AT 2′ 0″ & 3′ 0″ PANEL SPANS. IN ACCORDANCE WITH ASTM E AND AISI S TESTED FOR: Central States Manufacturing, Inc. Find the most up-to-date version of ASTM E at Engineering Designation: E – 04Standard Test Method for Static Load Testing of Framed Floor or Roof Diaphragm Constructions for Buil.

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Documents Flashcards Grammar checker. Abstract Pre-fabricated wood I-joists are routinely used to construct roof and floor systems in modern lightframe wood construction. One of the primary functions of a light-frame floor or roof is to serve as a diaphragm that collects in-plane lateral load and transfers it to the shear walls and foundation elements. Since the existing diaphragm design provisions contained within the model building codes are based on a combination of testing and analysis conducted with sawn lumber framing, designers often question whether they can be reasonably applied to diaphragms framed with I-joists.

This article summarizes some of the rationalization and limitations associated with I-joist framing for diaphragm construction. Introduction Modern light-frame roof and floor systems routinely combine pre-fabricated wood I-joists with wood structural panel sheathing. A primary function of a light-frame floor or roof is to serve as a diaphragm that collects lateral load and transfers it to the shear walls and foundation.

Diaphragm design provisions for light-frame wood construction have been successfully employed for decades and were originally developed for lumber framing. Designers often wonder if they are equally applicable to diaphragms framed with wood I-joists. The objective of this article is to provide some insight into how shear capacities are rationalized for I-joist diaphragms and to summarize potentially useful trends observed with full-scale testing. Diaphragm Design Diaphragms are typically modeled as deep, inplane beams.

Joists provide out-ofplane stiffening and load transfer between discrete panel sheathing elements. This makes sheathing-toframing attachment a critical element that often defines shear capacity of the assembly.

Tables, like IBC Table The original rationalizations for these tables were based on an analysis of sheathing and attachment schedules for lumber-framed diaphragms with plywood panel sheathing. They have been subsequently modified based on results from a variety of full-scale test programs that introduced additional materials, failure modes, and design considerations. Original I-joist framing products used laminated veneer lumber LVL or sawn lumber flanges with thicknesses of 1.

These thicknesses were consistent with 2 in.


As I-joist satm are optimized, it has become common to see LVL flange thicknesses less than 1. The industry has long recognized that reducing flange thickness beyond a certain threshold has the potential to adversely impact sheathing nail embed9 Table 1. Peak strength comparisons between similar full-scale diaphragm tests1, 2 3,4 Notes for Table 1: All of the tests summarized in this table used I-joist framing with laminated veneer lumber LVL flanges.

However, only a single diaphragm was tested in the following cases: Both manufacturers have developed related design recommendations and limitations that are included in their evaluation reports. In general, the manufacturers have proven equivalence to a subset of the current diaphragm design tables for sawn lumber. They generally do not permit 10 thinner flanged I-joist products to be used in the highest load applications that require the closest sheathing attachment schedules.

A variety of I-joist materials, sheathing products, diaphragm configurations, sheathing fasteners, and fastening schedules have been tested to verify shear transfer and deformation performance capabilities.

Typical diaphragm test configuration 24 x 24 ft. E455 all I-joist diaphragms have been tested with dimensions of 24 ft. Regardless of configuration, observed diaphragm behaviors are fundamentally consistent.


Initially, diaphragms deform elastically as a deep beam without perceptible relative movement between framing and sheathing. At loads in excess of design loads, visible Summer relative movement can be observed between adjacent sheathing panels and between panels and framing. Figure 3 illustrates these trends for a IBC Table Shear flow causes panels at the reactions to rotate in opposite directions towards the span centerline. The magnitude of this rotation is typically consistent between diaphragm tension and compression chords.

Due to panel geometry, the observed movement between adjacent sheathing panels is typically several times greater along long edge joints than at short 11 Figure 2. Illustration of atsm setup 24 x 24 ft. The large relative movement between panel edges creates a tension perpendicular-to-grain splitting force across the framing at the fasteners for adjacent panels.

At panel end joints, it induces perpendicular-to-grain forces into the framing as panel end joints rotate and r455 nails induce perpendicularto-grain prying forces into the framing. The Case 1 diaphragms tested exhibited similar behavior with the exception that panel bearing and crushing were also observed between interlocking panel rows. However, as with the benchmark sawn lumber tests, the dominant failure modes observed with I-joist diaphragms were tension perpendicular-to-grain fracture of the framing and sheathing nail withdrawal.

Research and Testing – Central States Mfg, Inc.

Sheathing related failure modes played a less significant role. Given that many of the potential diaphragm failure modes that limit capacity are not typically addressed by a connection analysis, the importance of test-based verification for diaphragm systems that depart significantly from the historical basis seems to be confirmed.

