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The need for greater freedom in design results in solutions that present a serious influence onto the seismic performances of a ... Jasmina Dražić and Nikolai Vatin / Procedia Engineering 165 ( 2016 ) 883 – 890. 1. ..... A manual for architects.
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ScienceDirect Procedia Engineering 165 (2016) 883 – 890

15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development”

The influence of configuration on to the seismic resistance of a building Jasmina Dražić a, Nikolai Vatin b,* b

a University of Novi Sad, Trg Dositeja Obradovića 5, Novi Sad, 21000, Serbia Peter the Great St. Petersburg Polytechnic University, Polytechnicheskaya 29, St. Petersburg, 195251, Russia

Abstract Configuration of a building, achieved by coordinating the demands of an urban project and designer’s style, and conditioned by the building’s function (interior design) and the choice of a structural system, has an effect on the building behaviour under earthquake. The need for greater freedom in design results in solutions that present a serious influence onto the seismic performances of a building. Consequences that can lead all the way to collapse demand for overall analyses and structural measures to achieve the set reliability degree of a building. Building configuration is defined in the initial design phases, when it is possible to evaluate the regularity of a structure and observe the influence of the proposed design solution onto the structural treatment (structure analysis, dimensioning, and modelling). It implies the design of regular structures (configuration) when it is necessary to provide the most economic design, building, and maximum predictability of the demanded seismic performances. Designing irregular structures, on the other hand, demands for a structural designer to be included from the initial stage of a conceptual design, the ability of an architect to accept necessary structural measures for seismic resistance and their integration into the design in order to reduce the consequences of irregularity and achieve the demanded aesthetic qualities without endangering the building integrity. © 2016 2016The TheAuthors. Authors. Published by Elsevier Ltd. is an open access article under the CC BY-NC-ND license © Published by Elsevier Ltd. This Peer-review under responsibility of the scientific committee of the 15th International scientific conference “Underground (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under scientific committee of the 15th International scientific conference “Underground Urbanisation as a Urbanisation as aresponsibility PrerequisiteoffortheSustainable Development. Prerequisite for Sustainable Development Keywords: innovative materials for seismic design, configuration, materials science, seismic resistance, regularity, seismic architecture;

* Corresponding author. Tel.: +7-921-964-37-62 E-mail address: [email protected]

1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development

doi:10.1016/j.proeng.2016.11.788

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1. Introduction Configuration (arrangement, establisment of contours, exterior shape) of a building defines a shape, size and relations of building dimensions. The terms “building concept” or “conceptual design” are often just freely used terms by architects to identify the configuration, referring to architectural (functional) characteristics, such as interior planning and surface organization in a building. Strictly speaking, building configuration refers to the indicators of shape and dimensions of a building as a unity, resulting from the project solution and related to the geometric proportion of the building contours [1]. In a wider sense, the configuration includes the type, dimensions and position of structural elements, also emphasizing the significance of structural properties of a building. Urban design and design plans for every settlement can influence the exterior of a building. In this context, urban planning demands sometimes dictate the maximum building heights, street profile (especially in densely populated urban surroundings), main building contours, need for an open first floor, vertical plane dimensions or other characteristics of architectural form. Regardless the fact that geometric parameters of a construction plot and the urban surrounding demands have an impact on the solution for a building’s foundations, the detailed design of the final building contours is based on the demands for the interior space design. The concept of an interior design includes the organization of adequate areas, by dimensions and shape, and the analysis of the surfaces for main contents of architectural space. Diverse solution variations for the interior space design in a building, in accordance with its function, can be linked to adequate possible solutions for the planned surfaces intended for human and material movements, communication zones (corridors, halls, staircases, elevators); they are based on a selection of one alternative or the combination of several alternatives. Quality of the space primarily depends on the properly set relations between individual functional zones in a facility. Wrong zoning or inadequate grouping of functional zones can destroy the overall functionality of a structure in general, resulting in a functional chaos in a building, unnecessary movement and wandering by building users. The functioning of the main (working) zones in a structure depends on the well organized movement scheme, as well as the safety of the building users and their in-time evacuation in the case of an accident or a fire. Designing architectural structures implies to find the most satisfactory disposition, building foundation and appropriate height (number of floors) in order to satisfy the conditions defined in a project brief, yet also the selection of optimal and safe bearing structure to provide a rational solution and economic building of a structure [3]. 2. Configuration of the seismically resistant buildings With the selection of a configuration of a structure (building shape and dimensions), the architect directly influences the selection of the system of bearing elements in a structure, i.e. the structural system. The type, position and dimensions of main structural elements (columns, walls, floors, staircases), as well as the non-bearing walls and openings in the horizontal structural elements or exterior facade surface elements, have an impact on the behaviour of a structure under earthquakes. Planning the interior space in a building is conditioned by the demand for a greater freedom in designing, coordination of the urban project demands, and the designer’s style, and often it results in solutions such as: soft story; discontinuity of shear walls; a variation in the bearing capacity and stiffness of elements along the building circumference; and the irregularity of shape that has a serious influence on the seismic performances of a building. The consequences that can lead all the way to collapse demand for overall analyses and structural measures to achieve the demanded degree of the structure reliability. The observations of these types of design solutions and the possible structural measures are presented in tables: soft story (Table 1), discontinuity of shear walls (Table 2), variations in perimeter strength and stiffness (Table 3), and irregularity building forms in the plan (Table 4).

