Case Study: Using Methodology to Assess the Selected Details

Abstract

In this chapter the proposed methodology was used for evaluation of several most common building details/connections. It was shown how the proposed methodology can be used to separate better detail solutions from poorer ones, by recognizing inappropriate load-bearing capacity, stiffness, interruptions, asymmetrical solutions, and other important characteristics that affect the quality of a detail to be used in earthquake-resistant structure.

Based on the theoretical framework of the proposed methodology (Chap. 4), this chapter includes the presentation of the evaluation method with concrete examples of structural details. To select structural details to be assessed, we relied mainly on the solutions for energy-efficient buildings presented in previous chapters and catalogues of structural details for passive houses (see, for example, IBO (2008)). By selecting various structural details, we attempted to include a wide range of solutions. However, it must be noted that scores apply only to the analysed case, since the slightest change in the detail results in a different final score. Over twenty details intended to present the use of the evaluation methodology are presented. For a more general assessment of the suitability of a certain energy-efficient detail to be used in earthquake-prone areas, several solutions should be evaluated and assessments for as many details as possible should be substantiated with detailed experimental and (or) numerical analyses.

The following details were evaluated with the proposed methodology: (i) the building connection between an outer wall and the foundation slab (Sect. 5.1); (ii) the building connection between the load-bearing balcony structure and an outer wall (Sect. 5.2); (iii) the building connection between an outer wall and the unheated basement (Sect. 5.3); and the building connection between an outer wall and the roof structure (Sect. 5.4). The temperature range and heat flow through the structure were determined for the selected details with Thermal Bridge Simulation Tool in the Archicad software environment (Graphisoft 2015). On this basis, the factor of linear thermal transmittance ($\psi$) and the temperature factor ($f_{Rsi}$) were determined for each detail to define the parameters of the energy-efficient evaluation. The environmental assessment of a detail was based on the environmental and energy-efficiency parameters if materials used in the detail. The table with the environmental parameters of materials is summarised from (IBO 2008). The basis for the technical and structural evaluation is the analyses of the selected structural details and the review of literature on structural details of energy-efficient buildings. The scores of certain details were determined with the experiential approach and are not based directly on the numerical proof of the load-bearing capacity and other characteristics of the technical and structural evaluation.

To determine the temperature range and heat transfer through structural details, uniform boundary conditions determined for central European city with a continental climate (e.g. Ljubljana, Slovenia) (Table 5.1) were used in all cases. These boundary conditions are required as input data for the numerical analysis performed with Archicad (Graphisoft 2015). The programme numerically solves the differential equation of heat transfer through structural assemblies and the ground. Details must be defined as three-dimensional (3D) elements of a building. Subsequently, the section or analysed region in which heat transfer is to be evaluated must be determined. After determining the boundary conditions and materials, the location of (un)conditioned spaces and the course of the envelope must be defined in the programme. Then the finite element network is determined in relation to the desired accuracy of the calculation. A denser network brings more accurate results of the calculation (heat flow and the temperature range of the detail will be determined in several discrete points) but prolongs the time required for the calculation. The details of the numerical calculation (the number of iterations, the relative equilibrium, the asymmetrical index, etc.) are shown in (Blocon 2015).

Table 5.1 Input project data and requirements for the environmental and energy-efficiency evaluation of the analysed structural details

In addition to the input project data for the analysis (Table 5.1), structural assemblies (the selected materials, the thickness of all layers, thermal transmittance (U), etc.) and other characteristics (the characteristics of the elements that prevent thermal bridges, the characteristics of the fixing elements, connectors, etc.) are precisely described for each detail. Other input data for each analysed structural detail are provided graphically with a 2D cross-section of the detail. The simulation results of heat transfer through structural details are shown in diagrams for the temperature range and heat flow (see, for example, Fig. 5.2). The temperature range diagram shows the temperature range for each discrete point in the finite element network, which depends on the selected accuracy of the analysis. The latter is used to determine the lowest surface temperature ($\theta_{si, \text{min}.}$) required to assess a detail from the aspect of thermal comfort and to monitor the occurrence of condensation and mould. To monitor the occurrence of condensation, the temperature factor $f_{Rsi}$ (Eq. 3.11) is additionally calculated. The key result of each evaluation is a table with scores for the basic criteria, the selected weighting and external factors, and the final score (radial and column diagrams).

5.1 Building Connection Detail Between an Outer Wall and the Foundation Slab

The selected evaluation example is composed of a reinforced concrete (RC) outer wall and the reinforced concrete foundation slab (Fig. 5.2). The RC foundation slab runs below the entire floor plan of the building, and is thermally insulated with 2 × 12 cm thick XPS boards and the nominal compressive strength of 400 kPa. Thermal insulation boards can consist of other materials (e.g. EPS, cellular glass, etc.) with better or poorer properties (a lower or higher compressive strength, a better or poorer thermal conductivity). However, a hypothetical detail with characteristics described below is selected for evaluation. The geometrical thermal bridge at the contact between an outer wall and the foundation slab is prevented with additional thermal insulation (Fig. 5.1, detail 1*). The length of additional underground thermal insulation is 100 cm from the external point, while its thickness amounts to 20 cm. Other characteristics of the selected structural details are stated in Table 5.2.