Performance Trends The compiled database of full-scale I-joist diaphragm tests provides an opportunity to draw com12 parisons between similar test sets. While extrapolations beyond asgm conditions should be approached with caution, comparisons in Table 1 suggest trends that could be useful to the designer: Douglas-fir LVL e45 I-joists outperformed their southern pine counterparts in 4 out of the 5 similar diaphragm configurations tested Lines This trend contradicts what is expected based on a sheathing fastener connection analysis that assumes a higher specific gravity for southern pine.

This trend may be due to the difference in tension perpendicular-to-grain strengths or typical veneer thicknesses of the LVL fabricated with each species. How well these particular commercial species combinations fit the specific gravity-based fastener design models may also play a role. Regardless, it highlights that an I-joist manufacturer needs to evaluate the diaphragm performance of each primary species used for flange material.

It also suggests that designers should avoid applying the diaphragm recommendations for one I-joist product to another. The Line 6 comparison illustrates what a relatively subtle difference in I-joist product composition can have on capacity.

As with the last item, this would seem to confirm that diaphragm performance is product dependent. Typical diaphragm movement mechanisms Case 5 shown.

Line 7 illustrates the influence that blocking selection can have on capacity. Even with I-joist materials taken as being a constant between tests, use of low specific gravity blocking material e55.

This shows that selection of a blocking material is likely as important as selection of a joist and should be consistent with the design assumption. For example, avoid using spruce-pine-fir blocking if Douglas-fir diaphragm design values are targeted.

Comparisons on Lines illustrate that, as with sawn lumber, e55 framing results in increased capacity.

This is consistent with the code design provisions and can be attributed to the fact that wider framing tends to reduce splitting astn can provide for increased edge distance and staggered nail patterns that provide better load transfer. This highlights the importance of flange splitting and the need for astn manufacturer to address the resulting capacity limitations in their design guidance.


The design codes permit six different diaphragm configurations to be constructed. It is not intuitively obvious that they are all equal when it astmm to I-joist diaphragm performance. Since splitting was a primary concern, this was judged conservative because it maximized the number of fasteners and requires the full lateral load to be transferred through the I-joist flanges.

It also corresponded with a benchmark database for sawn lumber Countryman, As suggested by Lines 14 and 15, testing other sizes may result in slightly different answers. This highlights the importance for the manufacturer to evaluate a configuration that encourages realistic stress flows through the system if design values are being developed.

The designer should also specify products that have been rationalized accordingly. Lines 16 and 17 provide some insight into the relative influence of fastener selection. Eight penny 8d ring shank 0.

The fullscale tests of Line 16 suggest that the smaller diameter ring shank nail actually out-performed the larger diameter common nail. Line 17 provides a similar comparison for a proprietary fastener that claims superior diaphragm performance for some configurations based on small-scale astj testing and analysis. In reality, the proprietary fastener performed about the same as the smaller diameter ring shank nail. The designer should be cautious when ashm proprietary fasteners that claim diaphragm performance improvements that have not been verified against all failure modes possible in a full-scale diaphragm.

AC14-0611-R1 #4 – ICC-ES

Stiffness Observations In some cases, a designer will also need to predict diaphragm deformation. Calculation procedures developed for r455 lumber diaphragms also provide a reasonable means of predicting I-joist diaphragm deformation in the design range.

Figure 5 illustrates a comparison between calculation methodologies and the measured behavior for a Case 5 I-joist diaphragm configuration that conservatively combined large diameter fasteners with a tight spacing that tends to promote splitting. For this example, observed performance reasonably 4e55 modeled deformation predictions based on the tested Case 5 configuration.

It should be noted that the actual deformations are less than deformations predicted using the default apparent shear stiffness term in SDPWS. Failure modes — framing splitting from panel prying Case 1 shown. One of the benefits of testing diaphragms with a 1: A downside is that deflection measurements are small. This absolute differential arguably falls below the reasonable precision of the full scale test method and highlights that the absolute magnitudes of deformation should be considered when interpreting the accuracy of a predictive model.

However, the performance of s455 I-joist diaphragm assembly will be dependent on the specific I-joist product used and its relevant attributes i. Few I-joists can e45 as a direct substitute for sawn-lumber framing in the full range of applications addressed by building code diaphragm design provisions. American Society for Testing and Materials. National Design Specification for Wood Construction.

Special Design Provisions ast Wind and Seismic. Lateral Tests on Plywood Sheathed Diaphragms. Douglas Fir Plywood Association. Summer International Code Council.

Country Club Hills, IL. International Code Council Evaluation Service. Bibliography on Lumber and Asm Panel Diaphragms. Journal of Structural Engineering. We have reviewed the proposed revisions to AC14 and would like the committee to consider the following comments and suggested modifications.

The full-scale diaphragm test program shall include the following minimum elements: Loads may be applied using either two- or four -point loads equally spaced along the compression chord.

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