Solutions to problems caused by infill walls

Unfortunately, only three solutions are available the first is often not feasible and the other two, while simple in theory, are difficult to achieve in practice. (a) Symmetrical frame building with CoR and CoM co-incident (b) Infill walls cause CoR to move to right creating an eccentricity between CoM and CoR Horizontal movement of column furthest from CoR (c) A y direction earthquake force causes the building to twist about CoR 10.8 Asymmetrically placed infill walls cause building torsion...

Types of braced frames

Often concealed within the walls of building cores braced frames cantilever vertically from their foundations to resist the seismic forces transferred from diaphragms. The basic types of braced frames are illustrated in Fig. 5.23 . 5.23 Common types of braced frames. 5.24 Tension-only bracing. Light industrial building, Wellington. 5.24 Tension-only bracing. Light industrial building, Wellington. The diagonal members for all frame types except for tension-only braced frames are designed to...

References And Notes

Building configuration the architecture of seismic design. Bulletin of the New Zealand National Society for Earthquake Engineering, 17 2, 83-88. 2 European Committee for Standardization (2004). Eurocode 8 Design of Structures for Earthquake Resistance - Part 1 General Rules, Seismic Actions and Rules for Buildings (BS EN 1998-1 2004). 3 American Institute of Civil Engineers (2006). Minimum Design Forces for Buildings and Other Structures (ASCE SEI 7-05), American Institute...

Seismic hardware

There is increasing use of seismic isolators, structural fuses, dampers and bearings in modern buildings. Figure 17.2 illustrates mild steel cantilever dampers that are exposed around the perimeter of a building. This is possibly the first time that seismic isolation has been articulated to any significant degree. Such a design approach is worthy of further development. In most seismically isolated buildings, exciting and innovative technologies are hidden from public view and their expressive...

Damage avoidance

Given that the best method of damage avoidance, seismic isolation, is unsuitable in many situations, researchers are investigating other methods of avoiding damage - particularly to structural members. To a large degree, buckling-restrained braces achieve this goal but chunky diagonal braces are often unacceptable architecturally. Researchers have proposed several methods whereby damaged structural fuses are easily replaceable but none have been widely adopted.9 Precast concrete...

Dampers

Dampers perform the same function in a building as shock absorbers do in a motor vehicle. They absorb vibration energy in the system, reducing acceleration and movement to provide a smoother ride. Dampers are also known generically as energy dissipaters. They transform dynamic energy into heat, either reducing horizontal drifts in buildings (and therefore damage), or allowing designers to specify more slender structural members. The role of dampers in seismic isolation where they have most...

Resources

Two organizations lead the way in providing seismic design information relevant to building designers in developing countries. The main resource of the World Housing Encyclopaedia is its collection of more than 100 reports of housing types from 37 different countries.10 The reports, which include brief notes on the cultural settings of buildings and their inhabitants by describing many non-engineering aspects, focus their attention upon the earthquake resistance of buildings. In most cases...

Summary

Building demands a far broader approach and a wider range of skills. Not only are structural systems and elements to be provided, but they necessitate thorough integration with architectural planning hopefully enhancing the building function and architectural design concepts. During the process of configuring structure, many other architectural issues demand attention. Entry, circulation, quality of interior spaces and natural light, are but a few of the issues to be addressed concurrently. And...

Earthquakes

Chapter I dwelt with the nature of ground shaking as it affects buildings. This chapter now outlines the basic principles of seismic resistance for buildings. Factors such as the dynamic characteristics of earthquakes, their duration and the effects of site conditions are all external to a building. No matter how well or poorly designed, a building has no control over those effects. But as we shall see, a combination of factors such as the form of a building, its materials of construction and...

Bridging between buildings

An extreme example of spanning a seismic gap between independent structures occurs when they are bridged. In urban environments bridges spanning between buildings are a common sight. Designers must ensure that when the buildings move out-of-phase with each other the bridges remain undamaged. The form of bridging may be a literal bridge, providing horizontal circulation from one building to another, or perhaps a glazed roof canopy that creates a sheltered courtyard. The primary design challenge...

Client

As mentioned above, conversations between client and architect rarely include structural issues. Perhaps the need for some floor areas to support heavy file-storage systems warrants discussion, but otherwise a client expects the architect and structural engineer to deliver an economic and trouble-free structure. After all, the client is familiar with the concept of gravity forces. A gravity resisting structure is experienced every day of the week although mostly at a subconscious level. And,...

Structural design approaches

Two new approaches to structural design are gathering momentum within the structural engineering profession. Of the two, ' displacement-based design' has fewer implications for architects although it does provide a more rational basis for achieving acceptable levels of performance in design earthquakes. Rather than a structural engineer commencing a seismic design by calculating the stiffness and natural period of a building and then determining inertia forces, displacement-based design begins...