Fig. 5.1

Analysed building connection detail between the RC outer wall and RC foundation slab

Fig. 5.2

Results of the numerical simulation of heat transfer through the building connection detail with a thermally insulated foundation slab

Table 5.2 Composition of structural assemblies for the building connection detail between an outer wall and the foundation slab

To assess and define external parameters, the analysed structural detail is assumed to be installed in a four-storey residential building with the floor area ratio of 2: 1 ($A/B = 16/8$ m) and located in central Europe (i.e. Ljubljana, Slovenia). Based on the location, climatic conditions and the level of seismic hazard can be defined. It is assumed that the building sits on a good foundation base (type A ground) with the design ground acceleration of 0.25 g. The design climatic conditions for the environmental and energy-efficiency evaluation of the analysed detail are stated in Table 5.1. Given the importance factor, the building falls into Category II (regular building) according to the definition in Eurocode 8. Additional penetrations in the area of the analysed connection detail are not planned. A comparison of the evaluation results with and without taking into account external factors is shown for the analysed detail.

A good thermal response of a detail may be substantiated with the heat transfer simulation results presented in Fig. 5.2. The temperature profile for certain boundary climatic conditions is shown on the left and the pertaining heat flow on the right. We can see from the results that the inner surface temperatures ($\theta_{si}$) are very high. The minimum surface temperature is reached in the corner of the connection between an outer wall and the foundation slab, standing at θ_{si, min} = 17.8 ℃. This was to be expected, since in theory, this region contains a geometrical thermal bridge, which is also reflected in the course of heat flow (see the right side of Fig. 5.2). The results on heat flow also show that thermal insulation successfully halts a stronger flow through the soil and prevents a thermal bridge in the critical region. In addition to the temperature range, the analysis may be used to calculate relative linear thermal transmittance (ψ [W/m K]), which is generally used to describe the extent of the thermal bridge and effect on the use of energy. The linear thermal transmittance factor for the analysed structural detail is ψ = 0.01 W/(m K). Based on the analysis boundary conditions, the temperature factor was also calculated, amounting to f_Rsi $=0.92$.

According to the environmental and energy-efficiency evaluation, the detail was mainly well assessed (Table 5.3). To determine parameter E1, both structural assemblies in the building connections were deemed to have a lower thermal transmittance than required by the PH standard (U_max = 0.15 W/(m² K)). Nevertheless, one score lower than the highest score (6) was deducted for the detail, as the PH standard recommends even lower values of thermal transmittance for houses (the value of 0.10 W/(m² K) is recommended). Parameter E2 received the highest score, since thermal insulation is continuous, and the thickness of thermal insulation on the outer wall is increased at the critical spot where a geometrical thermal bridge may occur. Consequently, the detail’s surface temperatures are high, which was taken into account in the assessment of thermal comfort (E3). Nevertheless, a minimum deduction from the score was required, as materials with a high thermal capacity (see Table 5.2, installed materials) were installed as finishes, which evokes a cold feeling when touching an outer wall or the floor. Parameter E4 received the highest score, as the details shows a very low value $\psi$, which could only be lower in the case of negative values. The highest score was also determined for parameter E5, as the detail is simple to construct, and the plastering and the reinforced concrete structure provide a good airtightness. The detail’s scores from the aspect of durability and environmental impact are slightly lower. A lower score of E6 also results from the fact that the XPS was used whose parameters had high values for the LCA (i.e. GWP, AP, PEI). Deduction for durability (E7) is justified, since the detail is in contact with the ground which is constantly moist. Therefore, the installation of all protective layers is essential for the detail to function well throughout its lifetime. Weighting factors for the environmental and energy-efficiency evaluation are determined on the basis of the assessment which parameters are crucial to the foundation detail on XPS.

Table 5.3 Values of basic parameters and weighting factors for the analysed structural detail

Since the seismic response may worsen due to the use of flexible XPS under the foundation slab, many points were deducted in the detail from the structural aspect (Table 5.3). With correct detailing, the solution with thermal insulation under the foundation slab can also be used in earthquake-prone areas, whereby sliding between thermal insulation boards, rocking on thermal insulation and extended fundamental period must be taken into account when modelling the global response. To determine the load-bearing capacity (K1) parameter, it was taken into account that the load-bearing capacity of the detail with XPS is worse in the event of an earthquake than if founded on the soil. The load-bearing capacity is greatly affected by the selection of material (XPS400 in our case). In preliminary studies, analyses showed that maximum compressive strength on the edge of the foundation slab may be exceeded (rocking may result in stress concentration) and irreversible compressive deformation may occur in XPS. It is difficult to determine the influence of the load-bearing capacity on the local level, which is why the influence of external factors (e.g. Z1—location and Z3—influence on the global analysis) should be taken into account. Similar is found for the influence of stiffness, which is reduced by the insertion of XPS under the foundation slab. A change in stiffness increases the structure's fundamental period, whereby higher buildings are subject to a greater change. To determine the score for K3, we were guided by material, as in a horizontal structural assembly, the selection of the material for the load-bearing structure is asymmetrical due to the foundation slab being placed on thermal insulation. A slightly lower score was given to parameter K4, since the load-bearing structure in the detail is not continuous all the way to the foundation base. The insertion of thermal insulation signifies a new material with poorer properties, violating the principle of uniformity. Parameter K5 scored well, as it does not contain any explicit eccentricity. Deduction for parameter K6 was established on the basis of the fact that irreversible compressive deformation and (or) uncontrolled sliding of XPS under the foundation slab may occur in a strong earthquake. Since this is a load-bearing layer under the foundations of a building, it should be protected. If it is damaged, it is virtually impossible to replace it. The last parameter (E6) scored well for the concrete structure, but received deduction because the detail is in constant contact with moisture. Weighting factors on the second level were determined on the basis of the assessment of the importance of parameters established with a parametric study of various structures founded on thermal insulation.

