Sustainability, prefabrication and building optimization under different durability and re-using scenarios: Potential of dry precast structural connections

1Sustainability, Prefabrication and Building Optimization under Different Durability and Re- 2using Scenarios: Potential of Dry Precast Structural Connections 3Jorge Navarro-Rubio1, Paloma Pineda2*, Antonio García-Martínez3 41NR Proyectos - Engineering and Architectural Consulting, Almería, Spain 52 Department of Building Structures and Geotechnical Engineering, Universidad de Sevilla, Avda. 6Reina Mercedes, 2, 41012 Seville, Spain 73 Department of Building Construction, Universidad de Sevilla, Avda. Reina Mercedes, 2, 41012 8Seville, Spain 9*Corresponding author. E-mail address: [email protected] (Paloma Pineda) 10 1 1Sustainability, Prefabrication and Building Optimization under Different 2Durability and Re-using Scenarios: Potential of Dry Precast Structural Connections 3Abstract 4Eco-efficiency and building optimization potential of prefabricated structures to be used in 5new buildings are studied, focusing on the analysis of a novel dry precast beam-column 6connection under different durability and re-using scenarios. The analyses include 7structural response (via numerical models), optimization potential (material take off, 8building schedule and economic cost) and environmental impact (via Life Cycle 9Assessment, LCA). The connection is applied to a case study which is representative of 10 common buildings: a seven-story concrete structure with frames and deck slabs. The 11 structural response of the connection accomplishes the Eurocode safety prescriptions. Man- 12 hours and task duration decrease around 80%, and the global schedule undergoes 60% 13 diminution. Focusing on economic issues, when the prefabricated structural elements are 14 reused the accumulated economic cost significantly decreases. LCA shows that durability, 15 in terms of service life, is directly related to the environmental impact. However, other 16 design options, such us re-using, have less repercussion in the impact categories (i.e. Global 17 Warming Potential and Embodied Energy), and in the global cost. Results from this 18 research could contribute to the implementation of prefabricated elements in the building 19 stock promoting eco-efficiency. 20 21 22 Keywords: Life Cycle Assessment (LCA); Prefabrication; Dry Precast Concrete; Building 23 Optimization; Re-using; Durability. 24 1. 2 26 1. Introduction 27 Most of the structural works within the architectural built environment apply cast-in-place 28 techniques, following conventional procedures. But, as stated by Zhang et al [1] 29 conventional construction methods are directly related to some negative issues such us low 30 field productivity, unreliable quality, high resource and energy consumption, workplace 31 accidents and environmental pollution. Both buildings and their associated technologies 32 have a crucial effect on the environment. Indeed, the built environment is responsible for 33 about 40% of the total energy use, one third of green house gas emissions, 30% of raw 34 materials use and 25% of solid waste generation [2]. Thus, it is highly necessary to promote 35 constructive systems that combine the following three features of sustainable development 36 in a balanced way: economic, social and environmental [3]. The use of eco-efficient 37 building systems and the re-use/recycling of structures are great challenges for the present- 38 day architecture and civil engineering [4]. In fact, one of the main challenges that the 39 construction industry has to face is the implementation of industrialisation and 40 prefabrication, in order to reduce costs and environmental impact. Therefore, 41 standardization of design, prefabrication of structural components and mechanization of on- 42 site construction techniques are key issues that should be integrated in the building 43 methods. In addition, reduction in energy and resource consumption can be achieved by 44 recovering building wastes after demolition through material reuse and recycling, or 45 building repurposing through selective deconstruction and building system reuse [5]. 46 From the aforementioned, it can be concluded that prefabricated concrete elements have a 47 strong potential within the built environment, especially due to issues that are directly 48 related to the building stage (speed of assembly and easy erection). As far as the 49 environmental impact is concerned, more research is required, especially if durability and 3 50 re-using are also coupled variables. 51 The main objective of this research is six-fold: 52 1. To design a novel dry-precast concrete beam to column connection (with and 53 without post-tensioning), focusing on reducing costs and working times, 54 guaranteeing the adequate structural performance. The union will be used in 55 new buildings; 56 2. To assess the structural performance, comparing conventional cast-in-place 57 connections with the novel prefabricated elements, by means of numerical 58 models. 