Manual Performance Based Building Design 2: From Timber-Framed Construction to Partition Walls

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One can say RC was used in a casuistic manner, following a cost-benefit balance differing from building to building. During this period, it is common to find buildings in which only the wet areas, or the service stairs, or all the floors in the rear volumes, or the floors of the first floor or terrace are built with RC, the remaining being of wood. Apartment buildings with mixed structure of masonry and RC exist all over the city of Lisbon, although they are predominant in streets or areas urbanized during the 30 and 40 s. In Figure 2A the areas of Lisbon are identified, with the apartment mixed buildings from the two types of groups.

Figure 2. Some of the mixed masonry RC apartment buildings and their insertion areas. A Location of the buildings. Thus, in the following the focus will be given on this area. Moreover, this area corresponds to the first large-scale urban operation planned to expand Lisbon by public initiative prepared at the beginning of the s Alegre and Heitor, In that way, it is the only twentieth century Lisbon neighborhood where urban and building design was thought as one, totally coherent.

Its significant extension within the city fabric and its social, design and construction concerns turn this Lisbon area an exceptional case study for both Architects and Engineers. It was only possible because the City Hall totally changed its current methodology for city planning. This area was programed to integrate social and low rental housing, supported in equipment: school, market, civic center and small industry.

Pedestrian circulation is enabled by paths that cross the backyards of housing blocks. Other public facilities, particularly the market and the civic center, are distributed to be easily accessible by the dwellers of each cell. Public parks and gardens were designed as large common outdoor spaces for the enjoyment of residents Alegre and Heitor, Figure 3.

E Primary school as a central element City Hall 1. This is surely related with the international academic education of the Portuguese urban planner but also with research that was made by the city hall technicians, as presented in contemporary papers and reports edited by LNEC the Civil Engineer National Laboratory.

The construction of those two cells was divided in four constructed groups. The buildings in the first three groups were built with rubble stone masonry with hydraulic mortar for the exterior walls and brick masonry for the interior walls. In the last group, walls were built with hollow or massive concrete blocks masonry because of effective cost control. Floor and roof structures were made by timber beams, excepting for kitchen, bathrooms and stairs, where RC slabs were used.

Figure 4. Buildings from different cells. C Buildings in Cell IV. The construction of economic rent houses on cells V and VI was developed between and Cell V Figure 4D comprises about buildings and the urbanization of this housing project was finalized in Furthermore, in the same year, the construction of 62 more buildings was planned for the cell VI Figure 4D. The design of the buildings is like the design of the Economic Rent Houses; however, these buildings are slightly larger, allowing for more spacious rooms, and have larger balconies.

The information given in this section would provide only the principal structural characteristics of the typology under examination. The typical foundation system was made with very stiff stone masonry and with hydraulic mortar. The foundation works as a thick continuous wall, which was enlarged in its base with a minimum depth which varies from 0. Further, in this period, the first RC foundations appear in some buildings, where the reinforced concrete was used: i isolated foundation; ii foundation below the side walls; or iii foundation slab. Existing exterior, interior and partition walls are constituted by a diversity of materials: rubble stone masonry Figure 5A , solid or hollow brick Figure 5B and concrete block Figure 5C with hydraulic or cement mortar.

Figure 5.

Masonry walls with different type of materials. In general, these walls are characterized with reduction of the thickness in height of the buildings. For the buildings under study, together with the variation of the thickness of the walls, the type of materials may also vary in height. Namely, in case of the interior structural walls, solid brick was used for the lower floors, particularly for the first floor and basement, together with the staircases; on the other side, hollow brick was implemented in the upper floors.

In the transition period, the wood as a material for the partition walls practically was eliminated, except in the case of attics or mansard or in the case of the certain conditions which do not permit the use of more durable material. It should be mentioned that material used in the case of the basement' walls, when in the contact with the soil, was rubble stone and hydraulic mortar; in the parts which were placed below the ground level impermeable and resistant coating was used as covering on one side.

It should be mentioned that only in exceptional cases these buildings are not placed into the blocks. Thus, aggregate condition should be considered for the seismic assessment of an individual building that compose the block. Moreover, cases when the buildings share the side walls or not, should be also analyzed in detail, since that both situations can appear in these structures. Namely, connection between the exterior and interior walls cannot be considered as appropriate, since that such walls were built with different materials; thus, vulnerability of this connection is increasing due to the difficulties of interlocking the different masonry units e.

Moreover, even if the materials between exterior walls were the same, the connection cannot be considered completely reliable due to the bad quality of masonry at corners Figure 5D , that can be associated to construction of connected walls at different times. In any case, additional in-situ inspections and experimental tests are recommended to confirm this issue. The characteristics of RC structural elements, as well as their location, depends on the number of floors in the building. For example, in case of the buildings from Cell I and II Economic Income Houses, with a rectangular plan configuration , in general, only RC beams at the height of the window, i.