Jasmina Dražić and Nikolai Vatin / Procedia Engineering 165 (2016) 883 – 890 Table 1. Soft story . Soft story Soft story is linked to the problem of the change in strength and stiffness of vertical elements of a floor and the adequate elements of other floors. It can appear anywhere, but most often it occurs in the ground floors where it is the most dangerous. Soft story implies the more complex behaviour of a building. Great horizontal movements and inadequate effects of the second order influences caused by the upper building floor weight increase the building sensitivity; damages in the ground floor spread rapidly, the building cannot regain its stability and it finally collapses.

The purpose of a structure, where the function of the ground floor is different from the function of upper floors and demands for large openings, can cause the appearance of the stiffness discontinuity, a “flexible floor”. A.

The difference in the elements’ stiffness vertically as a consequence of larger floor height in the ground level.

B.

The consequence of the project solution with large free spaces in the ground level leads to the wall failure at the first floor level, the discontinuity of stiffness and the indirect direction of load transfer.

C.

Open ground level, the alteration of the structural system; columns carry the heavy structure and walls. This is especially dangerous due to the break in the continuity of the braced walls if they are primary seismic resistant elements.

Flexible ground level presents a dangerous structure. The acceptance of such a solution demands for a complex analysis, with a high knowledge level from the structure dynamics and nonlinear structure behaviour, as well as adequate structural SOLUTIONS:

1. add columns

2. add bracing

3. add external buttresses

Table 2. Discontinuity of shear walls. Discontinuity of shear walls Discontinuity of shear walls leads to the interruption in the direct way of the load transfer from the horizontal elements via walls to the foundations. The alteration in the strength and stiffness vertically produces the tension concentration on the joint between ground and first floors, at the most dangerous location.

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From the structural point of view, the satisfactory solutions imply the application of uninterrupted diaphragms along the height from the top to the foundations of a building. If the project solution, building function or the evacuation roads presume the interruption in diaphragms, the possible consequences of such a solution should be analyzed in detail immediately on the conceptual design level.

Table 3. Variations in perimeter strength and stiffness. Variations in perimeter strength and stiffness During the seismic load action, the structural element characteristics along the building perimeter have a significant influence on the building behaviour. In the case of diverse strength and stiffness of elements placed along the structure perimeter, the centre of the mass does not coincide with the centre of the resistance, causing undesired torsion effects and severe damage even on the regular foundation contour buildings. Structures with open facades, one, two or three, are common project solutions for shops (individual or in the malls), fire stations, etc.

In order to reduce the possibility of torsion, SOLUTIONS are found in balancing structural characteristics (stiffness) of elements located along the structure circumference.

light cladding Light cladding in the zone of closed facade planes or separating the heavy sheathing from the primary structure moment frame

stiff walls Stiff shear walls to balance the stiffness of the open facade with the elements in the closed facade planes stiff diaphragm

Moment frame at the open front

Combination of frames, walls and stiff diaphragm (for relatively small structures)

Table 4. Irregularity building forms in the plan. Irregularity building forms in the plan Demands for a large number of light and large rooms in the building often result in complex building forms (in plan, shape of an L,T,H etc., or a combination of these shapes).

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First possible problem occurring with the complex forms in the plan structures is the concentration of tension at the position of foundation breaks (angles). Second problem is torsion, due to the impossibility of coinciding the centre of mass and the centre of resistance for all directions of earthquake action. The problem depends on the characteristics of soil movement, building mass, structural system type, wing length and their proportions, wing height and the ratio between height and depth.

Table 5. Irregularity building forms in the plan. First SOLUTION is to separate buildings into wings, and the second approach are structural strengtheners to balance and provide building resistance for the earthquake action (for smaller structures).

1.

2.

3.

3. Regular or irregular configuration The influence of the building configuration onto its behavior under the earthquake action classifies structures into regular and irregular. Regular, satisfactory building configurations refer to simple and spatially balanced solutions that can be relatively easy encircled in a seismic analysis, structural systems that are easily modeled and analyzed; thus, these buildings present better and safer behavior, with less damage under severe earthquakes. Irregular building structures demand the application of more complex dynamic analysis methods or the increase in bearing capacity with the application of simple calculation methods. Structural treatment often requires the introduction of unjustified simplifications during modeling and analyses, which can lead to errors in the evaluation of the real structure motion under earthquake action. The behavior of irregular structures is difficult to predict, and the oversimplified or inadequate calculation presumptions can result in unreliable or non-economic solutions. The possibility to evaluate design solutions in the conceptual design phase for an aseismic structure and the definitions of the building regularity enable an architect to face the consequences that the proposed design solution has on the building behavior (structure analysis, modeling and dimensioning) in the initial design phases [3]. Irregular buildings can occur as a result of urban planning, as a search by an architect for an original form, and often as a result of inadequate education in aseismic design. The solution for the problems related to the lack of knowledge and the incapability of the idea realization within the group of earthquake resistant structures can be provided by the “earthquake architecture”. The solutions inspired by the seismic engineering technologies, where