59 3. To assess the environmental impact, under different structural scenarios, 60 comparing conventional cast-in-place connections with the novel prefabricated 61 proposals. 62 4. To assess the environmental impact, under different durability conditions, 63 assuming two service life periods (50 and 100 years), for both the cast-in-place 64 and the prefabricated elements; 65 5. To assess the environmental impact when the prefabricated element are re-used 66 in a new building. 67 6. To analyse and compare the direct cost of both cast-in-situ and precast concrete 68 elements. 69 In order to achieve the objectives, after designing the prefabricated connection, the 70 structural performance of the novel element is analysed by means of three-dimensional 71 finite element models. The numerical models assume linear behaviour for concrete and 72 steel elements and nonlinear behaviour in the contact between surfaces, and in the post- 73 tensioning. After performing incremental static analysis, weakness and strengthens are 4 74 obtained from a structural safety perspective. As a main concern of this study is to assess 75 the actual feasibility of reducing working times and environmental impact, the proposed 76 connection is applied to a case study which is representative of the building stock in the 77 South European urban context: a seven-story concrete building with frames and deck slabs. 78 The Life Cycle Assessment is the selected method to analyse eco-efficiency. The building 79 optimization potential is studied after analysing the material take off, the building schedule 80 and the economic cost. 81 The proposed novel connection as well as the hybrid design method (as a combination of 82 environmental, structural and building optimization factors) will allow for increasing 83 competitiveness within the construction industry. Thus, a productivity increase during the 84 construction phase could be reached, as well as a reduction of working times and 85 environmental impact. 86 1.1. Background 87 1.1.1. Background and opportunities from the building methods 88 Depending on the prefabrication level, the construction methods could be classified into 89 these categories: Conventional Construction (CC), Mixed System (MS) and Industrialized 90 Building System (IBS). IBS is the technique that uses prefabricated structural components, 91 which are manufactured off-site, for the assembly and construction of buildings. Precast 92 system, which is the process of assembling precast elements into a structure, as well as IBS, 93 are recognized as efficient procedures to minimize time and cost of project construction [6]. 94 The Mixed System is an interesting intermediate step that incorporates new construction 95 techniques in the Conventional Construction. Lachimpadi et al. [7] analyse and compared 96 the construction waste usage efficiency, waste generation, reuse and recycling rates of 97 Mixed System and IBS vs. Conventional Construction in Malaysia, concluding that, from 5 98 an environmental point of view, IBS and MS were the most advantageous solutions (for 99 instance, the waste generation ratio of MS is 37% less than that of CC). 100 As far as strengthening and/or refurbishment works is concerned, it is remarkable 101 the research by Foraboschi [8]. In that work, the author focuses on the capabilities and 102 opportunities of two-way RC floors, coupled with the selection of the best building 103 technique to avoid serviceability failures. The proposed RC floor comprises T-section RC 104 joists arranged in two-directions between two flat-beams and edge-beams along the entire 105 boundaries. The structural solution also includes a permanent mold with substantial bearing 106 capacity. 107 As stated by Foraboschi [9], if the bulk of the fabrication is done in workshop with the 108 right machinery, lighting and work conditions, time and cost are significantly reduced. 109 From the aforementioned, precast concrete exhibits several advantages, such as better 110 quality, timely erection, independence from weather conditions, elimination of scaffolding 111 and schedule adaptability [6]. In addition, the construction technique is not only plain 112 practice but is also part of the design process [8]. 113 1.1.2. Background and opportunities from the structural design of precast 114 concrete elements 115 One of the main concerns of this type of elements is to guarantee the safety of the 116 connection, ensuring the structural integrity and the adequate load transfer between 117 structural parts. The structural performance and safety response of precast concrete frames 118 are directly related to the type of connections. Connections must transfer vertical and 119 transverse horizontal shear, axial tension and compression and bending moment and, 120 occasionally, torsion between precast elements. Besides, as the stiffness of precast concrete 121 buildings is, in general, less than that of cast in-situ buildings, under seismic loading it is 6 122 crucial to provide enough ductility and redundancy. As far as the type of connection is 123 concerned, different classifications are provided from the literature and Codes (e.g. [10, 124 11]. One of the most common is to classify them as: as pinned, hybrid or emulating cast in 125 situ but as wet connections [12] with a sub classification of each item in wet or dry. Several 126 studies have been developed in relation to pinned, hybrid or emulated cast in situ as wet 127 connections using concrete or grouting in the last case (e.g. [13, 14, 15]). 