construction, a time effect factor λ is also included). Per the LRFD approach, the design

tie strength must be greater than or equal to the required tie strength:

Design Tie Strength = Φ Rn ≥ Required Tie Strength

Equation (3-1)

where

Φ

= Strength reduction factor

Rn

= Nominal Tie Strength calculated with the

appropriate material specific code, including over-

strength factor Ω where applicable.

The required tie strength for horizontal and vertical ties is defined for each

material type in Chapters 4 through 8. The structural elements used as ties must not

only provide sufficient tie strength, but they must also be adequately connected so that

the tie forces can be distributed throughout the rest of the building.

The design tie strengths are considered separately from the forces that are

typically carried by each structural element due to live load, dead load, wind load, etc.;

in other words, the design tie strength of the element or connection with no other loads

acting must be greater than or equal to the required tie strength.

Some of the tie forces are based on the dead and live loads. In some cases,

a structure may have different loads, such as a corridor load or office load, on the same

floor. In such cases, use an averaged dead or live load, by computing the total force

acting on the floor and dividing by the total plan area. When tie forces are based on a

span L that varies along the length of a tie, the largest span in a continuous tie should

be used for the tie force calculation.

If all of the structural elements and connections can be shown to provide the

required tie strength, then the tie force requirement has been met. If the **vertical **design

tie strength of any structural element or connection is less than the **vertical **required tie

strength, the designer must either: 1) revise the design to meet the tie force

requirements or 2) use the Alternate Path method to prove that the structure is capable

of bridging over this deficient element. **Note that the AP method is not applied to**

3-2

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