Using in situ reinforced Concrete and level slabs and composite steel frames in two different locations and design were commissioned for typical commercial office edifices located in the UAE ‘ABU DHABI industrial area- B-C1, B-S1 and
B-C2, B-S2.the edifice were based up on 7.5 ten 7.5 thousand structural grids, tablet foundation and specification suited to local
Market conditions public presentation and cost Criteria dictated square air ‘ conditioned edifice with drape palisading on the
B-C1 and B-S1rectangular of course ventilated edifice with insularity block in work facing on the B-C2 and B-S2.
The designs were
Taken up to normal system phase, the lone different being straight attributable to the structural frame stuff
Budget costs were assigned to all elements of building ‘from infrastructure, superstructure and external walls
Through to external plants, and preliminaries.
Findingss in footings of overall building cost, the seven storey steel- framed edifice was found to be 5.5 % more expensive than the Concrete equivalent on the B2 site and, 2.6 % more expensive on the B1 site. The three-storey steel-framed edifice was Found to be 5.2 % more for the rectangular B2 edifice and 2.6 % more for the square B1 edifice. The steel edifices had between 0.30 and 1.48 % less net getable country. The differences in cost are greater if net floor country is considered instead than gross. With respect to overall velocity of building, the survey found little to take between the two stuffs.
Analysis of building costs shows that the most important nest eggs occur with the edifice frame. For illustration, the combined Cost of construction and internal walls of the three-storey edifice in Reading ( B1 ) are 32 % more utilizing a steel frame instead than concrete.
Rectangular steel edifices had 10 % more external facing. The consequences indicate that concrete building gives more liability infinite and leads to take down Finance costs. Apart from the frame stuff, the sizes of cost derived functions are chiefly related to be after form, figure of floors and the type of airing.
B1 Roof Plan:
B-2 Roof Plan:
Main decisions
The chief decisions are that, for a broad scope to edifices, taking concrete instead than steel can give up to:
* 24 % nest eggs in frame costs
* 5.5 % nest eggs in overall building costs
* 1.5 % more getable country with:
o equal overall building times
O And lower finance costs.
2-Introduction
The Cost Study was undertaken to supply both a comparing and an apprehension of the building costs Associated with concrete- and steel-framed edifices.There has been much argument over the comparative virtues of the two signifiers of building, peculiarly in footings of cost and velocity, but really small dependable published information Exists. Constantly altering market conditions, gauging patterns, contract conditions and monetary values have confused the issues involved. It rapidly became evident that a elaborate survey, covering a scope of edifices, was required in order to derive comprehensive image. The aim of the survey was to supply an impartial comparing between Concrete and steel frames for edifices of three- and seven-storeys in the UAE ‘ABU DHABI industrial country ; indistinguishable specifications were required with the lone allowable fluctuations being straight attributable to the stuff used in the Structural frame.
The cost theoretical accounts were developed utilizing best current pattern for both concrete and steel and are reported upon in
This publication to an extent the pick of edifices has influenced the replies obtained ‘and inquiries raised ‘
.nonetheless these, and the factual Aspects of the survey, raise many interesting issues for those commissioning, planing
And building edifices in the 1999there are many utile decisions to be drawn. The publication of this
Work is intended to carry through several map.First, to exemplify the existent difference between
Building in concrete and edifice in steel.Second, to set an in situ concrete ‘sponsored cost theoretical account survey against
Those prepared by the steel and precast concrete industries in the past. Third, to give the Designer & A ; contractors more information to design and constructing for lower cost edifice to be economize.
3-Method of survey
Brief
The brief given to the design squad asked for the strategy designs of multi-storey B-1and B-2. The designs,
In concrete and steel, were to reflect modern-day commercial pattern and the design squad ‘s best Judgment.
They would be used for fixing Budget costs, doing comparings and for look intoing other issues.
Concepts and initial surveies:
The edifices were to be located in the B1and B2 expressway corridors and were attributed to be section & A ; gauging severally local market conditions prescribed building cost budgets, for the intents of the survey, of 75AED/ft2 & A ; 55 AED/ft2.these budgets indicated that different specifications and designs were required for each location.the edifice constellations hence reflect the two different budgets, being chiefly associated with the usage or non of air conditioning.
The form and signifier of the edifices were determined to accommodate local demands in footings of public presentation and cost and non to favor concrete.
The budget B1 corridor edifices permitted the usage of an all-air VAN or fan coil unit air-conditioning system. The usage of air
Conditioning called for a square envelope, in order to minimise the wall to floor ratio, arranged around a cardinal services nucleus. Performance, cost and architectural standards allowed for curtain-wall facing. The budget for the B2 edifices merely allowed for natural airing with convection warming. The demand for cross airing meant that these edifices were configured into two wings of 15m deepness, organized around a cardinal nucleus.