128 During the last two decades, several researchers have focused on the structural 129 performance and design of precast concrete buildings, (e.g. [16, 17]). But, as stated by 130 Bournas et al. [18], the behaviour of precast concrete structures is an open research field 131 where more studies are required. As far as the recent advances on precast moment resistant 132 frames are concerned, most studies focus on wet connections (e.g. [19, 20, 21, 22]). In 133 those elements, on-site grouting or concrete is used to obtain a rigid behaviour of the joint. 134 Other researchers propose the use of steel elements to increase the flexural strength [23, 24, 135 15, 25, 26]. Mixed solutions, combining on-site grouting and steel elements have also been 136 developed [13, 27, 18, 14, 28]. Koshikawa [29] analyses the moment and energy dissipation 137 of a post-tensioned precast connection using a friction device. Bahrami et al. [30] and de 138 Lima Araujo et al. [31] propose steel elements that are embedded into the column to 139 temporarily support beams until the assembly process is completed. Regarding dry moment 140 resistant precast concrete connections, recent advances have been developed. Thus, 141 Aninthaneni et al. [32] propose a system of two pairs of steel plates which are located in the 142 precast concrete beam ends –one embedded and the other one bolted to the precast concrete 143 column-. Stiffeners are welded to the beam. After performing numerical and experimental 144 tests on frames, the authors conclude that the hysteretic behaviour of the proposed 145 connection is similar to that of the monolithic frame. The researchers emphasize that the 7 146 proposed dry connection is removable. Shufeng et al. [33] design an end plate connection 147 with welded reinforcements and rods. The rods cross the precast column to connect beams 148 and column. A welded plate is used to anchor post-tensioned tendons inside the beams. 149 Thus, only the beams are under post-tensioning. Xiao et al. [34] propose a beam to beam 150 connection that welds the steel at both ends of the reinforced concrete beams, and covers 151 the area with post-cast concrete. The aforementioned research highlights the advantage 152 when structural dismantling is required. 153 1.1.3. Background and opportunities from environmental assessments 154 The importance of considering environmental issues is remarked by some of the works (e.g. 155 Xiao et al. [34]) and the option of removal and re-using is also highlighted (e.g. [32, 34]). 156 From an environmental context, recent studies focus on the eco-efficiency of 157 prefabricated structural systems. De Barba Junior et al. [3] developed a research on 158 sustainability in conventional and industrialized systems built in Brazil. They concluded 159 that, in order to improve the economic performance, the percentage of materials extracted, 160 processed or manufactured within a maximum range of 300 km should be increased. The 161 authors also highlight that re-using of components and minimization of residues generated 162 during the work should be promoted. During the last decades, several authors have 163 analysed the application of the Life Cycle Assessment (LCA) to building structures. Thus, 164 according to the classification proposed by Eleftheriadis et al. [35], there are four main 165 active research areas that focus on the following structural parts or related issues: (i) 166 structural frames; (ii) walls; (iii) floors; and (iv) material properties. Regarding structural 167 frames, some relevant studies have been carried out, focusing on the building level. 168 Dimoudi and Tromba provide the LCA of a concrete structural frame [36]. Dijk et al. [37] 169 propose a parametric model to interrelate structural input parameters of concrete 8 170 components and embodied environmental impacts. Sang Cho et al. [38] compare different 171 structural bracing systems in high-rise steel buildings from the perspective of LCA. 172 Pajchrowski et al. [39] conduct the LCA of four single-family dwellings under the premise 173 of promoting intensification of wood usage. Several authors have also compared steel and 174 concrete structures [40, 41]. Also concrete and timber structures have been analysed and 175 compared [42, 43, 44, 45, 46]. Thus, Bolin and Smith compare timber and steel structures 176 [47] and concrete, steel and timber structures have been also compared [48, 49]. Takano et 177 al. [50] apply the LCA methodology to analyse different structural options: cross-laminated 178 timber, reinforced concrete, aircrete, brick, steel and lightweight timber. As far as walls are 179 concerned, a number of recent LCA studies have been conducted. For instance, Kahhat et 180 al. [51] carry out the environmental assessment of different wall systems: concrete block, 181 insulated concrete, poured-in-place concrete, wood frames, steel stud and structural 182 insulated panels. Puskás and Moga compare a concrete structure with a masonry load- 183 bearing structure [52]. More recently Balasbaneh and Masorno perform a LCA of six 184 different wall-based structures [53] and D’Alessandro et al. [54] compare the 185 environmental impact of straw bale constructions with different building materials. 