 |
 |
 |
|
Many publications on lateral design do not address the design of diaphragms, chords and collectors in much detail. Guide to the Design of Diaphragms, Chords and Collectors: Based on the 2006 IBC and ASCE/SEI 7-05 fills that void by explaining the role that diaphragms, chords and collectors play in buildings and providing detailed examples of how to determine the seismic forces and design the diaphragm, chords and collectors for various types of buildings located in Seismic Design Category (SDC) B and D.
This guide is based on the 2006 International Building Code and ASCE/SEI 7-05: Minimum Design Loads for Buildings and Other Structures. The book's design examples also apply to the 2009 International Building Code because it references ASCE/SEI 7-05 as well. Although the 2009 International Building Code references the 2008 ACI 318 standard, there are only minor changes from ACI 318-05 in regards to the design of concrete diaphragms, chords and collectors. The design examples presented in this publication are based on seismic load effects. However, lateral forces due to wind loads also produce loads in the diaphragms, chords and collectors, and the basic principles involved in the design of these elements are essentially the same.
Detailed design examples are provided for the following:
- Four-story concrete office building with concrete diaphragms.
- Three-story office building with CMU walls, glue-laminated beams on steel columns and wood-frame roof and floor diaphragms.
- Four-story steel-braced frame building with steel beams and columns and steel deck roof diaphragm.
- Four-story steel-braced frame building with steel beams and columns and concrete-filled steel deck floor diaphragms.
Each design example includes analysis and design of the diaphragm, determination of chord forces, determination of collector forces and design of collectors to resist combined axial and flexural loads.
From the Preface
Three very important elements of the lateral-load-resisting system (LLRS) are the diaphragm itself; the diaphragm chord, which resists tension and compression due to bending moment; and collectors, which distribute lateral forces from the diaphragm to the vertical resisting elements (shear walls, frames, etc.). Without properly designed diaphragms, the lateral forces will not be adequately distributed to the vertical resisting elements. Because chords and collectors play an important role in resisting the lateral loads imposed on them during a seismic event and in transferring the demands adequately to the building's vertical LLRS, it is critical that the chords and collectors are properly designed and detailed. Properly designed and detailed diaphragm chords and collectors are especially critical in the higher seismic design categories in which large forces are anticipated; recognizing this, building codes require that in higher seismic design categories certain elements such as collectors be designed for amplified forces that approximate the system overstrength. To complicate matters, most buildings have openings in roof and floor diaphragms that can significantly affect distribution of shear, which in turn affects the determination of chord and collector forces. In addition to the above, consideration of torsional effects, where diaphragms are not flexible, will further add to the complexity and will result in making the analysis and design of chords and collectors a formidable task.
Many publications on the design of lateral-load-resisting systems do not address the design of diaphragms, chords and collectors but provide only a cursory discussion of the subject without any details of how to actually design these crucial elements. This guide fills that void by explaining the role that diaphragms, chords and collectors play in buildings and by providing detailed examples of how to determine the seismic forces and of how to design the elements for various types of buildings located in Seismic Design Category (SDC) B and SDC D. This guide also addresses the issue of diaphragm design when large openings are present in the diaphragm. The introduction covers in detail all aspects of diaphragm behavior such as diaphragm stiffness, diaphragm flexibility, force distribution, etc., and also discusses the purpose and behavior of collectors. Although the design examples presented in this publication are based on seismic load effects, lateral forces from wind produce similar loads in the diaphragms, chords and collectors. Although the determination of lateral forces are different for seismic and wind effects, the basic principles involved in the design of the diaphragms, chords and collectors are essentially the same.
The discussion and examples in this guide are based on the structural provisions of the 2006 International Building Code (IBC) and the American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-05) standard. Although the 2009 IBC references the 2008 edition of the ACI 318 standard, there are only minor changes from ACI 318-05 in regards to the design of concrete diaphragms, chords and collectors. Because the 2009 IBC references ASCE/SEI 7-05, the design examples in this publication are applicable to the 2009 IBC as well.
Detailed design examples are provided for the following:
- Four-story concrete office building with concrete diaphragms.
- Three-story office building with CMU walls, glue-laminated beams on steel columns and wood-frame roof and floor diaphragms.
- Four-story steel-braced frame building with steel beams and columns and steel deck roof diaphragm.
- Four-story steel-braced frame building with steel beams and columns and concrete-filled steel deck floor diaphragms.
Each design example includes analysis and design of the diaphragm, determination of chord forces, determination of collector forces and design of collectors to resist combined axial and flexural loads.
An example showing the design of collectors, using the alternate approach for the design of collectors for buildings with concrete diaphragms and beams, developed by the SEAONC Seismology's concrete subcommittee, is also presented in this guide. |
|
|
|
|
|
|
|
|