Interdisciplinary interaction

When urban planners respond to the general seismic hazard posed by ground shaking, as well as to the specific earthquake-induced hazards mentioned above, they must work as members of interdisciplinary teams. Due to the complexity of seismic damage scenarios, planners need experts from other disciplines to help them refine their proposals and to check for any unintended negative effects that might arise. Teresa Guevara-Perez warns how seismic vulnerability can increase when planners neglect to...

Federal Emergency Management Agency FEMA httpwwwfemagov

Publications for US architects and engineers including procedures for rapid assessment of earthquake damaged buildings, information on school safety, techniques for seismic retrofitting and (2006). Design for Earthquakes A manual for architects (FEMA 454). The publication aims 'to help architects and engineers become better partners, not to further their separation, and to encourage a new level of architect and engineer collaboration'. It contains in-depth and wide coverage of topics relevant...

Shear walls

Shear walls are structural walls designed to resist horizontal force. The term 'shear wall ' originally referred to a wall that had either failed or was expected to fail in shear during a damaging quake. Now that a primary objective for contemporary structure is to avoid shear failure, 'shear wall ' is a somewhat inappropriate description for a modern well-designed wall. However, given the term's international popularity, its on-going usage is justified by appreciating that a shear wall is...

Ground Shaking

According to the Natural History Museum, London, the ground upon which we build is anything but solid. The Earth Gallery illustrates how rocks flow, melt, shatter, are squeezed and folded. But more than that, the continents that support the earth's civilizations are in constant motion. Hundreds of millions of years ago the continents were joined, but now they are dispersing ever so slowly. Once, the east coast of South America nestled neatly against the west coast of Africa. Now, separated by...

Contemporary architecture in seismic regions

Without entering the territory of Earthquake Architecture (Chapter 17), where ideas and concepts expressive of seismic effects inspire architectural designs, a brief examination of contemporary architecture in seismically active regions is warranted. Is the architecture of seismic regions different from that of seismically quiescent areas Do the rules and recommendations regarding regularity, symmetry and so forth necessitated by seismicity, exercise a stultifying influence upon architecture...

Innovative structural configurations

The search for innovative structural configurations to outwit quakes is still very much alive, after having exercised many minds over the centuries. Indeed, the list of those searching has included more than structural engineers. Witness a physician's patent for base-isolation, and architect Frank Lloyd Wright's commendable yet flawed attempt to use soft ground as a seismic isolation system for the Tokyo Imperial Hotel.11 The discovery of the ultimate 'earthquake-proof' system or configuration...

Contractor

Traditionally, architects communicate their design intent to the contractor through plans and specifications. The success of this approach depends on the clarity with which information is presented, the care with which the contractor reads the contract documents and the degree of familiarity the contractor has with the construction detailing as drawn. Where contractors are not familiar with aspects of seismic design and detailing the seismic safety of buildings may be jeopardized. A US study of...

Casestudy the Villa Savoye

As an example of meeting the requirements for seismic resisting structure and the challenge of integrating it architecturally, consider one of the iconic buildings of the Twentieth Century Le Corbusier's Villa Savoye. Completed in 1929, it is located in the seismically benign city of Paris (Figs 3.6 and 6.26). What if an identical building were to be built in a seismically active city like Tokyo or Istanbul The gravity forces of the Villa are carried by reinforced concrete flat slabs including...

Diaphragms

Imagine it to be a typical floor of a medium-rise building. For most of its design life the floor structure Section Inertia forces in one storey from y direction shaking 4.1 Inertia forces within a multi-storey building shown in plan and section. resists gravity forces dead and imposed forces that act vertically. But during an earthquake, that perhaps lasts only between 10 to 100 seconds, the floor structure resists horizontal seismic forces. During this...

Soft storeys

Soft storey configuration describes structure where one storey of a building is more flexible and or weaker than the one above it from the perspective of seismic forces. Rather than earthquake energy absorbed by ductile yielding of steel reinforcing bars, or structural steel sections in plastic hinge zones, or structural fuses throughout the whole structure as shown in Fig. 5.44(b), in a soft storey configuration earthquake energy concentrates on the soft storey (see Fig. 5.44(a)). Serious...

Bond beams

Precast Shear Walls

Bond beams, introduced in Chapter 2, offer another approach to resisting horizontal inertia forces and transferring them sideways to bracing elements (see Fig. 2.19). In the absence of a floor or roof diaphragm a bond beam can span horizontally between lines of vertical bracing elements like shear walls. Although designers use bond beams frequently in masonry construction the same principle can be applied 4.16 A hidden eccentrically braced frame immediately behind precast concrete panels is...