186 Focusing on the global structural system, Omar et al. [55] compare the environmental 187 performance of pre-cast panels and reinforced concrete. Venkatarama and Jagadish [56] 188 focus on load-bearing masonry walls. Different options of load-bearing walls (rammed 189 earth, brick and concrete blocks) are analysed by Galan-Marín et al. [57]. Recently, 190 Arrigoni et al. [58] have studied the environmental impact of different rammed earth walls, 191 which incorporate recycled concrete aggregate. With regard to the analysis of the 192 environmental impact of structural slab, recent relevant advances have been provided (e.g. 193 those of provided by the research teams of Hajek [59] and Miller [60] focusing on 15 291 292 Figure 5. (a) Maximum vertical loading and equivalent vertical loading; (b) Precast 293 concrete vs. cast in place under horizontal displacement; (c) Precast concrete vs. cast-in- 294 place, (VL 0.12 MPa and HD 0.0075 m) 295 In the case of VL (Figure 5(a)), a maximum S3 of 21.14 MPa is obtained when the 296 maximum load (0.20 MPa) is applied, that is, the connection is able to increase the load or 297 the concrete strength limit has not been reached. In the precast concrete model, S3 is 298 reached in beams when VL is equal to 0.12 MPa. Nevertheless, 0.12 MPa on the top face of 299 the beam is equivalent to 16 kN/m2 in 3 m span. That value is suitable in common 16 300 architectural structures, accomplishing Eurocode 2 prescriptions. The VL limits of concrete 301 in column and steel in plates or screws are higher than those of beams (0.144, 0.17 and 0.20 302 MPa respectively). This kind of analysis, comparing VL in beam with the equivalent 303 surface loading, helps designers to improve the structural behaviour. That is, the designers 304 could graphically identify the element that requires an improvement (in terms of dimension 305 or material) if the response is not adequate. Regarding HD, the concrete (CiP) reaches the 306 limit when a 0.01163 m displacement is imposed on the top of the column. In PC, the limit 307 (0.00938 m) is reached in the concrete of the beam. Also in PC, the HD limit is higher than 308 the one obtained for the concrete in beam. Finally, in a second stage of the FEM analysis, a 309 pressure of 0.12 MPa and a horizontal displacement of 0.0075 m are applied in both cases. 310 For the novel connection the beam stresses are higher in both cases VL and HD. Regarding 311 the columns, the stress for the cast-in-place connection (HD scenario) is higher. That is due 312 to a high transmission coefficient or to joint rigidity. The vertical deformation (VL 313 scenario) is 85% higher in the PC connection (0.0021 to 0.0039 mm). 314 Under incremental static loading or under imposed displacement, the structural 315 performance of the novel connection is less satisfactory than that of the in-situ solution. 316 That conclusion is obtained after analysing the first element that reaches the yield stress in 317 the linear range (Figure 5 (a) and (b)). Under vertical loading, although the equivalent 318 loading is 60% less in the precast connection, it is a satisfactory value in building structures 319 (16 kN/m2). Regarding horizontal displacements, the value of the novel element only 320 exhibits 16.62% decrease. The analysis of the single structural elements (beams, column, 321 plates and screws) allows for predicting the non-linear behaviour. It is also possible to 322 single out which element requires modification or re-dimensioning in order to reach the 323 equivalent vertical loading (EVL). Thus, under hypothetical VL increase, the concrete 17 324 strength of the beams could be increased. The collapse sequence in the prefabricated system 325 is beam-connection-column, which is satisfactory if ductile behaviour is required. With 326 regard to the maximum vertical deformation, L/1530 is obtained (0.00392 m), neglecting 327 rheological features (Figure 5(c)). The compliance factor α is obtained, following the 328 Eurocode 2 [69] prescriptions. As shown in Figure 6, the minimum α (1.56) is obtained for 329 the beam in the drift analysis (HD). The compliance factors for the maximum drift are less 330 than the obtained for the vertical loading except in the case of the column that is slightly 331 higher. 