Beam To Column (BTC) connections remain a point of contention when examining their ability to maintain load-carrying capacity post-earthquake, both custom and pre-engineered. During a seismic event, forces are imposed to the structural system and resulting displacements between consecutive floors will cause rotations at these BTC connections. Typical design drift limits are within the range of 1.5%-2.5% in North America, but no test or design standards are adequate in addressing the acceptable behaviour of such gravity connections in mass timber, which are not a part of the lateral force resisting systems (LFRS).
Aligning with the trend of mass timber’s meteoric rise in the application of taller structures, MTC Solutions has been focused on working with partners in the design, development, and analysis of testing programs to evaluate the seismic performance of pre-engineered beam hanger systems. The most recent testing MTC Solutions has conducted regarding this topic recently concluded & with this new testing data also comes an additional member in our product line-up, the MEGANT-E.
This post highlights the differences between the MEGANT-E and the regular MEGANT as well as providing key information about the tests performed, the behaviour observed and an overview of the results.
Approximately 4-minute read.
What’s the MEGANT-E ?
The MEGANT-E is a modified version of the MEGANT system, with a slight increase in the height of the clamping jaws at the upper and lower extremities of the connector of 3/8” [10mm] each. A MEGANT 430×150 with the extended clamping jaws now becomes a MEGANT-E 450×150. The MEGANT features a 1.97” [50 mm] clamp, with 1.18” [30 mm] of material and grade 6082 aluminium where the MEGANT-E has a 2.36” [60 mm] deep clamp with 1.57” [40 mm] material and grade AW6082 aluminium
The rationale for this modification was to guarantee that there would be enough material in the extremities of the connector based on the understanding of how the MEGANT connector behaves at BTC connections when drift limits are met and exceeded. First, we must understand how these connections perform under gravity loads, and what its load path looks like:
The compression jaws provide a clamping force between the two connector plates, through a threaded rod tightened with a nut and washer.
Testing Set-up & Behaviour
The test, examined in depth in the associated White Paper, was designed to simulate an as-built environment with fire design considered for the connector at the beam end. This means that the connection was concealed with no gap at the column and with a CLT floor plate superimposed on the beam, butting into the column. Previous tests by MTC Solutions and other research groups have neglected to fully capture this detail; it is important to highlight the lack of any gap in this most recent program. Drift test results with a discernable gap may provide acceptable results but fail to capture the true behaviour of mass timber BTC rotational effects in a seismic or high wind event, nor are they acceptable designs from a fire design perspective.
When fully loaded to its design gravity bearing capacity of 22.67 kip [100.8 kN] in the test setup, an actuator applied loading protocol near the BTC interface induces a rotation at the beam hanger which simulates a drift scenario. The observed behaviour was spring-like, where connector plates deflected outwards at the mid-section while the top and bottom were restrained by the clamping jaws. It is worth noting, that in previous full-scale tests conducted, the prototype clamping jaws were thought to not have sufficient material to resist the splitting force of the connector plates moving outward. In this previous model, the clamping jaws were 1.57” [40 mm] deep, with 0.79” [20 mm] of solid grade AW6005 aluminium. Failure was observed in this older prototype due to clamps being too thin, as can be seen in the figure below.
As mentioned, the clamps were designed slightly deeper to provide the required section resistance against the pulling effects of the opposing connector plates. This behaviour is more ideal as it leads to ductile yielding in the MEGANT beam hanger plate rather than fracture of the top/bottom clamps.
Test Results Overview
The full-scale loading tests are covered under the Clause 220.127.116.11 of the NDS 2018 for typical gravity design, which provide an alternative accepted use condition. It is important to note that the MEGANT-E
We are excited to continue pushing the boundaries of what is achievable in tall mass timber buildings and providing both reliable and informed advice to industry. For more information on the MEGANT E and our testing, download & read the associated white paper on Interstory Drift Performance of Megant E Connector.
If you have any questions, contact our Technical Support Team 🙂
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