Available online at ScienceDirect. Procedia Engineering 150 (2016 )

Transcription

1 Available online at ScienceDirect Procedia Engineering 150 (2016 ) International Conference on Industrial Engineering, ICIE 2016 Framing Systems in Residential Construction A.A. Antonov a, M.V. Molodtsov a, *, V.E. Molodtsova a a South Ural State University, 76, Lenin Avenue, Chelyabinsk, , The Russian Federation Abstract Large-panel construction has become the most widespread method of residential construction in Russia. High factory productivity, low labor intensity and high speed of construction considerably impair such important features as living comfort and architectural expressiveness of the building. A strong alternative to large-panel construction today is presented by framing structures. Adapting industrial framing systems to residential construction ensures high consumer qualities of buildings, flexibility of architectural and volume-planning decisions and possibility of modernization and redevelopment of facilities during maintenance at minimum cost. Compared to cast-in-place, large-panel and masonry buildings, framed buildings possess the lowest estimated cost, provide greater volume and area of the premises and reduce the consumption of materials. The article gives the comparative analysis of expenditures on steel and reinforced concrete frame assembly as well as the description and characteristic features of the current framing systems present on the market The Authors. Published by Elsevier by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing committee of ICIE Peer-review under responsibility of the organizing committee of ICIE 2016 Keywords: residential construction; large-panel construction; prefab cast-in frame; column; beam; floor slab; bolt joint. 1. Introduction Historically, large-panel construction has become the most common method of construction of residential buildings in Russia [1-3]. It was stipulated due to a number of advantages of such construction type. High factory productivity provides low labor intensity and high speed of construction. But, at the same time, it impairs significantly such important features as living comfort and architectural expressiveness of the building [4]. * Corresponding author. Tel.: , address: molodtcovmv@susu.ac.ru The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing committee of ICIE 2016 doi: /j.proeng

2 A.A. Antonov et al. / Procedia Engineering 150 ( 2016 ) The aim of the study is to analyze the systems of concrete frame construction existing on the market today, determine the possibility of their use for residential construction, and choose the one with the technical and economic parameters equal to or better than of the large-panel construction. 2. Background A strong alternative to large-panel construction today is framing structures. The framing system has long been used for the construction of multi-storey industrial buildings and proved its efficiency [5]. Wide experience in design and effective technology solutions are accumulated [6]. Adapting such systems to residential construction results in construction of buildings with high consumer qualities [7]. These buildings have the flexibility of architectural and volume-planning decisions at all stages of the construction process combined with the possibility of modernization and redevelopment of facilities during maintenance at minimum cost [8]. To analyze the construction systems, we compared 24 residential apartment building of standard building type in various structural embodiments. The following types of residential buildings were compared: masonry, large-panel, cast-in-place and cast-in-place framing. Technical and economic parameters of different systems are presented in Table 1. Table 1. Technical and economic parameters of buildings. Parameter 1. Estimated cost in the prices of 2015 per 1m² Compared types of buildings Unit Cast-in-place frame Large-panel Cast-in-place Masonry thous. rub. 25,76 33,54 30,83 26, cement t 0,28 0,34 0,37 0,24 - cement mod. to 400 t 0,24 0,33 0,37 0,24 including pre-cast units t 0,07 0,26 0,16 0, Steel t 0,02 0,04 0,04 0,02 - steel mod. to 38/23 t 0,02 0,05 0,05 0,03 - including pre-cast units t 0,02 0,05 0,03 0,03 3. Concrete and reinforced concrete m³ 0,7 1,06 1,3 0,34 including: heavy in-situ m³ 0,54 0,09 0,1 0,01 light in-situ m³ - 0,01 0,73 0,07 Heavy pre-fab m³ 0,03 0,61 0,37 0,48 light pre-fab m³ - 0,56 0,1 0,08 4. Timbering m³ 0,16 0,12 0,11 0,07 5. Brick m³ 0,32 0,01 0,01 0,38 6. Total structural volume m³ 12427,1 6219,4 5980, Gross area m² 2538,4 1455,2 1461,2 1374,04 8. Living area m² 1226,80 824,8 836,7 856,2 9. Summer area m² 218,3 67,2 18,2 118,5 As it can be seen from the table, framing buildings have the lowest estimated cost per square meter of housing. The cost of the large-panel and cast-in-place buildings exceeds the value of the framed building by 30,2-19,7% (Fig.1). The consumption of material is significantly reduced compared to large-panel and cast-in-place buildings. But the main advantage of such building type is the significant increase in operational parameters such as building volume, total and residential space. Therefore, the choice of framing systems for residential buildings is obvious, as they provide greater volume and space of the living area, and reduce the consumption of materials and thus the overall cost of construction.