332 Case of analysis Element EC-2 R D α = R/D Beam 16.00 2.52 Column 19.20 3.02 Steel Plate 22.67 3.57 Screws 26.67 4.20 Beam 0.00938 1.56 Column 0.01875 3.13 Steel Plate 0.01163 1.94 Screws 0.02250 3.75 Vertical deformation Beam L/500 0.012 0.00392 3.06 Compliance Factor α Vertical Load Drift H/500 0.006 6.35 1.35 SW+1.35 DL + 1.5 LL 2.52 3.02 3.57 4.20 1.56 3.13 1.94 3.75 3.06 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 Beam Column Steel Plate Screws Beam Column Steel Plate Screws Beam Vertical Load Drift Vertical deformation Compliance Factor α 333 Figure 6. Compliance factor (α) in precast concrete connection elements 334 Figure 7 depicted the stress-strain distribution in the numerical model. 18 335 336 Figure 7. Stress and strain fields. Comparative analysis between PC and CiP with VL 337 loading (left) and HD loading (right). Units in MPa. 338 As expected, the principal stresses S1 and S3 are located in the upper and lower face of the 339 beam, respectively, and close to the column. As the stresses dramatically decrease in the 340 direction of the beam, it is also expected that the major damages appear in this area. S1 is 341 over the concrete limit, and rebar steel will be needed in the first loading stages. The 342 concrete in the PC beam reaches the compressive limit when the loading level is 0.12 MPa. 343 In the cast in place, the limit has not been reached for the limit value of 0.20 MPa. Shear 344 stresses are concentrated around the joint, and with the highest values in XZ direction. In 345 the precast concrete connection, a shear concentration between screws and plate is 346 observed. As in S1 case, it is also expected that rebar steel will be necessary in the first 347 stages. 348 As a way of conclusion, it could be assessed that the structural performance of the novel 19 349 connection is lower than that of the in-situ ones, in terms of deflection, horizontal drift and 350 maximum vertical loading resistance. However those values accomplish the established 351 limits for building structures. 352 353 4. Building Optimization Analysis and Life Cycle Assessment (LCA) of the novel 354 connection 355 In order to analyse the feasibility of reducing working times, as well as the environmental 356 impact, the proposed connection is applied to a case study which is representative of the 357 building stock in the South European urban context: a seven-story concrete building with 358 frames and deck slabs. As the economic impact and the LCA are analysed, it is necessary to 359 assume a specific location (in this case, Almería, Spain). Figure 8 provides the geometric 360 description of the building. 361 The case study comprises two different configurations, CS-1 and CS-2, which depends 362 on the optimization level of the structural element dimensions: (i) CS-1, maximum 363 optimization of the prefabricated elements and cast-in-place element dimensions equal to 364 those of the precast ones; (ii) CS-2, maximum optimization for both prefabricated and cast- 365 in-place elements. The dimension optimization has been obtained after performing 366 numerical analysis on the structural response, by using the commercial software 367 CYPECAD [72]. Following the Eurocode prescriptions [73, 74, 75], the next loading data 368 and conditions have been considered, (i) Gravity load: deck slab self-weight (SW) is equal 369 to 2.35 kN/m2, dead load (DL) is equal to 2 kN/m2, live load (LL) is equal to 2 kN/m2; (ii) 370 Wind load: reference wind speed is equal to 26 m/s, the terrain category is III and plain 371 terrain orography is considered; (iii) Seismic loading: a dynamic modal spectral analysis 372 has been performed, considering a regular structural system with low ductility, type C soil, 20 373 and importance class II. The behaviour factor (q) is 3.6, and the reference peak ground 374 acceleration (agR) is equal to 0.14g m/s2. 375 Figure 8. Description of the building: (a) General plan and section; (b) General view 376 and detail of the cast-in-situ connection; (c) General view and detail of the prefabricated 377 connection 378 379 The following specific structural elements are considered within each configuration: 380 CS-1: 381 oPC-PT: the proposed dry-precast concrete beam to column connection, 382 including the post-tensioned tendons; 383 oPC: the proposed dry-precast concrete beam to column connection, without 21 384 post-tensioned tendons; 385 oCiP: the cast-in-place structure is equal to the prefabricated elements in 386 terms of dimensions. 387 CS-2 388 oPC-PT; 389 oPC; 390 oCiPOp, the cast-in-place structure is optimized in terms of dimensions and 391 quantity of steel. 392 Regarding durability, the service life periods are 50 and 100 years. 393 394 4.1. Building work optimization and economic impact 395 In order to evaluate the building work optimization, a comprehensive assessment is 396 performed, comparing all the cases for each configuration, CS-1 and CS-2. The analysis 397 focuses on the following issues: quantity of structural materials, building schedule and 398 economic cost. 399 4.1.1. Quantity of structural materials 22 400 401 Figure 9. (top) General MTO; (bottom) 50 years-service life MTO comparison 402 403 The material take off (MTO) for each configuration (Cast in Place, Cast in Place 404 Optimized, Precast Concrete Post Tensioned and Precast Concrete) is obtained (Figure 9). 