These elements avoid, for this typology, the out-plane behavior of the masonry walls, i. In the buildings from 3 to 5 floors, slender RC frame structures started to appear at the ground floor when larger spans and open spaces were needed to be used for commercial occupation. The reinforcement of the RC structural elements was used in a casuistic manner.

There is an evident absence of specific design features in terms of the amount and detailing of the reinforcement to ensure the structural safety and ductility of the system. There are mainly two types of floors: timber floors and RC slabs. The timber floors Figure 6 are commonly constituted by parallel timber beams, made of Pinus pinaster Ait, spaced about 40 to 60 cm and with sections of 0.

The floorboards are placed perpendicular to the timber beams and both elements are traditionally connected by wire nails. The timber floors are presented mainly at the front, in the social and private areas. These constructions represent the last examples of the use of timber floors and they started to be strengthened by peripheral RC beams supported on the exterior masonry walls. Figure 6. The RC slabs started to be introduced in services areas located on the back of the buildings kitchens, bathrooms, and balconies. These RC slabs were barely reinforced by steel rods and generally, with only one layer of reinforcement for positive moments; there is no guarantee on the continuity of the reinforcement between spans, thus, the slabs do not work as a continuous floor.


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RC slabs reinforced in two directions with the 0. The most common types of roof are still the timber framed of Pinus pinaster Ait. Figure 7 , as in the case of timber floors. A range of perpendicular beams, distancing from 0. In these buildings started to appear RC roofs: flat roof and alongside the traditional solutions of sloping roof.

The main stairs were made with the concrete or wooden materials and are usually located in the middle of the building. Though, buildings with more than three floors have stairs preferably constructed in RC and with the capacity to install an elevator.

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On the other side, the buildings with more than four floors, next to the main stairs, have a service staircase with access from the street and built in RC or iron. For the global seismic behavior of buildings four main methods of structural analysis are proposed in more recent codes e.

Despite one can say that linear dynamic method and nonlinear static methods, are the ones that can be used in common practice, the former is still the most common in engineering offices. For the former, and according the EC classification, a q-factor approach is followed which request the use of a q-factor value. In this section values of q-factors are defined for most representative type of mixed masonry-RC buildings.

Thus, the case-study corresponds to buildings with rectangular shape, characterized by the similar type of material and similar structural elements i. The values of q-factors are defined from the pushover curves considering different sources of uncertainties that influence the global seismic behavior. The case study consists of three floors, constant in the height, with two flats per floor.

They are with rectangular shape with overall dimensions Only walls around the services stairs in the ground floor and intermediate walls of the stairs below the first floor were built with solid bricks. Figure 8. Drawing of the case study. B front left and back right fascades. RC elements are placed on the external walls, which are strengthened belted on all floors by RC beams at the height of the window lintels with the thickness of the wall and 0.

There are two types of floor construction used in these buildings: timber floors in the rooms and concrete floors in the services areas. For case study, only the global seismic response is considered, whereas the local flexural behavior of floors and the out-of-plane walls' response are not explicitly computed as, according to the authors opinion it is not relevant. This is due to the presence of RC ring beams which reduce the vulnerability to the out-of-plane failure modes of masonry walls.

The global response of the buildings is examined through the equivalent frame modeling approach, using 3Muri Tremuri program 3Muri 2 ; Lagomarsino et al. The nonlinear response of masonry panels, concentered at walls divided into piers and spandrels, is described through nonlinear beams characterized by piecewise-linear law Cattari and Lagomarsino, a. For the definition of the backbone curve, the elastic response is described regarding to the beam theory by defining the initial Young E and Shear G modulus of masonry.

Afterwards, the progressive degradation is approximated using a secant stiffness. The elastic values are defined by multiplying the secant stiffness by a coefficient k el , which values are defined in Table 1.

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Table 1. Parameters adopted for sensitivity analyses in terms of aleatory uncertainties. The maximum shear and bending strength are defined assuming the criteria proposed in codes and literature by considering the occurrence of different failure modes: shear, flexural and mixed. Reinforced concrete elements are modeled as nonlinear beams by assuming elasto-perfectly plastic hinges concentrated at the end sections Cattari and Lagomarsino, b.