On the basis of analyses carried out, the load-bearing capacity criterion (K1) is assessed to have proportionately greater weight, since the detail is placed on the building foundation which is crucial to the response of the whole building. The highest weighting factor may be attributed to the stiffness parameter (K2). The analysis showed that a change in stiffness brought on by the insertion of thermal insulation may indirectly change the fundamental period of the whole building, affecting the magnitude of seismic forces acting on the building. In relation to the first two structural parameters, the symmetry parameter (K3) carries lower weight, as it does not have a significant influence in the analysed type of a detail. A higher weighting factor may be attributed to the continuity of the load-bearing structure (K4), since inserting thermal insulation under the foundation slab may violate the principle of the continuity of the load-bearing structure to the foundation base with a good load-bearing capacity. The parameter of the eccentricity of the load-bearing structure in relation to its primary load-bearing structural axis (K5), and the parameter of connections between the primary and secondary load-bearing structures (K7) are among the structural parameters deemed to have a low impact. This may be substantiated with the fact that this is an underground structural detail, which is only possible with a reinforced concrete load-bearing structure. In such a case, shifts in the load-bearing structure in relation to the main load-bearing structural axis can be solved more easily, and it is easier to fix secondary structural elements on account of the continuous primary load-bearing structure. The capacity design method (K6) also has a higher weighting factor than the structural parameters, since the detail is placed where the building is fixed, where potential damage in an earthquake would result in a more difficult and expensive restoration than in other structural details on the envelope of the building, which are more easily accessible.

Weighting factors for the environmental and energy-efficiency evaluation are determined in a similar way. Energy analyses showed that energy indicators on the local level are strongly affected by thermal transmittance (E1). Therefore, the weighting factor of this parameter is proportionately increased. It was also shown that the underground solution makes it irrelevant whether thermal insulation is continuous at all locations, which is why the influence of E2 is reduced. A high weighting factor is also attributed to the thermal comfort and condensation criterion (E3), as the detail is composed of a walk-on floor slab, whose surface temperature is the most important for the well-being of users (see Table 4.2). Analyses of influence on the use of energy showed that the influence on energy use parameter (E4) is important for such a type of a detail, resulting in an increase of its weight. A lower weighting factor is attributed to the airtightness parameter (E5) and the life cycle assessment (E6). A lower weighting factor for E5 can be substantiated by the fact that the detail is under the ground, where airtightness is not a significant component. On the basis of the review of materials for thermal insulation under the foundation slab, it can be stated for E6 that, in the current practice, there is no material that would provide a high load-bearing capacity, insulation and low environmental impact at the same time. Therefore, parameter E6 will have a lower weighting factor in the selection of structural solutions for such a detail. The highest weighting factor considering all environmental and energy-efficiency parameters is attributed to durability and stability (E7). Since the detail is under the ground, where potential aging and damage of materials would result in a considerably more expensive replacement or restoration of the detail, a higher weighting factor is sensible.

The total score (average) of the environmental and energy-efficiency parameters before weighting stands at 4.86 (81.0%) and of technical and structural parameters at 3.71 (61.9%). Such average score would be achieved by the detail with an even distribution of weighting factors and considering neutral external factors, which is used to compare the influence of external factors and weighting factors on the final score. This influence is disregarded for the other analysed details, as it is not important for detail comparison. In the next step, external factors (the level of influence on the significance of the criteria) are determined to correct the weighting factors from the second step of evaluation (Table 5.3). Weighting factors (the percentage of increase or decrease) and the division of categories of individual external criteria must be adapted to earthquake-prone areas and climatic conditions (E1) during evaluation, the importance of a building (E2) must be evaluated, the effect on the global analysis of a building (E3) must be known, the complexity of construction (E4) must be assessed, and the location and amount of penetrations (E5), and the input of funds for earthquake resistance and energy efficiency of the detail (E6) must be determined. An example of defining external factors by individual parameters is shown in Table 5.4 and follows the boundary conditions of the building connection detail. The final evaluation results with included unevenly distributed weighting factors and external parameters are given in Table 5.5.

Table 5.4 External parameters influencing the environmental and energy-efficiency, and technical and structural evaluation

Table 5.5 Final evaluation results with included unevenly distributed weighting factors and external parameters

According to Table 5.5, the total average score at the end of evaluation (after taking into account the weighting factors and the influences of external parameters) stand at 5.08 (84.7%) for the environmental and energy-efficiency evaluation and 3.43 (57.2%) for the technical and structural evaluation. Weighting and taking into account external factors are barely noticeable in the comparison of final score, as score for individual examples differ by a maximum of five percent.

