5) Bulges.

(6) Abrupt irregularities

Repair of Foundation Surface Defects with Pre-Packed Grouting

(1) Hack all unsound and cracked concrete up to a depth exceeding 50mm. In areas where rebar is exposed, remove concrete behind rebar.

(2) For corroded rebar, loose rust scales shall be removed by wire brushing. Treat the rebar with an anti corrosion primer.

(3) Feather edges shall be removed along the perimeter of the hacked area by means of a disc grinder.

(4) Clean loose dirt and dust from the prepared surface using clean water.

(5) Pack clean, hand washed aggregates into hacked area and secure with a fine wire mesh.

(6) Install grout tight formwork to prepared surface and secure formwork with suitable ties.

(7) Dispense clean water into formwork assembly through inlet ports using a hand-operated grout pump. Ensure prepared surface and aggregates achieve Saturated Surface Dry condition (SSD).

(8) Mix grout with adequate quantity of water in a mixing drum. Ensure grout achieves a homogeneous consistency while stirring.

(9) Dispense grout mix into the formwork assembly through the inlet ports. Grouting shall proceed from the lower-most inlet port. As soon as grout is observed appearing from the adjacent port, lock off the first port and grout through the adjacent inlet port. Continue grouting in sequence until the entire formwork assembly is filled with grout.

(10) Remove formwork assembly and cure by means of curing compound or wet gunny sacks (burlap).

(11) If necessary, grind the surface to an even finish.

• CONCRETE
• CONSTRUCTION
• GEOTECH
• HOW TO GUI

WORK PROCEDURE – EXCAVATION

EXCAVATION is the preliminary activity of the construction project. It starts from the pits for the building foundations and continues up to the handing over of the project.

Materials and Tools Used:

The following are the materials used for the earthwork for foundation.

1. Spade,
2. Kassi,
3. Pick Axe,
4. Crow Bar,
5. Rammer,
6. Wedge,
7. Boning Rod,
8. Sledge Hammer,
9. Basket,
10. Iron Pan,
11. Line and Pins

Drawings Required

1. Centerline Drawing

2. Layout Plan

Size of Foundation

a. For Main Walls 4’0” Depth

b. For Partition Walls 2’0” Depth

Scope of the work:

• Setting out of corner benchmarks.
• Survey for ground levels.
• Survey for top levels
• Excavation to approved depth.
• Dressing of loose soil.
• Making up to cut off level
• Constructing dewatering wells and interconnecting trenches.
• Marking boundaries of the building.
• Constructing protection bunds and drains

Working Procedure

• The extent of soil and rock strata is found by making trial pits in the construction site. The excavation and depth is decided according to the following guidelines in the site

i. For Isolated footing the depth to be one and half times the width of the foundation

ii. For adjacent footings with clear spacing less than twice the width (i.e.) one and half times the length

iii. 1.5m in general and 3.5 m in black cotton soils

In this site open foundation pits for columns and trenches for CR Masonry was carried out. The maximum depth was upto 3m.

Setting out or ground tracing is the process of laying down the excavation lines and center lines etc. on the ground before the excavation is started. The center line of the longest outer wall of the building is marked on the ground by stretching a string between wooden or mild steel pegs. Each peg may be projected about 25 to 50 mm form the ground level and 2m from the edge of the excavation. The boundary is marked with the lime powder. The center lines of other walls are marked perpendicular to the longer walls. A right angle can be formed by forming 3, 4 and 5 triangles. Similarly, outer lines of the foundation trench of each cross walls and are set out.

Removal of Excess Soil

· Estimate the excavated stuff to be re-utilized in filling, gardening, preparing roads, etc.As far as possible try to carry excavation and filling simultaneously to avoid double handling. Select and stack the required material in such a place that it should not obstruct other construction activities. The excess or unwanted material should immediately be carried away and disposed off by employing any of the following methods.

• Departmental labour.
• Tractor.
• Trucks.

QUALITY CHECKS FOR EXCAVATION

• Recording initial ground level and check size of bottom.
• Disposal of unsuitable material for filling.
• Stacking suitable material for backfilling to avoid double handling.
• Strata classification approval by competent authority.
• Dressing bottom and sides of pits as per drawing with respect to centerline.
• Necessary safety measures observed.

QUALITY CHECKS FOR FILLING

• Recording initial ground level
• Sample is approved for back filling.
• Necessary marking/ reference points are established for final level of backfilling.
• Back filling is being carried out in layers (15cm to 20cm).
• Required watering, compaction is done.
• · Required density is achieved.

TYPES OF FOUNDATION FAILURE ON SOILS AND REMEDIES

Foundation failure can cause the building to collapse. Foundation is the first element of a building where the construction starts, but when it fails, it can cause many defects in the building including failure or collapse of the building. Repair of defects in foundations are most difficult and very costly, so it is most important to understand the types of foundation failure to avoid them by taking necessary steps before construction starts.

There are three main functions of a building foundation:

1. To sustain and safely transmit the loads from building / structure to the ground in such a way that it does not impair the stability or cause damage to the building or surrounding buildings.

