Antique roof modeling construction process improvement points?

In China's long history of ancient architectural design, to the Tang, Ming and Qing styles mainly in Chang'an as a representative, and more the Forbidden City in Beijing for the architects door to learn to watch. In this, we can often see the rafters in the roof of ancient buildings. The rafters themselves are ancient roof eaves support stress components, but in the reinforced concrete modern antique buildings, rafters have become a kind of antique modeling decorative structure. Therefore, the practice of cast-in-place concrete rafters constructed at the same time as the roof becomes somewhat redundant. This paper discusses the construction process of antique roof modeling rafters, proposes the construction method of prefabricated rafters, improves the original cast-in-place construction method. And optimize the construction program, listed in detail, feasible construction methods.

1 cast-in-place concrete rafters and prefabricated rafters process advantages and disadvantages of comparison

1.1 process comparison

Rafters themselves are the support of the roof eave of the ancient architecture of the supporting force components, but in the reinforced concrete of the modern antique building, rafters have become a kind of antique modeling of the decorative structure. Concrete eave molding for cast-in-place structures requires a single pour. The design spacing of the rafters is usually 100mm, the rafter gap is small and many, which leads to a more difficult construction, the template leveling and dimensional standards require high, the original bamboo, wood plywood cutting, splicing is cumbersome, the eaves template, if spliced together, in the crevice of the construction is difficult, the size of the deviation is larger, and it is difficult to grasp the appearance of the unmolded. It is difficult to grasp the appearance after removing the mold. The precision of carpentry operation is extremely high. And sporadic template fragments can not be removed, need to be sanded, chiseling treatment, otherwise affect the modeling of aesthetics. The requirements for the support structure in the formwork construction process are also high, and the seams of each piece of rafter need to be reinforced. Precast concrete rafter reinforcement installation work is also very complex, each rafter location are required to individually cloth reinforcement, and then tied with the eaves reinforcement connected to the whole, the process is complex. If the rafters are replaced with precast structures, they need to be installed and embedded before the cast-in-place concrete roof eaves are constructed, which is easy to do, especially for the carpentry templates, where the accuracy requirements are greatly reduced. Precast concrete rafters can be reused by machining several forms at once according to the drawing dimensions. Before the concrete is poured, the reinforcement and embedded parts can be installed on the ground in a single operation, easy to operate. Wooden rafters can be processed according to the drawings while fixing the embedded parts in place. Not only is the operation of the eaves part simple, but the associated support and structural components can also be restored to conventional practice. Can greatly save construction time, reduce construction difficulties. In this paper, the subsequent construction process will be explained.

1.2 economic comparison

One-time cast-in-place rafters, the price of concrete, steel and prefabricated wooden rafters are similar. If the use of precast concrete rafters can also be used, precast concrete rafters can save the amount of templates, but also to ensure the quality of the concrete rafters view. However, a larger site needs to be provided for precast construction. There is no need for a second grinding correction, which can ensure that the corners are beautiful. The one-time cast-in-place concrete rafters will definitely use the angle grinder and other machinery in the later stage, and carry out the secondary grinding treatment on the concrete surface. All the cast-in-place rafter supporting formwork is a one-time investment, labor and material construction costs are high. If precast rafters are used, the above costs can be saved by considering only the advance processing of precast wood. The use of finished concrete panels of moderate strength, easy to cut, flat surface, smooth and beautiful advantages, can replace the bamboo, wood plywood flat plate use. Prefabricated concrete panels are inexpensive and much lower than the bamboo and wood plywood formwork used in existing projects. The structural eaves and precast wooden rafters (or concrete rafters) together with the concrete pouring, a molding, and do not have to mechanically grind the concrete surface landscaping, you can directly carry out the subsequent sandpaper, painting, painting and other construction processes. In the past practice, workers prefer to use this approach, can save labor and material economic costs, shorten the construction period.

