Estimation of the structural frame’s cost
By the quantities estimates, we calculate the amount of materials and labor required for the building’s erection prior to the construction. Based upon these estimates and by taking into ac- count the prices offered in the market, we estimate the cost.
After the completion of every constructional phase, as built data must be collected (quantity sur- vey) so as to calculate the exact amount of materials used. The final work cost will be defined based upon these measured quantities and the initial bids. When there is an accurate detailing and a meticulous supervision, the quantities estimates prior to the construction and the quanti- ties measurement after the construction’s completion approximate one another.
The estimates of the various quantities prior to the construction must never be neglected be- cause apart from calculating the initial work cost, these quantities are used for ordering the vari- ous materials.
The final work cost depends upon a range of factors like the size and location of the construc- tion, the number of columns and beams, the seismic risk zone, the type of foundation etc.
In November 2008, the mean value of the reinforced concrete’s price was ranging between 250 and 320 €/m3 of concrete. This price includes all cost factors like materials, labor, material’s VAT and every other material and labor indirectly required. On the other hand it does not in- clude the cost of the thermal insulation boards, the additional formwork cost when visible con- crete surfaces are required (off-form concrete, architectural concrete), the additional cost due to the possible use of self compacting concrete, the personnel’s social insurance, the VAT regard- ing the labor on site, etc.
The cost of the individual work procedures is analytically presented below: Concrete supply
It includes the material’s purchase, transportation and pumping as well as the use of su- per-plasticizers. At the present time, the price ranges from 74 up to 85€/m³.
It includes the use of appropriate timber and moulds, all the necessary steel support elements, the transportations, the required labor for the formwork’s assembling and re- moval, the use of every necessary machinery or tool as well as the casting, compaction and curing of concrete.
Normally, the price should be referred in €/m², but in the market it is usually found per m3 of concrete. There is no need to mention that the offered price in m3 is set based on the corresponding m2 of formwork. Nowadays, the current price varies between 55 €/m³and 75 €/m³.
Supply or reinforcement bars properly cut and shaped (VAT included)
It includes the steel’s purchase, cut, shaping, transportation and up-lifting.
5 The most crucial factor that determines the cost for the formwork implementation is the m² of moulds, in combination with the m³ of concrete. Therefore, the bids and the billing of the formwork’s implementation are provided per m³ of concrete, or per m² of formwork.
The current price ranges from 0.6 €/kg up to 0.9 €/kg.
Rebars implementation
It regards the labor for the implementation of the entire reinforcement, bars, wire meshes etc, with the exception of stirrups. The current price varies between 0.12 €/kg and 0.16
€/kg
Supply of stirrups6
It includes the supply of properly shaped, ready-to-use stirrups. At the present time, the price ranges from 0.75 €/kg up to1.0 €/kg
Stirrups implementation
It regards the labor for the stirrups implementation in the work. The current price varies between 0.20 €/kg and 0.30 €/kg
Spacers cost
It regards the supply and positioning of every type of reinforcement spacers, plastic, re- bar chairs, etc. Nowadays, the price ranges from 4 €/ m3 up to 5 €/ m3
Social insurance of workmen and technicians
In a work, the social insurance cost is extremely large and therefore, it should be care- fully evaluated. A low-priced workforce that requires a large number of wages might not be that economical when compared to an expensive workforce that requires a smaller number of wages. A solution that allows for fewer wages is the use of industrial form- works and industrial reinforcements, mainly industrial stirrup cages. Another important factor that affects the number of wages is the size and the difficulties of the work.
The labor cost for the formwork implementation varies between 0.4 and 1.2 wages/m³ and for the reinforcement implementation from 0.15 up to 0.3 wages/m³. This means that the total labor cost ranges from 0.50 up to 1.4 wages/m³ and if we consider an average cost for social insurance around 60 €/wage, the cost of the structural frame reaches 30 to 84 €/m³!
Apart from the cost of the basic materials and labor that were mentioned in the previous paragraphs, there are other quantities that have an effect upon the cost of the building’s structural frame construction. These quantities are either considered as separate cost elements (e.g. the thermal insulation boards which are integrated inside the structural frame), or they are indirectly calculated in the cost of other quantities. In every case, these quantities constitute a large amount of the final cost no matter in which phase and in what labors they are apportioned to.
6 The large fluctuation of the stirrups’ cost which includes both the supply and the implementation labor, is caused mainly by the different types of stirrups available (see § 2.7). Furthermore, the decisive factor of the supply cost is whether the stirrup cage is industrially produced or not.
Filling
It includes the amount of soil or/and the amount of aggregates required for the founda- tion filling upon which the basement floor will be constructed.
The cost of the filling depends mainly upon its quantity, because in the case of the soil the cost is determined by the transportation and mainly by the required machinery. In the case of the aggregates usage, the supply cost is in the order of 35 €/m³
Miscellaneous
In case of extruded polystyrene usage in the form of boards for thermal insulation and since these boards are integrated inside the structural frame during the construction, the quantities are required in m² per board thickness. Apart from the cost for the material supply, which is in the order of 12 €/m² for a 5cm thick board, there is also the cost for their placement inside the moulds which ranges from 1 up to 2 €/m² .
In cases of ribbed slabs’ construction with the use of enlarged polystyrene, the supply cost is in the order of 56 €/m³ for density equal to 20 kg/m³
The amount of common wire for tying together7 rebars ranges around 2.0 kg/t of rein- forcement and its cost is approximately 3.5 €/kg.
The amount of gas and oil, the transportations and the nails (when using conventional formworks) as well as every other required material, depend upon the contractor’s equipment.
7 If the reinforcement wiring is done by means of special machinery, the cost of the appropriate wire is much higher but on the other hand, the labor cost is much lower. Between those two solutions the one with the special machinery is by far more economical.