Diaphragms are modeled as an equivalent membrane with an equivalent thickness of 0. Concerning the uncertainties, two types are considered: aleatory related to the mechanical parameters and epistemic related to the structural details. These variables include mechanical properties in terms of Young modulus, shear modulus and compressive strength of rubble stone and hollow brick masonry X1 and X3, respectively and shear strength of rubble stone and hollow brick masonry X2 and X4 , then the parameters which control the drift and strength decay of piers and spandrels, respectively X5 and X6 , the parameters which control the degradation for the initial elastic stiffness X7 , the parameters connected to the stiffness of the timber and RC floor, respectively X8 and X9 , the parameters which control the connection between external walls X10 and the parameters which control the different thickness of the reinforced concrete slab X To each variable, it is defined a plausible range of variation - a minimum value X low , a median one X mean and maximum value X up - used for the proceeding of the sensitivity analysis.

The mechanical properties were defined based on the values from Italian standard and on the values obtained from experimental tests performed on the buildings, similar as the one under the examination. Detailed explanation about the procedure how the parameters were defined can be found in Milosevic et al.

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Table 1 represents the aleatory variables considered as the most relevant and included in the sensitivity analyses. Table 2 includes the gravity and live loads adopted for the examined building. The values related to drift limit and strength degradation are adopted from the experimental tests available in the literature. On the other hand, to model good connections between the walls, the equivalent beams assume values resembling a rigid link. Detail description about the calibration of the effectiveness of the wall to wall connections could be found in Milosevic et al.

The model A is considered as more representative and realistic; nevertheless, the q-factor is provided for both models see section Structural Behavior Factor. Nonlinear static pushover analyses were performed by considering each main direction X and Y in both senses positive and negative and two load patterns distributions uniform, proportional to the mass, and triangular, proportional to the product between mass and height , as recommended in EC8 and NTC.

The load distribution was adopted regarding the conclusions presented in the previous study performed on similar types of buildings Cattari et al. However, regarding the results obtained from nonlinear dynamic analyses, which is out of scope of this paper, the more comprehensible load patterns for buildings under study was defined for each direction, i.

For detailed results see Milosevic et al. Control node was selected at the top level in the wall that first collapses, as recommended in Lagomarsino and Cattari Figure 9 represents the normalized pushover curves in case of both analyzed models for each main direction and both load distributions. The overall base shear is normalized to the total weight W, while the top displacement d to the total height H of the buildings. The pushover curves depend, among others, on the material's strength, deformation capacity of each structural element and on the structural details. In the present study, the values of mechanical parameters are varied between min-median-max values, together with the two different models in terms of the connection between walls, series of the pushover curves are obtained Figure 9.

In total analyses were performed for each defined model A and B. Next to the pushover curves obtained by median values of mechanical parameters red and blue for uniform and triangular load distribution, respectively , pushover curves obtained for all models represented in gray color considered in the sensitivity analysis are also presented; in this way, it is possible to observe the variability of the behavior of the structure, considering different values of mechanical parameters. According to Figures 9A,B , which refers to Model A, it is possible to observe that both, stiffness and base shear capacity are higher in case of the X direction for both load patterns, whereas the higher ductility is obtained for Y direction due to the flexural behavior damage of the walls in such direction.

Comparing the two load patterns considered in the analysis, it is worth highlighting that in both directions the uniform pattern distributions gives higher capacity, whereas the triangular pattern distributions leads to higher ductility, mainly in X direction. Concerning the median pushover curves obtained in positive and negative directions, there is no such a big difference, particularly in the X direction, due to the symmetry of the buildings. However, based on the results obtained for all performed analyses, the dispersion in the displacement is more emphasized in case of the triangular load distribution.

Namely, the values adopted for drift in case of piers for different DLi group X5, Table 1 are the ones that significantly affect the final ductility of the buildings Figure 9A. Figure 9. As concern the Model B, similar conclusion as to the Model A is reached: bigger strength is obtained in case of the uniform load pattern for both analyzed directions. Comparing the Model A and Model B, obtained base shear is higher for the latter one, particularly in case of the Y direction, where the bad connections between walls were mainly considered Milosevic et al.

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Based on the more appropriate load pattern defined for each direction Milosevic et al. It should be mentioned that pushover curves are presented only until the value of the ultimate displacement d u , i. The evaluation of damage levels DLs assuming to have a direct relation to Limit States, LSs from nonlinear static analysis is not an easy task, and different approaches may be adopted. For instance, in the Eurocode 8 CEN Eurocode 8, a heuristic approach is followed, where LSs are defined based on conventional limits directly defined on the pushover curve, usually in terms of decay percentage or reaching of the maximum value of the overall base shear.

Though, in case of existing old masonry or mixed masonry-timber and masonry-RC buildings, application of this approach may lead to untrustworthy results. In fact, while in case of a box-type behavior with in-plane almost rigid floor behavior it is realistic to assume that many structural elements and walls reach almost at the same time a certain damage level DLi , in case of existing buildings with timber floors this condition is far to be true due to the existence of flexible floors. In fact, for unreinforced masonry buildings URM with flexible diaphragms, the limited load transfer between vertical elements leads to a more independent behavior of the walls.