1.3 Comparison of safety

The integrality of the spliced formwork is poor, and the raised parts cannot be boarded. Subsequently, it is also necessary to construct reinforcing steel and concrete pouring and other processes on top of it. Whether it is rebar tying or concrete vibration, there are difficulties. At the edge of a high place like the roof, unstable roof formwork is a greater safety hazard. The support structure of the rafters is connected to the roof as a whole, and the demolding of the overhanging members needs to meet the design requirements, which affects the demolding time. If prefabricated rafters are used, the size of the prefabricated rafters under the eaves is 100mm×100mm, and the prefabricated rafters can be utilized as the secondary keel of the formwork support, and the upper part of the formwork is made of concrete slabs with a flat surface, so that the construction personnel can stand directly on the surface of the formwork to carry out the construction, which provides favorable conditions for the safety of the construction work. The prefabricated rafters themselves can be used as an independent, safe support structure, or they can be connected to the girder slab frame. It has no influence on the subsequent construction and the demolding of the main girder slab.

2 Prefabricated rafters construction process and operation points

2.1 Antique roof modeling eaves steel pipe scaffolding support

After computerized drawings sampling, determine the rafter bottom elevation and location. Set up steel pipe scaffolding support, support erection quality standards need to meet the construction program and design requirements. Because of the long demolding time of the overhanging members, it is recommended to use a separate support structure to avoid the impact on the subsequent construction process.

2.2 wooden rafters (or concrete rafters) elevation control template installation

Installed in the steel pipe scaffolding used to fix the wooden rafters (or concrete rafters) probe support template (shown in Figure 1), in the rafters nailed to the head of the fixed baffle to determine the good elevation and location, used to prevent displacement of the wooden rafters (or concrete rafters). This project used a steel pipe scaffolding support connected to the beam and plate frame body, which can improve the overall stability and save rental materials.

2.3 rafters (or concrete rafters) installation

Calculate the rafters (or concrete rafters) tail elevation and location, the use of bamboo, wood plywood template, An according to the design dimensions, pre-processed into a sawtooth groove for the rafters (or concrete rafters) installed in place at once. The rafters (or concrete rafters) installed to the existing template groove, the tail into the beam 20mm can be. The top of the rafter (or concrete rafter) is placed over the control formwork for fixing. This picture shows the effect of rafter construction without anchoring for force within the concrete beam. If precast concrete rafters, according to the design size requirements can be inserted into the beam 20mm (as shown in Figure 2).

2.4 precast concrete sheet cutting and field installation

Use of angle grinder will be precast concrete sheet cutting into each size: 120mm × rafter design length, in the rafters (or concrete rafters) spacing gap on the laying, the use of nails or nails will be concrete sheet and wood rafters (or concrete rafters) to be reinforced together (as shown in Figure 3). This practice is the essence of prefabricated rafters to be able to replace cast-in-place concrete rafters. The author's organization had used formwork in previous projects, but the new formwork was slightly more costly and the surface of the formwork was too smooth to work with when subsequent putty or scraping paste was applied. Wooden templates in the long-term weathering there is a potential risk of rotting, peeling. Therefore, the construction of the finished concrete sheet. Its role is to replace the original wooden formwork, avoiding the wooden formwork cutting and splicing problems. No dismantling of the mold, cheap, easy to operate, can perfectly achieve the desired results, but also for the late putty, paint construction exempted from the sanding process. There is no hidden danger of rotting and peeling. Avoid the occurrence of rework, saving the construction period and the economic cost of labor and materials. Subsequent construction, directly on which the installation of eave reinforcement, pouring eave concrete can be.

2.5 Eaves template and reinforcement installation

(1) eaves template, steel processing and installation, the indicators and dimensions need to meet the design and specification requirements; (2) template construction, the need to ensure that the length of the eaves, thickness, cross-section size, etc.; (3) reinforcement processing to ensure that the design of the length of the steel bar and the location of the hook, size, spacing. Pay attention to the height of stirrups and the number of pads to ensure the thickness of the protective layer to meet the design of the overhanging elements and reinforcing steel construction requirements. Do a good job of hidden project inspection records, if necessary, notify the supervision representative to carry out side station.

