Estimating quantities

Introduction to Estimating Quantities in Construction Management

Overview of Quantity Estimation

• The lecture introduces the principles of construction management, focusing on estimating quantities from drawings, using a boundary wall as an example.

• Key components of the boundary wall include piers (pillars), the wall itself, and barbed wires above a certain height.

• Understanding cost estimation requires identifying different work items, their quantities, and unit rates associated with each item.

Steps for Cost Estimation

• The process involves listing items (A, B, C, D), determining their quantities (e.g., square meters or cubic meters), and establishing unit costs for each item.

• Once all data is collected regarding items and their respective costs, total project costs can be calculated effectively.

Analyzing Drawings for Quantity Estimation

Drawing Interpretation

• A plan view of the boundary wall is presented to illustrate how photographs translate into technical drawings necessary for quantity estimation.

• Details such as thickness (230 mm), spacing between pillars (2.5 m center-to-center), and brickwork specifications are discussed.

Foundation Considerations

• The drawing indicates dimensions relevant to openings for gates and other structural elements that may affect overall design but are not part of this discussion.

• Specifications include plaster thickness (15 mm in 1:6 mortar), brickwork details in 1:3 mortar, and support structures beneath ground level.

Reinforced Concrete Pillar Details

Structural Components

• The reinforced concrete pillar's dimensions are specified as 230 by 300 mm with M25 concrete; it includes six 16 mm bars with stirrups at specific intervals.

• Footing dimensions are provided alongside reinforcement details crucial for ensuring structural integrity during construction.

Excavation Guidelines

• Excavation must allow an additional 200 mm beyond minimum width requirements to facilitate construction activities effectively.

Ground Level Restoration

Backfilling Process

• After constructing the boundary wall, backfilling ensures that original ground levels on both sides remain consistent post-construction.

Plastering Requirements

• Plaster extends 100 mm below ground level on both sides of the wall to enhance durability against environmental factors.

Identifying Construction Operations

List of Required Items

• Essential operations include excavation, plain cement concrete placement (PCC), brickwork installation, plastering application, shuttering setup, barbed wire installation, reinforcement work, and structural steel implementation.

Quantity Calculation Format

• A standard format is introduced for calculating quantities which includes item description along with required measurements leading to total volume calculations.

Earthwork Calculations

Trench Creation

• Earthwork involves creating trenches along the length of the boundary wall; specific lengths and breadth measurements are detailed for accurate volume calculation.

Final Volume Determination

• Adjustments made due to pillar placements lead to final earthwork volume being approximately 87.83 cubic meters after deductions.

Reinforcement Quantities

RC Pillars & Footings

• Total number of pillars estimated at 23; calculations yield approximately 4.25 cubic meters needed for pillars based on given dimensions.

PCC Volume Calculation

• PCC volume determined through similar methods used in earthwork calculations while accounting for necessary deductions resulting in about 3.78 cubic meters required.

Brickwork Estimates

Brick Dimensions

• Brickwork estimates involve calculating volumes based on clear distances between pillars leading to a total requirement of around 41.49 cubic meters after considering overlaps during construction processes.

Plastering Calculations

Surface Area Measurement

• Total area requiring plastering calculated at approximately 210.84 square meters factoring in height adjustments due to ground level considerations.

Shuttering Requirements

Support Structures

• Shuttering needs assessed based on perimeter measurements around columns and footings leading up to a total area requirement of about 83.61 square meters throughout construction phases.

Barbed Wire Installation

Length Requirement

• Total length needed for barbed wire installation amounts to approximately 220 m across four layers positioned atop the constructed boundary wall structure.

Calculating Steel Requirements for Construction

Footing and Bar Length Calculations

• A is set at 100, while B is calculated to be 720, derived from the footing size of 800 minus two times the cover of 40 mm. This calculation focuses on center line lengths rather than extreme lengths.

• The cut length totals 920, combining two segments plus the straight portion. The total required length of 12 mm bars for the footing is determined to be 296 m, equating to a weight of approximately .888 tons or 263 kg.

• An additional consideration includes a wastage factor of about 1% or half a percent. It’s noted that materials are not interchangeable; thus, spare bars may not be useful in other applications like pillars.

Pillar Bar Requirements

• For the 16 mm bars, a distance of 250 leads to a calculated length of 2825. The total number needed for pillars is specified along with their unit weight, resulting in a requirement of 670.5 kg.

Stirrups and Total Steel Calculation

• Stirrups require calculating lengths and breadth from drawings, including hooks in the total count. This results in needing approximately 139 kg of 8 mm bars for stirrups.

• The overall steel requirement for boundary wall construction sums up to around 1073 kg, with an allowance for additional weight due to potential wastages.

Reference Material and Assignments

• For further reading on this topic, reference B.N. Dutta's "Estimating Costing and Civil Engineering," specifically the latest edition available.

• An assignment involves completing a table detailing excavation quantities, brickwork involved, plastering details, etc., based on calculations made during class discussions.

• The session concludes with reminders about previous assignments related to structural angles needed for RCC pillars and summarizes key points discussed regarding boundary wall quantity calculations.