Keywords

1 Introduction

The main goal is to have a sustainable economic growth by improving the life of citizen. For this, the terms sustainable cities, smart cities or new technology communities are coined. There are many components of a smart city like energy, governance, environment, mobility and building and services. The use of advanced material as one of the parameters is for judging the smart city network [1]. As per [2] the smart building is defined as a component of smart city and for that focus is given on the selection of innovative materials. As per [3] apart from sustainable environment, smart communication spaces, smart devices and smart cities also refer to a city using smart material. The smart material refers to a material having superior strength, ductility, toughness, initial and life cost efficiencies, ease of manufacture and application [4]. As per [5] smart structure is defined as the key component of smart city which apart from fulfilling technical criteria must also fulfil economic, sustainability and environment criterion. Therefore, there is a need to look beyond conventional steel and RCC framed structure and focus on those advanced construction technologies and materials which have better properties in terms of durability, sound insulation, earthquake resistance, strength and at the same time the project can be completed in lesser time with cost feasibility. As per [6] in his research titled “Smarter Material for Smart Cities” there are eleven smart materials defined, TMT bars was one of those. It is manufactured primarily from recycled scrap. Reinforcement with this higher capacity could provide various benefits by reducing member cross sections and reinforcement quantities, leading to savings in material, shipping, and placement costs. MMFX2 rebar can be found in the world’s best-engineered construction projects. Since 2002, this revolutionary steel product has been specified in public infrastructure and public/private development projects throughout the USA, Canada, Mexico and the Middle East.

2 Methodology

The methodology involves exploratory research on MMFX bars. To achieve the objective a building is modelled on ETABS 2016 using MMFX as well as Fe-500 bars as per case study. The ETABS 2016 model is then analysed for various structural properties and a relationship is defined among structural parameters of design and cost modelling after taking values of the various loading conditions according to the case study model. Then, at last a cost model is obtained from the relationship established.

3 Comparison with Stainless Steel Rebars

MMFX bars were invented at the University of California by Prof. Gareth Thomas [7]. The organisation based in USA, producing MMFX bars is the MMFX Steel Corp [8]. The MMFX bars have higher strength, fatigue resistance and ductility as compared to other high-strength bars because of its microstructure laminated lathe structure. Because of these changes at microstructure level MMFX bars has longer service life as well as lower construction cost. In terms of corrosion resistance, MMFX is similar to stainless steel. Comparing service life span both MMFX bars and SS rebars gives 100 years of service life but cost-wise MMFX is not even half of the cost of SS rebars if comparatively similar strength bars is selected as per American scenario [9]. As per Virginia Transportation Research Council (VRTC), the MMFX products are designated as the most cost-effective solution [10].

Further, MMFX rebar can be handled just like conventional steel bars, without the special handling requirements associated with SS bars. For example, MMFX is not considered dissimilar to carbon steel for galvanic corrosion purposes. Therefore, MMFX does not need to be isolated from carbon steels in construction, as SS bars do.

The drawback to reinforcing steel is its susceptibility to corrosion. One of the potential alternative to this problem is MMFX bars. MMFX bars do not corrode and come in many different forms that lend themselves to both exterior application for rehabilitation of existing RC columns and use as internal reinforcement to extend initial design life. As per [11] MMFX bars reduce the vulnerability of reinforcement to corrosion and works as an effective high-strength bar. The MMFX bars as compared to the conventional steel when used in an experiment provided better crack control after the yielding [12]. MMFX bars have the yield strength of approximately 828 N/mm2 [13].

4 Structural Modelling of six Storey Commercial Block

The case study of a building considered is a super structure with the plan as shown in Fig. 1 Structural plan of building considered for case study. The building is modelled using ETABS 2016 having dimensions of 19 × 13.5 m and it is of six storey (G + 5). The building in the study considered is a commercial block with column, beam and slab type framed structure with shear walls. Since the effect of MMFX bars is being checked, the building is first modelled using Fe-500 conventional bars and then using MMfx bars. The building has non-uniform grid in both the directions. There are three different types of column which are 22 in numbers along with three different types of beams. The shear wall is provided in the lift core.

Fig. 1
figure 1

Structural plan for building considered for case study showing columns C7 and C20

Full size image

The structural model of building is prepared, analysed and designed in ETABS 2016 version. The load combination for different types of forces is applied on the structure. The member sizes and details are fixed by analysing the structure. Analysis is performed and results are compared for base shear, support reactions, storey drift, mode shapes, etc. The following criteria are assumed while analysing the building:

  • The floor diaphragm is assumed to be rigid.

  • Dynamic analysis to be performed using response spectrum method.

  • All dimensions are in m, unless otherwise specified.

  • The size of the framing plan is 19 m × 13.5 m.

  • The framing plan is assumed to be Special Moment Resisting Frame (SMRF) (Table 1).

    Table 1 Structural modelling of building
    Full size table

The modelling design and analysis are done using ETABS 2016 software. The building is analysed and designed for conventional Fe-500 and MMFX bars. The effect of brickwork is also taken into account along with the portal frame.