3 2140 A.A. Antonov et al. / Procedia Engineering 150 ( 2016 ) Fig. 1. Estimated percentage of construction cost depending on the framed building costs of various building types Framework material Multi-storey industrial constructions are traditionally built of reinforced concrete or steel. The choice of the framework material depends on the size of the building, types of loads affecting on the frame, for example, technological equipment and operating conditions [9]. The next step of the study was to determine and compare the costs of the erection of the concrete and steel frameworks. For the purpose of analysis, we calculated the cost of the construction of the standard floor frameworks consisting of identical 6 6m structural cells in low-rise public buildings. Bearing structures of the reinforced concrete cell (1) are made of precast concrete and are standard mm columns section with the height equal to a floor and a mm beam [10]. Load-bearing structures of the steel cell are metal columns and beams, chosen in accordance with the loads of the concrete structure [11]. The results of the comparative analysis of the bearing structure costs and assembly costs are presented in Table. 2. Table 2. Comparative analysis of the bearing structure cost. Parameter Unit Quantity Price, rub. Cost, rub. Prefab cast-in-place reinforced concrete framework Assembly of prefab cast-in-place framework 100m I Total assembly works Column m 3 188, Beam m 3 927, II Total materials TOTAL (I+II) Steel framework Assembly of steel framework 100m I Total assembly works Column t 735, Beam t 221, II Total materials TOTAL (I+II)

4 A.A. Antonov et al. / Procedia Engineering 150 ( 2016 ) The table indicates that the costs for the assembly of load-bearing structural elements of precast concrete cells are by 54% less than of the metal framework. It should be noted that the metal framework is used for large span constructions and harsh operating conditions, and the comparison does not take slabs and walls into account, but nonetheless, the difference in cost is very significant. Additionally, the usage of the metal framework presupposes fire protection measures increasing its costs, which are practically not required for the concrete structures. Besides, for residential buildings in contrast to industrial ones, there is a possibility to significantly reduce the load on the framework and provide more comfortable working conditions of construction. Therefore, we conclude that the prefab cast-in-place frame type of constructions is the most progressive for residential building [12]. Due to the design features, they can combine the advantages of both cast-in-place and precast concrete frameworks. Currently, a number of variations of such systems has been developed and successfully applied in the construction of public, industrial and, partially, residential buildings in various regions of Russia [13]. A prefab cast-in-place structure includes 3 basic elements: columns, beams and slabs. Columns are fabricated in the form of sections. The length of the section depends on transportation and assembly conditions. Columns are joined by welding, plug-in or by means of bolts. At the place of junction with beams and slabs, the column body is deprived of concrete, which allows to run the beam reinforcement through the column (Fig. 2). Subsequently, during joint concreting, it forms a rigid junction unit, providing stability to the framework. Fig. 2. Junction unit of the frame bearing elements: a) "ARCOS" system; b) "Recon" system. Beams, usually being of prefab cast-in-place type, are manufactured of reinforced concrete. Production and assembly of prefab cast-in beams is performed in 2 steps. The lower part of a beam with pre-stressed reinforcement is manufactured in factory settings. The protruding reinforcement of the upper surface of such a beam ensures its joint with the slab. The upper part is concreted directly on the construction site, after installing the beam in the design position and placing the working reinforcement of its upper part. Thus, there is a T-working section where the prefab beam works as a rib, and the adjacent part of the slab serves as a cantilever. Moreover, there exists a beam-free system, where slabs are installed directly on the column (the "CUBE" system), and frameworks with a fully cast-in-place beams, for example, "ARCOS" system. Standard precast hollow-core slabs resting on beams, with the following joint concreting, or overlapping cast-in slab are in common use. For comparative analysis we took the following most common systems of prefab cast-in frameworks:

