INTRODUCTION:

Waste management is one of the key concepts in the Lean Construction philosophy. Any improvement in building materials management on construction sites has the potential to enhance the construction industry’s performance with cost-saving benefits. For building construction, the structure that is most often built is reinforced concrete because it costs less than other types of structures. The major cost of the structure consists of concrete, reinforcing steel, and formwork. Concrete and reinforcing steel are permanent materials that exist along with the life of the structure while formwork is considered to be a temporary work that will be removed after the structure can support itself. One problem that a constructor often encounters is that there are a large number of lengths of reinforcing steels used in construction. The standard length in India is 12 meters. In construction, the required steel lengths are cut from the standard lengths, causing a large amount of wastes of reinforcing steels in a project. Construction waste has caused serious environmental problems in many large cities. In order compensate for the wastage, more than required construction materials are usually purchased. Reduction of such wastages can contribute significantly to the reduction in project cost and its environmental impact. Waste management also results in reduction of non-value adding activities on construction site.

BACKGROUND OF THE STUDY:

Several studies from different countries have confirmed that waste represent a relatively large percentage of production costs. The contributions of material wastage to project cost overruns have been calculated to be 11% as per a study conducted by the Hong Kong Polytechnic and the Hong Kong Construction Association. In Netherlands, the same has been calculated to be 20-30% of project cost overruns as per a study conducted by Boss ink and Bounwers (1996). Similarly, the contributions of material wastage to project overruns in United Kingdom has been reported to be 15% as per a study conducted by Skoyles in Tam et al. (2007). Identifying the extent of waste generated by the various building material and their implication on final project cost will be of immense benefits both to the environment and the construction industry of developing economies. Hence the need for the present study which aims at examining the effect of material wastage on construction sites on project cost and their mitigation measures.

OBJECTIVE OF THE STUDY:

The objective of this study is to find the effectiveness of various software in reducing waste of reinforcing steel from cutting and study its impact on improving the construction process.

Scope of this study:

1. Use RGS REBAR software and calculate project cost savings and improved efficiency in construction process

2. Use a linear programming model in Excel Solver for reducing rebar cut off wastage

MATERIALS AND METHODS:

Materials and tools:

1. A set of PC- CPU: with minimum 1 GB RAM

2. Software:

- Operating system: Windows XP & Above

- Other software package: AutoCAD, RGS Rebar, Microsoft Excel Solver (Office 7)

Methods

Optimization of Rebar using RGS Rebar

About RGS Rebar:

RGS REBAR is the state of the art Rebar Detailing software developed to meet the challenging quality requirements of large sized projects with frequent revisions and fast turnaround time. This product is developed by RGS-CAD, an experienced and highly respected international rebar detailing company. The main focus of RGS REBAR detailing software is to reduce scrap and off cuts generation. It provides a great option for the detailers to preview the possibility of off cut bars and scrap generated from the drawing in the stage of detailing itself. The detailers can adjust the detailing lengths without violating the engineer’s intent shown in the structural drawings. An optimized Bar Bending Schedule (BBS) / Bar list can be automatically generated. This Optimized Bar list will aid in savings in Fabrication. [1]

ADVANTAGES:

1. It can automatically generate bar list, placing list, and other reports

2. It has powerful filter options to select rebar entities

3. It also allows for partial take offs so that daily planning or segregated planning can be done

4. It also facilitates addition/deletion of bars from bar list already taken

5. BBS can be generated in the interface or also in excel sheets to facilitate execution at site

6. The bar marks can be easily tracked. It supports multiple country detailing codes

7. The rebar detailing can be globally outsourced and managed efficiently

8. The fabrication status, placement status, “Heat Number” of the stock rebar used to fabricate the bar etc could be found at the click of a button from the placing drawing

9. It also has many revision friendly tools in case of changes

1.1. Procedure For RGS Rebar Implementation:

Figure 1.Steps to follow for implementing RGS Rebar

1.2. Interface Of RGS Rebar:

RGS Rebar has IS 2502 detailing data included in it. So the bar shape desired is entered first followed by Stock Length , Bar Diameter, Center to center distance, lap length, Shear Bars , Bend Bars Coil Fabrication , Special Bends , Special Length. [2] After entering the basic required data the software automatically calculates the cutting length of the Bar with a unique Bar Mark.