The storey and grid systems are defined and then the material properties of different items taken in the structural modelling followed by the load cases, then the earthquake resistant design parameters.

5 Modelling Results

It deals with both the structural comparative analysis was done using ETABS 2016 as well as cost comparative analysis of building modelled using Fe-500 and MMFX grade 100 bars. The below-mentioned graphs are showing storey drifts when the rebar is changed for Fe-500 to MMFX grade 100 rebars.

It is observed from Fig. 2 that storey drift for building with Fe-500 is more than building modelled using MMFX bars. The changes in the properties of MMFX bars in comparison to Fe-500 may be the reason behind this (Figs. 3 and 4).

Fig. 2
figure 2

3D view of commercial block modelled in ETABS 2016

Full size image
Fig. 3
figure 3

Representation of storey drift in X direction when the rebar is changed for Fe-500 to MMFX grade 100 rebars

Full size image
Fig. 4
figure 4

Storey drift in Y direction for Fe-500 and MMFX grade 100 rebars

Full size image

The same happened with storey drift in Y direction, because of the changes in the material properties of MMFX bars as compared to conventional FE_500 bars (Figs. 5 and 6).

Fig. 5
figure 5

Percentage variation of moment in column C20 (middle column)

Full size image
Fig. 6
figure 6

Percentage variation of moment in column C7 (front right corner)

Full size image

As per the architectural plan shown in Fig. 1, the middle column (C20) and the front corner column (C7). The variation in moment is about 5–17% on different stories for the same column modelled using Fe-500 and MMFX bars. The variation in moment is due to the different properties of Fe-500 and MMMFX bars (Table 2).

Table 2 Weight of steel obtained in building modelled using Fe-500
Full size table

6 Reinforcement Quantity Calculation and Comparison

The area of reinforcement calculated by ETABS is further modified after the detailing done by using conditional formatting function of MS-Excel and the actual area which is got at the end is used for further calculation of cost. The same procedure is repeated for building modelled both using Fe-500 bars as well as MMFX bars. The total quantity of reinforcement thus obtained is summarised in Table 3 as follows in and the summary of total quantity if reinforcement for MMFX bars is made in Table 4.

Table 3 Weight of steel used in building modelled using MMFX grade 100 bars
Full size table
Table 4 Cost of importing MMFX rebars at Delhi location
Full size table

7 Cost Comparison

The rate of the Fe-500 bars is taken for Delhi location from site with the brand name of TATA Tiscon TMT Steel Bars. The rate is ₹33,560/ton, which is ₹33.56/Kg. Similarly, the rate for MMFX bars is taken from the site negotiated rate at Dubai location which is 2600 Dirhams/ton.

Excluding Fe-415 bars which are used for shear reinforcement, as per Table 5, the total quantity of Fe-500 and MMFX grade 100 bars are as follows.

Table 5 Cost comparison of Fe-500 and MMFX bars
Full size table

The cost of MMFX bars is higher than the cost of Fe-500 by 25%. Hence, the benefit–cost ratio comes out to be negative which shows non-feasibility for such scale projects.

8 Inferences

The following inferences are drawn from the study done in this research:

  • The MMFX bars have superior strength and corrosion resisting property than conventional Fe-500 bars due to its nanostructural arrangement.

  • The exploratory study shows that there is no such Indian Standard code which defines the use of MMFX bars in Indian context.

  • The density of MMFX bars is slightly more than that of Fe-500 bars (negligible).

  • The minimum yield strength of MMFX bars used in this case is 690 MPA and that of Fe-500 is 500 MPA. The former is 38% more than the later one. This results in stiffer structure.

  • The quantity of reinforcement obtained in the modelling done using MMFX bars is 29,378 kg and the quantity of reinforcement consumed in building modelled using Fe-500 bars is 34,281 kg. The quantity of reinforcement saved in the modelling done using MMFX bars approximately 16.69%.

  • The cost of reinforcement obtained in the modelling done using MMFX bars is INR 1005069 and the cost of reinforcement obtained in building modelled using Fe-500 bars is INR 1254986. The cost difference of 25% is seen as per the study.

9 Conclusions

As seen from the above results, the MMFX bars are better for storey drifts in both X and Y direction. The case study considered in this research is of a mercantile building with six storey. Even after saving 16.69% of reinforcement as compared to Fe-500 bars, the import cost shows that the cost of reinforcement is approximately 25% higher if we opt for MMFX rebars. The possible reasons for this higher cost are that, in this case, the building is considered is of six storey only, and hence the lesser amount of reinforcement is used as compared to tall buildings in terms of total weight of reinforcement. The fright charge from Dubai to Kolkata and the transportation cost from Kolkata to Delhi may have decreased if we would have ordered the same MMFX bars in bulk against the present ordered quantity of just 20 ton. As the code does not takes into consideration of MMFX bars, this study is a kind of way forward for the use of MMFX bars in Indian context as an innovative material for building smart cities but can not be treated as recommendation for use of MMFX bars.