5 2142 A.A. Antonov et al. / Procedia Engineering 150 ( 2016 ) Prefab Cast-In-Place Frame Technology (PCF) by JSC "Recon" This system applies columns fabricated in the form of sections decreasing in a cross-sectional area alongside the increase of floor construction. Sections of columns are joined together by a special connector of the "plug" type without welding. The lower part of the beam is made of heavy concrete with pre-stressed reinforcement. The upper parts of beams contain protruding closed clamps (see. Fig. 2) to ensure subsequent joint of the beam with the prefab cast-in-place slab by installing additional reinforcement and further concreting. Ceilings are made of 60 mm precast concrete pre-stressed slabs, employed as permanent formwork for the bearing cast-in-place slab to obtain the design thickness [14]. Framing elements are made in the factory premises providing a high level of their quality and speed of building assembly. Lightweight constructions reduce shipping costs and make it possible to use small capacity cranes for the assembly works (Fig. 3a). The absence of necessity for welding works at the construction site brings low requirements for the qualification of workers. However, the disadvantage of this structural system is the cantilever of the beam projecting beyond the plane of the ceiling, thus creating the need for a cantilever to be hidden in the hollows of the interior partitions or the installation of suspended ceilings hiding the inner space of the room. In addition, the use of epoxy adhesive for the plug joint of the columns leads to a requirement for lengthy technological breaks ARCOS system ARCOS framing system has been developed in Belarus. The basis of the framework is comprised of cast-in-place or prefabricated columns and entirely cast-in-place beams. Standard hollow-core panels are used as slabs, significantly reducing the consumption of concrete and reinforcement [15]. This system enables the construction of buildings up to 30 floors, provides free planning space without protruding beams and gives an opportunity to employ the existing production premises for manufacturing of precast concrete bearing elements of the building. However, expensive formwork and support structures are required when installing cast-in-place beams in the position (Fig. 3b). The amount of formwork, in this case, is calculated not only on the basis of the weight of cast concrete of the beams, but the total weight of the precast floor slabs resting on it. Non-pre-stressed beams increase the overall amount of metal, necessary for reinforcement, working at the same loads that act upon the frame of the building. The necessity for tub welding of column joints increases the time and labor expenditures of assembly. In addition, requirements for the qualification of welders are much higher. Fig. 3. (a) assembly of RECON frame slabs; b) assembly of ARCOS frame.

6 A.A. Antonov et al. / Procedia Engineering 150 ( 2016 ) CUBE system The CUBE system is a beamless frame where slabs are installed directly on the column through the holes in them [16]. Column slabs are set in the first place. To center the slabs when installing them in the design position, a special jig with a cleat is used (Fig. 4). The next step consists in positioning adjacent and medium slabs on temporary support devices or racks. Later, the reinforcement is set in the joints of the slabs and concreted. This system allows the erection of buildings up to 25 floors, including the areas with high seismic activity [17]. The minimum amount of welding work is the unconditional advantage of the given system as columns and slab joints do not require tub welding of the working reinforcement. Reduction in the complexity and overall costs is achieved by eliminating the need to install and dismantle the formwork. Works are carried out by a small number of installers on the construction site, which increases the safety of the works. The possibility to make slabs cantilever over the axis of the end columns (up to 1.5 m) and give the butt ends of the slabs almost any shape makes this system very promising in creating architectural expressiveness of buildings. However, the system has a number of shortcomings that limit its wide usage. Among them are the difficulty of slab elements transportation, complex and highly labor-consuming assembly of joints between the slabs, and last but not the least, the need for special fixtures (racks, jigs and cleats) required for the installation of floor slabs. Fig. 4. Column slab assembly in the CUBE system. V.A. Shembakov in his study "Prefabricated cast-in-place framed housing: a guide to decision-making" [13] cites a number of comparative characteristics, such as the consumption of steel, in-situ and precast concrete for various prefab cast-in-place frames. The above characteristics are given in comparison with the industrial braced framing of the multiservice application for standard series designed in 1987, and beamless frame with a completely cast-in-place slabs. The results of the comparative characteristics of prefab cast-in-place frame are presented in table 3. As it can be seen from the table, the consumption of prefabricated and precast concrete in the above systems varies slightly. Consumption of steel on slabs increases by 1.5 times in systems with cast-in-place non-pre-stressed beams, and by 2 times in the CUBE in the system with its cantilevered prefabricated slabs. However, all of the above systems have relatively high labor costs and a longer duration of assembly works compared with the new system developed by the Association of Construction Industry Enterprises "Miass Concrete" MKT system [18].

