In recent years, with the continuous development of highway and bridge engineering technology, new structures, new materials and new technologies are widely used, and more and more design drawings and materials are used to guide design and construction, which increases the difficulty of project cost valuation. Before preparing the budget, you must be familiar with the design drawings and conduct on-site investigation. Drawings and engineering specifications determine the quantities and construction methods, and some quantities, such as concrete marks, masonry specifications and construction requirements, are implicit in the drawings. Familiarity with design drawings is the basis of correct calculation of engineering quantity. Field investigation, including natural conditions and technical and economic conditions, can often find better construction methods and technical organization measures to reduce engineering costs, and can test the possibility and economic rationality of project implementation. These two tasks are important links and necessary means for compiling project budget. This paper mainly expounds the method of determining the budget cost of bridge engineering from the aspects of construction organization design, correct calculation of engineering quantity and correct application of highway quota.
Influence of construction organization design on bridge engineering cost
Construction organization design is an important guiding technical document for budgeting. It is based on the construction point of view, fully investigates the proposed project site, analyzes and compares the specific construction conditions and technical economy, and puts forward the optimized construction organization, construction methods and technical measures. The influence of construction organization design on the budget is various, but it mainly affects the direct cost. Now analyze the main factors that have great influence.
Layout of construction site
The layout of the construction site is a comprehensive description of the construction organization design in space, including the layout and arrangement of material supply and transportation routes, power supply, water supply, temporary works, on-site warehouses, service areas, gas stations, prefabricated yards, mixing yards, large-scale mechanical equipment working faces, etc. The determination of the layout also determines the direct costs of the budget, such as on-site transportation price, temporary project cost, land lease cost, site leveling cost, transportation material cost, etc. This also has a great impact on giving full play to the work efficiency of machinery and equipment and workers, thus directly affecting the labor, machinery use fees and material costs.
construction period
In the construction organization design, labor arrangement, material supply and mechanical equipment should be carried out in a reasonable time limit. Project quality, cost and schedule are mutually restricted. On the premise of ensuring the quality of the project, we must reasonably choose the construction period, arrange the project progress and control the project cost. For example, in the prefabrication and installation project of bridge superstructure, the design stipulates that members need to reach 90% of the design strength before hoisting. If the arranged construction period is short, the number of precast member foundations will increase, thus increasing the direct cost.
Selection of construction methods
Bridge design should adopt standard design as far as possible, which is not only beneficial to construction, but also can reduce the cost of auxiliary engineering (technical measures). The construction methods of bridge superstructure include cast-in-place construction, precast installation, cantilever construction, swivel construction, jacking construction, hole-by-hole construction, transverse construction, lifting and floating construction, etc. , each has its own scope of use or conditions. In the design, the selection should be based on the principles of quality, safety and reliability, technical economy and rationality. For example, the hoisting of precast beam bridge includes single guide beam, double guide beam, span pier gantry, etc. Pay attention to different construction methods, different auxiliary facilities and different expenses when budgeting. If there are several bridges with the same structure in a project, flow operation should be organized within the control period to improve the utilization efficiency of supports and templates and reduce costs.
Transport organization
Generally speaking, transportation organizations should meet the following requirements: the shortest transportation distance and the smallest transportation volume; Reduce the number of operations and strive for direct access to the construction site; Fast loading and unloading, convenient operation; Make full use of the original traffic conditions and reduce the investment in temporary facilities; Give full play to the bearing conditions of means of transport. In practice, in order to meet the above requirements, it is generally necessary to go through necessary analysis and calculation.
For example, there are X and Y2 sites. The daily sand quantity of X site is 220m3, and that of Y site is 140m3. There are three stock yards A, B and C, and the daily output of each stock yard is 120m3. See the table below for the unit freight to the construction site.
According to the principle of minimum freight, the material supply scheme is as follows: yard A supplies to station X 120m3, yard B supplies to station Y 120m3, and yard C supplies to station Y 100m3. The minimum freight is 7,200 yuan, and the minimum average freight is 7,200/(220+/kloc-
How to Strip and Extract Engineering Quantity from Bridge Budget
The compilation method of design drawings of highway construction projects in China is different from that of housing construction projects (the state has implemented the valuation mode of bill of quantities of construction projects). As the basic data for compiling project cost, engineering quantity is usually calculated by designers while completing design drawings. Therefore, the key of construction valuation is how to extract the engineering quantity from the design drawings.
Determination of auxiliary engineering quantity
According to the characteristics of bridge engineering construction technology, the basic data of engineering quantity valuation include the following three aspects.