Figures 5.3 and 5.4 are graphic presentations of the evaluation results. The radial diagram shows that the environmental and energy-efficiency evaluation scored better than the technical and structural evaluation. The form of the so-called floral diagram shows which parameters were not taken into account in the design of structural details. In this way, we can immediately see that virtually all parameters in the environmental and energy-efficiency evaluation were assessed as well, apart from parameter E6 which describes environmental impact. As mentioned, the weighting factor of this parameter was reduced. A very low weighting factor is also reflected in the value of the standard deviation, which is rather high (42.2%). A standard deviation may be used to recognise during evaluation whether any of the parameters significantly deviates from the average score. Therefore, this value can also be an indicator of balance of the consideration of all parameters of each evaluation. It can be stated for the specific detail that more attention should be paid to the development of materials and production processes with a low environmental impact. The technical and structural evaluation shows that the detail is assessed as satisfactory in most cases, but should be improved to produce a better response of the structure to seismic action. For this purpose, the following measures are recommended: selecting a thermal insulation material with a higher compressive strength, the use of additional horizontal stoppers and vertical restrainers to limit sliding and rocking of the building, installation protection, etc. (e.g. see the description in (Azinović et al. 2015b, 2016). Given the criteria for final evaluation in Sect. 4.6, the detail is assessed as “limited use”.

Fig. 5.3

Evaluation results of the building connection detail between the RC foundation slab and an RC outer wall presented in a radial diagram

Fig. 5.4

Evaluation results of the building connection detail between the RC foundation slab and an outer wall presented for uniformly (top) and unevenly distributed weighting factors (bottom)

Figure 5.4 is shown particularly to facilitate the comparison of the influence of weighting and external factors, and contains diagrams with evenly and unevenly distributed weighting factors. The horizontal dashed line showing the average results can also be used to comment on the results from the column charts. The greater the shift in both lines that show the average, the more unbalanced the principles of the environmental and energy-efficiency, and technical and structural evaluation. To design each detail, both parts of evaluation should be as balanced as possible, which may be graphically shown by aligning the horizontal lines that show the average. In the concrete case, the difference between both parts of evaluation increases if weighting and external factors are taken into account. In addition to changing average final scores, on which the impact is not significant in the concrete case (max. 5%), the application of weighting and external factors also affects standard deviation. The latter is reflected in the significantly changed shape of the graph, which is an important piece of additional information for the assessor. More results for various foundation details are shown in the appendix, which consider the evaluation criteria equally. Even distribution of weighting and external factors is used for simplification.

5.2 Building Connection Detail Between the Load-Bearing Balcony Structure and an Outer Wall

This section discusses the building connection between the reinforced concrete (RC) balcony slab and an outer masonry wall (Fig. 5.5). The thermal bridge that occurs due to the penetration of the RC slab is reduced or eliminated by inserting a precast load-bearing thermal insulation element (1*). The heat transfer simulation results and the numerical analysis of the seismic response are used to evaluate the detail according to the proposed methodology (Azinović et al. 2014, 2015a). The thickness of the load-bearing thermal insulation element (LBTIE) is 8 cm and its thermal conductivity stands at $\lambda = 0.12$ W/(m K). It is assumed that the precast element contains the longitudinal reinforcement only in the upper part of the slab. Such elements were examined in detail in previous studies (Ge et al. 2013; Goulouti et al. 2014), making it easier to assess individual evaluation parameters based on those results. The detail is composed of an outer masonry wall insulated with mineral wool ($U = 0.11$ W/(m² K)), an interstorey slab and a RC balcony slab. All data on the analysed structural assemblies are provided in Table 5.6.

Fig. 5.5

Analysed building connection detail of the RC balcony slab with LBTIE

Table 5.6 Composition of structural assemblies for the building connection detail between the RC balcony slab and LBTIE

Figure 5.6 shows the results of the numerical simulation of heat transfer through the analysed connection detail between the RC balcony slab and LBTIEs. The left part of Fig. 5.6 reveals how precast elements successfully prevent a thermal bridge. Surface temperatures are very high and are not lower than θ_{si, min.} =18.5 ℃ in any part of the detail. The analysis of the temperature range gives rise to the finding that the thickness of the thermal envelope is reduced at the location of the LBTIEs, which does not significantly affect the inner surface temperature. On the other hand, a certain effect on the use of energy must be expected, since heat flow is still more intensive at this critical part of the envelope despite the use of thermal insulation elements (the right side of Fig. 5.6). The linear thermal transmittance coefficient of the analysed detail is $\psi = 0.25$ W/(m K). This could be improved with a thicker load-bearing thermal insulation element or better precast elements with a lower thermal conductivity.

Fig. 5.6

Results of the numerical simulation of heat transfer through the building connection detail between the RC balcony slab and LBTIEs

As shown by the heat transfer simulation results, a thermal bridge resulting from the penetration of the RC slab may be reduced by inserting a LBTIE. This is taken into account in the detail evaluation with a high total score from the environmental and energy-efficiency aspect (Table 5.7). The outer wall structural assembly has a good thermal insulation with a low thermal transmittance that corresponds to the PH standard. Therefore, the detail receives the highest score for parameter E1. Deduction from the full score was assumed for parameter E2, as the thickness of the LBTIE is lesser than thickness of thermal insulation on the outer masonry wall. In addition, the thermal conductivity of this element is higher than the conductivity of the remaining thermal insulation. The analysis of the temperature range showed high surface temperatures, which ensure thermal comfort, and prevent condensation and mould. To assess the effect on the use of energy, it must be taken into account that the penetration of a cantilever slab is among the most complex thermal bridges, since a combination of a structural and geometrical thermal bridge usually appears at this location. We believe that the effect on the use of energy could reduce if high-quality load-bearing thermal insulation elements were used. Therefore, the score for parameter E4 is slightly lower than the full score. In the case of wider balconies, these thermal bridges are still recommended to be considered in the calculation of energy use in the building. From the aspect of airtightness (E5), the detail was well assessed because of the simplicity of construction, and because the plastering and RC structure provide good airtightness. Certain deduction was made on account of openings (windows, the balcony door), which are indispensable in the balcony structure detail. The detail was strictly assessed from the aspect of its environmental impact (E6) resulting from the used materials (RC, XPS and brick). As the detail is tested and frequently used in practice, there was no significant deduction for E7.