2. The construction of foundations must safeguard the building against damage by physical forces generated in the subsoil.

3. Foundations must resist the chemical compounds present in soil to prevent corrosion to reinforcement.

The properties of soil have the major influence on the design, stability and sustainability of foundations to make it perform its functions.

Foundation failure due to Soil Movement:

When water present between soil particles is removed, the soil tend to move closer together. When water is absorbed by soil, the soil starts to swell. This movement of soil is based on the type of soil. Large movement is seen with clayey soils than sandy soils. These kind of movement of soil due to change in water content affects the foundation settlement. Foundation tends to settle to and excessive settlement of foundation may lead to differential settlement and damage to the structure.

Soil movement can occur due to following:

1. Presence of vegetation or remains of old cut tress

2. Presence of mining areas

3. Shrinkable soils

Remedies for foundation failure due to soil movement:

1. Use of pile foundations where the soil is shrinkable, so that forces are transferred to the hard strata or rock.

2. Taking the foundation levels down to avoid foundation on shrinkable soils.

3. The vegetation is removed from the construction site and its roots are removed. Any cavity due to roots of vegetation shall be compacted and filled with concrete.

4. Presence of any mining areas needs to be inspected and professional help shall be taken while construction new buildings in such areas.

Foundation failure due Settlement of Soil Fill

If the building is constructed on a newly developed land by soil filling, the foundation on such soils tend to settle more with time as long time is needed for such soil to settle and become compact to resist the loads from the building foundation.

Remedies:

It shall be ensured that such soils are adequately compacted before construction begins on them. The foundation depth shall be increased to the hard strata or rock below the filled soil or pile foundations shall be used to prevent subsidence of foundation.

SETTING OUT A BUILDING PLAN ON GROUND

A building is set out in order to clearly define the outline of the excavation and the centre line of the walls, so that construction can be carried out exactly according to the plan. The centre line method of setting out is generally preferred and adopted.

PROCEDURE.

                                               FIG 1

Example plan to be set out on the ground

 1. From the plan (fig 1), the centre line of the walls are calculated. Then the centre lines of the rooms are set out by setting perpendiculars in the ratio 3:4:5. Suppose the corner points are a, b, c, d, e, f and g which are marked by pegs with nails on top.

2. The setting of the corner point is checked according to diagonals ac, bd, cf and eg.

3. During excavation, the centre points a, b, c, d, e, f, g may be removed. Therefore the centre lines are extended and the centre points are marked about 2m away from the outer edge of excavation. Thus the points A1, A2, B1, B2 and like wise, are marked outside the trench. Centre line are shown clearly by stretching thread or rope. The centre points fixed 2m away from the excavation are marked with sit out pegs.

4. From the plan details, the width of excavation to be done is also marked by thread with pegs at appropriate positions.

5. The excavation width is then marked by lime or by with furrow with spade.

6. If the plan is much to complicated and follows a zigzag pattern, then the centre pegs are kept at suitable positions according to site conditions.

RCC WALL DESIGN GUIDELINES

1 The limiting slenderness ( ) if any for unbraced wall is 30 and for braced wall is 45

For short braced RC wall (< 12),

Pu = 0.4 x fck x Ac+ 0.67 x fy x Ast

3. For short unbraced RC wall, along with the above axial load Pu, the moment due to minimum eccentricity is checked for emin= t/20 or 20mm, where, M = P x e.

For the above axial load and moment, the RC wall is designed similar to RC column subjected to axial load and uniaxial moment.

Slender braced wall (< 45):

The additional moment due to additional eccentricity as per Table 1 of SP16 is considered. Where the additional eccentricity,

                                   

he additional moment due to eccentricity is added with the moment on the column and moment on the wall. The wall is designed for axial load with uniaxial moment.

5. For slender unbraced wall [ limited to 30]: Similar procedure as in case 4 is adopted.

                              

6.Detailing of reinforcement [IS456 Guidelines]:

a. For plain concrete wall, minimum vertical steel is 0.12% for HYSD bars and 0.15% for mild steel bar.

b. For RC wall, minimum vertical reinforcement is 0.4% of c/s

c. In plain concrete wall, transverse steel is not required

d. In RC wall, transverse steel is not required (not less than 0.4%)

e. Maximum spacing of bars is 450mm or 3t, whichever lesser

f. The thickness of wall in no case should be less than 100mm

g. If thickness is greater than 200mm, double grid reinforcement is provided along both the faces.

7. Detailing of reinforcement (BS 8110 guidelines):

a. Horizontal reinforcement same as IS456

b. Vertical reinforcement not to be greater than 4%

c. When compression steel is greater than 2% of vertical reinforcement, horizontal reinforcement of 0.25% for HYSD bars or 0.3% of MS bars are provided. [As per IS456, it is 0.2% for HYSD bars and 0.3% for mild steel bars].