The main part of the project
The main works include bridge foundation, lower and upper works. The general design drawings have been given, and it is relatively easy to determine the various quantities of valuation according to the quota requirements.
ancillary works
Auxiliary engineering is relative to the main project. It has a specific engineering service object and is a necessary measure to complete the main project. It does not constitute the entity of the main project, and some facilities or work will be demolished after completion. Usually, its cost is integrated into the cost of the corresponding user. If it belongs to foundation engineering, there are excavation, cofferdam, drainage, working platform, casing, mud boat and its circulation system. It belongs to the upper and lower engineering, including arch cap, bracket, lifting equipment, lifting formwork, construction elevator, etc. It is not only related to the foundation, but also related to the superstructure, such as concrete component transportation, prefabrication yard and its facilities (such as large prefabricated component foundation, tensioning pedestal, gantry, etc.). ), mixing station (ship) and steam curing facilities. The valuation quantities of these auxiliary projects, except for foundation pit excavation, should be determined according to the actual situation of the construction project and the requirements of construction organization design, and with reference to previous successful experiences, which are not reflected in the design drawings and have great plasticity and extremely important influence on the project cost. Therefore, it is of great practical significance to correctly determine the valuation quantity.
temporary construction
Temporary works indirectly serve construction projects. After the project is completed, it should be completely demolished to restore the original ecological features. It includes two aspects. First, the temporary buildings (structures) and other temporary facilities required by the production and life of construction enterprises are included in the on-site funds in the form of rates. Second, large-scale temporary works, including temporary track laying, service roads, temporary bridges, temporary power lines, temporary communication lines, temporary docks, etc. , according to the construction method and construction organization design, and item by item included in the bridge cost.
Engineering quantity extraction sequence
There are many valuation items for bridge and culvert engineering, and it is difficult to calculate and extract the engineering quantity. Practice has proved that it is generally more accurate and faster to extract quantities according to the usual construction sequence. That is, according to the order of foundation excavation → foundation → lower works → upper works, and corresponding auxiliary works, the working procedure is systematized to avoid missing items or repeated mistakes to the maximum extent.
Extraction method of engineering quantity of each sub-division project of bridge
According to the work content and measurement rules of highway quota.
Foundation pit excavation
According to different conditions such as earthwork, stonework, depth, dry place or wet place. Count the number of cofferdams respectively, and reasonably determine the types and quantities of cofferdams, the consumption standard of foundation pit drainage team and the technical safety measures that must be taken in combination with the river bed water level during construction. Understand the long-distance transportation and treatment of foundation excavation waste, restore the original terrain, river dredging, etc. , and according to the principle of proceeding from reality and leaving no hidden dangers, determine its valuation quantity, and the required expenses shall be included in the project cost.
Foundation engineering
There are many structural forms of bridge foundation engineering, such as masonry, concrete, open caisson, piling and cast-in-place pile, but generally digging piles, bored piles, masonry and concrete are used to expand the foundation.
Masonry foundation shall be statistically summarized according to flaky and rubble respectively. When preparing the budget, special attention should be paid to dividing the mortar label. If the design label is different from the quota, it should be replaced. If there is only the total number of masonry in the design drawing, the price shall be 80% rubble and 20% rubble, respectively, considering the factors such as the outer edge of foundation and layered masonry.
When compiling the budget of concrete foundation, statistical summary should be made according to different labels and whether flaky is mixed. If the design label is different from the quota, it should also be replaced.
Should be combined with the actual situation and the implementation of construction organization design, so we should pay attention to the following points.
(1) According to the field geological conditions and eight kinds of borehole soils corresponding to different soil thicknesses, the rig model and quota are selected, and the corresponding auxiliary quantities are determined (Note: in the hole-forming quota, different soils in the same hole, regardless of depth, are subject to the total hole depth quota). For example, the pile foundation geology of Nanshanya Bridge is fine sand 1.8m→ weakly weathered granite 7.2m→ weakly weathered granite 6m. Pile length 15m, designed pile diameter1.5m. It is designed as end-bearing pile, so GCF-2000 impact drilling rig is selected, and 4-24-25, 4-24-3 1 and 4-24-32 are used respectively.
(2) When the cofferdam is used for island filling in drilling construction, the quantities of cofferdam and island filling can be determined according to the width of the outer edge of the cast-in-place pile of about 3.0m When calculating the number of buried liners, it should be regarded as "dry place". For example, Renxing River Bridge has 32 piles in the water, and we design to build an island with cofferdam to fill the core and drill holes. When applying the quota, we compared the unit price of dry parts and wet parts, and the unit price of wet parts per ton of steel lining was about 6 times higher than that of dry parts. Therefore, it is necessary to strictly distinguish between dry and wet quotas, otherwise the budget value will be greatly deviated.