Table 5.7 Final evaluation results of the building connection detail of the RC balcony slab with LBTIEs

On the other hand, it is more poorly assessed from the technical and structural aspect and must be improved to be used in earthquake-prone areas. To determine the score for parameter K1, it was taken into account that the load-bearing capacity of the detail is good under vertical static loads (experimentally tested), while the reinforcement in the lower part of the cross-section, which would provide the load-bearing capacity during the cantilever uplift in the event of stronger (vertical) seismic action, was not taken into account. In addition, reduced stiffness (parameter E2) of the RC balcony cantilever slab where fixed must be considered, as it increases deflections also in the case of vertical static loads. Therefore, designers must pay special attention to the limitation of the maximum length of the fixed cantilever to meet the controls of the maximum deflection in the serviceability limit state. During the assessment of parameter K3, it was found that the detail is not symmetrical (the longitudinal steel reinforcement is not placed on the compressive and tensile side). Since the load-bearing structure is not completely continuous (load-bearing thermal insulation elements interrupt the RC cantilever slab), a significant deduction was made also for parameter K4. To determine the score for K5, it was taken into account that there is no explicit eccentricity, except in the precast thermal insulation element. The principle of the capacity design method is not taken into account in the analysed detail. However, K6 of the detail is relatively well assessed, as it is not critical to the global stability of the building. The contact between secondary (non-)load-bearing elements and the primary load-bearing structure is generally not problematic, but this detail has an increased thickness of thermal insulation and a ventilated layer. In addition, load-bearing thermal insulation elements are placed at the location of maximum bending moment (fixed end of the cantilever), where a load-bearing substructure for the balcony door must be ensured. For these reasons, the score for parameter K1 is suitably lower.

Weighting factors on the second level of the evaluation were determined on the basis of the assessment of the importance of parameters established with a structural and energy analysis of precast cantilever elements (see Table 5.7). The influence of external factors is neglected (default value 1) for simplification. The analyses showed that the load-bearing capacity (K1) was not relevant in most cases on account of high safety factors for vertical static loads, which is why parameter K1 is attributed a lower weighting factor. On the other hand, an increase in stiffness (K2) and the asymmetric placement (K3) of steel reinforcement significantly affect the response of the cantilever structure due to the insertion of more flexible load-bearing thermal insulation elements. Therefore, parameters K2 and K3 are attributed a higher weighting factor. The analyses also showed that the discontinued connection of the load-bearing structure has a great influence on the structural response. For this reason, parameter K4 is attributed a higher weighting factor. The parameters of the eccentricity of the load-bearing structure in relation to the axis (K5) and the capacity design method (K6) proved to have a very low impact on the response. This is a detail, which generally does not significantly affect the global seismic safety of the load-bearing structure, but is basically accessible on the building envelope. Therefore, K5 and K6 do not have a significant effect as in the foundation detail. A higher weighting factor is attributed to parameter K7, as this is a detail of the »+« type connection, in which the fixing of secondary (non-)load-bearing elements is more complex.

For the weighting factors of the environmental and energy-efficiency evaluation of the cantilever structure detail, the results of energy analyses were taken into account, indicating that the thermal transmittance of an outer wall has less influence on the energy properties of the detail than continuous thermal insulation (see the results in Fig. 3.16). Therefore, the weighting factor for parameter E1 is suitably lower than for parameter E2. Experience from practice, which prompted the emergence of precast thermal insulation elements, shows that the main problem of such a type of detail is its effect on the use of energy, and the occurrence of condensation and mould. To this end, the highest weighting factor is attributed to parameters E3 and E4. Greater influence is also assumed for airtightness (E5), as this is a »+« type detail, in which ensuring an airtight plane is difficult. No specifics are assumed for the life cycle assessment (E6). That is why an even distribution of weighing factors is maintained. A lower weighing factor is assumed for durability and stability (E7), as this is a frequently used detail on the envelope exposed to usual external actions. In addition, the detail is accessible, and can be replaced in the event of damage (e.g. caused by ultimate limit state) more simply and at lower costs than, for example, the foundation detail.

The diagrams in Fig. 5.7 present the final evaluation of the fixed RC cantilever with LBTIEs. Due to the potential cantilever uplift in the event of a strong earthquake and the lack of lower steel reinforcement the final detail score is unsuitable.

