What is dynamic base shear?

What is dynamic base shear?

Base shear is an estimate of the maximum expected lateral force that will occur at the base of the structure due to the seismic ground motion. During the analysis, the codes required for the use of the equivalent static force procedure and a dynamic lateral force procedure.

How base shear is calculated using the equivalent static method?

Minimum Base Shear Limit In many seismic codes, the equivalent static lateral force V is used as a reference value of the total seismic design base shear. For instance, the base shear calculated using the modal response spectrum analysis should not be less than 80 % or 90 % of the equivalent lateral base shear.

What is scale factor in Etabs?

Therefore, the response-spectrum scale factor is I g / R, where g is acceleration due to gravity (386.4 in/sec2 for kip-in and 9.81 m/sec2 for kN-m). In this case, the new scale factor would be (I g / R) * (0.85 * static base shear / response-spectrum base shear).

What is the difference between base shear and storey shear?

Base shear is an estimate of the maximum expected lateral force that will occur due to seismic ground motion at the base of a structure. Storey shear factor is the ratio of the story shear force when story collapse occurs to the story shear force when total collapse occurs.

How do you calculate base shear manually?

The base shear formula is: V = 0.2 (W) V represents the shear force that will be generated at the base of a building. 0.2 represents earthquake force. W represents the weight of the building.

What is static base shear?

The lateral forces exerted on the structure by ground vibrations may be determined by the static or equivalent lateral force procedure (ASCE 2003a,b, ASCE 2000/FEMA 2000). Base shear is an estimate of the maximum expected lateral force on the base of the structure due to seismic activity.

What is scale factor in earthquake?

When you define a ground motion, there is a scale factor you can specify by which all points of the input accelerogram will be multiplied. I assume you are referring to the second scale factor – the one in the Define Target Spectrum box. This second scale factor is applied to the response spectrum.

What is base shear capacity?

Base shear is an estimate of the maximum expected lateral force on the base of the structure due to seismic activity. It is calculated using the seismic zone, soil material, and building code lateral force equations (Figure 10.3).

Which is greater static base shear or dynamic base shear?

So the rule is, the static base shear should be less than or equal to the dynamic base shear.But for the shear in the X-direction, the static base shear is greater than the dynamic base shear. So we need to scale it up depending on the ratio of the two which is Static/Dynamic which we derive a scaling ratio of 1.264.

When does base shear need to be scaled?

UBC-97 section 5.3.17 requires that if the base shear determined by a dynamic analysis is less than that of the static lateral force procedure, it must be scaled to equal that determined by the equivalent static force procedure.

How to balance dynamic and static seismic shears?

The UBC97 code provides 3 conditions on how much (snippet below). We never applied 1631.5.4 (1) which is Dynamic = 0.90*Static and 1631.5.4 (2) Dynamic = 0.80*Static just to have some fat stored in the design because usually structural analysis and design finishes first before having fixed architectural drawing references are available.

How to get static base shear in ETABS civil?

Get the static base shear. After running the model, you should be able to get the table for auto seismic load by clicking the Display -> Show Tables and ticking the Auto Seismic – UBC 97 and by clicking the Ok button. You should be able to get a table that looks like that below.