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...

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...

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...

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...

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...