Fig. 5.7

Evaluation results presented in radial and column diagrams for the building connection detail between the RC balcony slab and LBTIEs

5.3 Building Connection Detail Between an Outer Wall and the Unheated Basement

This section addresses the building connection detail between an outer masonry wall and the unheated basement (Fig. 5.8). From the aspect of preventing thermal bridges, the detail is very complex, as the intensive heat flow towards the unheated basement and outdoor air must be prevented. To reduce a thermal bridge, designers used to decide on the solution to extend thermal insulation to the basement wall. This improves the temperature profile, but does not eliminate the thermal bridge towards the unheated basement. There is basically no solution to completely eliminate a thermal bridge without interrupting the load-bearing structure. With skeleton load-bearing structures, a thermal bridge in columns should be accepted, since interruptions in this section of the primary load-bearing structure are not admissible either from the aspect of the load-bearing capacity under vertical static loads or the aspect of seismic action. However, as presented in Sect. 3.2, an insulation base block can be used to interrupt or reduce a thermal bridge in certain masonry load-bearing structures. Such solutions are possible mainly due to lower compressive stresses in primary load-bearing structures in comparison with skeleton load-bearing structures. Solutions with base insulation blocks at the location where they are fixed stem particularly from earthquake-non-prone areas, where the only structural control is to ensure sufficient compressive strength for these blocks. However, additional loads, which may occur at this location of the load-bearing structure (where outer walls are fixed) must be considered in earthquake-prone areas.

Fig. 5.8

Analysed building connection detail between an outer masonry wall and the RC unheated basement

In the selected evaluation case, the following structural assemblies were analysed (Table 5.8): (i) an outer masonry wall insulated with mineral wool (U₁ = 0.11 W/(m² K)); (ii) the RC interstorey slab insulated with perlite aggregate (U₂ = 0.16 W/(m² K)); and (iii) a basement wall from concrete hollow bricks insulated with XPS (U₃ = 0.18 W/(m² K)). A thermal bridge that occurs due to the contact between an outer wall and the unheated basement is interrupted by an insulation base block (1*) with vertical (longitudinal) thermal conductivity λ = 0.13 W/(m K). In the concrete case, it is assumed that the insulation base block is made of autoclaved aerated concrete with greater porosity to achieve lower thermal conductivity of the base block. On the other hand, such autoclaved aerated concrete masonry is characterised by lower compressive strength. More options of base insulation blocks are provided in Sect. 3.2 (see, for example, Table 3.4). The thermal insulation on the basement wall is installed at least one metre below the underground section (2*).

Table 5.8 Composition of structural assemblies for the connection detail between an outer masonry wall and the RC unheated basement

Figure 5.9 shows the results of the numerical simulation of heat transfer for a structural detail with an insulation base block. The analysis of the detail took into account the simplification that the temperature of the unheated basement is equal to the outdoor temperature ($\theta_e$). The performed numerical analysis enables us to distinguish two values of linear thermal transmittance: (i) for heat flow towards outdoor air and (ii) for heat flow towards the unheated basement. Both values are very low and depend particularly on the vertical thermal conductivity of the insulation base block (see, for example, Figs. 3.11 and 3.12). The results also showed that surface temperatures are very low and do not fall to values lower than θ_{si, min.} = 17.1 ℃. This means that condensation and mould cannot occur in any part of the detail, and the desired thermal comfort is achieved, as temperatures are close to the indoor air temperature ($\theta_i$). The right side of the figure indicates that heat flow is greater towards the unheated basement, which is supported by the values of linear thermal transmittance ($\psi_2 > \psi_1$).

Fig. 5.9

Results of the numerical simulation of heat transfer through the building connection detail between a masonry wall and the unheated basement separated by base insulation blocks Ψ₁…linear thermal transmittance in direction of the external air; Ψ₂…linear thermal transmittance in direction of the unheated basement

Due to low thermal transmittance, favourable temperature range, the environmental and energy-efficiency parameters of the detail received a good total score. To assess parameter E1, it was taken into account that the thermal transmittance of both structural assemblies was lower than the PH standard requirements, but higher than recommended by current regulations in most Central European regions (i.e. 0.10 W/(m² K)). From the aspect of the continuity of thermal insulation (E2), the score is reduced due to a change in the thickness of thermal insulation at the location of the insulation base block. In addition, the vertical thermal transmittance of the base block is poorer than of the selected thermal insulation. As shown by the analysis results of the temperature range and heat flow, the detail has little influence on the use of energy and thermal comfort, making the scores for E3 and E4 suitably high. As the detail is relatively complex (many different materials, connections, etc.), certain airtightness requirements (simplicity, the continuity of the plane, airtightness cannot be ensured, etc.) are violated, reducing the score for E5. The scores for E6 and E7 are also slightly lower due to the used non-renewable materials (e.g. XPS, concrete, etc.). Therefore, a greater environmental impact may be expected. In the durability assessment, the installation complexity of a ventilated wooden façade was taken into account. To ensure the durability of a wooden façade and its thermal insulation role, numerous protective layers (e.g. wind barrier, UV protection, etc.) must be installed.