(3) Burying liners in a dry place can generally be calculated according to the length of each liner of 2.0m or the design quantity; Steel liners buried in water can be calculated according to the design quantity, and the recovery quantity can be calculated according to the regulations. For example, when the pile casing is buried in water, when the water depth is less than 5m, the general design requires the buried depth of 3m, and the actual length of the pile casing is 5m+3m=8m.
④ Determination of casing diameter. The diameter of casing can be determined with reference to the relevant provisions of bridge construction specifications. The diameter of casing is related to the type of drilling rig and geological conditions. Generally speaking, it is enough to add about 0.2m according to the pile diameter.
For example, in the construction of underwater pile foundation of Xiwei Bridge 17, the original design used a bamboo cage cofferdam with a height of 4m as the construction platform according to the water depth of 3.5 1m, but the measured water level reached 6.51m.. Therefore, the design is changed to adopt the "underwater platform" construction scheme, set up an underwater drilling operation platform, bury the integral steel casing (sink with DZJ60 vibrating pile hammer, and enter the weathered layer more than 50cm), and drill holes with a cross bit impact drill or a rotary drill. In the calculation of the design change amount, the underwater steel casing is calculated according to the total design quality, and the amount of the casing alone will increase by 530,000 yuan.
⑤ When drilling in water, the working platform of cast-in-place pile, mud boat and circulation system should be listed.
⑥ The soil quota in the hole is divided into 8 kinds, which are divided into several quota standards according to the difference of pile diameter and hole depth. Therefore, the number of drilling holes should be determined according to the geological drilling data and the fixed soil type. Because the unit of measurement for drilling holes is meters, the drilling depth should be based on the depth between the ground and the design pile bottom. When the cofferdam is used for island filling in water, the depth from the top surface of the cofferdam to the design pile bottom shall prevail. If drilling waste needs long-distance transportation, it shall be separately priced according to the average transportation distance of waste.
⑦ Under normal circumstances, if there are only two cast-in-place pile foundations with/kloc-0 piers, the pile caps are not set, but are designed as tie beams. This tie beam project should be priced according to the cap quota. When the pile caps or tie beams are constructed on land (or the cofferdam is used to build islands and drill holes), the amount of foundation excavation and the long-distance transportation of drainage and waste materials should be calculated according to the actual situation.
⑧ The quantities of pouring underwater concrete are calculated by multiplying the designed pile diameter section by the designed pile length, and the reaming amount is not included in the quantities. If it is necessary to set up a mixing boat (station) for concrete mixing, the cost can be determined and calculated according to the actual situation.
Low-level engineering
Bridge substructure works include masonry, cast-in-place concrete and precast concrete members.
(1) When preparing the budget, the quantities are extracted one by one according to the partial projects. The valuation quantities of piers and abutments are pier body and wing wall, pier cap, arch frame, capping beam, ear back wall, abutment, etc. And the hat stone below the second floor (when there is a sidewalk 1 the hat stone below the floor), and the different labels of flaky and rubble, mortar and concrete should be distinguished. The filling and compaction of abutment back and cone slope also need to be priced separately.
(2) The quantity of pier masonry, if there is no clear division between rubble and rubble on the construction design drawing, can be determined according to 75% rubble and 25% rubble on the abutment, 60% rubble and 40% rubble on the pier.
(3) All piers, abutments, pier facing, arch stones, cap stones, railings, etc. Using mortar concrete precast blocks, the number of precast blocks should be multiplied by the coefficient of 0.92 according to the design masonry.
Superstructure engineering
In order to avoid repetition and omission, the valuation quantities of superstructure should be extracted in the order of roadway → deck pavement → sidewalk.
Prefabrication and installation of structural main works
In recent years, precast and installed concrete structures are mostly used in bridges. When preparing the budget, the items that should be stripped include prefabrication, installation and transportation, all of which are subject to the design volume of components. As for the average transportation distance of components, it should be determined according to the construction organization design; Steel bars, steel strands or high-strength steel wires, cast-in-place joint concrete, drainage pipes, supports and expansion joints (in terms of lane width) shall be subject to the design data of construction drawings. If the service life of lifting equipment exceeds 4 months specified in the quota, the amortization fee of the equipment can be adjusted according to the planned construction period. The planned service life of the equipment shall include round-trip transportation from the equipment warehouse to the construction site, trial assembly before installation, and all the time required for cleaning, trimming and painting after dismantling; The number of small components such as prefabricated sidewalks, kerbs, railings and handrails should be increased by 65,438+0% based on the volume of the designed components, resulting in on-site transportation and operation losses.