2.6 antique roof modeling eaves concrete pouring

Eaves with the roof concrete poured together, need to pay attention to the eaves pouring process of finished product protection work, strictly prohibit people from stepping on, pay attention to the use of inserted vibrator vibration, construction control vibration time should not be too long to avoid the impact of the integrity of the concrete sheet, do not touch the concrete sheet, to prevent the occurrence of rupture of the concrete sheet. The concrete sheet should not be touched to prevent the concrete sheet from cracking. Avoid touching the steel nails and hooks fixed on the rafters, otherwise it will cause displacement or loosening of the rafters. If loose rafters are found at a later stage, they can be re-nailed from the bottom. Other construction precautions are the same as the "floor slab concrete pouring method".

2.7 Demolding

After reaching 75% of the design strength of the concrete, you can dismantle the formwork of the eave side gangs, and proceed with the subsequent putty and hanging plaster construction in advance. Eaves for cantilevered elements, its support system needs to wait for the eaves of the concrete strength to reach the design value of 100% after the demolition. Removal should pay attention to the rafters (or concrete rafters) and support formwork between the reinforcing connecting elements (such as long nails), to be removed in advance, so as not to cause damage to the rafters (or concrete rafters). After removing the mold directly on the rafter surface for the next process, putty, paint and other construction can be. If the rafters are found to be loose or falling, measures need to be taken to install timely repair in place. After the effect of demolding see the attached picture, this project for the antique Ming and Qing dynasty traditional rafters (as shown in Figure 4) or flying rafters, also known as stacked rafters (as shown in Figure 5). Subsequent putty or plaster construction can be directly on its surface construction, wooden rafters should be in accordance with the antique building practices for the construction of related processes, this paper does not elaborate. For more details, see:Code for Construction and Quality Acceptance of Ancient Architecture Construction Projects (JGJ159-2008)[1].

3 other notes

3.1 main materials

Wooden rafters (or concrete rafters, prefabricated in advance), long nails, finished concrete sheet 6mm ~ 8mm thick, steel pipe scaffolding, supporting fasteners, wooden templates, commercial concrete and so on.

3.2 Main machines and equipments

Chainsaw, angle grinder, crane, etc.

3.3 Operating conditions

Select steel pipe, formwork, concrete and other materials to meet the requirements according to the drawings, specifications and construction program requirements. Prefabricated rafters (or concrete rafters). Cut the concrete sheet for spare. Reasonable choice of concrete slump and good technical delivery. Vibrators and other equipment business is safe and reliable after trial operation. At the same time with full-time mechanics, overhaul at any time. Wooden mold in the concrete before pouring with mold releasing agent evenly painted and sprinkled with water to wet. Check the power supply, line, and make good preparation for night construction lighting.

3.4 Quality Standards

The quality standards involved in this thesis follow the implementation of:Code for Construction and Quality Acceptance of Ancient Architectural Construction Projects (JGJ159-2008)[2] and Code for Quality Acceptance of Concrete Structural Engineering Construction (GB50204-2015)[3].

3.5 Finished product protection

Do a good job of finished product protection of reinforcing steel, concrete sheet, etc. during concrete pouring. When the template is removed, the side mold can be removed only when the concrete strength can ensure that its surface and corners are not damaged by the removal of the template. Bottom mold and winter construction formwork removal, must be the same condition maintenance test block compressive strength to reach the provisions of the schedule before removal. The structure of the removed formwork and support can bear the full use of load only after the concrete reaches the design strength level; when the effect produced by construction load is more unfavorable than that produced by use load, it must be accounted for and temporary support must be added. Template project work organization, should follow the support mold and demolding unified by a work team to perform operations. The advantage is that the support mold only consider the convenience and safety of demolding, demolding, personnel familiar with the situation, easy to find demolding key points, demolding progress, safety, protection of templates and accessories are beneficial.

4 Conclusion

In the construction of antique building roof rafter modeling, from the feasibility of process operation, the economy of labor and materials, construction period, construction safety, etc. Comprehensive comparison, prefabricated wooden rafters (or concrete rafters) are superior to the original cast-in-place rafter construction method. It can be predicted that the design and construction of cast-in-place concrete rafters will eventually be replaced by prefabricated rafters. It is recommended that the future construction of antique rafters, in advance, with the construction unit, the design unit to do a good job communicating with this process in advance of the application of the design, to facilitate the design of the design unit will be optimized for the design of the eaves parts, in order to save the construction and construction unit of economic costs.

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