Can Composite Structures and Steel be used in Medium-rise Buildings?

Using steel as building material people talk about LGFS (Light Gauge Framing Systems)buildings up to 2-3 stories and composite structures in high rise buildings. Yes in all highrise buildings one must have to consider steel as important building material and no onecan ignore composite structure in a high rise building. Steel and composite structure helpsin reducing mass of the building which is very important in a high rise. In a high rise, wetalk of high wind loads, high seismic loads, soil bearing capacity, overhead costs,temporary form cost & cost of cranes etc. Keeping all these things in mind steel usingcomposite structure offers lot many solutions and these concepts are used world over. Butin India we are not using these advanced technologies so much. In India we are notmaking so much high rise but why we are not focusing to use these technologies inmedium rise buildings where it offers the same advantages as in high rise.

In a medium rise building we can use similar frame structure as we are using in a RCCbuilding. Frame structure of a building need to be built using steel columns and beams.UC (Universal Columns) sections in high strength steel should be used for columnswhich are now available in India. These sections are quite compact sections and havinghigh steel thickness. These sections are most robust sections and used widely world over.UC sections help in reducing size of a column, H section offers ease in bolt connectivity,by encasing concrete on top of it gives it composite nature which in turn gives furthersavings in structure cost. Rusting is never a problem using UC section due to higher steelthickness. It is considered that cost goes high using these sections compared to tubes orbox columns. If UC sections are used in a column it does not increase much cost butoffers so many advantages over box columns. Beams need to be fabricated using highstrength plates as per span requirement. Composite beams offer savings of around25-30% in steel as concrete slab is joined with beams using shear studs. Steel joistsspanning 3-4m offers most economical and simple design. These beams and columns arejoined using high strength nut and bolt where there is no welding at site. Simple pinconnections are most preferred in place of moment connections and bracing are used tostabilize a building. Bracings offer higher stability to a building compared to momentconnections but a combination of both can be used as per requirement.

Is it safe in comparison to a RCC building?

In a RCC building formwork is quite expensive and cumbersome. Using steel we caneither eliminate formwork or reduce it to negligible levels. Using steel columns andbeams there is no need of formwork. Once frame structure is ready, galvanised deckingsheets are used to replace temporary formwork. These sheets are prefabricated and cut insizes as per building plans and supplied at sites along with required trims. After fixing ofdeck sheets trims are fixed along the edges for concrete casting. 25-30% concrete is savedin slabs using these deck sheets having similar RCC properties. Welded mesh of 6 mmwire with 200mm c/c is required in RCC slab. Once studs are fixed welded mesh isplaced on top of deck sheet before concrete casting. Studs are welded at site using aspecial machine which can be operated by any person with 1-2 hours training. In a single

shift 5000 studs (area 800 sqm) can be easily fixed using one machine.

What is the cost of Steel in comparison to a RCC building?

In a medium-rise building, up to 7-8 stories, Steel consumption is around 5.5-6 Kg/sqft.The cost of steel building in comparison to a RCC building is almost same or 10%expensive now. But as its use will increase, cost of composite steel building will be lowerthan a RCC building.