Auxiliary engineering of prefabricated installation structure
Find out the affiliated project, and take the precast installation of 25m prestressed T-beam bridge as an example to explain as follows.
(1) The plane area of the prefabrication yard shall be determined according to the size of the construction project, and the gravel cushion layer laid according to the design needs shall be considered.
(2) The number of large prefabricated plane pedestals shall be determined according to the possible turnover times of the construction progress.
For example, Jikou Bridge and Xiwei Bridge in a certain section adopt prefabricated yard, and Jikou Bridge has 80 T-beams with a length of 25m；; Xiwei Bridge has 70 T-beams 30 meters long. The construction pedestal was originally planned as 16. However, considering that the length of the pedestal of the West Tail Bridge increased by 5m, the pedestal of 12 was finally adopted, and the international bridge was prefabricated first and then the West Tail Bridge was prefabricated, which not only saved the site, but also saved the funds.
(3) Generally, the portal frame of the prefabrication plant can be priced according to the construction organization design, and the amortization fee of the equipment can be adjusted according to the planned service life.
(4) Double guide beam lifting equipment can refer to the notes in the quality quota. In the budget quota, a variety of construction methods and supporting hoisting equipment for hoisting components are formulated, but each has its own scope of application. When making a budget, be careful not to miss the plan. If the rectangular plate is equipped with a herringbone pole, each bridge is equipped with a herringbone pole; Don't double-calculate. If cable lifting equipment has been listed in a budget, it should not be listed as a transport cableway facility, and cables should be regarded as transport materials.
⑤ Track laying of precast yard is listed as a temporary project in the budget project list, so it cannot be calculated in the cost of bridge superstructure.
⑥ If the prefabrication yard is used for * * *, the transportation distance of the beam should be fully considered. For example, in order to save transportation distance and reduce interference, it is decided to transport beams on the existing subgrade, and this alone will save 6.5438+0.9 million yuan.
Reinforcement engineering
Steel works and concrete are measured separately, and the unit is tons. The quantities should be extracted according to the requirements of partial projects and primary and secondary steel bars.
(1) The reinforcement should be based on the theoretical quality calculated by its design length, and the operation losses such as construction welding and blanking have been included in the quota, not included in the reinforcement quantity.
(2) The quantities of steel strand and high-strength steel wire are the sum of anchorage length and working length, such as prestressed hollow slab (standard span is 10m~ 16m), which can generally be calculated according to the increase of slab length1.5m..
(3) The height of cast-in-place pier, platform and tower is greater than the length of general reinforcement. When steel bars need to be extended in sections, the number of required tower connection lengths can be separately included in the number of steel bars according to 20D~30D(D is the diameter of steel bars).
(4) In the general bill of quantities, steel bars are divided into primary and secondary steel bars according to international practice, but they are combined in the quota, and they are not separated according to primary and secondary steel bars. Therefore, some technical treatment should be carried out when applying such quotas. Taking "Cast-in-situ Simply Supported T-Beam Superstructure (44-3)" as an example, the rated dosage of I and II steel bars is determined.
In the budget quota of highway engineering promulgated by the Ministry of Communications, most of the quotas are relatively stable in labor, materials and machinery consumption. Whether calculating the first-class reinforcement or the second-class reinforcement, after considering the processing loss, the unit fixed consumption per ton of reinforcement should be1.025 t.
In the norm 4-44-3, according to the professional knowledge, it can be judged that the consumption of welding rods and electric welding machines is aimed at Grade II steel bars, and Grade I steel bars generally do not need electric welding or butt welding. Therefore, the consumption should be removed when calculating the I-graded reinforcement, and added when calculating the II-graded reinforcement. For example, the calculation formula of AC electric welding machine team with the secondary reinforcement consumption within 30kVa is: (0.410.82) × 0.205+0.41= 0.513.
Obviously, the usage fees of 20#~22# iron wires and small machines and tools in the quota 4-44-3 are for the first-class steel bars and the second-class steel bars. Even if there are some changes, it is insignificant for the whole quota, so it will not be adjusted. Practice has proved that after such treatment, the unit price of primary and secondary steel bars has been enlarged, otherwise, the unit price of primary and secondary steel bars is very close.
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