405 Focusing on the cast-in-place models CiP and CiPOp, when the service life is 100 years a 406 minimum increase for the reinforcing steel is obtained. Comparing the optimized model 407 CiPOp vs. CiP, concrete and formwork undergo a significant decrease (21.4% and 29.4% 408 respectively), and, as aforementioned, the values remain stable both for 50 and 100 years. 409 The quantitative difference between precast concrete element models, PC-PT and 410 PC, is associated to the use of the PT. Thus, a minimal increase in concrete in the case of 411 PC, and an increase of 6175.96 kg in the weight of the steel (PT-steel) are obtained. In 412 prefabricated models, there are not changes in dimensions of concrete or rebars under 50 413 and 100 years of service life. 414 Focusing on the 50 years-service life MTO , Figure 9 bottom, a reduction in steel up 415 to 41% between PC-PT and CiP is obtained. As expected, an increase in formwork between 416 precast models and CiP (33.33%), and minimal change (3%) in comparison to CiPOp is 23 417 observed. However, the reduction in concrete is up to 16.50% in CiPOp model, while 418 minimal changes are observed between prefabricated and CiP models (2.25% maximum). 419 As explained, minimal changes are observed between 50 and 100 years of service 420 life in MTO. 421 422 4.1.2. Building schedule 423 An estimation of the building schedule is obtained, adopting data from local industry [76], 424 official construction database [77] and from the calculated MTO. The building elements 425 that are considered are beams, columns formworks and deck slabs. The number of days for 426 each step, as well as the time dependency during erection are taken into account. It is 427 assumed that a minimum equipment and team is on-site or in workshop, that is, it is 428 presupposed that there is a minimum number of people per activity, under the premise that 429 no too much people is performing the same task. After evaluating the task performance, the 430 man-hours required to carry them out, as well as the duration are obtained for each case 431 (Figure 10). 432 Figure 10. Man-hours and task duration 433 434 When the prefabricated system is used, a substantial working time reduction, in terms of PC-PT PC CiP (50 years) CiP (100 years) CiPOp (50 years) CiPOp (100 years) PC-PT PC CiP (50 years) CiP (100 years) CiPOp (50 years) CiPOp (100 years) PC-PT PC CiP Columns Beams Deck slab Man-Hours needed 215.84 215.84 926.55 926.55 742.79 751.36 373.03 280.84 1786.03 1792.45 1546.78 1530.90 365.19 365.19 365.19 Task duration 143.99 143.99 781.82 781.82 629.82 638.38 232.70 186.61 1453.58 1460.00 1293.29 1282.29 241.16 241.16 241.16 Task Duration Decrease (%) 81.58 81.58 83.99 87.16 81.58 81.58 83.99 87.16 78 79 80 81 82 83 84 85 86 87 88 0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 Decrease (%) Hours Man-Hours needed Task duration Task Duration Decrease (%) 24 435 man-hours and task durations, are obtained for the columns and beams building works 436 (Figure 10). Thus, with regard to columns, the novel dry precast connection provides 437 81.58% task duration decrease. As far as the beams are concerned, a significant decrease is 438 also obtained (83.99% with post-tensioned tendon and 87.16 without it). However, for the 439 deck slabs no variation is observed. The results show that the variations due to the service 440 life are negligible. 441 From the obtained data, it is possible to estimate the global schedule, being only 442 necessary to obtain the activity duration by levels (Figure 11). For each floor, the following 443 common tasks are considered: placement of reinforcement, placement and removal of 444 formwork or pouring of concrete. Regarding durability, no changes in the schedule between 445 the prefabricated and the cast-in-situ schedule are expected, so only the service life of 50 446 years is considered. After determining the schedule to execute each floor, as well as the 447 exact time in which the building of the next level could be started, a global schedule is 448 obtained. For the cast-in-place structures the global schedule for CiP and CiPOp are 241 449 days and 223 days (Figure 10). The same procedure is applied to the precast-based 450 structures, concluding that the number of days required to erect the building is 85 with post- 451 tensioned tendons and 78 days without post-tensioning. As the deck slab is the same in both 452 cases, no schedule variation is obtained. 