Calculating the Equivalent Static Forces Following NZS1170.%
- Subject Code :
CIVL206
- University :
Other Exam Question Bank is not sponsored or endorsed by this college or university.
- Country :
New Zealand
Calculating the Equivalent Static Forces Following NZS1170.%
Part 1: Determine the seismic weight of the building
- Dead loads: Calculate the dead weight on each floor. The dead weight comes from the structural members and any permanent super-imposed loads (e.g. floor coverings, ceiling tiles, piping, HVAC. You will need to make assumptions here based on the structural material you are using, the use of the building, and any permanent non-structural components you will have in your building. It is important to state your assumptions here.
- Exterior Walls: In addition to the weight you have at each level, you will also need to consider the external walls or cladding. You should assume that each floor support half the exterior wall above it and half the exterior wall below it.
- Live loads: The live load for the building will be based on the building occupancy. You will need to look in AS/NZS1170.1 to get an appropriate live (imposed) load for your structure.
- Roof Load: The loads will be different on the roof than on the other levels. The dead load will only support half of the exterior wall below it, the roof slab may be made out of a different material or thickness to be lighter, the live loads will be based on roof size and access.
Fill out the table below to help you determine what the loads and then the weight (load*floor area) for each floor.
Floor | Loading (description) | Load (kN/m2) | Weight (kN) |
First floor | |||
Second floor | |||
Roof |
Part 2: Determine the factored load for each level (NZS 1170.5 4.2)
The seismic load for each level is not the total weight at each level, but uses a load combination to determine the factored seismic weight. This load combination uses all of the dead load and fraction of the live load (ranging from 0-60%) depending on the access and storage use for each floor.
Determine the factored seismic weight at each floor and sum the entire building weight in the table below.
Floor | Factored Seismic Weight |
First Floor | |
Second Floor | |
Roof | |
Total |
Part 3: Determine the base shear of the building
Next you need to determine the base shear or the building. The base shear is calculated as a percentage of the seismic weight. This is calculated by determining the horizontal design coefficient for the structure. The horizontal design coefficient is an indication of the potential seismic force on the building. It is based on the Importance Level of the building, ductility and material, building location, and building period.
Use the following Tables to determine the base shear of the building.
Design Criteria | Information |
Importance Level | This is based on your building occupancy, should be IL2 |
Ductility | Ductility is based on the material and type of seismic resisting system. We will assume the building remains elastic, = 1.0 |
Site Class | This is dependent on the specific location of the building. For building where we do not have specific soil data or ground conditions, we should assume site class D or E. |
Estimated Period | An estimate period can be calculated based on the material type and seismic resisting system. There is an equation for estimating the period in the 1170.5 Supplementary. |
Variable | Reference | Calculation and final Value |
Spectral Shape Factor, ????????(????) | NZS 1170.5, 3.1.2 This value comes from a table, it is based on the site class and the estimated building period. | |
Z-factor | NZS 1170.5 Table 3.3, based on your location, find the Z value from the table. | |
Return period factor, ???????? or ???????? | NZS 1170.0 Table 3.3 NZS 1170.5 Table 3.5 The return period will be based on what level of earthquake you are designing for. If you are designing for the ultimate level earthquake, the building will need to be designed for higher return periods than a service level earthquake. Decide what level of earthquake you are design for, state it in your assumptions. Get the return period from 1170.0 and then use the return period to get the ????S or ????u value from the table in 1170.5 | |
Shortest distance to fault, D | NZS 1170.5 Table 3.3, this is the distance to a fault line. Values are listed in 1170.5 for different locations in NZ. If |
no distance is listed then your N value will be 1. | ||
Near Fault Factor, ????(????, ????) | NZS 1170.5 3.1.6.2 This is a function based on the period of your building and the distance from the fault. | |
Elastic Site Spectrum, ????(????) | NZS 1170.5 3.11 Calculate the Elastic Site Response | |
Structural performance factor, ???????? | NZS 3404, 12.2.2.1 NZS 1170.5, 5.2.1.2 This is accounting for structural material behaviour. For most materials, Structural performance factors are given in material specific standards. If we are unsure, or using the Service Limit State, then you can use a value of 0.7. | |
????_???? | NZS 1170.5, 5.2.1.1 This is based on the ductility of the seismic force resisting system and the building period. | |
Horizontal design action coefficient, ????????(????) | NZS 1170.5, 5.2.1.2 This determines the horizontal design action coefficient | |
Seismic Weight | This come from part 2 of this worksheet. | |
Base Shear | NZS 1170.5 6.2.1.2. The base shear is the seismic weight multipled by the horizontal design action coefficient. |
Part 4: Use the equivalent static method to determine the horizontal force at each level.
Once the shear force has been determined, the next step is to distribute the lateral force to each storey, obtaining the equivalent lateral force at each level that would be developed under an earthquake load.
NZS 1170.5 6.2.1.3
Floor | ?i m | ????i kN | ?i????i kNm | ????t kN | 0.92????(????i?i) ?(????i?i) kN | ????i kN |
First Floor | ||||||
Second Floor | ||||||
Roof | ||||||
Sum |