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the elements and the technology levels of earthquake engineering are utilized as the elements of architectural expressions [2], [4], reduce the limitations of traditional principles to aseismic design. The scheme in Figure 1 presents the conceptual design phase and the influence of the selected configuration (regular or irregular structure) onto the design flow of a seismically resistant building. Following simultaneously the evaluation criteria related to the architectural concept and the ability of the structural system to accept seismic actions, it is possible to classify buildings according to diverse degrees in seismic architecture [5]. Buildings with a high degree of seismic architecture index refer to the structures resistant to earthquake action.

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DESING OF ASEISMIC BUILDINGS

CONCEPTUAL DESIGN PHASE

DEFINING THE CONFIGURATION

The influence of the configuration onto the building behaviour under earthquake action

EVALUATION AND SELECTION OF A SOLUTION (configuration)

REGULARITY CRITERIA

REGULAR CONFIGURATIONS

When it is necessary to provide the most economic design and building

When it is necessary to provide maximum predictability of set seismic performances

When it is necessary to provide best seismic performances for the lowest cost

BUILDINGS WITH A HIGH DEGREE OF SEISMIC ARCHITECTURE INDEX

Dance centre in Aix-enProvence, France

Sendai City Multimedia Library in Sendai, Japan

IRREGULAR CONFIGURATIONS The architect should be aware of the influences of the selected configurations onto the structural treatment and behaviour of the building under the earthquake action, as well as the fact that the problem of irregular configuration cannot be solved by seismic calculations

Structural designer showing interest for the proposed architectural solution should be included at the very beginning of the design process

It is expected from the architect and the designer to maximally utilize their knowledge and imagination in order to reduce the consequences of irregularities and achieve the set aesthetic qualities without endangering the structure stability

Tod's Omotesando Building in Tokyo, Japan

The architect should be able to accept the proposed structural measures which can alter the design, i.e. to integrate these measures and use them in designing the solution

Bird's Nest, Olympic Stadium in Beijing, China

Design solutions that include extreme irregularities can demand for special and expensive structural solutions, hence the significance of the building has to justify the needed financial investments into the seismic protection.

Fig. 1. The influence of the selection of configuration onto the design flow for a seismically resistant building.

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4. Conclusion The influence of the building configuration onto its behavior under the earthquake action implies the significance of a good conceptual design. Educating architects for aseismic design implies the possibility of evaluating design solutions in the initial design phase (structure regularity) and introduces them to the consequences that the selected configuration has on the building behavior (analysis, modeling, dimensioning of a structure). Regular building structures behave satisfactory under the earthquake action and can be enclosed relatively well in a seismic analysis (they are easily modeled and analyzed), and hence they imply economic solutions with the best seismic performances. The behaviour of irregular structures during earthquakes is extremely complex, often unpredictable and it is very difficult to accurately determine the seismic response of a building. Designing irregular configuration buildings demands the introduction of a structural designer from the initial design phases. The knowledge of the design principles for seismically resistant structures and the earthquake engineering technology enable an architect to utilize the structural measures for seismic resistance while designing the solution and, together with the structural designer, to accept the responsibility for the building realization in these conditions. By designing buildings with a high degree of seismic architecture, the architect achieves the set aesthetic building qualities without endangering the stability of a structure. Acknowledgements The work reported in this paper is a part of the research within the research project TR 36043 "Development and application of a comprehensive approach to the design of new and safety assessment of existing structures for seismic risk reduction in Serbia", supported by the Ministry for Science and Technology, Republic of Serbia. This support is gratefully acknowledged. References [1] C. Arnold, R. Reitherman, Building Configuration and Seismic Design, John Wiley & Sons, 1982, pp.194. [2] A. Guisasola, Base isolation in architecture, The 14th World Conference on Earthquake Engineering, Beijing, 2008. [3] J. Dražić, The Analysis of Interaction of Functional and Structural Building Properties in Aseismic Designing, Doctoral dissertation, University of Novi Sad, Faculty of Technical Sciences, Novi Sad, 2005. [4] M. Mezzi, Configuration and morphology for the application of new seismic protection systems, First European Conference on Earthquake Engineering and Seismology, Geneva, 2006. [5] S. Tomaž, V. Kilar, Assessment of Earthquake Architecture as a Link between Architecture and Earthquake Engineering, Znanstveni časopis za arhitekturu i urbanizam Prostor, Zagreb, 2008, pp. 154-167. [6] FEMA, No. 454: Designing for Earthquakes. A manual for architects. FEMA (Federal Emergency Management Agency). Building seismic safety Council. Washington, D. C., 2006.