Retaining wall, Magnitogorsk - wall plan, diagrams, work schedule, specifications.

Contents

Introduction

1. Source Data

2. Quantity takeoff

3. Calculation of labor costs

4. Selection of efficient methods of work execution

5. Selection of main machines and mechanisms

6. Calculation of winter concreting process parameters

7. Formwork Calculation

8. Description of the work process

9. Work Schedule

10. Quality Control and Acceptance

11. Safety precautions

Bibliographic list

Summary

Technologies of construction processes. Chelyabinsk: SUSU, AS; 2009, p., Bibliography of literature - titles. 1 drawing sheet f. A1.

The design of monolithic reinforced concrete foundations of the industrial building is considered in this course design.

The calculation and explanatory part of the project contains calculation of the scope of work, calculation of labor costs, selection of effective methods of work execution, selection of the main machines and mechanisms, calculation of winter concreting parameters, calculation of formwork, description of the method of work execution, calculation of the work schedule, quality control and acceptance of work, safety measures.

The graphic part is shown on the A1 sheet.

Introduction

The share of use of cast-in-situ concrete in industrialized foreign countries reaches 80% of the total volume of reinforced concrete structures. In recent years, there has been a noticeable increase in the share of monolithic construction in Russia. There are several reasons for this.

Firstly, structures made of monolithic reinforced concrete are more stable under seismic and other dynamic influences.

Secondly, since concrete has excellent plastic properties, structures of any shape can be formed from it, which gives the building or structure an individual appearance. This opens up huge opportunities for architects.

Thirdly, monolithic reinforced concrete has a number of advantages over prefabricated reinforced concrete structures, which is very important in market conditions. Thus, during monolithic construction, the cost of creating a production base is reduced by 4045%, metal consumption is reduced by 720%, concrete consumption is reduced by 40%.

However, in monolithic construction there is one technological limit - concrete hardening, which significantly affects the construction time of buildings and engineering structures. This is especially important for our country, since the cold season in different areas is from 3 to 10 months; at low positive temperatures, concrete hardens extremely slowly, and when it is frozen prematurely, the quality and durability of the constructed structures drops sharply.

Thus, the increase in the share of monolithic construction leads to the need to deeply study the structure of the technological processes of monolithic construction in winter conditions.

In this project, you should calculate and select the most profitable options for performing work during winter concreting of the retaining wall.

4 Selection of effective methods of work execution

4.1 Method of concrete mix supply, laying and compaction

Transportation and laying of concrete mixture shall be performed by specialized means ensuring preservation of specified properties of concrete mixture. Transportation of the concrete mixture from the place of preparation to the place of unloading or directly to the concreting unit is carried out mainly by road transport, and transportation from the place of unloading to the concreting unit is carried out in trays by cranes, lifts, conveyors, concrete stowers, vibrators, motor towers, concrete pumps and pneumatic blowers.

The vehicle used for concrete mixture delivery to the object under construction is a concrete truck. The body of a drop-shaped concrete truck with high sides is located on the chassis of the car in the zone of minimal vibration of the frame, thereby ensuring the safety of the transported concrete mixture from delamination and spraying. To protect the mixture from the effects of atmospheric precipitation and wind, the body is equipped with a cover, and from the effects of negative and positive temperatures - with a double skin with a gap between its sheets. In addition, motor vehicles are equipped with devices for washing the body, heating the body with exhaust gases, shaking the body during unloading .

A possible means of laying a concrete mixture in a concreting unit when using a concrete truck is an auto concrete pump. Currently, automotive concrete pumps are widely used, which are a concrete pump with a full-turn distribution boom mounted on a frame, which in turn is mounted on the chassis of the car. Automatic concrete pumps are designed to supply concrete mixture to the place of laying, both vertically and horizontally. Along the boom consisting of three articulated parts there is a concrete duct with hinges - inserts in places of boom joints ending with a flexible distribution hose. The mobility of the concrete mixture should be 6... 12 cm.

When preparing, transporting and laying, the concrete mixture is most often in a loose state; aggregate particles are located loosely and there is free space filled with air between them. To seal the concrete mixture, we will use an internal (depth) vibrator. The vibration method of compaction is most effective with moderately plastic concrete mixtures with mobility of 6... 8 cm.

