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4.1.8.1 Design for Low Seismic Loads
The method in 4.1.8.1.(3)-(15) to be used when a set of conditions for low seismic loading in 4.1.8.1.(2) is met. This method tends to create larger seismic loads than the Equivalent Static Procedure; its advantage is simplicity. It is not implemented in Shearwalls.
Upon seismic load generation, if the value IEFsSa(0.2) < 0.16 and IEFsSa(0.2) < 0.03, a message appears informing you of the simplified procedure, its limitations, and that it produces higher loads. The program proceeds to design with the Equivalent Static Procedure.
4.1.8.8 Direction of Loading
Since all structures in Shearwalls are oriented along orthogonal axes, only 4.1.8.8.(1)(a) applies, and Shearwalls generates loads and designs elements along each axis independently.
4.1.8.11.(7) Distribution of Force to Levels
Shearwalls distributes force Fx to the levels according to the formula in 4.1.8.7.11.(7) , including the top-level force Ft which is added to the force on the uppermost level when distributed to shear lines. It shows the calculation in a table in the Detailed Seismic Load Generation Output.
4.1.8.11.(9)-(11) Torsional Effects
Refer to Irregularities and Torsional Sensitivity.
4.1.8.12 Dynamic Analysis Procedure
Shearwalls does not implement the Dynamic Analysis Procedure; detailed numerical modeling, and or special studies are required.
4.1.8.13 Deflection and Drift Limits
Refer to Storey Drift Calculation, Allowable Drift, and Storey Drift Provisions Not Implemented
4.1.8.15.(4) - One-storey Buildings with Large Diaphragm Deflection
Single-storey structures with a wood roof diaphragm and with Rd greater than 1.5, require magnification of deflections and/or design forces if the diaphragm deflection exceeds ½ the storey drift of the adjoining shear walls. This affects only large structures with a large sufficient distance between shear lines to create large diaphragm deflection.
As Shearwalls does not currently calculate diaphragm deflections, a warning is displayed for structures susceptible to this condition. If the shortest distance between shear-resisting elements is greater than 100 feet (30 meters for metric) the warning asks you whether you want to reduce Rd to 1.5 and generate seismic loads, continue generating without reduction, or abort seismic load generation.
4.1.8.15.(5) Elements Supporting Discontinuous Wall
Shearwalls does not implement 4.1.8.15.(5) which states that elements supporting discontinuous walls must be designed for the shear wall capacity of the element being supported rather than the applied force. Structural Commentary 208 associated with A-4.1.8.15.(5), explains more fully thatthis is due to an irregularity 4 - In-Plane Discontinuity - Offset from NBC Table 4.1.8.6,
The conditions in where this might occur are
It is your responsibility to adjust the shear forces shown in Shearwalls accordingly to deal with these and any other similar situations. .