A thermal bridge is solved by an insulation base block, whose properties are generally poorer than of reinforced concrete and masonry walls. This means a weakening of the load-bearing structure at the location where the masonry wall is fixed. Due to better thermal insulation, most base insulation blocks are characterised by lower density than the load-bearing structure materials, which is why their load-bearing capacity for compression and shear is usually worse. Such a detail affects the total load-bearing capacity of masonry structures and must be considered in structural earthquake resistance evaluation. Since this is a critical detail in a structure, it is poorly assessed from the structural aspect (Table 5.9). Due to its porous structure, the used autoclaved aerated concrete is characterised by lower compressive and tensile strength. Therefore, the detail is assessed as unsuitable for earthquakes (see assumptions in Sect. 3.2). Since the insulation base block is also characterised at this location by lower stiffness than of the selected load-bearing structure materials, it is attributed a very low score for K1 and K2. To determine the score for parameter K3, the fact that the detail is not symmetrical in view of its horizontal load-bearing axis was taken into account, since it constitutes a change in the load-bearing structure material. The continuity of the vertical load-bearing structure is violated for the same reason, reducing the score for K4 (the masonry wall is not continuously connected with the RC base). It was taken into account for K5 that the masonry wall with protective layers is slightly displaced above the RC basement wall. When assessing consideration of the capacity design method (K6), it must be noted that this is a critical detail at the location where the load-bearing structure is fixed to the stiff RC basement. It was assessed that damage is very likely to occur at the unfavourable location where the wall is fixed due to the weakened load-bearing structure at this location. For this reason, the detail received the lowest possible score (0) for parameter K6. The score for K7 was also reduced because the increased thickness of thermal insulation and the ventilated layer make the fixing of secondary (non-)load-bearing elements difficult.

Table 5.9 Final evaluation results for the building connection detail between a masonry wall and the unheated basement

Unlike in Sects. 5.1 and 5.2, in which concrete cases were used to show the evaluation method and calculation procedure in the proposed methodology, external and weighting factors are not taken into account in this case, resulting in a more concise display of the results. Only final values (Table 5.9), and radial and column diagrams (Fig. 5.10) are displayed. The graphic display of the results shows a distinctly asymmetrical ratio between the scores for the detail’s structural parameters, which is evident from the difference between the average scores. From the structural aspect, the diagram is insufficient, while it is suitable for energy-efficient buildings from the environmental and energy-efficiency aspect. The detail was strictly assessed from the technical and structural aspect, as no experimental data are available for masonry with base insulation blocks. As mentioned in the chapter on assumed influence of base insulation blocks on seismic safety, the problem of base insulation blocks from the structural aspect has not yet been addressed in professional and scientific literature. In this case, the conservative values for the parameter assessment must be adopted in the proposed methodology, since scores can only be made on the basis of approximations and assumptions (e.g. the ratio between the load-bearing capacity of base insulation blocks and the remainder of the load-bearing structure, general engineering principles, etc.). Since base insulation blocks are mainly used in non-earthquake-prone areas, better thermal insulation is expected along the cross-section of the masonry wall, as reinforced concrete vertical ties are not required. In the case of masonry load-bearing structures in earthquake-prone areas, masonry must be additionally connected with horizontal and vertical reinforced concrete ties. It must be noted that a thermal bridge could still occur at the location, which would lead to a lower total environmental and energy-efficiency score. The latter may be taken into account in the proposed evaluation methodology with external parameters (e.g. Z1 and Z3).

Fig. 5.10

Evaluation results presented in radial and column diagrams for the building connection detail between an outer masonry wall and the unheated basement separated by base insulation blocks

Based on the scores according to the proposed evaluation methodology and assumptions in Sect. 3.2, it may be concluded that the detail's load-bearing capacity and ductility will be poorer, which is why it is not recommended in earthquake-prone areas. For better predictions of the response to seismic action and the use of such solutions, masonry with base insulation blocks should be experimentally tested and specific instructions for modelling, designing and executing in earthquake-prone areas must be provided. More examples of structural details with base insulation blocks are provided in the appendix.

5.4 Building Connection Detail Between an Outer Wall and the Roof

This section addresses the building connection detail between the RC flat roof and an RC outer wall with thermal insulation on the internal side (Fig. 5.11). The roof slab is extended with a cantilever over the outer wall to provide a RC canopy overhang. In the previous sections, details suitable for energy-efficient buildings were analysed. This section, however, addresses a detail that is not confirmed according to the PH standard. Therefore, greater influence on the use of energy than of previous details may be expected, as the used structural assemblies have higher thermal transmittance than required by the PH standard. Also disadvantageous for the detail from the energy aspect is that a thermal bridge occurs at the location of the RC structure connection, since thermal insulation at this location cannot be continuous. The thermal bridge in the analysed detail can be partially eliminated by installing thermal insulation at the location where the RC roof slab is fixed (1*). The length of thermal insulation from the location where the RC roof slab is fixed is 75 cm and its thickness is 5 cm. The installation of thermal insulation means that the dimension of the RC load-bearing structure is reduced in this part to maintain a flat surface for the final treatment of the ceiling. The detail is composed of an RC flat roof slab with pitched concrete and thermally insulated with XPS (U₁ = 0.19 W/(m² K)), and an RC outer wall thermally insulated with EPS (U₂ = 0.21 W/(m² K)). More information on the composition of structural assemblies is in Table 5.10.

Fig. 5.11

Analysed building connection detail between an RC outer wall and the RC flat roof with an overhang

Table 5.10 Composition of structural assemblies for the building connection detail between an RC outer wall and the RC flat roof with an overhang

Figure 5.12 shows the heat transfer simulation results for the analysed detail of a flat roof with an RC canopy overhang. On the left side of the figure, we can see that the temperature range of the structural assembly is not very favourable. In practice, walls with thermal insulation on the internal side are not desired, as the temperature drop at this location of thermal insulation is substantial. This means that condensation or the dew point could occur in thermal insulation. In theory, a vapour barrier would have to be installed on the internal side before thermal insulation. This would result in more complex details, since a vapour barrier and other protective layers require sealing to support the basic role of thermal insulation. Despite thermal insulation on the internal side, the proposed measure (decreasing the RC slab thickness) resulted in much higher surface temperatures in the detail. The minimum surface temperature in the detail stands at θ_{si, min.} = 16.1 ℃.

