Design of Concrete Slab as Seismic Collector
CHAPTER 1
INTRODUCTION
The seismic force-resisting system of a building structure is composed of vertical elements, horizontal elements, and the foundation (Fig.1.1). The vertical elements extend between the foundation and the elevated levels, providing a continuous load path to transmit gravity and seismic forces from the upper levels to the foundation. The horizontal elements typically consist of diaphragms, including collectors. Diaphragms transmit inertial forces from the floor system to the vertical elements of the seismic force-resisting system. They also tie the vertical elements together and thereby stabilize and transmit forces among these elements as may be required during earthquake shaking. Diaphragms are thus an essential part of the seismic force-resisting system and require design attention by the structural engineer to ensure the structural system performs adequately during earthquake shaking.
The horizontal elements can consist of truss elements or horizontal diagonal bracing and diaphragms are constructed as essentially solid, planar elements made of wood, steel, concrete or combinations of these. Fig.1.1 Isometric view of a basic building structural system comprising diaphragms, walls and frames, and foundation
1.1 Diaphragms
Diaphragms serve multiple roles to resist gravity and lateral forces in buildings (Fig.1.2). They include:
• Resist gravity loads.
• Provide lateral support to vertical elements against buckling, and tie these together so that they complete the three-dimensional framework to resist lateral loads.
• Resist out-of-plane forces developed by the exterior walls and cladding as a building responds to an earthquake, and also by the wind pressure acting on exposed wall surfaces.
• Resist large horizontal thrust from inclined columns, acting within the plane of the diaphragms due to gravity and overturning actions.
• Transfer lateral inertial forces to vertical elements of the seismic force-resisting system.
•
INTRODUCTION
The seismic force-resisting system of a building structure is composed of vertical elements, horizontal elements, and the foundation (Fig.1.1). The vertical elements extend between the foundation and the elevated levels, providing a continuous load path to transmit gravity and seismic forces from the upper levels to the foundation. The horizontal elements typically consist of diaphragms, including collectors. Diaphragms transmit inertial forces from the floor system to the vertical elements of the seismic force-resisting system. They also tie the vertical elements together and thereby stabilize and transmit forces among these elements as may be required during earthquake shaking. Diaphragms are thus an essential part of the seismic force-resisting system and require design attention by the structural engineer to ensure the structural system performs adequately during earthquake shaking.
The horizontal elements can consist of truss elements or horizontal diagonal bracing and diaphragms are constructed as essentially solid, planar elements made of wood, steel, concrete or combinations of these. Fig.1.1 Isometric view of a basic building structural system comprising diaphragms, walls and frames, and foundation
1.1 Diaphragms
Diaphragms serve multiple roles to resist gravity and lateral forces in buildings (Fig.1.2). They include:
• Resist gravity loads.
• Provide lateral support to vertical elements against buckling, and tie these together so that they complete the three-dimensional framework to resist lateral loads.
• Resist out-of-plane forces developed by the exterior walls and cladding as a building responds to an earthquake, and also by the wind pressure acting on exposed wall surfaces.
• Resist large horizontal thrust from inclined columns, acting within the plane of the diaphragms due to gravity and overturning actions.
• Transfer lateral inertial forces to vertical elements of the seismic force-resisting system.
•
References: 1. Jack P. Moehle, John D. Hooper, Dominic J. Kelly, Thomas R. Meyer, “Seismic design of cast-in-place concrete diaphragms, chords and collectors”, NEHRP Seismic Design Technical Brief No. 3, 29 pp, August 2010. 2. SEAOC (2005), “Design of concrete slabs as seismic collectors,” Seismology and Structural Standards Committee, Structural Engineers Association of California, 15 pp. (http://www.seaoc.org/seismpdfs/Positions/0505_Concreteslabs.pdf) 3. ACI (2008). Building code requirements for structural concrete (ACI 318-08) and commentary, American Concrete Institute, Farmington Hills, MI.