Historic buildings

The retrofit of historic buildings invariably requires a variety of conservation approaches. Any retrofit scheme must be consistent with, and fully integrated with, the chosen approach. For example, if the form and materials of an existing building are to be preserved, retrofitting techniques might need to be concealed. This may require the use of more innovative and sophisticated retrofit methods than normal. On the other hand, full or partial exposure of retrofit systems and details may be...

Gravity resisting structure

As explained above, the architectural integration of seismic and gravity resisting structure and architect-structural engineer collaboration is best begun early in the design process. In the early days of seismic design when suspended floors were cast-in-place rather than utilizing Area of floor supported by the perimeter frame (c) Separate seismic and gravity resisting structure 6.7 Floor plans showing different degrees of separation between seismic and gravity resisting structure. Area of...

Nonparallel systems

Mexico Earthquake 1985 Glass Damage

Figure 8.21 illustrates two non-parallel systems. In each case the directions of strength of the vertical structures are angled with respect to any sets of orthogonal axes. The ability of each configuration to resist horizontal forces and torsion is understood by considering the length of each vertical system as a strength vector. A vector can be resolved 8.22 A non-parallel system showing the orthogonal force components of each wall and secondary diaphragm stresses for a y direction force....

Transfer diaphragms

The diaphragms discussed previously are sometimes termed simple diaphragms. They resist the inertia forces from their own mass and those of elements like beams and walls attached to them. Transfer diaphragms resist the same forces but in addition they transfer horizontal forces (a) Notch destroys continuity of chord (c) Penetration where the diaphragm shear force is at its maximum (c) Penetration where the diaphragm shear force is at its maximum Area where diaphragm shear failure is likely (b)...

Seismic design and architecture 109

Proposed seismic resisting structure Proposed seismic resisting structure (c) Plan of first floor showing proposed structure 6.26 Simplified floor and roof plans of the Villa Savoye showing the proposed seismic structure if rebuilt in a seismically active area. out-of-plane inertia forces and structurally separated, as explained in Chapter 10. Due to their small diameter, the columns (or pilotis as they are usually called) are far too weak and flexible to function as members of moment frames...

Diaphragm discontinuities

Discontinuity The Shear Wall

In the ideal world of the structural engineer, diaphragms in buildings are not penetrated by anything larger than say a 300 mm diameter pipe. Diaphragms are also planar and level over the whole floor plan. However, the real world of architecture is quite different, because in most buildings quite large penetrations are required for vertical circulation such as stairways and elevators. Building services, including air ducts and pipes also need to pass through floor slabs and in the process...

Introduction

Chapters 4 and 5 introduced readers to the range of horizontal and vertical structural systems found in earthquake-resistant buildings. Each building requires a horizontal system that resists and then distributes inertia forces into the vertical structure for instance shear walls provided in a given direction. To account for directionally random shaking, vertical structure is provided in each of two plan orthogonal axes of a building and individual vertical elements are off-set from each other...

Approaches

Shear Failure Tower

Having considered the basic principles of seismic resistance in Chapter 2, we now step back and take a wider perspective to examine the current philosophy of seismic design. This chapter begins with a brief historical overview of earthquake resistant design, outlining some of the key developments directly relevant to the seismic design of buildings. This is followed by a review of the philosophy of seismic design as generally adopted internationally. Several important architectural implications...

Discontinuous and offset walls

At its upper levels y direction forces are resisted by shear walls at each end, but at ground floor level the left-hand wall, Wall 1, is discontinuous. Two perimeter moment frames 9.17 Ground floor damage caused by a discontinuous wall. 1980 El Asnam, Algeria earthquake. Bertero, V.V. Courtesy of the National Information Service for Earthquake Engineering, EERC, University of California, Berkeley . 9.17 Ground floor damage caused by a discontinuous wall....

Reentrant corners

Seismic Collectors Entrant Corners

Buildings that have suffered seismic damage due to re-entrant corners occasionally feature in earthquake reconnaissance reports. Although re-entrant geometries can take many shapes, what they share in common from a seismic design perspective, is their potential for damage resulting from the different dynamic properties of each wing Fig. 8.10 . For example, when the building in Fig. 8.11 is shaken in the y direction, the left-hand area of the building, and the wing to the right, react quite...

Diaphragm materiality

Horizontal Thrust Diaphragm

The choice of diaphragm materiality depends upon the spans of the diaphragm and the intensity of inertia force to be resisted. While a house ceiling or roof diaphragm might span as little as 3 m and support the inertia force of light wood framing, a roof diaphragm over a sports stadium could span over 100 m and support heavy and high concrete walls. In the first example the diaphragm web might consist of single sheets of plasterboard or plywood nailed to wood framing and wooden chords. In the...