453 31 Construction Site Vega de Acá, Almería. Spain Veg Steel Factory Siero, Asturias. Spain Ast Concrete Product Plan Paraje El Chumico, Almería. Spain Chu Concrete Precast Plan Alhama, Almería. Spain Alh Regional distributor Polígono Industrial la Redonda, Almería. Spain Red Wood Factory Valencia. Spain Val Final disposal site Punto limpio Consorcio sector segundo. Spain Plc Transport routes and distances From To Distance (km) Route Steel Steel Factory (Ast) Precast Plan (Alh) 989.50 DppS Concrete Precast Plan (Alh) Precast Plan (Alh) 0 _ Steel Steel Factory (Ast) Regional distributor (Red) 1005.30 DisS Wood Wood Factory (Val) Regional distributor (Red) 457.40 DisW Concrete Precast Plan (Alh) Site (Veg) 27.90 DppS Steel Precast Plan (Alh) Site (Veg) 27.90 DppS Steel Regional distributor (Red) Site (Veg) 31.40 DrdSt Wood Regional distributor (Red) Site (Veg) 31.40 DrdSt Concrete Concrete Product Plan (Chu) Site (Veg) 6.70 DisC All materials Site (Veg) Final Disposal (Plc) 7.10 Dfd Means of transport and distances Prefabricated connections In situ connections Building materials D1 D2 D1 D2 CIBP Concrete in beams _ _ DppSt C16 DisC C16 _ _ SIBP Steel in beams DppS C32 DppSt C16 DisS C32 DrdSt C16 WFBP Wood in beam formwork _ _ _ _ DisW C32 DrdSt C16 Beams SMBP Steel in beam mould DppS C16 _ _ _ _ _ _ CIPP Concrete in column _ _ DppSt C16 DisC C16 _ _ SIPP Steel in column DppS C32 DppSt C16 DIsS C16 DrdSt C16 SFPP Steel in column formwork _ C32 _ _ DisS C32 DrdSt C16 Columns SMPP Steel in column mould DppS C32 _ _ _ _ _ _ CISP Concrete in slabs DisC C16 _ _ DisC C16 _ _ Slab SISP Steel in slabs DisS C32 DrdSt C16 DisS C32 DrdSt C16 545 32 546 III. Inventory of construction processes. The energy used in the construction processes 547 has been calculated following the method proposed by Kellemberger [81]. Two types of 548 processes have been taken into account: 549 a) Diesel burned in building machine, 550 b) Electricity used in building machine. 551 IV. Determination of environmental input and output of each unit process. The 552 ECOINVENT V.2 database has been used to obtain the main environmental information of 553 each unit processes (Table 5). 554 V. Assessment. The impact assessment is carried out using the CML 2001 method in 555 relation to Global Warming Potential (GWP) 100 a impact. The Cumulative Energy 556 Demand method is used in relation to Embodied Energy (Table 5). 557 Table 5. Inventory list Building materials Component ID Name (Ecoinvent) Unit Global Warming Potential 100a CML 2001 kg CO2-eq Embodied Energy Cumulative Energy Demand MJ Concrete in beams 504 concrete, normal, at plant m3 265.2200 1447.2335 Steel in beams 1141 reinforcing steel, at plant kg 1.3442 20.9352 Wood in beam formwork 2507 sawn timber, softwood, kiln dried, at plant m3 -713.1300 12792.1890 Steel in beam mould 1141 reinforcing steel, at plant kg 1.3442 20.9352 Concrete in column 504 concrete, normal, at plant m3 265.2200 1447.2335 Steel in column 1141 reinforcing steel, at plant kg 1.3442 20.9352 Steel in column formwork 1141 reinforcing steel, at plant kg 1.3442 20.9352 Steel in column mould 1141 reinforcing steel, at plant kg 1.3442 20.9352 Concrete in slabs 504 concrete, normal, at plant m3 265.2200 1447.2335 Steel in slabs 1141 reinforcing steel, at plant kg 1.3442 20.9352 33 Transportation and construction process Component ID Name (Ecoinvent) Unit Global Warming Potential 100a CML 2001 kg CO2-eq Embodied Energy Cumulative Energy Demand MJ Transport C16 1915 transport, lorry 16 t tkm 0.3202 5.2735 Transport C32 1943 transport, lorry 32t tkm 0.1663 2.8149 Diesel (Const-Dem) 559 diesel, burned in building machine MJ 0.0910 1.3799 Electricity (Const-Dem) 698 electricity mix kWh 0.5004 10.9038 Final disposal processes Component ID Name (Ecoinvent) Unit Global Warming Potential 100a CML 2001 kg CO2-eq Embodied Energy Cumulative Energy Demand MJ Concrete final disposal 2.007 disposal, building, cement (in concrete), to final disposal kg 0.0148 0.3217 Concrete final disposal 2.007 disposal, building, cement (in concrete), to final disposal kg 0.0148 0.3217 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Wood final disposal 2.052 disposal, building, waste wood, untreated, to final disposal kg 1.4743 0.2038 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Concrete final disposal 2.007 disposal, building, cement (in concrete), to final disposal kg 0.0148 0.3217 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to kg 0.0569 0.8638 34 recycling Concrete final disposal 2.007 disposal, building, cement (in concrete), to final disposal kg 0.0148 0.3217 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 558 559 4.3. Results of the Life Cycle Assessment 560 The following phases have been considered for the LCA: manufacturing (A1-A3); transport 561 (A4), construction (A5), maintenance (B2-B5), deconstruction (C1), transport to landfill 562 (C2), final disposal management and treatment (C3-C4) and recycling (D). Figure 13 563 shows the comparison for global warming potential and embodied energy of the buildings 564 that adopt the prefabricated and cast-in-place connections, respectively. The results are 565 given for the two studied cases CS-1 and CS-2. In each case, three structural scenarios have 566 been calculated: a) considering a service life of 50 years; b) considering a service life of 567 100 years; and c) considering a service life of 50 years, and a reusing scenario where beams 568 and columns are recoverable. 