7 2144 A.A. Antonov et al. / Procedia Engineering 150 ( 2016 ) Table 3. Comparative characteristics of prefab cast-in-place frame. Framing type braced framing of multiservice application /87 Modified slab thickness, cm Steel consumption per 1m2 of floor slab, kg. Share of in-situ concrete per floor slab, m 3 14,7 14,2 0,01 0,27 Cast-in-place beamless frame of 6m spacing 16 13,46 0,214 0 PCF "Recon" with a slab as permanent formwork 14,6 9,8 0,08 0,12 PCF "Recon" with a hollowcore slab 14,2 8,8 0,015 0,17 «CUBE» system 16 20,2 0,02 0,25 «ARCOS» system 14,2 14,6 0,06 0,18 Prefab cast-in-place concrete consumption per 1m 2 of total area, m MKT frame The main feature of the system is the bolting type of column joints, providing high speed of assembly (Fig. 5a). The foundation is implemented as a cast-in-place concrete slab, with preliminary built-in threaded anchor blocks, which are subsequently mounted on the column. Each floor is comprised of prefab cast-in-place beams and floor slabs. Beams are manufactured in two steps. Firstly, on the factory premises the lower parts are made of 110 mm height. The pre-stressed reinforcement is used as the working reinforcement. Beams are placed on the technological integral joists of the column. The integral joists have the form of a cantilever made of L-shaped members. Then, when the slabs are installed, the working reinforcement of the upper part of beams is run through the holes in columns and concreted. Undercut hollow core panels, with beams forming a smooth ceiling, are used as floor slabs (Fig. 5b). In systems with a protruding beam cantilever designers must either hide it in the hollows of the interior partitions or install suspended ceilings hiding the inner space of the room. The advantages of this system are the extremely high speed of assembly, absence of need for additional devices during assembly works, reduction in concrete and reinforcement consumption. A widespread use of bolted joints, absence of critical welds and large mounting tolerances allow to reduce the requirements for the qualification of workers to a minimum. Fig. 5. (a) column bolting joint; (b) undercut hollow core panel resting on beam.

8 A.A. Antonov et al. / Procedia Engineering 150 ( 2016 ) Conclusion Prefab cast-in-place frames have several advantages over other structural systems. For example, compared with the large panel construction the weight of the building is considerably reduced. Also, there appears a possibility of free redevelopment of inner space both in the process of construction and the maintenance of the building. It should be also noted, that the wear life of large buildings is significantly less than that of the frame ones. The given construction system has advantages over cast-in-place frames. Due to the use of prefabricated elements the construction speed rate significantly increases, the amount of labor-consuming formwork and welding works reduces. Also, the consumption of reinforcing steel and concrete is significantly decreased. Thanks to these advantages prefab cast-in-place frames are one of the most promising trends of the development in residential construction. However, each of the current framing systems has some flaws and the development of a new framing system, incorporating the advantages of its predecessors, is the subject of further research References [1] V.S. Samoilov, Residential construction: The builder s reference book, Adelant, Moscow, [2] P.T. Lementar, The industrialization of construction: large-panel construction, Budivelnyk, Kiev, [3] D.S. Meyerson, Residential construction in the Soviet Union in the 11th Five-Year Plan, Stroyizdat, Moscow, [4] I.A. Shereshevskii, Construction of civil buildings, C Architecture, Moscow, [5] A.I. Mordich, V.N. Belevich, V.N. Simbirkin, Effective structural systems of multi-storey residential and public buildings for the construction under the conditions in the cities of Moscow and the Moscow region, to the most meeting the requirements of modern marketing, NIEPUP BelNIIS Institute, Minsk, [6] I.A. Shereshevskii, Project engineering of industrial buildings, C Architecture, Moscow, [7] A.S. Semchenkov, Regionally adapted prefabricated cast-in-place construction systems for multi-storey buildings, Concrete and reinforced concrete. 3 (2010) 2 6. [8] Structural and technological solutions for precast cast-in-place buildings of economy class, Construction materials. 3 (2011) [9] V.S. Kuznetsov, Reinforced concrete structures of multi-storey buildings: study material for majoring in Industrial and residential construction, Publishing Association of building universities, Moscow, [10] Design of concrete precast cast-in-place structures, A Reference Guide to the SNIP , Stroyizdat, Moscow, [11] G.S. Vedenikov, E.I. Belen, V.S. Ignatieff, Metal structures, textbook for high schools, 7-th ed, Stroyizdat, Moscow, [12] V.A. Shembakov, The tasks of modern construction technology using prefabricated cast-in-place frame housing, Residential construction. 6 (2011) [13] V.A. Shembakov, Prefabricated cast-in-place frame housing: a guide to decision-making, Apple, Cheboksary, [14] Information on [15] Information on [16] Information on [17] A unified system of prefabricated monolithic frame bezrigelnogo KUB 2.5, Issue 1-1, TSNIIP Monolith, Stroyizdat, Moscow, [18] Information on