                                                                                                    

d. The diameter of transverse bars (horizontal) should not be less than 6mm or 

8. Links are provided when the compression steel is greater than 2%. Horizontal links are provided for thickness less than 220mm. Diagonal links are provided when thickness is greater than 220mm. The spacing of links should be less than 2t and diameter of links not 

                         

less than 6mm or 

                                                                                 

1. Both ends fixed (Restrained against rotation and displacement) 

                          

2. Both ends hinged 

                                

3. One end fixed and other end 

                                     

4. One end fixed and other end hinged

              

RCC SLAB CASTING – WORK PROCEDURE

Materials and Machinery used

• Batching plant.
• Transit mixer
• Concrete pump
• Vibrators
• Chute and CI Pipes

Scope of the work

• Marking the slab
• Placing the reinforcement
• Form work for slab
• Placing the concrete

Reinforcement

It shall be as per BBS prepared according to approved drawing. The R/F shifting and binding shall be started as soon as shuttering is completed. R/F binding shall continue as formwork and shuttering work is progresses.

Concreting

Construction joint

The construction joint shall be pre decided and fixed prior to start of the concreting. It is planned to have two construction joints for main building as decided. In case of major break down of the Batching plant, the additional Construction joint may be left. The location of the construction joint shall be at the one-third span. Construction joint shall be straight and have profile of ‘L’shape so that successive layer of concrete shall be perfectly bonded with previous laid layer.

Preparation of construction joint shall include roughening, removing all laitance adhering to the joint and application of thick slurry before start of the new concrete.

Production and placement of concrete.

Stock of material shall be sufficient to start the concrete. It shall be ensured by stores/purchase dept that concreting is not stopped on account of materials.

All plant and machinery are checked and made in working conditions.

Concrete of grade M-25 shall be produced from our batching plant and directly pumped to the location of concrete placement through the pipeline. The pouring sequence shall be from grid A towards construction joint. Since the grade of concrete for column is M-40 and surrounding concrete is M-25, sufficient offset around column shall be casted with M-40.The offset dimensions shall be provided by PMC.

Proper walkways/platforms shall be arranged so that the supports of the pipeline and manpower are not directly stand on reinforcement.

Sufficient carpenters along with supervisor shall inspect the behavior of supports below the slab during the casting. Extra Props shall be stocked below slab to provide additional supports in case of any failure of supports.

Curing

The curing shall be started immediately after thumb set of the concrete laid. Hessian clothe /Plastic shall be covered over the set concrete to reduce moisture evaporation from the concrete during hardening and thus to minimize shrinkage crazy cracks. These cracks are inheriting property of the concrete specially appears during casting of flat surfaces.

Final curing shall be done by ponding and stacking water for minimum period of 7 days.

RCC SLAB DESIGN AND DETAILING GUIDE

RCC Slab design and detailing guidelines for depth of slab, loads on slab, reinforcement guide for one-way and two-way slabs have been tried to present here. Following are the RCC Slab Design and Detailing guidelines.

RCC Slab Design Guidelines:

 Effective span of slab.

Effective span of slab shall be lesser of the two

1.  L = clear span + d (effective depth )

2.  L = Center to center distance between the support

Depth of slab.

The depth of slab depends on bending moment  and deflection  criterion.  the trail depth can be obtained using:

• Effective depth d= Span /((L/d)Basic x modification factor)
• For obtaining modification factor, the percentage of steel for slab can be assumed from 0.2 to 0.5%.
• The effective depth d of two way slabs can also be  assumed using cl.24.1,IS 456 provided short span is ?3.5m and loading class is <3.5KN/m2

Type of support	Fe-250	Fe-415
Simply supported	L/35	L/28
Continuous support	L/40	L/32

Or, The following thumb rules can be used.

• One way slab d=(L/22) to (L/28).
• Two way simply supported slab d=(L/20) to (L/30)
• Two way restrained slab d=(L/30) to (L/32)

 Load on slab.

The load on slab comprises of Dead load, floor finish and live load. The loads are calculated per unit area (load/m2).

Dead load = D x 25 kN/m2 ( Where D is thickness of slab in m)

Floor finish (Assumed as)= 1 to 2 kN/m2

Live load (Assumed as) = 3 to 5 kN/m2 (depending on the occupancy of the building)

Detailing Requirements of RCC Slab as per IS456: 2000

Nominal Cover:

For Mild exposure – 20 mm

For Moderate exposure – 30 mm

However, if the diameter of bar do not exceed 12 mm, or cover may be reduced by 5 mm. Thus for main reinforcement up to 12 mm diameter bar and for mild exposure, the nominal cover is 15 mm.

Minimum reinforcement: The reinforcement in either direction in slab shall not be less than

• 0.15% of the total cross sectional area for Fe-250 steel
• 0.12% of the total cross-sectional area for Fe-415 & Fe-500 steel.

Spacing of bars: The maximum spacing of bars shall not exceed

• Main Steel – 3d or 300 mm whichever is smaller
• Distribution steel –5d or 450 mm whichever is smaller Where, ‘d’ is the effective depth of slab. Note: The minimum clear spacing of bars is not kept less than 75 mm (Preferably 100 mm) though code do not recommend any value.

Maximum diameter of bar: The maximum diameter of bar in slab, shall not exceed D/8, where D is the total thickness of slab.