Structural design in the United States has long been governed by a complex patchwork of codes and standards, some of which are standardized nationwide and some of which are amended to varying degrees by individual states. In Calcs.com, we support the usage of several recent revisions of the International Building Code (IBC), International Residential Code (IRC), and ASCE 7, as well as a couple of individual states’ modifications where there are particularly significant structural amendments (such as in California). However, it’s important to understand what it means to be designing under a particular code and the aspects of your design that are and are not affected in Calcs.com.
The Legally Required Code
The building code governing your design is legally prescribed by legislation adopted independently in each individual state. All 50 states have adopted codes that are based upon the same ‘model legislation’, in the form of the International Building Code and/or the International Residential Code. Those codes are related to the entire construction of a building, including not just structural design, but also architectural design, fire design, accessibility, etc. In most cases, when states have amended the IBC or IRC, they’ve amended only or primarily those latter sections and generally have not modified the structural design meaningfully. In most states, therefore, you can accurately perform your structural design using the basic IBC or IRC. The code versions in current use by each state may be viewed for the International Building Code here and for the International Residential Code here. The actual amended text for each state is also viewable on Up.Codes here. Note also that certain larger commercial or industrial structures sometimes make use of a clause in the IBC that allows for the ASCE 7 standard to be used in lieu of most of the IBC’s load calculations, and Calcs.com therefore additionally offers a couple revisions of ASCE 7 as a ‘building code’ option as well.Material Design Standards
While the IBC and IRC are the governing legislation, those building code documents are not self-contained and do not define every step of the structural design themselves. They generally define the loads that should be applied and the load combinations that should be used, but they do not define how to calculate the strength capacity of all the different materials - wood, steel, concrete, etc. Instead, they refer out to standards developed by various industry bodies, such as the National Design Standards (NDS) for wood, American Institute for Steel Construction (AISC) 360 for steel, or American Concrete Institute (ACI) 318 for concrete. In Calcs.com, when you select a building code to use, we’ll change the load combinations to reflect the building code you want to use, but we will still use the most recent revision of the relevant material standard. We do not currently match material standard revisions to building code revisions. Most states explicitly allow you to use newer revisions of the material design standards, but please check with your individual state to ensure that this is the case.
Notable State Variations
A couple of states do make notable modifications to the structural design portions of the building codes. One of these is California, where there are numerous additional clauses for detailing and design largely as a result of earthquake requirements. However, California also defines the need to abide by its various amendments based upon the type of building being designed and thereby the relevant government agency. Buildings under the purview of the Office of Statewide Health Planning and Development (most medical buildings) or the Division of the State Architect—Structural Safety (mostly schools) are particularly stringent in added clause requirements, and Calcs.com does NOT include support for all the numerous amendments relevant for these buildings. Calcs.com DOES, however, support the California amendments for Department of Housing and Community Development (grade 1) buildings, also known as HCD-1 buildings. However, even in the HCD-1 amendments, California also notably amends the concrete material design standard specifically. Unfortunately, Calcs.com has not yet added support for the concrete amendments; for now, the California Building Code supports all materials except for concrete. If you would like to see an additional state added, please send us a request!Reduced Companion Live Load
Calcs.com supports reduced companion live load in some calculators, but not IBC tributary-area live load reduction inside beam design sheets. Reduced companion live load (ASCE 7)In Steel Beam (LRFD) and Wood Beam (LRFD), open the Loads section and set Use Reduced Companion Live Load? to Yes or No. The default is No. When set to Yes, live load is multiplied by 0.5 in the combinations where it acts as a companion load — those written with
f_1L, such as 1.2D + 1.6L_r + f_1L and 1.2D + 1.0W_dn + f_1L + 0.5S. Combinations where live load is the primary action, such as 1.2D + 1.6L + 0.5L_r, are unchanged. Current calculators cite ASCE 7-22, Cl. 2.3.1.1; the older AISC 360-16 and NDS 2018 revisions cite the same clause in ASCE 7-16. See How to Design a Steel Beam to AISC 360-16 for a screenshot of this control.
ASCE 7 permits this reduction only for live loads under 100 psf, and not in garages or places of public assembly. Calcs.com does not check those conditions for you, so confirm your occupancy qualifies before selecting Yes.
IBC area-based live load reductionCalcs.com does not currently calculate IBC 1607 tributary-area live load reduction inside beam calculators. If your design qualifies for that reduction, calculate it separately and enter it as a load magnitude in Distributed Loads, Line Loads, or Point & Moment Loads: set Load Type to (L) Live Load and type the reduced value into Magnitude Per Area (or the equivalent magnitude field on line and point loads). Those cells are ordinary numeric inputs; the calculator does not recompute live load from tributary area. See Project Defaults (US). If you would like Calcs.com to calculate IBC 1607 live load reduction inside a calculator, email help@calcs.com with how you would use it — we prioritize based on feedback.