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,...

Seismic zone

The seismic zones of most earthquake-prone countries reflect varying levels of seismicity. In large countries like the USA and India, seismicity varies from very high to zero. In areas where the seismic hazard is low, designers can ignore seismic effects and wind forces become the dominant horizontal design force. But some countries' structural codes still wisely require minimum detailing standards - at least for reinforced concrete construction - to provide some ductility or resilience should...

Retrofit techniques

An extensive range of options is available to architects and structural engineers who retrofit a building by improving its existing structure. Some of the more common techniques applicable to elements like columns and beams are illustrated in Fig. 12.9. Where new horizontal and vertical structural systems are required they are designed and detailed as outlined in Chapters 4 and 5. They are essentially identical to systems utilized in new buildings, but need to be structurally connected to the...

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...

Setbacks

A setback is where a plan dimension of a storey above a certain level in a multi-storey building reduces (Fig. 9.21). Seismic codes categorize buildings with abrupt setbacks as irregular. Sophisticated structural analyses quantify the ' notch effect' of a setback, but even though structural engineers avoid notches wherever possible because of stress concentrations, setbacks can be designed satisfactorily. The need for 3D modelling of setback buildings can be appreciated from Fig. 9.21(b) '...

Assessment

As mentioned previously, assessment is the first step in the process of retrofitting. The seismic vulnerability of a building must first be ascertained before deciding whether or not to retrofit. Building assessment usually consists of two stages. An initial or preliminary assessment begins the process. Some countries have developed assessment procedures based upon extensive knowledge of their local building types, construction methods and materials and history of seismic code devel-opments.7,...

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...

Postearthquake

In the aftermath of a destructive quake in an urban area, thousands or maybe hundreds of thousands of buildings require safety assessments. Beginning as soon as possible after the quake the objective of a rapid safety evaluation procedure is to get people back into safe homes and businesses as quickly as possible, and to keep them out of unsafe structures. Building officials, volunteer structural engineers and experienced architects undertake this work. The ideal is for each building in the...

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....

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

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

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...