0 Introduction

In February 2016, the State Council issued “Several Opinions of the Central Committee of the Communist Party of China State Council on Further Strengthening the Management of Urban Planning and Construction”, striving to make the proportion of assembled buildings reach 30% of new buildings within 10 years, and assembled concrete residential buildings will usher in huge development.

The assembled concrete residential buildings meet the government’s 9070 policy requirements, the parameters and structural forms are scientific, the industrialization effect is good, and good construction results and economic benefits have been achieved in Vanke and other real estate projects. The construction of assembled concrete residential buildings requires strict construction deepening design, construction plan and construction organization design, and strict control of construction safety, quality and process, which can achieve resource saving, shorten construction period, reduce cost, ensure quality, reduce impact and achieve good construction and use effect.

1 Project overview

A residential building in Guangdong Province is located in the downtown area, with more restrictive construction conditions, tight schedules, energy saving and strict requirements for the site environment, etc. After comprehensive analysis, it was decided to adopt a new form of assembled concrete building. The building has nine floors above ground and one underground garage, with a construction area of 11,678m2. The core cylinder and the main load-bearing structure are constructed by casting-in-place, and the prefabricated assembly parts mainly include exterior walls, dormer windows, floor laminated panels, staircase sections and non-load-bearing walls, etc.

2 Deepening design of assembled concrete residential building construction

2.1 Deepening design of building construction based on performance

The project construction attaches importance to the requirements of seismic and disaster prevention engineering, and the construction deepening design is implemented based on five major performance targets, namely: elastic working target under normal use conditions (requirements of seepage and crack resistance), elastic working target of the main structure under small earthquake conditions, repairable target of all damages under medium earthquake conditions, safety target of the main body under large earthquake conditions and requirements of continuous collapse prevention.

2.2 Deepening design points

The general construction contractor needs to integrate the information of all parties involved in the construction to deepen the design with justification and clear ideas, and to clarify the handover surface. The personnel involved in deepening design of assembly building construction must have strong comprehensive quality and sufficient understanding in both civil construction and installation. The deepening design focuses on two aspects: functional requirements and production and construction requirements, and integrates the requirements of each profession to improve and deepen the design content. The design results need to be coordinated and contradicted by all parties, finalized by the construction side and started construction.

The quality of prefabricated components is a reliable guarantee for the assembled building, and the deepening design is significant for the whole construction process. In the assembly of formwork and inspection work, the surface of the bottom mold is kept highly flat to ensure the appearance effect of the components, the bolts between different formwork are required to be complete and tightened, the side mold is positioned with high precision, and the joints are often filled with atomic ash and then smoothed and ground smooth. Strict inspection and acceptance procedures are in place, and any problems that do not meet the design requirements must be solved before proceeding to the next process.

Prefabricated components commonly used diesel oil mixed release agent, deepen the design of this part must be clear painting process and component protection, usually painted once must be wiped by cotton gauze, oil film thin layer to be uniform. Retest face brick process need to face brick back treatment process detailed instructions to ensure the quality of the face brick as well as the gap requirements.

In addition, it is necessary to deepen and strictly control the construction in detail and manage the construction of concrete pouring of bonding layer, treatment of insulation layer, construction and fixing of pre-installed parts, construction of reinforcement skeleton into the mold, concrete pouring of structural layer, maintenance of concrete and demolding, lifting and stacking.

3 Construction organization design of assembled concrete residential building

Assembled concrete residential buildings depend more on the quality of construction organization design than conventional buildings, and their site coordination ability such as lifting needs to be well controlled. The arrangement of the site and the choice of machinery bear the brunt, and the stacking of the components needs to follow the correspondence between the storage stress state and the installation stress state, so that the components cannot be damaged in the process of turning over. The design of exterior wall component nodes, exterior wall connections, stairs and waterproofing nodes are difficult points for deepening the design of assembly-type buildings.

The construction flow, resource input and unit section division are improved by drawing on the experience of traditional reinforced concrete construction and combining with the characteristics of assembly-type buildings. Figure 4 shows the flow chart of prefabricated wall panel assembly construction. The construction organization of this sub-project is divided into four stages, and standardized operation is adopted to ensure the construction quality.

4 Construction details of assembled concrete residential buildings

Detailed construction methods and detailed practices were determined before construction, and the construction process must be strictly implemented in accordance with safe construction and high-quality construction standards to ensure standardized, industrialized, logistic and specialized high-efficiency construction. The key work quality control details for the construction of assembled concrete residential buildings include prefabricated production and processing of components, transportation and on-site stacking of components, positioning and alignment of reinforcement, preparation before installation, installation of connections, and casting-in-place nodes and handling of protection.

The stacking of components at the site needs to be managed by dedicated personnel, and different types of components combined with the characteristics of different stacking frames and support measures. Paying attention to the quality of node construction is a feature of the construction of assembled buildings. Figure 5 shows the prefabricated to construction of node members for exterior walls. Each prefabricated component ensures that lifting, positioning and connecting utensils are in place in advance, and the construction flow is smooth to ensure efficiency is one of the key elements of control. 　　

According to the parameters of the equipment, environmental situation analysis, determine the on-site lifting method, lifting position and lifting details, pay attention to control the center of gravity of prefabricated components as the lifting point, according to the production and installation state analysis of the structure to determine the reinforcement measures. Auxiliary stabilization tools are more frequently used in the construction process of assembled buildings, and are strictly selected according to the characteristics, size and construction sequence of prefabricated components. Figure 6 shows a monolithic component assembly site, where protection during construction is very important. The variable fence and removable protection frame shown in the figure play a significant role in the safety and security work of this project.

The new pin-type variable barrier tool was used for the assembly of the components, while the movable guard frame tool was used for the rear hanging wall panels. The construction follows the principle of load-bearing members first, then non-load-bearing members, and after the main beam and column are cast-in-place, the prefabricated members are installed, and the members are pre-buried at the node joints and cleaned up and then cast-in-place to ensure the integrality. The application of adjusting bolts in the construction process of assembled buildings is very common, simple and quick to achieve precision control.

5 Quality control of assembled concrete residential buildings

　Construction quality control should be strictly regulated from the quality management system to ensure control of the whole process of prefabricated installation of high quality requirements, zero defect requirements, fast progress requirements and avoid waste and pollution. We should grasp all aspects of technical, material and construction details, strictly review drawings and technical plans, unify the deployment and calibration of work equipment, strictly control material inspection, and provide comprehensive and efficient quality assurance through self-inspection of the project department, mutual inspection and handover inspection of all parties involved in the construction. We pay close attention to the site environment, temperature and humidity, and other conditions, so as to reasonably organize the construction time and flowing plan, real-time observation during the lifting process to make sure the lifting wire rope is always in the vertical state, check the quality of detailing at the joints before the node pouring, and ensure the grouting is full.

6 Conclusion

The assembled concrete residential building, which passed the quality assessment and acceptance with full excellence, has achieved the expected construction objectives of.

① deepening design and refining construction management realized standardized and high-precision construction, fully planned flow, programmed and sequenced operation, reduced environmental pollution, efficient turnover of work apparatus and avoided the occurrence of quality common problems.

② In terms of water saving, electricity saving, reducing the use of formwork, reducing the use of scaffolding and reducing the discharge of waste, etc., the assembled building has achieved remarkable results and realized a breakthrough in many aspects of economic and social benefits.