Consequently, the reaching of serious damage in a wall may not appear evident on the global pushover curve, when this wall offers a small contribution to the total base shear force. Aiming to monitor the occurrence of significant damage in parts of the structure that may not be evident in the pushover curve, Lagomarsino and Cattari and Lagomarsino and Cattari proposed a multi-scale approach to define DLs on the pushover curve that defines the behavior of the buildings at three scales: i local, with damage on structural elements, piers and spandrels, ii macro-elements like masonry walls or floors and iii global represented by the pushover curve.

It may be mentioned that reference is made to the attainment of damage levels 2, 3, and 4 assumed to correspond respectively to the Damage Limitation, Life Safety and Near collapse as defined in the part 3 of Eurocode 8 CEN Eurocode 8, According to the multi-scale approach, the DLi is defined by the minimum displacement threshold obtained from the verification of conventional limits at the three scales, explained briefly in the following:.

Local scale: related with the assessment of the cumulative rate of damage in piers that reach DLi in accordance to the element multi-linear constitutive law Lagomarsino and Cattari, ;. In this study, the following limits are considered: 0.

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For the macro-element scale, a new formulation is adopted in this study, as proposed by Marino et al. It refers to the attainment of a given DL on all piers located on a story at a certain level with the aim of checking the occurrence of a soft-story mechanism. Figure 10 presents the final position of DLi in the pushover curve in X and Y directions for the Model A and the for the most representative cases in terms of load pattern distributions.

Figure The determination of the expected behavior factor q-factor according to the part 1 of Eurocode 8 CEN Eurocode 8, , for existing buildings is of great importance from the engineering point of view. Indeed, as linear analysis are still the most used in various countries and well-known among practicing engineers, suggesting adequate values of q-factors would contribute for a more predictable seismic structural performance of existing building stock. Moreover, considering the probabilistic approach Thomos and Trezos have been derived the behavior factor for reinforced concrete structures.

However, neither of these structures correspond completely to the structures under investigation. Indeed, a lot of variety exist in terms of material and structural elements and in principle q-factor should be defined for each typology. In the presented casestudy, q-factor is estimated based on nonlinear static sensitivity analysis. After having defined the pushover curves section Pushover Curves , DLis explained in section Definition of Limit States were defined on each pushover curve. Finally, after the definition of all these data, the q-factor was calculated following different criteria.

Generally most materials will not remain sealed over the long term and this system is very limited, but ordinary residential construction often treats walls as sealed-surface systems relying on the siding and an underlayment layer sometimes called housewrap. Moisture can enter basements through the walls or floor. Basement waterproofing and drainage keep the walls dry and a moisture barrier is needed under the floor. Control of air flow is important to ensure indoor air quality, control energy consumption, avoid condensation and thus help ensure durability , and to provide comfort.

Control of air movement includes flow through the enclosure the assembly of materials that perform this function is termed the air barrier system or through components of the building envelope interstitial itself, as well as into and out of the interior space, which can affect building insulation performance greatly. The physical components of the envelope include the foundation , roof , walls , doors , windows , ceiling , and their related barriers and insulation. The dimensions, performance and compatibility of materials, fabrication process and details, connections and interactions are the main factors that determine the effectiveness and durability of the building enclosure system.

Common measures of the effectiveness of a building envelope include physical protection from weather and climate comfort , indoor air quality hygiene and public health , durability and energy efficiency. In order to achieve these objectives, all building enclosure systems must include a solid structure, a drainage plane, an air barrier, a thermal barrier, and may include a vapor barrier. Moisture control e. The thermal envelope , or heat flow control layer, is part of a building envelope but may be in a different location such as in a ceiling.

The difference can be illustrated by understanding that an insulated attic floor is the primary thermal control layer between the inside of the house and the exterior while the entire roof from the surface of the roofing material to the interior paint finish on the ceiling comprises the building envelope. Building envelope thermography involves using an infrared camera to view temperature anomalies on the interior and exterior surfaces of the structure.

Analysis of infrared images can be useful in identifying moisture issues from water intrusion, or interstitial condensation. From Wikipedia, the free encyclopedia. Main article: Air barrier. Expanded Edition. Burlington: Elsevier, Advanced building technologies for sustainability. Hoboken, N. Building Science for Building Enclosures. Building Science Press, Westford, Straube, J. Guideline for condition assessment of the building envelope.

Reston, Va. Dutt and K. Oak Ridge National Laboratory.