Figure 2.RGS Rebar Data input interface

Case Study:

Embassy Manyata:

Highlights:

Embassy Manyata is one of the largest Business Parks in India. Developed across a sprawling 110.5 acres, housing 41 companies and catering to a workforce of 90,000. It is an integrated facility with commercial, residential, hospitality and retail components. The Business Park offers SEZ and Non-SEZ options for office occupiers. On an experimental basis, Building “G4” of the facility has been used in the analysis. The data was recorded till Ground floor roof construction [3] . The details of the project are as below:

Table 1.Project Details of G4 Building till 12^th Floor

SL No.	Description	Qty	Units
1	Cost	85	Cr
2	Area per floor	7654 (86 X 89)	Sqm
3	Floor	10+2
4	RCC	41800	CUM
5	Steel	4690	MT
6	CUM/Slab	1400	CUM

Data Collection:

The data were prepared from the detailed Reinforcement drawings of Beams, Columns, Slab etc. from excavation till Ground Floor Roof Construction of Building “G4” as mentioned earlier.

Output Without RGS Rebar:

Table 2.Rebar Wastage when BBS Prepared and cut manually

Sl No	Component	Units	Concrete Qty	BOQ Steel Qty	Actual Site Report	% wastage
1	FOOTING-G3-Teak	Cum	4235.12	169.40	176.18	3.85%
2	Grade slab ,Grade Beam	Cum	1234.96	98.80	101.96	3.10%
3	UB TO GF COLUMN	Cum	350.30	70.06	72.58	3.47%
4	Ground Floor Column	Cum	310.00	62.00	64.29	3.57%
5	Upper basement floor Slab	Cum	1449.91	159.49	164.12	2.82%
6	UB Beam	Cum	109.00	19.08	19.78	3.57%
7	Ground Floor Slab	Cum	1402.78	196.39	201.89	2.72%
8	GF Beam	Cum	292.00	56.94	59.16	3.75%

Output With RGS Rebar:

Table 3.Rebar Wastage when BBS Prepared by using RGS Rebar

Sl No	Component	Units	Concrete Qty	BOQ Steel Qty	Actual Site Report	% wastage
1	FOOTING-G3-Teak	Cum	4235.12	169.40	170.25	0.50%
2	Grade slab ,Grade Beam	Cum	1234.96	98.80	99.39	0.60%
3	UB TO GF COLUMN	Cum	350.30	70.06	70.27	0.30%
4	Ground Floor Column	Cum	310.00	62.00	62.37	0.60%
5	Upper basement floor Slab	Cum	1449.91	159.49	159.81	0.20%
6	UB Beam	Cum	109.00	19.08	19.21	0.70%
7	Ground Floor Slab	Cum	1402.78	196.39	197.96	0.79%
8	GF Beam	Cum	292.00	56.94	57.28	0.60%

Comparison Of Outputs

Table 4.Comparison of the wastage in rebar while manual BBS preparation and while using RGS Rebar

Sl No	Component	Units	Manual Qty	RGS Qty	Variance (MT)	Cost Saved
1	FOOTING-G3-Teak	Cum	176.18	170.25	5.93	326,104.38
2	Grade slab ,Grade Beam	Cum	101.96	99.39	2.57	141,279.93
3	UB TO GF COLUMN	Cum	72.58	70.27	2.31	127,157.81
4	Ground Floor Column	Cum	64.29	62.37	1.92	105,710.00
5	Upper basement floor Slab	Cum	164.12	159.81	4.31	236,842.98
6	UB Beam	Cum	19.78	19.21	0.57	31,473.75
7	Ground Floor Slab	Cum	201.89	197.96	3.93	216,027.97
8	GF Beam	Cum	59.16	57.28	1.88	103,346.10
				TOTAL	23.42	12,87,942.92

Cost Of Implementation

Table 5. Total Cost of implementation of RGS Rebar

Sl No.	Software Name	Type	Price(Rs)
1	Autodesk AutoCAD 2015 Commercial	Standalone	1,90,806
2	RGS Rebar	Standalone	40,000
		TOTAL	2,30,806

USING EXCEL SOLVER:

About Excel Solver:

A model in which the objective function and all of the constraints are linear functions of the decision variables is called a linear programming problem. Excel includes a tool called Solver that uses techniques from the operations research to find optimal solutions for all kind of decision problems.

FEATURES:

It may be used to solve linear and nonlinear optimization problems.

It allows integer or binary restrictions to be placed on decision variables.

It can be used to solve problems with up to 200 decision variables.

Collecting data:

The data needed for the analysis are bar bending lists that show types, sizes, lengths, and number of each reinforcing steel bars used in construction. This data are used to generate possible cutting patterns. The data were collected from construction projects that already had prepared bar bending schedules.