Initial layouts affecting in board columns and cantilevers were non pursued as they may hold unduly favorite concrete. Originally six-storey edifices had been envisaged.they were non pursued as the steel strategies would hold needed firemen ‘s lifts whilst The concrete strategies would non investigations to find the optimal structural grid for the proposed edifices were carried out.grids of 7.5 ten 7.5m, 9.0×6.0m and 9.0×9.0m were considered.
Based upon overall undertaking costs and floor country computations, the 7.5×7.5 m and 9.0×6.0m grids appeared to be optimal for the steel strategies and the 7.5×7.5m grid appeared optimal for the concrete strategies. Therefore, the 7.5×7.5m grid was established as optimum for both stuffs and locations, and was adopted for all edifices in the survey.
Architectural floor programs were adjusted to suit.
These initial surveies hence determined the footing for the survey. Concrete and steel framed options were to be developed utilizing two floor constellations each at three and seven floors. Therefore, eight strategy designs were to be undertaken to give four braces of edifices for comparing. And need all paperss to give Integrated Study.
Overall Costss
In footings of overall building cost, the Steel-framed edifices were found to be between 2.5 and 5.5 % more expensive Than their concrete equivalents, as illustrated in the figure and tabular array below, the seven-storey steel-framed edifice on the B-2 was found to be 5.49 % more expensive than its concrete Equivalent and on the B-1 site 2.55 % more expensive. The three-storey steel-framed edifices were found to be more expensive than their concrete equivalents, bing 5.18 % more for the Rectangular B-2 edifice and 2.61 % more for the square B-1 edifice. These figures are based on cost per M2 of gross External country. The differences in cost would hold been greater if net Floor countries had been considered ( see costs per cyberspace gettable country ) & A ; see table no 10-1.
Cost Savingss
Analysis of building costs showed that the most important nest eggs occurred with the superstructure, with noteworthy
Contributions from the external facing and internal planning. For illustration, the combined cost of the superstructure and he-man breakdown ( internal planning excepting doors ) for the three-storey steel-framed B-1building is 32 % greater than the concrete-framed edifice. Rectangular steel edifices had 10 % more country of external cladding than their concrete-framed equivalents.
SUBSTRUCTUES
Costss for the land floor slab and associated land works appear to be indistinguishable. Foundations for the steel-framed edifices cost between 2 1 % and 47 % less than the concrete equivalents. This is the effect of smaller tablet foundations for the igniter steel frame. The foundations in the theoretical accounts must be regarded as being really simple.
Table 10-1 Over cost
General note * cost AED ( Dec1999 ) per gross external M2
**Percentage differences, steel, concrete
Superstructure
The construction of the steel-framed edifices cost between 24 % and 32 % more than the concrete equivalents. This is chiefly due to the extra disbursal office protection for the steel frame. .
External Facing
The external facing ( chief lifts and roof works facing and screens ) of steel framed edifices cost between 1 % and 9 % more than for the concrete framed edifices. Costss of roof works facing and screens are the same. Cladding to the chief lifts costs between 1.5 % and 9.6 % , more on the steel framed edifices. The cost is related to the country of facing required. This is due to the necessary additions in storey highs, from 3990mm to 4ll0mm on the B-1 strategies, and from 3300mm to3600mm on the B2 strategies, to suit the increased allowance for the structural zones of 340mm and 660mm.
Table 10-3 Structure costs
* Glass drape wall @ DH 275/m2
# Brick pit wall @ DH190 /m2
Internal Planning
The internal planning ( stud dividers and internal doors ) of steel-framed edifices costs more than for concrete framed edifices. Stud Partitioning is between 26 % and 63 % more expensive in the steel-framed edifices than in the concrete equivalents. This is due to the double usage of the concrete wall columns and nucleus walls for both construction and internal walls in the concrete strategies.
ROOF FINISHES AND INTERNALM FINISHES, FIXTURES AND FITTINGS
There was small or no discernible difference between the concrete and steel frames with respect to the cost of roof coatings and fixtures and adjustments.The little fluctuations in internal coatings reflect the different getable and non ‘gettable countries and the dissimilar floor heights..
MECHANICAL AND ELECTRICAL SERVICES
There was no difference between concrete and steel frames with respect to the cost of the lifts, mechanical services, electrical installing or builders ‘ work in connexion with services. This is due to the premise that the frame Material had no influence on services Provisions.