All work on the construction of a reinforced concrete retaining wall is divided into two stages. The first stage is the construction of a foundation slab. The second stage is concreting the top of the wall. For the rhythmic implementation of construction production, the site was divided into grabs (5 grabs - Ietap, 11 grabs - III stage). In the course project, a consistent method of performing work was adopted, carried out by an integrated brigade - a brigade, performing several types of interconnected work. Such a team consists of 5 working several professions. The distribution of labor in such a team is characterized by the combination of professions, since in the course of work the same workers, along with the performance of the main work in their leading profession, also carry out other work in a related profession.

4.2 Winter concreting methods

Winter conditions begin when the average daily outside air temperature decreases to + 5 ° C, and during the day there is a temperature drop below 0 ° C.

At negative temperatures, water that has not reacted with cement passes into the ice and does not enter into a chemical compound with cement. As a result, the hydration reaction is stopped and therefore the concrete does not harden. At the same time, significant internal pressure forces develop in concrete, caused by an increase (about 9%) in the volume of water when it passes into ice. With the early freezing of concrete, its unfinished structure cannot withstand these forces and is violated. Upon subsequent thawing, frozen water again turns into liquid and the cement hydration process resumes, but the broken structural bonds in the concrete are not completely restored.

Freezing of freshly laid concrete is also accompanied by the formation of ice films around reinforcement and aggregate grains, which, due to the influx of water from less cooled zones of concrete, increase in volume and squeeze cement dough from reinforcement and aggregate.

All these processes significantly reduce the strength of concrete and its adhesion to reinforcement, as well as reduce its density, resistance and durability.

If the concrete has a certain initial strength before freezing, then all the above mentioned processes do not adversely affect it. The minimum strength at which freezing for concrete is not dangerous is called critical.

The value of the rated critical strength depends on the concrete class, type and operating conditions of the structure and is: for concrete and reinforced concrete structures with non-stressed reinforcement - 50% design strength for B7.5... B10, 40% for B12.5... B25 and 30% for B 30 and above; for structures with pre-stressed reinforcement - 80% of design strength; for structures subject to alternate freezing and thawing or located in the zone of seasonal thawing of permafrost soils - 70% of design strength; for structures loaded with design load - 100% of design strength.

The construction industry has an extensive arsenal of efficient and economical methods of maintaining concrete in winter conditions, allowing to ensure high quality of structures. These methods can be divided into three groups: the method involving the use of the initial heat content introduced into the concrete mixture during its preparation or before laying in the structure, and the heat generation of cement accompanying the hardening of concrete - the so-called "thermos" method; methods based on artificial heating of concrete laid in the structure - electrical heating, contact, induction and infrared heating, convective heating; methods using the effect of lowering the eutectic point of water in concrete using special anti-frost chemical additives.

These methods can be combined. The choice of one or another method depends on the type and mass of the structure, the type, composition and required strength of concrete, meteorological conditions of work, power equipment of the construction site, etc.

The most common methods of winter concreting are thermos, preheating, electrical heating and heating in a heating formwork.

4.2.1 Thermos method.

Construction of monolithic structures without artificial heating is the most economical method of winter concreting.

The technological essence of the "thermos" method is that having a positive temperature (usually within 15... 30 ° C) concrete mixture is laid in insulated formwork. As a result, concrete of the structure gains the specified strength due to initial heat content and exothermic heat generation of cement during cooling to 0 ° C.

In the process of concrete hardening, exothermic heat is released, which quantitatively depends on the type of cement used and the holding temperature.

High-grade and fast-hardening Portland cements have the greatest exothermic heat generation. Concrete exothermy provides a significant contribution to the heat content of the structure maintained by the "thermos" method.

Therefore, when using the "thermos" method, it is recommended to use a concrete mixture on high-exothermic portland and fast-hardening cements, lay with an increased initial temperature and carefully insulate.

4.2.2 Preliminary electrical heating.

Electrical heating of the concrete mixture is carried out at a current voltage of 380 and less than 220 V. To organize electrical heating at the construction site, a post with a transformer, a control panel and a distribution board is equipped. Electric heating of concrete mixture is carried out mainly in trays or in bodies of car dump trucks.

