Chapter 16: Structural Design - iccsafe.org

1 2012 INTERNATIONAL BUILDING CODE COMMENTARY16-1 SECTION Scope. The provisions of this Chapter shall govern thestructural Design of buildings, structures and portions thereofregulated by this code. While a significant portion of Chapter 16 is dedicatedto the determination of minimum Design loads, it alsoincludes other important criteria that impact thedesign of structures, such as the permitted designmethodologies, as well as the combinations of designloads used to establish the required minimumstrength of Structural members. Unless stated other-wise, the criteria found in this Chapter are applicableto all buildings and structures. See Chapter 34 forapplication of these requirements to alterations, addi-tions or repairs to existing 1602 DEFINITIONS AND Definitions.

2 The following terms are defined in Chap-ter 2: Definitions facilitate the understanding of code provi-sions and minimize potential confusion. To that end,this section lists definitions of terms associated withstructural Design . Note that these definitions arefound in Chapter 2. The use and application ofdefined terms, as well as undefined terms, are setforth in Section STRESS , , OF LOAD (ROOF).LOAD AND RESISTANCE FACTOR Design (LRFD).LOAD 16: 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 toresist the loads and forces that are likely to be encoun-tered.

3 The loads specified herein have been establishedthrough research and service performance of buildingsand structures. The application of these loads andadherence to the serviceability criteria will enhance theprotection of life and property. The earthquake loads,wind loads and snow loads in this Chapter are based onthe 2010 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 designand construction of buildings and structures with theintent to minimize hazard to life and improve the occu-pancy capability of essential facilities after a designlevel event or DESIGN16-22012 INTERNATIONAL BUILDING CODE COMMENTARYOTHER (PART OF A STRUCTURE).

4 RESISTANCE , , Weight of ice in accordance with Chapter 10 of effect of horizontal and vertical earthquakeinduced forces as defined in Section of ASCE due to fluids with well-defined pressures andmaximum Flood load in accordance with Chapter 5 of ASCE due to lateral earth pressures, ground waterpressure or pressure of bulk live load greater than 20 psf ( kN/m2) andfloor live Roof live load of 20 psf ( kN/m2) or Design wind speed (3-second gust), miles perhour (mph) (km/hr) where Ultimate Design wind speeds (3-second gust), miles perhour (mph) (km/hr) determined from Figures 1609A,1609B, or 1609C or ASCE due to wind Wind-on-ice in accordance with Chapter 10 of ASCE7. These notations are used to refer to specific nominalloads that are determined in this Chapter for use inthe load combinations in Section 1605: D is the nominal dead load determined in Sec-tion 1606.

5 Also see the definition of Dead load. Di is the weight of ice. See the ASCE 7 provi-sions referenced in Section 1614. Earthquake load effect, E, in Section ofASCE 7 includes the effects of the horizontalload, Eh, as well as a vertical component, E, Ehis the product of the redundancy factor, , andQE, the effects of horizontal earthquake accounts for vertical acceleration due toearthquake ground motion, taken as that its magnitude is not intended to repre-sent a total vertical response, since that is notlikely to coincide with the maximum horizontalresponse. It is essentially a portion of the deadload, D, that is added in additive load combina-tions or subtracted in counteractive load com-binations. The term SDS, Design spectral re-sponse acceleration at short periods, isexplained in the commentary to For example, when this expression is used in thealternative allowable stress Design load combinationsof Section that include earthquake loadeffects the resulting combinations are as follows:Equation 16-21D + L + S + =(1 + )D + L + S + + = ( - )D + Design criteria is provided in Section1613, which, in turn, references the relevant ASCE 7provisions for computation of the earthquake loadeffects.

6 While these loads are necessary for estab-lishing the required strength, the computed forcesapproximate the expected deformations under thedesign earthquake ground motions and are notapplied to a structure in an actual earthquake. F refers to the nominal load due to fluids having well defined pressures and maximum heights. Unlike most other nominal loads, there is nocode section governing the determination offluid loads. Also note that F includes a verticalcomponent (fluid weight), as well as a horizontalcomponent (lateral pressure). Fa is used to refer to the flood load that is deter-mined under Chapter 5 of ASCE 7. Note that Fais not explicitly included under other loads listedfor the alternative ASD combination in H is used to refer to the nominal load resultingfrom lateral soil pressure, lateral pressure ofground water or the lateral pressure of bulkmaterials.

7 Section 1610 specifies minimumrequirements for lateral soil loads. Note thatthere are not specific provisions for the determi-nation of load resulting from the lateral pressureof bulk materials. L in the nominal live load determined in accor-dance with Section 1607 (also see the definitionof Live load ). In addition to floor live loads, itincludes roof live loads that exceed the limit onLr. Lr represents nominal roof live loads up to 20psf ( N/m2). R is the nominal rain load determined in accor-dance with Section DESIGN2012 INTERNATIONAL BUILDING CODE COMMENTARY16-3 S is the nominal snow load determined in accor-dance with Section 1608. T is used to refer to self-straining forces result-ing from contraction or expansion due to tem-perature change, shrinkage, moisture change orcreep, as well as movement due to differentialsettlement.

8 A thermal gradient at an exterior wallis an example of a Structural element wherethese self-straining forces can affect the most other nominal loads, there is nocode section governing the determination ofself-straining forces. T is not included directly inthe load combinations, but reference to it isfound in Sections and Vasd is the term used to refer to nominal designwind speeds that are determined in Vult is the term used to refer to the mapped windspeeds in order to differentiate them from thenominal Design wind speeds. W is the strength-level wind load determined inaccordance with Section 1609. Wi is the wind-on-ice loading. See the ASCE 7provisions referenced in Section 1603 CONSTRUCTION General. Construction documents shall show the size,section and relative locations of Structural members withfloor levels, column centers and offsets dimensioned.

9 Thedesign loads and other information pertinent to the structuraldesign required by Sections through shallbe indicated on the construction : Construction documents for buildings con-structed in accordance with the conventional light-frameconstruction provisions of Section 2308 shall indicate thefollowing Structural Design information:1. Floor and roof live Ground snow load, Ultimate Design wind speed, Vult, (3-second gust),miles per hour (mph) (km/hr) and nominal designwind speed, Vasd, as determined in accordance withSection and wind Design category and site Flood Design data, if located in flood hazard areasestablished in Section Design load-bearing values of soils. The term construction documents is defined inChapter 2. It is commonly used to refer to calcula-tions, drawings and specifications but it includesother data that is required to indicate compliance withthe code as described in Section 107.

10 The purpose ofthis section is to specifically require the Design pro-fessional to provide the building official with theappropriate Structural details, criteria and Design loaddata for verifying compliance with the provisions ofthis Chapter . Note that additional Structural informa-tion and specific submittal documents may also berequired to be incorporated by Chapters 17 construction documents are required to con-tain sufficient detail for the building official to performplan review and field inspection, as well as for con-struction activity. Dimensions indicated on architec-tural drawings are not required to be duplicated onthe Structural drawings and vice versa. The designloads, to be indicated by the Design professional onthe construction documents, are to be consistent withthe loads used in the Structural calculations.