Table 6. Sample site BBS for input

Bar mark	Bar Dia	Length (mm)	Quantity
1	20	11850	6
2	22	3000	2
3	22	3500	48
4	22	4000	30
5	22	4500	2
6	22	5000	36
7	25	3500	2
8	25	4000	18
9	25	5000	30

1.3. Develop a subprogram for inputting data:

A subprogram for inputting data is needed in order to keep the data as a file that can be accessed later. The data include the lengths of reinforcing steels and the amount of reinforcing steel for each length.

Table 7. Program in Excel solver for Minimization

Assumptions:

1.The summation of lengths of reinforcing steels in any pattern cannot be greater than 12 m. (Standard length).

2. The number of bars required are integers and finite.

Develop subprograms for calculation process:

Table 8. Setting Variable cells and constraints in Excel Solver

Objective function:

Min Z = C1 * X1 + C2 * X2 + …………+ Cn * Xn

Constraints:

L1: a11 * X1 + a12 * X2 + …………+ a1n *Xn = b1

L2: a21 * X1 + a22 * X2 + …………+ a2n *Xn = b2

: : : :

Lm: am1 * X1 + am2 * X2 + ………+ amn *Xn = bm

Xj ≥0 and integer for j = 1 to n

Where:

Min Z = the objective function. For this model, it is to minimize waste from cutting steel

Cj = fraction of reinforcing steel in group j which is unutilized ; j = 1 to n.

Xj = input variables’ = 1 to n.

aij = coefficients

bi = amount of steel for each length

This subprogram generates all possible cutting patterns using data from the previous step. Each pattern will be checked with the assumptions 1, and 2. Only if it passes the assumptions, then the pattern will be used as a variable.

Developing mathematical model:

This subprogram uses the string variables from the data files in the previous steps to generate the mathematical model in a matrix form (m x n). The mathematical model includes variables (Xj), coefficients (aij), waste (Cj), and amount of steel for each length (bi). The mathematical model will be saved in a data file.

Solving the model:

The model from step 2.2 can be solved using any mathematical programming software, for instance, Microsoft Excel Solver. However, to eliminate interfacing issues between different software programs, this research uses a subprogram that has been developed by the author in order to solve the model. The subprogram is verified by comparing the solution from the subprogram with the solution from a standard software. The solution from the subprogram will be saved in a data file for the next step.

Obtaining Output:

This subprogram generates output using the solution in the previous steps. The output shows the number of cutting patterns needed, standard length(s) used, and the fractions from the cutting patterns.

Table 9. Output in Excel Solver after running the Minimization Linear Program

RESULTS AND DISCUSSION:

Table 10. Result Obtained in Excel Solver

• We require 22 (15+4+3) No. of full 12 m bars.

• 15 Bars will be cut as (5000+5000)

• 4 Bars will be cut as (4000+4000+4000)

• 3 Bars will be cut as (3500+4000+4000)

CONCLUSIONS AND RECOMMENDATIONS:

Using RBS REBAR software, the cost savings in the case study project from foundation to ground floor slab (includes 2 basement floors) alone have worked out to be Rs. 12 lakhs (approximately). The overall cost savings for the entire project which includes numerous towers could be enormous. The average wastage as per manual BBS is 3.36%. The wastage using RBS REBAR software works out to be 0.53% which is 23.42MT savings in steel. After comparing all the pros and cons of both the methods the authors would recommend to use RGS Rebar for projects which have a large amount of steel reinforcement involved in the construction work and by using this software they can incur a substantial amount of savings by reducing rebar wastage. On the counterpart, use of Excel solver is suggested on every site because the steelyard bar cutting is done as per the BBS Sheet supplied by site officers and without considering the proper cutting pattern to reduce off-cut bars.

REFERENCES:

1. About RGS Construction Teshnologies - site: http://www.rgsrebar.com/download/DEMO/RGSREBARDEMO.pdf

2. RGS Rebar Interface – site: http://www.rgsrebar.com/rebar.aspx

3. Embassy Manyata, Business Parks in Bangaloresite:http://www.embassyofficeparks.com/park/embassy-manyata

4. Santi Chinanuwatwong - Reducing Waste from Cutting Reinforcing Steel in Construction Projects - Kasetsart J. (Nat. Sci.) 34 : 526 - 535 (2000)

Received on 14.11.2015 Accepted on 22.12.2015

Int. J. Tech. 5(2): July-Dec., 2015; Page 329-334

DOI: 10.5958/2231-3915.2015.00043.7