In the first case, the prepared mixture (in a concrete factory), having a temperature of 5... 15 ° C, is delivered by car dump trucks to the construction site, unloaded to electric factories, heated up to 70... 80 ° C and laid in the structure. Most often, ordinary badges (shoes) with three electrodes made of steel 5 mm thick are used, to which wires (or cable cores) of the supply network are connected using cable connectors. For uniform distribution of concrete mixture between electrodes at loading of bucket and better unloading of heated mixture into structure, vibrator is installed on bucket body.

In the second case, the mixture prepared at the concrete factory is delivered to the construction site in the body of the car dump truck. The car dealership enters the heating station and stops under the frame with electrodes. At operating vibrator electrodes are lowered into concrete mixture and voltage is supplied. Heating is carried out for 10... 15 min till mixture temperature on fast-hardening Portland cement 60 ° C, on Portland cement 70 ° C, on slag Portland cement 80 ° C.

To warm up the mixture to such high temperatures in a short period of time, large electric power is required. So, to warm up 1 m of the mixture to 60 ° C in 15 minutes, 240 kW is required, and in 10 minutes - 360 kW of installed power.

4.2.3 Electrical heating.

The physical essence of the electrical heating (electrode heating) is identical to the method of electrical heating of the concrete mixture discussed above, that is, the heat generated in the laid concrete when electric current passes through it is used.

Heat generated is used to heat concrete and formwork to the specified temperature and to compensate heat losses to the environment that occur during the holding process. The temperature of concrete during electrical heating is determined by the amount of electrical power released in concrete, which should be assigned depending on the selected heat treatment mode and the amount of heat loss that occurs during electrical heating in the cold.

Various electrodes are used to supply electric energy to concrete: plate, strip, rod and string.

The following main requirements are imposed on the electrode structures and their arrangement diagrams: the power released in concrete during electrical heating must correspond to the power required by thermal calculation; the electric and therefore temperature fields should be as uniform as possible; the electrodes should be located as far outside the heated structure as possible to ensure minimum metal consumption; installation of electrodes and connection of wires to them must be carried out before the concrete mixture laying (when using external electrodes).

Plate electrodes satisfy the requirements most.

Plate electrodes belong to the category of surface and are plates made of roofing iron or steel, sewn on the inner surface of the formwork adjacent to concrete and connected to different phases of the supply network. As a result of current exchange between opposite electrodes, the entire volume of the structure is heated. With the help of plastic electrodes, weakly reinforced structures of the correct shape of small sizes (columns, beams, walls, etc.) are heated.

Strip electrodes are made of steel strips with a width of 20... 50 mm and, like plate electrodes, sewn onto the inner surface of the formwork.

Current exchange depends on the circuit for connecting the band electrodes to the phases of the supply network. When opposing electrodes are connected to different phases of the supply network, current exchange occurs between opposite faces of the structure and the whole mass of concrete is involved in heat generation. When adjacent electrodes are connected to different phases, current exchange takes place between them. The first scheme is used to warm up weakly reinforced structures with a thickness of not more than 50 cm. Peripheral electrical heating is used for structures of any massively.

Single-sided placement of strip electrodes is used in electrical heating of slabs, walls, floors and other structures with a thickness of not more than 20 cm. In case of complex configuration of concreted structures, rod electrodes are changed - reinforcement bars with a diameter of 6... 12 mm installed in the body of concrete.

With electric heating of concrete elements of small cross section and significant extent (for example, concrete joints up to 3... 4 cm) single rod electrodes are used.

When concreting horizontally located concrete or having a large protective layer of reinforced concrete structures, floating electrodes are used - reinforcement bars 6... 12 mm to be heated into the surface.

String electrodes are used to warm up structures whose length is many times larger than the dimensions of their cross section (columns, beams, runs, etc.). The string electrodes are installed in the center of the structure and connected to one phase, and the metal formwork (or wooden with deck skin with roofing steel) to the other. In some cases, working valves can be used as another electrode.

Electric heating is carried out at reduced voltages within 50... 127 B. The average specific consumption of electricity is 60... 80 kWh per 1 m3 of reinforced concrete.