Preliminaries
The budget for preliminaries for each brace of edifice was based on a ball amount to let for one ‘off points such as Establishing site, Crane bases etc. , and a amount per hebdomad to let for supervising and hire charges. Preliminaries Costs hence vary harmonizing to the difference in the Programmers ‘ . Detailed consideration of preliminaries, e.g. Sizes of Cranes, hire continuances, etc, was beyond the range of this survey.
External plants
There was no difference between concrete and steel With respect to external plants,
Table 10-5 Preliminaries costs
Table 10-7 NET/GROSS RATIOS
Table 10-9 CONSTRUCTION PROGRAME DURATIONS
Table10-11 ADDITIONAL COST OF AIR CONDITIONING
Areas
The brace of edifice were designed to hold the same gross external and gross internal floor countries. The steel edifice had between 0.30 % and 1.48 % less net getable floor country than the concrete edifice.This is chiefly due to the extra countries required fit lavatories and nucleuss around the steel construction. The floor Area lost to suit steel Bracing is notable. The B1 steel strategies have Ground floor response lobbies some 20m2 larger than their concrete Equivalents, due to architectural Considerations. Nonetheless, had Identical response anterooms been used, the steel edifices would still hold had between 0.5 % and 1.24 % less net getable floor country.
Net getable Areas
The difference I countries are besides reflected in the net to gross internal floor country ratios.
Costss per cyberspace getable countries
In footings of the cost per getable country, the steel ‘framed edifices were found to be between 3.7 % and 6 % more expensive than their concrete framed equivalents. The derived functions were found to be Greater for the B-2 edifice compared to the B1 edifice and greater at 7 floors instead than 3 floors. Analysis of the costs per cyberspace getable Area reveals that most nest eggs emanate from the superstructure. Significant Savings besides arise from the external Cladding, internal planning and mechanical and Electrical services.the salvaging apparent from M & A ; E services is wholly due to the difference in the net getable countries.
Construction programmes
The building coders for the concrete strategies are up to two hebdomads faster than their steel equivalents. This is due to the demand to fire cogent evidence steelwork, the effects of fire proofing on the Programmers, and, on the B2 theoretical accounts, Additional sums of external Cladding. Steelwork frames can get down earlier and are erected quicker than their concrete equivalents. This allows the external Cladding and roof coatings get downing and, to some extent, completing Oklahoman. However, the Fire proofing of steelwork wholly eliminates this early advantage. This activity requires each floor to be have oning her tight before margin inside informations can be completed. The false external facing and roof coating inside informations must be basically complete, before fire proofing can be completed. The net consequence is to detain the effectual starts of fire shell, 1st hole and subsequent critical Activities. The extra measures of external block work cladding on the B-2 steel. Framed edifices called for larger pack sizes than the concrete edifices. One or two hebdomads would hold been added to this critical activity had the same pack sizes been assumed. The continuances of 1st hole trades, 2nd hole trades and fixtures and adjustments are basically the same. In the steel options, the start of 1st hole trades is governed by fire proofing. Little differences in measures appear to do small difference to the coders. By and large, the steel Frames allow an earlier start and extra float on so on-critical mechanical and electrical elements. However, the float for lifts on the B1-S7building is less than for the B-1C7 edifice. External plants are non-critical. The B-2 edifices take longer than their B1 equivalents. Whilst the B2 edifices can be treated as two halves and starts made earlier, completions are controlled by the two halves coming to garner over the nucleus countries. They besides have extra measures of cladding
Overall procurance times
Traditional signifiers of contract under Traditional signifiers of contract the pre-contract period was assessed as being 20 hebdomads for all edifices, leting two hebdomads for contractor mobilisation. Differences contract coders ‘ ( and hence overall procurance times under traditional ball amount signifiers of contract ) flexible joint on the allowances required for steel ‘s long lead-in clip.This lead-in clip causes possible hold which can merely be absorbed by pre-letting ( as assumed ) . Had stamps, mobilisation, foundations and / or substructures taken longer, steel ‘s lead-in clip would hold become less or non-critical as critical activities could hold run in analogue. Alternate methods of procurance there would be overall clip advantages, utilizing building direction and design and construct signifiers of contract for the concrete options. These alternate signifiers of contract appear to be less attractive for the steel options as lead-in times delay the effectual starts on site. Lead-in times besides make late finalized design and fluctuations more hard to suit. As earlier, had detailed design, mobilisation, foundations and/or substructures taken longer, steel ‘s lead-in clip would hold become less or non-critical and these alternate methods of procurance would hold become more attractive. General Overall procurance times are really Much influenced by the method of Procurement, type of contract used and lead-in times. The more by and large held position is that there is no important difference in overall procurement clip between steel- and concrete-framed Buildings.
