Chapter 16: Structural Design - iccsafe.org

1 SECTION provisions of this Chapter shall govern thestructural Design of buildings, structures and portions thereofregulated by this a significant portion of Chapter 16 is dedicatedto the determination of minimum Design loads, it alsoincludes other important criteria that impact the designof structures, such as the permitted Design methodolo-gies, as well as the combinations of Design loads usedto establish the required minimum strength of struc-tural members. Unless stated otherwise, the criteriafound in this Chapter are applicable to all buildings andstructures. See Chapter 34 for application of theserequirements to alterations, additions or repairs toexisting 1602 DEFINITIONS AND following words and terms shall, forthe purposes of this Chapter , have the meanings shown terms are used in the code to describe some-thing very specific to the related subject matter whileother terms may have multiple meanings that can varybased on the subject matter and context.

2 To avoid mis-understandings, it is preferable to reach a consensuson the meaning of these terms. Definitions areintended to facilitate the understanding of code provi-sions and to minimize potential section contains definitions of terms associatedwith Structural Design and minimum load criteria. Notethat these terms are also listed in Chapter 2 with across reference to this section. Definitions that pertainprimarily to Structural Design loads are included withinthis Chapter to provide convenient access to themwithout having to refer back to Chapter 2. The use andapplication of all defined terms, including thosedefined herein, as well as undefined terms are setforth in Section STRESS method of proportion-ing Structural members, such that elastically computed stressesproduced in the members bynominal loadsdo not exceed spec-ified allowable stresses (also called working stress Design ).

3 VThis definition describes the allowable stress designmethod, which is one of the Design approaches recog-nized under the code in Section In thisapproach, the computed stresses determined from theunfactored, or nominal loads (see definition on page16-4) cannot exceed allowable stresses, which pro-vide a factor of safety. The material chapters of thecode specify either the allowable stresses for a givenmaterial or, in some cases, provide allowable capaci-ties of specific assemblies, such as the wood struc-tural panel shear wall capacities specified in weight of materials of constructionincorporated into the building, including but not limited towalls, floors, roofs, ceilings, stairways, built-in partitions, fin-ishes, cladding and other similarly incorporated architectural2009 INTERNATIONAL BUILDING CODE COMMENTARY16-1 Chapter 16.

4 Structural DesignGeneral CommentsThis Chapter contains the commentary for the followingstructural topics: definitions of Structural terms, con-struction document requirements, load combinations,dead loads, live loads, snow loads, wind loads, soil lat-eral loads, rain loads, flood loads and earthquake Chapter provides minimum Design requirements sothat all buildings and structures are proportioned to re-sist the loads and forces that are likely to be encoun-tered. The loads specified herein have been establishedthrough research and service performance of buildingsand structures. The application of these loads and ad-herence to the serviceability criteria will enhance theprotection of life and property.

5 The earthquake loads,wind loads and snow loads in this Chapter are based onthe 2005 edition of ASCE 7. The earthquake criteria andASCE 7 load requirements are based on the NationalEarthquake Hazards Reduction Program s (NEHRP)Recommended Provisions for Seismic Regulations forNew Buildings and other Structures(FEMA 450). TheNEHRP provisions were prepared by the Building Seis-mic Safety Council (BSSC) for the Federal EmergencyManagement Agency (FEMA).PurposeThe purpose of this Chapter is to prescribe minimumstructural loading requirements for use in the Design andconstruction of buildings and structures with the intent tominimize hazard to life and improve the occupancy ca-pability of essential facilities after a Design level event :\data\commentary\2009 I-Codes Commentary\Building\Final VP_Chgo\ , January 22, 2010 11:27:52 AMColor profile.

6 Generic CMYK printer profileComposite Default screenand Structural items, and the weight of fixed service equipment,such as cranes, plumbing stacks and risers, electrical feeders,heating, ventilating and air-conditioning systems andautomatic sprinkler definition of Dead loads identifies the type ofitems that must be accounted for (also see for inclusion of items on landscaped roofs).This definition is necessary to distinguish dead loadsfrom other loads, and for use in load combinations, asspecified by Section 1605. Dead loads are consideredpermanent in the load combinations. The nominaldead load is to be determined in accordance with Sec-tion weights of service equipment, such as plumb-ing stacks and risers; heating, ventilating and air-con-ditioning (HVAC) equipment; elevators and elevatormachinery; fire protection systems and similar fixedequipment are to be included in the dead load .

7 For themost part, tracking the weights of each utility system isnot practical and the Structural Design is thereforebased on a dead load allowance for these items. Attimes the actual weight of equipment to be installed isunknown during the Design phase of a buildingbecause the supplier of the equipment has yet to bedetermined. The Structural Design must often proceedbased on an estimated equipment dead load . Foradditional comments on dead load estimates, see thecommentary to Section product of the nominal strengthand a resistance factor (or strength reduction factor).vThis definition is needed to apply the strength designrequirements in the code.

8 The Design strength is thenominal strength multiplied by a resistance or strengthreduction factor that is less than one. The designstrength and corresponding strength reduction factorsare specified in the applicable material Chapter of thecode or a standard that is referenced horizontal or sloped system acting to trans-mit lateral forces to the vertical-resisting elements. When theterm diaphragm is used, it shall include horizontal and roof diaphragms act to transfer the lateralforces, such as wind or seismic loads, to the verti-cal-resisting elements ( , shear walls, bracedframes, moment frames, etc.)

9 Supporting them at theirperimeter or intermittent , light-frame construction, a dia-phragm in which all sheathing edges not occurring on a fram-ing member are supported on and fastened to diaphragms are horizontal or nearly horizon-tal assemblies designed to resist high shear forces inlight-frame construction. Diaphragm sheathing maybe applied with its long dimension either perpendicularor parallel to the main framing members. When theedge of the sheathing is not supported by the mainframing member, it is considered to be is accomplished by installing a framing mem-ber parallel to the otherwise unsupported edge of thesheathing.

10 In some cases, the code may require block-ing, while in other cases, the capacity of a diaphragmassembly will vary based on whether it is blocked light-frame construction, a locationwhere shear is transferred into or out of the diaphragm sheath-ing. Transfer is either to a boundary element or to anotherforce-resisting boundary is typically the connectionbetween the floor or roof sheathing and the bandboard surrounding the diaphragm boundary element perpen-dicular to the applied load that is assumed to take axial stressesdue to the diaphragm diaphragm acts as a deep horizontal beam.