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....

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...