Other observations
Number of floors
The cost per gross external M2 was found be between 6.8 % and 7.8 % cheaper for he seven-storey edifices compared to he three-storey edifices. The nest eggs are due to comparative decreases in preliminaries, external facing, coatings and foundations. ‘They more than away set excess costs for Services and superstructure.
Cost per gross m* , storeys/3storeys I
B1 Concrete -7.74 %
Steel 7.79 %
B2 Concrete -7.12 %
Steel – 6.85 %
Air conditioning
The air-conditioned edifices appear to be about 30 % more expensive to build than their of course ventilated equivalents. Detailed analysis and comparing is complicated by farther differences in specification, and different rates used for the two locations. However the premium for air-conditioned edifices over of course ventilated edifices are in the above.
Construction costs
Main decision
The chief decision to be drawn from the survey is that, for a scope of edifices, building utilizing concrete frames is more economic than utilizing steel frames.
Choosing concrete instead than steel gave to up to 32 % nest eggs in frame costs and up to 5 % nest eggs in overall building costs. The construction accounts for a comparatively little proportion of entire building cost, yet the pick of frame stuff has noticeable effects on other cost elements.
Difference in cost
Foundations for the concrete options cost more but history for comparatively little proportion of overall cost and so are more than compensated for by nest eggs in other cost elements.the chief beginning of nest eggs utilizing concrete prevarications in the superstructure. The costs of formwork, support and concrete for the concrete options must be compared with the costs of steelwork, adorning and concreting floors, and fire shell for steel options.fire casing histories for the bulk of the difference. Apart from the frame, the other chief beginnings of nest eggs utilizing concrete are cladding of the chief lifts and internal breakdown. there are minimum differences in the costs of coatings and, presuming the same contract periods, there is small evident difference in the costs of preliminaries. there are no differences in the costs of mechanical services and electrical installing due to the design premises made.
Area and costs of net getable country
The concrete options give greater ratios of cyberspace to gross floor countries, with up to 1.5 % more net getable country. This appears to be due to the flexibleness of concrete walls as dividers, and the allowance for steel brace zones. together with the fact that the concrete options are more economic to build on gross external country footing, the costs per cyberspace getable country are significantly less.
Finance costs
Analysiss of each flows during building show that the steelwork options require greater outgo earlier than their concrete equivalents.the steel work edifice require, hence more funding during the building stage and are accordingly capable to greater finance costs.all other things being equal, concrete building ‘s wage as you pour ‘ principle saves on finance costs this point can be illustrated by utilizing the seven ‘story B1 theoretical accounts as bases.
10- Consequences
* Overall, concrete is more economic than steel.
* Concrete building gives more net getable infinite ( therefore the cost per cyberspace getable country is significantly less )
* Substructure and superstructure history for a comparatively little per centum of overall costs.
* The higher costs of concrete frames foundation are more than offset by nest eggs in other cost elements.
* The pick of superstructure has a noticeable consequence on other elements of costs.
* Whether utilizing in situ reinforced concrete composite steel frames, overall procurance times and contract continuances are the same for these types of edifices.
* Shorter lede times favour concrete as a frame stuff, particularly for untraditional signifiers of contract.
* All other things being equal, concrete building leads to take down finance costs.
* Overall, the seven-storey edifices are 7 % to 8 % cheaper to construct per gross floor country than the three ‘storey edifices.
* The air-conditioned edifices are about 30 % more expensive to build than of course ventilated edifices.
9-Appendices
11-A / planning & A ; programming
* Overall procurance clip
Method of procurance:
The effects of the method of procurance on pre-contract and overall undertaking programmes were briefly considered. three types of contract were reviewed:
_Traditional ball amount where the plants are designed and later measured by the client ‘s adviser, for pricing by stamps.
_Design and construct where the chief contractor takes on the extra duty of design and where the chief contractor takes on the extra duty of design and prepares his ain subcontract stamp certification.
_Construction direction where a series of trade contracts are let by the building director on behalf of the employer. direction undertaking where trade subcontracts are let through the direction.
The steel-framed options did non look to be every bit suited to building direction or design and construct signifiers of contract as the concrete as the concrete options. This is due to the effects of lead-in times detaining effectual start building.
* Pre-contract programme
The pre-contract programme was prepared on the footing of a traditional ball amount signifier of contract. It was assumed that design times are similar for the two stuffs.
It was assumed that the start of concrete frame building on site was controlled by the release of initial bending agendas & A ; procurance of support “ about 1-3 hebdomads for normal bringing “ , and that beginning of steel frame building was controlled by release of its design “ & A ; its procurance “ presently 10-12weeks ” . No allowance was made for delayed blessings.
