The Connectors plugin handles hangers for wood member connections. Other functionality will be added in the future, such as connections of wood members to concrete/masonry walls, and post caps and post bases for wood posts.
The Connectors plugin uses Simpson Strong-Tie’s latest connector capacity information from their “Wood Construction Connectors” catalog (2019-2020).
Here is some notable information about the Connectors plugin calculations:
Connector Demand (Loads)
ASD Load Combinations
The Connectors plugin uses Allowable Stress Design (ASD) load combinations, even if Load and Resistance Factor Design (LRFD) is chosen for the member.
This is because Simpson Strong-Tie’s catalog values use ASD.
You can still design the member using LRFD, and the plugin will use the unfactored support reactions to create the ASD factored loads for connectors.
Duration Factor Load Groups
The loads are run through every ASD load combination, and the resulting factored ASD loads are sorted into 10 duration factor groups (5 for positive/downward and 5 for negative/uplift conditions) based on the highest duration factor needed for that combination.
The duration factor groups that the load combinations are grouped into are:
CD = 0.9 for dead load
CD = 1.0 for live load
CD = 1.15 for snow, rain and ice loads
CD = 1.25 for roof live loads
CD = 1.60 for wind and seismic loads
The resulting loads from the ASD combinations are sorted based on the highest duration factor required in a given combination. For example:
D+L would be part of the CD = 1.0 group for live loads
D+0.75L+0.75Lr would be part of the CD = 1.25 group for roof loads
D+0.75L+0.75S would be part of the CD = 1.15 group for roof loads
The largest load for each of the 10 duration factor groups is saved for comparison with the corresponding 10 capacities, derived from the catalog tables (see below).
Catalog Duration Factor Capacity Groups
Typically the Simpson catalog values include cases for Uplift (CD = 1.6), Floor (CD = 1.0), Snow (CD = 1.15) and Roof (CD = 1.25).
The Connectors plugin takes these catalog capacity values and extrapolates them into the additional groups as appropriate.
For example, typically the uplift case given is for a duration factor of 1.6, which assumes the uplift is from wind/seismic loading. These values are then reduced by the appropriate duration factors to come up with the capacity for other load cases. So for uplift that is from dead load only, the capacity for that case would be multiplied by a factor of 0.9/1.6 = 0.5625.
Capacity reductions such as these are always applied, but capacity increases are only applied if the catalog indicates that this is appropriate.
For example, if a downward Roof (CD = 1.25) capacity is given, but not a capacity for downward Wind (CD = 1.6), then the Roof capacity is conservatively used for the Wind cases as well, without an increase. But where the catalog indicates that increases are allowed, they are applied.
Catalog Capacity Adjustment Factors (Slope, Skew, Top Flange Conditions)
Connector capacities are automatically adjusted by the factors given in Simpson Strong-Tie’s catalog, such as for sloped and skewed seats and various top flange conditions.
These factors are typically given in notes, footnotes, or tables for each hanger type in the catalog.
In some cases, where the catalog includes options that aren’t covered in the program (such as square cut vs bevel cut members), the most conservative appropriate factor is applied.
In other cases where actual maximum load values are given instead of adjustment factors, the adjustment factors are back-calculated based on the values given.
Additional Capacity Adjustments and Limitations
Species Adjustment Factor
Where a different species of wood than those indicated in the catalog is used for either the supporting or the hanging member, the connector capacities are adjusted based on the specific gravity of the members (per note ‘f’ on page 17 of the catalog).
Hanger Width Limitations
The list of passing connectors is limited to hangers that are no more than 1” wider than the member (or ⅛” wider for I-joists). The designer should review the conditions for each beam, and provide shims where appropriate.
Hanger Height Limitations
The height (depth) of the supporting member must be at least as big as the height of the hanger for Face-Mount and Concealed hangers, and for Top-Flange hangers that have a specific minimum height requirement.
Most I-joist hangers require web stiffeners, and the name of the hanger will reflect “WSR” (web stiffeners required).
Those that do not require web stiffeners typically require that the top flange be braced by the hanger.
If a hanger does not require web stiffeners, it is only included in the list if it is within 1” above or below the I-joist depth to ensure that the joist is able to be braced by the connector. The designer should review these connectors to ensure that the I-joist is appropriately braced by the hanger in these situations, or provide web stiffeners where needed.
Where the supporting member width is too narrow for the required fastener length (based on the fasteners specified in the catalog), the appropriate reduction factor is applied for shorter fasteners to be used where indicated in the catalog.
If no adjustment factor is given, the connector is removed from the list of allowable connectors if the supporting member is too narrow for the fasteners.
Top Flange Width
The supporting member must be wide enough to support the full top flange width for a top-flange hanger to be included in the list.
The results screen displays the loads for the 5 most common duration factor groups at the top.
The other duration factor groups are used in the calculations but not displayed.
Capacity (Passing Connectors)
The results screen also displays the capacity of passing hangers for the 5 most common duration factor groups.
The other duration factor groups (including back-calculated groups mentioned above) are used in the calculations, but not displayed.
The adequacy percentage is listed for each passing connector, and is calculated using the 10 duration factor demands with their corresponding 10 duration factor capacities.
The Print Preview includes a Connectors table with the name of the hanger and the alternates, as well as the other custom conditions set by the user (skew, slope, top flange conditions, etc).
Where custom conditions are used, an additional line at the bottom will include the required additions to the hanger specification.
These will say things like “X SKL20” where the “X” indicates special conditions, and the “SKL20” indicates the hanger is skewed left 20 degrees. See page 97 of the Simpson catalog.
Note that if a hanger comes with a standard skew built in, the skew need not be added to the hanger spec (for example, the SUR/L and HSUR/L hangers come with a 45 degree skew standard).
For some hangers the height is also required, and the designer will need to add the height to the specification using the format “H=___”.
Where a connector name includes “R/L” for right/left skews, only the direction of the skew needed for that hanger needs to be included in the spec.
For example, an HSUR/L that has skew to the left would be specified “HSUL”.