Fig. 5.12

Results of the heat transfer numerical simulation for heat transfer through the building connection detail between the RC outer wall and the RC flat roof with an overhang

On the other hand, the measure of adding thermal insulation on the account of reducing the size of the load-bearing structure only reduces the thermal bridge. As seen from the right side of Fig. 5.12, intensive heat flow is interrupted in the corner, where thermal insulation is installed. However, heat transfer can still be expected in other sections of the load-bearing structure (around thermal insulation). Since thermal insulation is not continuous, the linear thermal transmittance coefficient still stands at $\psi = 0.25$ W/(m K). From the aspect of preventing thermal bridges, the only option in the analysed case is to interrupt the load-bearing structure. Theoretically, there are two options: (i) installing thermal insulation around the overhang and interrupting the load-bearing wall or (ii) interrupting the load-bearing roof structure. None of these solutions is desired in earthquake-prone areas from the structural aspect.

As shown in the analysis of the temperature range, the thermal bridge is not completely eliminated in the analysed detail, making the latter only conditionally useful from the aspect of the environmental and energy-efficiency parameters (Table 5.11). The detail is poorly assessed for almost all parameters. To assess E1, the fact that the thermal transmittance of the outer wall and the roof is higher than required by the PH standards and very close to the minimum value from the common technical guidelines used in Central Europe, which is not appropriate for modern energy-efficient buildings, was taken into account. To assess E1, the fact that thermal insulation is not continuous along the envelope was considered. The continuity is partly saved by the reduced thickness of the load-bearing structure in the critical region, resulting in slight bonus for the final score. In view of the input project data, condensation and mould cannot occur (parameter E3), but the solution is poorer from the aspect of condensation, as thermal insulation is located on the internal side (a vapour barrier must be installed). The score for parameter E3 received a bonus for the detail’s location on the roof (the effect on thermal comfort is lower). The influence on the use of energy is significant due to high linear thermal transmittance ($\psi = 0.25$ W/(m K)). It was additionally taken into account that the detail runs along the edge of the roof. Therefore, the score for E4 is suitably low. Parameter E5 was well assessed because of the simplicity of construction, and because the plastering and brick provide good airtightness. The environmental and energy-efficiency score for E6 of this detail is low due to the used materials, i.e. XPS and RC. Regarding durability (parameter E7), it was taken into account that the detail was tested and simple to build.

Table 5.11 Final evaluation results for the building connection detail between an outer wall and the roof

In structural terms, the detail was poorly assessed (Table 5.11), as the thermal bridge was reduced by decreasing the dimension of the load-bearing RC roof structure. This made the detailing of the contact in earthquake-prone areas difficult, which requires, in critical regions, higher ratio of steel reinforcement, a symmetrical set-up of steel reinforcement, suitable stiffness and the load-bearing capacity of the contact. In addition, weakening must be considered in the capacity design method principle, the global model of the building, and the seismic analysis. To determine the parameters for the technical and structural aspect, experiential engineering approach was applied, which follows the principles of Eurocode 8. To determine the score for the load-bearing capacity (K1), the assumptions of a lower load-bearing capacity under vertical static and cyclic loads (due to weakening in the roof), reduced load-bearing capacity (potential damage to the RC roof in the case of substantial loads), and the critical region made difficult due to the reduced dimensions of the load-bearing structure were taken into account. A similarly low score was attributed to K2, since stiffness is expected to reduce due to an interruption in thermal insulation. Such a weakening must be taken into account in seismic analyses—a partially stiff joint is analysed. Parameter K3 was assessed as satisfactory. There was a deduction from the full score, as the detail is not symmetrical in view of the horizontal load-bearing axis resulting from the insertion of thermal insulation (reduced dimension of the load-bearing roof structure). From the aspect of continuity (parameter K4), it may be foreseen, on the basis of the known data, that the detail is continued vertically but not horizontally, as it is complicated to anchor reinforcement for the overhang. It is also difficult to ensure continued longitudinal steel reinforcement to the outer wall. A slightly lower score may be expected for K5 due to a shift in relation to the horizontal axis brought on by the insertion of thermal insulation. In the assessment of K6, it was taken into account that the detail is not critical in the global context of the building. There is also weakening in the load-bearing roof structure, and the vertical load-bearing structure is protected, which is favourable for the capacity design method parameter. Nevertheless, designers should foresee weakening in the load-bearing structure in the global seismic analysis. As already mentioned, the reduced thickness of the load-bearing structure in the critical region results in difficult fixing of secondary (non-)load bearing elements and the anchoring of the overhang. Therefore, the score for K7 is slightly lower (Fig. 5.13).

Fig. 5.13

Evaluation results presented in radial and column diagrams for the building connection detail between an RC outer wall and the RC flat roof with an overhang

Overall, we believe that the evaluated detail should be redesigned or replaced. Several options for the building connection detail between an outer wall and the roof are shown in the appendix.