569 The results for the Cumulative Energy Demand, CED, and for Global Warming 570 Potential (GWP) are quite similar (Figure 13). Thus, the prefabricated connection without 571 post-tensioning (PC) exhibits the highest values in all the cases, excepting CS-1 for 50 572 years-durability and if the reuse scenario (C1 RH-50) is considered. Under those premises, 573 the cast-in-place connection CiP presents the highest results. Focusing on durability, if of 574 the service life is 50 years, the cast-in-place connections provide the lowest impacts. 575 Applying 100 years-service life, the in-situ solution is the most adequate from an 576 environmental perspective. The prefabricated connection without post-tensioned strands 577 (PC) closely follows these results. In the re-using scenario (RH) the results are different 578 from CS-1 and CS-2. In CS-1the highest value is obtained for the cast-in-place solution 35 579 (CiP) and the lowest impact is produced by the novel connection (PC-PT). In CS-2and 580 assuming a re-using scenario, the prefabricated connection without post-tensioning (PC) 581 provides the highest value. Under those premises, the in situ connection (CiPOp) yields the 582 lowest results. With regard to the novel connection PC-PT, there were no variations in CS- 583 1 and CS-2. Thus, the CED values are 37.14 MJ, 33.21 MJ and 18.59 MJ in scenarios a, b y 584 c, and the GWP are 2.92 kg CO2-eq, 2.55 kg CO2-eq, and 1.46 kg CO2-eq in scenarios a, b 585 y c respectively. Similarly, there were no variations for PC in CS-1 and CS-2: 38,23 MJ, 586 33,93 MJ and 19,14 MJ for CED, and 3.01 kg CO2-eq, 2.62 kg CO2-eq, and 1.51 kg CO2- 587 eq for GWP. Obviously, the reuse factor do not influence the values provided by the cast- 588 in-place connections CiS and CiSOp. It is important to highlight the significant reduction of 589 embodied energy in the 100 years service life scenario: around 57% decrease with respect 590 to the other scenarios, both for CED and GWP. 591 592 593 Figure 13. Environmental impact: (Left) Global Warming Potential (GWP) 100a (Kg 594 CO2-eq) for each connection; (Right) Cumulative Energy Demand (MJ-eq) for each 595 connection 596 597 5. Conclusions 598 In order to reduce costs and environmental impact, the implementation of industrialisation 36 599 and prefabrication is one of the main challenges that the building industry has to face. From 600 this concern, a novel dry-precast concrete beam to column connection has been designed 601 and analysed. To assess the actual performance under common building scenarios, the 602 connection has been applied to a case study: a seven-story concrete building with frames 603 and deck slabs. Re-using and different service life periods (50 and 100 years) have been 604 also considered. As the purpose of the present research was to focus on the performance of 605 the novel connection as structural element in new construction works, a promising future 606 research line will be to analyze the feasibility of using it in refurbishment-retrofitting- 607 strengthening works. 608 From the numerical structural analyses these conclusions are obtained: 609 1. Under incremental static loading and imposed displacements, the response of the 610 novel connection (as single structural element) is less satisfactory than that of the in- 611 situ solution (in terms of deflection, horizontal drift and maximum vertical loading 612 resistance). However it accomplishes the established limits for building structures. 613 2. Under equivalent vertical loading (as integrated element of a building frame) the 614 novel connection accomplishes the Eurocode compliance factors (in terms of 615 deflection, horizontal drift and vertical loading resistance). 616 From the building optimization analyses, it is concluded that: 617 1. Man-hours and task duration exhibit around 80% decrease when the novel connection 618 is used. 619 2. The global schedule undergoes 60% decrease by using the novel connection. 620 3. The service life period (50 vs. 100 years) does not impact the global building 621 schedule, both considering in-situ and the prefabricated systems. 37 622 4. The service life period (50 vs. 100 years) does not impact the construction cost, both 623 considering in-situ and the prefabricated systems. 624 5. In the prefabricated elements, the use of steel plates and screws leads to a MTO 625 increase. However, the rebar steel is 18% less in the novel connection than in the in- 626 situ elements. 627 6. 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Concrete final disposal 2.007 disposal, building, cement (in concrete), to final disposal kg 0.0148 0.3217 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Wood final disposal 2.052 disposal, building, waste wood, untreated, to final disposal kg 1.4743 0.2038 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Concrete final disposal 2.007 disposal, building, cement (in concrete), to final disposal kg 0.0148 0.3217 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638 Concrete final disposal 2.007 disposal, building, cement (in concrete), to final disposal kg 0.0148 0.3217 Recycling reinforcement steel 2.156 disposal, building, reinforcement steel, to recycling kg 0.0569 0.8638